I get lots of interesting questions from those who follow my tumblr, most of which I do intend to answer… eventually. But in any case, today I decided to tackle this one, from dancing-thru-clouds:
I would like for you to talk about the whys of evolving the prostate, please! Like, seriously, what function does the thing serve? And why does it get cancer so easily?
Excellent question, my dancing friend. The prostate- such an oddly magical part of the body (amirite, prostate owners?) yet so egregiously abused by fanfic writers. Guys, please, it’s just a delicate little gland, it needs a breather sometimes!
Flashbacks to 2009 aside, the prostate is really quite important for mammalian reproduction. It’s odd to me that it’s barely discussed in most sex ed classes- maybe they think that mentioning it will ~make kids gay~? (Regardless of the fact that enjoying prostate stimulation has nothing at all do do with one’s sexual orientation.)
Well, come with me (ha ha) and let’s learn about prostates. Warning- there are a couple of not-quite-safe-for-work anatomical diagrams behind the cut!
Note: some of the videos embedded in this article show predators eating animal carcasses.
To describe what kleptoparasitism is, I’m going to use a Pixar film.
I don’t remember this poster looking so ominous.
Yes, Pixar’s 1998 film A Bug’s Life, while incorrectly making worker ant Flik a male*, provides a very excellent example of kleptoparasitsm. Poor Flik’s ant colony is forced to gather extra food every year in order to offset the losses from the larger and more aggressive grasshoppers, who regularly come and steal the ants’ food.
While real grasshoppers aren’t known for pilfering from ant food stores (they would find themselves very quickly dismembered and tossed on the pile), this type of interaction is very common between types of species that share the same food source, or need the same types of resources, such as nest-building material. Generally, it is the larger, more powerful species that nabs the resource from the smaller one. Hence the term ‘kleptoparasitism’: parasitic theft.
Most kleptoparasitism takes place opportunistically- few species have evolved to be thieves one hundred percent of the time because it’s simply not practical. The only exceptions to this occur if you consider brood parasitism a kind of kleptoparasitism. For example, common cuckoos exclusively make use of the nests built by other birds and have lost the ability to care for their own young. Conversely, slave-making ant species actually steal the young of other ants to do all the work in their colony. Et tu, Flik?
Kleptoparasitisitic relationships can also occur between members of the same species- one could consider the nabbing of prime territory or mates a form of kleptoparasitism. In fact, many species that have kleptoparasitic relationships with one another are very closely related, particularly in insects. This makes sense- the more similar you are, the more you compete for the same resources.
The relationships I want to talk about the most today, however, are the ones between species that are not closely related, but share the same ecological niches. And I want to discuss an interesting hypothesis, one that was also explored in A Bug’s Life. If you’ve seen the film, you’ll remember the ending:
Yep, Flik saves the day and helps his colony defeat the grasshoppers by reminding them that they vastly outnumber their parasites and, additionally, are equipped with limb-severing pincers. The ants are then able to overwhelm the grasshoppers with sheer numbers and presumably feast upon their remains offscreen.
So: how effective are numbers as a defense against kleptoparasitism?
Kleptoparasitic Relationships Between Large African Predators
Kleptoparasitism is a major problem for mammal species of a particular kind: small, lightweight, and specialized predators. On the African savannah, two species are notable targets for kleptoparasitism: the cheetah and the African wild dog.
Of the large mammalian predators on the savannah- the lion, leopard, cheetah, hyena, and wild dog- it is the cheetah and the dog who have the highest hunting success rates, of about 50 and 80 percent, respectively. Comparatively, hyenas and lions have closer to 30% success rates when they attempt to make a kill.**
Hyenas and lions, while not as speedy or efficient as the dogs and cheetahs, certainly know how to use their greater weight to their advantage- hyenas weigh about twice as much as both species, while lions have nearly four times their bulk. It is estimated that about 50% of all cheetah kills are parasitized by lions or hyenas, a rather grim statistic for an endangered species.
Unfortunately, there is very little a single cheetah can do against a hyena. Aside from the differences in weight and power, the specialized hunting style of the cheetah means that any injury could be fatal. Cheetahs (and wild dogs) are cursorial hunters, which means that they chase their prey over long distances. This requires a lightweight body and excellent stamina. A lion might be able to stalk and ambush its prey with minor injuries, and even with major ones it still has a chance of using its weight to steal prey from smaller creatures. But cheetahs and wild dogs hunt nearly exclusively for their own food.
