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. 2019 Dec 4;7(1):coz093.
doi: 10.1093/conphys/coz093. eCollection 2019.

Chronic captivity stress in wild animals is highly species-specific

Clare Parker Fischer  1 , L Michael Romero  1
Affiliations

Chronic captivity stress in wild animals is highly species-specific

Clare Parker Fischer et al. Conserv Physiol. .

Abstract

Wild animals are brought into captivity for many reasons-conservation, research, agriculture and the exotic pet trade. While the physical needs of animals are met in captivity, the conditions of confinement and exposure to humans can result in physiological stress. The stress response consists of the suite of hormonal and physiological reactions to help an animal survive potentially harmful stimuli. The adrenomedullary response results in increased heart rate and muscle tone (among other effects); elevated glucocorticoid (GC) hormones help to direct resources towards immediate survival. While these responses are adaptive, overexposure to stress can cause physiological problems, such as weight loss, changes to the immune system and decreased reproductive capacity. Many people who work with wild animals in captivity assume that they will eventually adjust to their new circumstances. However, captivity may have long-term or permanent impacts on physiology if the stress response is chronically activated. We reviewed the literature on the effects of introduction to captivity in wild-caught individuals on the physiological systems impacted by stress, particularly weight changes, GC regulation, adrenomedullary regulation and the immune and reproductive systems. This paper did not review studies on captive-born animals. Adjustment to captivity has been reported for some physiological systems in some species. However, for many species, permanent alterations to physiology may occur with captivity. For example, captive animals may have elevated GCs and/or reduced reproductive capacity compared to free-living animals even after months in captivity. Full adjustment to captivity may occur only in some species, and may be dependent on time of year or other variables. We discuss some of the methods that can be used to reduce chronic captivity stress.

Keywords: captivity; glucocorticoids; immune; reproduction; stress.

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Figures

Figure 1
Figure 1
Examples of experimental designs to assess the effects of captivity on a physiological variable (e.g. GC concentration) (A) Comparison of captive individuals to free-living populations. In some cases, the free-living samples were acquired at the same time that the study population was brought into captivity. In other designs, the free-living samples were taken from entirely different populations than the origin of the captive animals (e.g. comparing zoo-housed animals to wild conspecifics). (B) Each individual measured immediately at capture and again after a period of captivity (days to months). (C and D) Each individual measured immediately at capture and resampled at multiple timepoints. Some studies focused on the first few days, with sampling points relatively close together (C). Other studies may not have taken another sample until several weeks after capture (D).
Figure 2
Figure 2
Weight change as a function of captivity duration. Data were collected from 35 studies listed in Table 1, with studies counted multiple times if they measured multiple time points after introduction to captivity. The number of species that lost weight in captivity (relative to wild, free-living animals) decreased with captivity duration.
Figure 3
Figure 3
Change in baseline or integrated GCs as a function of captivity duration. Data were collected from the 47 studies listed in Table 3 that had a well-defined wild baseline value (i.e. plasma samples were collected within minutes of capture; fecal or urine samples were collected shortly after capture), with studies counted multiple times if they measured multiple time points after introduction to captivity. This figure does not include studies with seasonal effects on the GC response to capture.
Figure 4
Figure 4
Changes in neutrophil or heterophil (N or H:L) to lymphocyte ratio in captivity as a function of time. Data were collected from 19 studies listed in Table 4, with studies counted multiple times if they measured multiple time points after introduction to captivity. The percent of studies that recorded elevated N or H:L ratio in captivity decreased with the amount of time spent in captivity.
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