Virginia Hayssen’s research examines the evolution of reproduction across mammals, specifically exploring how litter size, gestation length, neonatal length and lactation length are influenced by the physical characteristics of an animal as well as by its ancestry and ecology.

A second research emphasis is on pleiotropy, the multiple phenotypic effects a single genetic locus can have on the biology of an animal. Specifically, investigating the agouti coat-color locus, which alters the external color of an animal’s fur but also alters its behavior and internal anatomy.

In addition, Hayssen publishes synthetic reviews of individual mammalian species including all aspects of their biology, their distribution, their conservation and their historical names.

Representative Publications

Hayssen, V., T.J. Orr. 2017. Reproduction in mammals: the female perspective. Johns Hopkins University Press, Baltimore, MD.

Noonan, P., Prout, S., Hayssen, V.; 2017. Pteronura brasiliensis (Carnivora: Mustelidae). Mammalian Species 49: in press

Lurz, P.W.W., Fielding, I., Hayssen, V.; 2017. Callosciurus prevostii (Rodentia: Sciuridae). Mammalian Species 49(945): 40–50.

Hayssen, V.  2016. Reproduction in grey squirrels: from anatomy to conservation. Pp. 115-130 in ‘The grey squirrel: ecology and management of an invasive species in Europe’ (Shuttleworth, C, Lurz, PWW, and Gurnell, J, eds.). European Squirrel Initiative, W. O. Jones, Llangefni, Wales

Hayssen, V. 2014. "Cabassous unicinctus (Cingulata: Dasypodidae)." Mammalian Species 46(907): 16–23.

Hayssen, V. 2014. "Cabassous chacoensis (Cingulata: Dasypodidae)." Mammalian Species 46(908): 23–27.

Hayssen, V. 2014. "Cabassous tatouay (Cingulata: Dasypodidae)." Mammalian Species 46(909): 28–32.

Lurz, P.W.W., V. Hayssen, K. Geissler, S. Bertolino. 2013. "Callosciurus erythraeus (Rodentia: Sciuridae)." Mammalian Species 45(902): 60–74.

Stein, A., V. Hayssen. 2013. "Panthera pardus (Carnivora: Felidae)." Mammalian Species 45(900): 30–48.

Hayssen, V., J. Ortega, A. Morales-Leyva, N. Martinez-Mendez. 2013. "Cabassous centralis (Cingulata: Dasypodidae)." Mammalian Species 45(898): 12–17.

Hayssen, V., F. Miranda, B. Pasch. 2012. "Cyclopes didactylus (Pilosa: Cyclopedidae)." Mammalian Species 44(895): 51–58.

Hayssen, V. 2011. "Tamandua tetradactyla (Pilosa: Myrmecophagidae)." Mammalian Species 43(875): 64–74.

Hayssen, V. 2011. "Choloepus hoffmanni (Pilosa: Megalonychidae)." Mammalian Species 43(873): 37–55.

Ward, A., V. Hayssen. 2010. Measuring cortisol in hair and saliva from dogs: coat color and pigment differences. Domestic Animal Endocrinology 39: 171-180.

Hayssen, V. 2009. "Bradypus variegatus (Pilosa: Bradypodidae)." Mammalian Species 42(850): 19–32.

Hayssen, V. 2009. "Bradypus tridactylus (Pilosa: Bradypodidae)." Mammalian Species 839: 1–9.

Hayssen, V. 2009. "Bradypus torquatus (Pilosa: Bradypodidae)." Mammalian Species 829: 1–5.

Hayssen, V. 2008. "Reproductive effort in squirrels: ecological, phylogenetic, allometric, and latitudinal patterns," Journal of Mammalogy 89(3): 582-606.

Hayssen, V. 2008. "Reproduction within marmotine ground-squirrels (Sciuridae, Xerinae, Marmotini): patterns among genera." Journal of Mammalogy 89(3): 607–16.

Hayssen, V. 2008. "Patterns of body and tail length and body mass in Sciuridae," Journal of Mammalogy 89(4):852–73.

Hayssen, V. 2008. "Bradypus pygmaeus." Mammalian Species 812: 1–4.

Haas, S. K., V. Hayssen and P. R. Krausman. 2005. "Panthera leo." Mammalian Species 762: 1–11.

Gardner, A.L., and V. Hayssen. 2004. "A guide to constructing and understanding synonymies for Mammalian Species." Mammalian Species 739: 1–17.

Hayssen, V., J. M. Harper, and R. DeFina. 2002. "Fecal corticosteroids in agouti and nonagouti deer mice (Peromyscus maniculatus). Comparative Biochemistry and Physiology, Part A. Molecular and Integrative Physiology 132: 439–46.

Hayssen, V. 2001. "Body and organ mass in agouti and nonagouti in deer mice (Peromyscus maniculatus)." Comparative Biochemistry and Physiology 130A: 311–21.

Lapseritis, J. M., and V. Hayssen. 2001. "Thyroxine levels in agouti and nonagouti deermice (Peromyscus maniculatus)." Comparative Biochemistry and Physiology 130A: 295–99.

Hayssen, V. 1999. "Chisel-toothed kangaroo rat, Dipodomys microps." pp. 534–35 in The Smithsonian Book of North American Mammals (D. E. Wilson and S. Ruff, eds.). Smithsonian Institution Press, Washington, D.C., 750 pp.

Goodwin, N., V. Hayssen, D. W. Deakin, and A. P. F. Flint. 1999. "Influence of social status on ovarian function in farmed red deer (Cervus elaphus)." Physiology and Behavior 65: 691–96.

Hayssen, V. 1998. "Effect of transatlantic transport on reproduction of agouti and nonagouti deer mice, Peromyscus maniculatus." Laboratory Animals. 32: 55–64.

Hayssen, V. 1997. "Effects of the nonagouti coat-color allele on behavior of deer mice (Peromyscus maniculatus): A comparison with Norway rats (Rattus norvegicus)." Journal of Comparative Psychology 111: 419–23.

Jabbour, H., V. Hayssen, and M. Bruford. 1997. "Conservation of deer: Contributions from molecular biology, evolutionary ecology, and reproductive physiology." Journal of Zoology 243: 461–84.

Kunz, T., C. Wemmer, and V. Hayssen. 1996. "Assessment of sex, age, and reproductive condition in mammals." pp. 279–90, in Measuring and monitoring biological diversity: Standard methods for mammals. D. E. Wilson, F. R. Cole, J. D. Nichols, R. Rudran and M. S. Foster, eds. Smithsonian Institution Press, Washington, DC, 409 pp.

Hayssen V., and T. H. Kunz. 1996. "Allometry of litter mass in bats: Comparisons with maternal size, wing morphology, and phylogeny." Journal of Mammalogy. 77(2): 476–90.

Hayssen, V. 1995. "Milk: It does a baby good." Natural History Magazine. 104(12): 36.