The lion is the heaviest predator on the savannah, and they know it: as many as half of the kills a lion eats might be stolen from other predators. They kleptoparasitize even more than the much-maligned hyena, which in some studies hunts for as much as 95% of its own food.
However, hyenas can also kleptoparasitize the larger and more powerful lions. Their secret? Just as with the ants, it lies in numbers. If a group of hyenas outnumbers the lions feeding at a kill by a factor of four, they may challenge them. It’s a toss-up to whether or not they will succeed, though the presence of much larger male lions can make things much more dangerous. One study found that 71% of all hyena mortality was due to lions.
In fact, lions are a major cause of death for all of their competitors. African wild dogs and cheetahs also have much to fear from lions: lions will seek out and kill their cubs without even bothering to eat them afterwards. For this reason, while these species can forge a rough coexistence with hyenas, they actively avoid spaces that lions frequent.
You’ve been lied to, folks: Lions ain’t majestic beasts with flowing hair. Lions are gigantic assholes that make up for their crappy hunting skills by stealing meat from smaller animals. You say lion king, I say lion tyrant.
Remember, son, hyenas are inherently evil and there’s nothing wrong with stealing their food and murdering their young. Now go eat your rotting carcass.
So on the savannah, killing your prey may be the simple part: the harder part is keeping it. Leopards, at least, have solved this issue by dragging their prey up into trees to eat at their leisure, though this doesn’t always work. Other species with less of an inclination for tree-climbing will make their kills in tall grass or dense foliage to avoid detection, though inevitably small scavengers like jackals and vultures will give them away. In fact, at times the scavengers can oust the killers themselves.
Much of the behavior of these smaller hunters, in fact, is heavily influenced by kleptoparasitism- more than you might think. After all, evolution doesn’t work in a vacuum, and if there’s someone out there making it, there’s always someone else ready to try and steal that success.
This raises a rather interesting question: are some of our assumptions about the social nature of these hunters wrong? Recall that if they greatly outnumber lions, hyenas can steal their kills. Conversely, this means that even the lions need to be in large groups to resist losing their spoils. Do these predators group up specifically to reduce kleptoparasitism?
But wait, I hear you say. The reason why animals hunt in groups hunt in groups is because they need to work together as a team to kill much larger animals!
Well… yes and no. Animals that hunt together in groups are actually restricted to larger prey***, because they need to have enough food to feed everybody when they’re done. What feeds six lions more effectively: one impala or one Cape buffalo?
This buffalo looks like it’d eat a few impala itself on an off day. (Photo source.)
If you think about it this way, hunting larger prey is a handicap and not at all an advantage- especially when you consider the increased danger from things such as injuries. That cute little impala isn’t going to kick your head in with the same force that a Cape buffalo will. (Also, the impala is less likely to turn around and stomp on your remains to be sure the job is done.)
It’s a fact that most predatory animals- estimates range from 85-90%- hunt by themselves. So what led some animals to seek out big, dangerous prey that they couldn’t finish alone? Probably not the thrill of it all. Remember how dangerous injuries are for some predators? There has to be a big payoff for all that risk.
But perhaps we’re looking at it the wrong way- maybe the tendency to group up evolved before predators started attacking oversized prey. In that case, why did the hunters start working together?
Resource distribution may be a large factor: if prey animals are spread out evenly through the environment, predators will probably have the most success hunting alone. But if prey animals are clumped all together and tend to try to defend one another, a group may have a better chance of splitting somebody away from the herd than a solo hunter.
However, the distribution of resources doesn’t neatly tie up every loose end. While some species have a higher likelihood of making a kill in larger groups, many do not. In fact, most mammalian predators are quite capable of hunting smaller prey by themselves- single wild dogs can kill impala, and it is actually more common for hyenas to kill prey alone than when in a group. In a large study of species that either hunted in groups or alone, ecologists Packer and Rutton actually found that there tended to be no overall benefit in terms of hunting success when animals hunted in groups.
Additionally, most group hunters live in larger groups than the ones they hunt in- hunting parties tend to be cliques that split away from the main group. And the phrase ‘group hunting’ itself may be misleading. While African wild dogs statistically have increased hunting success in larger groups, individual dogs within a hunting party may all initially be pursuing different prey animals at first, then converge upon the first animal that becomes vulnerable. In this sense, they are hunting “alone” until the final moments.
