Submitted to: Current Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2011
Publication Date: 3/14/2011
Citation: Facon, B., Hufbauer, R., Tayeh, A., Lombaert, E., Vitalis, R., Guillemaud, T., Lundgren, J.G., Estoup, A. 2011. Inbreeding depression is purged in the invasive insect Harmonia axyridis. Current Biology. 21:424-427. Interpretive Summary: Invasive species that colonize new regions generally do so with very small populations, which leads to inbreeding and a number of problems associated with it; this phenomenon is called a genetic bottleneck. This study examines the worldwide invasion of Harmonia axyridis, the multi-colored Asian lady beetle. We found that H. axyridis experienced a severe genetic bottleneck when it invaded eastern North America. The data suggests that the population that recovered from this bottleneck was much more resistant to the deleterious effects of inbreeding compared to those populations collected in their native ranges. Essentially, invading species that overcome this problem are thereby more suited for invading future regions because they have purged deleterious traits that might hamper the subsequent expansion of their ranges.
Technical Abstract: Invaders face a genetic barrier when they pass through bottlenecks in population size, which can reduce genetic diversity and increase inbreeding among close relatives. Although low fitness among consanguineous offspring, or inbreeding depression, is widespread, why it is that invaders appear not to be limited by bottlenecks or, consequently, by inbreeding depression, remains an open question. In laboratory environments, intense inbreeding can purge deleterious alleles that cause inbreeding depression and hence increase overall fitness. We use the world-wide invader Harmonia axyridis to compare levels of inbreeding depression between replicate introduced and native populations. We show that invasive populations, which endured a bottleneck, experience almost none of the inbreeding depression suffered by native populations. Thus, deleterious alleles leading to inbreeding depression may be purged during bottlenecks, enabling the evolution of invaders with higher mean fitness overall than their native counterparts.