The ecological genetics of two populations of the house sparrow, Passer domesticus
The biochemical genetics of two natural populations of house sparrows, Passer domesticus, at sites 20km apart in Nottinghamshire, England, were investigated. Seven polymorphic protein loci were sampled non-destructively by taking blood samples from over 1500 individually marked birds. A detailed investigation of the genetics of these loci was conducted for 124 clutches containing 357 nestlings where the parents were also sampled. Segregations at four loci (6PGD, PEPD2, PEPD3 and lDHC) agreed with a simple Mendelian model of codominant inheritance. One locus (EST2) contained null alleles. Two loci (PEPD3 and GP1) showed segregation distortion in all sex, site and year classes. This distortion was not attributable to the misinterpretation of gel patterns; possible causes involving the operation of natural selection were discussed. Linkage analyses were conducted, and no significant evidence was obtained for linkage between any combination of loci. Of the nestling genotypes, 12.9% were interpreted as being genetically incompatible with those of their parents. Exclusion probabilities were calculated as 43-51% for nonpaternity and 59-67% for nonparentage. The applicability of these estimated probabilities was tested by the random reassortment and comparison of observed parental genotypes among observed sibship genotypes. Significantly fewer nestlings were excluded in these simulations than expected from calculated exclusion probabilities, though the distribution of multiple mismatches did not differ from expectation. A deficiency of multiple mismatches was found in the field data, implying the occurrence of errors; the possible sources of error were considered. The most parsimonious interpretation of those mismatches that did not appear to be due to errors was that they resulted from a rate of nonpaternity of about 6%. No heterogeneity in the rate of mismatches was observed within or among breeding seasons or sites. Genotype and allele frequencies were presented for each locus in each age, sex and sampling year class at each study site. The samples were not found to depart from Hardy Weinberg equilibrium, and there was no evidence for significant inbreeding within sites. There were no differences in allelic distributions between the sexes or among years for adults within the populations. No differences were found among age groups or nestling year classes when allowance was made for sib correlations. Heterozygosities were higher at Brackenhurst than at Sutton Bonington for most loci, and the overall difference was significant. There was a particularly large difference in allele frequencies between nestlings in each population for GP1. Digenic gametic disequilibria were investigated. A detailed analysis of the mating types was made. No evidence was obtained for any departure from random mating at the protein loci. There was a significant tendency amongst the loci and samples for the inbreeding coefficients of the successful breeders to be negative. Significant assortative mating was found with respect to weight and tail-length in one population.