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之间的关联，以及在群居生活模式与维持最优种群规模的需求背景下，此类关联如何影响繁殖权衡。本研究以两种同域分布的松列队蛾（Thaumetopoea pityocampa）种群作为研究模型，二者发生季节不同，因此经历的气候条件存在差异。松列队蛾是一种在整个幼虫期均保持严格群居性的毛虫，在地中海盆地各国的冬季完成幼虫发育。但1997年葡萄牙境内发现了一个特殊种群，其幼虫发育阶段发生在夏季，被命名为夏季种群（SP）；与之相对的常规冬季种群（WP）则与SP在同一片森林中共存，冬季取食同一寄主植物。本研究对这两个种群开展了为期三年的监测工作，评估了幼虫期时长及其与多种气候变量、最终体重与成虫体型、卵的大小与数量、种群规模以及不同生命阶段死亡率的关联。由于发育处于一年中温度较高的时段，SP的幼虫期显著缩短，但其最终体重与成虫体型与WP并无差异。尽管两个种群的成熟个体体型相当，但二者之间存在卵大小与繁殖数量的权衡关系：SP产下的卵数量更少，但单枚卵的体积更大。这一结果与其他鳞翅目（Lepidoptera）物种的普遍规律相反——后者在寒冷环境中发育时，往往会以繁殖力为代价产下更大的卵；但该结果与松列队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，会产下更多但体积更小的卵。本研究结果表明，在寒冷环境中，卵的数量至关重要，因为群居毛虫在这类环境中发育时，较大的种群规模具有生存优势；研究还结合动物体型相关的主流理论展开了深入讨论。