The ecological and genetic basis of annual worker production in the desert seed harvesting ant, Veromessor pergandei

Analysis of ants’ rescue behavior reveals heritable specialization for first responders

“…In ants, some of the most diverse and abundant eusocial species (Brady et al, 2006), behavioral specializations vary greatly within and between species and include such common tasks as foraging, brood care, nest maintenance, waste management and defense of the colony (Hölldobler and Wilson, 1990;Robinson, 1992). Over the last few decades, a variety of increasingly sophisticated tools, from behavioral genetic techniques (Frumhoff and Baker, 1988) to molecular genetic markers (Grover and Sharma, 2016), have been used to demonstrate the heritability of task specialization in eusocial hymenopterans (Robinson and Page, 1988;Gordon, 2015;Friedman and Gordon, 2016;Robinson et al, 2005;Smith et al, 2008;Schlüns et al, 2011;Gotzek and Ross, 2007;Waddington et al, 2010;Jaffe et al, 2007;Leniaud et al, 2013;Julian and Fewell, 2004;Hughes et al, 2003;Wiernasz and Cole, 2010;Kwapich et al, 2017). Although most studies have focused on honeybeesindeed, some researchers have argued that behavioral genetic analyses of ants are much needed (Friedman and Gordon, 2016) genetic tools have been able to illuminate the critical role of polyandry in creating heritable task specializations and, thus, have helped solve an intriguing evolutionary puzzle.…”

The non-additive effects of body size on nest architecture in a polymorphic ant

“…Ants were foragers, collected from 13 colonies located in Casa Grande, AZ, USA, in September and October of 2017. Although never studied explicitly in this species, we chose foragers for a number of reasons that support their role in the establishment of new nests: across ant species, foragers are associated with the initiation of new nests [22][23][24]; we observed that foraging activity ceased or was strongly reduced when wild V. pergandei colonies excavated new nests; in a study of forager allocation across the annual cycle, marked foragers represented a large proportion of the excavating force; new nests were initiated along foraging routes and foragers were the only individuals to travel a substantial distance from the nest on these routes [18].…”

“…One clear outcome of polymorphism in our study was a relative increase in the rate of new nest growth. In xeric habitats, reducing exposure to surface temperatures by excavating a larger nest more rapidly could increase individual longevity, which averages just 18 days following the onset of foraging [18]. Many other colonylevel characteristics of V. pergandei depend on avoidance of desiccation [39].…”

“…Veromessor pergandei is a polymorphic seed harvesting ant of the Sonoran and Mojave deserts, and an ideal species for studying the interplay between worker variation and variation in nest architecture. Within colonies, large workers are more than two times the size of small workers, and the abundance and frequency of each body size varies considerably across populations [17], across seasons [14,15] (figure 1a) and with respect to colony identity (figure 1b,c) [18]. Body size does not predict the seed size that each individual collects, or the tendency of an individual to participate in nest excavation and foraging behaviour.…”

“…Body size does not predict the seed size that each individual collects, or the tendency of an individual to participate in nest excavation and foraging behaviour. Rather, changes in body size allow V. pergandei colonies to maintain a stable work force, despite seasonal variation in resource abundance [15,18]. The largest colonies maintain a large foraging force by dramatically reducing new worker body size following sexual reproduction.…”