Data from: Small spermatophore size and reduced female fitness in an isolated butterfly population

The Glanville fritillary butterfly (Melitaea cinxia) has a small population (Ne ~100) on the small island of Pikku Tytärsaari (PT) in the Gulf of Finland. The population has remained completely isolated for ~100 generations, which has resulted in greatly reduced genetic variation and high genetic load (low fitness). In particular, females lay small egg clutches with low egg-hatching rate in comparison with a large reference population in the Åland Islands (ÅL). Here, we analyze to what extent egg clutch size and egg-hatching rate are influenced by male population and spermatophore size. Spermatophore size increases with male body size, is smaller after the first mating, and is smaller in the small PT population. In the ÅL population but not in the PT population, egg-hatching rate increases with spermatophore size. Egg-hatching rate of PT females is higher when mated with ÅL males than when mated with PT males (heterosis), but there is no such effect on clutch size. Clutch size of ÅL females is however reduced when mated with PT males. These results indicate that both male and female traits contribute to reduced reproductive fitness in the small isolated population.

格纹蛱蝶（Melitaea cinxia）在芬兰湾的皮库·蒂塔尔萨里小岛（PT）上拥有一个小型种群，其有效种群大小（Ne）约为100。该种群已完全隔离约100代，由此导致遗传变异大幅降低以及较高的遗传负荷（适合度低下）。与奥兰群岛（ÅL）的大型参考种群相比，该种群的雌蝶尤为特殊：其所产卵簇更小，且卵孵化率更低。本研究旨在分析雄性种群与精荚（spermatophore）大小在多大程度上影响产卵簇大小与卵孵化率。精荚大小随雄性体型增大而增加，首次交配后精荚尺寸会缩小，且在小型PT种群中精荚整体更小。仅在奥兰群岛（ÅL）种群中，卵孵化率随精荚大小提升而升高，PT种群未呈现该规律。与PT雄性交配相比，PT雌蝶与ÅL雄性交配时的卵孵化率更高（杂种优势），但这一优势并未体现在产卵簇大小上。然而，当ÅL雌蝶与PT雄性交配时，其产卵簇大小会出现降低。上述结果表明，雄性与雌性的相关性状均会导致小型隔离种群的繁殖适合度下降。