Glucose Concentrations in Closely Related Titmice () Species Linked to Regional Habitat Differences Across an Avian Hybrid Zone
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Aims:We used physiological data, in conjunction with habitat information, to elucidate the interactions between two hybridizing songbirds within a hybrid zone.Background:Hybrid zones are ideal regions to examine a variety of ecological, behavior, and evolutionary processes. In addition to genetics, behavior, and morphology, physiological differences may impact hybrid fitness, genetic introgression, and even the stability of a hybrid zone.Objective:To assess physiological differences in hybridizing species, we investigated selected venous blood analytes in two species of songbirds hybridizing along the Balcones Escarpment in central Texas.Methods:Using a portable blood analyzer, we assayed blood samples from Black-crested Titmouse (Baeolophus atricristatus) and Tufted Titmouse (B. bicolor) individuals along a longitudinal transect that included the contact zone. Ecologically, this transect varies from higher elevation semi-arid regions on the Balcones Escarpment (and west across the Edwards Plateau) to lower elevation mesic forests east of the escarpment.Results:As expected, several blood analytes differed with age, sex, and sedative administration; however, we observed relatively increased blood glucose concentrations in Black-crested Titmice, which occupy the semi-arid habitats of west Texas. Furthermore, glucose concentrations were further elevated following rainfall events. Blood glucose concentrations often increase during stressful conditions and or related to changes in diet.Conclusion:We suspect that Black-crested Titmice have relatively increased blood glucose concentrations as a product of living in a semi-arid environment that causes chronic stress from unpredictable food and water resources. The link between rainfall and glucose may be a result of the increased and greater diversity of food availability after rainfall. Although further research is needed, we suspect that habitat differences and associated lack of physiological adaptations may be a limiting factor in westward range expansion in the more aggressive Tufted Titmice.
