The thing in the photo above, I’m sad to say, is a penis. It belongs to the male seed beetle. And just in case you’re holding out hope that appearances are deceiving, I can assure you they are not. Those spikes are hard and sharp, and they inflict heavy injuries upon the female beetles during sex. Why would such a hellish organ evolve?
This isn’t just about beetles. The animal kingdom is full of bafflingly-shaped penises adorned with spines, spikes, and convoluted twists and turns. In some animal groups, like certain flies, penis shape is the only clue that allows scientists to distinguish between closely related species.
For a male, sex isn’t just about penetration. After he ejaculates inside a female, his sperm still have to make their way to her eggs to fertilise them and pass on his genes. If she mates with many suitors, her body becomes a battleground where the sperm of different males duke it out. Females can influence this competition by being choosy over mates, storing sperm in special pouches, or evolving their own convoluted genital passages. Males, meanwhile, have evolved their own tricks, including: guarding behaviour; self-castration; barbed sperm; chemical weapons in their sperm; mating plugs; ‘traumatic insemination’; and having lots of sperm.
And spiky penises. That too.
Four years ago, I wrote about a group of African frogs that remind me of the Marvel Comics character Wolverine, who fights with three retractable claws in each arm. The frogs, belonging to the family Arthroleptidae, also have bone claws in their feet. They use these in defence, as many naturalists discovered to their dismay.
They’re not alone. On another continent, Noriko Iwai from the University of Tokyo has studied a different species – the Otton frog – that carries a similar bony spike in its foot. It’s large for a frog, growing to around 12 centimetres in length. The males use their spikes as anchors to latch onto females, and flick-knives for duelling with rival males.
Stranger still, the Otton frog houses its spike in a “thumb”, which other frogs lack. Frogs have five toes on their hind legs, just like us, but most species have just four on their front legs. There are exceptions, though, and the Otton frog is one of them. It has a fifth front toe – a “pseudothumb” – which houses its spike.
It’s said that beauty is in the eye of the beholder, but that’s only half-true for the Gouldian finch. Jennifer Templeton from Knox College, Illinois has found that these beautiful birds only display their famous fussiness over mates if they’re looking with their right eye. If the right is shut, and the left eye is open, the birds have more catholic tastes. As Templeton writes, “Beauty, therefore, is in the right eye of the beholder for these songbirds.”
The Gouldian finch, found in northern Australia, looks like a bird painted by Gauguin. Its palette includes a purple chest, yellow belly, green wings and cyan highlights. But it’s the head that really matters. They come in red or black (there’s a very rare yellow variant too, but we can ignore that here), and they strongly prefer to mate with partners of their own colours. This isn’t abstract fussiness – genetic incompatibilities between the black-heads and red-heads mean that their offspring are often infertile and feeble. Indeed, these two variants could be well on the way to becoming separate species.
Red and black finches are so easy to tell apart that scientists could be forgiven for neglecting how they do so. But Templeton suspected that the act of choosing a mate was more complicated that anyone had thought.
In North America’s Sonoran desert, there’s a fly that depends on a cactus. Thanks to a handful of changes in a gene called Neverland, Drosophila pachea can no longer make chemicals that it needs to grow and reproduce. These genetic changes represent the evolution of subservience – they inextricably bound the fly to the senita cactus, the only species with the substances the fly needs.
The Neverland gene makes a protein of the same name, which converts cholesterol into 7-dehydrocholesterol. This chemical reaction is the first of many that leads to ecdysone – a hormone that all insects need to transform from a larva into an adult. Most species make their own ecdysone but D.pachea is ill-equipped. Because of its Neverland mutations, the manufacturing process fails at the very first step. Without intervention, the fly would be permanently stuck in larval mode. Hence the name, Neverland—fly genes are named after what happens to the insect when the gene is broken.
