Scott Miller and Dr. Jerry Johnson, Biology
Among some of the most exciting research in evolutionary biology involves animal social behavior. Of particular interest is whether social behaviors are inheritable. If social behaviors are inheritable, they become a selective force and are capable of shaping the life history of an animal. Dr. Culum Brown has pioneered much of the research in this field with fishes. My research is based on his preliminary research and supplemented with work by Dr. Jerry Johnson. The goal of my research was to test if behaviors evolve in response to differences in mortality pressures in the environment. A greater understanding of how predation affects life history will enhance our ability to understand selective forces and help preserve endangered species. Perhaps more interesting though is the insights that might be gained in understanding complex human behaviors.
Two species of Brachyraphis indigenous to Central America were used in the research process. The species live in close proximity to one another in the wild (same drainage system), but are separated by a waterfall into upstream and downstream habitats. One species, Brachyraphis Roseni, inhabits an area with few natural predators. The other species, Brachyraphis Terrabensis, inhabits a predator dense region of the drainage system. Using three generations of each species in the assay, we are able to infer whether or not behavioral traits are inheritable. If traits are inheritable, we should see similar behavioral responses to predation in all of the generations of a particular species. If traits are not inheritable, there should be few differences in the behavioral responses between the two species among all generations.
The assay used to determine inheritance of behaviors is referred to as a bold/shy assay. The bold/shy assay used is based on the research of Yoshida et al. (2005) and Brown (2007). A tank measuring 24” x 17” x 10” and divided into four 6” intervals is placed in a soundproof chamber. A computer monitor is placed at the right end of the tank. A fish is placed in the far left quadrant of the tank and given fifteen minutes to adjust to the new surroundings. After adjustment, a video presentation is projected on the computer screen. The fish is kept in the far left 6” quadrant of the tank using a clear piece of acrylic capable of being raised. The first few minutes of the presentation show empty water. After 5 minutes, the acrylic door is raised and the fish is allowed to move about the tank as it pleases. I recorded the activity of the fish by marking how often the fish crossed each 6” line drawn on the tank. After ten minutes passes from the time the acrylic door opens, a natural predator (African cichlid) is displayed, startling the fish. I then recorded the amount of time it took for the fish to emerge from shelter (a small plant was placed in the far left corner of the tank.
In preparation for the trials, 10 female fish from each filial generation were subject to a twelve hour light:dark cycle and housed in separate tanks according to their appropriate generation (wild, F1, F2). The fish were fed twice daily with Tetra-Min commercial flake food. Each generation was given three weeks to recover from trials before being experimented with again.
I hypothesized that fish that were raised in predator dense areas in the wild would be shyer than fishes raised without predators. In this assay we describe shy as a fish that emerges from shelter less quickly after being exposed to a predator whereas a bold fish would emerge quickly after being startled by a predator. The following table graph describes my findings:
An analysis of the data shows a statistically significant difference in the emerge time between the wild B. Terrabensis and the wild B. Roseni. As predicted, the wild B. Roseni emerges from shelter more quickly than B. Terrabensis. This is likely because the wild B. Roseni subjects are from a predator naïve environment. However, there is no statistically significant differences between the emerge times of the F1 and F2 generations from both species. This data suggests that mortality pressures induced by predation do not evolve behaviors that are subject to selective forces.
It would be difficult to make a conclusive decision on the how selection effects behaviors in the wild based on this data alone. Most of the fish available in the Evolutionary Ecology Laboratory have been in captivity for several years. Their behaviors are likely to be different than fish currently in the wild. Captive breeding also affects the F1 and F2 generations in the study. The study also lacks a large sample size. Both of the species used in this study are protected by law and it is difficult to obtain large stock from the natural habitat.
In conclusions, it is interesting to note the difference in emerge time between the wild B. Terrabensis and the wild B. Roseni which suggests that behaviors are altered in response to predation. Further studies with wild stock may change the outcome of the F1 and F2 generations and reveal that selective forces are at work. I believe the experimental setup will be of great use to further research in this field. Dr. Johnson’s students will continue to use the assay I designed to further test my hypothesis.
References
- Brown C, Braithwaite VA, 2005. Effects of predation pressure on the cognitive ability of the poeciliid Brachyraphis episcopi. Behavioral Ecology 16:482–487.
- Yoshida M, Nagamine M, Uematsu K, 2005. Comparison of behavioral responses to a novel environment between three teleosts, bluegill Lepomis acrochirus, crucian carp Carassius langsdorfii, and goldfish Carassius auratu. Fisheries Science 71: 314–319.