Applying morphometrics to choose optimal captive brood stock for an endangered species: A case study using the freshwater pearl mussel, Margaritifera margaritifera (L.)

To maximize captive breeding success for the globally endangered freshwater mussel Margaritifera margaritifera, morphometrics was applied to develop a tool for selecting optimal brood stock. There was high discrimination between brooding and non-brooding individuals and the presence of brood explained the variation in the percentage of mussels with a typical brooding morphology. Brooding individuals were significantly wider than non-brooding individuals. However, after reclassifying those non-brooding individuals with morphology highly indicative of brooding individuals using Mahalanobis distance modelling, only shell curvature along the ventral region differed significantly. The Mahalanobis model explained more variation in shell morphology than a model based on field observations, highlighting that shell morphology is a good predictor of brooding mussels. In addition, it could be argued that an identified novel morph is that of hermaphroditic M. margaritifera, which has developed in response to historic low population density. This is the first application of a non-invasive, morphometric technique to optimize captive breeding programmes for an endangered species. Since a greater number of species are under threat of extinction from climate change, there will be a demand for captive breeding programmes, emphasizing the importance of this study.