Tag Archives: mating

Highly venomous sea snakes may be attacking scuba divers as a mating behavior

Credit: Jack Breedon.

There has been a worrisome amount of documented attacks by venomous Olive sea snakes on scuba divers over the years. This has always struck marine biologists as very odd seeing how the vast majority of these encounters were unprovoked. A new study may finally explain what’s going on -and it’s not getting any less weird. Apparently, the snakes may be confusing the divers with potential mates, accidentally biting them as part of their courtship behavior.

According to an analysis of Olive sea snake encounters, researchers in Australia found that the vast majority of attacks were performed by males during the mating season, between May and August.

To some snakes, humans may look just like oversized females

A curious Olive sea snake approaching a diver. Credit: Claire Goiran.

Richard Shine, professor of biology at Macquarie University in Australia and corresponding author of the new study, knows firsthand about the bizarre behavior of Olive sea snakes (Aipysurus laevis). Between 1994 and 1995, Lynch had 158 encounters with these sea snakes, 74 of which resulted in approaches, while diving in the Great Barrier Reef. It was data on these encounters that Lynch and colleagues analyzed in order to spot any meaningful patterns that may explain some of these dangerous unprovoked attacks.

In general, although they’re greatly feared by humans, terrestrial snakes would much rather escape than confront an approaching person. Why would sea snakes be any different? What’s more, why would a snake approach and bite a human that has not harassed it, is obviously too large to constitute prey, and could easily be evaded by maneuvering around the coral? The researchers set out to answer these questions.

Looking closely at the encounter data, the researchers noticed that 39 of 58 approaches involved males while 35 of 100 were males. Outside the breeding season, males were rarely observed approaching divers, whereas the proportion of females approaching divers did not differ significantly between breeding and non-breeding seasons.

Another notable difference was that males were also more likely to tongue-flick divers. In 13 encounters, all during the breeding season, the sea snakes rapidly charged at divers aggressively. Charges involving males occurred immediately after an unsuccessful chase of a female or interaction with another rival male. In the rare instances that females charged a diver, they did so after they were chased by males and encountered the diver in their vicinity.

Three males were particularly odd, coiling around the diver’s fin, a behavior typically seen during courtship. Luckily, no bites were recorded during these interactions although the snakes struck at their reflections in camera lenses.

“However, snakes readily tried to bite when harassed during capture, or (especially) when handled on the boat after capture. Male snakes can be highly persistent in their attempts to approach divers. On one occasion the diver attempted to flee from a snake by swimming vigorously for 20 min but was unable to outpace his follower. When the diver finally stopped, the snake tongue-flicked him for a minute and then left,” the researchers wrote in the journal Scientific Reports.

Terrestrial snakes, the sister group to hydrophiinae like Olive sea snakes, rely on pheromones to locate and recognize females. However, such chemicals are not water-soluble and hence, cannot be detected from a distance in marine environments. And although Olive sea snakes have better visual acuity than some other species in their group, their eyesight is not nearly as good as their terrestrial cousins. They likely see quite poorly underwater.

Taken together, these observations seem to point to the idea that male Olive sea snakes mistake human divers for other male rivals or potential mates. This wouldn’t be the first time since this behavior is almost identical to that of males of the Turtle-headed sea snake (Emydocephalus annulatus).

However, the potential consequences are very different. While the Turtle-headed sea snake is small and non-toxic, the Olive sea snake is large and possesses a deadly venom, which is why the researchers ended their study on a cautionary note.

“If mistaken identity underlies most “attacks” by sea snakes on divers, the best strategy for divers in such a situation may be to allow the snake to investigate them and in particular to allow for the snake to investigate chemical cues with its tongue; a bite is unlikely unless the animal is threatened or injured. Attempting to flee is likely to be futile and may even increase the ardour of the pursuit; and attempting to drive the animal away may induce retaliation,” the researchers advised. 

Male butterflies ‘dibs’ their mates with a repulsive odor to ward off other suitors

Heliconius melpomene butterflies mating in captivity in Panama. Credit: Kelsey Byers.

Some butterflies have evolved the ability to produce a chemical in their genitals that they spray right after sex to deter other males from persuing the females they’ve marked. Intriguingly, these same chemicals are produced by a flower to entice butterflies for pollination. So the same chemical can either deter or attract other butterflies, all depending on the context, researchers explained.

This striking mating behavior was recently identified by biologists in a species of tropical butterfly endemic to Panama known as Heliconius melponene. A research team led by Chris Jiggins, a professor at  St John’s College, University of Cambridge, sequenced the butterfly’s genome and mapped the scented chemical compound to find the gene responsible for it.

In doing so, the researchers learned that the gene responsible for producing the powerful anti-aphrodisiac pheromone called ocimene in the genitals of male butterflies is also found in some plants.

“For a long time it was thought insects took the chemical compounds from plants and then used them, but we have shown butterflies can make the chemicals themselves – but with very different intentions. Male butterflies use it to repulse competitors and flowers use the same smell to entice butterflies for pollination,” Dr. Kathy Darragh, lead author of the paper, said in a statement.

Female Heliconius melponene butterflies have few sexual partners compared to other species and can store the sperm to fertilize their eggs over a number of months after a single mating. The males, however, are far less picky and will basically have as many mates as possible. Each time the male mates, he releases ocimene in order to increase the odds he may become the lucky one to fertilize the eggs

But, as discussed, ocimene, a terpene, is also produced by a variety of flowers, serving as a floral attractant to aid pollination. So what makes it act differently in plants, allowing it to produce two opposing reactions — attraction and repulsion — in the same species? “Context is key,” Dr. Darragh says.

