Department of Neurobiology and Behavior
Mudd hall, 215 Tower Rd, Ithaca, NY
There is striking variation in behavioral phenotypes in the natural world. Some of these behaviors play a key role in ecological performance and constitute adaptive traits. Other behaviors are used to signal sexual maturity, attract and court a mate of the opposite sex, show off the quality of one's genes, or simply impress with arbitrary aesthetics. To a large extent, it remains a mystery why behavioral phenotypes differ so dramatically in closely related species and what the evolutionary and molecular mechanisms are that drive that variation. I address these essential and fascinating questions in various species of crickets. There are around 900 species in the family Gryllidae (true crickets). These species show strong divergence in the male song and female preference behavior. Once, when the continents were still one and our planet was dominated by the ancestors of the dinosaurs, the characteristic songs of crickets may well have been the earliest form of music on earth.
Cricket males sing by rubbing their forewings against each other. With each closing movement of the wing, the ‘plectrum’ on one wing excites the teeth on the other wing, producing a near pure tone sound pulse. In most species, several of these pulses are produced consecutively in groups, known as chirps. Each species has its own, stereotypical song(s). Some males sing different songs for a variety of purposes, for example during aggressive encounters or when courting a female. The most common song that males produce is the calling song: a highly species-specific, long-distance mate attraction signal.
Cricket females, upon hearing a male calling, evaluate the ‘quality’ of the song. Quality in this case means that the rhythm of the pulses and chirps matches certain templates that are hard-wired in the female nervous system and is of sufficient duration and intensity. When she likes what she hears, she will navigate towards the sound source in a locomotion behavior called ‘phonotaxis’. The examination of the song and the rejection of certain male songs over others, wields sexual selection on males with specific song traits. Because of the close coupling of song attractiveness and mating success among males, the selection from female mating preferences in crickets has the potential to drive allele frequencies correlating with more and less favorable song rhythms. The observation that many cricket species are similar in morphology and ecology, but differ strikingly in their songs and corresponding preferences has led to the suggestion that speciation in crickets is largely contingent on song and preference evolution.
I am interested in the way female preference variation is expected to drive variation in the male song, ultimate leading to reproductive isolation among closely related species. I measure female preferences for different song traits and determine which male traits most strongly predict female preference of the calling song. I have been working on this during my PhD in a variety of Gryllus species in the lab of Prof. Matthias Hennig at the Humboldt University in Berlin. We used a set of artificial cricket song-like stimuli for which we can carefully control variation in different phenotypic dimensions. Female preferences to these stimuli were tested on a track ball, or luftkugel, which enables the researcher to accurately measure preferences in highly controlled experimental conditions and in real time without interfering. These behavioral analyses have taught us a lot about the variation in female preference functions in closely related species, the extent of trait-preference coupling across song traits, and whether female preference evolution is partially driven by latent biases in song evolution mechanisms. To further understand signal evolution, I also used a suite of approaches that aim to unravel the genetic basis and evolvability of traits (and preferences), generally known as quantitative genetics.