TESTING SPECIES BOUNDARIES IN BIODIVERSITY STUDIES

A paper recently published by Phillips et al. (1996) reported a molecu lar genetic study of all recognized subspecies of the common snapping turtle (Chelydra serpentina) and concluded from patterns of geographic variation in isozyme and mitochondrial DNA restriction fragment patte rn data that three evolutionary species should be recognized in this g roup. We suggest that this paper is fundamentally flawed because it fa ils to present any species concept as a testable hypothesis. Data are collected in the absence of any conceptual framework for diagnosing sp ecies boundaries, so no criteria for acceptance or rejection of a pref erred hypothesis are formulated, and species boundaries are determined in a nonrigorous, Post hoc manner. Further, the absence of specific c riteria for species diagnosis in this case leads to flaws in sampling design, data collection, and data analysis. Because these design flaws are typical of many studies, ute briefly outline three different line age-based operational species concepts (phylogenetic, concordance, and cohesion) and present an alternative interpretation of the Chelydra d ata, insofar as this is possible given the design limitations We concl ude the following: (1) species status may not be warranted for the Cen tral and South American taxa, (2) more-detailed analysis is warranted in the US population because distinct lineage may be obscured by poor lab technique or introgression of mtDNA, and (3) the Ecuadorean popula tion may deserve species status based on fixed nuclear isozyme loci. W e recommend the following procedures for implementation of lineage-bas ed species concepts within a rigorous hypothesis testing framework. Fi rst, if an animal is to be sacrificed, proper care should be taken to utilize different tissues for multiple pass electrophoresis. This will unmask hidden heterogeneity and maximize the number of resolved loci. Second, when phylogenetic relationships are reconstructed with restri ction fragment length polymorphism data, fragment data should be conve rted to site data to avoid uncertainties in homology. Finally, a prope r sampling scheme should be designed to address the question of specie s status in terms of numbers of individuals, genetic loci, populations , and geographic regions.