Wednesday, December 13, 2006 - 1:47 PM

Nest density correlates with queen size and queen founding behavior in the queen-polymorphic ant Temnothorax longispinosus

Kenneth J Howard, and Robert L Jeanne, University of Wisconsin - Madison, 546 Russell Labs, 1630 Linden Dr, Madison, WI

Many characteristics of social insect colonies correlate with their nest-founding strategy, generally characterized as either dependent founding, in which queens begin raising offspring with the help of workers in established nests, or independent founding, in which queens initiate new nests on their own. Several factors favor the dependent strategy over the independent strategy, including competition for limited nest sites, independent queen mortality due to harsh conditions or predation, and the size or degree of isolation of favorable habitat. We related nest-founding behavior of several populations of the ant Temnothorax longispinosus to nest densities by measuring queen body size, fat content, ability to independently found, and the number of queens and female alates per nest at each site. This species has three queen-size morphs, but the largest morph is relatively rare and not easily identified following wing-loss, so we lumped the two larger morphs together and calculated the proportion of large-to-small queens for each collection site. We found significantly higher queen numbers per nest at higher-density sites, while the proportion of large-to-small queens, number of female alates produced, and mean fat content of females were all lower. In addition to being less frequently produced, large females from high-density sites forced to found independently in the lab had lower survival and produced less brood than large females from low-density sites. Queen presence is known to lead to increased production of the small queen morph, so queen effects could function as a critical link in these populations between environmental conditions, in this case high nest densities, and a developmental response such as the production of dependent-founding queens. Consistenly high nest densities may have led to the evolution of greater specialization for dependent founding, such as reduced stored resources in large queens.

Species 1: Hymenoptera Formicidae Temnothorax longispinosus

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