Incomplete premating and postmating reproductive barriers between two parapatric populations of a social spider mite

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.

Patterns of reproductive isolation in a haplodiploid – strong post‐mating, prezygotic barriers among three forms of a social spider mite

“…Males easily fight with other males and kill each other for ownership of nests, and HG males tend to win against LW males in any nest (Sato et al, 2013b). In addition, HG males show higher activity in mating behaviour towards both HG and LW females, compared to LW males (Sato et al, 2015). Together, this suggests that LW females suffer reproductive interference by HG males in their contact zone, whereas HG females are protected from reproductive interference by strong, aggressive and active HG males.…”

“…These differences appear in line with ecological and behavioural relationships between HG and LW forms. The females construct woven nests, and both types of males enter the nests regardless of the type of the female who constructed the nest (Sato et al, 2015). Males easily fight with other males and kill each other for ownership of nests, and HG males tend to win against LW males in any nest (Sato et al, 2013b).…”

“…Much less is known, however, of the occurrence of premating reproductive barriers (e.g. Sato et al, 2015;Clemente et al, 2016) or post-zygotic barriers (e.g. Osakabe & Komazaki, 1996;Gotoh et al, 2009;Knegt et al, 2017), even though the detection of genetic incompatibilities is facilitated in haplodiploid organisms compared to diploids (Knegt et al, 2017).…”

Phylogeography of lethal male fighting in a social spider mite

“…The LW form may be physiologically able to expand its range into warmer regions (lowland), although the HG form cannot expand its range into colder regions (highland) because of its lighter diapause attribute (Saito et al, ). However, the LW form has a difficulty to expand its range into the areas where the HG form occurs, because LW females easily suffer reproductive interference by HG males (Sato et al, ; Sato, Sabelis, et al, ). Therefore, if we assume that the LW form occupied Kyushu Islands and Honshu Islands first, subsequently the HG form invaded and drove the LW form into the north and highlands after the climate warmed, then the present geographic and ecological relationship would be easily explained.…”

“…The frequency of male killing (hereafter, male-male aggressiveness) varies among populations, and male-male aggressiveness is low in colder regions, high in warmer regions, and mild in subtropical regions in Japan (Saito, 1995;Saito & Sahara, 1999;Sato, Egas, et al, 2013). Populations with low and high aggressiveness are discriminated as LW and HG forms, because of their behavioral, ecological, and morphological differences (Saito & Sahara, 1999;Saito, Sakagami, & Sahara, 2002;Yano, Saito, Chittenden, & Sato, 2011), their molecular phylogeny (Ito & Fukuda, 2009;Sakagami, Saito, Kongchuensin, & Sahara, 2009;Sakamoto et al, 2017) and also incomplete but strong reproductive isolation between them (Sato, Breeuwer, Egas, & Sabelis, 2015;Sato, Saito, & Mori, 2000a, 2000b. Recently, populations with mild male-male aggressiveness and intermediate male weapon morph were found (Sato, Egas, et al, 2013), yet their ecological and phylogenetic relationships with the LW and HG forms are unclear .…”