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Individuals’ expected genetic contributions to future generations, reproductive value, and short-term metrics of fitness in free-living song sparrows (Melospiza melodia)


Reid, Jane M; Nietlisbach, Pirmin; Wolak, Matthew E; Keller, Lukas F; Arcese, Peter (2019). Individuals’ expected genetic contributions to future generations, reproductive value, and short-term metrics of fitness in free-living song sparrows (Melospiza melodia). Evolution Letters, 3(3):271-285.

Abstract

Appropriately defining and enumerating “fitness” is fundamental to explaining and predicting evolutionary dynamics. Yet, general theoretical concepts of fitness are often hard to translate into quantities that can be measured in wild populations experiencing complex environmental, demographic, genetic, and selective variation. Although the “fittest” entities might be widely understood to be those that ultimately leave most descendants at some future time, such long‐term legacies can rarely be measured, impeding evaluation of the degree to which tractable short‐term metrics of individual fitness could potentially serve as useful direct proxies. One opportunity for conceptual and empirical convergence stems from the principle of individual reproductive value (Vi), here defined as the number of copies of each of an individual's alleles that is expected to be present in future generations given the individual's realized pedigree of descendants. As Vi tightly predicts an individual's longer term genetic contribution, quantifying Vi provides a tractable route to quantifying what, to date, has been an abstract theoretical fitness concept. We used complete pedigree data from free‐living song sparrows (Melospiza melodia) to demonstrate that individuals’ expected genetic contributions stabilize within an observed 20‐year (i.e. approximately eight generation) time period, allowing estimation of individual Vi. Considerable among‐individual variation in Vi was evident in both sexes. Standard metrics of individual lifetime fitness, comprising lifespan, lifetime reproductive success, and projected growth rate, typically explained less than half the variation. We thereby elucidate the degree to which fitness metrics observed on individuals concur with measures of longer term genetic contributions and consider the degree to which analyses of pedigree structure could provide useful complementary insights into evolutionary outcomes.

Abstract

Appropriately defining and enumerating “fitness” is fundamental to explaining and predicting evolutionary dynamics. Yet, general theoretical concepts of fitness are often hard to translate into quantities that can be measured in wild populations experiencing complex environmental, demographic, genetic, and selective variation. Although the “fittest” entities might be widely understood to be those that ultimately leave most descendants at some future time, such long‐term legacies can rarely be measured, impeding evaluation of the degree to which tractable short‐term metrics of individual fitness could potentially serve as useful direct proxies. One opportunity for conceptual and empirical convergence stems from the principle of individual reproductive value (Vi), here defined as the number of copies of each of an individual's alleles that is expected to be present in future generations given the individual's realized pedigree of descendants. As Vi tightly predicts an individual's longer term genetic contribution, quantifying Vi provides a tractable route to quantifying what, to date, has been an abstract theoretical fitness concept. We used complete pedigree data from free‐living song sparrows (Melospiza melodia) to demonstrate that individuals’ expected genetic contributions stabilize within an observed 20‐year (i.e. approximately eight generation) time period, allowing estimation of individual Vi. Considerable among‐individual variation in Vi was evident in both sexes. Standard metrics of individual lifetime fitness, comprising lifespan, lifetime reproductive success, and projected growth rate, typically explained less than half the variation. We thereby elucidate the degree to which fitness metrics observed on individuals concur with measures of longer term genetic contributions and consider the degree to which analyses of pedigree structure could provide useful complementary insights into evolutionary outcomes.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Institute of Evolutionary Biology and Environmental Studies
Dewey Decimal Classification:570 Life sciences; biology
590 Animals (Zoology)
Language:English
Date:1 June 2019
Deposited On:07 Feb 2020 12:28
Last Modified:07 Feb 2020 12:29
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:2056-3744
OA Status:Gold
Publisher DOI:https://doi.org/10.1002/evl3.118
Project Information:
  • : FunderFP7
  • : Grant ID309453
  • : Project TitlePOLYINBREED - Coevolutionary Quantitative Genetics of Polyandry and Inbreeding in the Wild: New Theory and Test

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