Happy Valentine’s day! Testicle size and mating systems

I really despise Valentine’s day because I do not appreciate society telling me when I should feel romantic and loved-up and when I should not. HOWEVER as a bit of fun, I thought I would write a post about love, romance and sex but most importantly SCIENCE!

And testes*.

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Testicles are funny things, and almost all healthy male vertebrates boast two of them. In many mammals, including ourselves, they hang from the body in a scrotum because the valuable sperm they contain are mighty fussy, and mammalian body temperature tends to be just a little too hot for them. So natural selection kindly began dangling the sperm of males from two sacs between the rear legs, nice work evolution. But it turns out that we can tell a lot about a species’ mating system (i.e. how monogamous or promiscuous they are) just from looking at the size of the male testis. The diagram below is both hilarious and helpful:

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Here you can see the gonad size of various primate species in relation to body size. The top row are the males – the big circle represents their body size, the arrow is the penis and the balls are, well, the balls. (No laughing at the gorilla and yes guys, your penis is quite large compared to our primate cousins). The bottom row shows the female sexual organs of the same species – I can’t help but giggle at the human female. MASSIVE BOOBIES!

So the size of the testes can tell us a lot of information about the mating system adopted by various species. We have to remember that although in our culture monogamy is often (rightly or wrongly) seen as the norm, this is far from the case in most other mammalian species. There are lots of different mating systems: monogamy (one male one female), polygyny (one male, several females), polyandry (one female, several males) and promiscuity (basically a free-for-all orgy where it is completely acceptable for anyone to have sex with anyone).

Males of species with promiscuous mating systems (such as chimpanzees) tend to have the largest testes, and this makes sense because of something called sperm competition. In a promiscuous mating system, lots of males are having sex with lots of females, and everyone wants a good shot at fathering the most offspring, because this means passing on your genetic material and is a big fat evolutionary WIN. So for this reason it is advantageous to have a lot of sperm, and big old testes to store the little guys in.

However, the males of species with polygynous mating systems (e.g. gorillas)  tend to have smaller testes, because a single male has almost guaranteed access to at least a couple of females. So there is no need to waste extra energy on producing lots and lots of sperm in giant testicles, because his chances of impregnating a female is pretty high and he has no competition to wane off.

Now I know what you’re thinking. Where do we fit in all of this? Well guys, I have to say, your testicles are classified as “moderate”. Bigger than a gorilla, but shy of a chimp. This actually fits well into the mating system hypothesis – although humans are often socially monogamous, they do participate in moderate levels of non-monogamy (SHOCK HORROR KLAXON)!!

So there you have it. The bigger the balls, the more promiscuous the sexy-times. But smaller testicles aren’t for losers – it just means they don’t have to try so hard! Quality over quantity perhaps? Maybe that just means more time and energy can be spend on post-coital cuddles or, you know, child-rearing.

So whether you have testes or ovaries, and regardless of their size, I wish you all a very happy and sexy V-day.

A bonobo with large testicles chillin’ out.  Source

*I will leave it up to you to guess what type of mating system this squirrel may participate in.

The naked mole rat: More than an ugly face

If you live in the UK, have you been watching the latest BBC Attenborough offering, Africa? If you answered “no”, WHY THE HELL NOT? and if you answered yes, OMIGODHOWGOODISIT??

“Sahara”, the episode that aired last night (30/1/13) has probably my personal highlight so far, not least because it featured one of my favourite funny looking creatures in the world ever: The naked mole rat.

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Despite it’s appearance, this creature is not actually an old wrinkly penis with buck teeth growing from it’s nostrils.The naked mole rat is so ugly it is almost adorable. But not only does it look so goddamn horrendous that it becomes some sort of mythical being that you can’t quite drag your screaming yet sympathetic eyeballs away from, it is also a very interesting little creature, for several really cool reasons. Let’s start with its physical appearance, since we’re all judging it already. DON’T PRETEND YOU’RE NOT.

It’s hard to miss the fact that naked mole rats are, well, naked. But if you look closely you will see that they are not completely hairless, oh no. Natural selection has given them the mole-rat equivalent of a fig leaf and provided them with some lovely long super-sensitive whiskers which help them feel around, which is handy when you live in narrow tunnels under the ground (they can also run backwards just as effectively as forwards, which is also handy for the environment they live in). Because they are perfectly adapted to living in underground burrows, the naked mole rats have practically lost the need for their eyes, which are present but are located underneath their skin and are essentially useless. And who can ignore those gnashers? Like all rodents, the incisor teeth of the naked mole rat never stop growing. They protrude in front of the lips (which are sealed behind the teeth) in order to stop the critters swallowing soil when they are using their wallies to dig through the soil – all of which I’m sure you will agree just adds to their sex appeal. 

A naked mole rat’s reaction to being shown a mirror. [Source]

Although they are mammals, naked mole rats do not regulate their body temperature the same way most mammals (including ourselves) do, through a process called thermoregulation. Sweating, shivering and panting are examples of thermoregulation, whereby an organism keeps it’s core temperature at a stable level, regardless of the temperature surrounding it. Rather, naked mole rats are cold-blooded thermoconformers, meaning that their core body temperature changes depending on how hot or cold their environment is. But because they live underground in the African desert, the habitat of the naked mole rat has a more-or-less constant temperature which is comfortable for them.

