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).