The impact of parental investment on lifetime reproductive success in Iceland

Abstract

BackgroundDemonstrating the impact that parents have on the fitness of their children is a crucial step towards understanding how parental investment has affected human evolution. Parents not only transfer genes to their children, they also influence their environments. By analyzing reproductive patterns within and between different categories of close relatives, this study provides insight into the genetic and environmental effects that parents have on the fitness of their offspring.MethodsWe use data spanning over two centuries from an exceptionally accurate Icelandic genealogy, Íslendingabók, to analyze the relationship between the fertility rates of close relatives. Also, using genetic data, we determine narrow sense heritability estimates (h2) to further explore the genetic impact on lifetime reproductive success. Finally, we construct four simulations to model the expected contribution of genes and resources on reproductive success.ResultsThe relationship between the reproduction of all full sibling pairs was significant and positive across all birth decades (r = 0.19) while the reproductive relationship between parents and offspring was often negative across many decades and undetectable overall (r = 0.00) (Fig. 1 and Table 1). Meanwhile, genetic data among 8,456 pairs of full siblings revealed a narrow sense heritability estimate (h2) of 0.00 for lifetime reproductive success. A resources model (following the rule that resources are transmitted from parents to children, distributed equally among siblings, and are the only factor affecting reproductive success) revealed a similar trend: a negative relationship between parent and offspring reproduction (r = − 0.35) but a positive relationship among full siblings (r = 0.28). The relationship between parent and offspring lifetime reproductive success (LRS) and full sibling LRS was strongly and positively correlated across time (r = 0.799, p < 0.001). Similarly, the LRS among full siblings was positively correlated with both the LRS among half siblings (r = 0.532, p = 0.011) and the relationship between the LRS of aunts and uncles with their nieces and nephews (r = 0.438, p = 0.042).DiscussionWe show that an individual’s lifetime reproductive success is best predicted by the reproduction of their full and half siblings, but not their parents, grandparents or aunts and uncles. Because all siblings share at least one parent, we believe parental investment has had an important impact on fitness. Overall, these results indicate that direct parental investment, but not genes, is likely to have had an important and persistent impact on lifetime reproductive success across more than two centuries of Icelandic history.

The Impact of Stress Within and Across Generations: Neuroscientific and Epigenetic Considerations

“…178 In another study (in which socioeconomic factors were not felt to have affected findings), young women who had volunteered for a paramilitary organization during World War II displayed accelerated reproductive schedules, with less time before reproduction, shorter inter-birth intervals, and greater number of offspring compared to their nonserving peers or sisters. 179 It is very difficult to generalize such findings in human populations, as destructive events can increase reproductive behaviors 180,181 as well as decrease them. 182 In the latter case, individuals may choose to invest in their own survival and that of their existing offspring, while waiting to see if having additional children is viable.…”

Humans as a model species for sexual selection research

“…Historical documents [39][40][41] and records of marriages, births and deaths [42] can provide insights into the lives of people long dead. Studies using detailed genealogies can provide a time-depth of centuries [43], far longer than any primate field study. Human studies can take advantage of enormous sample sizes, such as a database of 500 000 genotyped individuals [44], greater than the number of chimpanzees on the planet [45].…”

What are the contributions of maternal and paternal traits to fecundity and offspring development? A case study in an amphibian species, the spined toadBufo spinosus

“…As a consequence, it is often difficult to tease apart the relative contributions of parental (including both maternal and paternal organisms) and environmental factors on reproductive success ( Ridley 2007 ; Hoy et al 2016 ). All of these sources of variation of reproductive success and offspring development have been grouped within the concept of parental effects with a strong focus on their evolutionary consequences ( Rollinson and Hutchings 2013 ; Lynch and Lynch 2017 ). Accordingly, this corpus of literature has highlighted that phenotypic correlations between parents and offspring can reflect both parental effects and direct genetic correlations between parents and offspring ( Amos et al 2001 ; Fan et al 2015 ).…”