ABSTRACT
In Parus major, P. caeruleus, and P. ater the genetic variation of 16 isozyme loci was determined. The focus was on esterases that show high phenotypic variation in natural populations of these species. The degree of heterozygosity of the "non-esterase" loci was 0.029 +/- 0.008 (P. major); 0.023 +/- 0.012 (P. caeruleus), and 0.034 +/- 0.034 (P. ater). Including the esterase loci with up to six alleles per locus the overall degree of heterozygosity increased to 0.130 +/- 0.056 (P. major); 0.143 +/- 0.067 (P. caeruleus), and 0.194 +/- 0.090 (P. ater). We explain the high level of variability of esterases by gene amplification and subsequent selection for high allelic heterogeneity. Substrate specificity of loci is assumed to allow for multiple resistance against various toxic components. Large allelic valiation of esterases, therefore, increases the fitness of Parus species and allows for utilizing new food resources.
Subject(s)
Esterases/genetics , Genetic Variation , Genetics, Population , Songbirds/genetics , Alleles , Animals , Electrophoresis, Polyacrylamide Gel , Gene Amplification , Germany , Heterozygote , Isoelectric Focusing , Isoenzymes/genetics , Isoenzymes/metabolism , Polymorphism, Genetic , Retrospective Studies , Selection, Genetic , Species Specificity , Substrate SpecificityABSTRACT
Huxley's rule predicts lower recombination rates in the heterogametic sex than in the homogametic one. The genotyping of Parus major and P. caeruleus families at 8 microsatellite and 4 enzyme loci yielded contradicting data. Significant genotypic disequilibrium was observed between esterase-1, esterase-2 and esterase-3 in adults of P. major and between esterase-2/esterase-3 and esterase-2/microsatellite PK-12 in P. caeruleus. Support comes from linkage analyses of nuclear families. In P. major, the recombination rate of esterase-2/esterase -3 in males is significantly lower than in females (theta(male) = 0.076, theta(female) = 0.145). The opposite is found for the recombination rates of esterase-1/esterase-2 and esterase-2/esterase-3 in P. caeruleus (EST-1/EST-2: theta(female) = 0.218, theta(male) = 0.5, EST-2/EST-3: theta(female) = 0.109, theta(male) = 0.194). We conclude that the basis of differences in recombination rates cannot be heterogamety, per se, but must have multiple genetic causes including chromosomal rearrangments that have evolved after the cladogenesis of the two species.
