Queen–worker caste ratio depends on colony size in the pharaoh ant (Monomorium pharaonis)

Abstract

The success of an ant colony depends on the simultaneous presence of reproducing queens and nonreproducing workers in a ratio that will maximize colony growth and reproduction. Despite its presumably crucial role, queen-worker caste ratios (the ratio of adult queens to workers) and the factors affecting this variable remain scarcely studied. Maintaining polygynous pharaoh ant (Monomorium pharaonis) colonies in the laboratory has provided us with the opportunity to experimentally manipulate colony size, one of the key factors that can be expected to affect colony level queen-worker caste ratios and body size of eclosing workers, gynes and males. We found that smaller colonies produced more new queens relative to workers, and that these queens and workers both tended to be larger. However, colony size had no effect on the size of males or on the sex ratio of the individuals reared. Furthermore, for the first time in a social insect, we confirmed the general life history prediction by Smith and Fretwell (Am Nat 108:499-506, 1974) that offspring number varies more than offspring size. Our findings document a high level of plasticity in energy allocation toward female castes and suggest that polygynous species with budding colonies may adaptively adjust caste ratios to ensure rapid growth.

Artificial selection on ant female caste ratio uncovers a link between female‐biased sex ratios and infection by Wolbachia endosymbionts

“…There was a small effect of generation ( F 2,335 = 3.62, P = 0.028) and a strong effect of total colony productivity ( F 1,334 = 15.52, P < 0.001), confirming that caste ratio is lower (i.e. more workers relative to gynes) in more productive colonies (Schmidt et al ., ). All the other terms in the model were nonsignificant (see R scripts in Appendix S3).…”

“…initial queen number, which can have cascading effects on colony productivity, caste ratio and sex ratio, etc. ; see Table S3 in Appendix S1 and Schmidt et al ., ). Specifically, we note that colonies in one replicate low line (‘Low2’) in the last generation of selection did not show consistent sex ratio differences compared to the previous generations (Fig.…”

“…In May 2009, we dequeened the colonies to trigger sexual production (Schmidt et al, 2011b). After 4 weeks, we surveyed colonies every 5 days and counted and removed worker, gyne (i.e.…”

Genomic Signature of Kin Selection in an Ant with Obligately Sterile Workers

“…Queen removal stimulates the production of new reproductives (i.e., new queens and males) (Edwards 1987; Schmidt et al 2010) so that following queen removal, a portion of young brood (eggs and first instar larvae) are reared as reproductives, whereas all older brood are reared as workers.…”

Eusocial insects as emerging models for behavioural epigenetics

“…However, in a few species -such as the parthenogenetic honeybee subspecies Apis mellifera capensis 132 , the Halictid bee (also known as the sweat bee) Lasioglossum albipes 35 , the ponerine ant Harpegnathos saltator 28 and the doryline ant Cerapachys biroi 34 -all individuals are capable of laying female eggs. In addition, a large percentage (~25%) of queen-destined brood can be experimentally produced in the pharaoh ant species Monomorium pharaonis 141 . Moreover, in honeybees, queens can be reared by placing embryos in honeycomb cells that are specially prepared for queens 128 .…”