The Pleistocene history of the sheepshead minnow (Cyprinodon variegatus): Non-equilibrium evolutionary dynamics within a diversifying species complex.

The sheepshead minnow, Cyprinodon variegatus, is a widespread fish species that typically inhabits coastal tidal marsh and mangrove swamp environments, ranging from Cape Cod, Massaschusetts to northern Mexico and into the Caribbean. This wide range crosses several biogeographic boundaries which are coincident with genetic structuring within numerous species originating in the Pleistocene. In addition, the more northerly reaches of this species range have been further subject to the evolutionary consequences of Pleistocene glaciation due to local extinction and recolonization of formerly glaciated sites.

The tripartite associations between bacteriophage, Wolbachia, and arthropods.

By manipulating arthropod reproduction worldwide, the heritable endosymbiont Wolbachia has spread to pandemic levels. Little is known about the microbial basis of cytoplasmic incompatibility (CI) except that bacterial densities and percentages of infected sperm cysts associate with incompatibility strength. The recent discovery of a temperate bacteriophage (WO-B) of Wolbachia containing ankyrin-encoding genes and virulence factors has led to intensifying debate that bacteriophage WO-B induces CI.

Cytonuclear coevolution: the genomics of cooperation.

Without mitochondria we would be in big trouble, and there would be a global biological energy crisis if it were not for chloroplasts. Fortunately, genomic evolution over the past two billion years has ensured that the functions of these key organelles are with us to stay. Whole-genome analyses have not only proven that mitochondria and chloroplasts are descended from formerly free-living bacteria, but have also shown that it is difficult to define eukaryotes without reference to the fusion and coevolution of host and endosymbiont genomes.

The roles of positive and negative selection in the molecular evolution of insect endosymbionts.

The evolutionary rate acceleration observed in most endosymbiotic bacteria may be explained by higher mutation rates, changes in selective pressure, and increased fixation of deleterious mutations by genetic drift. Here, we explore the forces influencing molecular evolution in Blochmannia, an obligate endosymbiont of Camponotus and related ant genera. Our goals were to compare rates of sequence evolution in Blochmannia with related bacteria, to explore variation in the strength and efficacy of negative (purifying) selection, and to evaluate the effect of positive selection.

Wolbachia interactions that determine Drosophila melanogaster survival.

We have recently described a mutualistic symbiosis in which Wolbachia bacteria were shown to improve the fitness of some Drosophila melanogaster stocks. Wolbachia did not extend longevity in all Drosophila genotypes, even though 16s rDNA sequences indicated that our Drosophila stocks were infected with the same Wolbachia strain. Here, we use reciprocal hybrid crosses between two Drosophila strains, one that lived longer with Wolbachia (Z53) and one that did not (Z2), to investigate the inheritance of the survival phenotype and its dependence on the host genotype, sex, and mating conditions.

MILDLY DELETERIOUS MUTATIONS IN AVIAN MITOCHONDRIAL DNA: EVIDENCE FROM NEUTRALITY TESTS.

To determine whether mildly deleterious mutations (MDMs) are present in nonrecombining genomes such as avian mitochondrial DNA (mtDNA), I analyzed molecular data from 14 studies using the neutrality tests of Tajima (1989a) and McDonald and Kreitman (1991). The presence of MDMs in mtDNA is inferred from trends observed across species in estimates of heterozygosity (θ and π) and by comparisons of polymorphism and divergence using the neutrality index (NI). Assuming neutrality, θ equals π and NI equals one.