Polymorphic microsatellite DNA markers in the ant Gnamptogenys striatula

The role of microgynes in the reproductive strategy of the neotropical ant Ectatomma ruidum

Miniaturized queens, microgynes, are regarded as an alternative reproductive strategy sparsely present through the ant world. The described roles of miniaturized queens include alternative short-distance dispersal morphs, an adaptation to polygyny and inquiline parasites. Some of these inquiline parasite microgynes have been described as a separate species from their host. In the poneromorph group, miniaturized queens are only reported in two Mexican populations of two Ectatomminae: Ectatomma tuberculatum, in which small queens represent an inquiline species (Ectatomma parasiticum) and Ectatomma ruidum. E. ruidum presents apparently facultative polygyny with microgynes. We used mitochondrial DNA markers and newly developed microsatellite loci to investigate the status as well as the role of microgynes in E. ruidum. We confirmed that microgynes and macrogynes are from the same species. This species is almost exclusively monogynous and monoandrous, supernumerary dealate queens of both types being actually daughters of the mother queen. An apparently polygynous nest was more often headed by a macrogyne than a microgyne. We didn't find any inbreeding or isolation by distance in the studied population, indicating that new gynes are inseminated by unrelated males and can establish a new nest far from their natal nest. However, re-adoption of daughter queens seems to be the rule and rate of microgyny appears to be linked to nest density and environmental factors.

Similar evolutionary potentials in an obligate ant parasite and its two host species

The spatial structure of host-parasite coevolution is shaped by population structure and genetic diversity of the interacting species. We analysed these population genetic parameters in three related ant species: the parasitic slavemaking ant Protomognathus americanus and its two host species Temnothorax longispinosus and T. curvispinosus. We sampled throughout their range, genotyped ants on six to eight microsatellite loci and an MtDNA sequence and found high levels of genetic variation and strong population structure in all three species. Interestingly, the most abundant species and primary host, T. longispinosus, is characterized by less structure, but lower local genetic diversity. Generally, differences between the species were small, and we conclude that they have similar evolutionary potentials. The coevolutionary interaction between this social parasite and its hosts may therefore be less influenced by divergent evolutionary potentials, but rather by varying selection pressures. We employed different methods to quantify and compare genetic diversity and structure between species and genetic markers. We found that Jost D is well suited for these comparisons, as long as mutation rates between markers and species are similar. If this is not the case, for example, when using MtDNA and microsatellites to study sex-specific dispersal, model-based inference should be used instead of descriptive statistics (such as D or G(ST) ). Using coalescent-based methods, we indeed found that males disperse much more than females, but this sex bias in dispersal differed between species. The findings of the different approaches with regard to genetic diversity and structure were in good accordance with each other.

Microsatellite loci are not abundant in all arthropod genomes: analyses in the hard tick, Ixodes scapularis and the yellow fever mosquito, Aedes aegypti

Plasmid libraries enriched for microsatellites were generated in the tick, Ixodes scapularis and in the mosquito Aedes aegypti. Libraries were enriched for genomic DNA containing (AC)n, (AG)n, (ATG)n, (CAG)n, (TAG)n, (AAT)n, (CTGY)n or (GATA)n motifs. Clones containing each motif were sequenced in both species for PCR primer design. In I. scapularis, most primers amplified a single locus and alleles varied in the number of microsatellite repeats and segregated as codominant markers. In contrast (AC)n, (TAG)n and (GATA)n microsatellite loci extracted from Ae. aegypti appeared to be members of multigene families. A primer pair designed to amplify a particular TAG locus instead amplified many independently segregating loci, some of which did not contain TAG microsatellites. Alleles at the TAG loci segregated as dominant markers and there was limited evidence for length variation among alleles. These results suggest that microsatellite loci are not universally abundant in arthropod genomes nor do alleles always segregate as codominant markers.

Population structure and mating biology of the polygynous ponerine ant Gnamptogenys striatula in Brazil

Gnamptogenys striatula is a polygynous ponerine ant, whose colonies contain either several differentiated queens or several gamergates. Population structure, queen mating frequency and deviation from random mating were investigated in a north-eastern Brazilian population. Eight workers from each of 33 queenright colonies and 17 queens and their progeny (20-40 offspring) were genotyped using eight variable microsatellite markers. Population differentiation tests indicated limited gene flow at the scale of several kilometres, and tests of isolation by distance revealed population viscosity at the scale of a few metres. This population structure, together with the frequent colony migrations and fissions observed in the field, suggest that new nests are founded by budding in G. striatula. Genetic data showed that 13 of our 17 queens were single-mated and four were double-mated. The estimation of the range of maximal frequency of double-mated queens in the population was 0.232-0.259, demonstrating that mating frequency is low in G. striatula. The low estimated mean relatedness between the 17 queens and their mates (-0. 04 +/- 0.49) indicated no evidence of inbreeding in G. striatula.