I mentioned earlier that hyenas usually make their kills by themselves: however, they may be trailed by other members of their clan that attempt to take the meat for themselves once the hard work is done. So not only do group-living animals have to share their meat, they might have to share it with individuals that didn’t even help get it. How’s that for a raw deal!
So exactly what advantages do hunting in groups confer? Resistance to kleptoparasitism may actually be a big factor. A hyena may be able to steal from a lone wild dog. But what about ten?
(They may not be able to kill the hyena, but they sure can annoy the shit out of her.)
In this video, finally, the smaller hunters are able to drive off the larger ones and finish their meal. Just like Disney taught us in A Bug’s Life!
Now, I’m not going to suggest that this resistance to kleptoparasitism is the only reason some predators hunt in groups- there’s a whole host of other factors that I haven’t even touched on, like the ones that have nothing to do with eating- group living confers other benefits, especially for a little fellow who might become prey as easily as predator. But I do challenge you to reconsider what you thought you knew about why animals hunt in groups.
Let me close with cheetahs, since I discussed them a great deal earlier. Most cheetahs hunt alone. However, many male cheetahs hunt in groups of 2-3 related individuals known as ‘coalitions,’ some females hunt with their cubs, and some adolescents of either sex will hunt together.
Most studies of cheetahs conclude that while coalitions enable cheetahs to seek out larger prey, the amount each animal eats is no higher than it would if it hunted alone (and may even be less). Resistance to kleptoparasitism may provide benefits- though, surprisingly, one hyena is still capable of scaring three fully grown male cheetahs off a kill.
The answer this time, in fact, probably lies with social behavior and has nothing to do with hunting at all. Female cheetahs tend not to be territorial, and live in vast home ranges overlapping those of many other females. This makes it more difficult for male cheetahs to defend access to females- unless they have wingmen to back them up.
So in the end, cheetahs still kinda get screwed no matter what. Good luck, guys.
No wonder they’re always crying. (Photo by William Warby.)
Or just return to the Nonfiction section to see a list of all articles I’ve written. Thanks for reading!
References
Cangialosi, K. R. (1990). Social spider defense against kleptoparasitism. Behavioral Ecology and Sociobiology, 27(1), 49-54.
Carbone, C., Du Toit, J. T., & Gordon, I. J. (1997). Feeding success in African wild dogs: does kleptoparasitism by spotted hyenas influence hunting group size?. Journal of animal Ecology, 318-326.
Carbone, C., Frame, L., Frame, G., Malcolm, J., Fanshawe, J., FitzGibbon, C., … & Du Toit, J. T. (2005). Feeding success of African wild dogs (Lycaon pictus) in the Serengeti: the effects of group size and kleptoparasitism. Journal of Zoology, 266(02), 153-161.
Caro, T. M. (1994). Cheetahs of the Serengeti Plains: group living in an asocial species. University of Chicago Press.
Cooper, S. M. (1991). Optimal hunting group size: the need for lions to defend their kills against loss to spotted hyaenas. African Journal of Ecology, 29(2), 130-136.
Creel S. (1997). Cooperative hunting and group size: assumptions and currencies. Animal Behavior 54: 1319–1324.
Creel, S. and N.M. Creel (1995). Communal hunting and pack size in African wild dogs, Lycaon pictus. Animal Behavior 50: 1325-1339.
Durant, S. M. (2000). Living with the enemy: avoidance of hyenas and lions by cheetahs in the Serengeti. Behavioral Ecology, 11(6), 624-632.
Hayward, M. W., Hofmeyr, M., O’brien, J., & Kerley, G. I. H. (2006). Prey preferences of the cheetah (Acinonyx jubatus)(Felidae: Carnivora): morphological limitations or the need to capture rapidly consumable prey before kleptoparasites arrive?. Journal of Zoology, 270(4), 615-627.
Höner, O. P., Wachter, B., East, M. L., & Hofer, H. (2002). The response of spotted hyaenas to long‐term changes in prey populations: functional response and interspecific kleptoparasitism. Journal of Animal Ecology, 71(2), 236-246.
MacDonald, D. (1983). The ecology of carnivore social behavior. Nature 301: 379-384.
Packer, C., & Caro, T. M. (1997). Foraging costs in social carnivores. Animal Behaviour, 54(5), 1317-1318.
