Evidence that female preferences have shaped male signal evolution in a clade of specialized plant-feeding insects

Abstract

Mate choice is considered an important influence in the evolution of mating signals and other sexual traits, and-since divergence in sexual traits causes reproductive isolation-it can be an agent of population divergence. The importance of mate choice in signal evolution can be evaluated by comparing male signal traits with female preference functions, taking into account the shape and strength of preferences. Specifically, when preferences are closed (favouring intermediate values), there should be a correlation between the preferred values and the trait means, and stronger preferences should be associated with greater preference-signal correspondence and lower signal variability. When preferences are open (favouring extreme values), signal traits are not only expected to be more variable, but should also be shifted towards the preferred values. We tested the role of female preferences in signal evolution in the Enchenopa binotata species complex of treehoppers, a clade of plant-feeding insects hypothesized to have speciated in sympatry. We found the expected relationship between signals and preferences, implicating mate choice as an agent of signal evolution. Because differences in sexual communication systems lead to reproductive isolation, the factors that promote divergence in female preferences-and, consequently, in male signals-may have an important role in the process of speciation.

Palomena prasina (Hemiptera: Pentatomidae) vibratory signals and their tuning with plant substrates

“…The difference in this case is in the range of several hundred Hz and is likely to be a result of micro-habitat choice that determines the most efficient signal frequency [15], as well as divergent evolution due to shaping of female preference [29,30]. However, this not the adaptive phenotypic plasticity that is implied by our results.…”

Genetic variation in social influence on mate preferences

“…Female mate preferences for signal frequency are unimodal (or 'closed'; i.e. they favour intermediate frequency values), and females from different species in the complex favour different signal frequencies [27,29].…”

“…These insects communicate with plant-borne vibrational signals, and pair formation occurs through male-female signalling duets [26]. Females exhibit strong mate preferences on the basis of male signals, mainly signal frequency, which is the most divergent adult trait among the members of this species complex [27,28]. Female mate preferences for signal frequency are unimodal (or 'closed'; i.e.…”

“…Males produce an advertisement signal, and if a female finds that signal attractive, she responds with her own signal [27,29]. A female's likelihood of responding is strongly correlated to the number of responses she gives to a signalling bout [29,34,35].…”

“…That means that a female's sexual response is a function of the signals she encounters. We described mate preferences by presenting individual females with a range of male signals and quantifying their responses to create mate preference functions [27,37]. We presented females with these stimuli using vibrational playback experiments.…”