Convergence Patterns in Subsocial Insects

Subsocial behavior is the most primitive level of social interaction involving parents and offspring (79). Although preovipositional behaviors such as nest construction (48, 77) or various resource manipulations (10, 162) eventually benefit offspring, subsociality by definition is restricted to postovipositional parental behavior that promotes the survival, growth, and development of offspring (33). Insect parental adaptations comprise a continuum of care rang­ ing from passive egg guarding to an array of complex grooming, feeding, protective, and nesting behaviors (for comprehensive reviews see 33, 54, 171). Although levels of complexity are diverse, parental care can be categorized into three primary behaviors: (a) those that physically protect the young from danger, (b) those that protect resources vital to offspring, and (c) those that facilitate offspring feeding. The effectiveness of these behaviors in neutralizing or alleviating conditions detrimental to young is evidenced by their repeated convergence throughout vastly different animal lineages (30, 62, 73, 125, 157, 159, 168). In the insects, parental behavior lies at the core of all levels of insect sociality and has arisen independently in at least 13 different orders (33). Wilson (172) has identified four environmental "prime movers" that create conditions favorable to the evolution of parental care: stable or structured environments, physically stressful environments, rich and ephemeral re­ sources, and predation. He proposed that in different ways each prime mover produces demographic consequences that promote parental care. There is little doubt that reproductive losses from predation, competition, or physical harsh­ ness can be reduced by subsocial interactions between parents and their young.