Packer, C. and L. Ruttan (1988). The evolution of cooperative hunting. The American Naturalist 132: 159-198.
Packer, C., Scheel D., and A.E. Pusey (1990). Why lions form groups: Food is not enough. The American Naturalist 136: 1-19.
Rostro-García, S., Kamler, J. F., & Hunter, L. T. (2015). To Kill, Stay or Flee: The Effects of Lions and Landscape Factors on Habitat and Kill Site Selection of Cheetahs in South Africa. PloS one, 10(2), e0117743.
Trinkel, M., & Kastberger, G. (2005). Competitive interactions between spotted hyenas and lions in the Etosha National Park, Namibia. african Journal of Ecology, 43(3), 220-224.
van der Meer, E., Moyo, M., Rasmussen, G. S., & Fritz, H. (2011). An empirical and experimental test of risk and costs of kleptoparasitism for African wild dogs (Lycaon pictus) inside and outside a protected area. Behavioral Ecology, arr079.
Watts, D.P. and J.C. Mitani (2002). Hunting behavior of chimpanzees at Ngogo, Kibale National Park, Uganda. International Journal of Primatology 23: 1-28.
*No, I will never get over this.
**Note that these percentages are extremely rough, and vary tremendously based on factors such as group composition, environment, and the experience of the animals involved.
***There are some circumstances where this does not hold true. Chimpanzees, for instance, hunt small prey in groups so that each hunter hopefully catches his own prey, and dolphins and other group-hunting marine predators usually hunt schools of smaller fish.
I can hear all you bird fanatics out there revving your engines, but that’s not just my personal opinion (ok, it mostly is). Still, there are some sound scientific facts in there.
Look, if you compare the effortless soaring of something like a turkey vulture to the frenetic flapping of a little brown bat, of course the bird is going to seem better off. But most people haven’t spent a lot of time around bats, or watching bats fly. Because they generally fly at night.
I spent a summer mist-netting for bats in rural Ohio once, and let me tell you, your opinion on bat flight prowess changes after you have seen a bat fly within a few centimeters of a vertical wall of net and completely reverse direction in midair. All in a split second.
Bats are really, really good at flying.
But we still managed to net some because, according to my supervisor, “they get lazy with their sonar.” (The bats were not harmed, just irritated.)
There have been only four major groups of animals that have achieved liftoff, and they all achieved it quite differently. The first is the insects, of course, which are among some of the most successful and diverse fliers out there- from dragonflies to butterflies to actual flies. The remainder are among the vertebrates: the pterosaurs, the birds, and of course, the bats. (Arguably, humans too, if you count building flying metal thingies.)
All other “flying” animals you may have heard of, such as flying squirrels, are actually gliders.
We caught THEM in our nets as well. You may not know this, but flying squirrels are incredibly evil and they bite a million times harder than bats do.
The difference between gliding and flight is, very simply, that a flying animal is able to generate thrust. This is why gliders generally hold themselves stiff to maximize their surface area- they don’t have the power to generate it. Fliers do via all that flapping.
Ok, so I’m gonna attempt to do a very, very quick breakdown of basic powered flight mechanics and terminology. Bear with me here.
In order to fly, you need to a) get up into the air and b) stay in the air without falling. Gliders, of course, are falling after they get into the air, unless they happen upon a lucky gust of wind. They’re just falling with style.
Birds, bats, and flying insects (and airplanes) employ what is called an airfoil to help them generate lift- i.e., upward motion. An airfoil is a wing shape that is more sharply curved on the top than the bottom. It looks something like this.
When an airfoil is put with its thicker surface into the wind and angled upwards, something peculiar happens. Due to the sharp curve of the top surface compared to the bottom surface, the air moves faster over the airfoil than under it. This creates less pressure over the top of the wing than underneath it- in other words, it subverts gravity!
That’s how airfoils generate lift. But then why all the flapping? Well, in order for an airfoil to work, you’ve got to have air constantly flowing over the thicker surface. This is called thrust and flapping is what moves that air. Airplanes, of course, achieve thrust with their engines, which is why they don’t have to flap their wings.
There are two main wing motions in animal flight: upstroke and downstroke. The downstroke is what generates thrust by forcefully pushing the airfoil surface through the air. The animal maximizes the surface area of the wing pushing down against the air in this motion. Pushing the wings closer together underneath the body also creates more air pressure that provides additional lift. The upstroke is used to maneuver the wing back into position for the next downstroke, and animals usually minimize the surface area of their wing pushing against the air (to reduce their chances of generating backwards thrust!)
