Inbreeding and TB threaten captive recovery of a rare rainforest duck

Captive breeding is often a cornerstone of efforts to save species on the brink of extinction, but bringing wild animals into human care also exposes them to new challenges. The white-winged wood duck (WWWD) Asarcornis scutulata is a striking example: once distributed across South-East Asia, it has suffered severe declines, local extirpations and range fragmentation, and is now one of the world’s rarest birds. Conservationists have started captive breeding programs to try to prevent extinction, but these efforts have been hampered by a high susceptibility to Mycobacterium avium, the bacterium that causes avian tuberculosis (TB). In the study led by Christopher N. Balakrishnan, researchers used genome-wide data to investigate why these birds are so vulnerable and how their history affects conservation options. They set out to describe patterns of genetic diversity across the species, reconstruct demographic and phylogeographic history, measure inbreeding in both wild and captive birds, and probe the causes of TB susceptibility—work intended to provide a genomic foundation for future management of this critically endangered species.

Using genome-wide analyses and demographic reconstructions, the team compared captive birds—originating from northeast India—with wild birds sampled in Sumatra, Indonesia, and also compared expression patterns with a resistant species, the redhead duck Aythya americana. The results showed clear genetic differentiation between the captive Indian-origin birds and the wild Sumatran birds, consistent with long-standing phylogeographic structure. Demographic analyses indicated that long-term population declines during the Pleistocene predated recent human-caused declines, a pattern shared with other codistributed, forest-dependent species. Across all sampled WWWD populations genetic diversity was extremely low, but importantly wild-sampled birds retained higher Major Histocompatibility Complex (MHC) diversity, pointing to functionally important variation in the wild. The researchers found that genetic diversity has eroded over time in captivity, and birds with higher levels of inbreeding died sooner after becoming infected with TB, consistent with inbreeding depression. Finally, by comparing gene expression between susceptible WWWD and resistant Aythya americana, they identified possible mechanisms underlying the WWWD’s heightened TB susceptibility.

These findings carry clear implications for conservation practice. The contrast between captive and wild genetic variation—especially at the Major Histocompatibility Complex—suggests that remaining wild populations harbor functionally important diversity that captive programs have already lost. The evidence that inbreeding correlates with earlier death from Mycobacterium avium infections provides a direct warning: captive breeding without careful genetic management can increase vulnerability to disease through inbreeding depression. The genetic differentiation between northeast Indian and Sumatran birds also means managers must consider phylogeographic structure when moving birds or mixing stocks, because regional lineages may represent distinct reservoirs of diversity. By comparing susceptible WWWD to the resistant Aythya americana, the study points toward biological pathways to investigate further for disease resistance. Taken together, this work offers genomically guided objectives for future management and serves as a cautionary tale about the risks of ex-situ conservation when disease and low genetic diversity intersect.