When mummies attack! Why specificity matters for coevolution

Evolutionary change by means of Natural Selection needs a couple of things in order to happen: heritability and variation in fitness. That is, offspring need to resemble their parents at least a little (heritability) and individuals need to differ in their survival and offspring production (fitness). WORDLE Rouchet Vorburger 2012We’ll worry about heritability in another post, but variation is something that seems like it might be hard to maintain. Some forms of Natural Selection will reduce variation as more fit individuals become frequent and all the different kinds of less fit individuals are eliminated from the population. However, there is a force, common in nature, which may maintain variation, parasites.

Interactions between hosts and parasites can generate strong selective pressures on each player, especially if your life depends on infecting a host. Often, biologists make an analogy to an arms race where players are developing bigger and better defenses or weapons. Antagonistic interactions may also generate negative frequency dependence where a rare host type is favored because the parasites are adapted to a common type. You can learn more by checking out CJ’s post on the Red Queen Hypothesis or Jeremy’s post on a different coevolutionary puzzle. A key component for maintaining variation via negative frequency dependent selection is specificity. There must variation in the interaction among different host genotypes and parasite genotypes. This is sometimes referred to as a GxG interaction. If parasites can infect all the hosts, there is no specificity. Specificity allows different hosts to be favored over time depending on the composition of the parasite population.

Theoreticians love to use different models of interactions between hosts and parasites, but without empirical evidence, there seems little point. In a recent paper by Rouchet and Vorburger (2012), the authors looked for evidence of just the kind of genetic specificity would result in the maintenance of genetic variation.

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Friday Coffee Break, Vienna Style!

Every Friday at Nothing in Biology Makes Sense! our contributors pass around links to new scientific results, or science-y news, or videos of adorable wildlife, that they’re most likely to bring up while waiting in line for a latte.

From Devin:

The future of online learning. PLOS Computational Biology puts together a great set of online resources for biologists or more specially a bioinformatics Curriculum. “…in an exhaustive meta-analysis of 51 published head-to-head trials, found that ‘on average, students in online learning conditions performed better than those receiving face-to-face instruction'” 

From Sarah:

Even “living fossils” have evolved over time.  The term debunked in this piece on the Wired Science Blog. “The new fossil described by Briggs and colleagues records a critical transformation in horseshoe crab history. Discovered at an exceptional site in the 425 million year old rock of Herefordshire, England, the new genus is justly called Dibasterium durgae – a tribute to the invertebrate’s mysterious limbs and to Durga, ‘the Hindu goddess with many arms.'”

From Jeremy:

Which professions do you think drink the most coffee?  If you guessed Scientists you’d be right.  Learn more here from a poll by Dunkin Donuts and CareerBuilder to determine the most caffeinated workers. “Scientists today are spending much more time working than initially intended. They are deprioritizing their hobbies, leisure activities, and regular exercises, which negatively influenced their mental and physical health.”

From Noah:

Native Inuit of Canada face new challenges with increased climate change and rapid retreat of sea ice along with encroaching industry. “Some Inuit feel they are losing control of a homeland whose ice-covered expanses had acted as a barrier to the outside world. A growing number of interests — mining and oil companies, scientists and conservationists, military vessels from Canada and other Arctic nations — are appearing in the Inuit’s traditional homeland…”

Finally From Jon:

The trend of Doctors turning away from insurance and moving to cash only concierge service could pose a problem for the future of access to care for uninsured and underinsured patients. “a new survey of 13,575 doctors from around the country by The Physicians Foundation found that over the next one to three years, more than 50 percent plan to take steps that reduce patient access to their services, and nearly 7 percent plan to switch to cash-only or concierge practices, in which patients pay an annual fee or retainer in addition to other fees.”

Evolution vs. Creationism: A completely unambiguous, logically unassailable scientific test. Now we can all stop arguing on the internet about it.

Bill Nye the Science Guy.

Bill Nye (the Science Guy!) has recently thrust himself into the public eye with some commentary on the implications of the persistent fights over the teaching of evolutionary theory in the United States. One of the soundbytes that emerged from the whole thing really jumped out at me:

Your world just becomes fantastically complicated when you don’t believe in evolution.

As an evolutionary biologist, my first defense against any religious impingement on science is often to say that appeals to divine intervention are not rejectable. Therefore they cannot be addressed using in the hypothetico-deductive method and so should be excluded from scientific inquiry. I often add when talking to undergraduates that if any of them came up with a rigorous, falsifiable model of divinity, they would certainly be famous for it.

But when I read this quote, I realized I’d been selling science short. Bill Nye’s statement suggests that we don’t HAVE to view religious hypotheses as untestable simply because they are unrejectable. In many cases in science, we are interested in finding a useful working model of some phenomenon. In those cases we regularly view the issue as one of choosing the best model from among a set of candidates rather than one of rejecting all models that are wrong. In at least one case I can think of, we apply a complex, unrejectable model in a test of the adequacy of a much simpler model (about which, more below).

When we engage in this process, we often employ Information Theory to guide our selection. Without getting into the details, we can think of information theoretic criteria for model selection as formally implementing Occam’s Razor: the simplest model with the most explanatory power is to be preferred. By preferring simple models, you guard against overinterpreting data, a pitfall that can make models poor predictors of new observations.

So, I realized as long as we can formulate any mathematical model of “The Hand of God”, rejectable or not, we can compare it to an evolutionary model in this framework. If, as Nye suggests, evolutionary theory is simple and powerful, and creationism is a model of fantastical complexity that doesn’t much improve our understanding of the data, information theory would help us sort that out.

So why not give it a whirl?

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