Perhaps the most peculiar thing about naked mole rats concerns their social structure, as they are one of the very few mammals which are described as “eusocial”: Eusociality is a hierarchical social structure more commonly found in social insects like ants and bees, wherein each colony (for a naked mole rat this is around 80 individuals) has a reproductive “queen” who produces all the offspring in the group, and all the other individuals are “workers” who are sterile. When the queen rat dies, some of the other females in the colony begin to develop eggs within a week of her death. Older females in the colony develop eggs first, and often fight to the death for the right to become the breeding female.

Hopefully I have convinced you that naked mole rats are more than just a pretty face. But the interesting facts do not end there, oh no. It turns out that these creatures may hold a very important secret which could lead to huge breakthroughs in cancer research: Mole rats are thought to be the only mammals who never develop cancer, and scientists have possibly found out why. Cancer is caused by unregulated cell growth, and the cells of naked mole rats poison and kill themselves when they multiply too much, thus cutting out cancer.

So there you have it. Cold-blooded, eusocial, cancer-resistant, bald mammals. Naked mole rats are awesome.

 

Sources

BBC Nature:
http://www.bbc.co.uk/nature/life/Naked_mole_rat

Wired: Why Blind Mole Rats Don’t Get Cancer:
http://www.wired.com/wiredscience/2012/11/blind-mole-rat-cancer/

 

 

Will the real slow loris please stand up… Slowly.

Dearest readers, I have a confession to make: I am not actually a loris. I am a human.

Yesterday was my birthday, and yesterday it also occurred to me that for the last 2 years or so I have had the audacity to be masquerading a pygmy loris without so much as writing a single blog post about these most adorable little creatures (because these are the sorts of things one reflects on when one gets a year older, n’est-ce pas?). This is my attempt to correct this discrepancy. Ladies and gentlemen, please meet the slow loris.

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When I show people a picture of a loris, I generally get one of two reactions:

1. “Euugh what a freak!”

2. “AWWWWW SO CUTE!”

If your reaction was 1., get off my blog. Right now. If your reaction was closer to 2., I’d like to say OMG I KNOW RIGHT?! I mean just LOOK at those ginormous beautiful eyes and those big chubby fingers! Let’s talk about how CUTE and AMAZING they are!

I had never heard of lorises until I was in the third year of my undergraduate degree, where I took a compulsory module on animal behaviour. “Pah, animal behaviour.” I thought to myself, “what use is that going to be to me?” as I shrugged at the back of the lecture theatre and stuck my head back into a book entitled “symbolic interactionism”. Then, in my very first animal behaviour lecture, my professor showed a slide with this very picture on it:

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I had never seen anything that looked remotely like this little creature before. What the hell was it? It looks like an alien. And I instantly fell in love. I remember few specific facts from that lecture, but I did learn that this odd creature is called a slow loris because it is really, really slow and it has chubby fingers because it uses them to pick up bugs like caterpillars and eat them. I also learned that animal behaviour would be by far the most interesting part of my entire degree.

Lorises aren’t just cute, they’re freaking cool and unique too, and not unique in the way that parents assure their children they’re unique, lorises really are special: they are the only venomous primate. Yep, don’t be fooled by this cutie’s slow and shy nature, she can do some serious damage. The venom is produced in what appears to be an overly complicated rigmarole – oil is secreted from a gland near the loris’s elbow which only turns deadly when combined with her own saliva via licking (fun fact: I can lick my own elbow, which is often assumed to be impossible, just another reason I feel the lorises and I are kindred spirits). It’s not known exactly why this venom system evolved in lorises, but it is likely that it has something to do with protection from predators. Because of the need to combine the arm-venom with saliva from the mouth, it is not surprising that the defense pose of the slow loris is one in which the arms are held up, above its head… Sort of like this.

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Some of you may recognise this image, it’s taken from a viral video entitled “Slow loris loves getting tickled”. I would argue that this loris probably does not love getting tickled and that in fact it is terrified by the whole situation.

Unfortunately because they are so freakishly attractive, people in some parts of the world think lorises would make excellent pets. The internet is riddled with videos of them being all cute and cuddly but in reality these animals are not suited to being domestic pets at all. They are solitary nocturnal (not to mention venomous) animals. But when people want people get, and so the vulnerable loris is hunted (which is not a difficult task due to their slow moving nature and the shine from their huge eyes at night), their sharp teeth are removed and they are sold on the black market as pets to countries like Japan and Indonesia.

It’s so easy to see the videos of pet lorises and think they are cute and funny – they are, if you don’t really know how these animals live in the wild. But they should not be kept as pets, and the rather wonderful Anna Nekaris and colleagues have set up the Little Fireface Project highlighting the importance of saving this beautiful creature from extinction through ecology and education.

I will leave you with a teeny weeny video of a slow loris in its natural habitat, in a tree, at night, just so you can see how wonderfully and peacefully they move around, and because it’s the only video I could find that did not make me want to cry and save all the lorises and return them back to the wild.