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Abstract 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.

Infectious disease dynamics operate across biological scales: pathogens replicate within hosts but transmit among populations. Functional changes in the pathogen-host interaction thus generate cascading effects across organizational scales. We investigated within-host dynamics and among-host transmission of three strains (SAT-1, -2, -3) of foot-and-mouth disease viruses (FMDVs) in their wildlife host, African buffalo. We combined data on viral dynamics and host immune responses with mathematical models to ask the following questions: How do viral and immune dynamics vary among strains? Which viral and immune parameters determine viral fitness within hosts? And how do within-host dynamics relate to virus transmission? Our data reveal contrasting within-host dynamics among viral strains, with SAT-2 eliciting more rapid and effective immune responses than SAT-1 and SAT-3. Within-host viral fitness was overwhelmingly determined by variation among hosts in immune response activation rates but not by variation among individual hosts in viral growth rate. Our analyses investigating across-scale linkages indicate that viral replication rate in the host correlates with transmission rates among buffalo and that adaptive immune activation rate determines the infectious period. These parameters define the virus's relative basic reproductive number (ℛ0), suggesting that viral invasion potential may be predictable from within-host dynamics. [ABSTRACT FROM AUTHOR]

Abstract 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.

Selection coefficients at the mammalian Y chromosome typically do not deviate strongly from neutrality. Here we show that strong balancing selection, maintaining intermediate frequencies of DNA sequence variants, acts on the Y chromosome in two populations of African buffalo (Syncerus caffer). Significant correlations exist between sequence variant frequencies and annual rainfall in the years before conception, with five- to eightfold frequency changes over short time periods. Annual rainfall variation drives the balancing of sequence variant frequencies, probably by affecting parental condition. We conclude that sequence variants confer improved male reproductive success after either dry or wet years, making the population composition and dynamics very sensitive to climate change. The mammalian Y chromosome, interacting with ecological processes, may affect male reproductive success much more strongly than previously thought.

Within‐host parasite interactions can be mediated by the host and changes in host phenotypes often serve as indicators of the presence or intensity of parasite interactions.Parasites like helminths induce a range of physiological, morphological and immunological changes in hosts that can drive bottom‐up (resource‐mediated) or top‐down (immune‐mediated) interactions with co‐infecting parasites. Although top‐down and bottom‐up interactions are typically studied in isolation, the diverse phenotypic changes induced by parasite infection may serve as a useful tool for understanding if, and when, these processes act in concert.Using an anthelmintic treatment study of African buffalo, Syncerus caffer, we tracked changes in host immunological and morphological phenotypes during helminth‐coccidia co‐infection to investigate their role in driving independent and combinatorial bottom‐up and top‐down parasite interactions. We also examined repercussions for host fitness.Clearance of a blood‐sucking helminth, Haemonchus, from the host gastrointestinal tract induced a systemic Th2 immune phenotype, while clearance of a tissue‐feeding helminth, Cooperia, induced a systemic Th1 phenotype. Furthermore, the Haemonchus‐associated systemic Th2 immune phenotype drove simultaneous top‐down and bottom‐up effects that increased coccidia shedding by changing the immunological and morphological landscapes of the intestine.Higher coccidia shedding was associated with lower host body condition, a lower chance of pregnancy and older age at first pregnancy, suggesting that coccidia infection imposed significant condition and reproductive costs on the host.Our findings suggest that top‐down and bottom‐up interactions may commonly co‐occur and that tracking key host phenotypes that change in response to infection can help uncover complex pathways by which parasites interact. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.12.013 Byline: Vanessa O. Ezenwa, Anna E. Jolles Abstract: The evolution and maintenance of elaborate secondary sexual characters in males have been the subject of intense interest since Darwin's time. Parasite-mediated sexual selection (PMSS) suggests that elaborate ornaments serve as honest indicators of male health and parasite resistance. Studies testing this key prediction of PMSS have largely focused on ornaments, with the role parasites might play in the maintenance of elaborate weapons being relatively understudied. Here, we tested whether weapon (horn) size was an indicator of health status in male and female African buffalo, Syncerus caffer. We examined whether individuals with larger horns were less likely to be infected with parasites, and had lower parasite loads and stronger immune systems. In males, horn size was significantly negatively correlated with the number of different parasites infecting an individual (parasite richness), the likelihood of infection with strongyle nematodes and coccidia, and strongyle intensity. In females, horn size was significantly negatively correlated with parasite richness, occurrence of coccidia infection, coccidia intensity and white blood cell count. These findings were robust when the effects of body condition, age and season were controlled for, consistent with the idea that horns function as honest indicators of health in both sexes. Our study provides new insight into the evolution and maintenance of elaborate weapons in mammals, suggesting a role for PMSS in both males and females. Author Affiliation: (a) Division of Biological Sciences, University of Montana, U.S.A. (a ) College of Veterinary Medicine and Department of Zoology, Oregon State University, U.S.A. Article History: Received 4 July 2007; Revised 17 August 2007; Accepted 4 December 2007 Article Note: (miscellaneous) MS. number: A10808R