By Cody Trotter and Lynn Davis, College of Natural Resources
Few relationships in life are closer or more important than those between a mother and her offspring. In many wildlife species, mothers raise and nurture their young until they are independent, teaching valuable life lessons along the way. In addition, mothers influence their young based on the habitats they select for nesting, the types of food they supply, the amount of energy and other materials they provide to their eggs, and the behavioral interactions they have with their young during early development.
These non-genetic investments made by females in their young, called maternal effects by evolutionary ecologists, play a huge role in defining offsprings’ physical appearance, health, and abilities later in life, says William Hopkins, associate professor of fisheries and wildlife science at Virginia Tech. Hopkins and his colleagues conduct research to determine how the physiology and behavior of female amphibians, turtles, and birds affect their offspring and the consequences these interactions may have for population health.
A classic example of maternal effects is incubation behavior in birds. Birds incubate their eggs to maintain an optimal temperature for proper development of their embryos. However, many birds must also leave the eggs periodically for other activities, including feeding. Leaving the nest comes at a cost because it decreases incubation temperatures for the embryos. A decrease of even a couple degrees in incubation temperature can have important effects on the offspring.
Sarah DuRant, a wildlife Ph.D. student in Hopkins’ lab, tests how the incubation behavior of wood ducks affects their development before they hatch and whether it has lasting effects after hatching. She is trying to understand how changes in a female’s incubation behavior might influence development of the ducklings’ behavior, their endocrine system, and their immune system, all of which are critical to their survival. The initiative is a collaboration between researchers from the Virginia Tech Department of Fisheries and Wildlife Sciences and Department of Biological Sciences, Auburn University, and the University of Georgia, funded by a large grant from the National Science Foundation. The research is being conducted in South Carolina, where there is a considerable amount of information about the long-term life history of a wood duck population, making the link between female incubation practices and the effects it has on overall population health easier to identify.
To study wood ducks and other birds that nest in tree cavities, such as tree swallows, Hopkins’ research team places nest boxes throughout the birds’ breeding grounds to attract breeding pairs. Females build their nests and lay eggs inside the boxes, which are monitored throughout the reproductive season. Immediately after the eggs are laid, researchers remove some of them for incubation tests.
The borrowed eggs are incubated at various temperatures that mimic the natural range eggs would experience in the care of the mother. DuRant and Hopkins measure responses to different temperatures during development and examine the health of ducklings after hatching. The ducklings are released near their original nests to determine how they fare when returned to the wild. Auburn and Georgia researchers monitor the behavior of ducklings and determine first-year survival and return rates.
This year, the research team achieved exciting insights into how subtle changes in female behavior may have lasting consequences for their young. “We discovered that less than one degree difference in average incubation temperature is enough to strongly influence growth rates and endocrine responses during early life,” says DuRant. “This work will be important for conservation efforts because human-dominated landscapes can produce suboptimal habitat for nesting birds. When females are forced to spend more time away from the nest to find food, they spend less time incubating their eggs. Our work demonstrates that even moderate changes in a mother’s behavior could be important to the success of her young.”Share