Mothers affect the quality of their offspring. As humans, this seems obvious. For example, expecting mothers often take prenatal vitamins, limit their consumption of certain foods, and avoid kitty litter knowing that these minor environmental factors can affect the normal development of the fetus. Related statements could be made for the relationship of a mother and child after birth. Understanding the precise effects that parents have on their offspring has been of great interest to biologists from many disciplines as they disentangle the genetic and environmental factors that underlie differential survival and reproduction for individuals within a population (fitness). Because Anolis lizards can be easily maintained in captivity and their eggs readily manipulated they provide a useful model for the examination of maternal effects. Warner and Lovern took advantage of these qualities and tested the role of maternal body condition on offspring quality in the brown anole, Anolis sagrei.
Nutritional stress is a well-studied example of how maternal condition may affect juvenile quality; if the mother is malnourished the quality of her egg yolk may suffer, which, in turn, affects embryonic development. The authors tested this hypothesis in A. sagrei by manipulating the amount of food gravid females received, feeding approximately 168 crickets per lizard in a “high-prey” treatment versus 84 crickets in a “low-prey” treatment distributed over 11 weeks. During this time the authors carefully assessed the number and size (mass) of the eggs and, subsequently, the quality (mass-and-snout to vent length) of the hatchlings. Impressively, the authors didn’t stop there. They also experimentally manipulated the amount of nutrition in a subset of eggs by removing yolk with a syringe. Followed by a battery of statistical models, this study is quite a nice physiological analysis that has evolutionary implications.
When comparing the two diet regimes, Warner and Lovern found that body condition does affect the quality of offspring; females maintained on the “low-prey” diet produced eggs 6.6% smaller than females raised on the “high-prey” diet. In turn, smaller eggs also tended to hatch more quickly and smaller eggs produced smaller hatchlings, both probably due to the lower amount of available nutrition (paradoxically, neither incubation time or hatchling mass was directly correlated with maternal prey availability). Low prey availability also results in hatchlings with slower growth rates. The experimental reduction of egg yolk supports the results of the prey availability study: hatchlings from yolk-reduced females were 8% shorter and 23% lighter and grew more slowly than those hatched from unmanipulated eggs. It is clear from their results that nutrition has an effect on hatchling quality well into life, after the obvious maternal effects have passed. There are a number of other interesting correlations (and statistical caveats) described within the text that may also be of interest to some readers.
What is becoming clear from studies like these is that environmental stressors can have lasting effects on organismal development that transcend generational boundaries. Mechanistic studies, such as those on the American alligator, illustrate that these effects are mediated by heritable methylation patterns of key regulatory genes. The stressors do not need to be long lasting; physiological responses can result from acute events that occur within key developmental windows, often when a particular organ is maturing. While stressing the embryo too far results in abnormal embryonic development, more subtle effects may not arise until late in life or subsequent generations. Anoles, and A. sagrei in particular, may provide a number of opportunities for environmental health research in the future. Studies such as the one described above could be performed to more precisely dissect the organ-specific effects of maternal nutritional stress or whether the effects dissipate with age. Similar to the alligator studies, eggs laid in polluted soils may allow opportunities for developmental toxicology research. Growing genomic resources may allow for examination of genome-wide and gene-specific methylation patterns within and outside of polluted habitats. The possibilities are broad and the impact cannot be predicted at this time, but the potential is there for much more detailed mechanistic research on the relationship between developmental physiology and the environment.