Crossbreeding Threatens Milky Stork Conservation

Milky storks are breeding with their genetically related cousins, the painted storks, leading to hybridization and potential loss of this endangered species of bird.

AsianScientist (Feb. 11, 2019) – A team of researchers from the National University of Singapore (NUS) has discovered that the conservation of milky storks (Mycteria cinerea), is threatened due to crossbreeding with their more widespread cousins, the painted storks (Mycteria leucocephala). Their results are published in the journal Biological Conservation.

Milky storks are a species of wading bird native to Southeast Asia, typically found in coastal mangroves, mudflats and estuaries. It is currently considered endangered on the International Union for the Conservation of Nature Red List, with about 1,500 individuals left in the wild. About seven to ten percent of them are found in the region around Singapore and Johor, Malaysia.

Since the late 1980s, milky storks and their sister species, the painted storks, have been held together in captivity in Singapore and Malaysia. The painted stork is differentiated from the milky stork by the presence of a black pectoral band and a pink flush in the inner wings.

In this study, scientists led by Assistant Professor Frank Rheindt of NUS found that the co-housing of milky and painted storks has resulted in inadvertent crossbreeding or hybridization between the two stork species. To find out how the gene pool of milky storks has been affected, the NUS team carried out genomic analysis of tissue samples of 46 storks from both captive and wild environments of Singapore.

Their results showed significant genomic ‘contamination’ of painted stork alleles in the milky storks’ genetic profile following crossbreeding for several generations. Although originating from a limited number of introduced painted storks, these hybrids are now an integral part of both the wild and captive Singaporean and southern peninsular Malaysian stork population.

The research team determined that the genomic composition of more than half of the sampled storks is affected by genetic infiltration from the painted stork. These results indicate that due to their very small populations, such globally endangered species may eventually be absorbed into the genome of the more widespread species.

“Apart from habitat loss and fragmentation, extinction through hybridization is one of the major threats to endangered species. Our study is the first to provide an estimation of the population genomic status of the endangered milky stork in Singapore, and the findings can contribute to the design of effective solutions for conservation management of the globally endangered species,” said Rheindt.

The research team thus recommends that hybrid storks in bird parks, zoos and the Singaporean wild be identified and isolated from pure milky storks to prevent crossbreeding. Thorough genetic analysis can also be conducted to ensure each individual’s purity in any planned breeding programs or releases. In addition, the team proposes removing hybrids from the wild, along with the release of genetically pure milky storks, to ensure the continued survival of milky storks.

The article can be found at: Baveja et al. (2018) Impact of Genomic Leakage on the Conservation of the Endangered Milky Stork.


Source: National University of Singapore; Photo: Eddy Lee Kam Pang.
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