Key Insights – Mokkonen et al. 2011

Mokkonen M., H. Kokko, E. Koskela, J. Lehtonen, T. Mappes, H. Martiskainen & S.C. Mills. 2011. Negative frequency-dependent selection of sexually antagonistic alleles in Myodes glareolus. Science 334: 972-974.

OVERVIEW:

This study used artificial selection in the laboratory to create sexually antagonistic (SA) lines of bank voles (Myodes glareolus), such that higher fitness males had lower fitness sisters, and vice versa. To test whether negative frequency dependent selection was acting on males and/or females, individuals were released to large outdoor field enclosures to survive and reproduce. Prior to any births, individuals were all live-trapped out of the enclosures to obtain measures of survival, and after giving birth in the laboratory, reproductive success. These field results were parameterized and incorporated to a mathematical model to assess whether negative frequency dependence could maintain sexually antagonistic genetic variation over many generations.

NOVEL FINDINGS:
-SA alleles, associated with higher male behavioral dominance and testosterone levels, are maintained in field populations of bank voles through negative frequency dependent selection (NFDS)
-absence of NFDS (in models) resulted in SA alleles going to fixation/elimination
-NFDS only acted on males, not females

OTHER NOTABLE DETAILS:
implicit frequency dependence, by which only one of the two male morphs was affected by NFDS, is enough to maintain genetic variation (as is explicit frequency dependence that affects all male morphs).
-only a portion of individuals in a population are affected by frequency dependence