Submitted to: Annual Review of Entomology
Publication Type: Abstract Only
Publication Acceptance Date: 5/23/1998
Publication Date: N/A
Technical Abstract: In evolutionary ecology, risk-spreading (-bet-hedging) is the idea that unpredictably variable environments favor genotypes with lower variance in fitness at the cost of lower mean fitness. Variance in fitness can be reduced by physiology or behavior that spreads risk in time or space. Such risk-spreading can be achieved by a single phenotype that avoids risks (conservative risk-spreading) or by phenotypic variation expressed by a single genotype (diversified risk-spreading). Across these categories, three types of risk-spreading may work under a broad range of population sizes, but within-generation risk-spreading appears to work only when populations are small. I review the types of evidence that could be used to test for risk-spreading and discuss evidence for risk-spreading in facultative diapause, migration polyphenism, spatial distribution of oviposition, egg size and other miscellaneous traits. Although risk- spreading theory is voluminous and well developed in some ways, rarely has it been used to generate detailed, testable hypothes about the evolution of risk-spreading. Although there is evidence for risk-spreading, particularly in facultative diapause, I have been unable to find any definitive tests with unequivocal results which have shown that risk- spreading has been a major factor in evolution of insect behaviors or life- histories. We need: (a) explicit empirical models that predict levels of diversifying risk-spreading for several insect populations in several environments which vary in uncertainty, (b) tests of these models using measurements of phenotypes and their fitnesses over several generations in each environment.