“The visual cues the butterflies get will be important – when the scent is detected in the presence of flowers it will be attractive but when it is found on another butterfly it is repulsive to the males,” she added.

According to the researchers, the ocimene-producing gene appeared independently in butterflies and plants, signifying a convergent evolutionary event.

“We are very excited about this opportunity to study the genetics of trait evolution at multiple phylogenetic levels. In Heliconius butterflies, there are other closely-related species pairs which differ in their production of ocimene. We hope to study these other pairs to see whether changes in ocimene production is associated with similar types of genetic changes as found in our current study,” Darragh said.

The findings appeared in the journal PLOS Biology.

Wild grey seals clap underwater to find a mate

An international team led by researchers from the Monash University found that grey seals (Halichoerus grypus) can clap their way into a date.

A grey seal.
Image credits Mateusz Włodarczyk / Wikimedia.

Marine mammals such as whales and seals aren’t afraid to be vocal. They’re highly social animals and use all sorts of calls and whistles to chat with their friends. But grey seals aren’t afraid to take a more hands-on approach when it comes to finding a mate, and they will clap for love. This is the first time seals have been seen clapping completely underwater of their own accord.

“The discovery of ‘clapping seals’ might not seem that surprising, after all, they’re famous for clapping in zoos and aquaria,” said lead study author Dr David Hocking from Monash University’s School of Biological Sciences.

“But where zoo animals are often trained to clap for our entertainment — these grey seals are doing it in the wild of their own accord.”

The findings are based on video footage collected by naturalist Dr. Ben Burville, a Visiting Researcher with Newcastle University and paper co-author, after 17 years of diving and observing the animals.

During the breeding season, the authors report, males voluntarily engage in underwater clapping. The team believes this is meant as a show of strength to intimidate competitors and attract potential mates. While it may sound very cute, the claps themselves are “impressively loud”, according to Dr. Burville, producing a gunshot-like sound. He recounts that at first “I found it hard to believe what I had seen.”

“How could a seal make such a loud clap underwater with no air to compress between its flippers?,” he adds.

This isn’t the only known case of marine mammals engaging in ‘clapping’: the behavior is relatively common among the group, with other species producing “similar types of percussive sound by slapping the water with their body or tail,” said Associate Professor Alistair Evans from Monash University, co-author of the paper. However, it is the first time this behavior was seen for grey seals in the wild.

“Depending on the context, the claps may help to ward off competitors and/or attract potential mates,” Dr Hocking said.

“Think of a chest-beating male gorilla, for example. Like seal claps, those chest beats carry two messages: I am strong, stay away; and I am strong, my genes are good.”

The findings show that there is still much to learn about the animals we share a planet with. Furthermore, it showcases how impactful noise pollution can be for marine species in general and grey seals in particular. Clapping seems to be an important social behavior for the seals, so anything that could disturb it could impact breeding success for the whole species.

“Human noise pollution is known to interfere with other forms of marine mammal communication, including whale song,” Dr Hocking said. “But if we do not know a behaviour exists, we cannot easily act to protect it.”

The paper “Percussive underwater signaling in wild gray seals” has been published in the journal Marine Mammal Science.

Small Amazon bird has the loudest call in the world

Some birds sing sophisticated and enchanting songs to court their mates. Male white bellbirds (Procnias albus), however, are not that artistic. Instead, they make up for their lack of musical talent with an in-your-face call. According to a recent study, their bird calls are the loudest ever recorded.

White bellbird calls are the loudest in the world. Credit: Anselmo d’Affonseca, Instituto Nacional de Pesquisas da Amazonia

Although they’re the size of a dove, these birds emit a deafening call that’s three times louder than that of screaming pihas (the previous record holder for the loudest bird call) and even louder than the calls of howler monkeys and bison.

Jeff Podos, a biologist at the University of Massachusetts Amherst, used cutting edge sound recorders, sound-level meters, and high-speed cameras to measure the amplitude of the bellbird’s calls with extremely high temporal precision.

“This allows us to see how amplitude changes and peaks within individual singing events,” he said in a statement.

These measurements showed that the bellbird emits calls that are louder than any musical instrument — an impressive feat for a creature that only weighs a quarter of a kilogram (half a pound).

The white bellbird’s call, by the way, sounds like a cross between a digital sound alarm and a really bad synthesizer. Judge for yourself from the recording below.

“We were lucky enough to see females join males on their display perches. In these cases, we saw that the males sing only their loudest songs. Not only that, they swivel dramatically during these songs, so as to blast the song’s final note directly at the females. We would love to know why females willingly stay so close to males as they sing so loudly,” he says. “Maybe they are trying to assess males up close, though at the risk of some damage to their hearing systems.”

In order to understand how such small animals are able to emit loud sounds, the researchers measured the bird’s breathing muscles, head and beak size, and its throat shape. Although this kind of analysis is still in its infancy, the authors found that there’s an inherent trade-off between size and loudness — as the birds get louder, they get smaller. They hypothesize that this may be due to the bird’s respiratory system, which has a finite ability to control airflow.

Previously, Podos and colleagues found that bellbirds have unusually well-developed abdominal muscles and ribs. In the future, the researchers would like to further study “the physical and anatomical structures and behaviors that allow bellbirds to produce such loud sounds and to endure them without hearing damage.”

