Mechanical barriers to introgressive hybridization revealed by mitochondrial introgression patterns inOhomopterusground beetle assemblages

Abstract

To reveal the role of diverged body size and genital morphology in reproductive isolation among closely related species, we examined patterns of, and factors limiting, introgressive hybridization between sympatric Ohomopterus ground beetles in central Japan using mitochondrial NADH dehydrogenase subunit 5 (ND5) gene sequences. We sampled 17 local assemblages that consisted of two to five species and estimated levels of interspecific gene flow using the genetic distance, D(A), and maximum-likelihood estimates of gene flow. Sharing of haplotypes or haplotype lineages was detected between six of seven species that occurred in the study areas, indicating mitochondrial introgression. The intensity and direction of mitochondrial gene flow were variable among species pairs. To determine the factors affecting introgression patterns, we tested the relationships between interspecific D(A) and five independent variables: difference in body size, difference in genital size, phylogenetic relatedness (nuclear gene sequence divergence), habitat difference, and species richness of the assemblage. Body and genital size differences contributed significantly to preventing gene flow. Thus, mechanical isolation mechanisms reduce the chance of introgressive hybridization between closely related species. Our results highlight the role of morphological divergence in speciation and assemblage formation processes through mechanical isolation.

Diversification in a fluctuating island setting: rapid radiation ofOhomopterusground beetles in the Japanese Islands

“…Nevertheless, interspecific gene flow is limited, and species boundaries are maintained by geographical barriers. Introgressive hybridization has also occurred between sympatric species but is largely prevented by differences in the genital and body sizes (Nagata et al 2007b). By contrast, divergence among populations within species is ongoing, for instance, in polytypic C. arrowianus in central Honshu (N. Nagata, K. Kubota, Y. Takami & T. Sota 2008, unpublished data).…”

Molecular Genetic and Hybridization Studies ofDiorhabdaspp. Released for Biological Control ofTamarix

“…Nonetheless, examples of lock-and-key mismatch are rare (Gröning and Hochkirch 2008;Shapiro and Porter 1989;). One example was documented in the beetle genus Ohomopterus (Nagata et al 2007;Sota and Kubota 1998) and Diorhabda may provide a second example in a beetle. It has been noted that uncoupling of mating pairs may not occur when D. carinulata are crossed with the other species (Tracy and Robbins 2009) but the nature of the physical damage has yet to be shown, as it was in Ohomopterus (Sota and Kubota 1998).…”

“…The Diorhabda species complex and the new ecological settings they encounter in western North America may provide ideal starting material for hybridization, hybrid zones, and gene flow. Hybrid zones are known to form between beetle congeners (Nagata et al 2007;Sota 2002), including chrysomelids (Gatto et al 2008;Peterson et al 2005), and these may (Sota 2002;Sota and Vogler 2001) or may not (Peterson et al 2005) result in genetic introgression. In the case of the Diorhabda species complex it is probable that there will be formation of hybrids in the field and that their fate will be a function of selection for new genetic combinations.…”

Ecological differentiation and habitat unsuitability maintaining a ground beetle hybrid zone

“…2007; Nagata et al. 2007a,b; Kubota et al. 2013), but no study has examined exogenous selection via environmental factors (cf., Tsuchiya et al.…”

“…However, introgression of mitochondrial genes is extensive in this study area (Nagata et al. 2007a); thus, advanced generation hybrids with parental morphology might not have been excluded.…”