Fortunately, in the wild, D.pachea can compensate for its genetic problem by feeding on the senita cactus. The cactus produces lathosterol—a chemical related to cholesterol. D.pachea’s version of Neverland can still process this substitute, and uses it to kickstart the production of ecdysone.
The senita is the only plant in the Sonoran desert that makes lathosterol, the only one that lets the fly bypass the deficiency that would keep it forever young. It has become the fly’s dealer, pushing out chemicals that it cannot live without, and all because of changes to a single fly gene.
Here’s yet another reason why humans are weird: menopause. During our 40s, women permanently lose the ability to have children, but continue to live for decades. In doing this, we are virtually alone in the animal kingdom. From a cold evolutionary point of view, why would an animal continue to live past the point when it could pass on its genes to the next generation? Or put it another way: why don’t we keep on making babies till we die? Why does our reproductive lifespan cut out early?
One of the most popular explanations, first proposed in the 1966, involves helpful grandmothers. Even if older women are infertile, they can still ensure that their genes cascade through future generations by caring for their children, and helping to raise their grandchildren.* There’s evidence to support this “grandmother hypothesis” in humans: It seems that mothers can indeed boost their number of grandchildren by stepping out of the reproductive rat-race as soon as their daughters join it, becoming helpers rather than competitors.
Now, Emma Foster from the University of Exeter has found similar evidence among one of the only other animals that shows menopause: the killer whale.
It’s June in the Arctic tundra, and male pectoral sandpiper hasn’t slept for weeks. He’s too busy trying to have sex. The females will only be fertile for three short weeks, and they’re very choosy. A male has to spend his time chasing the females and displaying with his puffed-up breast, while fighting off rivals and maintaining control of his territory. With so much at stake and so little time, there is simply no time for sleeping.
You might have thought that this constant activity would take its toll on the male. Sleep, after all, is important for our physical and mental wellbeing. Males who go without it for too long should be too tired and addled to make successful suitors. But not so – John Lesku from the Max Planck Institute for Ornithology found that the males who slept the least actually sired the most offspring.
Conservation work usually involves restoring wildlife and natural habitats. For the people behind the Sustainability in Prisons Project (SPP), conservation work is about restoring people too. The project recruits inmates from prisons around Washington, USA in efforts to protect endangered butterflies, frogs, flowers and mosses. They breed individuals either in the prisons or under supervision in outside facilities. They get training, education and a small wage. And they get a chance to give something to society.
I learned about the project at the Ecological Society of America Annual Meeting, and it was a highlight. These prisoners aren’t just providing manual labour. They’re also creatively tweaking and improving what they do, and rearing animals that put competing facilities to shame. The ones who are breeding Oregon spotted frogs have produced animals that are bigger and healthier than those from Oregon Zoo and the organisations that trained them in the first place.
And they’re doing actual science. The inmates who are breeding endangered Taylor’s checkerspot butterfly have worked out which plants the butterfly likes to lay its eggs on. That was unknown, and since one of those plants is also endangered, the results could help to fuse two disparate conservation projects together.
It’s a wonderful initiative, and the prisoners are enthused and empowered by it. Dennis Aubrey, a student who leads the butterfly project, told me, “They talk about how it completely changes how they think. Most people are in the prison yard talk about who did them wrong. Then, all of a sudden, guards will tell us they hear people saying, ‘Hey did you see how that moss was growing?’”
I’ve written about the project in more detail for Nature News. Head over there for the full story.
Image of Taylor’s checkerspot, courtesy of inmate research assistant, Sustainability in Prisons Project
Some folks just can’t help being loud in bed, but noisy liaisons can lead to a swift death… at least for a housefly. In a German cowshed, Natterer’s bats eavesdrop on mating flies, homing in on their distinctive sexual buzzes.
Based on some old papers, Stefan Greif form the Max Planck Institute for Ornithology knew that Natterer’s bats shelter in cowsheds and sometimes feed on the flies within. What he didn’t know was how the bats catch insects that they shouldn’t be able to find. They hunt with sonar, releasing high-pitched squeaks and visualising the world in the returning echoes. Normally, the echoes rebounding from the flies would be masked by those bouncing off the rough, textured surface of the shed’s ceiling. The flies should be invisible.