The findings were reported in the journal Current Biology.

Seminal fluid blinds honeybee queens so they’re less likely to mate with other males

Carniolan Queen Bee in the hive. Credit: Wikimedia Commons.

In many social species, the reproductive strategies of males and females are so different that they often cross the barrier into conflict. Take honeybees, for instance. A new study found that inseminated honeybee queens can become visually impaired, thereby reducing their chances of mating with other males.

The sexual arms race

Males often employ strategies that increase their fertilization success whereas females tend to want the best genes for their offspring. Honeybee queens have a short of a period of time during their early lives when they fly out of their hives to mate with as many males as they can in order to enhance genetic diversity, thus improving hive health.

After her first flight, a queen may embark in subsequent flights out of the hive to find more males. For males which already mated with the queen, this behavior is against their agenda of passing down their own genes to offspring. So, to null the competition, the males have developed a biological trick to offer them a sexual advantage.

Previous observations have suggested that insemination alters the activity of genes connected to vision in the queen’s brain. In a new study, researchers at the University of Copenhagen in Denmark and the University of Western Australia sought to verify this hypothesis.

The study showed that, indeed, seminal fluid can trigger changes in the activity of vision-related genes in honeybee queens. In experiments, queens that were inseminated with seminal fluid were less responsive to light whereas, queens that were exposed to an inert saline solution could sense the stimulus. What’s more, tracking devices mounted on inseminated queens showed that the insects left for mating flights sooner but were also more likely to get lost and not return to their hives.

The findings, which were published in the journal eLife, show that males have developed this tactic in order to reduce a queen’s possibility to complete more mating runs. But the queens haven’t stood idle. To counter the debilitating effects of male sperm, the queens leave for mating flights sooner, which increases their chances of finding more mates and increase the genetic diversity of their colonies.

In the future, the researchers plan on conducting more studies that might determine whether this ‘arms race’ is affected by seasons, bee race, and geography. Beyond unraveling a fascinating fascet of mating in the animal kingdom, the findings could also find practical use. The information could be exploited by beekeepers whose business depend on queen mating success and hive health.

This is just an example out of numerous instances of male adaptions to sperm competition that gives rise to sexual conflict — i.e. traits that increase the fitness of one sex while reducing the fitness of the other. Male cockroaches that have become sperm depleted will guard females to enforce monogamy.

Other species employ strategies that involve blocking the female genital tract with a copulatory plug — there is evidence for this in rodents, in which a number of different ejaculatory proteins form the plug. And another way for males to maximize fitness returns when faced with the risk of sperm competition is to simply ‘care less’. Such males will either not mate with or allocate fewer resources to already mated females. If males allocate fewer resources (i.e., fewer sperm or smaller ejaculates), or are less willing to mate with nonvirgin females, this could reduce female fertility. 

Bonobo.

Bonobo mothers help their sons get dates — it makes them 3x as likely to become fathers

If you’re tired of your parents asking you when you’re getting married, tell them they could be more like bonobos and help you out.

Bonobo.

“You’re not going out groomed like that, young man!”
Image via Pixabay.

Many social animals share child-rearing duties among members of the group, but new research from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, found that one species takes this to the extreme: the bonobos. Mother bonobos, the team reports, take an active role in ensuring their sons father children. Sons who are aided by their mothers have three times the chance of becoming fathers compared to those who aren’t.

‘I gave your number to a cute girl’

“This is the first time that we can show the impact of the mother’s presence on a very important male fitness trait, which is their fertility,” says Martin Surbeck, a primatologist at the Max Planck Institute for Evolutionary Anthropology.

“We were surprised to see that the mothers have such a strong, direct influence on the number of grandchildren they get.”

Surbeck and his team worked with populations of wild bonobos in the Democratic Republic of Congo, as well as groups of wild chimpanzees in the Ivory Coast (Tanzania) and Uganda. Both chimpanzee and bonobo mothers would take the role of advocating for their sons in male-on-male conflicts, the team reports — but bonobo mothers also seem to aid their sons in romance.

Some of the behaviors they’ll use to this end include protecting their sons’ mating attempts from other males and intervening in other male’s mating attempts. Bonobo mothers will also leverage their rank in the group (bonobos have matriarchal societies) to give their sons access to popular spots within social groups in the community and help them achieve higher status — which increases their mating prospects. Chimp mothers also engage in such interactions, albeit rarely, the team notes. However, male chimpanzees hold a dominant position over females, socially, making their efforts much less effective than those of bonobo females.

Bonobo mothers don’t seem to extend the same kind of help to their daughters — either socially or romantically.

“In bonobo social systems, the daughters disperse from the native community and the sons stay,” Surbeck says.

“And for the few daughters that stay in the community, which we don’t have many examples of, we don’t see them receiving much help from their mothers.”

In the future, the team wants to understand why bonobo females engage in such behavior. Their working theory so far is that by helping their sons father children, they’re indirectly supporting the continuation of their own genes. This will require a long-term, collaborative effort, he says, to gather data on post-reproductive lifespans of females in chimp and bonobo communities.

“These [bonobo] females have found a way to increase their reproductive success without having more offspring themselves,” Surbeck says.

The team notes that a similar mechanism may have taken place in humans (the ‘grandmother hypothesis‘), listing the long stretch of the post-reproductive human female lifespan as well as the early-age at which human women can no longer bear children (menopause) as evidence in support of this.

