Near-infrared spectroscopy identifies the colony and nest of origin of weaver ants, Oecophylla smaragdina

The ability of social insects to differentiate between colony members and others is essential for the survival of the colony. It enables individuals to direct altruistic behavior towards colony mates, while protecting the colony from intruders. Colonies have a distinct chemical signature that facilitates colony-mate recognition. However, in large polydomous colonies, this signal is likely to be modified by factors unique to each nest. We demonstrate, using near-infrared spectroscopy (NIRS), that individual weaver ants, Oecophylla smaragdina, can be differentiated with respect to their colony and nest of origin. 76.5% of individuals from four colonies could be correctly assigned to their colony of origin; and 79.6% of individuals could be assigned to the correct nest (of two) within their colony. Despite the differences between nests within colonies, in most cases individuals from one nest were more similar to individuals from the other nest within the colony than they were to individuals from any nest outside the colony. Therefore, a distinctive colony identity is maintained despite differences between nests within colonies. We discuss the advantages of using NIRS as a faster and less expensive alternative to the analysis of cuticular hydrocarbons following extraction and identification with gas chromatography/mass spectroscopy

Social and genetic structure of a supercolonial weaver ant, Polyrhachis robsoni, with dimorphic queens

We studied a population of the Australian weaver ant Polyrachis robsoni with regard to variation in the morphology of its winged queens using six newly-developed microsatellite markers. Morphometrically the queens fell clearly into two groups, macrogynes and microgynes, with the latter an isometric reduction of the former. Aggression tests showed that hostility between ants from different nests was minimal. Nests frequently contained numbers of both queen types, with microgynes about twice as numerous as macrogynes. Nestmate workers, microgynes, and macrogynes, were significantly related to others within their caste, with macrogynes more highly related than the other castes. Relatedness values between these groups of nestmates were also significant. Pairwise relatedness values were consistent with both queen morphs producing workers. At the population level, microgynes from different nests were also significantly related and there was a weak inverse relationship between pairwise relatedness value between individuals and distance between nests. We conclude that this species is supercolonial and that the two queen morphs are part of the same population

Social and spatial organisation in colonies of a primitively eusocial wasp, Ropalidia revolutionalis (de Saussure) (Hymenoptera: Vespidae)

We investigated individual reproductive flexibility and the division of labour in five post-emergence colonies of the primitively eusocial wasp Ropalidia revolutionalis, by relating behavioural observations of individuals at the nest to their ovarian development. Analysing time-activity budgets with principal components and canonical discriminant analysis revealed three distinct groups of individuals, based on their spatial distribution relative to the nest. Individuals could be assigned to a group based on: whether they spent most of their time near or away from the nest (first principal component, 75% variance); whether they sat on or next to the comb when in the nest vicinity (second principal component, 16% variance); or whether they sat on or off the capped cells (that contain pupae) when sitting on the combs themselves (third principal component, 6% variance). Colonies had either one or two reproductive individuals, but the distinct groups they belonged to could vary. In three monogynous colonies reproductive individuals spent the majority of their time sitting on capped cells. In two polygynous colonies, primary reproductives were also located on capped cells but the secondary reproductives, with smaller oocytes, were located either next to the nest or on the capped cells of a second comb. In all colonies levels of aggressive interactions were low. These findings indicate that spatial position is an important component of social organisation and that there are multiple pathways through which an individual can achieve reproductive dominance. Finally, comparison with other Ropalidia species shows that the pattern of social organisation varies in this wasp genus

Breeding system, colony and population structure in\ud the weaver ant Oecophylla smaragdina

Weaver ants (Oecophylla smaragdina) are dominant ants in open forests from India, Australia,\ud China and Southeast Asia, whose leaf nests are held together with larval silk. The species,\ud together with its sole congener O. longinoda, has been important in research on biological\ud control, communication, territoriality and colony integration. Over most of the range, only\ud one queen has been found per colony, but the occurrence of several queens per nest has\ud been reported for the Australian Northern Territory. The number of males mating with\ud each queen is little known. Here we report on the colony structure of O. smaragdina using\ud published and new microsatellite markers. Worker genotype arrays reflect the occurrence\ud of habitual polygyny (more than one queen per colony) in 18 colonies from Darwin, Northern\ud Australia, with up to five queens inferred per colony. Monogyny (one queen per colony)\ud with occasional polygyny was inferred for 14 colonies from Queensland, Australia, and 20\ud colonies from Java, Indonesia. Direct genotyping of the sperm carried by 77 Queensland\ud queens and worker genotypic arrays of established colonies yielded similar results, indicating\ud that less than half of the queens mate only once and some mate up to five times.\ud Worker genotype arrays indicated that queens from Java and the Northern Territory also\ud often mate with more than one male, but less often than those from Queensland. A strong\ud isolation-by-distance effect was found for Queensland samples. The variation uncovered\ud means that O. smaragdina is a more versatile study system than previously supposed

Colony genetic structure in the Australian jumper ant Myrmecia pilosula

Eusocial insects vary significantly in colony queen number and mating frequency, resulting in a wide range of social structures. Detailed studies of colony genetic structure are essential to elucidate how various factors affect the relatedness and the sociogenetic organization of colonies. In this study, we investigated the colony structure of the Australian jumper ant Myrmecia pilosula using polymorphic microsatellite markers. Nestmate queens within polygynous colonies, and queens and their mates, were generally unrelated. The number of queens per colony ranged from 1 to 4. Queens were estimated to mate with 1–9 inferred and 1.0–11.4 effective mates. This is the first time that the rare co-occurrence of polygyny and high polyandry has been found in the M. pilosula species group. Significant maternity and paternity skews were detected at the population level. We also found an isolation-by-distance pattern, and together with the occurrence of polygynous polydomy, this suggests the occurrence of dependent colony foundation in M. pilosula; however, independent colony foundation may co-occur since queens of this species have fully developed wings and can fly. There is no support for the predicted negative association between polygyny and polyandry in ants