Sequential divergence and the multiplicative origin of community diversity.
Phenotypic and genetic variation in one species can influence the composition of interacting organisms within communities and across ecosystems. As a result, the divergence of one species may not be an isolated process, as the origin of one taxon could create new niche opportunities for other species to exploit, leading to the genesis of many new taxa in a process termed "sequential divergence." Here, we test for such a multiplicative effect of sequential divergence in a community of host-specific parasitoid wasps, Diachasma alloeum, Utetes canaliculatus, and Diachasmimorpha mellea (Hymenoptera: Braconidae), that attack Rhagoletis pomonella fruit flies (Diptera: Tephritidae). Flies in the R. pomonella species complex radiated by sympatrically shifting and ecologically adapting to new host plants, the most recent example being the apple-infesting host race of R. pomonella formed via a host plant shift from hawthorn-infesting flies within the last 160 y. Using population genetics, field-based behavioral observations, host fruit odor discrimination assays, and analyses of life history timing, we show that the same host-related ecological selection pressures that differentially adapt and reproductively isolate Rhagoletis to their respective host plants (host-associated differences in the timing of adult eclosion, host fruit odor preference and avoidance behaviors, and mating site fidelity) cascade through the ecosystem and induce host-associated genetic divergence for each of the three members of the parasitoid community. Thus, divergent selection at lower trophic levels can potentially multiplicatively and rapidly amplify biodiversity at higher levels on an ecological time scale, which may sequentially contribute to the rich diversity of life.
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556; ghood@nd.edu.
Glen R
GR
Hood
Department of Biology, University of Iowa, Iowa City, IA 52242;
Andrew A
AA
Forbes
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556; Department of Entomology and Nematology, University of Florida, Gainesville, FL 32611;
Thomas H Q
TH
Powell
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556; Environmental Change Initiative and Advanced Diagnostics and Therapeutics, University of Notre Dame, Notre Dame, IN 46556; Department of Biosciences, Anderson Biological Laboratories, Rice University, Houston, TX 77005;
Scott P
SP
Egan
Department of Biology, University of Iowa, Iowa City, IA 52242;
Gabriela
G
Hamerlinck
Department of Entomology and Lyman Briggs College, Michigan State University, East Lansing, MI 48824.
James J
JJ
Smith
Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556; Environmental Change Initiative and Advanced Diagnostics and Therapeutics, University of Notre Dame, Notre Dame, IN 46556;
Jeffrey L
JL
Feder
D000818:Animals; D004272:DNA, Mitochondrial / Q000235:genetics; D018895:Microsatellite Repeats / Q000235:genetics; D008969:Molecular Sequence Data; D014863:Wasps / Q000145:classification / Q000235:genetics / Q000502:physiology*
D004272:DNA, Mitochondrial
Rhagoletis; ecological speciation; host plant adaptation; parasitoid; tritrophic interactions