The paper “Males with a mother living in their group have higher paternity success in bonobos but not chimpanzees” has been published in the journal Current Biology.

Why do bachelors exist in the animal world?

Imagine a pride of lions: one regal male residing elegantly over his hard-won harem of females, shaking out his mane and lying his lovely, savage head upon his paws as the hot sun beats down. The lions eat the gazelles, the gazelles feed on the grass, and nature’s great balance (one might even say, the circle of life) is at peace. Except, wait a tic: where are all the other boy lions? How can there be so many females and so few males? That doesn’t seem balanced at all.

Those bachelors who are unable to mate, or as science mercilessly refers to them, “zero-class males,” have probably formed a bachelor posse and are roaming the savannah elsewhere doing their best to stay alive. But Charles Darwin would interject: if they are not reproducing, then why has nature selected them to exist? Evolutionary theory is pretty ruthless about it: any strategy that consistently fails to reproduce shouldn’t persist because such individuals will ultimately die off without passing on their genes. And yet.

The different appearances of the bluegill sunfish; illustration by Sarah Nason

Some bachelors are just biding their time before they make their move, like a calculating Scar waiting for an opportune wildebeest stampede. Eventually, the harem’s current owner will age and weaken and one of our young, strong bachelors can successfully fight him for ownership. But a lot of animal systems don’t work that way: oftentimes, the bachelors will never grow to be strong enough to face off against a dominant harem owner. For example, take the bluegill sunfish. Bizarrely, only a certain number of males reach a large body size and defend nests of females’ eggs; meanwhile, a separate faction of miniature males (smaller even than the female) apparently wanders aimlessly.

And they’re not exceptional: these tiny wandering males can make up nearly a third of the male population. Evolution, are you drunk?

Turns out, most bachelors are probably not single

Predictably, even though it looks like it makes no sense, nature knows exactly what it’s doing. To the naked eye, it appears that these bachelors have no way of mating and should be dubbed as “zero-class.” (rough.) However, after watching their behaviour more closely, biologists figured out that the smaller males were using entirely different tactics compared to their dominant counterparts. Their small and agile bodies make them well suited for a decidedly underhanded, but effective, alternative mating strategy: “sneaking.” While the dominant male’s back is turned, the sneaker male darts quickly in, sprinkles some sperm on the female’s eggs, and is gone in an instant.

Genetic studies later confirmed these nefarious tactics, showing that the dominant male defending a nest fathers less than 80% of the offspring on average. Meaning not only are our so-called bachelors able to sneak in there, but they must also possess some pretty aggressive sperm to grab that big of a slice of the paternity. This leads us to a fascinating niche of evolutionary biology called sperm competition, which is exactly what you think it is: sperm duking it out against each other for the prize of fertilizing an egg.

What do sperm battles look like?

In the case of group-spawning animals like fish, sperm wars are mainly staged in terms of quantity. You might have even been thinking that those mini-males look pretty cute, but what if I told you that their testes-to-body-size ratio is four times as large as the dominant males’? When you only have one second to stage your attack, you want to make sure you’ve got plenty of ammo: sneaker males inundate their targets with a barrage of gametes to rival their opponents’. The open battlefield of the aquatic environment means that males are rarely pitted one-on-one against each other, but this all changes when it comes to species that internally fertilize.

Introducing, the weaponized world of the dragonfly (literally). Male dragonflies possess an array of elegant weaponry varied in form and style, but you’ll never see a dragonfly casually toting the trident of Zeus: their weapons are subtly stored, and are for the express purpose of scouring away the sperm of other males. Specially shaped penises featuring scraping appendages are used to deftly remove sperm from previous matings before a male’s own sperm is transferred to the female.

Examples of dragonfly penis morphology; illustration by Sarah Nason, adapted from Córdoba-Aguilar et al. 2003: Sperm competition in Odonata (Insecta): the evolution of female sperm storage and rivals’ sperm displacement.

Because they are able to manually displace the sperm of their opponents, dragonflies are able to avoid any real kind of sperm face-off. But in the event that sperm from two different males are in the same female’s reproductive tract at the same time (in fact, a common scenario), this is where it really goes down: the individual sperm, or spermatozoa, are built for the race. In more competitive environments, sperm can develop ultra-long tails or invest in more energy-producing structures in order to increase their velocity. While we’ve known for a long time that speed determines which particular spermatozoid reaches the egg, competition becomes exponentially fiercer when it’s the sperm of two different males facing off.

Through a combination of sneaky behavioral strategies and superior sperm, evolutionary biologists suspect that the apparent “bachelors” roaming the animal kingdom actually probably have a heck ton of game. So next time you see a photo of a majestic lion, ruler of the savannah, master of his kingdom? Just sayin’, he’s probably compensating for something.

Tinder-like app for orangutans lets females in zoos chose who they mate with

A Dutch zoo is exploring the merits of Tinder-like software in boosting their orangutans’ sex lives, by allowing them more leeway in choosing a mate.

Gotta look good for that profile picture.
Image credits Tambako The Jaguar / Flickr.

As part of a four-year long experiment dubbed “Tinder for orangutans,” 11-year-old female Samboja of the Apenheul primate park in Apeldoorn, Holland, will be the first of her species to swipe, swipe, match. Thomas Bionda, a behavioural biologist at the zoo, will delight the orangutan with pictures of males on a touchscreen to learn more about the species’ mating choices.

