Rapid diversification of sexual signals in HawaiianNesosydneplanthoppers (Hemiptera: Delphacidae): the relative role of neutral and selective forces

Abstract

Changes in sexual signals have the potential to promote rapid divergence and reproductive isolation among populations of animals. Thus, identifying processes contributing to variation in signals is key to understanding the drivers of speciation. However, it is difficult to identify the processes initiating changes in signals in empirical systems because (1) the demographic history of populations under study is usually unclear, and (2) there is no unified hypothesis-testing framework for evaluating the simultaneous contribution of multiple processes. A unique system for study in the Hawaiian Islands, the planthopper species Nesosydne chambersi, offers a clear demographic context to disentangle these factors. By measuring variation in male vibratory sexual signals across different genetic populations on the island of Hawaii, we found that that multiple signal traits varied significantly between populations. We developed a mixed modelling framework to simultaneously test competing hypotheses about which processes contribute to changes in signal traits: genetic drift, sensory drive or reproductive character displacement. Our findings suggest that signal divergence proceeds along different axes for different signal traits under the influence of both neutral and selective processes. They are the first, to our knowledge, to document the relative importance of multiple processes on divergence in sexual signals.

Did maize domestication and early spread mediate the population genetics of corn leafhopper?

“…Thus, while our AFLP results do not provide a timeline for the evolution of genetic structuring in corn leafhopper, either instance of maize farming retreat from the vicinity of perennial teosinte habitat (i.e., ∼800 or ∼30 years ago) may have promoted a localized process of habitat‐ or host‐associated differentiation at this particular location, consistent with our hypothesis derived from our haplotype analysis (above). Geographic variation in the occurrence of host‐associated differentiation has been observed in other hemipterans (Goodman et al ., ; Forbes et al ., ). Moreover, the durations of processes putatively beginning with either instance of maize farming retreat, whether hundreds or dozens of years, are consistent with the lengths of processes leading to genetic structuring in other insect herbivores (Winter, ; Claridge, ; Cocroft et al ., ; Bennett & O'Grady, ; Medina, , ; Goodman et al ., ; Forbes et al ., ).…”

Community assembly on isolated islands: macroecology meets evolution

“…Structure within species may allow populations to take independent evolutionary trajectories, especially when aided by other evolutionary processes acting differentially across species geographic ranges. A variety of factors have been associated with the genetic divergence of populations and species in the lineages described here, including combinations of genetic drift associated with geographic isolation (Percy, ; Mendelson & Shaw, ; O'Grady et al ., ; Goodman et al ., ), adaptation associated with competition, predation and mutualism (Gillespie, ; Roderick & Percy, ; Brewer et al ., ) and sexual signalling (Mendelson & Shaw, ; Percy et al ., ; Magnacca et al ., ; Goodman et al ., ).…”

“…The Nesosydne planthoppers provide evidence that some period of geographic isolation preceded the divergence of sexual signals (Goodman et al ., , ). Shifts in plant host use are also associated with diversification in this group (Roderick & Percy, ).…”

Multiple, independent colonizations of the Hawaiian Archipelago by the family Dolichopodidae (Diptera)

“…Members of this family are known to have complicated courtship behavior (Zimmer, Diestelhorst & Lunau, 2003). Though this has never been studied in the Hawaiian fauna, it may be a contributing factor to the development of reproductive isolation as has been shown with the Hawaiian Drosophilidae (Kaneshiro, 1976; Price & Boake, 1995), Laupala (Grace & Shaw, 2011) and Nesosydne (Goodman et al, 2015), and suggests fruitful research directions. There seems to be no correlation between the age of colonization and the diversity of each lineage.…”