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Mammalian Reproductive Biology, Eco-Immunology, and Aging

Two Hamsters

My lab's principal area of interest is mammalian physiology, with a focus on the life history trade-offs associated with the timing of hormone secretion, reproductive effort, and immune function.  We study the effects of photoperiod and melatonin on female reproductive development and aging in Siberian hamsters, Phodopus sungorus. We are presently performing integrative studies at the molecular, cellular, and organismal levels to elucidate the mechanisms that underlie the photoperiod-induced deceleration of reproductive aging.

Because life history theory postulates that the timing of reproductive effort modulates somatic aging and longevity, we are interested in determining if photoperiod-induced deceleration of reproductive aging also slows somatic aging. To that end we are measuring the accumulation of DNA double-strand breaks, a potential biomarker of somatic aging, in hamsters with differing photoperiodic histories and life history trajectories. We are also investigating age-associated changes in neurobiology and behaviors (e.g., hippocampal neurogenesis and female mate choice) to determine if they are modulated by short photoperiod.

Methods used:


Some other systems and questions we're investigating:

Dogs and Cats - anti-Müllerian hormone for spay status and ovarian remnant syndrome (with Janet Scarlett, Bettina Wagner and James Flanders at Cornell University)

Horses - anti-Müllerian hormone in granulosa cell tumors (with Barry Ball and Al Conley, University of California, Davis) and seasonal variation in metabolic hormones (with Don Walsh, Homestead Veterinary Hospital)

Mice - role of estrogens in development of the external genitalia (with Larry Baskin and Jerry Cunha, University of California, San Francisco).

Monito del monte - seasonal variation in melatonin and leptin in a Chilean marsupial, the "little mountain monkey" (with Roberto Nespolo, Universidad Austral de Chile)

Spotted hyenas - natural masculinization of female external genitalia (with Steve Glickman, University of California, Berkeley - see below)

Sexual differentiation and behavior in spotted hyenas

Hyena Baby and Mom

The female spotted hyena, Crocuta crocuta, is the most highly masculinized female mammal known. Note the female cub's erect clitoris in the accompanying photo. Females have a peniform clitoris that is traversed to its end by a single uorgenital canal, through which they copulate, void, and give birth. They lack an external vaginal opening that is separate from the urethra and instead carry a pseudoscrotum. The Field Station for the Study of Behavior, Ecology, & Reproduction at the University of California, Berkeley is home to a captive colony of spotted hyenas. The director of the Berkeley Spotted Hyena Project, Professor Steve Glickman, has assembled a group of collaborators from across North America to investigate the mechanisms that underlie the masculinization of this amazing species. Along with our fellow collaborators we are trying to determine which elements of genitalia differentiation and development are androgen dependent and independent. Recent findings suggest estrogens, acting through either the androgen and/or estrogen receptor(s) (ER) may play a role in the development of the spotted hyena clitoris. We are assessing how reductions in estrogen synthesis affect the development of the external genitalia by administering a potent aromatase inhibitor (letrozole) to pregnant dams during early to mid gestation.

Some of the behaviors in spotted hyenas are equally fascinating (e.g., neonatal sibling aggression, female dominance over adult males) and we are investigating how prenatal androgen and estrogen exposure influence those behaviors. My hyena research takes me to Berkeley once or twice a year to engage in face-to-face meetings with Professor Glickman and other collaborators, as well as with the hyenas.