Pamela Wiener

Muscle-related traits in cattle: The role of the myostatin gene in the South Devon breed.

In this paper, we examined the effects of an 11-bp mutation within the GDF-8 gene, originally identified in Belgian Blue cattle, in the South Devon breed. The mutation was found at moderate frequency (0.37) in the South Devon population. We quantified the effects of this mutation on growth, body composition and calving traits in South Devon cattle. We found that the mutation significantly increased muscle score and calving difficulty and decreased fat depth. The mutation did not significantly affect weight at 200 and 400 days or muscle depth. Its effect on muscle score and fat depth was additive while its effect on calving difficulty was recessive. The mutation accounted for a significant proportion of the phenotypic variance in muscle score and calving difficulty. There was an economic benefit of the mutation for this data set, however, calculations were sensitive to changes in the parameter values. Additional data would be required to refine these calculations.

Genetic effects on coat colour in cattle: dilution of eumelanin and phaeomelanin pigments in an F2-Backcross Charolais × Holstein population

BackgroundIn cattle, the gene coding for the melanocortin receptor 1 (MC1R) is known to be the main regulator of the switch between the two coat colour pigments: eumelanin (black pigment) and phaeomelanin (red pigment). Some breeds, such as Charolais and Simmental, exhibit a lightening of the original pigment over the whole body. The dilution mutation in Charolais (Dc) is responsible for the white coat colour of this breed. Using an F2-Backcross Charolais × Holstein population which includes animals with both pigment backgrounds, we present a linkage mapping study of the Charolais dilution locus.ResultsA Charolais × Holstein crossbred population was investigated for genetic effects on coat colour dilution. Three different traits representing the dilution of the phaeomelanin, eumelanin, and non-pigment-specific dilution were defined. Highly significant genome-wide associations were detected on chromosome 5 for the three traits analysed in the marker interval [ETH10-DIK5248]. The SILV gene was examined as the strongest positional and functional candidate gene. A previously reported non-synonymous mutation in exon 1 of this gene, SILV c.64A>G, was associated with the coat colour dilution phenotype in this resource population. Although some discrepancies were identified between this mutation and the dilution phenotype, no convincing recombination events were found between the SILV c.64A>G mutation and the Dc locus. Further analysis identified a region on chromosome 28 influencing the variation in pigment intensity for a given coat colour category.ConclusionThe present study has identified a region on bovine chromosome 5 that harbours the major locus responsible for the dilution of the eumelanin and phaeomelanin seen in Charolais crossbred cattle. In this study, no convincing evidence was found to exclude SILV c.64A>G as the causative mutation for the Charolais dilution phenotype, although other genetic effects may influence the coat colour variation in the population studied. A region on chromosome 28 influences the intensity of pigment within coat colour categories, and therefore may include a modifier of the Dc locus. A candidate gene for this effect, LYST, was identified.

Escape in time: stay young or age gracefully?

We compare two modes of ‘escape in time’ from an unpredictable environment: developmental delay (‘stay young’) such as seed dormancy, and reproductive delay (‘age gracefully’) such as delayed flowering. We find that developmental delay and reproductive delay are symmetric with respect to fitness i.e. they have the same effect on growth rate if they have equal costs, and if the environmental pattern is time-reversible. We describe this property by saying that if one kind of delay is an ‘escape into the future’, the other is an ‘escape into the past’. When the costs of the two kinds of delay are equal, and we add a little delay to a life cycle that has none, the increase in growth rate is equal whether we add developmental delay, reproductive delay, or a combination of the two. When the costs of delay are equal, and we consider a life cycle that has just one form of delay, the largest gain in fitness tends to come from an increase in the delay that is already present. Thus, changes in the amount of delay tend to be self-reinforcing. Hence we expect evolution to lead to an entrainment so that life cycles will often contain mainly one or other kind of delay. As the amount of delay increases, the growth rate reaches a maximum that may be regarded as an ESS, and then falls. Geometrically, this maximum is a ‘ridge’ on the fitness surface when environments are moderately variable i.e. there are many combinations of delays that yield the maximum growth rate. When the environment becomes highly variable, or strongly positively autocorrelated, this ‘ridge’ is replaced by a pair of ‘peaks’. Two combinations of delay then lead to the highest growth rate, one where reproductive delay is dominant and one where developmental delay is dominant.

The effects of the mating system on the evolution of migration in a spatially heterogeneous population

SummaryVerbal explanations for the evolution of migration and dispersal often invoke inbreeding depression as an important force. Experimental work on plant populations indicates that while inbreeding depression may favor increased migration rates, adaptation to local environments may reduce the advantage to migrants. We formalize and test this hypothesis using a two-locus genetic model that incorporates lowered fitness in offspring produced by self-fertilization, and habitat differentiation. We also use the model to address questions about the general theory of genetic modifiers and the modifier reduction principle. We find that even under conditions when migration would increase the mean fitness of a population, migration may not be favored. This result is due to the associations that develop between genotypes at a locus subject to overdominant selection and at a neutral locus controlling the migration rate. Thus, it appears that, in this model, the forces of local adaptation, which favor a reduction in the migration rate, overwhelm those of inbreeding depression, which may favor dispersal.