An Electrophoretic Analysis of Holarctic Hylid Frog Evolution

Abstract

The phylogenetic relationships of 30 taxa of Holarctic hylid frogs were examined using starch gel electrophoresis. Allelic variation was scored at 33 presumed genetic loci and genetic distance data were used to construct trees representing the phylogenetic relationships. There are two major groups: (A) Hyla regilla, H. cadaverina, H. crucifer, Limnaoedus ocularis, and all presently recognized species of Pseudacris; and (8) the remaining species of Holarctic Hylli. The positions of Acris and H. meridionalis are unclear. In general, the relationships based on electrophoretic data agree well with immunological, hybridization, and chromosome studies, but conflict with some morphological studies. A phylogenetic classification requires that H. regilla, H. cadaverina, H. crucifer, and L. ocularis be transferred to the genus Pseudacris. This genus is characterized by terrestrial species that breed during cold weather and possess small digital pads and spherical (or ovoid) dark testes. Holarctic Hyla are arboreal species that breed during warm weather and possess large digital pads and elongate white (or yellowish) testes. The correlation between albumin immunological distance (AID) and Nei's electrophoretic distance (D) is significant, with 1 D = 70 AlD. Calibration of the molecular clock for Holarctic hylid frogs suggests that Pseudacris diverged from a Hyla-like ancestor in the early Tertiary. The physiological traits associated with cold-weather breeding and the morphological trait (small digital pads) associated with terrestrial habits appear to have been key innovations that allowed Pseudacris to undergo an adaptive radiation in North America coinciding with the radiation of Holarctic Hyla. (Electrophoresis; phylogeny; genetic distance; molecular clock; Hylidae; Acris; Hyla; Limnaoedus; Pseudacris.) Molecular techniques such as electro­ phoresis, microcomplement fixation, and DNA-DNA hybridization have become important tools in systematic research. However, techniques other than sequenc­ ing are indirect in their assessment of ge­ netic differences. Redundancy of the ge­ netic code, differences between reciprocal comparisons, and convergence in electro­ phoretic mobility are a few of the sources of error that may influence the results of these methods. One approach to revealing the strengths and weaknesses of molecu­ lar techniques is by com paring the results of two or more techniques applied to the same taxonomic group. Concordant re­ sults between two independent molecu­ ar data sets suggest that both may be providing a good estimate of relation­ ships. For example, the correlation be­ tween electrophoretic distance and albu­ min immunological distance is usually highly significant, although slopes vary among taxonomic groups (Wyles and Gor­ man, 1980). In one group of salamanders