Alternative reproductive tactics and their consequences in the ant genus Cardiocondyla

The ant genus Cardiocondyla is characterised by the occurrence of �workerlike�, ergatoid males that mate inside the nest. In many species of this genus, �normal�, winged males occur in addition, and a dimorphism of wingless and winged males is exhibited. The two male morphs represent alternative reproductive tactics with aggressive territorial males and peaceful disperser males. The latter mate inside the colony and then leave after several days to establish further matings with alien queens. The male morph is determined environmentally and thus the result of a conditional strategy. Generally, in the male dimorphic species C. obscurior only ergatoid males are produced. The bigger and more �expensive� winged male develops only in case where environmental conditions become worse. Investigations have shown that the larvae themselves are insensitive to changes in environmental conditions, but that workers determine the winged male morph by treating the larvae differently. The colony is able to react to environmental changes quickly, as the sensitive phase of morph determination is late (at the end of the second larval instar). After approximately two and a half weeks, adult winged males can already eclose and disperse to reach new habitats. At an individual level, males would appear to be better winged, as they are not recognized by ergatoid males as competitors (due to female mimicry) and thus avoid being killed, and still have the opportunity to mate inside the nest before dispersing. However, larvae appear to have no possibility to influence their fate as it is usual in an eusocial community. Local mating within the colony is accompanied with high levels of inbreeding. Inbreeding in haplo-diploids is less detrimental than in diploid organisms, as deleterious and lethal alleles are purged in haploid males. Exceptions are Hymenoptera with a complementary sex determination system, because in these, inbreeding leads to diploid male production. The study demonstrates that the inbreeding level in Cardiocondyla is very high. Inbreeding in addition to local mate competition, leads to even more female-biased sex ratios. As expected, another sex determination system than single-locus complementary sex determination or multi-locus complementary sex determination (with few loci), based probably not on heterozygosity, evolved in Cardiocondyla. Nevertheless, inbreeding depression can be seen after several generations of sib mating in the laboratory. Genetic data suggest that events of outbreeding alternate with inbreeding in the colonies, and this may prevent inbreeding depression in nature. As queens appear to be able to recognize kin from non-kin, they may prefer to mate with unrelated males when a selection is available. Furthermore, multiple mating may promote outbreeding, and the costs of intranidal mating in terms of risk of pathogens and predators can be neglected. Moreover, mating has no negative effect, as it can be seen in many species with sexual conflict, but instead prolongs the lifespan of the queens. A dimorphism in the female sex of long winged and short winged queens is not representative of the typical alternative reproductive tactics of dispersing and territorial queens, but appears to correlate with the switch from polygynous, dependent founding ancestors to monogyny. All queens found their colonies independently after shedding their wings, but short winged queens invest into fat instead of flight muscle mass and consequently are more successful in establishing new colonies.