Genetic Variation in Cricket Calling Song Across a Hybrid Zone Between Two Sibling Species

Abstract

The sibling ground crickets Allonemobius fasciatus and A. socius meet along a mosaic hybrid zone at ≈ 40°N latitude in eastern North America. In this paper we report the findings of a genetic analysis of calling-song variation within and among six cricket populations sampled along a transect through the hybrid zone in southern New Jersey. We compared aspects of the calling song of both wild-caught and laboratory-reared crickets to test the hypothesis that population differences in song observed in the wild were genetically based. We found significant, species-level differences in all aspects of the calling song, and these differences persisted even after a generation of common-garden rearing in the laboratory, supporting the hypothesis that interspecific variation observed in the wild largely reflects genetic differentiation between the two taxa. A discriminant function analysis indicated that individual crickets could be assigned to the proper taxon with less than 10% error, supporting the premise that calling song could be used by female crickets as a mechanism for species recognition. One population, collected from within the hybrid zone and containing significant numbers of hybrid individuals, was intermediate in its calling song, presumably reflecting this population's mixed genetic makeup. In this hybrid zone population, song phenotype was highly correlated to a hybrid index score generated using species-specific alleles at four diagnostic allozyme markers, suggesting a multigenic basis to calling-song variation in these crickets as well as linkage disequilibrium between markers and song. Based on an analysis of laboratory-reared full-sib families, broad-sense heritabilities for calling-song characteristics were generally significant in the two A. socius populations, whereas many components of song showed no significant family effects in the three A. fasciatus populations. The genotypically mixed, hybrid zone population showed very high heritabilities for most calling-song components, which likely reflect the influence of interspecific gene flow on genetic variation for quantitative traits.

Signal components, acoustic preference functions and sexual selection in a cricket

“…chirp period was varied but chirp duration remained the same for the two species) or dominant frequency. Our results can explain this documented absence of female discrimination: while displaying call preferences based on chirp duration, which is not known to differ between the species, A. socius females appear unresponsive to variation in chirp rate (~ chirp period in Doherty & Howard, 1996), which indeed differs between the species (Veech, Benedix & Howard, 1996;Mousseau & Howard, 1998).…”

“…The male-limited mating call of A. socius consists of repeating short chirps, and varies in chirp rate, chirp duration and other components (Howard & Furth, 1986;Mousseau & Howard, 1998). To date, only one study has examined female call preference in this species: in a test of whether reinforcement accounts for reproductive character displacement between A. socius and the closely related A. fasciatus , Doherty & Howard (1996) failed to find a preference in A. socius females for songs typical of conspecifics over songs typical of A. fasciatus .…”

Mitochondrial DNA sequence divergence between two cryptic species of Lethenteron, with reference to an improved identification technique

“…In order to conserve such animals, their taxonomic status must first be clarified. While the classification of animal species can often be based on their morphological characteristics, distinguishing species belonging to a sibling or cryptic species' complex will rely on ethological and genetic traits (Walker, 1964; Gerhardt et al ., 1994; Mousseau & Howard, 1998; Wells & Henry, 1998).…”

The Genetic Basis of Zebra Finch Vocalizations

“…To fully understand the function and evolutionary implications of vocalizations in each of these contexts, it is important to know the sources of variation in vocal traits. However, the quantitative genetics of vocal traits have been studied only in a few taxa, predominantly in insects (Butlin and Hewitt 1986; Webb and Roff 1992; Aspi and Hoikkala 1993; Ritchie and Kyriacou 1994; DeWinter 1995; Ritchie and Kyriacou 1996; Mousseau and Howard 1998; Collins et al 1999), but also for instance in mice (Thornton et al 2005). Noticeably, rather little is known about the genetics of bird vocalizations, a group that has been studied very intensely in terms of vocal communication.…”