Fluctuations in population composition dampen the impact of phenotypic plasticity on trait dynamics in superb fairy-wrens

Date

2012

Authors

van de Pol, Martijn
Osmond, Helen
Cockburn, Andrew

Journal Title

Journal ISSN

Volume Title

Publisher

British Ecological Society

Abstract

In structured populations, phenotypic change can result from changes throughout an individual's lifetime (phenotypic plasticity, age-related changes), selection and changes in population composition (environment- or density-driven fluctuations in age-structure). The contribution of population dynamics to phenotypic change has often been ignored. However, for understanding trait dynamics, it is important to identify both the individual- and population-level mechanisms responsible for trait change, because they potentially reinforce or counteract each other. We use 22years of field data to investigate the dynamics of a sexually selected phenological trait, the timing of nuptial moult in superb fairy-wrens Malurus cyaneus. We show that trait expression is both climate- and age-dependent, but that phenotypic plasticity in response to climate variability also varies with age. Old males can acquire nuptial plumage very early after high rainfall, but 1- to 2-year-olds cannot. However, males of all ages that defer moult to later in the year acquire nuptial plumage earlier when conditions are warmer. The underlying mechanism appears to be that old males may risk moulting in the most challenging period of the year: in autumn, when drought restricts food abundance and during the cold winter. By contrast, young males always moult during the spring transition to benign - warmer and generally wetter - conditions. Temperature changes dominate this transition that heralds the breeding season, thereby causing both young and late-moulting older birds to be temperature sensitive. Climate and age also affect trait dynamics via a population dynamical pathway. The same high rainfall that triggers early moulting in old males concurrently increases offspring recruitment and thereby reduces the average age of males in the population. Consequently, effects of rainfall on trait dynamics through phenotypic plasticity of old males are dampened by synchronous rejuvenation of the age-structure. A long-term trend towards drier environments prompted phenotypic change because of plasticity, but this was masked by climate-driven demographic change (causing apparent stasis). This suggests a novel explanation for why trait change may fail to reflect the observed pattern of directional selection or phenotypic plasticity.

Description

Keywords

Keywords: adaptation; age structure; community composition; demography; gene expression; molt; nuptial gift; passerine; phenology; phenotypic plasticity; plumage; population dynamics; population structure; rainfall; recruitment (population dynamics); sexual selecti Age-related improvement; Age-structured population; Climate change; Malurus cyaneus; Moulting; Phenology; Population dynamics; Sexually selection; Time-to-event model; Trait stasis

Citation

Source

Journal of Animal Ecology

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

Restricted until

2037-12-31