Canadian Forest Service Publications
Life-stage differences in spatial genetic structure in an irruptive forest insect: implications for dispersal and spatial synchrony. 2014. James, P.M.A.; Cooke, B.; Brunet, B.M.T.; Lumley, L.M.; Sperling, F.A.H.; Fortin, M.-J.; Quinn, V.S.; Sturtevant, B.R. Molecular Ecology 24(2):296-309.
Issued by: Northern Forestry Centre
Catalog ID: 35905
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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.
Plain Language Summary
Cyclic population dynamics and their genetic consequences have long been the subject of study in ecology. The spruce budworm is a cyclic species of particular interest, as it undergoes outbreaks in which populations increase over several orders of magnitude, with significant economic consequences. We analyzed spatial patterns of genetic variation in the spruce budworm over a large landscape in Minnesota and northwestern Ontario to make inferences about population genetic structure and gene flow among populations. Using a set of extremely variable “microsatellite” genetic markers, we showed that: (1) gene flow among populations is probably very high across the study area; (2) there are important genetic differences between adult (moth) and juvenile (larvae) life-stages; and (3) a single localized spruce budworm outbreak in northwestern Minnesota was the likely source of moths captured on the shore of Lake Superior, several hundred kilometres to the east. This study demonstrates the potential and challenges of using molecular methods to distinguish residents from migrants. Further investigations into population dynamics using genetic analysis can help us to better understand the mechanisms that affect population cycles.