Effect of temperature on the physiology of two exotic frogs: possible causes of distribution

Abstract

Two Australian frogs were introduced to New Zealand over 100 years ago. Since their introduction they have become widespread and well established with Litoria ewingii being more prevalent in alpine and cooler areas of New Zealand, while Litoria raniformis is found in more temperate coastal areas. Very little physiological data exists for these frogs and aside from their distribution not much is known about them in New Zealand. Thus the effects of thermal acclimation and temperature change on respiration and locomotion were examined in these two exotic frogs. The more terrestrial and alpine dwelling L. ewingii was found to be able to thermally acclimate its respiration performance, where respiration was highest when acclimation temperature matched test temperature. It was also able to thermally acclimate its locomotory performance, jumping significantly further at lower temperatures, however, acclimation to high temperatures impacted its jump performance at cold temperatures. The frog L. raniformis was found to only be able to thermally acclimate its respiration and locomotion to high temperatures, as performance at low temperatures was often poor. The data shows that L. ewingii is a cold temperate frog rather than a warm habitat frog, while L. raniformis is an animal adapted to warm temperatures. From this we can begin to see the effect that temperature has on the physiology of these two exotic frogs and the major role that temperature may be playing in driving the differences seen in the distribution of these two species in New Zealand.