Evidence for the Absence of Worker Behavioral Subcastes in The

Hindawi Publishing Corporation Psyche Volume 2014, Article ID 232057, 7 pages http://dx.doi.org/10.1155/2014/232057 Research Article Evidence for the Absence of Worker Behavioral Subcastes in the Sociobiologically Primitive Australian Ant Nothomyrmecia macrops Clark (Hymenoptera: Formicidae: Myrmeciinae) Robert W. Taylor1,2 1 ARC Center of Excellence in Vision Science, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia 2 CSIRO Ecosystem Sciences, Canberra, ACT 0200, Australia Correspondence should be addressed to Robert W. Taylor; [email protected] Received 27 November 2013; Revised 2 March 2014; Accepted 20 May 2014; Published 18 June 2014 Academic Editor: Jacques Hubert Charles Delabie Copyright © 2014 Robert W. Taylor. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Activity in three colonies of the nocturnally foraging Australian ant Nothomyrmecia macrops is investigated. Workers apprehended while foraging were marked, released, and later recaptured within nests following excavation. Every forager in each nest was encountered and marked. It was expected that unmarked, nonforaging, domestic-specialist workers would be discovered in the nests. This was unexpectedly not the case as all workers, apart from one or two in each colony, had been marked, and therefore had foraged at least once during the three-night experiment. The few unmarked individuals are considered to have been temporarily residential nest-entrance guards. Behavioral subcastes comprising “domestic” versus “foraging” workers were thus not indicated, evidencing absence of worker caste polyethism in Nothomyrmecia. The experiment predated emergence in the nests of adult workers from cocoon-enclosed pupae at a season when large feeding larvae of the current annual brood were still being provisioned by foragers. Because Nothomyrmecia is univoltine and emergence of current-brood adults had not yet occurred, all workers present were from preceding annual broods and defined as “postjuvenile.” A previous laboratory study separately evidenced absence of polyethism in Nothomyrmecia. Relevance of the apparent absence of food sharing in N. macrops is discussed. DedicatedtothememoryofRogerBartell(1940–1985)esteemedfriendandcolleagueinmuchNothomyrmeciafieldwork 1. Introduction Nothomyrmecia macrops Clark (subfamily Myrmeciinae), seeking to determine whether or not dedicated domestic Following evolution of the gyne/queen and worker castes versus specialist foraging subcastes were differentiated among in ants, task specialization (division of labor or polyethism) Nothomyrmecia workers. The negative alternative was clearly among workers would likely early have involved distinction evidenced. between (1) intranidal domestic functions and (2) extranidal food-collecting activities. This could encourage situations Phylogenetically N. macrops is a member of the myrme- where workers operated either asdomesticsorasforagers,(1) ciomorph group of subfamilies in the formicoid clade [6, 7]. intermittently, (2) in age-based succession, or (3) in either role It appears to have retained many behavioural and sociobio- essentially for life (thus comprising two behavioral subcastes logical traits considered ancestral for ants as a whole [8, 9], exemplifying caste polyethism)(see[1–5]). and it lacks many of the sociobiologically advanced features The experiment reviewed here investigated the relativities knowninotherants[8, 9]. of intranidal versus extranidal activity among workers in The absence of caste polyethism has been previously three colonies of the Australian endemic Dinosaur Ant reported in only one other ant species, the “sociobiologically 2 Psyche primitive” Stigmatomma pallipes (Haldeman) (Amblyoponi- workers would possibly be lost during their first experience of nae) [10] (discussed there as Amblyopone pallipes, nomencla- winter colony dormancy, when foraging for prey by workers ture here follows Yoshimura and Fisher [11]). Alternatively, and behavioral acts related to eggs, actively feeding larvae or the Nothomyrmecia-related, evidentially more sociobiologi- pupae are suspended. cally derived, myrmeciines Myrmecia brevinoda Forel [12], The Nothomyrmecia colonies studied here were consid- and M. gulosa (Fabricius) have bimodally size-ranged poly- ered to be at least 3 or 4 years old (based on their worker morphic workers. In M. gulosa colonies the smallest workers numbers, and that their experimentally marked active nest associate with the queen, eggs and small larvae [13], and entrances had been noted approximately one and two years apparently never leave the nests [14 and pers. obs]. They previously). Whether their oldest workers were survivors