Non-additive effects on the morphology of hybrids between two species of large house spiders, Eratigena saeva and E. duellica (Araneae: Agelenidae)

Abstract

Hybridization and introgression in the wild between two species in the Eratigena atrica group of large house spiders, E. duellica and E. saeva, are well documented. However, the morphology of known F1 hybrids and subsequent F2 and backcross generations has not previously been explored. The phenotypes of these interspecific offspring have implications for the ease of introgression and for the morphological identification of individuals of hybrid origin. Here, the progeny from laboratory crosses are analysed using both simple characters and multivariate statistical techniques. F1 hybrids in both sexes are, morphologically, significantly biased towards E. duellica but backcross progeny tend to resemble their non-F1 parents more than expected in a model of additive, unlinked quantitative trait loci (QTL). It is possible that loci on the X-chromosomes affect the phenotype or that there are maternal influences. These biases may have consequences for the ease and direction of gene flow between the species. While female F1 hybrids can be distinguished from pure parents, for later generations, and for all generations of males, confusion with the parental species is highly likely and may have affected previous conclusions.