Pigeons are shown here generating both thrust and lift to get up into the air. The thicker part of their wing surrounding bone and muscle is what forms the shape of the airfoil. (Photo by Toby Hudson.)
Birds and bats both use these mechanics to stay in the air. But it’s the different ways that they approach them that makes it so fascinating.
When you look at videos of birds and bats flying, there aren’t many immediately apparent differences between the motions. In fact, for a long time researchers thought that they flew in essentially the same way: using their wings like rotating paddles.
Anybody who’s ever swum the butterfly stroke will be familiar with the motion: more or less throwing your arms forward to drag the water (or air) behind yourself. Take a moment to think about doing that, and then appreciate the sheer force that bird and bat muscles have to be able to generate.
However, while this is more or less how birds fly, it turns out that bats fly with a much more complex range of motions. They’re just a lot harder to see.
Consider the anatomical differences between bat and bird wings. The first is obvious: birds have feathers, while bats’ wings consist largely of skin membranes. The second is also pretty obvious: bird wings consist of elongated arms and a single finger, while bats use three fingers with the membrane stretched between them. Because the end shape of both is kind of similar, it’s easy to miss how large this difference actually is.
If you look closely at the above gif, you’ll notice that at several points during flight, the bat actually bends its fingers, which dramatically changes the shape of its wings. Birds do not have joints in their feathers, so they cannot do this. The huge amount of flexibility in bat finger joints is even more apparent when you look back at that picture above of a bat caught in a net- where the wings may appear crumpled are actually where the bat bent down its fingers.
Bats can bend their fingers to the point where their entire wings seem to disappear.
Here’s a better look at where all those little fingers get tucked away.
Flexible joints are not all the bat has in its arsenal. Its actual bones are flexible, due to a lack of calcium in its diet. This means that they deform and reform their shape during flight.
Birds minimize air resistance by rotating their primaries during their upstroke, allowing air to slip between the feathers. Bats, with solid membranes, can’t do this- so they have an even finer means of control. There are lines of muscle present within the bat’s wing membrane that can actually change the stiffness and malleability of its skin. You can see them quite clearly under the skin of our entangled bat friend.
This is a big brown bat (Eptesicus fuscus), by the way.
These muscles allow the bat to make their membranes flexible during their upstroke to decrease resistance, yet stiff during their downstroke in order to provide lift. It also allows them to change the camber (angle) of their wings on a whim!
This slow-mo video really displays just how incredibly flexible bat wings are.
Bat wings are also covered by millions of tiny, hyper-sensitive hairs that allow the bat to sense air currents and adjust accordingly.
So what does all this control do for the bat?
Well, for one thing, it means they’re not limited by symmetry. Bird wings will almost always mirror each other in shape, while bats may form two different wings shapes at the same time, allowing them to perform some crazy aerial acrobatics. Some insect-eating bats will actually grab an insect by wrapping one wing around it midflight (don’t believe me? You can see it in the beginning of this video!) and then get the insect in their mouth all in a split second, while still flying.
Now, in terms of speed, birds can generally outpace bats. But in terms of maneuverability, bats can fly circles around birds.
The fact that bats’ bones, unlike those of birds, aren’t hollow, and that their skin is heavier than feathers might seem like a disadvantage- but it isn’t. Birds have much more mass in the center of their body than they do in their wings; by contrast, bats have more mass distributed through each wing (12-20% per wing). This means that bats can actually push off their own mass do do things like flip, spin, roll, etc. No bird can stop midflight and flip over to land upside-down, but bats can.
Because they have such fine control over their airfoil shape, bats can also generate lift using less energy than birds. Remember when I talked about minimizing surface area during the upstroke and maximizing it during the downstroke? Bats can bend their fingers and ‘crumple’ their wings as they raise them, conserving energy. Think of it like opening and closing an umbrella. While birds can pull their feathers together more tightly, they can’t exactly clench them like fists.
Decreasing energy costs is good in any situation, but particularly for fliers. It takes a lot of energy to fly. In this case, bats can outcompete both birds and insects for energy efficiency- one study found that nectar-feeding bats, though the largest in size, expended the least energy hovering when compared to both moths and hummingbirds.
