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

Abstract

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 seven geographic locations. We show that (i) gene flow among populations is likely very high (Fst ≈ 0); (ii) despite an overall low level of genetic structure, important differences exist between adult (moth) and juvenile (larvae) life stages; and (iii) 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.

Spatial synchrony in sub‐arctic geometrid moth outbreaks reflects dispersal in larval and adult life cycle stages

“…() demonstrated low levels of genetic differentiation among O. brumata populations across a study region of comparable spatial extent to the present study in the Orkney islands and suggested that this was due to high gene flow resulting from dispersal of ballooning larvae. Genetic evidence for high rates of gene flow and dispersal across distances of tens to hundreds of kilometres has recently also been obtained for two other cyclic lepidopteran defoliators: the western tent caterpillar ( Malacosoma californicum pluviale Packard) (Franklin, Myers, & Cory, ) and the eastern spruce budworm ( Choristoneura fumiferana Clemens) (James et al., ). In both cases, the authors suggested that dispersal plays an important role in synchronizing populations at the spatial scales considered.…”

Population cycles: generalities, exceptions and remaining mysteries

“…In this case, mass flights of moths have been observed [68]. Geneflow among populations is high and genetic structure low [69].…”

Continent‐wide population genomic structure and phylogeography of North America’s most destructive conifer defoliator, the spruce budworm (Choristoneura fumiferana)

“…Larval-host interactions appear to be strongly tied to speciation in the spruce budworm species complex (Fagua, Condamine, Brunet, et al, 2018;Fagua, Condamine, Dombroskie, et al, 2018). James et al (2015) used microsatellite markers to study the population genetics of spruce budworm within the Border Lakes region of Ontario and Minnesota to detect dispersal by comparing larvae (residents) to adults captured in pheromone traps (potential migrants). James et al (2015) used microsatellite markers to study the population genetics of spruce budworm within the Border Lakes region of Ontario and Minnesota to detect dispersal by comparing larvae (residents) to adults captured in pheromone traps (potential migrants).…”

“…For C. fumiferana, May, Leonard, and Vadas (1977) studied electrophoretic variation of loci in spruce budworm collected in northern Maine and found no significant population differentiation. James et al (2015) used microsatellite markers to study the population genetics of spruce budworm within the Border Lakes region of Ontario and Minnesota to detect dispersal by comparing larvae (residents) to adults captured in pheromone traps (potential migrants). Recently, Larroque et al (2019) used SNP markers to detect spatiotemporal variation in population genetic structure during spruce budworm population outbreaks in Quebec.…”