Inheritance of song and stridulatory peg number divergence between Chorthippus brunneus and C. jacobsi, two naturally hybridizing grasshopper species (Orthoptera: Acrididae)

Abstract

Knowledge of the genetic basis of divergence in mating signal characters that contribute to reproductive isolation is critical to understanding speciation. Here, we describe a semi‐automated system for characterizing grasshopper acoustic signals. We used this system to study the genetic basis of divergence in three male calling song components [echeme (EL), syllable (SL) and phrase (PL) lengths] between Chorthippus brunneus and C. jacobsi, two species of grasshoppers that hybridize in northern Spain. We also studied the number of pegs in the stridulatory file. For all characters, additive effects accounted for most of the genetic differentiation between species. However, the three song components also showed small but significant epistatic effects. No sex linkage was detected. Wright–Castle–Lande estimates of the minimum numbers of genetic factors underlying song and peg number divergence were low: peg number (ne = 5.87 ± 5.84), SL (ne = 2.37 ± 4.79) and PL (ne = 0.87 ± 0.86). On the other hand, EL appeared to be controlled by many genes. These results suggest that divergence in SL and PL might be driven by sexual selection whereas EL might not be under selection. This is consistent with experimental results on female song preference in related species. However, the fact that few factors appear to underlie the differences in peg number is surprising. Peg number is not closely related to song characteristics. It often varies between closely related grasshopper species and it has been assumed to be a neutral character. The biometrical approaches used here tend to underestimate the number of factors influencing a trait but provide valuable background for subsequent quantitative trait loci analyses.

The genetic architecture of insect courtship behavior and premating isolation

“…Henry et al (2002) suggested that changes through few loci (which are capable of relatively large leaps in phenotype) should be characteristic of differences predominantly in sexually selected traits that are arbitrary with respect to natural selection, but changes through many loci (which are generally more gradual) may indicate that environmental adaptation accompanies sexual selection, making speciation adaptive, as in conditions underlying ecological speciation (Schluter, 2001;Rundle and Nosil, 2005). The data reviewed here, however, indicate that some species pairs that have diverged recently, in which behavior represents the only barrier to reproduction, exhibit polygenic architecture for isolating traits (for example, Saldamando et al, 2005;Shaw et al, 2007;Vedenina et al, 2007), which run counter to the predictions of Henry's (2002) hypothesis. Additional data are needed, however, for quantitative evaluation of the degree to which ecological versus nonecological speciation are underlain by different patterns of genetic change.…”

“…In some species pairs (Drosophila ananassae/pallidosa, Chrysoperla plorabunda/johnsoni, Chorothippus albomarginatus/oschei, Chorothippus brunneus/jacobsi, and Laupala paranigra/kohalensis), reproductive isolation has been considered to evolve quickly through changes in behavior alone, as there is a lack of postzygotic isolation, and ecology and morphology may be identical between species (Henry et al, 2002;Yamada et al, 2002;Saldamando et al, 2005;Shaw et al, 2007;Vedenina et al, 2007). When this subset of species pairs for which behavioral isolation represents the only reproductive barrier, or for which speciation is known to be rapid, is considered, a similar proportion, five of the nine traits Butlin (1996) Abbreviations: AFLP, amplified fragment length polymorphism; msat, microsatellite; QTL, quantitative trait loci; RFLP, restriction fragment length polymorphism.…”

The genetic basis of interspecific differences in genital morphology of closely related carabid beetles

“…Thus, we concluded that our estimations were fairly reasonable. Zeng (1992) modification of the Castle-Wright estimator, which incorporated a variation in allelic effect and recombination rate, resulted in larger estimates of effective number of loci, as in Saldamando et al (2005), but standard errors for CPW and VAL (at C a ¼ 0.57) exceeded over estimated numbers. Applying recombination index and genetic effect of other organisms could cause questionable output.…”

“…The Castle-Wright estimator has been used to evaluate the genetic background of various quantitative characters relevant to adaptation and speciation in a variety of animals, including insects (eg, Shaw, 1996;Hatfield, 1997;Wijngaarden and Brakefield, 2000;Albertson et al, 2003;Huttunen and Aspi, 2003;Saldamando et al, 2005). Several studies on the utility of the Castle-Wright estimator have suggested that the difference between the actual number of loci (confirmed in a QTL mapping study) and the number estimated with the Castle-Wright estimator is small if assumptions are met (Otto and Jones, 2000;Westerbergh and Doebley, 2002).…”

Quantitative genetic analysis of subspecific differences in body shape in the snail-feeding carabid beetle Damaster blaptoides

“…To estimate the effective number of loci involved in interspecific differences in body shape, we applied Lande's modification of the Castle-Wright estimator (Lande, 1981;Saldamando et al, 2005). This method estimates the minimum number of normally segregating loci that would be needed to explain the observed phenotypic means and variances of parental, F 1 and backcross populations.…”