World's most endangered tern threatened by hybridization

HANGZHOU, May 23 (Xinhua) -- The Chinese crested tern, the world's most endangered tern species, is in danger of hybridizing with a sister species because of its small population, said Chinese ornithologists.

The hybridization of two closely related species may erode their gene pools and accelerate the rate of the rare bird's extinction, said Chen Shuihua, deputy director of the Zhejiang Museum of Natural History in east China's Zhejiang Province.

He said the museum and two other Chinese institutes have collected non-invasive DNA samples from five Chinese crested terns for genetic conservation studies, as they have observed that hybridization is likely to occur between the rare bird and its more abundant cousin, the great crested tern.

The white migrating bird with a black beak was first spotted in 1861, and has remained small in number, listed as "critically endangered" by the IUCN Red Data Book with fewer than 100 individuals globally.

Chen said that at all of the bird's breeding sites in the Chinese mainland and Taiwan, nests of the Chinese crested tern were found within great crested tern colonies.

He said although the two species are members of the same Sternini tribe, they diverged about a million years ago.

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Hybrid chickadees found deficient at learning and memory

March 26, 2018, Lehigh University

For a long time, hybridization—when distinct species mate and produce offspring—was thought to be a mistake. Yet, advancements in genomic testing tools have revealed naturally occurring hybridization as a fairly common phenomenon—with a role in natural selection, in some cases.

Scientists estimate that as much as 10% of animals—and 25% of plants—engage in hybridization in nature. Genetic data has even shed light on modern-day humans' hybrid ancestry, with most Europeans and Asians thought to have approximately 2 percent Neanderthal DNA.

Sterility is common in hybrids and is thought to be a key factor in keeping two hybridizing species distinct. This is true for a particular hybrid chickadee population in the U.S., the result of mating between the northern Black-capped Chickadee and a southern species called the Carolina Chickadee. A lower percentage of the hybrid chickadees' eggs hatch compared to their pure-species parents—a key selective disadvantage.

The results of a new behavioral study out of Lehigh University and Franklin & Marshall College add a wrinkle to this paradigm: scientists found that hybrid chickadees have marked deficiencies in learning and memory compared to their pure species parents, which may be another selective disadvantage.

This discovery is the first time that learning and memory deficiencies have been identified in any hybrid of any species, opening up a new area of inquiry for understanding hybrids' selective disadvantage. The study results appear in the journal Evolution in an article that appears online today by Michael A. McQuillan, Amber M. Rice and Alex V. Huynh of Lehigh University and Timothy C. Roth II of Franklin & Marshall College called: "Hybrid Chickadees are Deficient in Learning and Memory."

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Will mallards hybridize their cousins out of existence?

September 6, 2017

Mallards—the familiar green-headed ducks of city parks—are one of a group of closely related waterfowl species, many of which are far less common. Interbreeding with Mallards can threaten the genetic distinctiveness of those other species and cause concern for their conservation. A new study from The Condor: Ornithological Applications investigates hybridization between Mallards and Mottled Ducks, a species specially adapted for life in Gulf Coast marshes, and finds that while hybridization rates are currently low, human activity could cause them to rise in the future.

In Florida, hybridization between domesticated Mallards and Mottled Ducks is a cause for concern, but the degree of hybridization in the western Gulf Coast region is less well known. Louisiana State University's Robert Ford and his colleagues took blood samples from Mottled Ducks captured on the coast of Louisiana in 2011-2014, supplementing them with samples from Mottled Ducks and Mallards from Texas, Alabama, and Mississippi. Analyzing the birds' DNA, they found that the hybridization rate in the western Gulf Coast region is currently only 5-8%, a level lower than what's been documented in Florida. However, that doesn't mean the western Gulf population is completely in the clear.

Currently, the two species have little opportunity to interact in the region during the breeding season; Mottled Ducks nest in coastal marshes, while most Mallards are migratory and breed outside the region. However, the ongoing loss of marsh habitat could cause Mottled Ducks to move into urban and suburban areas, where they will be more likely to encounter resident Mallards. To prevent future problems, Ford and his colleagues recommend ongoing monitoring of hybridization in the region and better protection of coastal marsh habitat.

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