Phenotype-limited distributions: short-billed birds move away during times that prey bury deeply.

Sjoerd Duijns,Jan A Van Gils,Jennifer Smart,Theunis Piersma

doi:10.1098/rsos.150073

Sjoerd Duijns, Jan A Van Gils + Show 2 more

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https://doi.org/10.1098/rsos.150073

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Abstract

In our seasonal world, animals face a variety of environmental conditions in the course of the year. To cope with such seasonality, animals may be phenotypically flexible, but some phenotypic traits are fixed. If fixed phenotypic traits are functionally linked to resource use, then animals should redistribute in response to seasonally changing resources, leading to a ‘phenotype-limited’ distribution. Here, we examine this possibility for a shorebird, the bar-tailed godwit (Limosa lapponica; a long-billed and sexually dimorphic shorebird), that has to reach buried prey with a probing bill of fixed length. The main prey of female bar-tailed godwits is buried deeper in winter than in summer. Using sightings of individually marked females, we found that in winter only longer-billed individuals remained in the Dutch Wadden Sea, while the shorter-billed individuals moved away to an estuary with a more benign climate such as the Wash. Although longer-billed individuals have the widest range of options in winter and could therefore be selected for, counterselection may occur during the breeding season on the tundra, where surface-living prey may be captured more easily with shorter bills. Phenotype-limited distributions could be a widespread phenomenon and, when associated with assortative migration and mating, it may act as a precursor of phenotypic evolution.

Highlights

Most organisms on the Earth live in seasonal environments with respect to climate and food [1]
We explored the possibility of a phenotypelimited distribution by analysing the monthly distribution in bill lengths using long-term datasets of measured and marked non-breeding females in the Dutch Wadden Sea and in the Wash, UK
Bill lengths of taymyrensis females were shorter than of lapponica (p < 0.001), though this subspecies showed the same pattern during the seven months they occurred in the Dutch Wadden Sea

Summary

Introduction

Most organisms on the Earth live in seasonal environments with respect to climate and food [1]. To reversibly change phenotype in response to a change in environmental conditions is called phenotypic 2 flexibility [2,3]. Animals making adjustments in digestive organ size to cope with different prey types or prey quality represent a well-known example of (often seasonally structured) phenotypic flexibility Some aspects of the phenotype are essentially inflexible. Traits such as bill length in birds that show determined growth are hardly flexible [7,8]. In response to environmental change, animals can show behavioural responses such as changes in foraging time In response to environmental change, animals can show behavioural responses such as changes in foraging time (e.g. [18,19]), diet [20,21], or the movement to sites where good food may be more favourable (e.g. [22,23,24])

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