So: bats can do all these cool things while flying. Is there a downside? Mmm… yeah. Besides sheer speed, birds do have one major ability that bats don’t: they can walk.
Ok, some bats can walk (four species) and some birds can’t (hummingbirds), but for the most part birds are fairly okay at waddling around on the ground. Most bats… not so much.
We can draw parallels between hummingbirds and bats in this respect, as hummingbirds are among the most maneuverable of all bird species. Selection for increased acrobatics in the air seems to come at the cost of land maneuverability. It makes sense.
And unlike birds, most bats can’t take off directly from the ground. It’s that pesky quadrupedal stance they have. Birds, being bipedal, can push off with their hind legs. Bats can’t do this, aside from a few exceptionally powerful species like the vampire bats and the eastern red bat. Generally if they land on the ground they have to climb up to a vantage point, like a tree trunk, before pushing off.
Interestingly, the other vertebrate fliers- pterosaurs- were also quadrupedal, but could push off from the ground. They used their forearms!
Anyhow, despite their land-based limitations, bat flight is simply incredible. I encourage you to go out on a summer night just after sunset and look to the skies. Maybe you’ll get to witness it for yourself!
Read on:I’ve written more on bats- an overview of bat diversity, a post on species called ghost bats, and a species overview of one of the few walking bats, the New Zealand pekapeka! To view a list of all my nonfiction articles, check the Nonfiction page.
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The new Jurassic World trailer made me want to learn more about marine reptiles, so that’s what this post is all about.
When you hear the phrase “marine reptile,” your first thought is probably something along the lines of a marine iguana, sea snake, saltwater crocodile, or sea turtle. And you wouldn’t be wrong. Those are all reptiles that spend a good amount of time in the water.
Those of you with a dab more prehistoric knowledge will also probably think of some extinct marine reptiles- your plesiosaurs, ichthyosaurs, mosasaurs, et cetera. Those of us who grew up with any knowledge of early 2000s viral videos will probably think of Liopleurodon thanks to Charlie the Unicorn.
But wait, some of you will now be saying, aren’t the liopleurodons and their long-necked brethren just, like, water dinosaurs?
This is a common misconception. There were no aquatic non-avian dinosaurs that we know of (though the reconstructed Spinosaurus might be a contender). Liopleurodon was much more closely related to modern lizards than to any dinosaur. However, not all marine reptiles are lizards, obviously- they are not a monophyletic group (meaning, they are not all on the same branch of the family tree). The moniker ‘marine reptile’ is kind of misleading, as is, actually, the word ‘reptile.’
Let’s quickly look at a vertebrate phylogeny.
The green area highlights branches containing animals commonly known as reptiles. As you can see, it does not perfectly cover any one section of the phylogeny. (Pisces = fish, Synapsida = mostly mammals, Testudina = turtles, Lepidosauria = lizards, snakes, and tuataras, Crocodylia = crocodilians, Aves = birds. Dinosaurs are not shown because this is a living phylogeny, but they would be just under Aves.)
I already mentioned that marine reptiles include sea turtles, crocodiles, and marine iguanas, so that means that marine reptiles actually appear independently in three different branches of this phylogeny. This is similar to how marine mammals like seals and manatees and whales all evolved independently of each other, though turtles and crocodiles are much more distantly related than any pair of mammals.
If we ignore freshwater reptiles and only focus on their seagoing relatives, there are about forty living species of marine reptiles today, and surprisingly, most of them are sea snakes. (Sea snakes are not eels, before anyone asks. Eels are fish, sea snakes are snakes.)
Did you know that most sea snakes give live birth? (Photo by Craig D.)
However, this is really just the tip of the iceberg. Before marine mammals took over the water- and became some of the largest lifeforms ever to exist- there was a very long history of diverse and impressive marine reptiles.
Quick disclaimer: a lot of the taxonomic relationships of these extinct reptiles are hotly in dispute, and as such, there are many conflicting theories out there about their placement. I did the best I could with the info I found, but please take it all with a grain of salt.
Why Members of Sexual Species May Choose to Stay Chaste
Sometimes I hear people making derisive comments towards people who prefer not to have sex, something along the lines of how it goes “against nature” to never have sex, therefore something is horribly wrong with them, etc., etc.
The specific plague I wish upon those unpleasant people is an infestation of termites. Why termites? I’ll talk about that in a bit.
