Adaptive division of growth and development between hosts in helminths with two-host life cycles

Parasitic worms (helminths) with complex life cycles divide growth and development between successive hosts. Using data from 597 species of acanthocephalans, cestodes, and nematodes with two-host life cycles, we found that helminths with larger intermediate hosts were more likely to infect larger, endothermic definitive hosts, although some evolutionarily shifts in definitive host mass occurred without changes in intermediate host mass. Life-history theory predicts parasites to shift growth to hosts in which they can grow rapidly and/or safely. Accordingly, helminth species grew relatively less as larvae and more as adults if they infected smaller intermediate hosts and/or larger, endothermic definitive hosts. Growing larger than expected in one host, relative to host mass/endothermy, was not associated with growing less in the other host, implying a lack of cross-host tradeoffs. Rather, some helminth orders had both large larvae and large adults. Within these taxa, though, size at matu...具有复杂生活史的寄生蠕虫（helminths）会在相继寄生的宿主之间分配生长与发育进程。本研究基于597种具有双宿主生活史的棘头动物（acanthocephalans）、绦虫（cestodes）与线虫（nematodes）的数据，发现寄生蠕虫的中间宿主（intermediate hosts）体型越大，其越易寄生于体型更大的恒温终宿主（definitive hosts）；尽管部分终宿主体重的演化转变并未伴随中间宿主体重的改变。 生活史理论（life-history theory）预测，寄生虫会将生长过程转移至能够让它们快速且/或安全生长的宿主体内。据此，若寄生蠕虫寄生于体型更小的中间宿主和/或体型更大的恒温终宿主，其幼虫阶段的生长量相对更少，而成虫阶段的生长量相对更多。 相较于宿主体重/内温性，在某一宿主体内长至超出预期体型的寄生蠕虫，其在另一宿主体内的生长量并未出现减少，这表明不存在跨宿主权衡（cross-host tradeoffs）。与之相反，部分寄生蠕虫类群兼具体型较大的幼虫与成虫。不过在这些类群中，成熟时的体型...