Similar to much basic research, this project does not directly translate into jobs or societal changes. The benefits are to science and to training undergraduate and graduate researchers. As part of this project, I have advised 18 undergraduates doing research, resulting in five Senior Honors Theses, four co-authorships, two presentations by undergraduates at national meetings, and 12 research presentations with undergraduate co-authors. Two undergraduates have come to Australia to do research with me. Three of my undergraduate researchers have received National Science Foundation Graduate Research Fellowship Program awards, in large part due to their research experience on this project.
impact statement issue
Why do some animals live in social groups while others are solitary? Throughout Animalia are examples of closely related taxa in which the majority of species live essentially solitary lives, while a few species have evolved to live in cooperative social groups. What factors make cooperation beneficial although closely related species succeed without those benefits? How do physiological and ecological constraints interact so that group-living becomes more beneficial than a solitary life style?
These questions are at the essence of understanding the costs and benefits of group-living in animals. These issues are particularly interesting in the spiders, which are all predators and typically cannibalistic. Only 1 percent of all spiders live in social groups. I am interested in the behavioral, developmental, and physiological changes that make group-living successful in essentially cannibalistic animals, because this information can be used to help understand the mechanisms behind sociality in other animals.
impact statement response
In laboratory studies we compared the development, early interactions in mother-offspring-sibling groups, patterns of prey sharing, rates of cannibalism, and metabolic rates in 14 solitary huntsman species with social Delena. Developmental patterns differ dramatically: all species emerge from egg sacs in the second instar, but all solitaries immediately molt to a more mobile and predatory third instar within hours, while Delena remains second instar for 10-plus days. Older Delena young remain closely associated with their mother and older siblings up to and beyond sexual maturity. Immature Delena delay dispersal from the natal retreat and share prey with their siblings and mother. In contrast, the solitary species explosively disperse by the fourth or fifth instar, only share prey with their siblings during the youngest instars, never acquire large prey from their mother, and regularly cannibalize each other.
Experiments comparing resting metabolic rate in four solitary huntsman species and Delena demonstrated that all of the solitary huntsman species have significantly higher metabolic rates than that of Delena, suggesting that large colonies of Delena could survive on less prey than comparable groups of the other species. Experimental comparison of growth and survival of young Delena and three solitary species in solo and group treatments demonstrated that the costs of being in groups were negligible for young Delena, but highly detrimental for other species.
In summary, there are many social benefits of group-living for young Delena combined with reduced costs; comparable benefits and cost reductions are not seen in the solitary huntsman species.
impact statement summary
Evolution of sociality must involve adaptive benefits to offset the costs of living closely with competitors, especially among potentially cannibalistic predators such as spiders. These adaptations may involve behavioral, ecological, and physiological strategies for living in groups.
Linda S. Rayor and her students have closely studied social and solitary species of Australian huntsman spiders to determine whether there are major differences in their behavior, life-history, ecology, or physiology that can explain why some are social. Her results demonstrate that even in closely related, similar species in the same habitats, there are consistent major biological differences that make group-living a successful strategy for certain species but a disastrous strategy for other species.
The research is important because they are discovering general patterns which are likely to be helpful in understanding why group-living occurs in both invertebrate and vertebrate carnivores.