Monkeying around

Well you might not know this was a problem up to now, but we kinda need orangutans to get down to business. Along with chimps, orangutans are our closest living relative — and of course, we cut down their habitat and even hunted them so much they’re now endangered.

Part of the effort to preserve this species comes from zoos, where orangutans are encouraged to mate. Available males and females are shipped around all over the world to do just that, but it doesn’t always go according to plan. That’s why Bionda and the zoo have been trying to figure out how females decide which suitors are worthy, by allowing them to take their pick on a touchscreen tablet and examining the results for patterns. Since flying in males can be a long and costly procedure — they could come from as far away as Singapore — the zoo hopes this research will limit stale encounters.

“Things don’t always go well when a male and a female first meet,” Bionda said.

“Often, animals have to be taken back to the zoo they came from without mating.”

I know your pain, male orangutans.

The team’s main problem was developing a device that wouldn’t break under the Samboja’s rough handling. Their first tablet was reinforced with steel and made it past the two week mark. Then Samboja’s mother Sandy — also known as Demolition Woman — got her hands on the device and destroyed it. The scientists are now waiting for a strong-enough screen, after which they will test if looks alone are enough to guarantee a successful encounter in the species.

“This is completely digital, of course,” he said. “Usually, smell plays an important role too. But with the orangutans, it will be what you see is what you get.”

Bionda however isn’t only interested in hooking up orangutans — his research plays into broader work looking at the role emotions play in animal relationships.

“Emotion is of huge evolutionary importance. If you don’t interpret an emotion correctly in the wild, it can be the end of you.”

We pick our mates by their genome — even if we aren’t aware of it

A new study found that we’re much more likely to choose mates that are similar to us — because we seek them out. These mating preferences are statistically relevant and play a part in shaping the human genome, the authors conclude.

Image credits Pascal Renet / Pexels.

A team from the University of Queensland, Australia, says that you’ll likely marry someone a lot like you. Someone who has a similar height, body weight, someone of similar intelligence. And it doesn’t happen because birds of a feather get together, as the saying goes — it happens because we actively search for mates with a genetic load-out similar to our own.

Gene-mates

The team worked with databases of people’s physical and genetic traits. They selected more than 24,000 married couples of European ancestry. For each couple, they selected one partner and isolated the genetic markers for traits including height and body mass index (BMI). Using this data, they then tried to predict the same characteristic in their partner. If one person’s genetic material suggested he was tall, for example, their partner was predicted to also be tall. The goal was to find correlations in these traits. So the final step was to compare these predicted characteristics against their actual value.

The team found a strong statistical correlation between one person’s genetic markers for height and the real height of their partner. They also identified a weaker but still statistically significant correlation between the genes governing BMI and the real BMI of their partners. The correlation is much stronger than what you’d expect to see in the case of random mating. These findings are evidence that people actively seek partners with a genetic makeup similar to their own, the team reports.

Picking mates based on similar traits is a pattern of sexual selection known as assortative mating. It allows individuals to pass traits to their offspring. In effect, this practice increases relatedness in family groups and helps offspring survive better — provided the trait is beneficial in their environment. It has previously been observed in animal populations: brightly colored eastern bluebirds mate with each other while bluebirds duller in color pair up among themselves, for example.

The team also found evidence of assortative mating for other traits in 7780 couples in a U.K. database. They report a “remarkably high correlation” for genetic markers linked to years of education. While it’s unlikely people chose their mates based on actual years spent in school, it does imply that they select for similar interests — which are often associated with levels of education, says team member Matthew Robinson, a postdoc in the lab of geneticist Peter Visscher at the University of Queensland in Brisbane.

Assortative mating “affects the genomic architecture of traits in humans,” Robinson added. As such, the findings are useful in establishing more accurate genetic models, which predict how likely it is that members of a family will inherit diseases or physical traits.

Robinson now plans to use the method to “understand why spouses are similar on many other, behavioral traits, such as IQ, political preference […] and psychiatric disorders.”

The full paper “Genetic evidence of assortative mating in humans” was published in the journal Science Human Behavior.

Fungus turns frogs into sex zombies, but then kills off whole species

A new study of Batrachochytrium dendrobatidis (Bd), a deadly fungus that affects amphibians worldwide, found that it spreads by making males’ mating calls more attractive to females. The pathogen alters the reproductive habits of different species of amphibians, explaining why frogs and related species continue to disappear across the globe.

“If true—that the fungus is manipulating individuals’ behaviors to facilitate its spread—then this is extraordinary,” says Michael Ryan, a herpetologist at the University of Texas, Austin, who was not involved in the study.

The Japanese frog is one of the few species resistant to Bd. But individuals are still becoming infected.
Image credits to wikimedia user Alpsdake

Bd causes a condition named chytridiomycosis or chytrid fungus disease, which destroys amphibians‘ skins, disrupts their immune systems and ultimately causes heart failure and death. It was first discovered in the 1990s when several species of frogs in Australia and Central and South America went through massive die-offs.

The extinction of hundreds of amphibian species in recent years has been attributed to Bd, and it could potentially affect one third of the amphibian species currently on the planet. While there is no known cure for the fungus, a few species of frogs are known to survive several years after infection — indicating a certain level of adaptation towards fighting it.

But as Bd has been relatively contained up to now and species are being exposed to it for the first time, usually there is little natural defense against the fungus.

