2.1 Literature review
We included all rare colour variants that have been reported in
scientific literature or online papers over the past five decades (from
1970 to 2023) and tried to retrieve genetic data from the population
where the colour variant occurred. We conducted common Google and
scientific web searches (e.g. Google Scholar and Web of Science) to find
rare colour variants. We define a rare colour variant as “a distinct
phenotypic form of coat colour or pattern that typically occurs in a
specific region and at low frequencies”. To the contrary, colour
polymorphism is described as
phenotypic variation that is well
established throughout a species’ range (Wildtype phenotypes), albeit at
different frequencies. Hence, we do not consider a rare colour variant
to be polymorphism at the species level. Although rare colour variants
may become of adaptive significance in the future, counting them as
polymorphism in this study may distort the correlation we make with
genetic drift and homozygote access. We included all land-living
carnivores and only those species for which scientific publications with
photographic evidence were available.
We used some of the following search strings: carnivores OR Carnivora OR
family name (of all 12 Carnivora families) AND colour morph OR anomalous
coloration OR phenotypic variation OR leucistic OR melanistic.
Scientific papers were also drawn from the reference list of the
articles that were found. We did not list a colour variant twice (i.e.,
from different locations), but instead included the best scientifically
documented case for each species. We acknowledge that our approach is
not holistic and prone to errors. For instance, camera traps can cause
biases in human perception and are not always able to tell the
difference between colour variants such as pseudomelanism versus
intraspecific coat variation or seasonal moulting, or between leucism or
albinism (Olson & Allen, 2019). Albinism is a recessively inherited
disorder that occurs throughout all taxa, whereas leucism can have
adaptive significance (Olson & Allen, 2019). Because albinism in a
species does not mean the presence of colour variation in a population,
we have excluded this from our dataset. Overlooking or mislabelling
colour variants will most likely not affect our overall results, which
aims to find a link between rare phenotypes and genetic diversity.