GENETIC AND MATERNAL ENVIRONMENTAL INFLUENCES ON EMBRYONIC PHYSIOLOGY: INTRASPECIFIC VARIABILITY IN AVIAN EMBRYONIC HEART RATES

ABSTRACT

The heart rate of embryos of altricial pigeons (Columba domestica) and bank swallows (Riparia riparia) was measured on a daily basis to investigate interclutch versus intraclutch variability in heart rate during development. In both pigeons and swallows, the developmental patterns of heart rate change in siblings (i.e., embryos from the same clutch) are statistically much more similar than those of embryos from other clutches of the same species. These findings could be explained on the basis of (1) measurement error (which cannot account for the present observations), (2) genetic effects, in which siblings are genetically predisposed to show particular physiological patterns, or (3) maternal and/or common environment effects, where environmental influences on either the mother or the offspring cause siblings to undergo more similar patterns of physiological development. Having defined and discussed these sources of variation, we indicate how experimental protocols might be designed that could determine the relative contributions of each of these sources of variation to physiological patterns observed during development.