Abstract
Inbreeding depression (ID) occurs when inbreeding negatively impacts fitness. Understanding ID in wildlife is crucial for conservation and management, but obtaining good estimates of inbreeding and fitness to study ID on such systems can be challenging. Furthermore, the possible modulation of ID by various intrinsic and extrinsic variables can make its detection and interpretation uncertain in the absence of detailed individual and environmental information. Here we tested for ID in the culturally important population of feral horses (Equus ferus caballus) of Sable Island, Canada, using inbreeding coefficients derived from ~ 30,000 Single Nucleotide Polymorphisms (SNPs) and individual-based data for three fitness-related traits (body condition [BC], strongyle fecal egg count [FEC], and age at first reproduction [AFR]). We further assessed whether the expression of ID in this population was modulated by intrinsic (age, sex, reproductive status) and extrinsic (location, year) variables. ID was detected for all traits but mediating variables differed. For both BC and FEC, ID varied among years and was greater in the western portion of the island. In contrast, ID for BC was strongest in juveniles and lactating mares while for FEC it was strongest for reproductive-aged horses and males. Lastly, ID for AFR was mediated by cohort effects. Our study indicates that ID is impacting the fitness and welfare of Sable Island horses, but that its intensity varies among traits and ecological contexts. This illustrates the importance of considering both intrinsic and extrinsic variables to understand the expression of ID in the wild.
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Data availability
The datasets generated and analysed during the current study are available from the corresponding author on reasonable request.
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Acknowledgements
The authors would like to thank the past and present members of the Sable Island field crew for their tireless efforts collecting data each summer. Special thanks also to Drs. Lucie Debeffe and Charlotte Regan for generating body condition scores, Dr. Charlotte Regan for her help with coding and model selection theory, and to Dr. Pirmin Nietlisbach for his assistance with the estimation of inbreeding loads.
Funding
This work was supported by the Natural Sciences and Engineering Research Council of Canada (Discovery Grants Nos 2016–06459 to PDM and 2019–04388 to JP, and Vanier Canada Graduate Scholarship to JC), the Canada Foundation for Innovation (Leaders Opportunity Grant No 25046 to PDM), a Leverhulme Trust Early Career Fellowship (ECF-2014-564 to JP), and the University of Calgary.
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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by JC and JP. The first draft of the manuscript was written by JC and all authors commented on previous versions of the manuscript. All authors have read and approved the final manuscript.
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All sampling, parasitology work, and genoty** was carried out under University of Saskatchewan Animal Care Protocol 20090032, University of Calgary Animal Care Protocol AC18-0078, and research permits granted by Parks Canada (SINP-2017-24036 and SINP-2021-38998). Researchers had express permission to enter Sable Island National Park Reserve to observe horses and collect samples in accordance with the Parks Canada wildlife interaction guidelines, the Canada Ship** Act and granted research permits. This study is reported in accordance with ARRIVE guidelines.
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Colpitts, J., McLoughlin, P.D. & Poissant, J. Inbreeding depression in Sable Island feral horses is mediated by intrinsic and extrinsic variables. Conserv Genet 25, 1–15 (2024). https://doi.org/10.1007/s10592-023-01549-8
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DOI: https://doi.org/10.1007/s10592-023-01549-8