Tag Archives: Males

Golf ball.

Primate males with more ornamentation seem to have smaller testes, a new study finds

Showing off takes stones for male primates. Small ones, it turns out.

Golf ball.

Pppppffff, show-off!
Image via Pixabay.

Gird your loins, ladies and gentlemen, because today we have a rather peculiar (but still interesting, and quite amusing) study to talk about. Hailing from the The University of Western Australia and the University of Zurich, the paper reports that flashy male primates tend to have smaller gonads, while their more average-looking counterparts sport larger ones. It all seems to be a product of how male primates handle social hierarchies and reproductive strategies.

Two kinds of primates

Dr. Cyril Grueter, a primatologist from UWA’s School of Human Sciences and a co-author of the present paper, says that male primates tend to live in relatively high-competition environments. They also pretty much all want the same thing: to impress (and impregnate) the females.

“But not all of them can have what they want,” he adds. “So how do they succeed? Well, next to simply fighting, they can produce so-called ‘badges of status’; showy ornaments that help their bearers control access to females by intimidating other males.

“And if males cannot keep others off their females, they can win by producing a lot of sperm to swamp those from their rivals.”

The study focused on primates because of their “tremendous variation in both testicle size and male ornamentation,” a press release accompanying the paper explains. Dr. Grueter seconds this view, saying that some primates they looked at in the study had testicles no larger than a peppercorn, while others’ could easily pass for tennis balls. Pun intended.

Pretty surprisingly, however, the team found that there’s a consistent link between different indicators of male virility throughout primate species. The team compiled data from over 100 species of primate (including humans) to show that ornamentation seems to come at the expense of testicle size and sperm production ability.

“We found the same thing with ornamentation – some species sport flamboyant accoutrements such as beards, manes, capes, and cheek flanges, and various shades of colour in their faces and fur,” he said.

“Others are pretty drab and look more like your Mr Average.”

In blunter terms, showy primate males have smaller testes. Dr. Grueter jokes that the “finding clearly shows that you can be well-adorned or well-endowed, but it’s hard to be both”. This either-or approach likely comes down to economics, the team suspects: it simply takes up too much energy to invest in both reproductive strategies.

The findings also tie in with some of Grueter’s past research. In a study published in the journal  Evolution and Human Behavior back in 2015, he and his team reported that male primates have developed more ostentatious ‘ornaments’ or ‘badges’ (such as beards in humans, cheek flanges in orangutans and so on) to help them navigate big, multilevel societies.

Such elements could help males attract the attention — and affections — of females while also helping them deal with male competition in a more direct way. Male rhesus macaques (Macaca mulatta) with darker red faces receive more ‘come-ons’ from females during the mating season, the team reported in that study, while men with beards could be seen as more aggressive and dominant than those without beards — helping them intimidate competitors and attract women drawn to seemingly powerful men. That paper also suggested these badges are particularly useful for males in large, complex groups, as proxies to show dominance or rank.

“When you live in a small group where everyone knows everyone because of repeated interactions, there is no need to signal quality and competitiveness via ornaments,” Greuter explained at the time.

“In large groups where individuals are surrounded by strangers, we need a quick reliable tool to evaluate someone’s strength and quality, and that’s where these elaborate ornaments come in. In the case of humans, this may also include phenotypic extensions such as body decoration, jewellery and prestige items.”

So, primate ladies in the audience, take heed: flashy males may catch your eye… but there’s really only enough energy to pursue a single reproductive strategy at a time.

The paper “Sexual ornaments but not weapons trade off against testes size in primates” has been published in the journal Proceedings of the Royal Society B: Biological Sciences.

Fruit fly.

Neuron cluster which can override sleep identified in the fruit fly brain

Certain neurons in the brains of male fruit flies will suppress the animal’s sleep if they have any female to court nearby.

Fruit fly.

Image credits John Tann / Flickr.

Who here hasn’t had to forgo the sweet embrace of sleep when something important pops up — a paper due in the morning, a book you just can’t put down. Or, if you’re a male fruit fly, because there’a a change you might get some action.

A team of researchers from the Sidney Kimmel Medical College at Thomas Jefferson University found that like humans, fruit flies (Drosophila melanogaster) can keep themselves awake if something important pops up. More specifically, they report that a certain group of neurons in the males’ brains can suppress their sleep so they can court female flies.

Up all night to get lucky

The study started from the observation that although male flies usually spend most of the night awake trying to court nearby ladies, those who have recently mated several times (and thus have a low sexual drive) tend to ignore females and simply go to sleep.

It would suggest that something in the fly’s brains has to (consciously or unconsciously) decide what was more important to the fly at one point — sex or sleep. But nobody knew exactly how this process unfolded, and that’s what the team set out to understand.

“The idea that sleep and courtship might compete with each other is intuitive but had not been studied experimentally, and the underlying neural mechanisms had not been explored. We wanted to know how the sleep drive and sex drive compete to determine behavior,” says Kyunghee Koh, PhD, Associate Professor of Neuroscience, Sidney Kimmel Medical College at Thomas Jefferson University and senior author on the study.

The team zeroed in on a bunch of neurons dubber MS1 (male specific 1) that seem to be at the root of this process. MS1 neurons aren’t part of any previously known groups of neurons which play a part in male sexual behavior, but work by keeping the males awake so they can ply their charm. They release octopamine, a neurotransmitter similar in function to noradrenalin, which will keep male flies awake in a sexual setting. Experiments showed that silencing the MS1 cluster caused males to go to sleep even if there were females around, and artificially activating the neurons kept males awake even in the absence of females.

Interestingly enough, while females have the same bunch of neurons they don’t seem to function the same — activating or inactivating the cluster had no effect on the females’ sleep.

We don’t yet know whether there are similar mechanisms functioning in our brains, but we do know that noradrenalin creates wakefulness in humans. This would suggest that the neurotransmitter plays a key role when we’re trying to consciously suppress sleep, the team notes.

But until we get a definitive answer on that, the team wants to identify which neuron communicate directly with the MS1 cluster, examine how their activation leads to sleep suppression and how MS1 neuronal activity is regulated.

The full paper “Identification of octopaminergic neurons that modulate sleep suppression by male sex drive” has been published in the journal eLife.