“Some people think that amphibian populations are declining primarily due to catastrophic die-offs caused by Bd,” says Bruce Waldman.

“But the story is much more complicated than that.”

Southern mountain yellow-legged frogs (Rana muscosa) killed by the chytrid fungus.
Image via sciencedaily

Waldman and his student Deuknam An studied Japanese tree frogs (Hyla japonica) in the wild to find out how Bd affects species seemingly resistant to it. This amphibian, which inhabits area in central Asia, Korea and Japan, hasn’t been experiencing the massive die-offs associated with the pathogen even though individuals are getting infected.

The team studied and recorded the mating calls of 42 male Japanese tree frogs from June to mid-August 2011 (during the mating season) in the rice paddies of South Korea. Here’s a recording of a normal call:

They looked for things such as the number of pulses per note, repetition rate of pulses, number of notes or total duration of the call. Out of this sample, nine frogs tested positive for Bd. These were slightly larger than their uninfected counterparts (40.17mm on average compared to 39.24mm.)

The team also reported that these males became lethargic, but put more effort into their calls compared to the others– for example, they produced longer songs, a trait which females are known to prefer. Here’s a recording of a Bd-infected male:

If you were a female Japanese frog, your lady-frog-parts would be on fire right now.

“Therefore one would expect the amount of calling to be lower in infected males,” Ryan notes.

“But this is not what the study found—and that’s very surprising.”

This suggests, he adds, that Bd can act like a parasite and turn its host into a zombie. These zombie males then go on to spread Bd further in the population by using their fungus-fueled sex appeal: the females they mate with become infected too, and their offspring inherit the fathers’ susceptibility to chytrid fungus disease.

The team hasn’t been able to figure out how Bd changes the host’s behavior, but they to have a theory. They point out that the force of natural selection may be looming over these males, which put an extra effort into their calls in order to reproduce faster as a way to compensate for their shorter lifespans.

But the end result is that while the infected males certainly get more action, the population as a whole is severely harmed.

“Bd has an impact on frog populations even when we don’t see outbreaks of chytridiomycosis,” says Cori Richards-Zawacki, a behavioral ecologist at the University of Pittsburgh in Pennsylvania.

Richards-Zawacki recently found that the disease causes male leopard frogs in the lab to up their reproductive efforts. Although it might seem that a species has adapted to Bd and shows no clinical signs of the disease, she says, “in reality it’s still stressed by the infection, which is likely to take a less dramatic but still important toll on the population over time.”

Waldman says that these “sublethal” effects can kill off a species even if it survives the initial die-off from the pathogen.

“Some of these populations that were hard hit are coming back, but slowly. Their populations are small, and that leaves them vulnerable to other random catastrophic events that might lead to extinction.”

The scientists looked at only one frog species—and only one of its life history stages, Waldman also notes.

“It shows that Bd continues to be an enigma.”

What a dinosaur mating dance might have looked like. Credit: Lida Xing and Yujiang Han/University of Colorado Denver

Dinosaur love dance impressed on sandstone offers first glimpse of dino courtship

What a dinosaur mating dance might have looked like. Credit: Lida Xing and Yujiang Han/University of Colorado Denver

What a dinosaur mating dance might have looked like. Credit: Lida Xing and Yujiang Han/University of Colorado Denver

Birds are literally dinosaurs, so many scientists suspect millions of years ago dinosaurs shared similar courtship tactics like fancy plumage or complex dances to impress potential mates. While fossils can teach us so much about how dinosaurs looked and, in some instances, behaved  (herd behavior, diet, hunting patterns etc.), inferences on mating rituals have been speculations at best thus far. A paper published in Scientific Reports offers some of the first tantalizing evidence that supports the idea that dinosaurs indeed employed similar courtship displays to modern birds. The researchers at University of Colorado, Denver found tracks etched into sandstone surfaces to create nest displays, hoping to attract a female to mate with. These scrapes are one of a kind, found nowhere else in the world.

Dino foreplay

Dinosaurs were wiped out some 65 millions years ago by an asteroid impact event. Luckily, scores of fossils have been found which allowed us to repiece how more than 900 dinosaur species looked like and even behaved. It’s not just bones and other fragments that lend valuable clues though. Fossilized tracks, for instance, taught us that T-Rex hunted in packs, not alone. Similarly, tracks discovered in the Dakota Sandstone of Colorado across four sites sketch out what dinosaurs mating must have looked like. The largest site features more than 60 scrapes on one sandstone surface.

“The size, depth and distribution of these scrapes is variable,” the study authors wrote. “However, most typically consist of parallel double troughs, comprised of multiple scrapes separated by a raised central ridge. … A few show complete outlines of three-toed theropod tracks, and some show thin aprons of excavated sediment aligned with the long axis of the scrapes.”

dinosaur tracks

Dinosaur tracks exhibit lek-like behaviour. Image: Scientific Reports

These sites look suspiciously similar to a lek – an arena where males perform mating dances to impress females. In our case, dinosaurs males likely dug deeply into the dirt to show of nest making abilities. The nests themselves would have likely been made somewhere nearby the lek.

“The scrape evidence has significant implications,” said Martin Lockley, lead author of the paper. “This is physical evidence of pre-historic foreplay that is very similar to birds today. Modern birds using scrape ceremony courtship usually do so near their final nesting sites. So the fossil scrape evidence offers a tantalizing clue that dinosaurs in ‘heat’ may have gathered here millions of years ago to breed and then nest nearby.”

