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Variation in selective regimes drives intraspecific variation in life-history traits and migratory behaviour along an elevational gradient

Journal of Animal Ecology
By:  and 
https://doi.org/10.1111/1365-2656.13134

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Abstract

  1. Comparative studies, across and within taxa, have made important contributions to our understanding of the evolutionary processes that promote phenotypic diversity. Trait variation along geographic gradients provides a convenient heuristic for understanding what drives and maintains diversity. Intraspecific trait variation along latitudinal gradients is well-known, but elevational variation in the same traits is rarely documented. Trait variation along continuous elevational gradients, however, provides compelling evidence that individuals within a breeding population may experience different selective pressures.
  2. Our objectives were to quantify variation in a suite of traits along a continuous elevational gradient, evaluate whether individuals in the population experience different selective pressures along that gradient and quantify variation in migratory tendency along that gradient.
  3. We examined variation in a suite of 14 life-history, morphological and behavioural traits, including migratory tendency, of yellow-eyed juncos along a continuous 1000-m elevational gradient in the Santa Catalina Mountains of Arizona.
  4. Many traits we examined varied along the elevational gradient. Nest survival and nestling growth rates increased, while breeding season length, renesting propensity and adult survival declined, with increasing elevation. We documented the migratory phenotype of juncos (partial altitudinal migrants) and show that individual migratory tendency is higher among females than males and increases with breeding elevation.
  5. Our data support the paradigm that variation in breeding season length is a major selective pressure driving life-history variation along elevational gradients and that individuals breeding at high elevation pursue strategies that favour offspring quality over offspring quantity. Furthermore, a negative association between adult survival and breeding elevation and a positive association between nest survival and breeding elevation help explain both the downslope and reciprocal upslope seasonal migratory movements that characterize altitudinal migration in many birds. Our results demonstrate how detailed studies of intraspecific variation in suites of traits along environmental gradients can lend new insights into the evolutionary processes that promote diversification and speciation, the causes of migratory behaviour, and how animal populations will likely respond to climate change.
Publication type Article
Publication Subtype Journal Article
Title Variation in selective regimes drives intraspecific variation in life-history traits and migratory behaviour along an elevational gradient
Series title Journal of Animal Ecology
DOI 10.1111/1365-2656.13134
Volume 89
Issue 2
Year Published 2020
Language English
Publisher British Ecological Society
Contributing office(s) Coop Res Unit Seattle
Description 15 p.
First page 397
Last page 411
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