Dr. Stephen Weeks

Dr. Stephen Weeks

Title: Professor
Dept/Program: Biology
Office: ASEC E501
Phone: 330-972-7156
Fax: 330-972-8445
Email: scw@uakron.edu
Website: http://www3.uakron.edu/biology/hmpg1.html


I earned a B.A. in Aquatic Biology from the University of California, Santa Barbara in 1983. I then earned an M.A. in Biology from the University of California, Riverside in 1986, conducting research on the ecological ramifications of different breeding systems in branchiopod crustaceans. I then went to Rutgers University in New Jersey for my Ph.D., working with Dr. Robert Vrijenhoek, again researching the ecological effects of sexual relative to asexual reproduction, this time in live-bearing fish (Poecillidae). I earned my PhD in 1991. From there, I did a short-term post-doc (1991) at Pennsylvania State University, in the Anthropology Department, studying the evolution of aging. I did a second post-doc at the Savannah River Ecology lab (run through the University of Georgia, Athens) from 1992-1994, working with Dr. Gary Meffe on life history evolution in another live-bearing fish (Gambusia affinis). I started at the University of Akron in 1994.


2010          Research on sex chromosomes featured in F1000 Biology

2007          Research Award, Buchtel College of Arts and Sciences, The University of Akron

2005-06     Research on mating systems featured in Nature (2005, 438:893), Science (2006,   313:1381) and Current Biology (2006, 16:R36-R37).

2005          “Top Researcher” in College of Arts & Sciences, University of Akron        

2000          Early Career Research Award, Buchtel College of Arts and Sciences, The University of Akron

1986-91     PhD - Ecology, Rutgers University

1983-86     MA - Biology, University of California, Riverside

1979-83     BA - Aquatic Biology, University of California, Santa Barbara


Research Accomplishments

I have long been interested in the evolution mating systems, working with both branchiopod crustaceans and livebearing fish. Currently, my research has focused on delineating the factors allowing the coexistence of male and hermaphrodite (termed "androdioecy") freshwater shrimp in ponds across the world. Over the years of studying this question, my research has evolved into an interdisciplinary (or "integrative") set of projects that combine to approach the complex question of how mating systems have evolved in these shrimp. Several graduate students and I are studying a variety of ecological and genetic aspects of the unique mating system found in one of these shrimp (Eulimnadia texana), seeking to discern the costs and benefits of selfing vs. outcrossing in this interesting system. Since this early work on this one species, we have expanded to study mating system evolution across the family Limnadiidae using phylogeographic, ecological, behavioral, and genetic approaches. We published a paper establishing that shrimp in the genus Eulimnadia have reproduced via androdioecy for 24-180 million years, which is orders of magnitude longer than predicted by models of this mating system and the only system in which androdioecy is known to be this long-lived. We also published a review outlining the various androdioecious animals described to date, and noted that our clam shrimp are the most specious taxon known that is entirely androdioecious. We are now pursuing another dimension to this research which will add a paleontological aspect to our comparisons. We have teamed up with Dr. Lisa Park (UA Geology Dept.) to begin to explore our ability to assess mating system type using only fossilized carapaces of Limnadiidae. If we can reliably ascertain mating system from the fossil record, we will then open up a broad range of research possiblities that would allow us to explore associations of mating system with habitat characteristics over broad time spans. Additional previous research on mating system evolution in Eulimnadia has focused on inbreeding depression, relative survival of males and hermaphrodites, and the effectiveness of males in fertilizing hermaphrodites (including the competitiveness of their sperm).

Our behavioral work centers on the mating behavior of clam shrimp. We are particularly interested in a type of behavior termed "mate guarding" in which males hold ("clasp") onto hermaphrodites for up to two hours before mating. This type of mating sets up an intersexual conflict in that the optimal timing of such mate guarding is often longer for males than it is for hermaphrodites. A former PhD student (Chiara Benvenuto) explored the effects of various social environments on the timing of mate guarding to test how such environments might influence such intersexual conflict.

