Hybridization Between the Western and Northern Call Races of the Limnodynastes-Tasmaniensis Complex (Anura, Myobatrachidae) on the Murray River in South Australia

Abstract

The Limnodynastes tasmaniensis complex consists of three call races: northern, southern and western. This paper documents differences in call structure between the western and northern races: differences in note repetition rate, dominant frequency, average number of notes per call and pulses per second note, but not in pulse repetition rate. The races also differ in egg size (smaller in northern) and egg number (higher in northern). There are zones of overlap between these two races west from Morgan and along the Marne River in South Australia. Mixed populations contain both parental and hybrid phenotypes. Hybrids were identified by a hybrid index based on the three call components that overlapped least (note repetition rate, dominant frequency and average number of notes per call). Temporary range expansions, associated with flooding on the Murray River, are documented for the northern call race. Artificial hybridisations revealed no evidence of hybrid inviability and this was supported by estimates of egg viability in field-collected egg masses from the Morgan zone of overlap. The hybrid zones are interpreted as zones of overlap with hybridisation where introgression is likely to occur. Biogeographic data suggest that the northern call race may be spreading south and west, displacing the western call race.