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R. David Maclaren, Ph.D.

Associate Professor



Ph.D., Ecology and Evolutionary Biology, Indiana University
B.A., Biology, University of Maine, Farmington


  • Animal Behavior (BIO3063)
  • Evolution (BIO3072)
  • Comparative Animal Anatomy & Physiology I: Nervous & Endocrine Systems (BIO3050)
  • Marine Biology & Sustainability (BIO3064)
  • Principles of Biology II Lecture & Labs (BIO1028)
  • Human Biology (BIO1106)
  • Directed Study/Research I and II (BIO4092;BIO4096)


I have three research foci:

  1. The role of sexual selection in fish evolution.
  2. Investigating the effects of environmentally realistic herbicide and pharmaceutical exposure on hormone concentrations, reproductive and aggressive behavior in fish.
  3. Behavior, ecology, and conservation of marine mammals in the Gulf of Maine.


Sexual selection in fish evolution: My research combines ethological, evolutionary, ecological, and phylogenetic approaches to investigate animal behavior.  Using experimental and observational methods, my interests focus on the elicitation, control, function, and evolution of behavior in fishes. Recent projects investigate visual signals and the mechanisms by which they control and mediate courtship, aggression, and other social behaviors. Much of my research to date involves experimental studies on mate choice, sexual selection and aggression in Poeciliid fishes.

Investigating of the effects of environmentally realistic exposure to pharmaceuticals and other anthropogenic chemicals on the physiology and behavior of fish: Students in my lab are currently investigation of the effects of metformin (the medicine most commonly prescribed for the treatment of Type II diabetes) on hormone concentrations (cortisol and 11-ketotestosterone) nest-building and aggressive behavior in the Siamese fighting fish, Betta splendens. Metformin is among the most abundant pharmaceuticals being introduced into the environment. Pharmaceuticals are increasingly found in wastewater and surface waters around the world, often due to incomplete metabolism in humans and subsequent excretion in human waste. These chemicals become part of the effluent discharged by wastewater treatment plants (WWTP) into local surface waters. Although these compounds generally leave WWTPs at low levels, risk analyses and exposure studies have raised concerns about potential negative impacts of pharmaceuticals at current environmental levels. Recent studies suggests the potential for metformin to act as an endocrine disrupting chemical (EDC), a common form of pollution caused by compounds that interfere with proper hormonal functioning. EDCs can alter reproductive success by affecting all aspects of the reproductive system, including sex organ development, production of hormones, eggs and sperm, sex determination, formation of egg shells, and production and maintenance of mating signals and behaviors. Exposure to such chemicals generates changes in behavior. Behavior is therefore an excellent indicator of environmental impacts on an organism as behavioral changes that interfere with a species’ health and sustainability in the environment may be observed long before physiological changes occur. Understanding not only individual, but the population level effects of EDC-altered reproductive and aggressive behavior is important to conservation biology. Many contaminants are persistent and remain in the environment at substantial concentrations for several years, spanning multiple generations of short-lived species. Multi-generational disruption of traits used for reproduction such as territorial aggression and mate choice can alter evolutionary trajectories and threaten the species continued existence in the polluted environment.

Experiments with Betta splendens and Poecilia latipinna my students and I (in collaboration with Dr. Stephan Theberge in Merrimack’s Dept. of Chemistry & Biochemistry) are currently working on in connection with this subject include the following:

  1. Effects of short- & long-term exposure to ecologically-relevant levels of pharmaceutical exposure on intraspecific aggression and male parental care (nest-building behavior).
  2. Effects of short- & long-term exposure to pharmaceuticals on female mate choice behavior.
  3. Effects of pharmaceutical exposure on11-ketotestosterone (male sex hormone) & cortisol (a stress hormone)levels.

