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

The heart rate of embryos of altricial pigeons (Columba domestica) and bank swallows (Riparia riparia) was measured on a daily basis to inve stigate interclutch versus intraclutch variability in heart rate durin g development. In both pigeons and swallows, the developmental pattern s 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 th e 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) materna l and/or common environment effects, where environmental influences on either the mother or the offspring cause siblings to undergo more sim ilar patterns of physiological development. Having defined and discuss ed these sources of variation, we indicate how experimental protocols might be designed that could determine the relative contributions of e ach of these sources of variation to physiological patterns observed d uring development.