A biologist at The University of Texas at Arlington is examining small Caribbean fish to study the evolution of how mothers pass on traits to their offspring to best prepare them for their environment.
Matt Walsh, professor of biology, is principal investigator of the project, which is funded by a three-year, $686,000 grant from the National Science Foundation's Division of Environmental Biology. The study is titled "The evolution of anticipatory maternal effects versus maternal condition transfer effects in Trinidadian killifish."
The environment in which an animal lives plays an important role in determining what traits get passed to offspring. One kind of maternal effect is referred to as anticipatory, such as when the mother anticipates that winter is coming and provisions her offspring to have more fat stores. Another kind is called condition transfer effect, meaning if the mother lives in a good environment, her offspring will likely do well regardless. This is also referred to as a "silver spoon" effect.
"Resource availability is predicted to be an important determinant of selection for condition transfer vs. anticipatory maternal effects," Walsh said. "What we want to do is to test hypotheses about what conditions favor maternal provisioning strategies. We're trying to get an idea of what favors one type of strategy over another."
Trinidadian killifish are a freshwater species native to Trinidad and Tobago, Grenada, Colombia and Venezuela. They are found in streams, pools, swamps and rivers. Some of their habitats are inaccessible to other fish because killifish can bypass waterfalls and travel to steep mountain streams. To avoid predators, they can also jump out of the water and survive on land for short periods of time.
"We're working with populations where we have predictions that should lead to the selection or evolution of different strategies," Walsh said. "That's the reason we study these different killifish populations, because the killifish in Trinidad are found in sites without predators. In areas where there are predators, they obviously eat the killifish. That means there are fewer killifish in those areas, but also a lot of resources for them because there's less density. So it's a really good environment for mom in the sense of provisioning offspring.
"We use those divergent, high- versus low-food environments to test how they influence the maternal provision strategies. That's the key aspect of the system."
The project has three central aims: • The first is to determine if predator-mediated divergence in resource availability favors evolutionary shifts in maternal effects—in other words, condition transfer vs. anticipatory effects. • The second is to test the connection between divergent natural selection, maternal condition and offspring fitness via "offspring outplant experiments," which will be performed in natural springs. • The third is to test the influence of resource availability on the evolution of maternal effects via long-term canopy-cover manipulations performed in natural streams.
"The grant itself is a series of lab experiments where we'll raise mom under different conditions and then evaluate the traits of the offspring," Walsh said. "We'll do all that right here in my lab at UTA."
For the second main goal of the project, offspring outplant experiments, Walsh and his students will raise killifish larvae in the lab, then put them into streams for the first time. The idea is to expose the mother fish to different conditions that will lead to her provisioning her offspring in a different manner. Those offspring will be hatched in the lab and the larvae will be chemically marked so they can be identified later.
"You can put them in streams and measure things like their ability to survive and grow and forage, then we can capture them later in the field and see which of the marked ones survived, which grew and by how much, and things like that," Walsh said.
Walsh and his students will make their first field trip for the project to Trinidad in June. He said the island has been a favorite place for field researchers since the 1950s because of the unique features of its steams.
"The simplified communities there allow you to address evolutionary questions of an organism because there's not a whole lot of other things going on, so you can have a really good understanding of the ecology," he said. "Also, the communities are really close together, just separated by barriers, meaning the environments are nearly identical — things like water temperature and physical structure."
Clay Clark, professor and chair of the Department of Biology, hailed Walsh's project for its potential to advance scientists' knowledge of how species evolve in their attempt to ensure the viability of future generations.
"This new study by Dr. Walsh is a great example of the tremendous research being done by our faculty in the Department of Biology," Clark said. "This work will provide new insights into how mothers determine what traits to pass on to their offspring based on their environment."
Since it is now known that many environmental stressors can cause nongenetic effects that persist for multiple generations, Walsh said the project has broad implications for understanding the mechanisms by which organisms respond to environmental change, as well as scientists' ability to forecast species' responses to novel environmental stressors.
"The overarching goals of the project are to better understand what determines how mom provisions her offspring and when she should create a few large individuals versus when she should create many small individuals," Walsh said. "Lots of organisms are sensitive to the environment and how that influences the number of offspring they produce, so this project will allow us to better understand what determines those patterns out in nature."
