Ecophysiological responses in life-history evolution: evidence for their importance in a geographically widespread insect species complex

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Abstract
Geographical patterns of variation among North American populations of Chrysoperla carnea provide strong evidence that ecophysiological traits are central to the evolution of life histories. Selection pressure and the types and amounts of genetic variability underlying the traits vary geographically. Western populations exhibit considerable genetic variability in their reproductive responses to both photoperiod and prey. This variability is expressed both at the interpopulation level by the diversity of locally adapted populations and at the intrapopulation level in the form of genetic polymorphisms. By contrast, eastern, midwestern, and northwestern regions contain two types of reproductively isolated, monomorphic populations. The two types differ in their photoperiodic requirements for reproduction, but neither uses prey as a cue to stimulate reproduction. Although most of the characteristic responses to photoperiod and prey can vary independently of each other, the separate traits tend to covary to form coadaptive sets. The covariance of a few responses appears to have a genetic or physiological basis, a condition that places constraints on the evolution of life histories. Our results also demonstrate that comparative studies at the intraspecific level are highly significant to the analysis of life-history evolution and to the taxonomic treatment of species complexes.