P1-103 Monday, Jan. 4 15:30 Hot Islands, Big Bills: The effect of gene flow and climate on morphology GAMBOA, MP*; GHALAMBOR, CK; FUNK, WC; SILLETT, TS; Colorado State University; Colorado State University; Colorado State University; Smithsonian Migratory Bird Center email@example.com
Natural selection across heterogeneous environments may favor locally adapted ecotypes, but identifying the mechanisms that underlie adaptive variation in natural populations remains a challenge. Disentangling the environmental and genetic underpinnings of phenotypic variation requires systematic sampling of populations across different environments and under varying degrees of isolation. Climatic variation is increasingly appreciated as a strong selective pressure on morphological characters. In birds, the bill may be used as a tool for thermoregulation by dissipating excess heat and, consequently, is under selection from climate. On the Northern California Channel Islands (Santa Cruz, Santa Rosa, San Miguel, and Anacapa), song sparrows (Melospiza melodia graminea) occupy a distinct east-to-west climatic gradient ranging from hot and arid on Santa Cruz Island to cold, wet, and windy on San Miguel Island. We genetically sampled and measured bill characteristics from song sparrows distributed on Santa Cruz, Santa Rosa, and San Miguel Island from 2014-2015. As predicted, bird bills were significantly larger on hotter islands (Santa Cruz) than those found on colder islands (Santa Rosa, San Miguel). STRUCTURE analysis and DAPC of thousands of SNPs reveal low FST values and distinct clustering by island suggesting population structure despite gene flow. Thus, climate may drive local adaptation and must be considered in the development of conservation management strategies, particularly of insular populations.