No inbreeding depression but increased sexual investment in highly inbred ant colonies

Abstract

Inbreeding can lead to the expression of deleterious recessive alleles and to a subsequent fitness reduction. In Hymenoptera, deleterious alleles are purged in haploid males moderating inbreeding costs. However, in these haplodiploid species, inbreeding can result in the production of sterile diploid males. We investigated the effects of inbreeding on the individual and colony level in field colonies of the highly inbred ant Hypoponera opacior. In this species, outbreeding winged sexuals and nest-mating wingless sexuals mate during two separate reproductive periods. We show that regular sib-matings lead to high levels of homozygosity and the occasional production of diploid males, which sporadically sire triploid offspring. On the individual level, inbreeding was associated with an increased body size in workers. On the colony level, we found no evidence for inbreeding depression as productivity was unaffected by the level of homozygosity. Instead, inbred colonies altered their allocation strategies by investing more resources into sexuals than into workers. This shift towards sexual production was due to an increased investment in both males and queens, which was particularly pronounced in the dispersive generation. The absence of inbreeding depression combined with increased reproductive investment, especially in outbreeding sexuals, suggests that these ants have evolved active strategies to regulate the extent and effects of frequent inbreeding.

Identification of microsatellite markers for a worldwide distributed, highly invasive ant species Tapinoma melanocephalum (Hymenoptera: Formicidae)

“…These are often a consequence of within-nest mating, limited dispersal of males and/or females or parthenogenetic reproduction (Pearcy et al, 2006) and have been documented in multiple ant species (Trontti et al, 2005;Thurin & Aron, 2009;Kureck et al, 2012).…”

Odor diversity decreases with inbreeding in the antHypoponera opacior

“…), varies between 0.20 and 0.75; Kureck et al. ), but also because the rarity of trophallaxis in ponerine ants means that less mixing of CHCs between nestmates should occur (Bagnères and Blomquist ). Hence the level of heterozygosity of an ant is more likely to be reflected in its individual hydrocarbon profile.…”

“…Surprisingly, however, these ants do not appear to suffer from inbreeding depression, as inbred colonies are as productive as outbred ones (Kureck et al. ) and highly inbred colonies are commonly found in nature. The only negative consequence is the occasional production of diploid males, which sporadically sire triploid offspring (Kureck et al.…”

“…The only negative consequence is the occasional production of diploid males, which sporadically sire triploid offspring (Kureck et al. ). However, inbreeding is also associated with a larger worker body size and altered reproductive allocation strategies (Kureck et al.…”

“…However, inbreeding is also associated with a larger worker body size and altered reproductive allocation strategies (Kureck et al. ). More inbred colonies shift their investment from workers to sexuals and this shift is particularly pronounced in the outbreeding, winged early‐summer generation.…”