Project Title: Biased Evolutionary Transitions in Mode of Development: Can Differences in Morphology and Digestive Function be Linked to Evolvability of gastropod Development?
Principal Investigator: Collin, Rachel
NSF Project Number: IOS 1019727
For over 100 years it has been thought that the loss of complex morphological structures or functions, like the loss of legs in whales and the loss of flight in ostriches, is irreversible. However, recent results suggest that some kinds of animals can regain lost structures or functions. One example of this is in a family of sea snails. In about 50% of these snails the free-living larval stage has been lost, but surprisingly it has been regained in 3 species. This research will use biomechanical, morphological and developmental approaches to understand how the larval structures and their function are lost, and if the different ways they are lost can either prevent or allow the reacquisition of the larval stage. Results will include detailed understanding of how the larvae of these snails capture particles from the plankton, how their ability to digest different food sources develops as the embryonic snails grow, and if simple laboratory manipulations can alter how they develop. Understanding the factors that affect the development of marine animals is important because the larval stage increases the ability of populations to survive local disturbances and relocate after habitat destruction. It also reduces the chances of extinction relative to species that lack the larval stage. Finally the presence of a free-living larval stage also increases the potential for species to become invasive pests. This project will train 3 undergraduate interns, 2 graduate students and one post-doctoral fellow, support an advanced undergraduate-level course, and produce a series of short educational videos provided to the public on YouTube.
Can Evolution Run in Reverse? Researchers have long believed that once an evolutionary change happens it is unlikely to be undone. This is particularly true when morphological features are lost. For example, the ancestors of snakes had legs, at some point during the evolution of snake ancestors the legs and the developmental mechanisms that produce legs were reduced and then lost, making it unlikely or impossible for legs to reappear. This idea is referred to as Dollo's Law. A less familiar example of Dollo's law involves the microscopic larval stages of marine invertebrates. Most species of sea snails, crabs, and other marine invertebrates produce millions of tiny larvae that swim and feed in the plankton. These larvae are linked to species' abilities to resist extinction, but may also limit their abilities to adapt to local environmental change. The evolutionary loss of these distinct larval stages is common in some invertebrates and was thought to be irreversible. However one group of snails, the slipper limpets prove to be an exception, with at least 2 species that have independently re-evolved larvae. To find out why slipper limpets break the rule Rachel Collin of the Smithsonian Institution and her students have travel to Florida, Panama, Chile, and Argentina. Comparing the developmental stages of slipper limpets from each of these regions shows something quite unexpected. Although many of these species do not produce larvae the embryos still grow the structures larvae use for swimming and feeding. Even more surprising, even though these early stages are too large to swim, they can capture particles of food and ingest them. Because these larval features are retained even when they do not seem useful, a larval stage could be regained easily millions of years after it is lost. This developmental flexibility likely drives the success of slipper limpets. Students working on this project have shared their experiences on a blog and YouTube channel.
