The evolution of life history traits in Iceland, 1650-1950

I analyzed heritability of lifespan and fertility over 300 years of Icelandic history, using computer simulations, a genealogical database called Íslendingabók (the book of Icelanders), and genetic data –single nucleotide polymorphisms (SNP’s)-from modern populations. There was no evidence that either lifespan or reproduction is heritable. There was, however, substantial evidence that parental investment (PI) has enhanced both the survival and reproduction of the people of Iceland. There was also strong evidence of a quantity-quality tradeoff for reproduction and lifespan; each additional child conceived by parents substantially reduced the lifespan and reproduction of all current and future offspring. I also searched for evidence of sexual antagonism (SA) in the Icelandic database. SA occurs when the reproductive interests of males and females conflict. Whenever variance in reproductive success is different between the sexes, each sex will have different and often conflicting strategies. Genes that benefit one sex are transmitted to opposite sex offspring (e.g. mothers to sons) which then have deleterious effects (Andersson, 1994). There was some suggestive, although not statistically significant, evidence of SA effects in Iceland (see chapter 3). Post-hoc testcrosses between high lifetime reproductive success (LRS) males and low lifetime reproductive success (LRS) females produced more grandchildren through their sons than through their daughters. Post-hoc testcrosses between high LRS females and low LRS males in contrast produced more grandchildren through their daughters than through their sons. Although statistically insignificant, these data did produce effects hypothesized by sexual conflict theory in both directions. Finally, I searched for evidence of reproductive advantages to sex biased parental investment (Trivers-Willard) in two separate databases. In one publicly available, on-line genealogy from the United States, there was significant evidence suggesting that sons from large families have more children than daughters from large families. Also, daughters from small families are more likely to have more children than sons from small families. In Íslendingabók, however, there was no evidence that biasing the sex ratio based on family size would confer any advantage to its practitioners. The discrepancy in these results suggests that Trivers-Willard effects may depend on yet to be determined environmental, social, or cultural variables.Ph. D.Includes bibliographical referencesby Robert Francis Lync