J. S. F. Barker

Defining Fitness in Natural and Domesticated Populations

The term ‘fitness’ has been applied differently and with different definitions throughout the history of population genetics. Five concepts and definitions are presented~– distinguishing (phenotypic) fitness, (genotypic) fitness, adaptedness, adaptability and durability. While the heritabilities of fitness components are low, substantial genetic change is achievable, and breeding programs should include in the breeding objectives genotypic fitness (for known QTLs) and fitness traits such as fertility and longevity, as well as production traits.

Genetic identification of wild Asian water buffalo in Nepal

The wild water buffalo is highly endangered, with the few remaining populations already affected or likely to be increasingly affected by hybridization with domestic buffalo. The work described here was done to evaluate a genetic method to discriminate wild from mixed ancestry (hybrid) and domestic animals, and to identify with high probability those most likely to be purebred wild. Samples from 45 animals (phenotypically classified into three groups - ten wild, 28 domestic and seven hybrid) were genotyped for ten microsatellite loci. Although genetic distances among the three groups were small, an assignment test identified two of the ‘wild’ and seven of the ‘domestic’ as hybrids. However, sample sizes also are small, indicating the need for a conservative approach in the first instance in using these results. As more animals are genotyped, assignments will become more accurate, and a translocation programme to establish a second Nepalese wild population in a protected area could be undertaken.

Genetic differentiation of water buffalo (Bubalus bubalis) populations in China, Nepal and south-east Asia: inferences on the region of domestication of the swamp buffalo.

Data from three published studies of genetic variation at 18 microsatellite loci in water buffalo populations in China (18 swamp type, two river type), Nepal (one wild, one domestic river, one hybrid) and south-east Asia (eight swamp, three river) were combined so as to gain a broader understanding of genetic relationships among the populations and their demographic history. Mean numbers of alleles and expected heterozygosities were significantly different among populations. Estimates of θ (a measure of population differentiation) were significant among the swamp populations for all loci and among the river populations for most loci. Differentiation among the Chinese swamp populations (which was due primarily to just one population) was much less than among the south-east Asian. The Nepal wild animals, phenotypically swamp type but genetically like river type, are significantly different from all the domestic river populations and presumably represent the ancestral Bubalus arnee (possibly with some river-type introgression). Relationships among the swamp populations (D(A) genetic distances, principal component analysis and structure analyses) show the south-east Asian populations separated into two groups by the Chinese populations. Given these relationships and the patterns of genetic variability, we postulate that the swamp buffalo was domesticated in the region of the far south of China, northern Thailand and Indochina. Following domestication, it spread south through peninsular Malaysia to Sumatra, Java and Sulawesi, and north through China, and then to Taiwan, the Philippines and Borneo.

The phenotypic variance gradient – a novel concept

Evolutionary ecologists commonly use reaction norms, which show the range of phenotypes produced by a set of genotypes exposed to different environments, to quantify the degree of phenotypic variance and the magnitude of plasticity of morphometric and life-history traits. Significant differences among the values of the slopes of the reaction norms are interpreted as significant differences in phenotypic plasticity, whereas significant differences among phenotypic variances (variance or coefficient of variation) are interpreted as differences in the degree of developmental instability or canalization. We highlight some potential problems with this approach to quantifying phenotypic variance and suggest a novel and more informative way to plot reaction norms: namely “a plot of log (variance) on the y-axis versus log (mean) on the x-axis, with a reference line added”. This approach gives an immediate impression of how the degree of phenotypic variance varies across an environmental gradient, taking into account the consequences of the scaling effect of the variance with the mean. The evolutionary implications of the variation in the degree of phenotypic variance, which we call a “phenotypic variance gradient”, are discussed together with its potential interactions with variation in the degree of phenotypic plasticity and canalization.