Data from: Flying the nest: male dispersal and multiple paternity enables extrafamilial matings for the invasive bark beetle Dendroctonus micans

There is an evolutionary trade-off between the resources that a species invests in dispersal versus those invested in reproduction. For many insects, reproductive success in patchily-distributed species can be improved by sibling-mating. In many cases, such strategies correspond to sexual dimorphism, with males–whose reproductive activities can take place without dispersal–investing less energy in development of dispersive resources such as large body size and wings. This dimorphism is particularly likely when males have little or no chance of mating outside their place of birth, such as when sperm competition precludes successful fertilisation in females that have already mated. The economically important bark beetle pest species Dendroctonus micans (Coleoptera: Curculionidae, Scolytinae) has been considered to be exclusively sibling-mating, with 90% of females having already mated with their brothers by emergence. The species does not, however, show strong sexual dimorphism; males closely resemble females, and have been observed flying through forests. We hypothesised that this lack of sexual dimorphism indicates that male D. micans are able to mate with unrelated females, and to sire some or all of their offspring, permitting extrafamilial reproduction. Using novel microsatellite markers, we carried out cross-breeding laboratory experiments and conducted paternity analyses of resulting offspring. Our results demonstrate that a second mating with a less-related male can indeed lead to some offspring being sired by the latecomer, but that most are sired by the first, sibling male. We discuss these findings in the context of sperm competition versus possible outbreeding depression.物种在扩散相关资源投入与繁殖相关资源投入之间存在进化权衡（evolutionary trade-off）。对于多数昆虫而言，斑块分布（patchily-distributed）物种种群的繁殖成功率可通过同胞交配（sibling-mating）得到提升。在多数情形下，此类策略与性二型性（sexual dimorphism）相关：雄性无需通过扩散即可完成繁殖活动，因此在体型、翅等扩散相关性状的发育上投入的能量更少。当雄性几乎或完全无法在出生地之外完成交配时——例如当精子竞争（sperm competition）会阻断已交配雌虫的成功受精过程，这种性二型性的表现尤为显著。具有重要经济价值的树皮甲虫（bark beetle）害虫Dendroctonus micans（鞘翅目：象甲科，小蠹亚科）曾被认为仅进行同胞交配，90%的雌虫在羽化前便已与同胞兄弟完成交配。然而该物种并未表现出显著的性二型性：雄性与雌性外形极为相似，且已有观测记录显示其能够在森林中飞行。本研究提出假说：这种性二型性的缺失，意味着雄性Dendroctonus micans能够与非亲缘雌性完成交配，并使其部分或全部后代以自身为父本，从而实现家族外繁殖（extrafamilial reproduction）。本研究利用新型微卫星标记（microsatellite markers）开展了室内杂交育种实验，并对所得子代进行了父权分析（paternity analysis）。研究结果表明：与亲缘关系更远的雄性进行二次交配，确实会使部分子代由后交配的雄性所抚育，但绝大多数子代的父本仍为首次交配的同胞雄性。我们结合精子竞争与潜在远交衰退（outbreeding depression）的相关研究背景，对本研究的发现展开了讨论。