At one point highly social behavior presented kind of a paradox to the traditional, selfish-gene style evolutionary theory. Charles Darwin famously admitted that it was the social behavior of the bee that was going to bring down his entire construction, because most bees- nay, the vast majority of all individual bees spend all their times leading pious, sexless lives centered around helping one other bee reproduce. At the peak of the season, honeybee colonies can have 60,000 nonbreeding individuals- and just one sexually active queen.
Darwin, of course, did not yet know about genes, but he had an inkling that heredity was a clue- that by helping their relatives, the bees were actually helping themselves. Later scientists have filled in more of the gaps using modern molecular science, and yes, from a genetic standpoint, helping a relative is something like helping a piece of yourself.
But at what point does the value of helping close relatives outweigh the value of actually reproducing? That is a question biologists have been grappling with for quite a while. Because in the game of evolution, what matters isn’t how big your species’ population is- what matters is how many of those individuals share your genes.
There are a lot of different pupil shapes among vertebrates (and some invertebrates, too).
The eye itself is kind of a weird misshapen organ, particularly in land animals where it has had to compensate for, you know, the fact that it originally evolved in the water. Light passes differently through water than it does in air, not to mention that now we have to worry about our lenses- which have to be moist to properly function- drying out.
But the focus (ha ha) today is on the pupil, the transparent bit inside the iris that allows light to enter the eye. Without it, our eyes would be functionless. With it, there are a whole bunch of different ways that animals can shape their vision- and their pupil- to their advantage.
Of course, no two scientists seem to agree on exactly what these advantages are.
Oh, sure, the Western scientific community calls this species the “New Zealand lesser short-tailed bat,” but I think we can all agree that the Māori name is much better, especially since you can then call it a pekapeka for short.
Pekapeka. God, I’m so happy.
Scientific name: Mystacina tuberculata. Sadly this was the only creative commons image of the pekapeka I could find, so I’ll ask you to use your imagination for the rest of the article.
Ok, so what’s there to distinguish the pekapeka from the hundreds and hundreds of other tiny insect-eating bats? Well, for starters, they’re one of only three mammal species native to New Zealand. Second, they spend roughly 30% of their foraging time not flying, but walking on the ground.
If that doesn’t sound impressive to you, you clearly don’t understand how much bats suck at walking. Imagine a seal, right? Sleek and beautiful under the water, pudgy-ground humping wobblers on land. Same deal for the bat, only replace the water with the air.
True, there are a few other bat species that are also good at walking, most notably the common vampire bat, which can not only walk but hop and run. But in terms of phylogeny the vampire bat is like a million light years removed from the pekapeka, which is more closely related to the not-so-great-at-the-walking-thing ghost-faced and mustache bats. And unlike the vampire bat, which uses its walking as a stealth maneuver to sidle up to sleeping hosts and give ’em a lil love bite, the pekapeka doesn’t drink blood.
No, the pekapeka may spend time on the ground for other reasons entirely. Remember, it lives in New Zealand, where there are only two other species of mammals (both bats) and no snakes, which means there are next to no terrestrial predators. New Zealand is also home to a lot of birds… and a lot of flightless birds, like the kiwi.
Could the pekapeka be on its way to being the first species of flightless bat?
Well, not if we drive it to extinction first, but I’m getting ahead of myself here.
I’ve spoken of neoteny before in regards to domestic dogs- the concept that domestic dogs retain juvenile traits of their ancestral species, the gray wolf, into adulthood. These traits can include folded ears, shorter snouts, barking, more limited social behaviors, and a higher incidence of “puppyish” behaviors.
For example, this dog is pestering me for attention right now.
But I think that while this concept isn’t new to those familiar with the evolution of the domestic dog, many people aren’t aware that there is an entire field of study devoted to examining the rates at which animals develop.
So what’s the deal with boobs, anyway? I mean… boobs! Wow, what a great invention. We wouldn’t even have lips without boobs, man. And what is the deep connection between the boob and the butt?
All right let’s talk about boobs and non-boob things on other animals and how it happened and where it went and yes, why men have nipples.
![A marine iguana doing as marine iguanas do. By Peter Wilton (Marine iguana Uploaded by Magnus Manske) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons](http://www.koryoswrites.com/wp-content/uploads/2014/12/1599px-Marine_iguana_4202531062.jpg)
