Burton, R.S. (1987). Differentiation and integration of the genome in populations of the marine copepod Tigriopus californicus. Evolution 41(3):504-513.

80086

Burton, R.S.

1987

41(3):504-513.

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Geographically separated populations of the intertidal copepod Tigriopus californicus are sharply differentiatedat several enzyme-encodinggene loci. Two studies were performed to investigatethe extentto whichthegene pools of local populationsare organizedintoharmoniously interacting(or "coadapted") genecomplexes. In thefirst,theeffectsof interpopulationhybridization on development time were assessed. Results showed that while F, hybrids did not differfrom parentallines, mean F2 developmental times were as much as 50% longer. The second study used two unlinked enzymepolymorphisms as genetic markers to determine the genotypicspecificity of F2 hybridbreakdown. For two sets of parentalpopulations,the relativeviabilities of the different two-locus genotypes were determined from segregation ratios among the F2 progeny.Sharp deviations fromMendelian ratios were observed; in the extreme, a block of genes marked by the Me-' allozyme fromthe LJ (La Jolla) population was foundto be nearly lethalwhen homozygous in the F2 of LJ x AB (Los Angeles) crosses. This same block of genes had a tenfoldhigherviability in crosses between LJ and SC (Santa Cruz). In the AB x LJ crosses, the two marker loci had independent(multiplicative) effectson viability. In the SC x LJ crosses, deviations from the multiplicativemodel were observed; the data indicate that parental homozygousgenotypeshave higherviabilitythan predicted by independence, while nonparental homozygoteshave lowerthan predictedviability. These results suggest that substantial integration of the genome has occurred within natural T. californicus populations.

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