Research in the Marler Lab centers around bi-directional interactions between endocrinology and animal behavior combined with the modifying influence of the surrounding social and physical environment. Currently, we are asking questions related to how past winning experience influences both future ability to win and androgen receptors in reward-related brain areas, how the reinforcing/rewarding effects of testosterone can alter the location where a male chooses to spend more time and which brain areas may be involved, how oxytocin shapes both classical affiliative behaviors (parental behavior and bonding) and division of labor, and how ultrasonic vocalizations are modified through hormone manipulations and social context. The primary focus is on the California mouse, Peromyscus californicus, because it is a monogamous, biparental, and territorial species that can be studied in both the laboratory and field.

Peromyscus californicus Photo by Mark A. Chappell
California mouse – Photo by Mark A. Chappell

Current Research Topics

Pair Bonding
How do hormones such as testosterone, oxytocin, and vasopressin interact to facilitate the formation and maintenance of a pair bond? Are pair bonding, mate fidelity and parent-offspring bonding regulated by the same or different mechanisms? Are there sex differences in regard to mate fidelity? Do certain behavioral or hormonal features during courtship predict pair bond strength? How do infidelity experiences affect the quality of the pair bond? When pair bonding occurs is there a change in the level of cooperation between individuals and how is this expressed? What are the hormonal mechanisms underlying this cooperation?

Social Communication
Do ultrasonic vocalizations (USVs) between opposite-sex individuals during courtship reveal characteristics of mate quality? Do USVs between same-sex individuals predict territorial dispute outcomes? How does acoustic communication change over the formation of the pair bond? Are patterns of chemical cues (via urinary scent marking) and features of USV production indicative of individual mating strategies? What features of social communication are regulated by hormones, and in turn, how do these features feedback to induce hormonal changes in the receiver?  Click here to listen

How are territorial behaviors modulated by the environment (home versus unfamiliar) and how do androgens interact with the environment to produce behavior? Is territoriality broadcasted between competing individuals via ultrasonic communication? Is the ‘winner effect’ (a phenomena in which winning an agonistic encounter increases the probability of winning future encounters) regulated via the ‘challenge effect’ (transient increase in testosterone after an agonistic encounter) and is this conveyed via ultrasonic vocalizations? What brain areas underlie the plasticity of these behaviors? How do male and female territorial behaviors differ in a monogamous species?

Parental Care
Are behavioral and hormonal signatures during courtship predictive of parental care quality? Does testosterone always decrease paternal behavior, or can testosterone increase paternal behavior via mechanisms that are similar to maternal behavior (i.e. aromatization of testosterone to estrogen)? What parental behavioral traits influence adult behavior of offspring? Can these traits be transmitted through multiple generations via epigenetic mechanisms? Does variation in paternal care underlie developmental changes in hormones and neurochemicals (such as arginine vasopressin) in the offspring? Do these early changes predict levels of territoriality as adults?

Do long term versus pulsatile patterns of T release impact behavior in different ways? How important is pulsatile release of T in shaping social behavior? Do the reinforcing and rewarding effects of T pulses alter behavior and does this occur via changes in location (via conditioned place preferences) and/or through the classical changes in probability of expression of behavior? Is there plasticity in the ability of testosterone to influence preferences for locations based on past experience and current location? If yes, what are the neural mechanisms underlying this plasticity? What are the natural functions of developing conditioned place preferences (laboratory and field)? How important is context for the effects of testosterone on social behavior? Since androgen receptor expression changes in reward-related brain areas (nucleus accumbens and ventral tegmental area) with winning experiences does this influence future aggressive behavior? Do other hormones and neurochemicals that influence social behavior act through the same mechanisms? Does this interact or influence behavioral responses or addictive properties of drugs?

Previous Research and Animal Models

Arginine Vasotocin and Acoustic Communication in Treefrogs and Tungara Frogs
How do neurohormones, such as arginine vasotocin, influence acoustic communication and how do the behavioral changes evoked through hormonal changes influence other individuals in the natural environment? Does arginine vasotocin simply increase calling behavior in frogs or are specific call characteristics changed and is the hormonal effect still influenced by the social environment?

Testosterone and Parasite Load in Mountain Spiny Lizards
The evolution of behavior/hormonal interactions can be studied by manipulating hormonal levels and examining the costs and benefits of the behavioral and physiological changes. What are the costs of elevated testosterone and aggression in the field? What are the survivorship costs associated with increased testosterone via detrimental effects on the immune system? Can answers to these questions be revealed through field studies examining of testosterone levels and ectoparasite activity in Sceloporus.

Mating System and Life History Differences: Comparative Approach between two Peromyscus species, the California and White-Footed Mouse
Does the winner effect and associated hormonal changes differ between species with different mating systems and levels of territoriality? What brain areas underlie species differences in paternal care and mate fidelity?