Along with our evolutionary questions involving E. texana, we are additionally interested in understanding its basic biology. We are currently working on understanding the reproductive system of these crustaceans, using both genetic and histological methods to understand whether these shrimp can store sperm, how hermaprhoditism may have evolved, the ultrastructure of the male gonad, and where and when fertilization takes place. The evolutionary research on mating systems has logically led us to reconstruct the phylogeny of the Limnadiidae, in collaboration with Dr. Randy Hoeh of Kent State University and Christopher Rogers of Kansas Biological Survey. We are also exploring the population genetics of these shrimp by genetically typing individuals from a number of natural populations and comparing these genetic metrics to those of a closely related congener (E. diversa). Additionally, we are documenting the extent of inbreeding in these natural populations using genetic techniques.


Benvenuto, C, and SC Weeks. 2011. Intersexual conflict during mate guarding in an androdioecious crustacean. Behav. Ecol. (in press).

Benvenuto C,and SC Weeks. 2011. Mate guarding behavior in clam shrimp: The influence of mating system on intersexual conflict. Behav. Ecol. Sociobiol. 65:1899-1907.

Weeks SC, TF Sanderson , BF Wallace, and B Bagatto. 2011. Behavioral cost of reproduction in a freshwater crustacean (Eulimnadia texana). Ethology 117:880-886.

Weeks SC, C Benvenuto , TF Sanderson, and RJ Duff. 2010. Sex Chromosome Evolution in the Clam Shrimp, Eulimnadia texana. J. Evol. Biol. 23:1100-1106.

Rogers DC, SC Weeks, and WR Hoeh. 2010. A new species of Eulimnadia (Crustacea; Branchiopoda; Diplostraca; Spinicaudata) from North America. Zootaxa 2413:61-68.

Weeks SC, EG Chapman , DC Rogers, DM Senyo, and WR Hoeh. 2009. Evolutionary transitions among dioecy, androdioecy and hermaphroditism in limnadiid clam shrimp (Branchiopoda: Spinicaudata). J. Evol. Biol. 22:1781-1799.

Benvenuto C, B Knott and SC Weeks. 2009. Mate guarding behavior in clam shrimp: A field approach. Behav. Ecol. 20:1125-1132.

Weeks SC, SK Reed , DW Ott, and F. Scanabissi. 2009. Inbreeding effects on sperm production in clam shrimp (Eulimnadia texana). Evol. Ecol. Res. 11:125-134.

Weeks SC. 2009. Can males successfully invade hermaphroditic populations of clam shrimp (Eulimnadia texana)? Current Science 96:98-102.

Weeks SC, TF Sanderson , M Zofkova, and B Knott. 2008. Breeding systems in the clam shrimp family Limnadiidae. Invertebrate Biology 127:336-349.

Brendonck L, DC Rogers, J Olesen, S Weeks, R Hoeh. 2008. Global diversity of large branchiopods (Crustacean; Branchiopoda) in freshwater. Hydrobiologia 595:167-176.

Weeks SC, and C Benvenuto. 2008. Mate guarding in the androdioecious clam shrimp Eulimnadia texana: male assessment of hermaphrodite receptivity. Ethology 114:64-74.

Weeks SC, M Zofkova, and B. Knott. 2006. Limnadiid Clam Shrimp Distribution in Australia (Crustacea: Branchiopoda: Spinicaudata). Journal of the Royal Society of Western Australia 89:155-161.

Duff RJ, C Benvenuto, T Branch, and SC Weeks. 2006. DNA extraction from cysts of the clam shrimp Eulimnadia texana (Crustacea, Branchiopoda, Spinicaudata). Journal of Crustacean Biology 27:154-157.

Weeks SC, SK Reed, M Cesari, and F Scanabissi. 2006. Production of intersexes and the evolution of androdioecy in the clam shrimp Eulimnadia texana (Crustacea, Branchiopoda, Spinicaudata). Invertebrate Reproductive Development 49:113-119.

Weeks SC, C Benvenuto, and SK Reed. 2006. When males and hermaphrodites coexist: A review of androdioecy in animals. Integrative and Comparative Biology 46:449-464.

Hoeh WR , ND Smallwood , DM Senyo, EG Chapman, and SC Weeks. 2006. Evaluating the monophyly of Eulimnadia and the Limnadiinae (Branchiopoda: Spinicaudata) using DNA sequences. Journal of Crustacean Biology 26:182-192.

Weeks SC, TF Sanderson, SK Reed, M Zofkova, B Knott, U Balaraman, G Pereira, DM Senyo, WR Hoeh. 2006. Ancient Androdioecy in the Freshwater Crustacean Eulimnadia . Proceedings of the Royal Society of London, Series B 273:725-734 .

