How many moths must a sloth carry off for the sloth to rely on the moths?

Three Toed Sloth

Is it easier being green? Photo by Bas Boemsaat.

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.

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Living at the edge, range expansion is a losing battle with mutations

Environments can vary substantially in habitat quality, local population abundance, or carrying capacity. Under some climate change scenarios, new, higher quality habitats become available along the margin of a species’ range (e.g. higher latitudes or altitudes) (Thomas et al 2001). These new habitats may be able to support larger population sizes. Factors of demography, evolution, and qualities of the abiotic and biotic communities all interact to determine where a species is found and may influence the ability of a species to expand its range. New research is building genetically explicit models in order to understand how the interplay of these different factors influence evolutionary changes,

Wordle of Peischl et al 2013

The authors of a recent study focus on how the interaction of the demographic process of range expansion changes the way that natural selection favors beneficial and deleterious mutations (Peischl et al 2013). Using both computer simulations as well as mathematical approximations, the authors find that at the range margins, individuals carry a substantial load of deleterious mutations.

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BAH! This looks amazing

BAHFest , the Festival of Bad Ad Hoc Hypotheses, is a competition to develop “well-argued and thoroughly researched but completely incorrect evolutionary theory.” The whole thing was originally proposed in a Saturday Morning Breakfast Cereal strip proposing that human infants have been evolutionarily optimized for long-distance dispersal by catapult.

Coming up with “obviously wrong” scientific hypotheses is clever because it helps us think about why, exactly, we choose to believe the hypotheses that we do, and how we use (and misuse) evidence to make those judgements. My personal favorite example is a 1983 article, published in the journal Evolution, which evaluates all the possible reasons that natural selection has made offspring smaller than their parents [PDF]—smaller offspring are easier to hide, cheaper to make, easier to disperse, and easier to control in the event that their interests conflict with their parents’—but completely (and deliberately) misses the obvious, actual reason.

Last year’s BAHFest winner, Tomer Ullman, proposed that babies cry because the irritating, high-pitched noise helps prepare their caretakers for battle:

The next iterations of BAHFest are scheduled for 25 October in San Francisco, and a date to be announced in Boston.

Reference

Ellstrand NC. 1983. Why are juveniles smaller than their parents? Evolution. 37(5): 1091-4. doi: 10.2307/2408423.

On the evolution of blind cave fish.

Astyanax mexicanus cave dwelling form.

Evolution requires variation in traits among individuals to act. If evolutionary fitness is determined by a given trait, and everyone in a population has the trait, then there is no basis for natural selection to discriminate among individuals. Furthermore, when variation does exist, it must be genetically based so that it can be passed down by successful parents to their offspring. The trait variation on which selection acts can either come from genetic variation existing in a population before selection begins or it can result from new mutations. Because natural selection acts to eliminate unfavorable variation, there is a question as to how selection in a changing environment could reverse change, or remove a trait it had previously favored. Where would the necessary variation come from?

One controversial hypothesis is that genetic variation for a given trait can be masked from selection by very stable (or “canalized”) developmental processes. These canalized processes result in highly uniform traits within a population despite underlying genetic variation. Under certain environmental conditions (in particular, stressful ones), they can be destabilized, allowing underlying genetic variation to cause traits to vary, thus providing grist for natural selection’s mill.

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Baba Brinkman says he wants my money

But he doesn’t want it badly enough to actually address the substance of any of my criticisms of his scheme to rid the world of meanness via “an entirely defensible ‘bottom up’ form of eugenics.”

Oh, and I see he’s speculating about my sex life. Real charmer, this guy.

In his non-response response, Brinkman doubles down on his fixation with the fact that, across human populations, males become more likely to be involved in violent crime right around the time we hit puberty:

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Inane pseudo-scientific claptrap of the week: “Don’t sleep with mean people”

The maestro behind the “Rap Guide to Evolution,” Baba Brinkman, has a new idea for changing the world: don’t sleep with mean people. I know, right? You hadn’t thought about doing that, either?

Are you amazed at the clarity of Brinkman’s insight into the roots of human suffering? Then he would like you to give him money to help make his plan a reality. Well, to make a music video and a documentary and some billboards, anyway.

Or, you know, you could do something more useful with your money, like baking it into muffins as a fiber supplement. Or shredding it up to mulch your vegetable garden. Or using it to line a bird cage.

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@NothingInBio at #Evol2013: What we’re presenting

Cecret Lake - Alta Utah

The Evolution 2013 meetings are nearly upon us, and most of the team here at Nothing in Biology Makes Sense! are going to be in Snowbird, Utah for the joint annual meeting of the American Society of Naturalists, the Society of Systematic Biologists, and the Society for the Study of Evolution. Rather than make you hunt through the online program, here’s where we’ll be, and what we’re presenting:

  • Amy will present “The population genetics of rapidly evolving reproductive genes: How much variation should we expect to find?” on Sunday at 9:30, as part of the Evolutionary Genetics and/or Genomics section in Cotton D/Snowbird Center. [program link]
  • Look for some of CJ’s work in a lightning talk by her dissertation advisor, Mark Dybdahl, titled “Identifying the molecular basis of coevolution: merging models and mechanisms” on Monday at 11:45, in Superior B/Cliff Lodge. [program link]
  • Noah will present “What can we learn from sequence-based species discovery? An example using sky island fly communities” on Tuesday at 9:30, as part of the Community Ecology and Evolution section in Peruvian A/Snowbird Center. [program link]
  • Sarah will present “Nature, nurture and the gut microbiota in the brood parasitic Brown-headed Cowbird” on Tuesday at 10:30, as part of the Community Ecology and Evolution section in Peruvian A/Snowbird Center. [program link]
  • Jeremy will present “Evidence for recent adaptation in genome regions associated with ecological traits in Medicago truncatula” on Tuesday at 2:45, as part of the Genetics of Adaptation section in Rendezvous A/Snowbird Center. [program link]

Looks like we’re in for a busy Tuesday! But this year, you won’t have to choose between us.

