Diacamma cyaneiventre

Distribution based on Regional Taxon Lists
Oriental Region: India.

Biology
After the death of the single gamergate or her absence following colony fission, the gamergate is replaced by a newly eclosed nestmate worker. After a replacement, colonies go through short-lived periods in which two matrilines of sisters co-occur. This is a situation which can be described as serial polygyny. To measure the consequences of serial polygyny, a genetic analysis was performed on 449 workers from 46 colonies of D. cyaneiventre using five microsatellite loci (André et al. 2001). The presence of more than one matriline among workers of the same nest was detected in 19% of colonies, indicating a recent change of gamergate. The average genetic relatedness among nestmate workers was 0.751 and did not significantly differ from the theoretical expectation under strict monogyny and monandry (0.75). A simple analytical model of the temporal dynamics of serial polygyny was developed in order to interpret these results. We show that the rate of gamergate turnover relative to the rate of worker turnover is the crucial parameter determining the level of serial polygyny and its effect on the genetic structure of colonies. This parameter, estimated from our data, confirms that serial polygyny occurs in D. cyaneiventre but is not strong enough to influence significantly the average genetic relatedness among workers.

In Diacamma, the single gamergate is replaced by one of her daughters (or occasionally by a sister). From a long-term genetic survey of nests of D. cyaneiventre, André et al. (2006) estimated the rate of gamergate turnover as well as the lifespan of workers and gamergate tenure using a maximum likelihood model developed for this purpose. We specifically compared the genotypes of two cohorts of workers sampled at 2 and 16 months interval from the same nests, using five microsatellite markers. To improve the accuracy of the estimates, we also used in the model the nests from the same population sampled only once and analysed by André et al. (2001). The model indicates that the possibility of the same nest not sheltering the same colony at two different sampling dates (colony turnover) was not significantly different from zero in our sample. The likelihood of the model was maximal for a probability of gamergate change pg = 0.005 per day (i.e. a gamergate tenure of 200 days) and a worker lifespan w = 60 days, indicating that the gamergate ‘s tenure is about 3 times longer than workers’ expected lifespan in the population studied. Moreover, the genetic analysis of the gamergate and brood in three colonies excavated completely, reveals that colony fission can occur just after a gamergate replacement with the sister of the new gamergate reproducing in the new propagule.

Doums et al. (2002) used both mitochondrial and microsatellite markers to assess the consequence of restricted female dispersal (due to the replacement of winged queens by gamergates) at three geographical scales: within a given locality (< 1 km), between localities within a given region (< 10 km) and between regions (> 36 km). Within a locality, a strong population structure was observed for mitochondrial DNA (mtDNA) whereas weak or nonexistent population genetic structure was observed for the microsatellites (around 5% of the value for mtDNA). Male gene flow was estimated to be about 20–30 times higher than female gene flow at this scale. At a larger spatial scale, very strong genetic differentiation for both markers was observed between localities — even within a single region. Female dispersal is nonexistent at these scales and male dispersal is very restricted, especially between regions. The phylogeographical structure of the mtDNA haplotypes as well as the very low genetic diversity of mtDNA within localities indicate that new sites are colonized by a single migration event from adjacent localities, followed by successive colony fissions. These patterns of genetic variability and differentiation agree with what is theoretically expected when colonization events are kin-structured and when, following colonization, dispersion is mainly performed by males.

Nomenclature

 *  cyaneiventre. Diacamma cyaneiventre André, 1887: 293 (w.) INDIA. Subspecies of rugosum: Forel, 1900d: 318. Revived status as species: Bingham, 1903: 78.