Why study behavior?
Behavior provides a unique perspective linking the physiology and ecology of an organism, and its environment. Behavior is both a sequence of quantifiable actions, operating through the central and peripheral nervous systems, and the cumulative manifestation of genetic, biochemical, and physiologic processes essential to life, such as feeding, reproduction and predator avoidance. Behavior allows an organism to adjust to external and internal stimuli in order to best meet the challenge of surviving in a changing environment. Conversely, behavior is also the result of adaptations to environmental variables. Thus, behavior is a selective response that is constantly adapting through direct interaction with physical, chemical, social, and physiological aspects of the environment. Selective evolutionary processes have conserved stable behavioral patterns in concert with morphologic and physiologic adaptations. This stability provides the best opportunity for survival and reproductive success by enabling organisms to efficiently exploit resources and define suitable habitats.
Since behavior is not a random process, but rather a highly structured and predictable sequence of activities designed to ensure maximal fitness and survival (i.e., success) of the individual (and species), behavioral endpoints serve as valuable tools to discern and evaluate effects of exposure to environmental stressors. Behavioral endpoints that integrate endogenous and exogenous factors can link biochemical and physiological processes, thus providing insights into individual- and community-level effects of environmental contamination. Most importantly, alterations in behavior represent an integrated, whole-organism response. These altered responses, in turn, may be associated with reduced fitness and survival, resulting in adverse consequences at the population level. [Kane et al. 2004.]
Primary efforts include characterizing and quantifying male and female reproductive behaviors of small fish models. Intial work has involved observations of mummichog (Fundulus heteroclitus) and fathead minnow (Pimephales promelas). These species are sexually dimorphic and have several critical reproductive behaviors within their reproductive behavioral repertoire that can be quantified. We are interested in examining the range reproductive of strategies used and determine if differences within this range of reproductive behaviors, and associated physiological endpoints, effect reproductive success in terms of maximizing clutch size, fertilization rate, and survival of offspring. These behaviors include, nest cleaning, courtship, spawning, egg maintenance and defense (see video clip below). Once the normal range of reproductive behaviors have been quantified, fluctuations in environmental parameters that can alter reproductive behavior and success can then be examined.
The design of our behavior laboratory includes 12 arenas with CCD cameras (below, left) that transmit data to a multiplexer and VCRs (below right). Computer-controlled recording allows for automatic and remote video data collection.
Schematic diagram (above, left) illustrating the behavioral quantification suite at the University of Maryland Aquatic Pathobiology Center. A water preparation room with carboys and computer-controlled pumps provide flow-through or static renewal media support to the videography room. The videography room contains aquaria that serve as reproduction arenas, water distribution and drainage lines (not shown), dedicated CCD cameras set to record from below, translucent tank dividers (not shown) and shadowless lighting (not shown). The observation room (above right) contains the control computer, a video multiplexer, and display monitor. This equipment permits simultaneous viewing of fish in real time during an experiment. Video signals are recorded on dedicated VCR decks that are controlled by X-10 computer software and hardware. Digitized video data can then have targets (fish) tracked over time (see movie below), and x,y coordinate data generated for each animal.
Tracking of fish groups.
The QuickTime movie on the left shows 5 minnows being followed by our tracking software as they acclimate over time in a circular arena. The magenta crosshairs indicate the mid-point of the body. Based on an algorithm that uses least squares analysis, when the paths of two fish cross, the tracking software can continue to follow individual fish with relativey excellent accuracy.
After determining the x,y coordinate data over time for each of multiple arenas, various questions can be asked of the data. These questions include trajectories of individual fish as well as relationships between fish targets (e.g., proximity, nearest neighbor angle, nipping/butting, circling, space utilization, tortuosity, etc.).
This QuickTime movie portrays a male fathead minnow under a spawning structure that is joined by a gravid female. This movie demonstrates several reproductive behaviors that are key to sucessful spawning of this species including parallel circling and a spawning attempt. The spawning attempt shows the male using his entire body length to guide the female to deposit eggs to underneath surface of the spawning structure. This behavior is often repeated several times prior to egg deposition.
Other key behaviors, not shown in this clip, include pre-spawning interactions (nipping & butting), male territoriality, egg guarding and egg fanning. These behaviors are sufficiently distinctive such that we can quantitatively discern them using our video analysis software.
Secondary Sex Characteristics
Panel A shows dorsal epithelial pad (arrow). Panel B shows breeding tubercles on the snout (arrows). Panel C shows ovipositor just anterior to anal fin; this is normal for a breeding female but not normal for males. Ovipositors can be observed on males exposed to low levels of estrogen-like compounds.
Since fathead minnows are sexually dimorphic (males and females look notably different), and the male exhibits secondary sexual characteristics in breeding condition, we can use changes in morphology of secondary sex characteristics as an ancillary endpoint to evaluate exposure effects of low-level endocrine disrupting chemicals. Expression of these secondary characteristics, like reproductive behavior, is hormonally-driven. Thus, by integrating behavior, hormones, and secondary sex characteristics, we can obtain a more holistic picture of biologically-relevant responses to endocrine disrupting chemicals.
Kane, A.S., Salierno, J.D. and Brewer, S.K. 2004. Fish models in behavioral toxicology: automated techniques, updates and perspectives. In Ostrander, G.K., ed. Methods in Aquatic Toxicology, Volume 2. Lewis Publishers, Boca Raton, FL.
Kane, A.S., Salierno, J.D., Gipson, G.T., Molteno, T., and , Hunter, C. 2004. Novel video-based movement analysis system to quantify behavioral responses of fish. Water Research. 38:3993-4001.
Salierno, J.D., Gipson, G.T. and Kane, A.S. 2008. Quantitative movement analysis of social behavior in mummichog, Fundulus heteroclitus. Journal of Ethology 26:35-42.
Lauer, L.E., McCarthy, M.M., Jong, J. and Kane, A.S. 2006. Sex differences in neuronal morphology in the killifish hypothalamus. Brain Research, 1070:145-149.
Histological Atlas of Normal Fathead Minnow Anatomy (coming soon)