Robert H. Kaplan

Performance is an important link between morphology and fitness. For this reason, studies of the causes and consequences of performance variability can provide us with a fuller understanding of natural selection and adaptation. The specific question being addressed here is how does variation in maternal investment interact with environmental variation during early embryonic development to effect morphology and performance at the ecologically critical hatching stage (i.e., when larvae are particularly susceptible to predation)? I found (Kaplan, 1992) that greater maternal investment in offspring can actually decrease offspring fitness (survivability) in the field. This unique phenomenon was mediated by naturally occurring temperature variation that influenced growth and developmental rates of embryos. This rate variation interacted with ovum size variation to result in larvae at hatching with body proportions that varied, so that embryos that developed from large eggs in warm environments had decreased tail lengths and were more susceptible to predation. This led to the hypothesis that locomotor ability was compromised.The field study was followed up by a laboratory study that approximated the limits of field conditions and looked at the effects of development and maternal effects on locomotor performance. The results of this study (Parichy and Kaplan, 1995) clearly indicated that the foregoing hypothesis could indeed be correct since locomotor performance was diminished in larvae that developed from large eggs in warm environments, while it was enhanced by increased egg size in cold environments.