BACKGROUND: The Y-chromosomal diversity in the African buffalo (Syncerus caffer) population of Kruger National Park
(KNP) is characterized by rainfall-driven haplotype frequency shifts between year cohorts. Stable Y-chromosomal
polymorphism is difficult to reconcile with haplotype frequency variations without assuming frequency-dependent
selection or specific interactions in the population dynamics of X- and Y-chromosomal genes, since otherwise the
fittest haplotype would inevitably sweep to fixation. Stable Y-chromosomal polymorphism due one of these factors
only seems possible when there are Y-chromosomal distorters of an equal sex ratio, which act by negatively affecting
X-gametes, or Y-chromosomal suppressors of a female-biased sex ratio. These sex-ratio (SR) genes modify (suppress)
gamete transmission in their own favour at a fitness cost, allowing for stable polymorphism.
RESULTS: Here we show temporal correlations between Y-chromosomal haplotype frequencies and foetal sex ratios in
the KNP buffalo population, suggesting SR genes. Frequencies varied by a factor of five; too high to be alternatively
explained by Y-chromosomal effects on pregnancy loss. Sex ratios were male-biased during wet and female-biased
during dry periods (male proportion: 0.47-0.53), seasonally and annually. Both wet and dry periods were associated
with a specific haplotype indicating a SR distorter and SR suppressor, respectively.
CONCLUSIONS: The distinctive properties suggested for explaining Y-chromosomal polymorphism in African buffalo
may not be restricted to this species alone. SR genes may play a broader and largely overlooked role in mammalian sexratio