Sister clade comparisons reveal reduced maternal care behavior in social cobweb spiders

Abstract

Animals living in cooperative groups experience fundamentally different environments than their nonsocial relatives, potentially changing the strength of natural selection on some aspects of their behavior. Using a comparative approach, we examined a potential example of this phenomenon: an association between reduced levels of maternal care behavior and sociality in cobweb spiders. We compared 6 different measures of maternal care behavior between species from 2 independently derived social clades and subsocial species from sister clades. In natural nests, we measured the mean distance between egg sacs and the nearest female and the proportion of egg sacs being attended. In the lab, we measured a female’s willingness to accept an egg sac, abandon her egg sac when disturbed, repair a damaged egg sac, and the speed at which a female reclaimed her egg sac when separated from it. Social species from both social clades scored significantly lower than subsocial species from sister clades on 6 and 4 of 6 of these assays of maternal care, respectively. We discuss alternative explanations of this pattern, including the potential role of relaxed natural selection in a social environment in permitting the evolution of a novel ‘‘low-parenting’’ phenotype. Key words: Anelosimus, cooperative breeding, evolution, maternal care, relaxed selection, social spider, sociality. [Behav Ecol]