Variation in signal–preference genetic correlations in Enchenopa treehoppers (Hemiptera: Membracidae)

Abstract

Fisherian selection is a within-population process that promotes signal–preference coevolution and speciation due to signal–preference genetic correlations. The importance of the contribution of Fisherian selection to speciation depends in part on the answer to two outstanding questions: What explains differences in the strength of signal–preference genetic correlations? And, how does the magnitude of within-species signal–preference covariation compare to species differences in signals and preferences? To address these questions, we tested for signal–preference genetic correlations in two members of the Enchenopa binotata complex, a clade of plant-feeding insects wherein speciation involves the colonization of novel host plants and signal–preference divergence. We used a full-sibling, split-family rearing experiment to estimate genetic correlations and to analyze the underlying patterns of variation in signals and preferences. Genetic correlations were weak or zero, but exploration of the underlying patterns of variation in signals and preferences revealed some full-sib families that varied by as much as 50% of the distance between similar species in the E. binotata complex. This result was stronger in the species that showed greater amounts of genetic variation in signals and preferences. We argue that some forms of weak signal–preference genetic correlation may have important evolutionary consequences.

Local population density and group composition influence the signal‐preference relationship in Enchenopa treehoppers (Hemiptera: Membracidae)

“…Stimuli were presented to a female by imparting them to a plant stem at an amplitude of 0.15 mm s −1 using a piezoelectric controller and actuator (Thorlabs, Newton, NJ, USA). Each bout varied from others only in dominant signal frequency, with all other signal values set to the mean of the population (Fowler‐Finn et al ., ). The playback stimuli had signal frequencies of 165 Hz, and steps of ± 2, 4, 6, 8, 10, 15, 20, 30, 40 Hz above and below this value.…”

“…). Selectivity is the PC summarizing variation in the aspects of the shape of the mate preference that are independent from the peak (Fowler‐Finn & Rodríguez, ; Fowler‐Finn et al ., ). They include responsiveness (the mean number of responses across all stimuli, which corresponds to the overall elevation of the preference functions), tolerance (how quickly the female response drops as the signal frequency deviates from the preferred signal values) and strength (the level of variation in responses between more and less preferred signal frequencies).…”

Mechanisms of Assortative Mating in Speciation with Gene Flow: Connecting Theory and Empirical Research

“…Pair formation involves male-female signal exchanges (duets), with strong female preferences for certain male signal features (Cocroft et al 2008). These signals and mate preferences likely represent a preference/trait mechanism because within-species genetic correlations between signals and preferred signal values are weak or absent (Fowler-Finn et al 2015), in spite of pronounced signal-preference coevolution between species (Rodríguez et al 2006;Cocroft et al 2008). Thus, a multiplicity of mechanisms plays a role in the process of divergence in this species complex, perhaps with different mechanisms making varying contributions at different stages.…”

Temperature coupling of mate attraction signals and female mate preferences in four populations of Enchenopa treehopper (Hemiptera: Membracidae)

“…In populations in which the mean male signal and female preference mismatch, temperature coupling would reinforce directional selection across temperatures—which would be expected in Columbia, MO, where the mean female peak preference averages ~30 Hz lower than the mean signal frequency. Sexual selection via female choice is important in shaping male signal variation in this clade (Rodriguez & Cocroft, ; Sullivan‐Beckers & Cocroft, ), and male E. binotata signals exhibit broad‐sense heritability (Fowler‐Finn et al., , ). Thus, if populations were to vary in the mean female preference, sexual selection across variable thermal environments could reinforce differential selection on male signals across populations, potentially contributing to rapid divergence across population (e.g.…”

“…Females become sexually receptive three to four weeks after the adult moult (Wood & Guttman, ), and so we assayed female preferences across the same range of temperatures one to two weeks after males(e.g. Fowler‐Finn, Kilmer, Cruz, & Rodríguez, ; Fowler‐Finn, Kilmer, Hallett, & Rodriguez, ; Fowler‐Finn & Rodriguez, ; Fowler‐Finn & Rodríguez, ; Kilmer et al., ; Rodríguez, Haen, Cocroft, & Fowler‐Finn, ).…”