Sloths are weird critters. Cute, in a certain light, but mostly weird. They’re members—with armadillos and anteaters—in a superorder of mammals called the Xenarthra, which are united by a unique form of multi-jointed vertebrae. Their diet consists mostly of leaves, which are poor quality food, and hard to digest. Fortunately, they also have one of the slowest, lowest-energy lifestyles of any mammal, using heavily modified limbs to hang upside down from branches while they browse, their most recent meal fermenting in their guts.
David Attenborough got up close with a sloth—which he calls a “mobile compost heap”—in The Life of Mammals. He also observes one of the sloth’s weirdest behaviors: to answer the call of nature, it climbs all the way down to the ground.
Why do sloths go to all that trouble—and risk—just to poop? Well, according to a recent paper in Proceedings of the Royal Society, they do it to feed poop-eating moths that help cultivate nutritious algae in their fur. No, but really.
Here at Nothing in Biology Makes Sense, we’re fascinated by all the weird, baroque ways that living things influence and coevolve with each other—so Ed Yong’s new TED talk about mind-controlling parasites is right up our alley. Just like his writing—currently on display at National Geographic‘s Phenomena, among many other venues—it’s a compendium of nifty natural history punctuated with highly educational gross-outs and the occasional black-belt level pun.
Brood parasites are definitely the bullies of the avian world. They lay their eggs in the nests of other birds, sometimes destroying the host’s own eggs or just waiting for their nestlings to do the dirty work after they hatch. They then outcompete any surviving host nestlings for food, while the poor host parents are worked to the bone to feed the monstrous nest invader.
In spite of the steep costs of nest parasitism, most avian host species do not have effective mechanisms for detecting and removing brood parasites from their nests. So, why don’t mama birds notice they have a GIANT intruder in their nest and carry out some infanticide of their own? One hypothesis is that the cost of a mother bird making a mistake and pushing the wrong baby out (i.e. her own) outweighs the benefit of developing such a behavior.
This week in Science, Canestrari et al. published evidence for another hypothesis – that sometimes, it might actually be good to have your nest parasitized.
Flowers that rely on animal pollinators
to remix their genetic material have evolved a tremendous diversity of strategies for attracting those pollinators—from beguiling scents
to elaborate visual displays
to pretending to be a lady pollinator
But there’s a downside to making a big, showy display to attract pollinators—you might also attract visitors who have less helpful intentions than gathering up some pollen and moving on to the next flower. Showy flowers might attract animals that steal the rewards offered to pollinators—or they might attract animals that eat the flowers themselves, or the developing seeds created by pollination. So the evolution of attractive floral displays might very well be a compromise between attracting the right visitors, and attracting the wrong ones.
Evolution by natural selection is not usually considered very peaceful—the “survival of the fittest” is usually assumed to come at the expense of competitors for food or shelter or other resources. But the “fittest” can also be those who recruit assistance from other individuals, or other species—and who provide assistance in return.
This was the perspective of Peter Kropotkin, a Russian prince and political anarchist who studied the wildlife of Siberia while working as an agent of the Czar’s government. In the harsh conditions of the Siberian winter, Kropotkin reported finding not a bitter struggle over scarce resources, but what he called “Mutual Aid” among species, as well as in the human settlements that managed to eke out a living.
Something like what Kropotkin described is documented in a new paper by Elizabeth Pringle and colleagues. Examining a protection mutualism between ants and the tropical Central American tree Cordia alliodora, Pringle et al. found that drier, more stressful environments supported more investment in the mutualism.
One of your future colleagues in the Smith Lab, hard at work in the field.
Friend of the blog—and longtime collaborator of mine—Chris Smith recently landed an NSF CAREER grant for new research on the causes of evolutionary divergence within the Joshua tree-yucca moth mutualism—and he’s looking for a postdoc to help with it!
The proposed work will take advantage of new genomic resources for the genus Yucca—Joshua tree population genetics is about to get a lot more powerful than the 10 microsatellite loci I used for my dissertation research. And it will involve fieldwork in the Mojave Desert, which is objectively one of the most beautiful empty spaces on the map of North America. Chris is on the faculty of Willamette University, which is an undergraduate institution, so the postdoc position is also a unique opportunity to do basic research in close coordination with an undergraduate teaching program.
