Data from: Life-stage differences in spatial genetic structure in an irruptive forest insect: implications for dispersal and spatial synchrony

Dispersal determines the flux of individuals, energy, and information and is therefore a key determinant of ecological and evolutionary dynamics. Yet, it remains difficult to quantify its importance relative to other factors. This is particularly true in cyclic populations in which demography, drift, and dispersal contribute to spatio-temporal variability in genetic structure. Improved understanding of how dispersal influences spatial genetic structure is needed to disentangle the multiple processes that give rise to spatial synchrony in irruptive species. In this study, we examined spatial genetic structure in an economically important irruptive forest insect, the spruce budworm (Choristoneura fumiferana) to better characterize how dispersal, demography, and ecological context interact to influence spatial synchrony in a localized outbreak. We characterized spatial variation in microsatellite allele frequencies using 231 individuals and 7 geographic locations. We show that: (1) gene flow among populations is likely very high (Fst ≈ 0); (2) despite an overall low level of genetic structure, important differences exist between adult (moth) and juvenile (larvae) life-stages; and (3) the localized outbreak is the likely source of moths captured elsewhere in our study area. This study demonstrates the potential of using molecular methods to distinguish residents from migrants and for understanding how dispersal contributes to spatial synchronization. In irruptive populations, the strength of genetic structure depends on the timing of data collection (e.g., trough vs. peak), location, and dispersal. Taking into account this ecological context allows us to make more general characterizations of how dispersal can affect spatial synchrony in irruptive populations.

扩散（Dispersal）决定了个体、能量与信息的通量，因此是生态与进化动态的关键决定因子。然而，相较于其他生态过程，量化扩散的相对重要性仍颇具挑战。这一点在循环种群中尤为突出：种群统计学（demography）、遗传漂变（genetic drift）与扩散共同塑造了遗传结构的时空变异（spatio-temporal variability）。为厘清驱动暴发型物种（irruptive species）空间同步性的多重过程，亟需深化对扩散如何影响空间遗传结构（spatial genetic structure）的认知。本研究以一种兼具重要经济价值的暴发型森林昆虫——云杉卷叶蛾（Choristoneura fumiferana）为研究对象，旨在解析扩散、种群统计学与生态背景如何协同作用，影响局部暴发种群的空间同步性。研究基于231个个体与7个采样点位，对微卫星（microsatellite）等位基因频率的空间变异进行了表征。结果显示：（1）种群间基因流（gene flow）水平极高（Fst≈0）；（2）尽管整体遗传结构水平较低，但成虫（蛾）与幼体（幼虫）两个生活史阶段间存在显著差异；（3）本研究区域内捕获的成虫，其来源大概率为该局部暴发种群。本研究证实了利用分子手段区分定居个体与迁移个体的可行性，同时为理解扩散如何推动空间同步性提供了新的研究视角。对于暴发型种群而言，遗传结构的强弱取决于采样时间（如种群低谷期与高峰期）、采样点位以及扩散过程。纳入此类生态背景信息，能够帮助我们更普适性地刻画扩散对暴发型种群空间同步性的影响机制。