A Multi-disciplinary Analysis of a Titmouse (Baeolophus) Hybrid Zone in Texas
Abstract
Hybridization, or interbreeding between two distinct species, can result in a variety of evolutionary consequences. To understand genetic introgression and stability of a hybrid zone, it is crucial to investigate multiple biological facets including behavior, communication, habitat, genetics, and even physiology. This study aims to better understand hybrid zone dynamics between the Black-crested and Tufted Titmouse by investigating differences in physiology, song structure, behavior, morphology, plumage, and genetic assignment across a hybrid zone in central Texas. Located along the Balcones Escarpment, an inactive fault zone, this hybrid zone occurs at a strong ecotone between the semi-arid scrub habitat of west Texas and the eastern mesic hardwood forests. By collecting individuals outside (both east and west) and within the hybrid zone, I was able to analyze blood analytes for physiological differences, compare morphological differences, and extract DNA for mitochondrial and microsatellite analyses. Furthermore, I conducted playback experiments and recorded songs to understand more about interspecific communication. Overall, species differed in physiology, song structures, aggression levels, body size, and mitochondrial haplotypes. Birds west of the Balcones Escarpment (including the hybrid zone) have higher glucose values that increase following rainfall events indicating Black-crested Titmice are physiologically adapted to the scrub habitat with intermittent rainfall. Songs of species are easily distinguished by note number and tempo and Tufted Titmice appears a more aggressive species. Tufted Titmice are large in body size compared to Black-cresteds with differences linked to habitat characteristics. In general, birds within the hybrid zone are more similar to Black-crested Titmice than Tufteds. This was shown by similarities in body size, physiology, song structure, plumage, mitochondrial haplotypes, and microsatellite cluster assignment. Nuclear admixture (hybridization) was observed in low numbers, primarily within the hybrid zone, but analyses did not reveal a distinct cluster of genetic hybrids. Most importantly, genetic assignment did not match with a commonly used hybrid index such that crest plumage is not a reliable indicator of hybrid individuals or even species. I recommend that future research include a greater diversity of molecular markers, increased site collection for clinal analysis, and more behavioral research to better understand mate selection and hybrid fitness costs.
Subject
ParidaeTitmouse
Hybrid Zone
Genetic analysis
Ecophysiology
Morphology
Communication
Behavior
Citation
Vaughn, Jennifer Cary (2020). A Multi-disciplinary Analysis of a Titmouse (Baeolophus) Hybrid Zone in Texas. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /192962.