MORPHOMETRIC ANALYSIS OF A HYBRID ZONE IN GEOCRINIA: LARVAL VERSUS ADULT CHARACTER SUITES (AMPHIBIA: ANURA: MYOBATRACHINAE)

ABSTRACT

The southeastern Australian frog species Geocrinia laevis and G. victoriana have distinctive advertisement calls, yet form narrow hybrid zones. Studies of allozyme variation indicated random mating in hybrid populations and revealed a peculiar pattern of steep, staggered clines in the frequencies of some marker proteins. To compare morphometric data with genetic and acoustic results, we measured two character suites: external morphology of tadpoles raised from field-collected egg masses and skeletons of adult males collected in the field. Larvae of G. laevis had wider interpupillar distances but smaller oral disks with fewer oral papillae than similar-sized tadpoles of G. victoriana. In adult frogs, the longer and narrower skulls and relatively longer urostyles of G. laevis differentiated it most from G. victoriana. Both larval and adult morphological traits showed fairly smooth transitions across the hybrid zone. However, for larval characters most hybrid populations resembled G. laevis, whereas in osteological features hybrids were often more similar to G. victoriana.