A project undertaken at the Jordan Laboratory, The University of Adelaide and supervised by James Menzies
Considering its land area, New Guinea probably has more frog species than any other wet tropical region despite having only four endemic frog families. Borneo, for instance has five frog families in its fauna. The reason for this is probably the highly diverse environment where habitats can change dramatically over short distances, resulting in the evolution of many ‘sibling species’ that are difficult to distinguish by their external features.
Figure 1.
Figure 2. A specimen of Nyctimystes traunae from Baiyer River, PNG
One example of this is the genus Nyctimystes, tree frogs most abundant in the hill forest to lower montane forest zones. At the last comprehensive revision of the genus, in 1958,14 species were known but now, due to new discoveries and taxonomic revisions, the total is 31. The largest section in this diverse genus is the cheesmanae group of species, including 15 medium sized brown frogs. If the frogs all look similar, how do they recognise each other at night? They probably have excellent night vision and some species, at least have rather pungent odours that may be species specific. But, for most species, if appears to be the voice of the male frog that is the important reproductive isolating mechanism.
Male frogs of the Nyctimystes cheesmanae group all have calls consisting of long trains of similar notes with a rough barking sound, without any musical character. Figure 1. shows three examples of their notes:
- In Figure 1a, N. traunae, each note is made up of ten pulses of sound.
- In Figure 2b, N. eucavatus, each note is also made of ten pulses of sound but the pulses are spaced out at first, but then accelerate. These two species live in the same area and one assumes that the differences in call structure enable females to hitch up with the right males.
- In Figure 1c, N. bivocalis, the notes are similar to the first and second examples but are uttered in pairs.
Conclusions are speculative, of course, and without actually being a female frog one cannot know what turns them on. Females can be tested, under studio conditions, but this is not easy in the mountains of New Guinea.