Behavioral and phylogenetic differentiation in a potential cryptic species complex, the canyon treefrog

Abstract

Detection of genetic and behavioral diversity within morphologically similar species has led to the discovery of cryptic species complexes. We tested the hypothesis that the canyon treefrog (Hyla arenicolor) may consist of cryptic species by examining mate-attraction signals among highly divergent lineages defined by mitochondrial DNA (mtDNA). Unexpectedly, calls exhibited little variation among the three U.S. lineages despite large mtDNA sequence divergences. We re-analyzed intraspecific and interspecific phylogenetic relationships by sequencing both mitochondrial and nuclear genetic markers among populations and a closely related, but morphologically and behaviorally different species, the Arizona treefrog (H. wrightorum). Discordance between mitochondrial and nuclear datasets suggests multiple instances of introgression of H. wrightorum's mitochondrial genome into populations of H. arenicolor. Furthermore, intraspecific population structure based on nuclear markers shows better congruence with patterns of call variation than population structure based on the mitochondrial dataset. Although the U.S. lineages do not appear to represent cryptic species, Mexican lineages do show biologically relevant call differences as assessed through female preference tests. Our results suggest that call variation can indicate genetic structure of populations; however, a multilocus approach should be used in defining genetic structure, as using only mtDNA may lead to erroneous conclusions.