Assortative preferences and discrimination by females against hybrid male song in the grasshoppers Chorthippus brunneus and Chorthippus jacobsi (Orthoptera: Acrididae)

Abstract

The grasshoppers Chorthippus brunneus and Chorthippus jacobsi are highly differentiated for male mating signals, and form a mosaic hybrid zone in northern Spain. At some sites within this zone, many hybrids are observed. At others, few hybrids are observed. Such bimodal sites may reflect recent contacts between parental genotypes, or local variation in levels of assortative mating or selection against hybrids. Playback of 12 parental and F1 male songs to 296 parental and hybrid females revealed positive assortative preferences in C. brunneus and C. jacobsi females, supporting a direct role of male mating signals in female choice. However, all female genotypic classes showed reduced responsiveness to F1 male songs. Such sexual selection against hybrids is consistent with the narrow cline width observed in the field for song characters relative to morphology. These results have implications for the genetic structure of the hybrid zone and for models of speciation by reinforcement.

Chromosome study in Schistocerca (Orthoptera-Acrididae-Cyrtacanthacridinae): karyotypes and distribution patterns of constitutive heterochromatin and nucleolus organizer regions (NORs)

“…Species of taxonomically related Acrididae and Romaleidae (John and King 1983;John et al, 1985;Bella et al, 1993;Rodriguez-Inigo et al, 1993;Loreto and Souza, 2000;Rocha et al, 2004;Souza and Kido 1995;Pereira and Souza 2000;56 Chromosome study in Orthoptera et al, 2003), have very similar karyotypes, but may differ in heterochromatin distribution and base-pair composition. In the acridoids Chorthippus brunneus and C. jacobsi, the pericentromeric regions of all chromosomes showed CMA 3 -positive CH blocks (Bridle et al, 2002). The romaleids Xyleus angulatus, Phaeoparia megacephala and Xestotrachelus robustus (Souza et al, 1998;Pereira and Souza, 2000;Souza et al, 2003) also presented CMA 3 -positive CH blocks on all chromosomes.…”

Natural and sexual selection against hybrid flycatchers

“…The existence of sexual selection against hybrids is known from other hybrid zones (e.g. West-Eberhard 1983;Wiernasz & Kingsolver 1992, Vamosi & Schluter 1999, Bridle et al 2006. However, few studies have attempted to estimate the relative importance of sexual selection in causing postzygotic isolation in natural populations.…”

“…Vamosi & Schluter 1999;Gray & Cade 2000;Bridle et al 2006), but the relative importance of sexual selection for postzygotic isolation is rarely investigated, due to it being a rather complicated undertaking. The most informative approach for estimating effects of hybridization is to measure the relative difference in fitness between hybrid and parental species under natural conditions.…”

Comparative analysis of the location of rDNA in the Palaearctic bushcricket genus Isophya (Orthoptera: Tettigoniidae: Phaneropterinae)

“…It is more likely that this cluster is a result of rDNA spread than a remnant of a NOR lost in other species due to fast divergence of the X chromosome. Although, there are differences in the rates of differentiation between sex chromosomes and the autosomes after hybridization between closely related grasshoppers (Gosálvez et al, 1997;Bridle et al, 2002).…”