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Sexual Selection and Horn Size Variation in Soay Sheep: Insights from Genetics and Natural Selection

This study examines the genetic and ecological factors influencing horn size variation in male Soay sheep. Over a 21-year period, data on 1,750 monitored sheep reveals that horn size is heavily influenced by genetic variants in the RXFP2 gene. Findings suggest that male reproductive success is linked to horn size, with larger horns associated with higher offspring production, yet survival constraints due to environmental factors limit fixation of this trait. Intermediate horn sizes may offer a heterozygote advantage, highlighting the complex interplay of fitness, selection, and genetic diversity.

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Sexual Selection and Horn Size Variation in Soay Sheep: Insights from Genetics and Natural Selection

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  1. Darren Monckton sexual selection of male horn size in Soay sheep

  2. inter-sex sexual selection

  3. intra-sex sexual selection

  4. natural selection should drive a sexually selected feature to fixation? • why are many sexually selected traits not driven to fixation? • trait is driven by variation in many different geneswith small effects and complex interactions • trait is constrained by other fitness effects

  5. St Kilda

  6. St Kilda

  7. St Kilda

  8. St Kilda

  9. Soay sheep

  10. winter

  11. coat colour variation

  12. horn variation

  13. rutting

  14. a highly studied population

  15. • 1,750 sheep monitored and 5,880 sheep sampled over a 21-year period

  16. horn variation in males is largely driven by variants in the RXFP2 gene Ho+/Ho+ HoP/HoP Ho+/HoP HoP/HoP

  17. horn variation in males is driven by variants in the RXFP2 gene RFXP2 genotype

  18. male reproductive success • large horned males produce the most offspring inany one season

  19. male survival • large horned males are the most likely to dieduring any one year

  20. fitness fitness ~ survival + reproductive success

  21. male fitness • intermediate horned males produce the most offspring during their lifetime

  22. a heterozygote advantage • a heterozygote advantage for male sheepmaintains RXFP2 diversity • effects on survival constrain horn size

  23. Darwin’s Galapagos island finches

  24. Darwin’s Galapagos island finches

  25. Darwin’s Galapagos island finches • whole-genome sequencing of 120 individuals representing all of the Darwin’s finch species and two close relatives • phylogenetic analysis reveals important discrepancies with the phenotype-based taxonomy • variants in ALX1 affect craniofacial development and beak shape diversity

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