Morphological convergence is one of the most striking patterns in evolution. Just among mammals there are spectacular and bizarre examples of distantly related species that share surprisingly similar adaptations. I bet you’ve heard of saber-toothed cats. But what about marsupial saber-toothed cats? Raccoons are surely familiar, but have you heard of raccoon dogs? Or the earless, eyeless oddity that is the golden mole, which somehow looks almost exactly like the equally earless and eyeless notoryctid marsupial mole? My favorite, though, might be the lesser hedgehog tenrec from Madagascar, which bears the same tiny coat of spiked armor as the common hedgehog but is more closely related to an elephant.
Skull from the marsupial saber-toothed “cat” Thylacosmilus.
Skull from a placental saber-toothed cat Smilodon.
Until recently, most scientists studying evolutionary convergence have focused on the converged phenotype (external appearance), but with the arrival of ever-cheaper DNA sequencing technologies, scientists can efficiently study patterns of convergent genotypes across thousands of genes in species that appear to have converged at the phenotypic level.
Now, I know dancing sharks are the preferred marine species of the moment, but allow me to reignite your interest in some other denizens of the sea. Last month, a team of researchers published a study in Nature examining how genes in three marine mammal lineages might have converged independently on the same solution to the very hard physiological problem of living in the ocean after millions of years evolving on land (Foote et al. 2015). Their results are hardly conclusive but do illustrate a compelling new way to think about and study convergence now that genomes are getting so cheap to produce.
Katy Perry and her dancing sharks at the 2015 Super Bowl
The pale-headed brushfinch, Atlapetes pallidiceps, is a conservation success story, or at least the first chapter of one. The birds were thought to be extinct, until a 1998 survey [PDF] of Ecuador’s Yunguilla Valley found four nesting pairs, and observed them foraging for insects and fruit. Following that rediscovery, the Fundacion Jocotoco secured a reserve encompassing the brush finches’ known territory, and took steps to control brood-parasitic cowbirds that were threatening them. Now, the population is five times bigger, with as many as 200 of the birds living in the reserve.
Have the brush finches’ rebounded enough to secure their population for the future? Populations that decline so precipitously can lose genetic variation, and may not regain it even if their numbers increase again. With reduced genetic variation, species that have undergone such a “population bottleneck” event may be unable to respond to natural selection imposed by disease or changing environments.
Domesticated animals are the product of unnatural selection. To view some of the unnatural diversity in turkeys – check out Porter’s Rare Heritage Turkeys. They have the Sweetgrass, the Chocolate Slate, the White Holland, the Red Phoenix, and – my personal favorite – the Pencilled Palm (amongst many more varieties). They even have information on feather color genetics and what makes a (Heritage) turkey a (Heritage) turkey. Happy Turkey Day!
Is that a White Holland I see?
In a recent keynote address at the High Throughput Sequencing for Neuroscience meetings, Sean Eddy from the Howard Hughes Medical Institute addresses the need for biologist to do their own sequence analysis. Although this talk was given by a neuroscience rather than an evolutionary biologist, the conversation is generally applicable to the entire biological community.
“But if you’re a biologist pursuing a hypothesis-driven biological problem, and you’re using using a sequencing-based assay to ask part of your question, generically expecting a bioinformatician in your sequencing core to analyze your data is like handing all your gels over to some guy in the basement who uses a ruler and a lightbox really well.”
“If you learned to implement it in Perl — and you could do this in an afternoon, with a few lines of Perl code — I think you would find yourself endowed with a superpower, like Wonder Woman with her golden lasso of truth, and it’s a superpower that a biologist can use with surprising effectiveness on large data sets.”
Find the whole article here.
Monarch butterflies (Danaus plexippus) are among the most widely recognized wild creatures in North America. Their distinctive orange-and-black wings, which warn predators that the butterflies are chock full of toxins from the milkweed they eat, make them easily spotted in backyard flower beds. They’re also known for a massive annual migration, flying thousands of miles between wintering colonies in central Mexico and summer sites across the United States and Canada. More recently, it’s been discovered that female monarchs infected by parasites respond by laying their eggs on food plants that can prevent the parasite from infecting their offspring.
Monarchs are also one of the more visible victims of the massive changes humans have made to the world around us. Increased conversion of farmland to corn production has reduced the supply of milkweed, the butterflies’ only food plant, across much of the Midwest. It’s gotten so bad the number of monarchs making the annual migration back to Mexico hit a record low last year, and while things were better in 2014, a nationwide campaign to encourage planting of milkweed in home gardens is only beginning.
For all our familiarity with monarchs, we’ve known remarkably little about their evolutionary history. That’s changing rapidly now, as evidenced by a paper published last month in the journal Nature, which uses a big new genetic dataset to trace the origins of some of the monarch’s most distinctive features.
Signalling individual identity is critical in many aspects of human social interaction (click for video!).
We all rely on our ability to recognize other people’s faces to get along in the world. Most people don’t think too hard about this, it’s so fundamental to our existence. But it turns out that in order to stand out in the crowd, you need to be, well different. A recent study shows that human faces are in fact, much more different from one another than other traits, and suggests that this high facial diversity has evolved specifically to signal individual identity. It’s a pretty interesting story, and I look forward to digging into the details.
Check out this NatGeo piece on the work, and the original publication (paywalled).
Sheehan, Michael J., and Michael W. Nachman. “Morphological and population genomic evidence that human faces have evolved to signal individual identity.” Nature Communications 5 (2014).
Okay, I’m paraphrasing in that headline, but only barely. From Science Insider:
A best-seller by former New York Times science writer Nicholas Wade about recent human evolution and its potential effects on human cultures has drawn critical reviews since its spring publication. Now, nearly 140 senior human population geneticists around the world, many of whose work was cited in the book, have signed a letter to The New York Times Book Review stating that Wade has misinterpreted their work.
The letter is online, and it doesn’t mince words:
Wade juxtaposes an incomplete and inaccurate account of our research on human genetic differences with speculation that recent natural selection has led to worldwide differences in I.Q. test results, political institutions and economic development. We reject Wade’s implication that our findings substantiate his guesswork. They do not.
We are in full agreement that there is no support from the field of population genetics for Wade’s conjectures.
To those of us who’ve been complaining about Wade’s misappropriation of basic population genetics in support of his ideas about what people of different races may or may not be “adapted” to do, this is the equivalent of that scene from Annie Hall, except with more than a hundred Marshall McLuhans. Updated to add: The full list of 139 folks who signed the letter is posted here.
Sometimes, life is kinda like that. Hat tip to Jennifer Ouellette for the Science Insider story.
Updated to add: See also coverage by Nature, with some choice quotes from signatories; and by Jennifer Raff, who writes, “A strong blow has been dealt to scientific racism today.” Also, from Ed Yong: