3.1 Genetic parameters
Twenty publications speculated about the underlying cause of the colour variant frequency, of which 10 papers hinted towards heterozygote deficiency (e.g. due to bottleneck, inbreeding, genetic drift), while 8 papers presumed a selective benefit. Three other papers speculated hybridization to be the underlying cause. In 17 variable phenotypic populations there was data on genetic diversity available from the population or region containing the colour variant, regardless of their frequency. In these populations, the average AR was 4.18, HO = 0.59, and HE = 0.66 (Table 1). This means that we found an overall heterozygote deficiency, with an average FIS of 0.086 (-0.05–0.19) across all colour variable carnivores (the full dataset is available in Table S1). In non-variable phenotypic populations, the average AR was 5.09, HO = 0.63, HE = 0.66, and FIS = 0.046 in non-variable populations (Table S2). In large and stable leopard populations, the number of alleles normally ranges between 5 to 20 per locus, and heterozygosity levels are usually high (0.70-0.75) with no or little heterozygote deficiency (0.0-0.05) (Spong et al., 2000), which can serve as a proxy for other carnivore species. When comparing the pairwise increase of heterozygote deficiency from non-variable populations to variable populations within species, we found a significant directional deviation from zero (T-test, t value = 1.88; P = 0.034). This implies an increase of heterozygote deficiency in populations where rare colour variants occurred (Figure 3a). We also found a negative deviation from zero for allelic richness (T-test, t value = -2.23; P = 0.016), implying that variable populations have reduced genetic diversity Figure 3b).