Abstract:
Conservation decisions based on neutral genetic diversity have been observed to promote
retention of useful quantitative variation in biological populations. An experiment
was undertaken to determine the association between microsatellite marker
polymorphisms and phenotypic variation in semen production and cryosurvival traits
in bulls. Thirty-five
ejaculates were collected from ten bulls of two breeds and evaluated
before and after cryopreservation for several semen traits. The bulls were also
genotyped using a set of sixteen bovine-specific
microsatellite marker loci. Fixation
indices (FST), heterozygosity and Nei's genetic distance measures were computed
from allele frequency data for each of the bulls. Molecular and phenotypic data were
used to compute tri-distance
matrices for the ten bulls and correlated using Mantel's
test in GenAIEx 6.5. The study revealed extensive heterogeneity in semen traits, heterozygosity
and FST values among the bulls. Large pairwise phenotypic and genetic
distances were also observed. Correlation between pairwise genetic distances and
phenotypic distances was significant and highly positive for sperm viability (r = .61,
p < .001) and moderately positive for sperm motility (r = .40–42,
p < .05) variables.
For sperm morphology, ejaculate volume and sperm concentration, correlation with
genetic distances was positive, low and not significantly different from zero (p > .05).
A tendency for a triangular-shaped
relationship between genetic and phenotypic
distances for post-thaw
motility and viability traits was also observed. Accordingly,
association with neutral genetic diversity was absent for semen production traits
and moderate to highly positive for sperm cryosurvival traits. Given these findings,
conservation decisions based on neutral genetic diversity may capture variation in
some adaptive traits, but not others.
