Papers by Susanne Foitzik
Behavioral Ecology, 2015
Social insect colonies defend themselves from intruders through nestmate recognition, yet the evo... more Social insect colonies defend themselves from intruders through nestmate recognition, yet the evolution and maintenance of recognition cue diversity is still poorly understood. We compared the recognition cue diversity of 9 populations of Temnothorax longispinosus ant colonies, including populations that harbored the socially parasitic slavemaker ant, Protomognathus americanus. Although ants recognize friends from foe based on recognition cues encoded in their cuticular hydrocarbon profile, which specific compounds are involved in recognition is unknown for most species. We therefore started by statistically identifying 9 putative recognition compounds involved in worker and colony aggression. We find that colonies that co-occur with slavemakers were more variable in these recognition compounds and hence less similar in their recognition profiles than unparasitized populations. Importantly, these differences appear to be regulated by processes that specifically act on the level of the colony, which rules out potentially confounding effects altering chemical profiles of populations, such as differences in abiotic conditions or standing genetic variation. Instead, our findings indicate that slavemakers drive recognition cue diversity in their ant hosts, in much the same way that avian hosts diversify their egg appearance in response to brood parasite pressure. Such recognition cue diversification through negative frequency-dependent selection favors rare host phenotypes and renders it impossible for parasites to match the recognition profile of all potential hosts.
Population structure can affect the evolution of parasite virulence and host defense, a hypothesi... more Population structure can affect the evolution of parasite virulence and host defense, a hypothesis that has been confirmed by studies focusing on large spatial scales. In contrast, we examine the small scale population structure of a host species and investigate whether it could explain the evolution of a defense trait against slavemaking ants. Slavemaking ants steal worker brood from host colonies, which will later serve as slaves to rear parasite offspring. The host species Temnothorax longispinosus has evolved an effective post-enslavement defense mechanism; instead of taking care of the slavemaker young, these slaves kill a high proportion of the parasite offspring. Because slaves never reproduce, they were thought to be trapped in an evolutionary dead end without the possibility of evolving such defense traits. Using detailed microsatellite data on a small spatial scale we can demonstrate that slaves can gain indirect fitness benefits by reducing parasite pressure on nearby hos...
Ethology, 2015
Variation in community composition over a species' geographic range leads to divergent selection ... more Variation in community composition over a species' geographic range leads to divergent selection pressures, resulting in interpopulation variation in trait expression. One of the most pervasive selective forces stems from antagonists such as parasites. Whereas hosts of microparasites developed sophisticated immune systems, social parasites select for behavioural host defences. Here, we investigated the link between parasite pressure exerted by the socially parasitic slavemaking ant Protomognathus americanus and colony-level aggression in Temnothorax ants from 17 populations. We studied almost the entire geographic range of two host species, including unparasitized populations. As previous studies have demonstrated that host colonies responding highly aggressively towards conspecifics fare better during slavemaker attacks, we predicted higher aggression levels in severely parasitized populations. Indeed, we demonstrate an increase in aggression towards conspecifics with parasite pressure, a pattern that was consistent over the two host species. In contrast to other studies, aggression against the parasite itself did not shift with parasite pressure. This may be explained by an absence of costs of parasite-specific aggression in parasite-free populations. The preferred host species T. longispinosus was generally more aggressive; however, the association between parasite pressure and aggression was found for both species, suggesting convergent co-adaptation. Two potentially confounding factors, colony density and the co-occurrence of a competing Temnothorax species in the community, could not explain the level of colony aggression in intra-and interspecific interactions. Instead, our study points to social parasite pressure as the determining factor shaping antagonistic interactions within, but not between, host species.
Journal of evolutionary biology, 2014
The evolution of parasite virulence and host defences is affected by population structure. This e... more The evolution of parasite virulence and host defences is affected by population structure. This effect has been confirmed in studies focusing on large spatial scales, whereas the importance of local structure is not well understood. Slavemaking ants are social parasites that exploit workers of another species to rear their offspring. Enslaved workers of the host species Temnothorax longispinosus have been found to exhibit an effective post-enslavement defence behaviour: enslaved workers were observed killing a large proportion of the parasites' offspring. As enslaved workers do not reproduce, they gain no direct fitness benefit from this 'rebellion' behaviour. However, there may be an indirect benefit: neighbouring host nests that are related to 'rebel' nests can benefit from a reduced raiding pressure, as a result of the reduction in parasite nest size due to the enslaved workers' killing behaviour. We use a simple mathematical model to examine whether the s...
... Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). (1) Department of Biology, Johan... more ... Affiliation(s) du ou des auteurs / Author(s) Affiliation(s). (1) Department of Biology, Johannes Gutenberg University of Mainz, ALLEMAGNE (2) Department of Biology II, Ludwig-Maximilians University, Munich, ALLEMAGNE Résumé / Abstract. ... Macho. ; Insecto social. ; ...
Proceedings of the Royal Society B: Biological Sciences, 2014
Molecular Ecology, 2012
Inbreeding can lead to the expression of deleterious recessive alleles and to a subsequent fitnes... more 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.
The evolution of colony size in social insects is influenced by both extrinsic and colony-intrins... more The evolution of colony size in social insects is influenced by both extrinsic and colony-intrinsic factors. An important intrinsic trait, per-capita productivity, often declines in larger colonies. This pattern, known as Michener's paradox, can limit the growth of insect societies. In this study, we first describe this problem, survey its occurrence across different ant species, and present a case study of eight cavitydwelling ants with very small colony sizes. In these species, colonies might never reach sizes at which per-capita productivity decreases. However, in six out of the eight focal species, per-capita productivity did decline with increasing size, in accordance with other studies on per-capita productivity in ants. Several mechanisms, such as resource availability or nest-site limitation, may explain the decrease in per-capita productivity with increases in colony size in our focal species. In these central-place foragers, the individual foraging mode is expected to lead to an increase in travel time as colonies grow. We suggest that polydomy, the concomitant occupation of several nest sites, could serve as a potential strategy to overcome this limitation. Indeed, for one species, we show that polydomy can help to circumvent the reduction in productivity with increasing colony size, suggesting that limited resource availability causes the observed decrease in per-capita productivity. Finally, we discuss the influence of other factors, such as the nesting ecology and colony homeostasis, on the evolution of colony size in these cavity-dwelling ants.
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Papers by Susanne Foitzik