Inbreeding depression and tuberculosis susceptibility in the critically endangered white-winged wood duck Asarcornis scutulata

The critically endangered white-winged wood duck (WWWD) Asarcornis scutulata has experienced substantial population declines, local extirpations and fragmentation of its former range in South-East Asia. Moreover, the success of captive breeding programs has also declined precipitously, driven primarily by the species’ high susceptibility to Mycobacterium avium , avian tuberculosis (TB). Here we compare genome-wide patterns of diversity between a wild population and a serially sampled captive population of WWWDs. Captive birds, which originated from northeast India, are highly genetically differentiated from wild birds sampled in Sumatra, Indonesia, likely reflecting long-standing phylogeographic structure in the natural population. Both the wild and captive populations have similarly low overall genetic diversity, comparable to other endangered species. Surprisingly, the wild-sampled birds had higher inbreeding coefficients than the captive birds, though captive genetic diversity has eroded over time. Most importantly, captive birds with higher levels of inbreeding succumb earlier to TB infections, suggesting inbreeding depression. Although wild Indonesian birds had low overall genetic diversity, reflecting long term and anthropogenically induced declines, they harbored significantly higher genetic diversity than captive birds in the Major Histocompatibility Complex (MHC), a key component of the adaptive immune system. We also find that MHC genes are differentially expressed between susceptible WWWDs and resistant redhead ducks Aythya americana , suggesting a possible mechanism for TB susceptibility. The greater MHC diversity in wild populations suggests that wild birds may yet harbor key functional diversity that provides hope for both ex-situ and in-situ conservation efforts.