The Adaptiveness of Worker Demography in the Attine Ant Trachymyrmex Septentrionalis

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Caste theory states that worker size distributions in ant colonies have evolved for efficient division of labor and predicts that they should vary with habitat and have an effect on fitness. We tested these predictions in a comparative study of worker size variation and colony fitness in Florida and Long Island populations of Trachymyrmex septentrionalis. Colonies from the two populations were excavated shortly before the time of the mating flights, so that workers and reproductive forms could be censused. We measured worker head widths in each colony and analyzed the resulting size frequency distributions using the mean, standard deviation, skewness, and kurtosis, and also principal components derived from these parameters. Size frequency distributions were unimodal and close to normal, with a tendency to negative skewness. Colonies in the Long Island population had both larger workers and greater size variation than those in Florida. Florida colonies followed a growth trajectory in which the mean and standard deviation of worker head width both increased with colony size, whereas in Long Island there was an inverse relationship between the mean and standard deviation that was independent of colony size. Analysis based on the principal components showed that worker size variation significantly affected fitness in both populations, and this was not a secondary effect of colony size. Population differences in colony life history strategies may account for the observed patterns: the Long Island population appears to be adapted for surviving the winter diapause, while the Florida population has experienced different selective pressures, possibly for rapid colony growth. Size variation that has evolved in the context of life history strategies may serve as a preadaptation for division of labor.

The Achilles' heel hypothesis: misinformed keystone individuals impair collective learning and reduce group success

“…A similar magnitude of effect was observed regardless of whether or not the trained individual was a keystone individual, and these effects lasted for a moderate number of trials (trial nos. [4][5][6][7][8][9][10]. All colonies, regardless of treatment, eventually converged on a similar latency to attack the prey stimulus by the end of our experiment ( figure 1).…”

Eusocial insects as superorganisms

“…They reveal a need for mechanisms underlying the flux, storage, and turnover of energy in these groups. Many factors may contribute to the sub-linear scaling because as colony sizes increase (ontogenetically and/or comparatively across species), so frequently does worker size, [18][19][20][21] polymorphism [22][23][24] and the division of labor. 25,26 Each may lead to a decrease of per-capita energy consumption of individuals…”

Alternative strategies by thermophilic ants to cope with extreme heat: individual versus colony level traits

“…Whether a species' size range is restricted or expanded over evolutionary time will depend on the selection pressures imposed on it (Wheeler 1991). The increase in worker size range is presumed to benefit colony fitness by allowing the colony to perform certain tasks more efficiently than it could if only one size of workers were present (Oster and Wilson 1978, Beshers and Traniello 1994, Retana and Cerdá 1994. Major workers of various ant species appear to arise as specialists for very few primary tasks, such as the transport of heavy loads (Franks 1986, Waller 1989, Wetterer 1994, Retana and Cerdá 1994, food storage (Rissing 1984) or defence (Wilson 1976).…”