Evol Ecol Res 9: 341-354 (2007) Full PDF if your library subscribes.
Ecological selection and hybrid fitness: hybrids succeed on parental resources
Karin S. Pfennig,* Amanda J. Chunco and Alycia C.R. Lackey‡
Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
Author to whom all correspondence should be addressed.
Hypothesis: Interspecific hybrids are competitively inferior to their parents because they possess intermediate phenotypes that are poorly adapted to either parent’s niche.
Organisms: Spadefoot toads, Spea multiplicata and S. bombifrons.
Methods: Where they co-occur, tadpoles of S. multiplicata and S. bombifrons specialize on different resources (detritus and anostracan fairy shrimp, respectively). This pattern reflects ecological character displacement promoting divergence in resource use to minimize resource competition between these species. We asked whether hybrids between these species are competitively inferior for parental resources. We used a paired design to measure growth of hybrid tadpoles in the laboratory when reared in competition with pure-species tadpoles (the experimental treatment) versus when reared with siblings (the control). In separate tests we also measured: (1) foraging behaviour of hybrid and pure-species tadpoles; (2) facultative shifts in foraging behaviour by hybrids; and (3) competitive ability for the resource (shrimp) on which S. bombifrons tadpoles specialize.
Results: Hybrid tadpoles grew as well or better when reared in competition with pure-species tadpoles than when reared with siblings. In terms of foraging behaviour, hybrid tadpoles exhibited a wider range of phenotypes than either pure-species type. Hybrids therefore may be able to utilize resources of both parent species. Generally, the occurrence of novel hybrid phenotypes could prevent speciation if, contrary to the ecological selection hypothesis, the greater range in hybrid phenotypes enables them to occupy both parents’ niches.
Keywords: competition, ecological speciation, hybridization, reinforcement, reproductive isolation.
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