Love at first flight: Mating errors, population genetics, and the slow spread of an invader

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University of New Brunswick


This thesis investigates mating interactions and population genetics of the invasive Tetropium fuscum Fabricius (Coleoptera: Cerambycidae) and its native congener, Tetropium cinnamopterum Kirby (Coleoptera: Cerambycidae) in Nova Scotia, Canada, to help explain the slow spatial spread of T. fuscum in North America. Tetropium fuscum first appeared in North America in about 1990 and has since outcompeted the native T. cinnamopterum in the sympatric zone and spread approximately 150 km from its point of entry but has since halted its spread. Tetropium fuscum and T. cinnamopterum have common host plants, overlapping flight periods and share the same male-produced sex-aggregation pheromone, fuscumol, that attracts both sexes. These species would have ample opportunity to encounter each other in the field due to these similarities suggesting hybridization is a possibility. Our mating behaviour experiments showed males of both species make mating errors under no-choice mating conditions. Under choice mating conditions T. cinnamopterum males show a strong preference for same-species females but T. fuscum is less discriminating. We designed a species discriminating SNP assay with the goal of detecting hybridization to confirm that mating errors also take place in the field. We found low levels of introgression in the sympatric zone as well as the presence of cryptic individuals that morphologically present as T. cinnamopterum while genetically presenting as T. fuscum. We investigated the possibility that female body size rather than species influences mate choice in Tetropium. Tetropium cinnamopterum females are significantly larger than T. fuscum females although body size was not a determining factor in male mate choice for these species. Our findings suggest heterospecific matings between these species happen but may be rare and the resulting offspring may not be as fit as their parents, which could exacerbate Allee effects at the edge range of T. fuscum and reinforce its apparently pinned range border.