Variable rates of hybridization among contact zones between a pair of topminnow species, and .

Pairs of species that exhibit broadly overlapping distributions, and multiple geographically isolated contact zones, provide opportunities to investigate the mechanisms of reproductive isolation. Such naturally replicated systems have demonstrated that hybridization rates can vary substantially among populations, raising important questions about the genetic basis of reproductive isolation. The topminnows, and , are reciprocally monophyletic, and co-occur in drainages throughout much of the central and southern United States.

Invasion genetics of the mummichog (): recent anthropogenic introduction in Iberia.

Human activities such as trade and transport have increased considerably in the last decades, greatly facilitating the introduction and spread of non-native species at a global level. In the Iberian Peninsula, , a small euryhaline coastal fish with short dispersal, was found for the first time in the mid-1970s. Since then, has undergone range expansions, colonizing the southern region of Portugal, southwestern coast of Spain and the Ebro Delta in the Mediterranean Sea.

Phylogenomic analysis of Fundulidae (Teleostei: Cyprinodotiformes) using RNA-sequencing data.

Fishes of the New World cyprinodontiform family Fundulidae display a wide variety of tolerance to environmental conditions, making them a valuable model system for comparative, evolutionary, and environmental studies. Despite numerous attempts to resolve the phylogenetic relationships of family Fundulidae, the basal structure of the phylogeny remains unresolved. The lack of a robust and fully resolved phylogeny for family Fundulidae and its most speciose genus Fundulus is an impediment to future research.

Hybridization and introgression in two ecologically dissimilar Fundulus hybrid zones.

Hybridization and introgression appear more common in rapidly evolving groups, suggesting an important role in the evolutionary process. Detailed studies of how extrinsic or intrinsic forces regulate hybridization and introgression have the potential for broadening our understanding of mechanisms generating diversity. Species in the Fundulus notatus species complex have broad overlapping ranges and occur in replicated hybrid zones along predictable stream gradients.

Contrasting phylogeographic histories between broadly sympatric topminnows in the Fundulus notatus species complex.

Sympatrically distributed closely related species provide opportunities for studying evolutionary patterns of diversification. Such studies must account for historical contingencies in interpreting contemporary patterns of variation. Topminnows in the Fundulus notatus species complex are distributed sympatrically across much of the southern and Midwestern United States.

Evolution of a sexually dimorphic trait in a broadly distributed topminnow (Fundulus olivaceus).

Understanding the interaction between sexual and natural selection within variable environments is crucial to our understanding of evolutionary processes. The handicap principle predicts females will prefer males with exaggerated traits provided those traits are indicators of male quality to ensure direct or indirect female benefits. Spatial variability in ecological factors is expected to alter the balance between sexual and natural selection that defines the evolution of such traits.

Relative influences of historical and contemporary forces shaping the distribution of genetic variation in the Atlantic killifish, Fundulus heteroclitus.

A major goal of population genetics research is to identify the relative influences of historical and contemporary processes that serve to structure genetic variation. Most population genetic models assume that populations exist in a state of migration-drift equilibrium. However, in the past this assumption has rarely been verified, and is likely rarely achieved in natural populations.

Acquisition of endonuclease specificity during evolution of L1 retrotransposon.

L1 is the most proliferative autonomous retroelement that comprises about 20% of mammalian genomes. Why L1s have proliferated so extensively in mammalian genomes is an important yet unsolved question. L1 copies are amplified via retrotransposition, in which the DNA cleavage specificity by the L1-encoded endonuclease (EN) primarily dictates sites of insertion.

Microsatellite analysis of the phylogeography, Pleistocene history and secondary contact hypotheses for the killifish, Fundulus heteroclitus.

The mummichog, Fundulus heteroclitus, exhibits extensive latitudinal clinal variation in a number of physiological and biochemical traits, coupled with phylogeographical patterns at mitochondrial and nuclear DNA loci that suggest a complicated history of spatially variable selection and secondary intergradation. This species continues to serve as a model for understanding local and regional adaptation to variable environments. Resolving the influences of historical processes on the distribution of genetic variation within and among extant populations of F.

Natural and synthetic alleles provide complementary insights into the nature of selection acting on the Men polymorphism of Drosophila melanogaster.

Two malic enzyme alleles, Men(113A) and Men(113G), occur at approximately equal frequency in North American populations of Drosophila melanogaster, while only Men(113A) occurs in African populations. We investigated the population genetics, biochemical characteristics, and selective potential of these alleles. Comparable levels of nucleotide polymorphism in both alleles suggest that the Men(113G) allele is not recently derived, but we find no evidence in the DNA sequence data for selection maintaining the polymorphism.

Teleost fish genomes contain a diverse array of L1 retrotransposon lineages that exhibit a low copy number and high rate of turnover.

Retrotransposable elements exhibit a wide range of variation in population dynamics, abundance, and lineage diversity among host genomes across taxa. This range of diversity is illustrated by a single well-defined constituent monophyletic clade of L1 non-LTR retrotransposons that is shared between mammalian and teleost fish genomes. Despite the clear phylogenetic relationships that exist between mammalian and teleost L1 sequences, these elements exhibit markedly different dynamics within their respective taxa.

Single-locus latitudinal clines and their relationship to temperate adaptation in metabolic genes and derived alleles in Drosophila melanogaster.

We report a study in Drosophila melanogaster of latitudinal clines for 23 SNPs embedded in 13 genes (Pgi, Gapdh1, UGPase, Pglym78, Pglym87, Eno, Men, Gdh, Sod, Pgk, Mdh1, TreS, Treh) representing various metabolic enzymes. Our samples are from 10 populations spanning latitude from southern Florida to northern Vermont. Three new clines with latitude were detected.

L1 (LINE-1) retrotransposon diversity differs dramatically between mammals and fish.

L1 retrotransposons replicate (amplify) by copying (reverse transcribing) their RNA transcript into genomic DNA. The evolutionary history of L1 in mammals has been unique. In mice and humans approximately 80 million years of L1 evolution and replication produced a single evolutionary lineage of L1 elements while generating approximately 20% of the genomic mass in each species.

Clines and adaptive evolution in the methuselah gene region in Drosophila melanogaster.

In an effort to characterize further the patterns of selection and adaptive evolution at the methuselah locus in Drosophila species, we extended an analysis of geographical variation to include single nucleotide polymorphisms (SNPs) in adjacent genes on either side of the mth locus, and examined the molecular variation in a neighbouring methuselah paralogue (mth2). An analysis of 13 SNPs spanning a region of nearly 19 kilobases surrounding the mth locus demonstrated that a clinal pattern associated with the most common mth haplotype does not extend to adjacent gene loci, providing compelling evidence that the clinal pattern results from selection on as yet unidentified sites associated with the functional mth locus. mth2 exhibited a significant pattern of adaptive divergence among D.