Geology topics

David B. Ledig

Publications and source records attributed to David B. Ledig.

2 recordsLinked to original sources

USGS2011

Will an "island" population of voles be recolonized if eradicated? Insights from molecular genetic analyses

We performed genetic analyses of Microtus longicaudus populations within the Crook Point Unit of the Oregon Islands National Wildlife Refuge. A M. longicaudus population at Saddle Rock (located approx. 65 m off‐shore from the Crook Point mainland) is suspected to be partially responsible for declines of a Leach's storm‐petrel colony at this important nesting site. Using Amplified Fragment Length Polymorphism markers and mitochondrial DNA, we illustrate that Saddle Rock and Crook Point function as separate island and mainland populations despite their close proximity. In addition to genetic structure, we also observed reduced genetic diversity at Saddle Rock, suggesting that little individual movement occurs between populations. If local resource managers decide to perform an eradication at Saddle Rock, we conclude that immediate recolonization of the island by M. longicaudus would be unlikely. Because M. longicaudus is native to Oregon, we also consider the degree with which the differentiation of Saddle Rock signifies the presence of a unique entity that warrants conservation rather than eradication

Oregon↗

USGS2000

Fatal toxoplasmosis in free-ranging endangered 'Alala from Hawaii

The ‘Alala ( Corvus hawaiiensis ) is the most endangered corvid in the world, and intensive efforts are being made to reintroduce it to its former native range in Hawaii. We diagnosed Toxoplasma gondii infection in five free-ranging ‘Alala. One ‘Alala, recaptured from the wild because it was underweight and depressed, was treated with diclazuril (10 mg/kg) orally for 10 days. Antibodies were measured before and after treatment by the modified agglutination test (MAT) using whole T. gondii tachyzoites fixed in formalin and mercaptoethanol. The MAT titer decreased four-fold from an initial titer of 1:1,600 with remarkable improvement in physical condition. Lesions of toxoplasmosis also were seen in two partially scavenged carcasses and in a third fresh intact carcass. Toxoplasma gondii was confirmed immunohistochemically by using anti- T. gondii specific serum. The organism was also cultured by bioassay in mice from tissues of one of these birds and the brain of a fifth ‘Alala that did not exhibit lesions. The life cycle of the parasite was experimentally completed in cats. This is the first record of toxoplasmosis in ‘Alala, and the parasite appears to pose a significant threat and management challenge to reintroduction programs for ‘Alala in Hawaii.

Hawai'i↗