What other mating or courtship rituals did dinosaurs employed? Sadly, we might never know. If they did something other than scrape the ground, it’s unlikely this behaviour left physical evidence. Even so, as they stand, the findings paint a more accurate picture of how dinosaurs evolved and lived millions of years ago. Watch out for intricate dinosaur dances in the next Jurassic Park movie.

A proud Ruff (Philomachus pugnax) male in breeding plumage. Credit: Pixadeus, bossum

Male ruff birds cross-dress to steal females, and it’s all in their genes

A proud Ruff (Philomachus pugnax) male in breeding plumage. Credit: Pixadeus, bossum

A proud Ruff (Philomachus pugnax) male in breeding plumage. Credit: Pixadeus, bossum

Self-preservation and reproduction are the most powerful instincts, and life forms on Earth have devised all sorts of gimmicks and tactics to become successful (pass on those genes). Just look at the male ruff sneak tactics to grab girls. There are three distinct approaches: the cocky aggressive, the sneaky ‘satellite, and the cross-dresser. You might think this isn’t necessarily peculiar in itself. After all, human males employ similar approaches to seek women’s attention. The peacock, the friend-zone dude, the jock, the joker etc. What’s odd about ruff males is that this behavior is coded inside their genes – from the way they act, to how their plumage looks like. And they’re all, ultimately, males of the same species.

“The ruffs provide a neat example of how small genetic changes can lead to major differences in attractiveness and behaviour. This process is fundamental to the formation of separate sexes and separate species,” said Professor Terry Burke from the University of Sheffield’s Department of Animal and Plant Sciences

Males on the TOP ROW are satellites. The REST are territorial "independents". Credit: D. Lank, montage: J. Dale

Males on the TOP ROW are satellites. The REST are territorial “independents”. Credit: D. Lank, montage: J. Dale

The ruff is a medium-sized wading bird that breeds in marshes and wet meadows across northern Eurasia. The adult male varies in color from dark rufous to light brown with considerable white. It has a thick mane of long feathers around its neck and thick head-feathers that can be puffed out. The female, called a Reeve, is mottled brown-and-buff with orange legs (sometimes olive or green). To mate, the ruff employs a ‘lek’ system, meaning males of the species gather together and invest all of their energy into attracting females to mate with them, and none into parental care. It’s actually quite common among birds, other examples including the  sage grouse, prairie chicken, great bustard and sharp-tailed grouse.

Lek mating arena, modeled on the sage grouse, in which each male, alpha-male (highest ranking), beta-male, gamma-male, etc., guards a territory of a few meters in size on average, and in which the dominant males may each attract up to eight or more females. Image: Wikimedia Foundation

Lek mating arena, modeled on the sage grouse, in which each male, alpha-male (highest ranking), beta-male, gamma-male, etc., guards a territory of a few meters in size on average, and in which the dominant males may each attract up to eight or more females. Image: Wikimedia Foundation

Ruffs, however, have turned lekking into an art. The most creative seem to be a group of male ruffs which impersonate females, so other males don’t give them too much attention when they’re pumping their plumage out to impress the gals.  By lacking ornamental feathers and mimicking females, these crafty males draw no attention to themselves – until they make their move that is, whisking off females from the resident males. This is one of three behaviors. There’s the territorial breeding males which have spectacular plumes around their neck and vary tremendously in colour, such that each males looks unique. Then there’s the ‘satellite’ males, all dressed in white plumage. These kind are non-territorial, but seem to be very good at stealing mates.

By sequencing the genomes of the birds, researchers at University of Sheffield discovered that these fascinating mating rituals are actually hard-coded in the birds’ genes. In fact, the researchers refer to a ‘supergene’ – a section of the chromosome made up of a hundred or more genes. This supergene surfaced a couple million years ago, allowing female mimickers to co-exist with territorial males.

“The special feature of the supergene is that it allows lots of genes that are next to each other on a chromosome – which in this case determine multiple traits including hormones, feathering, colour and size – to evolve together and create two distinct behavioural traits.”

“This process is similar to the one that led to the evolution of separate sex chromosomes, and indeed the alternative forms of the supergene combined together to create the third type of bird personality – the girlfriend stealer,” Prof. Burke added.

Females are not rational when it comes to choosing their mates – at least in frogs

Picking a mate is one of the most important decisions anyone (human or animal) makes in a lifetime, so it’s important to weigh all the pros and cons and make a rational decision. But that doesn’t go for frogs. Female túngara frogs often exhibit irrational behavior when choosing a mate. This challenges many previously held beliefs as well as several biological behavior models.

The Tungara Frog females sometimes make irrational decisions when it comes to mating. Image via Wikipedia.

If you live in central America, the odds are you’ve seen (or at the very least, heard) túngara frogs, as they can live everywhere from thick forests to urban puddles. They’re only 2 cm long, but they can be very loud – the males use these loud calls to lure mates. Amanda M. Lea and Michael J. Ryan, two behavioral biologists working at the University of Texas (Ryan lab), studied their calls in detail to see what turns females on. They found that there’s a specific type of call they prefer.

“They tend to like longer calls. They also like lower-frequency calls,” says Lea. “Then, the other thing that’s a really big one for these gals is the ‘call rate.’ They love faster call rates. The faster a male can call, the better.”

