Pelvic bone structures in free-ranging Eurasian lynx ( Lynx lynx ) from Switzerland: a radiological pelvimetry study

Abstract The observation of severe pelvic malformations in Eurasian lynx ( Lynx lynx ) from a population reintroduced to Switzerland raised the question as to whether inbreeding may contribute to the development of congenital pelvic malformations. We aimed at providing baseline data on the pelvic morphology of Eurasian lynx from the reintroduced populations in Switzerland, at assessing potential differences in pelvic conformation between the two main Swiss populations, among age classes and between sexes, and at detecting pelvic anomalies. We performed measurements of 10 pelvic parameters on the radiographs of 57 lynx of both sexes and different ages taken from 1997-2015. We calculated two ratios (vertical diameter/acetabula; sagittal diameter/transversal diameter) and two areas (pelvic outlet and inlet) to describe the shape of the pelvis. Our results showed that the Eurasian lynx is a mesatipelvic species, with a pelvis length corresponding to approximatively 20% of the body length. We found no statistically significant differences between the two examined populations but observed growth-related pelvis size differences among age groups. Sexual dimorphism was obvious in the adult age group only: two parameters reflecting pelvic width were larger in females, likely to meet the physiological requirements of parturition. By contrast, pelvis length, conjugata vera, diagonal conjugata, vertical diameter and sagittal diameter were larger in males, in agreement with their larger body size. Accordingly, the ratio between the sagittal and transversal diameters was significantly larger in males, i.e. adult males have a different pelvic shape than adult females. Furthermore, pelvimetry highlighted one adult individual with values outside the calculated reference range, suggesting a possible congenital or developmental pathological morphology of the internal pelvis. Our work generated baseline data of the pelvic morphology including growth and sexual dimorphism of the Eurasian lynx. These data could also be useful for estimating age and sex in skeletal remains.