Recent Stuff

A lot of interesting evolutionary genetics research gets published, and I don't have time to write an insightful commentary on all of it (some may argue that I have never written an insightful commentary on anything). Here's a brief overview of the stuff I have missed in the past few weeks:

• A population of sheep was started with the introduction of two individuals on a remote island in the southern region of the Indian Ocean. Surprisingly, genetic diversity has increased over time in this population (reported here). This increase in heterozygosity (measured by the amount of microsatellite polymorphism in the population) can be best attributed to natural selection (it's too high to be due to mutation and there was no migration into the population). The authors show that the population is in Hardy-Weinberg equilibrium, which indicates that cryptic population subdivision has not led to an increase in heterozygosity.

• R.A. Fisher famously argued that Gregor Mendel fabricated some of his results on inheritance in pea plants so that they better matched his expected ratios of each type of progeny. Dan Hartl and Dan Fairbanks have published a critique of the criticisms. I won't get into the details here, but they suggest that Fisher's allegations of fudging data were unfounded. It's not that Fisher's stats were bad, but some of his assumptions were incorrect.

• Researchers from The Institute for Genomic Research and the J. Craig Venter Institute (which are now one in the same) along with scientists from Singapore have sequenced the genome of a cartilaginous fish -- the elephant shark (reported here). The big finding of this paper is that gene order is more conserved between the chimaera (the elephant shark is, technically, not a shark) and tetrapods (the human genome in this case) than between teleosts (the largest extant group of ray finned fishes) and tetrapods. Sharks, skates and rays (cartilaginous fish) diverged from teleosts and tetrapods prior to the divergence of teleosts and tetrapods (see this figure from the paper). The high conserved gene order between elephant sharks and humans is most likely because teleost fishes experienced a whole genome duplication after their divergence with the tetrapods. This duplication event was followed by the loss of many duplicate genes (returning many genes to their ancestral single copy state), which can lead to dramatic differences in gene order when compared to a genome that did not experience a duplication event.

• Aphids depend on a bacterial symbiont to provide essential nutrients. Research from Nancy Moran's lab (their paper, popsci article) indicates that a single nucleotide deletion in the regulatory region of a heat-shock gene in the symbiont genome renders the aphids highly sensitive to heat exposure as juveniles. But aphids carrying symbionts with the deletion reproduce more successfully at lower temperatures. Both alleles can be found at appreciable frequencies natural populations, suggesting some sort of balancing selection (possibly temporally or spatially varying selection coefficients) maintains the polymorphism.