> Physa acuta Draparnaud 1805 
    "Physella heterostropha"

> Habitat & Distribution
Cosmopolitan. Although almost certainly native to North America, P. acuta has been spread through human agency around the world (Dillon et al. 2002). It is most common in lentic waters, especially in rich, disturbed and/or artificially eutrophic environments.

> Ecology & Life History
Physa acuta is a “weedy” or R-selected species, in the sense of Dillon (2000: 131-135). Its rapid maturation, high reproductive rate, and ease of culture have made it the “fruit fly of malacology,” spawning scores of detailed studies on life history (Clampitt 1970), behavior (McCarthy & Fisher 2000), competition (Kesler et al.1986), and predation (Crowl & Covich 1990, Alexander & Covich 1991, DeWitt et al. 1999, 2000).

Laboratory populations mature in 6 – 8 weeks, male function arriving slightly before female function, each adult laying 50 – 100 eggs weekly thereafter for up to a year (Wethington & Dillon 1993). They prefer to outcross, and can store allosperm for very long periods of time (Wethington & Dillon 1991, 1997). But they self-fertilize successfully in isolation, and low levels of self-fertilization even seem to take place in females with proven allosperm reserves (Dillon et al. 2005a). See Wethington & Dillon (1996) for a review of mating behavior. If, after reading all the Dillon & Wethington references cited below, some question still remains in your mind regarding any aspect of the reproductive biology of P. acuta, please notify me and I will attend to it immediately.

> Taxonomy & Systematics
Junior synonyms include heterostropha (Say 1817), integra (Haldeman 1841), virgata (Gould 1855) and many others (Dillon et al. 2002, 2005b, Wethington & Lydeard 2007).

Until recently it was believed that the North American Physidae numbered more than 40 species, and a variety of elaborate classification schemes have been proposed (eg, Te 1978, 1980).  All of the physids common in the southeastern U.S. have at times been referred to the genus Physella. It is now clear that most of this nominal diversity is attributable to phenotypic plasticity, and that the true number of American species is closer to ten (Wethington 2004a, Wethington & Lydeard 2007).  The simple two-genus system favored by earlier workers (Walker 1918) would seem sufficient, all species of the American southeast referable to the genus Physa.  See my essay of 12Oct07 for more regarding the classification of the Physidae.

> Essay #1
A very large P. acuta was figured in my 29Nov04 essay on gigantism in Pulmonates.

> Essay #2
The phylogenetic analysis of Wethington & Lydeard (2007) prompted me to review the systematics of the Physidae on 12Oct07.

> Maps of Physa distribution
Click the small map to enlarge it, or download the state-specific PDFs



North Carolina (PDF)

South Carolina (PDF)

Georgia (PDF)

