Data from: Evolutionary consequence of a change in life cycle complexity: a link between precocious development and evolution towards female-biased sex allocation in a hermaphroditic parasite

The evolutionary consequences of changes in the complex life cycles of parasites are not limited to the traits that directly affect transmission. For instance, mating systems that are altered due to precocious sexual maturation in what is typically regarded as an intermediate host may impact opportunities for outcrossing. In turn, reproductive traits may evolve to optimize sex allocation. Here we test the hypothesis that sex allocation evolved towards a more female-biased function in populations of the hermaphroditic digenean trematode Alloglossidium progeneticum that can precociously reproduce in their second hosts. In these precocious populations, parasites are forced to self-fertilize as they remain encysted in their second hosts. In contrast, parasites in obligate 3-host populations have more opportunities to outcross in their third host. We found strong support that in populations with precocious development, allocation to male resources was greatly reduced. We also identified a potential phenotypically plastic response in a body size-sex allocation relationship that may be driven by the competition for mates. These results emphasize how changes in life cycle patterns that alter mating systems can impact the evolution of reproductive traits in parasites.

寄生虫复杂生活史发生改变所带来的演化后果，并不局限于直接影响传播能力的性状。例如，在通常被视为中间宿主的宿主体内，因早熟性成熟而改变的交配系统，可能会影响异交机会。相应地，生殖性状可能会朝着优化性分配（sex allocation）的方向演化。本研究针对以下假说开展检验：在可于第二宿主体内早熟繁殖的雌雄同体复殖吸虫*Alloglossidium progeneticum*种群中，性分配演化出了更偏向雌性的分配模式。在这类早熟发育的种群中，寄生虫始终被包囊于第二宿主体内，因此只能进行自体受精。与之相对，专性三宿主种群中的寄生虫则可在第三宿主体内获得更多异交机会。我们的研究结果为该假说提供了强有力的支持：在早熟发育的种群中，雄性资源分配显著降低。此外，我们还发现了体型与性分配之间潜在的表型可塑性响应，这一响应可能由配偶竞争所驱动。上述研究结果凸显了，改变交配系统的生活史模式变化会如何影响寄生虫生殖性状的演化。