Behavior, ecology, and conservation of marine mammals in the Gulf of Maine: I also hold a strong interest in marine mammal behavior, ecology, and conservation. In Spring 2009 I established a partnership in research and education with the Blue Ocean Society for Marine Conservation (, a non-profit organization dedicated to marine mammal research, conservation, and education centered in Portsmouth, NH. During the summer months I serve as “Naturalist” aboard whale watch vessels, collecting behavioral and physical data on the whale, dolphin, and sea bird populations in the Jeffreys Ledge region of the Gulf of Maine and Stellwagen Bank National Marine Sanctuary while educating the public on marine mammal ecology and conservation. This work involves mentoring undergraduate students conducting summer research at Merrimack and/or interning with Blue Ocean. All the data collected are added to Blue Ocean’s data base, which we then analyze during the off season.  As part of this collaboration, Blue Ocean provides competitive internship/research opportunities to Merrimack students interested in marine mammal ecology, behavior & conservation. Click on the following link to view a gallery of pictures taken over the past few seasons on the water:!i=2687311517&k=x5SKjFr


Current Research

My students and I are currently working on two research projects:

  1. The fish behavior and physiology projects described above. 
  2. A collaboration with Blue Ocean scientists in the analysis of 18+ years of marine mammal data from the Jeffreys Ledge region of the Gulf of Maine and Stellwagen Bank National Marine Sanctuary. Research efforts cover a wide range of study questions primarily addressing humpback (Megaptera novaeangliae) and fin whale (Balenoptera physalus) behavior, ecology and conservation.

Selected Publications

* denotes undergraduate researcher

MacLaren, R.D., *Langone, A., *Rozen, J., MacLaren, C. *Marcelonis, K., *Zananiri , J., *Dadwal, S., *Shanley, M., and *Shahin, S.  2017. Environmental concentrations of metformin exposure affect behavior in the Siamese fighting fish, Betta splendens. Under review.

MacLaren, RD. 2017. Effects of male apparent length on female preference for absolute body size in Xiphophorus helleri. Acta Ethol.  20(1), 27-36. DOI 10.1007/s10211-016-0245-0

MacLaren, RD. 2016. Social environment affects female preference for male body color during development in artificially selected varieties of Poecilia latipinna. Ethology, Ecology & Evolution. DOI: 10.1080/03949370.2016.1220427

MacLaren, RD, *Fontaine, A. 2013. Incongruence between the sexes in preferences for body and dorsal fin size in Xiphophorus variatus. Behavioural Processes 92, 99-106: 10.1016/j.beproc.2012.10.013

MacLaren, R.D., Schulte, D. and Kennedy, J. 2012. Field research studying whales in an undergraduate animal behavior laboratory. Bioscene Journal of College Biology Teaching.

MacLaren, R.D. and *Fontaine, A. 2012. Female bias for male lateral projection area in Poecilia reticulata. Environmental Biology of Fishes. Vol. 93, Issue 1, 105-119.

MacLaren, R.D., *He, R., and *Gagnon, J. 2011. Bias for enlarged male body and dorsal fins in female Xiphophorus variatus. Behavioural Processes 87, 197-202.

MacLaren, R.D. and *Daniska, D. 2008. Female preferences for dorsal fin and body size in Xiphophorus helleri : further investigation of the LPA bias in Poeciliid fishes. Behaviour. 145, 897-913.

MacLaren, R.D. 2007. Female preference in Xiphophorus helleri: Further investigation of the LPA bias in Poeciliid fishes. 2007 Annual Animal Behavior Society Conference Abstracts. 

MacLaren, R.D. 2006. The effects of male proximity, apparent size, and absolute size on female preference in the sailfin molly, Poecilia latipinna. Behaviour. 143, 1457-1472 

MacLaren, R.D. and Rowland, W.J. 2006a. Female preference for male lateral projection area in the shortfin molly Poecilia mexicana; evidence for a preexisting bias. Ethology. 112, 678-690.

MacLaren, R.D. and Rowland, W.J. 2006b. Differences in female preferences for male body size in Poecilia latipinna using simultaneous vs. sequential stimulus presentation designs. Behaviour. 143, 273-292.

MacLaren, R.D., Rowland, W.J., and *Morgan, N. 2004. Female preferences for sailfin and body size in the sailfin molly,Poecilia latipinna. Ethology.110, 363-379.

Rowland, W.J., *Grindle, N., MacLaren, R.D., and Granquist, R.2002. Male preference for a subtle posture cue that signals spawning readiness in female sticklebacks. Animal Behaviour. 63.

See Also

Supplemental figures 4 & 5 accompanying “Field research studying whales in an undergraduate animal behavior laboratory” by MacLaren, R.D., Schulte, D. and Kennedy, J. Published in Bioscene Journal of College Biology Teaching in spring 2012.





Mendel 270