Data from: Copulation with immature females increases male fitness in cannibalistic widow spiders

Copulatory cannibalism of male ‘widow’ spiders (genus Latrodectus) is a
model example of the extreme effects of sexual selection, particularly in
L. hasselti and L. geometricus where males typically facilitate
cannibalism by females and mate only once. We show that these males can
increase their reproductive success by copulating with final-instar,
immature females after piercing the female's exoskeleton to access
her newly developed sperm storage organs. Females retain sperm through
their final moult and have similar fecundity to adult-mated females. This
is an adaptive male tactic because immature mating increases insemination
success relative to adult mating (which predicts higher paternity) and
moreover, rarely ends in cannibalism, so males can mate again. Although
successful only during a brief period before the female's final
moult, males may employ this tactic when they associate with final-instar
females in nature. Consistent with this, one-third of L. hasselti females
collected as immatures in nature were already mated. Immature mating
alters sexual selection on these otherwise monogynous males, and may
explain male traits allowing facultative polygyny in Latrodectus. Since
male cohabitation with immature females is common among invertebrates,
immature mating may be a widespread, previously unrecognized mating
tactic, particularly when unmated females are of high reproductive value.

雄性‘寡妇’蜘蛛（属Latrodectus）的交配食杀（copulatory cannibalism）是性选择极端效应的典型案例，尤其在哈氏球蛛（L. hasselti）和几何球蛛（L. geometricus）中——这些物种的雄性通常会促成雌性的食杀行为，且终生仅交配一次。我们发现，这些雄性可通过与末龄未成熟雌性交配来提升繁殖成功率：它们刺穿雌性外骨骼，以接触其新发育的储精器官。雌性会在最后一次蜕皮过程中保留精子，且繁殖力与成年交配雌性相当。这是一种雄性适应性策略：与未成熟雌性交配的授精成功率高于成年交配（这意味着更高的父权），且极少以食杀告终，因此雄性可再次交配。尽管该策略仅在雌性最后一次蜕皮前的短暂窗口期有效，但雄性在自然环境中遇到末龄雌性时可能会采用此策略。与此一致的是，在自然环境中采集的末龄哈氏球蛛雌性中，有三分之一已完成交配。未成熟交配改变了对这些原本单配制雄性的性选择压力，并可能解释Latrodectus属雄性具备兼性多配制能力的性状成因。鉴于雄性与未成熟雌性同居在无脊椎动物中较为普遍，未成熟交配可能是一种广泛存在但此前未被认知的交配策略——尤其当未交配雌性具有较高繁殖价值时。