Effects of physical impairments on fitness correlates of the white-footed mouse, Peromyscus leucopus.

Francesca I Rubino,Richard S Ostfeld,Kelly Oggenfuss

doi:10.1098/rspb.2021.1942

Abstract

Physical impairments are widely assumed to reduce the viability of individual animals, but their impacts on individuals within natural populations of vertebrates are rarely quantified. By monitoring wild populations of white-footed mice over 26 years, we assessed whether missing or deformed limbs, tail or eyes influenced the survival, body mass, movement and ectoparasite burden of their bearers. Of the 27 244 individuals monitored, 543 (2%) had visible physical impairments. Persistence times (survival) were similar between mice with and without impairments. Mice with eye and tail impairments had 5% and 6% greater mass, respectively, than unimpaired mice. Mice with tail impairments had larger home ranges than did unimpaired mice. Burdens of black-legged ticks (Ixodes scapularis) were higher among mice with tail and limb impairments while burdens of bot fly larvae (Cuterebra) were higher among mice with cataracts compared to mice without impairments. Our findings do not support the presupposition that physical impairments reduce viability in their bearers and are inconsistent with the devaluation of impaired individuals that pervaded early thinking in evolutionary biology.

Highlights

Physical impairments can be caused by trauma, disease or inheritance and may affect the behaviour, health and longevity of the individual
The perception that impairment inhibits individual fitness has influenced the management of wild animals [1,2,3] and multiple eugenic movements [4,5,6,7,8,9]
We analysed the associations between tail, limb and eye impairments and Peromyscus leucopus survival, body mass, home range size and ectoparasite burdens using years of mark–recapture data on 244 individuals, of whom 544 had impairments

Summary

Introduction

Physical impairments can be caused by trauma, disease or inheritance and may affect the behaviour, health and longevity of the individual. Studies conducted in laboratories often induce impairment and fail to replicate the challenges animals may encounter in the wild such as predation or density-dependent competition [10,11,12,13,14] Many of these studies have focused on limb loss in arthropods, showing contradictory effects of impairment on reproduction [15,16], survival [12,17], competition [18] and movement [19]. Spiders, insects and mice have provided much larger sample sizes but have focused on species that exhibit autotomy [17,18,24,25,26,27,28,29,30] This evolved trait enabling animals to self-amputate an appendage or limb represents a special case in which specific adaptations (vasoconstriction, segmentation) might minimize the acute consequences of appendage loss or damage. With large wild populations and a well-studied life history, this species provides a rare opportunity to gain insight into impairment in species with no apparent adaptations to facilitate autotomy

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