Data from: Temperature, size, reproductive allocation, and life-history evolution in a gregarious caterpillar

The present study aimed to investigate the relation between growth rate, final mass and larval development, and how this relations influence the reproductive trade-offs in the context of a gregarious life-style and the need to keep an optimal group size. We use as model two sympatric populations of the pine processionary moth Thaumetopoea pityocampa, occurring in different seasons and thus experiencing different climatic conditions. T. pityocampa is a strictly gregarious caterpillar throughout the larval period, which occurs during winter in countries all over the Mediterranean Basin. However in 1997 a population, in which larval development occurs during the summer, was discovered in Portugal, being called Summer Population SP, as opposed to the normal Winter Population WP, which coexists in the same forest feeding on the same host during the winter. Both this populations were monitored during three years, with assessment of the length of the larval period and its relation with different climatic variables, final mass and adult size, egg size and number, colony size, and mortality in different life stages. The SP larval period was reduced due to development in the warmer part of the year, however reaching the same final mass and adult size as the WP. In spite of equal size at maturity, a trade-off between egg size and number was found between the two populations: SP produced less but bigger eggs than WP. This is the opposite of what is generally found in other Lepidoptera species, where development in colder environments leads to larger eggs at the expense of fecundity, but corroborates the trend found at a macro-geographic scale for T. pityocampa, with females from northern latitudes and colder environment, producing more and smaller eggs. Results point to the importance of number of eggs in cold environments due to an advantage of large colonies when gregarious caterpillars develop in such environments, and are discussed according to the major theories regarding size in animals.

本研究旨在探究生长速率、最终体重与幼虫发育三者间的关联，以及在群居生活模式与维持最优群规模的需求背景下，此类关联如何影响繁殖权衡。本研究选取两种同域分布的松异舟蛾（Thaumetopoea pityocampa）种群作为研究模型，这两种种群的发生季节各不相同，因此所处的气候条件存在显著差异。松异舟蛾在整个幼虫期均为严格群居性毛虫，其幼虫期在整个地中海盆地诸国均处于冬季。然而1997年，葡萄牙境内发现了一个幼虫期在夏季的种群，该种群被命名为夏季种群（Summer Population, SP）；与之相对的常规种群为冬季种群（Winter Population, WP），后者与SP在同一片森林中共存，冬季期间以相同寄主植物为食。我们对这两种种群开展了为期三年的监测，评估了幼虫期时长及其与不同气候变量、最终体重、成虫体型、卵的大小与数量、虫群规模以及不同生命阶段死亡率之间的关联。由于发育阶段处于一年中温度较高的时段，SP的幼虫期有所缩短，但其最终体重与成虫体型与WP并无差异。尽管成熟个体体型一致，两种群间仍存在卵大小与数量的权衡关系：SP所产的卵数量更少但个体更大，这与其他鳞翅目（Lepidoptera）物种的普遍规律恰好相反——在其他鳞翅目物种中，低温环境下的发育会以繁殖力为代价，产出更大的卵；但该结果与松异舟蛾在大地理尺度上的研究趋势相符：来自高纬度寒冷环境的雌虫会产出更多但更小的卵。研究结果表明，在寒冷环境中，由于群居毛虫形成的大虫群具备生存优势，卵的数量至关重要；本研究还结合有关动物体型的主流理论展开了讨论。