Beware: The Sneaky Grass Goby

Grass Gobies

Grass Goby (Zosterisessor ophiocephalus) – Wikipedia Commons

Competition for mates drives the evolution of many of the exaggerated male traits, such as the bright plumage of tropical birds or the intricate horns of dung beetles, that are so easily appreciated (and photographed).  However, the elaborate consequences of competition for mates continue even after mate choice and copulation has taken place, inside of the female reproductive tract.  Much of the research on sperm competition has focused, for obvious reasons, on the quantity and morphology of the sperm produced by males with results that are no less fascinating or extreme.  For example, the fruit fly, Drosophila bifurca, produce sperm that are around 2.3 inches long, which is more than 20 times their body length and 1000 times the length of human sperm!

However, sperm constitute only a small portion of the male ejaculate transferred to females during mating.  The rest, up to 90%, is composed of a myriad of proteins and other compounds that constitute the seminal fluid.  In addition to being produced in abundance, seminal fluid proteins are also diverse.  For example, scientists have found that males, of many species, produce dozens, if not hundreds, of different types of seminal fluid proteins.  So, what then, do all these proteins do?  It turns out that these protein are involved in many different processes that indirectly influence male reproductive success, including influencing female physiology and interacting with a male’s own, as well as rival, sperm.

A recent study by Locatello et al., published in Proceedings of the Royal Society B, has taken advantage of some useful characteristics of the mating system of the grass goby, Zosterisessor ophiocephalus, (pictured above) to investigate how alternative male mating strategies may be paired with alternative sperm competition strategies to help level the playing field between males that vary in their ability to directly compete for mates.

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Carnival of Evolution: We’re hosting!

Evolution

Step right up, step right up, ladies and gentlemen, to submit your fine evolution-related blog posts to the 58th edition of the Carnival of Evolution, the one and only community-assembled, community-supported, community-hosted aggregation of the finest online writing on the illustrious topic of Descent With Modification and all its manifold modified descendents.

On the first day of March, this glorious Carnival will be found right here at Nothing in Biology Makes Sense!, the better to showcase the work of everyone from students to scientists to great fans of science, everyone and anyone, ladies and gentlemen, who believes and can demonstrate in mellifluous prose, captivating videos, eye-catching infographics, or hilarious LOLcats that bedrock principle of the modern life sciences, that nothing—no, ladies and gentlemen, not a gosh-darned thing—in the whole of biology makes sense, except in the light of evolution.

Think you’ve got what it takes to join this revolutionary celebration of evolutionary science? Send us links to your blog posts, essays, videos, and webcomics at this elegant and convenient form (it requires a log-in, but then what doesn’t these days?) or simply e-mail them direct to Jeremy Yoder, our local curator of carnivalian content. Please do send’em before the 26th of February, though, to ensure proper packaging and adequate care of all your delightful and illuminating work.

We thank you humbly and vociferously for your contributions, one and all—and we look forward to seeing you right here, at this very URL, for the Carnival of Evolution, in less than the span of one short month!

Of Salty Bahamian Ponds and Adaptive Radiation

A Mexican pupfish, Cyprinodon veronicae

One of the central hypotheses about how the diversity of life is generated is known as “adaptive radiation“. This term, popularized by G.G. Simpson in the mid 20th century, encapsulates an idea that is relatively easy to grasp: that the spectacular arrays of morphological and species diversity that we observe in the world are often the result of great bursts of speciation and morphological change. These bursts occur because a single species colonizes a new area, acquires a new adaptation, or suddenly escapes its competitors or natural enemies (possibly by their extinction). This opens up a new universe of possible lifestyles that evolution then drives that species to take up by rapid diversification. Think of the Hawaiian honeycreepers or Darwin’s finches.

The idea holds great sway because it is simple and powerful, but testing it empirically has proven very difficult. This is in part because the actual mechanisms underlying speciation and morphological diversification are exceedingly complex, and in part because many of the groups of organisms which we suspect have adaptively radiated did so long ago, leaving much of the evidence of those mechanisms buried under millions of years of subsequent evolutionary change. A recent experiment by Martin and Wainwright (2013) attacks these issues by manipulating a nascent adaptive radiation of Cyprinodon pupfishes on the island of San Salvador, Bahamas.

Cyprinodon are small fishes that have a habit of becoming isolated in unexpected places. In the United States they are best known for tentatively clinging to life in tiny springs in deserts of the southwest, where they’ve been embroiled in conflicts between conservation and urban and industrial interests over water rights. Almost all of them are dietary generalists that tend to eat a lot of algae. Martin and Wainwright’s study focused on three species that occur in another such unexpectedly isolated locale, a pair of hypersaline lakes on the island of San Salvador, Bahamas.

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