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Biological Sciences

College of Arts & Sciences

Jim Stewart

Jim  Stewart 

Adjunct Faculty
Contact:
423-439-6927 /
Brown Hall, Room 310

Research Interests:

My primary research interests are evolution of the amniotic egg and evolution of live bearing reproduction.  The egg and embryo of ancestral amniotes were evolutionary innovations that produced large, independent offspring.  Modern amniotes (turtles, lizards, snakes, crocodilians, birds, mammals) exhibit a wide diversity of life history patterns, yet embryos of these taxa share many characteristics inherited from a common ancestor.  One aim of my research is to understand how embryos have evolved in response to variation in life history characteristics.  For example, most amniotes reproduce by laying eggs, but mammals and squamate reptiles (lizards, snakes) have two modes of reproduction, egg laying (oviparity) or giving birth to live young (viviparity).  Lizards and snakes are rather remarkable because viviparity has evolved in more than 100 lineages and reproductive mode varies geographically in some species, i.e., there are both oviparous and viviparous populations.  Patterns of embryonic nutrition are likewise highly diverse.  Embryos of oviparous species are nourished by nutrients in yolk and in the eggshell, while some viviparous species have highly specialized placentas that deliver most or all of the nutrients required for embryonic development.  There are also species with intermediate patterns in which embryos are nourished by a large yolk mass, yet nutrients are transported to embryos via specialized placentas as well.  This reproductive diversity is the outcome of a large natural experiment that has produced an ideal model to study the evolutionary relationship between embryos and mothers.

Select Publications:

Peer-reviewed Papers

Stewart, J.R. and M.B. Thompson. 2009.  Parallel evolution of placentation in Australian scincid lizards.  J. Exp. Zool. 312B:590-602.

Stewart, J.R., T.W. Ecay and B. Heulin. 2009.  Calcium provision to oviparous and viviparous embryos of the reproductively bimodal lizard Lacerta (Zootoca) vivipara.  Jour. Exp. Biol. 212:2520-2524.

Linville, B.J., J.R. Stewart, T.W. Ecay, J.F. Herbert, S.L. Parker and M.B. Thompson.  2010.  Placental calcium provision in a lizard with prolonged oviductal egg retention.  Jour. Comp. Physiol. B. 180:221-227.

Stewart, J.R., A.N. Mathieson, T.W. Ecay, J.F. Herbert, S.L. Parker and M.B. Thompson.  2010.  Uterine and eggshell structure and histochemistry in a lizard with prolonged uterine egg retention (Lacertilia, Scincidae, Saiphos).  J. Morphol. 271:1342-1351.

Stewart, J.R. and T.W. Ecay.  2010.  Patterns of maternal provision and embryonic mobilization of calcium in oviparous and viviparous squamate reptiles.  Herp. Conserv. Biol. 5:341-359.

Stewart, J.R., T.W. Ecay, B. Heulin, S.P. Fregoso and B.J. Linville.  2011.  Developmental expression of calcium transport proteins in extraembryonic membranes of oviparous and viviparous Zootoca vivipara (Lacertilia, Lacertidae).  Jour. Exp. Biol. 214:2999-3004.

Stinnett,  H.K., J.R. Stewart, T.W. Ecay, R.A. Pyles, J.F. Herbert and M.B. Thompson.  2012.  Placental development and expression of calcium transporting proteins in the extraembryonic membranes of a placentotrophic lizard.  J. Morphol.  273:347-359.

Fregoso, S.P., J.R. Stewart and T.W. Ecay.  2012.  Expression of calcium transport proteins in the extraembryonic membranes of a viviparous snake, Virginia striatula. J. Exp. Zool.  (Mol. Dev. Evol.) 318:250-256.

Stewart, J.R. 2013. Fetal nutrition in lecithotrophic squamate reptiles: toward a comprehensive model for evolution of viviparity and placentation. J. Morphol.  274:824-843.

Elinson, R.P. and J.R. Stewart. 2014. The corn snake yolk sac becomes a solid tissue filled with blood vessels and yolk-rich endodermal cells. Biol. Lett. 10: 20130870. http://dx.doi.org/10.1098/rsbl.2013.0870

Elinson, R.P., J.R. Stewart, L.J. Bonneau nd D.G. Blackburn.  2014.  Amniote yolk sacs: diversity in reptiles and a hypothesis on their origin.  Int. J. Dev. Biol. 58:889-894.

Stewart, J.R.  2015.  Placental specializations in lecithotrophic viviparous squamate reptiles.  J. Exp. Zool. (Mol. Dev. Evol.) 324B:549-561.

Book Chapters

Stewart, J.R. 1997.  Morphology and evolution of the egg of oviparous amniotes.  pp. 291-326.  In S. Sumida and K. Martin (Eds.), Amniote Origins.  New   York: Academic Press.

Blackburn, D.G. and J.R. Stewart.  2011.  Viviparity and placentation in snakes.  Pp. 119-181. In R.D. Aldridge and D. M. Sever (eds), Reproductive biology and phylogeny of snakes. Volume 9, Reproductive Biology and Phylogeny series, B. G. M. Jamieson (ed). CRC Press, Boca Raton, Florida.  [Science Publishers, Enfield, NH.]

Stewart, J.R. and D.G. Blackburn .  2014.  Viviparity and placentation in lizards.  Pp. 448-563. In J. Rheubert, D. Seigel and S. Trauth (eds), Reproductive biology and phylogeny of lizards and tuatara. Volume 10, Reproductive Biology and Phylogeny series, B. G. M. Jamieson (ed). CRC Press, Boca Raton, Florida.  [Science Publishers, Enfield, NH.]

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