Two female tree swallows (Tachycineta bicolor) engage in territorial displays of aggression, a behavior that allows them to defend resources critical to their survival.
News — The way people behave is influenced by processes such as mood, personality, and (curiously) our social context–it is much easier to find angry people waiting in line at the bank than cycling on Sunday afternoons. However, can the social context of parents affect the behavior of their future children?
Leigh Bailey, an M.S. student working with Assistant Professor Alexandra Bentz at the University of Oklahoma, is interested in the influence that the social environment of female birds has on their offspring’s early development.
Tree swallows are a type of migratory bird found throughout North America. When nesting, they return to their favorite breeding grounds to find resources for their future offspring. If resources are scarce, swallows spend most of their time brawling with other birds to defend their territory.
The extent to which a bird acts aggressively partly hinges on its genetic makeup, similar to how some people are innately more abrasive, and others empathetic. This is information encoded in an animal’s genes since the moment they are conceived. However, other kinds of information that are not genetically encoded can also have a tremendous impact on behavior.
One example are sex hormones such as testosterone (T), a hormone typically associated with men’s sexual development and behavior that is also produced by females and across many species, including tree swallows. “There are two sources of testosterone,” Bailey explains; “circulatory T produced by the offspring later in development, and maternal T deposited by the mother into its eggs before they are laid.” Hormones that ‘come with the package’ communicate specific information about the environment that offspring are about to face. The influence that this information has on offspring development is referred to as a ‘maternal effect’.
Bailey and colleagues decided to investigate maternal effects in the wild: they divided tree swallows in different groups and either gave them few or many nesting sites, a critical resource during breeding season. “We knew that swallows were territorial, so we exploited this to ramp up aggression and test how maternal T affects the offspring.”
Bailey’s preliminary data shows that mothers in groups with few nests behave more aggressively. Based on previous work by her group, she expects this will increase how much maternal T they allocate to their eggs. With heightened levels of maternal T, past studies showed that bird offspring grow faster, demand more food, and act more aggressively, all important traits for surviving in a competitive environment.
This work will allow us to understand how maternal effects prepare birds to survive in adverse conditions, but it also highlights the importance of a mother’s environment on the development of her children. “It’s remarkable how quickly these processes happen and have an impact that lasts for the offspring’s entire life.”
The results of this research project will be presented by Leigh Bailey at SICB 2023 in Austin, TX.
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