Genetic linkage maps are valuable tools in evolutionary biology; however, their availability for wild populations is extremely limited. Fundulus heteroclitus (Atlantic killifish) is a non-migratory estuarine fish that exhibits high allelic and phenotypic diversity partitioned among subpopulations that reside in disparate environmental conditions. An ideal candidate model organism for studying gene-environment interactions, the molecular toolbox for F. heteroclitus is limited. We identified hundreds of novel microsatellites which, when combined with existing microsatellites and single nucleotide polymorphisms (SNPs), were used to construct the first genetic linkage map for this species. By integrating independent linkage maps from three genetic crosses, we developed a consensus map containing 24 linkage groups, consistent with the number of chromosomes reported for this species. These linkage groups span 2300 centimorgans (cM) of recombinant genomic space, intermediate in size relative to the current linkage maps for the teleosts, medaka and zebrafish. Comparisons between fish genomes support a high degree of synteny between the consensus F. heteroclitus linkage map and the medaka and (to a lesser extent) zebrafish physical genome assemblies.
This study builds on a long-term program that has shown Sumgayit, Azerbaijan to contain wetlands with high levels of a diversity of chemical contaminants. Previous contaminant and biomarker studies of turtles and frogs showed a correlation between somatic chromosomal damage and chemical contaminants at Sumgayit. The objective of this study was to determine if a recently arrived species (mosquitofish) has genetic impacts similar to native species (marsh frogs) thus confirming the pattern is not the result of historical events such as glacial cycles, but is associated with recent chemical contamination. Nucleotide sequences of the mtDNA control region of invasive mosquitofish (Gambusia holbrooki) from Sumgayit were compared to mosquitofish from pristine sites in Europe and Azerbaijan and to native North American populations. Persistent heteroplasmy for a hyper-mutable simple sequence repeat and low haplotype and nucleotide diversities were observed in all invasive populations. However, Sumgayit possessed four de novo haplotypes and heteroplasmic conditions. All of the observed variable nucleotide positions were within or adjacent to a cytosine mononucleotide repeat. This repeat was within a conserved secondary structure; the region likely undergoes expansion and contraction at a rate sufficient to prevent fixation of the common 1/3 heteroplasmy. Whereas the 1/3 heteroplasmy appeared coincident with the establishment of mosquitofish in Europe, other forms of heteroplasmy resulted from contaminant-induced de novo mutations in Sumgayit. We conclude that Sumgayit is a mutational hotspot caused by legacy contaminants from chemical factories from the era of the Soviet Union.
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