appear to constitute a nest-bound non-foraging domestic from the initial founding brood is not known. All workers worker sub-caste. present, however, would have been postjuvenile and more Most ants, including Nothomyrmecia, Myrmecia, and than 10 or 11 months old, given that the current nearly Stigmatomma, maintain perennial univoltine colonies [9]. mature ca 1-year-old annual brood comprised large larvae and In general, a single annual brood is reared from eggs laid cocoon-enclosed pupae and had not yet produced (prospec- by queens during a few weeks in spring. Development to tively juvenile) adults. Two, three, or more annual age cohorts adulthood takes around 12 months. The growing larvae are are estimated to have been represented. eventually overwintered and begin to pupate the following The experiment was conducted in mid-November, 48–54 spring, about a year after oviposition, at around the time eggs days after the vernal equinox, in Mallee Eucalyptus wood- of the next generation are being laid. Adult workers eclose land at 85 m elevation, just south of Poochera, South Aus- from pupation (prior to escaping pupal cocoons in the above tralia, about 600 m ESE of the Eyre Highway/Streaky Bay ∘ genera) during the late spring and summer, concluding at Road junction, at estimated coordinates 32 43 26.43 Sand ∘ around the autumn equinox. For this reason the presence 134 50 21.78 E. or absence and relative proportions of eggs, hatchling, and other small larvae, large larvae, and pupae vary seasonally, and there is a long autumn/winter period during which 2. Experimental Assumptions larvae of a single generation alone are present as brood in nests (and during which there is very little extranidal activity The following characteristics of Nothomyrmecia were by workers, apparently because the larvae do not feed in assumed when designing the experiment or relate to dis- winter, and prey collection is suspended [9]). Colonies in cussion of its results. All have been repeatedly observed spring contain eggs and recently hatched small larvae of the or experimentally demonstrated. (See also references latest generation, along with large previously overwintered [8, 9, 15–17].) old larvae and pupae of the preceding generation, with egg (1) Nests function independently of each other and there numbers declining as hatching proceeds and large-larval is no morphological polymorphism among workers. (2) Each numbersreducingaspupationprogresses.Astheseason nest has a single, obscure entrance hole about 4-5 mm in advances workers begin to eclose and escape from their pupal diameter. (3) At all times, night and day, single guard workers cocoons, and all emerge by late summer or early autumn, may be observed inside nest entrances. They emerge briefly leaving only part-grown larvae of the latest generation which following insertion of a disturbing filament or a live ant of are subsequently overwintered. These factors dictated the another species. (4) Foraging activity is strictly nocturnal. seasonal timing of the experiment described here. With the exception of assumption 11 below, Nothomyrmecia Univoltinism results in recruitment of a single cohort workers have never been observed naturally abroad in day- of newly emerged workers each year during summer and light. Departing foragers cross the ground promptly at dusk early autumn, covering the time from beginning to end of to ascend host trees on which they remain until returning eclosion of adults from pupation. Because of this, workers directly across the ground at dawn to home nests. (5) Foragers in mature colonies fall into discrete, usually morphologically depart nests en masse at dusk, emerging from the entrance, unidentifiable, age-cohorts, each on average approximately often partly queuing briefly in close single files, over a period one year younger than its predecessor. The number of worker of 10 to 20 minutes beginning at about the time they cease generations present in any particular nest is determined to be discernable by naked eye. (6) Each forager “head- by individual longevity and the age of the resident colony. scans” on leaving the nest entrance, apparently confirming Individuals of the earliest broods, including the first (initially or recording visual navigational landmarks. The head, which laid down by queens at colony foundation), would often is normally held parallel to the substrate, is pivoted slowly probably not survive to be represented in older colonies. from side to side over an angle of about 80–100 degrees for “Juvenile” Nothomyrmecia workers are defined here as upto20secondswhiletheantstandsotherwisemotionless adults under several months of posteclosion age,

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