There’s lots of cool stuff coming out in the speciation literature. The Questionable Authority has posted on two recent studies on sympatric speciation (see here and here). Nature, which published the two sympatric speciation papers, has a summary available here. I am of the opinion that most examples of sympatric speciation are actually allopatry with reinforcement (for more on this, see here). That is not to say that sympatric speciation is impossible, just extremely rare. In the end, some reproductive isolation is a requirement for speciation in sexually reproducing organisms (whether that comes about via spatial isolation, changes in mating periods, or some other factor). Once there is some hybrid incompatibility, reinforcement can encourage speciation at a rapid rate, and this will often look like sympatric speciation.
Another paper reports some work on the genetics of hybrid breakdown between populations of the copepod Tigriopus californicus. Like all animals, these copepods have two genomes: a nuclear genome and a mitochondrial genome. The nuclear genome encodes the cytochrome c (CYC) protein, which is oxidized by cytochrome c oxidase (COX) as part of the electron transport chain in cellular respiration. The COX protein complex consists of multiple proteins, some of which are encoded by mitochondrial genes and others by nuclear genes. The COX proteins must interact favorably with CYC for the electron transport chain to function properly. The authors identified mutations that changed the amino acid sequence of the CYC protein and deleteriously affected its ability to be oxidized by COX. They also showed that some populations of T. californicus differ by a single amino acid substitution in the CYC gene, and this difference contributes significantly to the hybrid incompatibility between populations.
Our final tour through the speciation literature takes a look at the evolution of mate choice in yeast (for a summary, see here). Saccharomyces cerevisiae (baker’s or brewer’s yeast) can reproduce both sexually and asexually depending on environmental conditions. The authors of this paper evolved prezygotic (I’m not sure how appropriate that term is for yeast) reproductive isolation between laboratory populations by continuously selecting against hybrids from two populations. Each time they wanted to exert selection against hybrids they mated an experimental population to a reference population and used a mutation in the reference population to remove all heterozygotes and reference homozygotes. After 36 rounds of selection, 11 of their 13 experimental populations had significant mating preference against the reference population.