Category Archives: evolution

One of these moths is not like the other … but does that matter to Joshua trees?

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A Joshua tree flower, up close
A Joshua tree flower, up close

Cross-posted from Nothing in Biology Makes Sense!

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 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.

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Nothing in Biology Makes Sense: A flower is an evolutionary compromise

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Pollination IMG_4730D Welcome, pollinators! But, um, everyone else can just stay out, okay? Photo by Yeoh Thean Kheng.

Over at Nothing in Biology Makes Sense!, I’ve written about a neat study of the tropical vine Dalechampia scandens, which has to solve an evolutionary puzzle that confronts most flowering plants:

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.

To see how a team of biologists directly measured this evolutionary compromise (spoiler: it involves counting pollen grains with a hand lens) go read the whole thing.◼

The Molecular Ecologist: Triangulating the targets of natural selection

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torridon view Photo by paul.mcgreevy.

At The Molecular Ecologist, guest contributor K.E. Lotterhos discusses an important consideration in designing studies that “scan” the genome for regions experiencing natural selection—to be truly informative, they must “triangulate” using independent data:

Let’s say a number of individuals were collected from heterogeneous environments on the landscape. Some SNPs were significant both in an FST outlier analysis and a [genetic-environement association]. Would we consider these SNPs to have two independent sources of evidence?

NO, because the two tests were performed on the same sets of individuals.

What counts as “independent” in this context? I think that’s still something of an open question—but go read the whole thing and se what you think!◼

Nothing in Biology Makes Sense: Stalking the wild holobiont

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figure made from dishes containing images of microbes Photo by Pickersgill Reef.

Over at Nothing in Biology Makes Sense!, Sarah Hird introduces us to the concept of the holobiont and its hologenome:

Most evolutionary biologists probably consider the individual as the fundamental unit of natural selection. We think about the genes of one mother or one father being passed on to one descendant. But is this view too constrained? The “hologenome” is all the genomes that belong to the “holobiont” – an organism and all its microbes.

Would natural selection be better understood as acting on organisms together with all the microbes they host? Go read the whole thing and see what you think.◼

Nothing in Biology Makes Sense: A fossil swift, and the origin of hummingbird flight

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Hummingbird Backside Photo by Extra Medium.

Over at Nothing in Biology Makes Sense, guest contributor Jessica Oswald explains how a new fossil of a bird that lived 52 million years ago helps explain the origins of some of nature’s greatest aerial acrobats:

Swifts are able to reach the highest speeds during level flight (Chantler 1999) and hummingbirds are well known for their hovering abilities and their sideways and backward flight. Swifts and hummingbirds, while sharing the same wing bone characteristics, have different lengths of flight feathers, resulting in different wing shapes across the group, which allows them to perform their different aerial feats. Hummingbirds have shorter wings relative to their body size compared to swifts, resulting in their hovering abilities. These different wing shapes are well suited for their modern functions, but we have almost no fossils from this group, so we don’t know how the wing shapes diverged, or anything about the ecology of ancient species in this lineage.

To learn what the common ancestor of swifts and hummingbirds (or, rather, one of its early descendants) looked like, go read the whole thing.◼

Nothing in Biology Makes Sense: Tropical trees, getting by with a little help from their mutualistic ants

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This week at Nothing in Biology Makes Sense! I’m discussing a nifty new study that suggests interacting species can sometimes tolerate stressful environments by helping each other out:

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.

To learn how ants can help a tree deal with drier climates—no, it doesn’t involve little tiny bucket brigades—you’ll have to go read the whole thing.◼

Nothing in Biology Makes Sense: Can we separate reproductive isolation and species formation?

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fork in the road Photo by dkwonsh.

This week at Nothing in Biology Makes Sense! Noah Reid takes a look at a study that attempts to disentangle the effects of reproductive isolation between species and the rate at which new species are formed. Why would you want to do that? So you can tell whether the former causes the latter!

RI [reproductive isolation] is often thought to be important in diversification because some theory predicts that even low levels of intermating between populations can prevent divergence from occurring and because hybridization between divergent populations can cause them to homogenize, or cause one population to become extinct. If these factors commonly prevent speciation or cause incipient species to go extinct, one might expect a positive correlation between the rate of evolution of RI and DR [species diversification]. This paper is the first test of this prediction.

But, of course, a lot of biologists would say that the evolution of reproductive isolation is the evolution of a new species … so things get a bit complicated. Go read the whole thing, and see what you think.◼

Nothing in Biology Makes Sense: Your dinner, or your life?

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2010 076 Masai Mara b 24 Photo by ngari.norway.

Over at Nothing in Biology Makes Sense!, I’ve written about a new study that tries to disentangle conflicting sources of natural selection to determine whether big herbivores like antelope, zebras, and ostriches have evolved to run because they’re always running away from predators.

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.

To find out whether gazelles are running for their lives, or running for dinner, go read the whole thing.◼

Nothing in Biology Makes Sense: Making sense of the missing human baculum

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Walruses on the corner If you think those tusks are impressive, you ain’t seen nothing yet. Photo by Joe King.

Over at Nothing in Biology Makes Sense! Sarah Hird discovers a case in which Creationists are willing to cite phylogenetic context to make a point, and that point is that God made Eve from the bone in Adam’s penis. What, you didn’t know that most mammals have a penis bone?

Baculum is the technical term for the penis bone. Many mammals have one – presumably to aid in sexual intercourse. For mammals that mate infrequently, prolonged intercourse ups the chances that a particular male sires some babies. For mammals that must mate quickly, the baculum provides immediate rigidity. And for all mammals, keeping the urethra straight while copulating is imperative, so maybe it’s there to prevent a kink in the works, so to speak.

To see the full phylogenetic context of the baculum, and learn some possible reasons why a male walrus has a two-footer but humans have none at all, go read the whole thing.◼

The Molecular Ecologist: Climate’s a-changin’. Will the living world evolve to cope?

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Warm Fire It’s getting hot out there. Photo by Kaibab National Forest.

Over at The Molecular Ecologist, I discuss a new study that uses phylogenetic estimates for 17 families of vertebrates to estimate how rapidly those animals have evolved in response to past climate change, and compares those estimates to how fast they’ll need to evolve to keep up with projected climate change. Spoiler alert: past rates of adaptation to climate aren’t anywhere near fast enough.

To keep up with projected climate change, Quintero and Wiens estimated that the species in their dataset would have to undergo adaptive change at from 10,000 to 100,000 times faster than the rates estimated in their evolutionary past.

Well, but maybe. To learn whether the data are telling us what the study’s authors say they’re telling us, go read the whole thing.◼