Recently, information on genetic diversity within and between populations of a given species has been useful for addressing critical questions in conservation biology, for example, in establishing and prioritizing management efforts for threatened or endangered species. Conservation efforts for sea turtles are a good example because these reptiles have experienced phenomenal losses in population numbers due to overhunting [ Norse, 1993]. Studies addressing species uniqueness of the Kemp's ridley turtle ( Lepidochelys kempi) are particularly relevant because this species ``is regarded as one of the world's most endangered vertebrates'' Bowen et al. [1993]. The range of the Kemp's ridley turtle once spanned the Gulf of Mexico to the North Atlantic, but now only a few hundred individuals remain at a single site in Mexico. The international program to protect this species represents the largest conservation effort ever for a marine turtle, and there has been concern whether such effort is scientifically justified.
In fact, the Kemp's ridley turtle has had a somewhat checkered taxonomic history; it shares many similarities, including external appearance, with the olive ridley turtle ( Lepidochelys olivacea), which is not endangered and has a widespread distribution in the east and west Pacific, Indian Ocean, and east and west Atlantic. Interestingly, however, olive ridley populations do not overlap with the remaining Kemp's ridley population, prompting the question of whether the remaining Kemp's ridley turtles might simply be a subpopulation or even a subspecies of the olive ridley.
In order to address this question, Bowen et al. [1991] determined the degree of similarity between the Kemp's and olive ridley turtles based on mtDNA (mitochondrial deoxyribonucleic acid) analysis. They found sufficiently large nucleotide sequence divergence between the Kemp's and olive ridley to merit separate species status for the Kemp's ridley, thus justifying its protection under the U.S. Endangered Species Act. Also, based on a provisional mtDNA ``clock'' calibrated from other marine turtles, they estimated that the two ridley species diverged about 3-6 million years ago, whereas olive ridley turtles from the Atlantic and Pacific diverged more recently (and not sufficiently to merit species-specific status). Thus, allopatric (occurring in different geographic regions) speciation of the Kemp's from the olive ridley may have occurred due to the formation of the Isthmus of Panama about 3 million years ago. This example illustrates how new information on genetic diversity can provide answers, simultaneously, to fundamental, applied and basic research questions.