The Conservation of Unisexual Vertebrate Populations

Abstract

Ranker and Arft (1994) brought needed attention to current ambiguity in the use of the term and the potential confusion this ambiguity can have on the protection of allopolyploid plants under the U.S. Endangered Species Act (ESA). This legislation denies protection to under the (not explicitly stated) rationale that hybrids as generally understood do not constitute independent evolutionary lineages and, hence, are undeserving of protection. Ranker and Arft correctly point out, however, that the term hybrid, denoting the F 1 progeny of interspecific matings, should not be confused with polyploid taxa that are originally of hybrid origin. The important distinction is that the former are evolutionary dead-ends that are most often sterile or have greatly reduced fertility relative to their parental species (Dobzhansky 1941; Mayr 1970), while the latter are independent lineages capable of persistence over evolutionary time scales. Ranker and Arft argue that the preclusion of protection for by the ESA pertains to the former group, while the latter, by virtue of their persistence and evolutionary independence from their parental species, qualify as species and, therefore, deserve protection under the ESA. I believe this argument to be accurate, but I would like to point out the existence among certain unisexual vertebrates of a third class of phenomena intermediate in nature to the distinction between primary, homoploid and aUopolyploid species noted by Ranker and Arft. I then consider how the questionable taxonomic standing of these unisexuals affects how they fare in current protection programs and argue that a process-oriented conception of biodiversity requires inclusion of such unisexual forms in protection efforts. Unisexual (all-female) populations of vertebrates were first described by Hubbs and Hubbs (1932) for the fish genus Poecilia. Subsequently, unisexual populations have been discovered in several families of freshwater fishes, salamanders, and lizards. Currently, unisexual lineages are known from at least 22 genera (see Vrijenhoek et al. [1989] for an almost complete listing), and a few of