Three pupfish (Cyprinodon) morphotypes (two endemic) occur in some of the young (6000 ypb) saline lakes on the Bahamian island of San Salvador. The 'normal' morph, a detritivore/omnivore, is not different in its general features from Cyprinodon variegatus from other Bahamian islands. 'Bulldog' is a scale-eater/piscivore that preys upon normal pupfish, and 'bozo' is a specialized molluskivore. Reproductive isolation among these morphs is not predicted by the evolutionary biology of congeneric species because sympatry of even morphogically and ecologically quite divergent pupfishes has usually resulted in hybridization/introgression. Survey of variation at eight microsatellite loci reveals that sympatric normal and bulldog populations are genetically distinctive by several criteria, and are therefore likely reproductively isolated. The bulldog morph in Crescent Pond is markedly divergent from those in Little Lake and Osprey Lake, a finding consistent with, although it does not prove, separate parallel origins of this morphotype. The data also suggest that the bulldogs in the latter two lakes did not evolve by intralacustrine speciation from the current sympatric normal populations. Some of the genetic data suggest that the bozo morph may also be reproductively isolated from the other two pupfishes, but only a small, pooled sample of this rare morphotype was available, and the issue is not resolved. Isolating mechanisms between bulldog and normal morphs are of special interest because of the possibility that they arose as a consequence of a predator-prey relationship. A strong correlation between reproductive isolation and predator-prey interactions could provide an important example of ecological speciation via direct selection against heterotypic interactions.
A dye process in a textile plant in southern Kentucky (USA) produces large quantities of saline wastewater which eventually enter Lake Cumberland via a municipal sewage treatment plant on Lily Creek . The impact of hypersaline conditions on two fish species native to the Cumberland River drainage system, redbelly dace (Phoxinus erythrogaster) and northern studfish (Fundulus catenatus), was assessed . These species were subjected to salinities of 0, 4, and 10% after which routine oxygen consumption values were determined . Significant correlations of salinity with oxygen consumption were demonstrated for both species with P. erythrogaster showing greater overall impact of salinity on metabolic rate .
The temperature regime of the intertidal microhabitat of two species of co-existing amphibious stichaeoid fishes, Anoplarchus purpurescens and Pholis ornata, were compared with experimentally determined tolerances t o elevated temperatures. Studies of the critical thermal maxima of the two species revealed only slight differences in temperature tolerance but exposure to a cycled pattern of high temperatures sharply differentiated the resistance times of the two species with P. ornata capable of tolerating greater cumulative exposure t o thermal stress when administered in a cycled program of temperature fluctuations with peak temperature at 27 " C. While the experimentally determined temperature tolerances exceeded those measured in the field, the greater tolerance of P. ornata may facilitate habitation of intertidal mudflats during summer months
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