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

Abstract

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. heteroclitus is crucial to a better understanding of how populations evolve in the context of contemporary environments. In this study, we analysed geographical patterns of genetic variation at eight microsatellite loci among 15 populations of F. heteroclitus distributed throughout the North American range of the species from Nova Scotia to Georgia. Genetic variation in Northern populations was lower than in Southern populations and was strongly correlated with latitude throughout the species range. The most common Northern alleles at all eight loci exhibited concordant latitudinal clinal patterns, and the existence of an abrupt transition zone in allele frequencies between Northern and Southern populations was similar to that observed for mitochondrial DNA and allozyme loci. A significant pattern of isolation by distance was observed both within and between northern and southern regions. This pattern was unexpected, particularly for northern populations, given the recent colonization history of post-Pleistocene habitats, and was inconsistent with either a recent northward population expansion or a geographically restricted northern Pleistocene refugium. The data provided no evidence for recent population bottlenecks, and estimates of historical effective population sizes suggest that post-Pleistocene populations have been large throughout the species distribution. These results suggest that F. heteroclitus was broadly distributed throughout most of its current range during the last glacial event and that the abrupt transition in allele frequencies that separate Northern and Southern populations may reflect regional disequilibrium conditions associated with the post-Pleistocene colonization history of habitats in that region.

Steep, coincident, and concordant clines in mitochondrial and nuclear‐encoded genes in a hybrid zone between subspecies of Atlantic killifish,Fundulus heteroclitus

“…Given the large population sizes of F. heteroclitus in these marshes (on the order of 10 5 individuals; Adams et al. 2006), this is consistent with broad‐scale movements of substantial numbers of fish within large marshes. However, little is known about dispersal between marshes, which would require dispersal across potentially unfavorable habitat along the coast.…”

“…; Adams et al. 2006), which coincides with the southern‐most extent of the Pleistocene ice sheet (Mickelson et al. 1983).…”

“…Fundulus heteroclitus fulfills these conditions, as these fish are present in extremely large numbers in their estuarine marsh habitats, with high effective population size (on the order of 10 5 individuals; Adams et al. 2006), and dispersal between marshes along the coast is likely to be relatively limited (Fritz et al. 1975; Lotrich 1975).…”

What is environmental stress? Insights from fish living in a variable environment

“…Fundulus heteroclitus macrolepidotus occupies the northern part of the species range and is replaced by F. heteroclitus heteroclitus in the south, with the transition between the two subspecies centred in or just north of New Jersey (Morin and Able, 1983). This variation takes the form of a cline in gene frequencies and phenotypic traits along the coast, with different genetic markers having clines of different steepness (Adams et al, 2006;GonzalezVilasenor and Powers, 1990;Powers et al, 1991;Ropson et al, 1990;Strand et al, 2012). Similar genetic and physiological clines are present in the Chesapeake and Delaware Bays, with F. heteroclitus heteroclitus (the southern subspecies) dominating at the coast and F. heteroclitus macrolepidotus dominating the freshwater reaches of these large estuaries (Powers et al, 1991).…”

Intraspecific variation in expression of candidate genes for osmoregulation, heme biosynthesis and stress resistance suggests local adaptation in European flounder (Platichthys flesus)

“…In addition, also physical parameters, such as temperature, salinity, oxygen concentration, ocean depth and pollution gradients have been described to be important for creating population structure in marine fishes. Wellknown examples include both latitudinal differences in temperature on the east coast of North America and salinity differences in the transition zone from the highsaline North Sea into the brackish Baltic Sea, where several studies have demonstrated high levels of genetic differentiation, isolation by distance and local adaptation among populations (Nielsen et al, 2003(Nielsen et al, , 2004Scott and Schulte, 2005;Adams et al, 2006;Fangue et al, 2006;Larsen et al, 2007;Hemmer-Hansen et al, 2007a). Alternatively, environmental variation can also result in changes in important life history parameters that potentially can result in subdivision in marine fishes.…”