Friend of the blog (and former contributor) Devin Drown is wrapping up his first year on the faculty of the University of Alaska Fairbanks, where he’s been teaching the Principles of Evolution course. As a final assignment, Devin’s students are contributing posts to a class blog, Evolution, Naturally — and the first couple are great!
Margaret Oliver digs into the phylogenetic data used to support the renaming of a genus of desert-adapted, clonally reproducing ferns — after Lady Gaga. It turns out that the singer’s stage name is literally encoded in the DNA sequence that helps differentiate the new genus from its closest relatives, as Oliver illustrates in the best. Phylogeny. Figure. Ever.
Meanwhile, Alexandria Wenninger explains how some species of ants steal larvae from other ant colonies and raise them as workers — and how entomologists are discovering that those kidnapped workers can resist this unasked-for reassignment.
However, there is a growing body of evidence suggesting that the [captured workers] are not always so oblivious to their origins, as researchers observe more and more situations of what they are calling “slave (host) rebellion”. Czechowski and Godzinska, in their recent review article, “Enslaved ants: not as helpless as they were thought to be”, identify four types of rebelling behaviors, which range from aggressive acts by individual ants to a collective uprising against the parasites.
A fungus called Cryptococcus gattii, has long known to be infective to humans… even though it’s found on trees.
This has particularly been a problem in Southern California, where people have been getting sick from C. gattii for yeas, and no one knew which tree was harboring the fungus. Find out who the culprit is and how they figured it out!
Here at Nothing in Biology Makes Sense, we’re fascinated by all the weird, baroque ways that living things influence and coevolve with each other—so Ed Yong’s new TED talk about mind-controlling parasites is right up our alley. Just like his writing—currently on display at National Geographic‘s Phenomena, among many other venues—it’s a compendium of nifty natural history punctuated with highly educational gross-outs and the occasional black-belt level pun.
Brood parasites are definitely the bullies of the avian world. They lay their eggs in the nests of other birds, sometimes destroying the host’s own eggs or just waiting for their nestlings to do the dirty work after they hatch. They then outcompete any surviving host nestlings for food, while the poor host parents are worked to the bone to feed the monstrous nest invader.
In spite of the steep costs of nest parasitism, most avian host species do not have effective mechanisms for detecting and removing brood parasites from their nests. So, why don’t mama birds notice they have a GIANT intruder in their nest and carry out some infanticide of their own? One hypothesis is that the cost of a mother bird making a mistake and pushing the wrong baby out (i.e. her own) outweighs the benefit of developing such a behavior.
This week in Science, Canestrari et al. published evidence for another hypothesis – that sometimes, it might actually be good to have your nest parasitized.
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). We’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.
Conventional wisdom suggests that pathogens and parasites are more rapidly evolving because of various reasons such as short generation time or stronger selection. Yet somehow, they have not completely won the battle against the host. Recently, a theoretical paper on coevolution in Nature caught my eye (Gilman et al., 2012). Here the authors address this paradox: “How do victim species survive and even thrive in the face of a continuous onslaught of more rapidly evolving enemies?”
Instead of treating a coevolutionary interaction between two species as the interaction of only two traits, the authors investigate the nature of an interaction among a suite of traits in each species. It’s not hard to think of a host having a fortress of defenses against attack from a parasite with an arsenal loaded with many weapons.
A reed warbler feeds a cuckoo chick
Brood parasitism, the reproductive strategy of choice for cuckoos and cowbirds, sounds like a lazy approach to parenting: lay your eggs in another bird’s nest, and let the unwilling adoptive parents take the trouble to raise your chicks. But contracting out parental care like this comes with many of its own complications. Chicks raised by parents of a different species have to eliminate competition from their adoptive nestmates, and may grow up a bit confused; reluctant host birds may need to be told, and reminded, that raising cuckoo chicks is an offer they can’t refuse.
But before crossing all those hurdles, a brood parasite’s first task is to lay eggs in the nest of a host who won’t immediately recognize and reject them. The strong natural selection imposed by host rejection has led cuckoos to evolve “host races” that lay eggs whose color and spotting pattern matched to those of their preferred host species. This kind of broad-scale pattern could arise without much direct effort by female cuckoos—those who lay eggs in the nest of the best matching host species would simply be the ones most likely to have chicks that survive to the next generation. But is it possible that cuckoos do take an active role in matching up to their hosts, seeking out host nests containing eggs that look like their own?
The answer, according to a series of studies over the last several years, is yes—probably.