Abstract
Closely related species with overlapping distributions often show premating reproductive barriers to avoid hybridization. Stigmaeopsis miscanthi (Saito) is a social spider mite infesting Chinese silver grass, and the species consists of two parapatric groups with frequent contacts within the contact zone. They differ in male–male aggressiveness, male morphology, female diapause traits, and life history parameters. There is incomplete but strong post-mating reproductive isolation between the two groups, and their DNA sequences are slightly different, suggesting that they diverged recently. In this study, we investigated premating reproductive barriers. We found that females from different groups frequently shared nest webs, indicating no barriers in the phase of nest establishment. However, inside nests, males from either group showed less courtship behaviour to females of the other group and they copulated less frequently with them when compared to females of the same group. However, the premating reproductive barrier was incomplete and asymmetric. Females of one group frequently resisted courtship by males from the other group, but females of the other group did not. We conclude that some gene flow may occur in the contact zone between the two groups.
Highlights
Related species often show overlap in their geographic distribution
Two different sets of experiments served to investigate the degree of premating reproductive isolation between high male aggression (HG) and low male aggression populations (LW)
LW couples were less likely to mate than HG couples in 1 h mating trials: not all LW males started drumming and not all LW females accepted drumming males (Table 1)
Summary
Related species often show overlap in their geographic distribution. This geographic overlap may emerge during sympatric speciation, parapatric speciation or at secondary contact after allopatric speciation (Bull 1991). Stigmaeopsis miscanthi (Saito) is a phytophagous mite on Chinese Silver grass, Miscanthus sinensis Andersson In this species, the female mite weaves a silken nest on the undersurface of the leaves of their host plant. Compared to intra-population crosses, crosses between HG and LW populations display reduced juvenile survival rate and a large number of males with only occasionally a few females (Sato et al 2000a, b). These characteristics indicate incomplete pre- and post-zygotic reproductive barriers, because this mite is haplodiploid: females develop from fertilized eggs whereas males develop from unfertilized eggs. All these behavioural and genetic observations suggest that these populations have recently diverged
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