Species Delimitation in Herpetology

The discovery and delimitation of species has changed dramatically over time. Species delimitation practices became more thorough and formal in the 1900s with the introduction of detailed studies of geographic variation, contact zones, and reproductive isolating mechanisms. In the 1960s, genetic methods for examining the allelic composition across many loci began to be used to test for gene flow and to delimit species boundaries. Methods for DNA sequencing were invented in the late 1970s, just as I started graduate school, when I set my sights on applying the vast stores of information in genomes to understanding biodiversity. In the late 1980s, a new method for rapid amplification of mitochondrial DNA led to ''barcoding'' of species and the subsequent splitting of species into mitochondrial haplotype groups. By the 1990s, widespread sequencing of nuclear genes led to the development of models that incorporated multispecies coalescent theory (MSC). Molecular-based methods provide new insights and opportunities for species delimitation, but many species delimitation studies do not adequately consider violations of underlying model assumptions before making taxonomic changes. Inadequate sampling and a lack of attention to contact zones often leads to the over-splitting of species into geographically proximate groups of populations. I predict the future will bring a synthesis of many older practices (careful sampling, with attention to reproductive isolation, contact zone analysis, and geographic variation) with the new powerful analysis of genomic data sets, leading to a reevaluation and reversal of much of the recent overly enthusiastic splitting of geographically variable species.