Population and colony structure and morphometrics in the queen dimorphic harvester ant, Pogonomyrmex pima

Abstract

The North American seed-harvester ant Pogonomyrmex (Ephebomyrmex) pima displays a dimorphism that consists of winged (alate) and wingless (intermorph) queens; both types of queens are fully reproductive. Microsatellite allele frequencies and a mitochondrial phylogeny demonstrate (1) alate and intermorph queens represent an intraspecific wing polymorphism, and (2) an absence of assortative mating and inbreeding by males. Surveys at our field site in southcentral Arizona, USA, demonstrated that only one type of queen (intermorph or dealate) occurred in each colony, including those excavated during the season in which reproductive sexuals were present. Colony structure appeared to vary by queen type as most intermorph colonies contained multiple mated queens. Alternatively, dealate queen colonies rarely contained a mated queen. Our inability to find mated dealate queens in these colonies probably resulted from difficulty in excavating the entire colony and reproductive queen, especially given that these colonies were only excavated over one day.A morphometric analysis demonstrated that intermorph queens are intermediate in size to that of workers and alate queens, but that intermorph queens retain all of the specialized anatomical features of alate queens (except for wings). Some colonies had queens that foraged and performed nest maintenance activities, and these queens sometimes accounted for a significant portion of colony foraging trips. Dissections revealed that these queens were uninseminated; some of these queens produced males in the laboratory.

Seasonal cycle of the nest composition in the Ponerine ant Cryptopone sauteri (Hymenoptera: Formicidae)

“…Five hypotheses on the presence of unmated queens have been proposed to date: producing trophic eggs, producing male-destined eggs, working queens, failure of nuptial flight and postponement of reproduction (Vargo 1993;Bourke & Franks, 1995;Brown 1999;Kikuchi & Tsuji, 2005;Johnson et al 2007). Yamaguchi et al (2016) suggested that the two possibilities (failure of nuptial flight or postponement of reproduction) are plausible for explaining the presence of unmated queens in C. sauteri, because the unmated queens had neither egg laying nor labor.…”

Phylogenetic Relationships among Populations ofVollenhoviaAnts, with Particular Focus on the Evolution of Wing Morphology

“…The two queen morphs had similar allele distributions for four microsatellite loci; they were clustered in each population, showing that the two queen morphs could be regarded as the same species. In the harvester ant Pogonomyrmex pima Wheeler with winged and wingless queens, Johnson et al (2007) showed that these two queen phenotypes belonged to the same gene pool and the same mitochondrial clade. Some winged and wingless queens had identical mitochondrial haplotypes.…”

The dimorphic queens of Polyrhachis australis (Hymenoptera: Formicidae)

“…In the case of different wing sizes, the extreme condition of co-existing wingless and winged queen morphs is found in a number of species, e.g. Ephebomyrmex (now Pogonomyrmex) imberbiculus (Heinze et al 1992) and Pogonomyrmex pima (Johnson et al 2007). Female dimorphism has been found (rarely) in taxa other than social insects, e.g.…”

“…Although a dual reproductive strategy is not the only interpretation (see, e.g. Ribeiro et al 2006 Heinze 1999;Heinze & Keller 2000;Howard 2006;Johnson et al 2007;Howard & Jeanne 2013).…”