> References
Alexander, J., and A. Covich (1991)  Predator avoidance by the freshwater snail Physella
virgata in response to the crayfish Procambarus simulans.  Oecologia 87:435-442. Britton, D. K. (In press) Environmental and genetically induced shell shape variation in the freshwater pond snail Physa virgata. American Malacological Bulletin. Bousset, L., P.-Y. Henry, P. Sourrouille, & P. Jarne (2004)  Population biology of the invasive freshwater snail Physa acuta approached through genetic markers, ecological characterization and demography. Molec. Ecol., 13: 2023-2036. Buth, D. G., and J. J. Suloway (1983) Biochemical genetics of the snail genus Physa:  A comparison of populations of two species. Malacologia 23:351-359. Clampitt, P. T. (1970) Comparative ecology of the snails Physa gyrina and Physa integra. Malacologia 10:113-151. Crowl, T., and A. Covich (1990) Predator-induced life-history shifts in a freshwater snail. Science 247:949-951. Dawson, J. (1911) The biology of Physa:  in J. B. Watson ed. Behavior Monographs. 1(4):1-120. DeWitt, T. J., A. Sih, & J. Hucko (1999) Trait compensation and cospecialization in a freshwater snail:  size, shape, and antipredator behaviour.  Anim. Behav. 58:397-407. DeWitt, T. J., B. W. Robinson, & D. S. Wilson (2000) Functional diversity among predators of a freshwater snail imposes an adaptive trade-off for shell morphology. Evolutionary Ecology Research 2:129-148. Dillon, R. T., Jr. (2000) The Ecology of Freshwater Molluscs.  Cambridge University Press, United Kingdom. 509 pp. Dillon, R. T., Jr., and K. Davis (1991) The diatoms ingested by freshwater snails:  Temporal, spatial, and interspecific variation. Hydrobiologia 210:233-242.  Dillon, R. T., Jr., T. E. McCullough and C. E. Earnhardt (2005a)  Estimates of natural allosperm storage capacity and self-fertilization rate in the hermaphroditic freshwater pulmonate snail, Physa acuta. Invert. Repro. Devel. 47: 111-115.  Dillon, R. T. , Jr., J. D. Robinson, T. P. Smith and A. R. Wethington (2005b) No reproductive isolation between freshwater pulmonate snails Physa virgata and P. acuta. Southwest. Nat. 50: 415 - 422. Dillon, R. T., J. D. Robinson, and A. R. Wethington (2007)  Empirical estimates of reproductive isolation between the freshwater pulmonates Physa acuta, P. pomilia, and P. hendersoni.  Malacologia 49: 283-292.   Dillon, R. T., Jr., and A. R. Wethington (1994) Inheritance at five loci in the freshwater snail, Physa heterostropha. Biochem. Genet. 32(3/4): 75-82.  Dillon, R. T., Jr., and A. R. Wethington (1995) The biogeography of sea islands: clues from the population genetics of the freshwater snail, Physa heterostropha. Syst. Biol. 44: 400-408.  Dillon, R. T., Jr., A. R. Wethington, J. M. Rhett, and T. P. Smith (2002) Populations of the European freshwater pulmonate Physa acuta are not reproductively isolated from American Physa heterostropha or Physa integra.  Invert. Biol. 121(3):226-234. Jarne, P., M-A Perdieu, A-F Pernot, B. Delay, and P. David (2000)  The influence of self-fertilization and grouping on fitness attributes in the freshwater snail Physa acuta: population and individual inbreeding depression. J. Evol. Biol. 13:645-655. Kesler, D. H., E. H. Jokinen, and W. R. Mumms (1986) Trophic preferences and feeding morphology of two pulmonate snails species from a small New England pond, U.S.A. Can. J. Zool. 64:2570-2575. McCarthy, T., and W. Fisher (2000) Multiple predator-avoidance behaviours of the freshwater snail Physella heterostropha pomilia: responses vary with risk. Freshw. Biol. 44:387-397. Te, G. A. (1975)  Michigan Physidae, with systematic notes on Physella and Physodon (Basommatophora:  Pulmonata). Malacological Review 8(1-2):7-30. Te, G. A. (1978) The systematics of the family Physidae (Basommatophora:  Pulmonata). Ph.D. Dissertation, University of Michigan, pp. 325. Te, G. A. (1980) New classification for the family Physidae (Pulmonata:  Basommatophora). Arch. Moll. 110:179-184. Wethington, A. R. (2004a) Phylogeny, taxonomy, and evolution of reproductive isolation in Physa (Pulmonata: Physidae)  Ph.D. dissertation, University of Alabama, Tuscaloosa Wethington, A. R. (2004b)  Family Physidae. A supplement to the workbook accompanying the FMCS Freshwater Identification Workshop, University of Alabama, Tuscaloosa. 24 pp. (PDF) Wethington, A. R. and R. T. Dillon, Jr. (1991)  Sperm storage and evidence for multiple insemination in a natural population of the freshwater snail, Physa. Am. Malac. Bull. 9:99-102. Wethington, A. R. and R. T. Dillon, Jr. (1993) Reproductive development in the hermaphroditic freshwater snail, Physa, monitored with complementing albino lines. Proc. Royal Soc. Lond. B 252:109-114. Wethington, A. R. and R. T. Dillon, Jr. (1996) Gender choice and gender conflict in a non-reciprocally mating simultaneous hermaphrodite, the freshwater snail, Physa.  Anim. Behav. 51:1107-1118. Wethington, A. R. and R. T. Dillon, Jr. (1997)  Selfing, outcrossing, and mixed mating in the freshwater snail Physa heterostropha:  lifetime fitness and inbreeding depression. Invert. Biol. 116(3):192-199. Wethington, A.R., R. T. Dillon, & J. M. Rhett (in prep.) Allozyme, 16s, and CO1 sequence divergence among populations of the cosmopolitan freshwater snail, Physa acuta.   Wethington, A.R. E.R. Eastman, & R. T. Dillon, Jr. (2000)  No premating reproductive isolation among populations of a simultaneous hermaphrodite, the freshwatesr snail Physa. In: Freshwater Mollusk Symposia Proceedings. Tankersley, RA, Warmolts DI, Watters GT, Armitage BJ, Johnson PD & Butler RS, eds. pp. 245 – 251. Ohio Biological Survey, Columbus.   Wethington, A. R. & C. Lydeard (2007)  A molecular phylogeny of Physidae (Gastropoda: Basommatophora) based on mitochondrial DNA sequences.  J. Molluscan Stud. 73: 241 - 257.