Scanabissi F, M Cesari, SK Reed, SC Weeks. 2006. Ultrastructure of the male gonad and male gametogenesis in Eulimnadia texana (Packard, 1871)(Crustacea, Branchiopoda, Spinicaudata). Invertebrate Biology 125:117-124.

Weeks, SC, RT Posgai, M Cesari, and F Scanabissi. 2005. Androdioecy inferred in the clam shrimp Eulimnadia agassizii (Spinicaudata: Limnadiidae). Journal of Crustacean Biology 25:323-328.

Duff, RJ WR Hoeh, DG Cook and SC Weeks. 2004. Isolation and characterization of thirteen polymorphic microsatellite loci from the clam shrimp Eulimnadia texana (Crustacea: Spinicaudata). Molecular Ecology Notes 4:397-399.

Weeks, SC. 2004. Seven generations of inbreeding does not purge inbreeding depression in the clam shrimp, Eulimnadia texana. Journal of Evolutionary Biology 17:475-484.

 Weeks, SC and RL Bernhardt. 2004. Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana: Field estimates of inbreeding depression and relative male survival. Evolutionary Ecology Research 6:227-242.

Weeks SC, CL Marquette, and E Latsch. 2004. Barriers to outcrossing success in the primarily self-fertilizing clam shrimp, Eulimnadia texana (Crustacea, Branchiopoda). Invertebrate Biology 123:146-155.

Weeks, SC and RJ Duff. 2002. A Genetic Comparison of Different Populations of Clam Shrimp in the genus Eulimnadia. Hydrobiologia 486:295-302.

Weeks, SC, V Marcus, R Salisbury, and D Ott. 2002. Cyst Development in the Conchostracan shrimp, Eulimnadia texana. Hydrobiologia 486:289-294.

Weeks, SC, J Hutchison, and N Zucker. 2002. Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana: Do hermaphrodites need males for complete fertilization? Evolutionary Ecology 15:205-221.

Hollenbeck VG, N Zucker, W Gould and SC Weeks. 2002. Maintenance Of Androdioecy In The Freshwater Shrimp Eulimnadia texana: Sexual Encounter Rates And Outcrossing Success. Behav. Ecol. 13:561-570.

Naida Zucker, Gabriela A. Aguilar, Stephen C. Weeks,  and L. Garner McCandless. 2002. Variation in reproductive cycle between selfing and outcrossing hermaphrodites in an androdioecious desert shrimp. Invertebrate Biology 121:66-72.

Gray, M and SC Weeks. 2001. A comparison of dietary use patterns of clonal and sexual fish (Poeciliidae: Poeciliopsis). Can. J. Fish. Aquat. Sci. 58:1313-1318.

Zucker, N, B Stafki and SC Weeks. 2001. Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana: Relative longevity of males to hermaphrodites. Can. J. Zool. 79:393-401.

Weeks, SC, BR Crosser, and MM Gray. 2001. Relative fitness of two hermaphroditic mating types in the androdioecious clam shrimp, Eulimnadia texana. Journal of Evolutionary Biology 14:83-94.

Medland, VL, N Zucker, and SC Weeks. 2000. Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana Parker: Encounters between males and hermaphrodites are not random. Ethology 106:839-848.

Weeks, SC, BR Crosser, B Bennett, MM Gray, and N Zucker. 2000. Maintenance of androdioecy in the freshwater shrimp, Eulimnadia texana: Variation in inbreeding depression between two populations.  Evolution 54:878-887.

Weeks, SC, BR Crosser, MM Gray, JA Matweyou, and N. Zucker. 2000. Is there Sperm Storage in the Clam Shrimp Eulimnadia texana? Invertebrate Biology 119:215-221.

Weeks, SC, and N Zucker. 1999. Rates of Inbreeding in the Clam Shrimp Eulimnadia texana. Can. J. Zool. 77:1402-1408.

Stockwell, CA and SC Weeks. 1999. Translocations and altered evolutionary trajectories in recently established populations of the western mosquitofish (Gambusia affinis) Animal Conservation 2:103-110.

Weeks, SC, V Marcus, and B Crosser. 1999. Inbreeding Depression in a Self-Compatible, Androdioecious Crustacean, Eulimnadia texana. Evolution 53:472-483.

