COUNTERVAILING SELECTION IN DIFFERENT FITNESS COMPONENTS IN FEMALE RED DEER

In individually monitored red deer (Cervus elaphus) living in the North Block of the Isle of Rhum, Scotland, juvenile survival is related to the genotype at the enzyme loci Mpiand Idh‐2(each with two alleles, fand s). To establish whether other fitness components also are related to genetic differences, we examined whether age at first breeding, fecundity, and adult survival of females were related to genotype at the same loci. Fertility in females shot outside the study area was also analyzed in relation to Mpiand Idh‐2genotype. The analyses controlled for phenotypic and environmental factors affecting female reproductive performance. At Mpi, f‐carrying females in the study area bred earlier than ssindividuals and tended to be more fecund. However, no association was found between Mpigenotype and adult survival. In culled females, Mpi f‐carriers were more likely to be pregnant than ssfemales. At Idh‐2, homozygous females in the study area started breeding earlier than heterozygous females. Idh‐2 fsand ssfemales were more fecund than fffemales though this relationship was complicated by an interaction with spring temperature in the year of birth. When the population was at high density, adult survival of Idh‐2 ssfemales was better than survival of fffemales, which was, in turn, better than survival of fsfemales. No association was found between Idh‐2genotype and fertility in culled females. Overall, the associations found in female reproductive measures favor those genotypes that survive particularly badly over the first two years of life. This result supports the idea that countervailing selection in different fitness components (antagonistic pleiotropy) is a common and powerful force maintaining polymorphism in natural populations. It may also explain how fitness components can have large heritabilities while overall fitness may have a low heritability.