And they mostly are. Greif filmed thousands of flies walking on the shed’s ceiling, and not a single one of them was ever targeted by a bat. That changed as soon as they started having sex. Greif found that a quarter of mating flies are attacked by bats. Just over half of the attacks were successful and in almost all of these, the bat swallowed both partners.
As first light tickles the air, songbirds croon to proclaim their territories and woo potential mates. There are many possible explanations for the timing of the beautiful dawn chorus, including the fact that sound travels further during the early hours of the day.
But Michael Beaulieu and Keith Sockman from the University of North Carolina have found another for the list. It’s based on a very simple observation: dawn is often very cold. And female Lincoln’s sparrows find songs sexier if they hear them in the cold.
Anglers ensnare fish with bait, or with man-made lures that look like bait. Anglerfish do the same thing – they have worm-like growths on their heads that act as living fishing lures to entice their prey. The swordtail characin, a small fish from Trinidad and Venezuela, has a similar lure, and it uses it not to attract food, but sex.
The male characin has a small bean-shaped patch attached to his gill flaps by a thin thread. When he swims, he holds these ‘flags’ against his body. When he encounters a female, he flares one of them out in front of her. The female clearly thinks that the flag is food, for she bites at it vigorously. While she’s occupied, the male sidles across and impregnates her with his sperm.
Unlike many other fish, which shoot sperm and eggs into the water, characins fertilise each other internally, just like us. The male, however, doesn’t have any sort of penetrating organ, so he needs to bump into the female just so. And his bizarre ornament ensures that she’s in exactly the right place.
Niclas Kolm and Göran Arnqvist have been studying the characins for several years, and they’ve shown that characins from different Trinidadian streams have distinctly shaped flags. Now, they think they know why.
The characins feed on manna from heaven – insects that fall into the water from overhanging plants. On average, half of their diet consists of tree-dwelling ants, but that proportion can vary between 10 and 75 per cent. The ant portion of their menu is dictated by their environment: if they live in wider streams, they have more plants growing overhead, and more ants fall within their reach. Now, Kolm and Arnqvist have shown that the flags of male characins look more like ants in streams where the female eats more ants.
Together with Mirjam Amcoff and Richard Mann, they captured characins from 17 different streams around Trinidad. They measured the shape of the male’s flag and the contents of the female’s guts, and showed that these traits are related. In streams where females eat more ants, the males’ flags are more tapered and curved towards their far end. This more closely mimics the shape of an ant with its narrow waist connecting a thick torso and abdomen. It’s very different to the oval shape of a beetle – the characins’ second favourite food.
Are these ant-like flags more successful at attracting ant-eating females? Kolm and Arnqvist found out by using characins that had been raised in captivity, and had never seen an ant before. They fed these females with either ants or other insects, before presenting them with males from different streams. Sure enough, females that had gorged on ants were more likely to attack the ant-like flags of males from streams where females naturally eat lots of ants.
It’s a really elegant experiment – one that strongly supports the idea that the male flags have evolved to tap into the sensory biases of the females. As Kolm writes, “The shape of the male flag ornament…has evolved to track the search images that females employ in foraging.” It’s a lure that evolves according to the preferences of its target.
But the important thing here is that those preferences are originally driven by the environment. It’s the width of the streams that determines how many ants the females encounter, and thus what shapes the males’ lures take. This process, where animal signals evolve to account for the properties of their environment and stand out more strongly, is known as sensory drive. And in this case, it’s driving the divergence of different characin populations.
Reference: Kolm, Amcoff, Mann & Arnqvist. 2012. Diversification of a Food-Mimicking Male Ornament via Sensory Drive. Current Biology http://dx.doi.org/10.1016/j.cub.2012.05.050