Reproductive Interactions Between Hyla crucifer and Pseudacris ornata (Anura: Hylidae)

Abstract

The reproductive relationships of two species of hylid frogs, capable of producing viable hybrids and having rather similar mating calls and breeding habits, were studied in the area of sympatry in southeastern Georgia and adjacent South Carolina. Breeding aggregations of the two species frequently shared the same sites, and there was no overt tendency for spatial isolation by species within these sites. Since there was no evidence of mismating, attention was directed to possible behavioral isolating mechanisms. Acoustical analyses of the recorded calls of the two species revealed several consistent differences, and gravid females of H. crucifer, given a choice between conspecific mating calls and those of P. ornata, responded only to conspecific calls. Some possible reasons for the different results reported by Martof (1961) were discussed. It was concluded that species recognition on the basis of mating call differences is a major factor in preventing heterospecific matings in the area of sympatry. INTRODUCTION The spring peeper (Hyla crucifer) and the ornate chorus frog (Pseudacris ornata) are well differentiated by external morphology and are currently assigned to different genera. Consideration of some of their other biological attributes, however, reveals several important similarities: both species are cool-weather breeders and usually use temporary pools or ditches as breeding sites; the mating calls of the two species have a similar structure; and genetic compatibility studies indicate that mismatings can result in viable hybrids. All except one of the crosses performed by Mecham (1965) resulted in fertilization and development to the larval stage, and seven of 20 hybrids (H. crucifer ? X P. ornata 6') were reared to sexual maturity. The geographic range of H. crucifer iticludes most of the eastem United States and Canada; P. ornata is restricted to the southeastern coastal plain from North Carolina to the Mississippi Embayment (Conant, 1958; Maps 219 and 233). Thus, the range of P. ornata is entirely overlapped by that of H. crucifer, except in peninsular Florida. A study of the reproductive relationships of these two species in sympatry takes on additional significance since it has been reported that females of H. crucifer from just outside the area of overlap with P. ornata did not discriminate between conspecific mating calls and those of P. ornata (Martof, 1961). This paper describes my research with the two species done mainly in the area of overlap near Savannah, 'Georgia, during 1968-1970. METHODS Field observations.-The breeding habitat and spatial distribution of calling nales were noted at each site where HI crucifer and P.