Current research

The role of performance integration 

in survival and adaptation

Low-predation guppies from Trinidad

With my PhD I have shown that performance integration, or the necessity for performance traits such as feeding and locomotion, to work together to achieve an outcome, is important to predator success and can be quantified readily. However, we still understand very little about what this means for an organism's ability to adapt to new environments.  For example, does a highly integrated organism have a difficult time modifying its behaviors in new environments, or do the strong links between behaviors allow for simultaneous and rapid changes in several behaviors?  A good way to begin to answer this question is by using laboratory experiments with a model organism to determine the effects of novel environments on these traits and their ability to work together. 

Fishes are ideal for studying performance integration because integration between locomotion and feeding is expected. Most fishes use some degree of suction to capture prey, but this feeding mode is only useful for short distances. This means when a fish used suction, it also has to use the locomotor system to position itself close enough to the prey for suction to be effective. The video below demonstrates what this looks like when it doesn't work.

Additionally, work in fishes suggests that fishes that have strong suction don't swim fast, and that there might be a tradeoff in performance between systems when both are used to accomplish the same task (prey capture). This led me to the question: 

"If the environment changes so that selection favors one or both systems differentially, how does this affect the ability to integrate systems during prey capture?"

And this question led me to Trinidadian guppies (Poecilia reticulata). These tiny fishes are found throughout the Caribbean and South America but their location on the island of Trinidad is unique because they have repeatedly evolved to differences in predation pressure along each river/stream, and the rivers flow into three separate drainages (image below). This provides a nice natural experiment to test questions of evolution and adaptation to new environments. 

The rivers and respective drainages of Trinidad

More specifically, the streams vary in abiotic factors such as depth, width, and vegetation cover, which leads to variation in biotic factors such as productivity and predator communities. Because most of the guppy predators are prevented from crossing barrier waterfalls that occur along the streams, dramatic changes in exposure to predators can occur across short distances. Guppies that have founded populations above these waterfalls then experience dramatic shifts in selection pressures that result in genetic, morphological, behavioral, and ecological differences from their downstream ancestors. Therefore, it is likely that selection favors locomotor performance (predator evasion) downstream and feeding performance (due to competition with other guppies) upstream. This provides a unique opportunity to understand how natural variation in the environments results in changes in performance and integration in natural populations.

A diagram I made showing the differences in habitats
above and below the barrier waterfalls.
Pike cichlids (large gray predator) prey on all
guppy life stages; Hart's killifish (smaller yellow predator)
only prey on juvenile guppies.

To determine how guppies rely on the locomotor and feeding systems, and their integration during prey capture, I am collecting 2 replicate populations from high and low predation sites: one pair from the north slope of the Northern Range Mountains, and another pair from the south slope. I am concentrating on adult females because this is the sex that is responsible for providing for the offspring, and prey acquisition is vital for fitness. I am filming each female with a high-speed camera as she captures live, evasive Daphnia. These videos will be analyzed for locomotor and feeding kinematics that will be used to determine integration. Below is a zoomed-in high-speed video of a guppy capturing its prey.

Once these trials are finished, each female will also be filmed performing an escape response. These videos will be analyzed for locomotor performance in the absence of feeding to determine if a tradeoff between locomotor and feeding performance exists. This project will tell us whether there are in fact changes in feeding performance across populations (as suggested by morphological work), whether or not there are changes in the tradeoff between locomotion (escape) and feeding, and how specialization for either behavior affects the ability to perform the behaviors simultaneously to capture prey. This work is the first to consider the role of integrated biomechanical traits on the ecology and evolution of an organism and can lead to insights into how the requirement for parts to work together to accomplish a task can affect how organisms respond to changing environments. 

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