Abstract
Social structure influences animal societies on various levels (e.g., relatedness, behaviour). In ants, both the number of matings per queen and the number of queens per colony can vary strongly. While workers from both monogynous and polygynous colonies often fight fiercely, in supercolonies (an extreme form of polygyny comprising thousands of queens in spatially separated but interconnected nests), non-nestmates interact peacefully. Studies on social and behavioural polymorphism within ant species can help elucidate their influence on genetic diversity and behaviour and the factors triggering variation in social structure and behaviour. Here, we reveal a behavioural and social polymorphism comprising monogyny with and without internest aggression in Tetramorium alpestre sampled in Tyrol, Austria. The social polymorphism is based on genetic and behavioural evidence and contrasts with the supercolonial organisation known from another location in Austria (Carinthia), 150 km away. Microsatellite genotyping using eight polymorphic loci revealed monogyny-monandry and high intranest pairwise relatedness. Interestingly, various experimental one-on-one worker encounters revealed only occasional aggressive behaviour between monogynous colonies, and thus a behavioural polymorphism. Mantel tests revealed a significant negative correlation between spatial distance and relatedness, while worker behaviour was not correlated with relatedness or spatial distance. These results indicate that behaviour might be influenced by other factors – for example, the experience of workers, ecological, chemical, and/or genetic factors not characterised in this study. However, workers distinguished nestmates from non-nestmates also when aggression was lacking. We hypothesise an adaptive value of reduced aggression. We speculate that the non-aggressive and partly aggressive encounters observed represent different options in the social structure of T. alpestre, the non-aggressiveness possibly also promoting supercolony development. The social and behavioural polymorphisms observed offer opportunities to identify the factors triggering these changes and thus further explore the behavioural and social polymorphism of this ant species.
Highlights
Social structure varies greatly among animal societies
We investigate the Alpine ant Tetramorium alpestre (Steiner et al 2010), which is known to be supercolonial in Carinthia (Steiner et al 2003) and thought to form monogynous-monodomous colonies in Tyrol, based on field observations
A two-sided t-test was calculated in R using the total antennation time from intranest and non-aggressive internest encounters to detect differences regarding worker discrimination. For both subsets, MICROCHECKER revealed the possible presence of null alleles in locus 55a, which was excluded from further analyses
Summary
Social structure varies greatly among animal societies. The number of reproductive individuals shapes its genetic diversity (Hughes et al 2008). Ants are among the most abundant and ubiquitous organisms in the world (Alonso 2009). Social structure varies, which is termed social polymorphism (Gyllenstrand et al 2002). Gynes either mate once (monandry) or multiply (polyandry), and males may mate with one or several gynes (Heinze 2008). Colonies are headed by one single queen (monogyny) or by several queens (polygyny; SchmidHempel & Crozier 1999), and monogynous and polygynous colonies can live in either one nest (monodomy) or two or more nests simultaneously (polydomy; Crozier & Pamilo 1996)
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