Potential and realized reproduction by different worker castes in queen-less and queen-right colonies of Pogonomyrmex badius

Abstract

Workers of the Florida harvester ant (Pogonomyrmex badius), the only North American Pogonomyrmex with a polymorphic worker caste, produce males when colonies are orphaned. In this study, we assessed the reproductive potential of workers of each caste group, minors and majors, in the presence and absence of the queen, and tested whether males produced in natural queen-right colonies are derived from workers. Worker size was positively correlated with ovariole number such that major workers had approximately double the number of ovarioles as minor workers. The number of vitellogenic oocytes, a measure of reproductive potential, was greater in major compared to minor workers and increased in both worker castes when queens were removed. Major workers have greater reproductive potential than minors although they represent a minority within the colony (~5 % of workers are majors). Worker produced eggs were visible in colonies 28 -35 days after queen removal. This time lag, from queen removal to egg production, is similar to other ants and bees. Though workers are capable of producing viable eggs, we found no evidence that they do so in queen-right colonies, suggesting that worker reproduction is controlled via some social mechanism (self restraint, policing, or inhibition). This result supports predictions of kin selection theory -that due to multiple mating by the queen workers are more related to queen-produced males than most worker-produced males and should thus favor reproduction by the queen and inhibit reproduction by other workers.

Vitellogenin Underwent Subfunctionalization to Acquire Caste and Behavioral Specific Expression in the Harvester Ant Pogonomyrmex barbatus

“…In contrast to honeybee nurses which can produce fertile eggs in queenless conditions and sometimes even in the queen presence, workers are sterile in most Pogonomyrmex species [32]. However, Pogonomyrmex workers can produce trophic eggs which are thought to be the main method of nutrient redistribution because trophallaxis – mouth-to-mouth food transfer - has not been observed in this genus [32]. Interestingly, a recent study in Pogonomyrmex californicus showed that nurses had significantly increased ovarian activity compared to foragers [53], suggesting that trophic eggs are specifically produced by nurses.…”

“…In contrast to honeybee nurses which can produce fertile eggs in queenless conditions and sometimes even in the queen presence, workers are sterile in most Pogonomyrmex species [32]. However, Pogonomyrmex workers can produce trophic eggs which are thought to be the main method of nutrient redistribution because trophallaxis – mouth-to-mouth food transfer - has not been observed in this genus [32].…”

“…Vg duplication and subsequent subfunctionalization to acquire caste-specific expression provides a unique opportunity to test whether the genes associated with reproduction were co-opted to regulate worker behavior. Second, also in contrast with bees and wasps, where workers are facultatively sterile, workers are fully sterile in a significant number of ant species, including P. barbatus and S. invicta [30]–[32], which allows one to test the hypothesis that Vg reproductive function was co-opted to regulate behavior in species with fully sterile workers.…”

Colony fusion and worker reproduction after queen loss in army ants

“…Forsyth 1981;Wenseleers & Ratnieks 2006;Dijkstra & Boomsma 2007;Smith et al 2007). In some species, however, functionally monogynous colonies contain additional inseminated queens that can become reproductively active replacement queens after the original queen is lost (e.g.…”

The potential for worker reproduction in the ant Aphaenogaster cockerelli and its absence in the field

“…Power to detect worker reproduction Following the protocol of Smith et al (2007), we tested for evidence of linkage of the two loci used for this study. We used both haploid males and diploid workers to test for linkage disequilibrium in colonies where the queen genotype was heterozygous at both loci (four of the seven colonies).…”