Data from: Role of propagule pressure in colonization success: disentangling the relative importance of demographic, genetic and habitat effects

High propagule pressure is arguably the only consistent predictor of colonization success. More individuals enhance colonization success because they aid in overcoming demographic consequences of small population size (e.g. stochasticity and Allee effects). The number of founders can also have direct genetic effects: with fewer individuals, more inbreeding and thus inbreeding depression will occur, whereas more individuals typically harbour greater genetic variation. Thus, the demographic and genetic components of propagule pressure are interrelated, making it difficult to understand which mechanisms are most important in determining colonization success. We experimentally disentangled the demographic and genetic components of propagule pressure by manipulating the number of founders (fewer or more), and genetic background (inbred or outbred) of individuals released in a series of three complementary experiments. We used Bemisia whiteflies and released them onto either their natal host (benign) or a novel host (challenging). Our experiments revealed that having more founding individuals and those individuals being outbred both increased the number of adults produced, but that only genetic background consistently shaped net reproductive rate of experimental populations. Environment was also important and interacted with propagule size to determine the number of adults produced. Quality of the environment interacted also with genetic background to determine establishment success, with a more pronounced effect of inbreeding depression in harsh environments. This interaction did not hold for the net reproductive rate. These data show that the positive effect of propagule pressure on founding success can be driven as much by underlying genetic processes as by demographics. Genetic effects can be immediate and have sizable effects on fitness.

可以说，繁殖体压力（propagule pressure）是定殖成功唯一一致的预测因子。更多的个体能够提升定殖成功率，因为它们有助于克服种群规模过小带来的种群动态后果（如统计随机性与阿利效应（Allee effects））。奠基者的数量同样可产生直接的遗传效应：个体数量越少，近交程度越高，由此引发的近交衰退（inbreeding depression）也就越显著；而个体数量越多，通常携带的遗传变异（genetic variation）也越丰富。因此，繁殖体压力的种群动态与遗传组分之间存在关联，这使得我们难以厘清究竟哪些机制对定殖成功起到主导作用。我们通过三项互补性实验系列，操控奠基者数量（少量或大量）以及释放个体的遗传背景（近交或远交），从实验层面解析了繁殖体压力的种群动态与遗传组分。我们以烟粉虱（Bemisia whiteflies）为实验材料，将其接种至其原生寄主（适宜环境）或新寄主（胁迫环境）。实验结果表明，更多的奠基者个体以及远交的个体均能提升子代成虫的数量，但仅有遗传背景能够持续影响实验种群的净生殖率（net reproductive rate）。环境因素同样具有重要作用，且与繁殖体大小共同作用决定了子代成虫的数量。环境质量还与遗传背景交互影响建群成功（establishment success）：在胁迫环境中，近交衰退的效应更为显著。不过这一交互作用并未体现在净生殖率上。本研究数据表明，繁殖体压力对建群成功的正向效应，其背后的遗传驱动机制与种群动态机制同样重要。遗传效应能够快速显现，并对适合度（fitness）产生显著影响。