But that’s only a general rule, and in real life, love calls can be very complicated. So they set up a controlled environment, in which females were placed in a room with some loudspeakers. From one speaker the scientists played a recording of frog call that had a really fast rate, but other features in its voice were less attractive. They then played another call which was slower, but featured other attractive features. In other words, they made the females choose between two “grey” options.

“They have two traits to evaluate,” Lea explains. “They have the call rate and they have the attractiveness of the call.”

The females consistently chose the fast guy, crawling repeatedly towards that speaker. But then, scientists added a third option: a call just like the slow, rejected one, except this one was much slower. The two other calls remained unchanged. What happened was surprising.

The females didn’t chose the third option, but its mere presence was enough to dissuade them from their original choice, rejecting the fast guy, and now choosing the slower one. The other, least attractive call, made the unattractive option seem more attractive.

“They actually switch their preferences,” says Lea. “So now call rate is no longer the most important thing.”

This is irrational and makes no sense – an option that should have no impact on anything actually makes females change their primary mating option; so far, there’s no explanation for that. The most unattractive guys just act as decoys.

“This is the first time we’ve found evidence for irrational mating behavior,” says Lea. “If they aren’t making rational decisions, then these [behavioral] models don’t hold up.”

So think about it guys, if you’re unattractive and want to pick up some girls, just have a more unattractive wingman. That has to work – at least if you’re a frog.

Journal Reference: Amanda M. Lea, Michael J. Ryan. Irrationality in mate choice revealed by túngara frogs. DOI: 10.1126/science.aab2012

Blue whales singing lower every year, baffled scientists say

Blue whales are not only the biggest living creatures in the world right now, but the biggest ever to have ‘walked’ the face of the earth; they’re also the loudest for that matter. After recovering from near extinction in the beginning of the 20th century, blue whales are finally getting a part of the respect they deserve.

However, researchers cannot understand what is causing these majestic creatures to ‘sing’ at lower frequencies year after year. No one is fully sure of all the uses of the blue whale songs, but it’s known they are used to communicate and as a mating ritual. However, ever since the 1960s, the frequencies which these giants use are getting lower and lower, without anybody being able to give an explanation.

full_bluewhale_6

Of course, some theories have emerged, the two most likely being that it’s a direct result of the water pollution or a sign that an almost extinct population is recovering. Mark McDonald, president of Whale Acoustics, a company that specializes in recording the songs of blue whales (yeah, really) originally thought the cause could be noise pollution caused by intensified traffic; however, if this would be the case and they would want to make themselves heard louder, they would use higher, and not lower frequencies. This may be a bit weird because generally lower frequency transmissions are used for long distances, but mister McDonald explains:

Across the frequencies of blue whale song, the underwater transmission losses are nearly the same regardless of frequency. It is absorption which is the primary cause of frequency dependent transmission losses, rather than dispersion in this case, and the absorption loss only begins to become significant when ranges reach thousands of kilometers. Theory tells us the whales can produce higher amplitude songs at higher frequencies, based on given lung volume.

whales

Another possible reason could be a change in the mating rituals. Scientists have long known that only male blue whales sing, and larger (which are usually more mature) specimens sing at lower frequencies. The hypothesis is that the younger guys are trying to emulate the older ones in order to attract females (that seems familiar). Either way, there are many we have yet to understand about the way these marine mammals act. The only good thing is that the blue whale populations is nearing a normal limit; let’s set this as an example for other species too, instead of treating them with less care now that they’re not on the brink of extinction anymore.

The mysterios green glow of the sea decoded

In the past the sea was considered a truly miraculous place especially as many phenomena seemed to have no logical explanation. Sea creatures have also troubled  the sailors as they were like nothing else they had ever seen. Now science proved that most of our fears are not justified, but also that miracles can have an explanation without losing their appeal.

One of these cases is the one of the green light to be seen below the ocean’s surface in tropical seas. No, no aliens to be blamed for this, but bioluminescent worms. Until recently there were still some questions to be answered, especially related to the way light is produced. At first, it was discovered that the light is highly important in  the mating ritual, but now it seems that it may also serve for protection. The biological mechanisms of the phenomenon are still to be decoded.

Keeping light stable for such a long period of time and identifying the exact protein which allows this would prove a helpful discovery for biomedical, bioengineering and other fields.

The fireworms which were studied (Odontosyllis phosphorea) live on the seafloor in tropical and sub-tropical shallow coastal areas. In summer, when mating season arrives, which is also known as swarming, females secrete a mucus that glows green before they release gametes into the water. The intense color attracts the males, which release their own gametes in the same area.

These displays of light were noticed especially n Southern California, the Caribbean and Japan, reaching the highest degree one to two days before each quarter moon phase, 30 to 40 minutes after sunset; they usually last for 20 or 30 minutes. But, as the young seem to secrete the same substance, it seems that the mucus may be used for protection as it distracts predators’ attention.

After studying hundreds of specimens, the main purpose of the researchers was to produce the luminous mucus in the laboratory. The bioluminescence proved to be active in temperatures as low as minus 20 degrees Celsius (minus 4 degrees Fahrenheit) and mostly in settings of low oxygen levels.

The scientists believe a light-producing protein, also called “photoprotein” may be involved. Further studies will be needed in order to isolate it successfully.

This work is inspired by the one of Osamu Shimamura, who won the Nobel Prize in Chemistry for discovering the fluorescent protein from the jellyfish luminescent system. So who knows what this research will lead to?

source: University of California – San Diego.