Why’d the zebra evolve its stripes? Perhaps because stripes seem to keep off horseflies, a new study suggests. There’s good evolutionary reason to escape the ravages of horseflies, at least for horses and their relatives; though flies are just annoying pests from the human perspective, horsefly-bitten horses can grow skinny and have trouble producing milk for their young. And as soon as baby-making is affected by something in the environment, adaptation isn’t far behind.
Other research has shown that horseflies prefer to land on black horses instead of white, which got Gabor Horvath, author of the recent study, thinking about how they’d react to black-and-white specimens, such as zebras. Of course, actual zebras can be hard to experiment on, as The Economist notes in an article on the research:
[Real zebras] insist on moving around and swishing their tails. The team therefore conducted their study using inanimate objects. Some were painted uniformly dark or uniformly light, and some had stripes of various widths. Some were plastic trays filled with salad oil (to trap any insect that landed). Some were glue-covered boards. And some were actual models of zebra. They put these objects in a field infested with horseflies and counted the number of insects they trapped.
Creatures as large as elephants are unusual; it takes a long time to evolve such size.
How long does it take for a mammal as small as a mouse to evolve into something as large as an elephant? A really, really long time, a recent study has found: about 24 million generations, at minimum.
To get that number, researchers looked at the evolution of body mass over the last 70 million years, after the dinosaurs went extinct and surviving animals expanded into the ecological niches they left behind. That estimate is far longer than earlier estimates, which, extrapolating from bursts of super-fast evolution in mice, range from just 200,000 to 2 million generations. Such speedy evolution, in actuality, is probably not sustainable over the long term—hence the lengthy new estimate.
In the form of brood parasites, the bird world has enough irresponsible moms to start a reality TV show: cowbirds, for instance, lay their eggs in other species’ nests, stab most of the hosts’ eggs to death, and then leave their offspring to be raised by the host parents. The standing explanation for this involves most host birds being not that sharp on the uptake (watch a tiny warbler fussing over a cuckoo chick ten times its size (above) and you’d think that too). But maybe, a new study suggests, it’s sometimes to the host’s benefit to let imposter eggs stay in their nests.
The researchers chose mockingbirds as their hosts and cowbirds as their parasites, because mockingbirds usually fight like crazy to keep cowbirds of their nests but get strangely quiescent once the invaders have laid their eggs, a behavior that piqued the researchers’ interest. Once all the birds in the sample population had laid, the researchers went around adding and removing eggs from nests to see whether having a certain number of cowbird eggs affected mockingbird survival. They found that mockingbird eggs that shared their digs with cowbird eggs and suffered repeated cowbird invasions were more likely to survive, apparently because when each cowbird arrived, it would stab a certain proportion of the eggs in the nest regardless of whether they were host eggs or the eggs of the previous cowbird. Letting the parasite’s eggs stay, then, means that more of the host eggs avoid getting stabbed. The researchers conclude that when there are a lot of cowbirds around and hence a high probability of multiple nest hijackings, it makes sense for mockingbird parents not to shove out the invaders’ eggs.
Nice. And with all this dubious parenting and wanton violence, it’s straight from an episode of Teen Mom meets Cops, no?
Hookworms are longer-lived than viruses and bacteria;
they could have had a more significant effect on human evolution.
Humans live in all sorts of places—high deserts, tropical lowlands, frigid tundra. Over the millennia, you’d expect each population’s assortment of genes to evolve to reflect the demands and dangers of its home environment: those who live in the deserts would possess genes for extra skin pigments to help keep their tender integument from burning (like African peoples), and those who live in sub-zero climes much of the year would have genes that keep them well-insulated in fat (like the Inuit). But what if factors other than climate, like the food available nearby or the viruses, bacteria, and parasites native to the area, also had an effect on various human populations’ genetic toolkits?
It’s a fascinating question, but, given that we have to reconstruct all this supposed evolution from the current state of modern genomes, finding an answer isn’t easy. A recent paper takes an important first step by looking for correlations between 500,000 different genetic markers and certain environmental characteristics, like humidity, temperature, the local diet, and the prevalence of parasites and other pathogens.
Above, the real deal; below, the clay models used to test predators’ reactions to local and foreign frog markings.
Sometimes, you have to make a thousand frogs from modelling clay to make your point.
A single species of poison dart frog sports ten completely different coloration patterns, depending on where they live. Are these color divisions being encouraged by the birds that prey on them?, wondered evolutionary biologist Mathieu Chouteau from the University of Montreal. To find out, he set out 1800 clay frogs, made by himself and his (saintly!) girlfriend, in the Peruvian forest.
