Sunday, August 4, 2013

Congratulations Scott Miller and Katherine Heldt

Scott Miller completed his Calhoun Honors College BS Thesis
Katherine Heldt completed her Biological Sciences MS Thesis

Effects of disease and ocean acidification on the den sharing behavior of juvenile Caribbean spiny lobster, Panulirus argus

Scott Donald Miller

Calhoun Honors Undergraduate Thesis
Department of Biological Sciences
Clemson University

Dr. Michael Childress
Thesis Advisor


Chemical cues play important roles throughout marine ecosystems, and different factors can alter the way that organisms detect or interpret these cues.  Diseases in populations and global water quality changes, such as ocean acidification, can greatly alter the behavior associated with information gathered from olfaction.  The Caribbean spiny lobster, Panulirus argus, is an organism that relies on chemical cues to find protective shelters and to mediate social behavior, and both disease and ocean acidification have the potential to impact its ability to rely on these cues for these behaviors.  Our study sought to see how disease would influence lobsters’ ability to compete for shelters and how ocean acidification impacts den sharing and social behavior in these lobsters.  This study comprised of three parts. 

The first portion of the study examined the interactions between diseased and healthy lobsters in a shelter-limited environment.  A healthy lobster was placed inside of the only den in an experimental aquarium, a diseased lobster was introduced, and physical interactions were observed.  This was repeated with the same lobster inside the den, but with a healthy lobster as the intruder.  We found that the presence of a diseased lobster lowered the aggression of both healthy and diseased lobsters and that in diseased trials, the healthy lobster spent more time in the den compared to the diseased individual.

In the second part of the study, the effects of ocean acidification on lobsters’ den sharing and aggressive behavior were examined.  Lobsters were housed in pairs and observed nightly for a week in both normal and lowered pH, where aggressive acts, den sharing, and olfactory sampling behaviors were measured.  Y-maze odor preference trials were run simultaneously to determine lobsters’ odor preferences.  The Y-maze trials were conducted in three rounds.  During the first round, lobsters were kept in normal pH water and the Y-maze contained normal pH water.  In the second round, home aquaria were kept the same, but the Y-maze contained lowered pH water.  For the third round, both home aquaria and the Y-maze pH were lowered.  During behavioral observations, we found lobsters to show less aggressive acts, less den sharing, less antennule flicks, and more antennule wipes after prolonged exposure to depressed pH.  Lobsters showed some evidence of altered odor preference when the Y-maze pH was reduced.

In the final portion of the study, scanning electron microscopy was used to determine if exposure to pH damages the sensory organs of the lobsters.  At the completion of the study, lobsters’ antennules were removed, fixed, and observed under SEM.  We found similar counts of setae in both groups.  There was evidence of damage in the group exposed to lower pH, but due to a small sample size, this was inconclusive.  This study provides evidence for significantly altered den sharing and social behavior in P. argus when exposed to various stressors that are projected to continue to be an issue in the future.

Individual behavioral variation of juvenile spiny lobster (Panulirus argus) denning behaviors and the role it plays in shelter competition during habitat loss

A Thesis Presented to the Graduate School of Clemson University
In Partial Fulfillment of the Requirements for the Degree Master of Science In Biological Sciences

Katherine A Heldt

Michael J. Childress, Committee Chair


Variation in juvenile spiny lobster (Panulirus argus) aggressive and gregarious behaviors may play an important role in structuring population level interactions.  Since aggressive and gregarious behaviors were not repeatable and were found to be highly correlated with size, these behaviors were found to be largely driven by a combination of behavioral plasticity and ontogeny.  Although larger individuals were found to be the most aggressive individuals, least gregarious and often occupied crevice shelters by themselves, they did not exclude smaller, less aggressive lobsters from crevice shelters.  Surprisingly, in shelter limited situations, small, less aggressive individuals were more likely to use dens and remain in dens, while large, more aggressive individuals were more likely to remain outside of dens and disperse.  In general, larger individuals are able to walk longer distances in less time and are less likely to be preyed upon while away from shelter, suggesting that vulnerability may play an important role in the decision to share dens or disperse.  Effects of prior experiences in natural shelter-rich or natural shelter-poor habitats were also found to influence denning behaviors with individuals from natural shelter-poor habitats better responding to sudden shelter loss. Therefore, prior experiences may also play an important role in denning behavior.  This thesis provides evidence for behavioral ontogeny and plasticity in juvenile spiny lobster social behavior and is an important first step in understanding the role of individual behavioral variation in den competition and behavioral mitigation of habitat loss.

No comments: