Moving from trends to benchmarks by using regression tree analysis to find inbreeding thresholds in a critically endangered bird

• Published in: Conservation biology 2021-08, Vol.35 (4), p.1278-1287
• Main Authors: Flanagan, Alison M., Masuda, Bryce, Grueber, Catherine E., Sutton, Jolene T.
• Format: Article
• Language: English
• Subjects: Animal breeding; Animal reproduction; aptitud; Benchmarks; Birds; Breeding; Breeding success; Coefficients; coeficientes de linaje endogámico; Conservation; conservation breeding; Corvus hawaiiensis; depresión endogámica; Eggs; Endangered & extinct species; Endangered animals; Endangered species; especie en peligro; fitness; Inbreeding; Inbreeding depression; Incubation; Incubation period; Life history; Offspring; Pedigree; pedigree inbreeding coefficients; Rare species; Recruitment; Recruitment (fisheries); Regression analysis; regression trees; reproducción para la conservación; Reproduction; Survival; Thresholds; Wildlife conservation; árbol de regresión
• ISSN: 0888-8892; 1523-1739
• DOI: 10.1111/cobi.13650

Understanding how inbreeding affects endangered species in conservation breeding programs is essential for their recovery. The Hawaiian Crow (‘Alalā) (Corvus hawaiiensis) is one of the world's most endangered birds. It went extinct in the wild in 2002, and, until recent release efforts starting in 2016, nearly all of the population remained under human care for conservation breeding. Using pedigree inbreeding coefficients (F), we evaluated the effects of inbreeding on Hawaiian Crow offspring survival and reproductive success. We used regression tree analysis to identify the level of inbreeding (i.e., inbreeding threshold) that explains a substantial decrease in ‘Alalā offspring survival to recruitment. Similar to a previous study of inbreeding in ‘Alalā, we found that inbreeding had a negative impact on offspring survival but that parental (vs. artificial) egg incubation improved offspring survival to recruitment. Furthermore, we found that inbreeding did not substantially affect offspring reproductive success, based on the assumption that offspring that survive to adulthood breed with distantly related mates. Our novel application of regression tree analysis showed that offspring with inbreeding levels exceeding F = 0.098 were 69% less likely to survive to recruitment than more outbred offspring, providing a specific threshold value for ongoing population management. Our results emphasize the importance of assessing inbreeding depression across all life history stages, confirm the importance of prioritizing parental over artificial egg incubation in avian conservation breeding programs, and demonstrate the utility of regression tree analysis as a tool for identifying inbreeding thresholds, if present, in any pedigree‐managed population. Moverse de las Tendencias a los Referentes Mediante el Análisis de Árbol de Regresión para Encontrar los Umbrales de Endogamia de una Ave en Peligro Crítico Resumen Es necesario entender cómo afecta la endogamia a las especies en peligro que se encuentran en programas de reproducción para la conservación para la recuperación exitosa de estas especies. El cuervo hawaiano (‘Alalā) (Corvus hawaiiensis) es una de las especies de ave que se encuentra en mayor peligro de extinción en todo el mundo. Esta especie se extinguió en vida libre en el 2002 y no fue hasta los recientes esfuerzos de liberación que iniciaron en 2016 que casi toda la población permaneció bajo cuidado humano en programas de reproducción para la conservación.