Life History and Developmental Variation of Tropical Versus Temperate Passerines

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Embryonic development is a critical stage in the life of organisms that shapes the physical and internal expression of the organism later in life. It can influence size, shape, and internal quality such as the strength of the immune system and quality of the neural/brain system. Rate of embryonic development varies dramatically among species, with an especially strong difference between tropical and north temperate organisms; tropical organisms develop much slower than organisms in North America, and this is very clear in songbirds. The classic explanation is that slower development is favored because it allows enhanced development of specialized cells, such as the immune system, to yield higher quality offspring. Yet, preliminary data raise questions about this long-standing view. This hypothesis will be explored along with 3 alternative hypotheses for the latitudinal variation in incubation periods of birds: 1) the classic trade-off with offspring quality hypothesis, 2) extrinsic adult mortality, 3) food limitation, and 4) nest predation. Proposed work will examine these hypotheses through continued studies of birds in the Andes of Venezuela to compare with related species in a long-term ongoing study in Arizona. The proposed work will use experimental manipulation of food and other hypothesized factors to test the alternatives, while also examining offspring quality based on size at hatching and measures of immune function.The proposed work has the potential to reverse long-standing views of the causes and consequences of slow development. At the same time, it will provide new insight into ecological factors favoring variation in the rate of development as well as the benefits and costs of that variation to quality of offspring. The proposed work will provide extensive opportunities for the integration and training of large numbers of undergraduate, graduate, and post-doctoral researchers of diverse U.S. and international (Latin American) communities. In short, the proposed work will provide a unique cross-cultural life experience as well as stringent educational and field experience for many undergraduates each year.