Semester of Graduation

Summer 2025

Degree

Master of Science (MS)

Department

Biological Sciences

Document Type

Thesis

Abstract

In 1817, George Ord documented the first North American records of Glossy Ibis (Plegadis falcinellus), a species native to the Old World. Over the next 200 years, Glossy Ibis expanded its breeding range to include the Atlantic coast to southernmost Florida and thence up the Gulf coast to eastern Texas. Forty-five to 75 years ago, its range expansion brought it into secondary contact with White-faced Ibis (P. chihi) in Louisiana, a native species whose breeding range includes freshwater wetlands in Louisiana and eastern Texas. Hybridization between the two species resulted in a large hybrid zone in southern Louisiana, providing an opportunity to investigate the roles of reproductive barriers in the early phases of secondary contact. In collaboration with other researchers, we established baseline data on population frequencies of White-faced Ibis, Glossy Ibis, and their hybrids based on morphological characteristics at three rookeries in south Louisiana – Miller’s Lake (Avoyelles Parish), Salvador Wildlife Management Area (St. Charles Parish), and Big Mar in the Caernarvon outflow area (Plaquemines Parish). We found that White-faced Ibis were most common (65.5%), followed by hybrids (25.6%) and Glossy Ibis (8.9%). We tested for premating reproductive barriers by examining whether the phenotypes of mated ibis pairs deviated from random expectations. Pearson’s X 2 tests of mated pairs failed to reject the null hypothesis of random mating on rookeries, suggesting an absence of premating reproductive barriers. We evaluated the extent to which ibis nest at multiple rookeries, either within or between breeding seasons. Movement data from six GPS-tagged birds showed that ibis can change rookeries between clutches within a breeding season (one bird moved approximately 38 km). Ibis tend to nest in the same rookery within and across breeding seasons. vi Our study demonstrated that premating reproductive barriers are either absent or weak between White-faced and Glossy Ibis, and that ibis are capable of long dispersal distances. Future work should focus on testing for postmating reproductive barriers, such as reduced viability or infertility of hybrids. In the absence of reproductive barriers, we predict extensive hybridization will eventually lead to reticulation of the White-faced and Glossy Ibis into a single recombinant species.

Date

5-19-2025

Committee Chair

Brumfield, Robb

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