Big spots in a small population: Analyzing characteristics and temporality of coat patterns in Croatian lynx population

Abstract

Quantification of animal phenotypic traits could allow objective description of individuals and their morphology, reducing bias caused by human subjectivity, skill and experience. The goal of our study was to research a quantitative approach to analyzing the four types of coat patterns recognized in endangered Eurasian lynx (Lynx lynx) in Croatia and to track frequencies of coat patterns over time. A total of 195 photographs of lynx individuals from Croatia, collected in the 1978–2019 period, were visually assigned to one of four types of coat patterns: no spots, small spots, big spots, and rosettes. Then, using metrics available within the public-domain software ImageJ, we quantified lynx spot traits and compared the characteristics of the four coat patterns to detect objective differences. All metrics that were analyzed differed significantly between “no spots” and other coat patterns (p < 0.05), whereas none of the metrics differed significantly between coats of small spots and coats of rosettes. Luckily, researchers visually distinguished easily coats of rosettes from coats of small spots. In contrast, when coats of big spots were numerically compared to those of small spots, they differed significantly in spot size on the whole body, while in some lynx individuals these two patterns proved to be most difficult for researchers to distinguish by eye. When looking at the occurrence of the four coat patterns inside the two temporal categories, they differed significantly between individuals photographed in 1978–1999 and those photographed in 2001–2019. The frequency of coats without spots fell from 14% to zero, the frequency of rosettes dropped from 23% to 9%, while the frequency of big spots increased from 46% to 80%. Significant inbreeding and low population size were genetically proven in Croatian lynx population, but to link inbreeding with the phenotypic change we observed, further research should be conducted.