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4. Adaptive significance of queen mating frequency in ants : In search of benefits of genetic variability

Author

Gertsch, Pia J. and Gertsch, Pia J.

Abstract

Fitness effects of polyandry, multiple mating by females, were studied on two ant speciesLasius niger and Formica truncorum. Particular emphasis was put on evaluating diploid male load, which happens when homozygosity in the sex determination locus leads to intendedfemales developing into sterile, diploid males. It has been hypothesised that under certainconditions diploid male load selects for polyandry. The power of spermatheca-PCR (genotyping stored sperm in the spermatheca of a femaleinsect) in identifying multiply mated females was scrutinised. Microsatellite amplificationsfrom artificial sperm mixes with known composition showed that alleles at and above 10%representation are reliably amplified and detected. Microsatellite markers were developed for L. niger and female survival and fecundityin relation to her mate number were studied in two populations: Uppsala, Sweden and Lausanne, Switzerland. Annual sexual production did not correlate with higher female mating frequency in either population. Colony survival appeared to be higher for multiple mated females in Lausanne but not in Uppsala. The possible higher survival of multiple mated queens is unlikely to be due to diploid male load as there was no sign of diploid males among broods of 479 queens which were kept in laboratory. Diploid male load in the colonies of the ant Formica truncorum was measured. Thecolony size was significantly negatively affected by diploid male production. However, theobserved frequencies of diploid males in the colonies did not comply with the theoreticalpredictions. Until the determinants of diploid male production in F.truncorum are clarified itis not possible to settle whether diploid male load selects for multiple mating in this species. A theoretical model was constructed to examine how the selection on mating frequencyfrom diploid male load changes when allelic diversity in the sex determination locus increases.Fitness of single and double mated females was compared. The fitn

Published
2000

11. Evolutionary transition from single to multiple mating in fungus-growing ants

Author

Villesen, P., Gertsch, Pia J., Frydenberg, J., Mueller, U. G., and Jacobus Boomsma

Subjects
behavior and behavior mechanisms, reproductive and urinary physiology
Abstract

Udgivelsesdato: November Queens of leafcutter ants exhibit the highest known levels of multiple mating (up to 10 mates per queen) among ants. Multiple mating may have been selected to increase genetic diversity among nestmate workers, which is hypothesized to be critical in social systems with large, long-lived colonies under severe pressure of pathogens. Advanced fungus-growing (leafcutter) ants have large numbers (104-106 workers) and long-lived colonies, whereas basal genera in the attine tribe have small (Myrmicocrypta ednaella, Apterostigma collare and Cyphomyrmex longiscapus. Microsatellite marker analyses revealed that queens in all three species were single mated, and that worker-to-worker relatedness in these basal attine species is very close to 0.75, the value expected under exclusively single mating. Fungus growing per se has therefore not selected for multiple queen mating. Instead, the advanced and highly productive social structure of the higher attine ants, which is fully dependent on the rearing of an ancient clonal fungus, may have necessitated high genetic diversity among nestmate workers. This is not the case in the lower attines, which rear fungi that were more recently derived from free-living fungal populations

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