A major question in understanding the natural world is how each species is able to successfully identify a mate to assure persistence of the species and how changing environmental conditions might influence its reproductive success. In many species male advertisement calls are essential for attracting a female to mate with as well as being used for species recognition when more than one species co-occurs within an area. The researchers have identified a novel system to quantify how male advertisement and recognition calls are altered when the calls are performed underwater among populations of northern red-legged frogs in the Pacific North West. This research on sound transmission and mating will be complemented by an investigation of the genetic differentiation among populations of this frog species throughout its geographic range. The research will be shared via an outreach initiative at Portland State University's "Better Know a Lab" that brings together the surrounding community and research labs to jointly conduct data collection all the way through to the presentation of their findings. Furthermore, networking is planned with local teachers to help design interdisciplinary curricula highlighting the role of communication, ecology, and the science of sound to engage students in learning about mating strategies and the important role animal communication plays in species successful persistence in nature.
The sensory drive hypothesis asserts that sensory conditions (environmental biophysics) and sensory systems drive divergence in mate signaling in a particular direction, one that optimizes signal propagation ultimately through resultant reproductive success. This research is unique in testing the sensory drive hypothesis with a terrestrial anuran that (1) calls underwater and (2) calls in shallow ponds that may dramatically alter "normal" acoustic attenuation. Attenuation of acoustic signal components is generally proportional to the square of sound frequency; higher frequencies attenuate much more quickly. However it has been shown that in shallow ponds, substrate and depth can dramatically increase the attenuation of lower frequencies. Because the energetically dominant frequencies upon which female choice is based fall in the lower range of the signal, a system where low frequencies may be dramatically attenuated is far more likely to create reproductive isolation among frog populations than the previous systems studied. The project will test the acoustic and genetic differentiation of allopatric northern red-legged frog populations compared across ponds with significantly differing acoustic profiles across a large geographical scale. How well male advertisement calls are matched to the frequency profile of the breeding site should determine reproductive success and create directional selection on spectral characteristics, and provide a first test for the sensory drive hypothesis through the utilization of underwater calling.