Belk, D, G Mura and SC Weeks. 1998. Untangling confusion between Eubranchipus vernalis and Eubranchipus neglectus (Branchiopoda, Anostraca). Journal of Crustacean Biology 18:147-152.

Weeks, SC and V Marcus. 1997. A survey of the branchiopod crustaceans of Ohio. Ohio Journal of Science 97:86-89.

Marcus, V and SC Weeks. 1997. The effects of pond duration on the life history traits of an ephemeral pond crustacean, Eulimnadia texana. Hydrobiologia, 359:213-221.

Weeks, SC and GK Meffe. 1997. "Grandfather Effects" on offspring size in the Eastern Mosquitofish, Gambusia holbrooki. Copeia 1997:869-874.

Weeks, SC, V Marcus and S Alvarez. 1997. Notes on the life history of the clam shrimp Eulimnadia texana. Hydrobiologia 359:191-197.

Weeks SC. 1996. A reevaluation of Red Queen model for the maintenance of sex in a clonal-sexual fish complex (Poeciliidae: Poeciliopsis). Canadian Journal of Fisheries and Aquatic Sciences 53:1157-1164.

Weeks SC. 1996. The hidden cost of reproduction: reduced energetic intake caused by spatial constraints in the body cavity. Oikos 75:345-349.

Weeks SC and GK Meffe. 1996. Quantitative genetic and optimality analyses of life-history plasticity in the eastern mosquitofish, Gambusia holbrooki. Evolution 50:1358-1365.

Meffe, G.K., S.C. Weeks, P. Mulvey, and K.L. Kandl. 1996. Genetic differences in thermal tolerance of mosquitofish from ambient and thermally elevated ponds. Canadian Journal of Fisheries and Aquatic Sciences 52:2704-2711.

Weeks, S.C. 1995. Comparisons of life-history traits between clonal and sexual fish (Poeciliopsis: Poeciliidae) raised in monoculture and mixed treatments. Evolutionary Ecology 9:258-274.

Heulett ST, SC Weeks and GK Meffe. 1995. Lipid dynamics and growth relative to resource level in juvenile eastern mosquitofish (Gambusia holbrooki: Poeciliidae). Copeia 1995:97-104.

Weeks SC and OE Gaggiotti. 1993. Patterns of offspring size at birth in clonal and sexual strains of Poeciliopsis (Poeciliidae). Copeia 1993:1003-1009.

Weeks SC. 1993. The effects of recurrent clonal formation on clonal invasion patterns and sexual persistence: A Monte Carlo simulation of the frozen niche-variation model. The American Naturalist 141:409-427.

Sassaman C and SC Weeks. 1993. The genetic mechanism of sex determination in the Conchostracan shrimp Eulimnadia texana. The American Naturalist 141:314-328.

Weeks SC. 1993. Phenotypic plasticity of life-history traits in clonal and sexual fish (Poeciliopsis) at high and low densities. Oecologia 93:307-314.

Connor A, KM Weiss and SC Weeks. 1993. Evolutionary models of quantitative disease risk factors. Human Biology 65:917-940.

Weeks SC, OE Gaggiotti, R Schenck, K Spindler, and RC Vrijenhoek. 1992. Feeding behavior in sexual and clonal strains of Poeciliopsis. Behavioral Ecology and Sociobiology 30:1-6.

Weeks SC and JM Quattro. 1991. Life-history plasticity under resource stress in a clonal fish (Poeciliidae: Poeciliopsis). Journal of Fish Biology 39:485-494.

Quattro JM and SC Weeks. 1991. Correlations of egg size and energetic content in sexual and clonal biotypes of Poeciliopsis. Journal of Fish Biology 38:331-334.

Weeks SC and C Sassaman . 1990. Competition in phenotypically variable and uniform populations of the tadpole shrimp Triops longicaudatus (Notostraca: Triopsidae). Oecologia 82:552-559.

Weeks SC. 1990. Life-history variation under varying degrees of intraspecific competition in the tadpole shrimp Triops longicaudatus (LeConte). Journal of Crustacean Biology 10:498-503.

Wetherington JD, SC Weeks, KE Kotora, and RC Vrijenhoek. 1989. Genotypic and environmental components of variation in growth and reproduction of fish hemiclones (Poeciliopsis: Poeciliidae). Evolution 43:635-645.