Rainfall-driven sex-ratio genes in African buffalo suggested by correlations between Y-chromosomal haplotype frequencies and foetal sex ratio.
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 sex-ratio variation.
van Hooft
Pim
P
Resource Ecology Group, Wageningen University, 6708 PB Wageningen, The Netherlands. pim.vanhooft@wur.nl
Prins
Herbert H T
HH
Getz
Wayne M
WM
Jolles
Anna E
AE
van Wieren
Sipke E
SE
Greyling
Barend J
BJ
van Helden
Paul D
PD
Bastos
Armanda D S
AD
D000818:Animals; D002020:Buffaloes / Q000235:genetics*; D002980:Climate; D005260:Female; D005333:Fetus / Q000378:metabolism; D006239:Haplotypes; D008297:Male; D018895:Microsatellite Repeats; D012744:Sex Ratio; D013019:South Africa; D014998:Y Chromosome