The Ecology of Slavemaking Ants and Their Hosts in North Temperate Forests

Abstract

Slavemaking ants are of great interest to biologists because of their highly specialized lifestyle. Slavemakers rely on the presence of heterospecific ''slaves'' to perform routine chores such as foraging and brood care. While we have considerable information on the behavior of these ants, mostly gleaned from laboratory studies, we know very little of their basic ecology. Here we report data collected over 20 yr in three geographic sites on the occurrence, spatial pattern, nest site use, and demography of two slavemaker species and three of the host species they enslave; all are small ants in the tribe Formicoxenini. We found geographic and temporal variation with respect to the interaction between social parasites and their hosts. The slavemaker Protomognathus americanus occurred in each geographic site, and in each its most common host was Leptothorax longispinosus; the other known hosts of this slavemaker, L. curvispinosus and L. ambiguus were less abundant. In a West Virginia site, slavemaker nests were smaller than in New York and Vermont sites. Additional data from West Virginia showed that the slavemaker is strongly constrained by its hosts there, but we found little impact of the parasite on its hosts. By contrast, in the New York site, we found strong evidence that the majority host was affected by the slavemaker: host nests showed important life history shifts between neighborhoods containing slavemakers vs. those that were parasite-free. Furthermore, the slavemaker was able to subjugate large host nests there and had large slave pools. In a third site in Vermont, parasite and host demography reflected their interaction weakly. We discovered a second slavemaking species there, and both parasites were preferentially found in areas of high host density. However, we uncovered no demographic or spatial evidence that slavemakers affected their hosts in Vermont. Likewise, we found no evidence in any site of demographic responses by the minority hosts to the presence of slavemakers. Thus our results imply that host-parasite interactions varied among host species and among geographic locales. The slavemaker system therefore is amenable to analysis in terms of parasite-host coevolution.

Collective defence portfolios of ant hosts shift with social parasite pressure

“…Whenever possible, we therefore included long-term collection data on parasite pressure from previously studied communities (i.e. Ohio North, West Virginia, Vermont and New York [23][24][25][26]). Moreover, we have evidence for consistent parasite occurrence from some other communities that have been sampled sporadically in the past (i.e.…”

Impact of Parasite Sympatry on the Geographic Mosaic of Coevolution

“…The evolutionary repercussion of being weakly adapted to multiple target species is the diminished rate and probability of fixing beneficial alleles or purging deleterious ones (Kawecki 1994, Whitlock 1996. Thus, variation in target species is capable of producing selection mosaics that differ in intensity and have variable coevolutionary outcomes (Thompson 1994, Thompson and Pellmyr 1992, Gomulkiewicz et al 2000; e.g., Benkman et al 2001, Foitzik et al 2001, Foitzik and Herbers 2001a, Herbers and Foitzik 2002. This is also true for systems with multiple enemies and a single target species (e.g., Wissinger and McGrady 1993, Benkman 1999, Siddon and Witman 2003, but most of these studies focus on the effect of multiple predators on a single prey whereas interactions between parasites are only just emerging as determinants of community dynamics (Poulin 1998).…”

Geographic distribution of the anti-parasite trait “slave rebellion”

“…If slavemaker brood rarely survives, slavemaking colonies remain small and nearby host colonies, which are potentially related to the slaves in the slavemaker nest, will experience a reduced raiding risk. The severe reduction in parasite brood survival presents an explanation why slavemaker nests of P. americanus are exceptionally small compared to nests of related species (Foitzik and Herbers 2002). The strong differences we find in brood survival between the three habitats suggest that these communities are at different stages in a coevolutionary arms race or that the costs/benefit trade-off for the trait differs between sites.…”

“…One potential explanation of the observed low survival of slavemaker pupae could be that it is a laboratory artefact, which is not relevant under natural conditions. However, earlier studies found very low per-worker-productivity in parasite nests under field conditions (Foitzik and Herbers 2002) indicating similarly low survival rates in the field. Secondly, the observed low survival of slavemaker pupae could be the result of enslaved workers generally caring less well for allospecific brood compared to conspecific brood.…”

“…We study hosts from three well-studied communities in New York (NY), West Virginia (WV) and Ohio (OH), which differ in their community composition, but are very similar in parasite prevalence (Herbers and Foitzik 2002;Brandt and Foitzik 2004). Previous studies have found differences between the three communities which may be important for our study.…”