Moreover, I can personally recommend Chris as a mentor and collaborator—to the extent that I’ve turned out to be a pretty decent scientist, he’s one of the principal reasons why. (And to the extent that I haven’t, well, that’s a reflection on me, not him.)
The complete job description, and instructions on how to apply, are after the jump.
In the evolutionary history of big herbivores and the carnivores that prey upon them, the phrase “arms race” is only technically a metaphor. Antelope and zebras are literally born to run, and many of the things that chase them, like wild dogs or cheetahs, are either masters of endurance or champion sprinters. The evolutionary story almost writes itself: over millions of years of chasing, and being chased, whenever the predators evolved to become faster, the prey were selected to run even faster—until a cat evolves that can go from 0 to 60 faster than my Volkswagen Rabbit.
Except of course there’s more to life than running for your life. An antelope’s frame is under more demands than evading cheetahs—it also needs to travel long distances to follow food availability with the shifting rainy season. In fact, the North American fossil record suggests that big herbivores on that continent evolved long legs for distance running millions of years before there were predators able to chase after them. And then again, not all predators run their prey down; lions, for instance, prefer to pounce from ambush.
In a paper recently released online ahead of print in the journal Evolution, Jakob Bro-Jørgensen sets out to disentangle exactly these competing explanations.
A Joshua tree flower, up close.
A huge diversity of flowering plants rely on animals to carry pollen from one flower to another, ensuring healthy, more genetically diverse offpsring. These animal-pollinated species are in a somewhat unique position, from an evolutionary perspective: they can become reproductively isolated, and to form new species, as a result of evolutionary or ecological change in an entirely different species.
Evolutionary biologists have had good reason to think that pollinators often play a role in the formation of new plant species since at least the middle of the 20th century, when Verne Grant observed that animal-pollinated plant species are more likely to differ in their floral characteristics than plants that move pollen around via wind. More recently, biologists have gone as far as to dissect the genetic basis of traits that determine which pollinator species are attracted to a flower—and thus, which flowers can trade pollen.
However, while it’s very well established that pollinators can maintain isolation between plant populations, we have much less evidence that interactions with pollinators help to create that isolation in the first place. One likely candidate for such pollinator-mediated speciation is Joshua tree, the iconic plant of the Mojave Desert.
Gorteria diffusa. If its spots look like sexy female bee flies to you, you might be a bee fly yourself. Photo by Flickr/thehumofbees.
The South African daisy Gorteria diffusa has a means of attracting pollinators that is either a mean-spirited or brilliant, depending on how much you sympathize with the pollinators in question: its dark-spotted petals fool male bee flies (Megapalpus capensis) into mating with the flower. This is, of course, a fruitless exercise for the bee fly, but not so for the daisy, since the decieved males pick up pollen in the process, which they’ll transfer to another daisy when they’re fooled again.
This is a bit salacious, but this kind of sexual deception isn’t exactly rare among flowering plants. What makes G. diffusa more interesting, to an evolutionary biologist, is that not all populations of the daisy practice this deception. The pattern of G. diffusa‘s petals varies across its range—and not all petal patterns prompt the pollinators to hump the flower. Actually, on all but three of the various forms of G. diffusa, bee flies mostly just come to feed on nectar.
That poses the interesting evolutionary question of why some populations of G. diffusa have evolved to trick their pollinators, when so many others have not. A paper just released online at the journal Evolution attempts to answer that question—but its authors find more new questions than they do concrete answers.
Over the past several years there has been a growing trend of parents that are terrified of vaccinating their kids citing reasons such as the debunked link to autism or that it just isn’t “natural.” A healthcare blog run by several infectious disease doctors called Controversies in Hospital Infection Prevention has run frequent stories reporting on the declining vaccination rates as well as problems that ensue because of that, most recently about the whooping cough epidemic in Washington and wondering why Jenny McCarthy has so much influence on national views on vaccinations.