Because of two missing amino acids, this tomcod can swim through PCBs—and survive.
PCBs are nasty pollutants—they mess with hormones and have been linked to cancer—but until they were banned in 1977, dumping them in US rivers was a common practice for companies like GE. While plenty of wildlife suffered from ingesting PCBs, some fish in the Hudson and other be-sludged rivers evolved an immunity to the poisons, a intriguing example of quick adaptation that scientists have been watching with interest. A recent Economist article focusing on this research describes the fascinating genetic ju-jitsu that allows fish in the Hudson and in the harbor at New Bedford, MA, to keep themselves alive in PCB-contaminated waters. (more…)
How did animals move from water to land? The answer may have just got a little murkier. A study published this month in the Journal of Experimental Zoology found that two distantly related fish share a similar method for jumping about on land, suggesting that a common ancestor evolved this ability long ago. But unlike amphibious fish such as the mudskipper, which has pectoral fins adapted to “walking” on land, these fish have no specialized equipment for leaping, and would therefore leave no evidence of their talent behind in the fossil record.
What’s the News: We may strive for humility, but we benefit from a little hubris, too, according to a study published last week in Nature. Overconfidence in your abilities can help you triumph in competitions you might not have won otherwise, the study found, and can impart an evolutionary advantage when the potential payoff is high compared to the cost of conflict.
What’s the News: Researchers have now found a well-preserved fossil of the earliest known member of the animal group that encompasses today’s placental mammals, which includes humans. The shrew-like creature, named Juramaia sinensis, or “Jurassic mother from China,” dates back to 160 million years ago, 35 million years earlier than the oldest mammal fossil previously discovered. The Nature study gives some tangible support to genetic evidence suggesting that the two main types of mammals split well before the previous oldest mammal fossils.
Three-dimensional model of an ancient whale skull.
What’s the News: Scientists have long held that archaeocetes, the precursors to modern cetaceans, had symmetrical skulls like most other mammals. Whale skulls only became asymmetrical as certain species evolved echolocation to hunt for food. But it turns out that archaeocetes actually had skewed skulls, which likely allowed the whales to hear better underwater, according a new study published in the journal PNAS.
The marsh-loving song sparrow uses its beak to stay cool.
What’s the News: Scientists have long known that the size and shape of a bird’s beak is largely dependent on its diet. A hummingbird’s long, thin beak, for example, allows it to reach deep down into a tubular flower to get nectar. But in a new study in the journal Ecography, scientists have found that birds in warm climates have evolved beaks larger than their cooler-climate counterparts as a means of staying cool (birds, like most animals, don’t sweat). The new study adds weight to past research suggesting the same thing.
What’s the News: We walking, talking agglomerations of cells have always thought of multicellular life as a profound jump in evolution. The first organisms were just single cells, but at some point, they began to work together for the good of the whole, divvying up tasks like nutrient transport and cellular messaging. Eventually, these colonies became the complex multicellular life that we know and love.
But maybe being multicellular isn’t as difficult to achieve as we thought. Scientists presenting at the Society for the Study of Evolution conference have, over just a couple months, gotten single-celled yeast to grow into colonies that function as multicellular organisms.
Early anthropologist Samuel George Morton, accused by
Gould of bias in his measurements of skulls, may finally
be exonerated.
What’s the News: Harvard biologist and popular author Stephen Jay Gould was a well-known advocate for evolution and denouncer of scientific bias. But a new study shows that one of his most famous claims—that an early researcher unconsciously manipulated his measurements of skulls to make Caucasians seem smarter—is baseless.
The researcher actually made few errors, and it looks like Gould never bothered to measure the skulls himself, as the study’s authors did, before crying bias. “Ironically,” the authors write, “Gould’s own analysis…is likely the stronger example of a bias influencing results.”
80beats is DISCOVER's news aggregator, weaving together the choicest tidbits from the best articles on the day's most compelling topics.
80beats is written by Veronique Greenwood and Valerie Ross. This team darts through each day's science news faster than the ruby-throated hummingbird that beats its wings 80 times per second. Send ideas, tips, suggestions, and complaints to [azeeberg at discovermagazine dot com].
Parasitic wasps have a terrifying but weirdly impressive knack for taking over the bodies and brains of other many-legged creatures, making 
Mosquitofish can leap with “skill and purpose.”
What’s the News: We may strive for humility, but we benefit from a little hubris, too, according to a 
Three-dimensional model of an ancient whale skull.
The marsh-loving song sparrow uses its beak to stay cool.
