, Volume 9, Issue 4, pp 299-324

Species pairs of north temperate freshwater fishes: Evolution, taxonomy, and conservation

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Abstract

Many fish species contain morphologically, ecologically and geneticallydistinct populations that are sympatric during at least some portion oftheir life cycle. Such reproductively isolated populations act asdistinct biological species, but are identified by a common Latinbinomial. These ‘species pairs’ are particularly common in freshwaterfish families such as Salmonidae, Gasterosteidae and Osmeridae and aretypically associated with postglacial lakes in north temperateenvironments. The nature of the divergences between sympatric species,factors contributing to reproductive isolation, and modes of evolutionare reviewed with particular emphasis on benthic and limnetic pairs ofthreespine sticklebacks, Gasterosteus aculeatus, and anadromous(sockeye salmon) and nonanadromous (kokanee) pairs of Oncorhynchusnerka. Phylogenetic analyses typically indicate that divergencesbetween members of replicate pairs have occurred independently and,hence, particular phenotypes are not monophyletic. Consequently,taxonomic resolution of such ‘species complexes’ is a vexing problem foradherents to our traditional Linnaean classification system. Sympatricspecies pairs represent a significant component of the biodiversity oftemperate freshwater ecosystems which may be underestimated because oursystem of formal taxonomy tends to obscure diversity encompassed byspecies pairs. Conservation of such systems should be recognized as apriority without formal taxonomic designation of members of speciespairs because taxonomic resolution will likely continue to proveextremely difficult when employing traditional hierarchies andprocedures.