Genomics of Tiger Populations in the Wild

Demographic history dictates the expected inbreeding and genetic variation in

species. Across species range populations can have independent demographic

histories. This shapes the distribution of genetic variation and determines inbreeding

in individuals. This in in turn helps in managing expectations of inbreeding and

genetic variation in a species and helps prioritize populations in need of attention.

Here we estimate demographic history, genetic variation and inbreeding in tigers

using whole genome sequences of tigers from across the range. We sequence 4 out

of 5 five extant subspecies of tigers. We observe that Bengal tigers have the highest

genetic variation among tigers but also have high inbreeding on an average. We use

runs of homozygosity (ROH) to estimate the history of inbreeding in tigers and

correlate it to the demographic history. We observe that before the systematic and

organized bounty hunting of tigers about 200-220 years ago tigers across the range

had similar levels of inbreeding. Bengal tigers have high number of individuals with

recent inbreeding.

Within Bengal tigers, the large connected population of Central

India are at par with the world tigers while the small isolated population of North-

West Indian tigers appear to be the most inbred tigers globally in our dataset. Our

findings reiterate the importance of large connected habitat patches for species

survival and indicates that even large carnivores with huge dispersal ranges can be

heavily impacted by habitat loss and fragmentation.

Within species variance in inbreeding and genetic variation is influenced by

differences in demographic history. Across wolves for example Tibetan wolves

(Canis lupus chanco) have always existed as a small isolated population, this has

led to present individuals having low genetic variation and being highly inbred. Isle

Royal wolves on the other hand, have been a part of the historically large Minnesota

wolf population, host higher genetic variation and less inbred individuals compared to

Tibetian wolves. However, Isle Royale wolves have higher recent inbreeding than

Tibetian wolves. Minnesota wolves have higher genetic variation and less inbred

individuals than Isle Royale and Tibetan wolves . Similar patterns are also observed across Gorilla populations,

humans and Puma.