> Habitat & Distribution

Physa acuta is the most common and widespread freshwater gastropod inhabiting our entire 21-state study area, east of the Mississippi River and west, a title it could probably claim for the entirety of North America, and quite possibly the world (Dillon et al. 2002).  Populations may inhabit any and all freshwaters whatsoever from the equator to boreal latitudes, but reach maximum densities in temperate, lentic environments, especially those that are rich, disturbed and/or artificially eutrophic.  FWGNA incidence rank I-5.

> 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, Martinez & Rogowski 2011), parasitism (Ebbs et al. 2018, Stoll et al. 2013) and predation (Crowl & Covich 1990, Alexander & Covich 1991, DeWitt et al. 1999, 2000, Dorn 2013).

Jokinen’s (1987) analysis of the distribution of P. acuta in Connecticut and New York (listed as P. heterostropha) led her to classify it as a “C-D tramp,” potentially present in nearly every community.  Dillon’s (2000: 360-363) reanalysis of these data suggested that P. acuta populations in Connecticut seem to be Undifferentiated with respect to life history adaptation.

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, Arendt 2015). 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, as well as essays 3Oct18 and 5Nov18, 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

A detailed study of the shell morphology of Physa acuta, together with a review of ecology and life history of populations in Europe, has been contributed by Cieplok et al (2022).  Laboratory populations of P. acuta (under a variety of synonyms) have demonstrated significant ecophenotypic responses in shell shape both to temperature (Britton & McMahon 2004) and to the introduction of crushing predators (DeWitt 1998, Langerhans & DeWitt 2002, Auld & Relya 2011, Salice & Plautz 2011). The common garden experiments of Gustafson et al. (2014) returned evidence of striking morphological plasticity in the shell form of P. acuta correlated with the (many) environmental differences between stream and pond as well.  Against this background, the discovery of Dillon & Jacquemin (2015) that the heritability of (multivariate) shell morphology in Physa might range as high as h^2 = 0.819 was especially surprising (Essay 15Apr15).

Throughout the nineteenth and twentieth centuries, North American populations of Physa acuta were identified as P. heterostropha (Say 1817) in the east, P. integra (Haldeman 1841) in the midwest, P. virgata (Gould 1855) in the far west, and by a variety of additional Latin nomina more local in character everywhere around the USA.  Only in recent years has it been discovered that all of these populations are conspecific with each other, and with European populations apparently introduced from America in the late eighteenth century, previously described as Physa acuta (Dillon et al. 2002, 2005b, 2011, Lydeard et al. 2016).  See my entire series of essays "To Identify a Physa" 1971, 1975, 1978, 1989, and 2000 from the links below for a review of the malacological dawning. 

See Dillon & Wethington (1992, 1994) and Essay 5Nov18 for research on classical, transmission genetics in Physa acuta, and David et al. (2022) and Essay 9June22 for research on non-classical cytoplasmic male sterility.  Dillon & Wethington (1995, 2006) have contributed studies of the population genetics of P. acuta in North America and Bousset et al. (2004, 2014) similarly for Europe.  The allozyme study of Dillon (2018) suggested that the effective size of a Charleston-area Physa acuta population fluctuated between Ne = infinite and Ne = 50 over a period of 7 years (Essay 14Jan19).  Molecular phylogenetic studies have been contributed by Wethington & Lydeard (2007), Wethington et al. (2009), Ebbs et al. (2018) and Young et al. (2021).

Throughout the history of North American malacology, the classification of physid gastropods has been as problematic as their identification.  The system proposed by George Te (1978, 1980), published in Burch (1989), recognized 69 species and subspecies in four genera: Aplexa, Stenophysa, Physa and Physella, the last genus with three subgenera, Costatella, Petrophysa, and Physella (ss).  All of the physids common in our study area have at times been referred to the genus Physella. 

It is now clear that almost all of the nominal diversity previously recognized in the North American Physidae 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 (Essay 12Oct07). 

> Maps and Supplementary Resources

• Physa distribution in the drainage of The Ohio (2019)
• Physa acuta distribution in Atlantic drainages (2023)
• Physa distribution in the Tennessee/Cumberland (2022)
• Physa acuta and P. gyrina in The Great Plains (2024)
• Virginia species account with county distribution (2011)
• Pretty photo of living Physa acuta, courtesy of David Liebman.
  
• Physa acuta on a mat of duckweek in Canandaigua Lake, New York.  This mat of vegetation and snails covered an access canal approximately 200 m long and 40 m wide.
  

• Physa acuta stars in a YouTube video, with special thanks to Bobby Martin of Martin Microscopes!

> Essays

• I explored the tangled taxonomic history of Physa acuta, Physa heterostropha, and Physa gyrina in my blog post of 14Oct08, "Backwards Snails Backwards!"
• For an historical perspective on the classification of the Physidae, see my three part series on the life and work of George A. Te: To Identify a Physa 1971, To Identify a Physa 1975, and To Identify a Physa 1978 plus my (more personal) follow ups: To Identify a Physa 1989 and To Identify a Physa 2000.
• The phylogenetic analysis of Wethington & Lydeard prompted me to review The Classification of the Physidae in my post of 12Oct07.
• Physa acuta appeared as a foil in my 7Apr10 "TRUE CONFESSIONS: I described a new species."
• The Dillon et al. (2011) paper on the evolution of reproductive isolation in Physa served as a jumping-off point for my blog post of 12July11, "What is a Species Tree?"
• A very large individual P. acuta was figured in my 29Nov04 post to the FWGNA blog, Gigantic Pulmonates.
• A misidentified population of P. acuta inhabiting the Snake River of Idaho was featured in my post of 12Mar08, "Red Flags, Water Resources, and Physa natricina".
• The Snake River population of "acuta-like Physa" also starred in a soap opera that ran on the FWGNA blog from Feburary - May, 2013.  Here's a link to the first installment: "The Mystery of the SRALP: A bidding."
• Our good friend Tom Pelletier from askanaturalist.com posted a very thorough review of P. acuta biology and life history on 2May14, "What are these jelly dots under rocks?"  His post features several nice photos and links to a couple cool videos as well.
• See my post of 26Sept14 for good, comparative figures illustrating "The egg masses of freshwater pulmonate snails."
• Here's an amazing fact.  The heritability of shell morphology in Physa is h^2 = 0.819!
• I reviewed some excellent research on the relationship between geographic distance and genetic divergence among populations of Physa acuta in my essay of 24Apr17, Accelerating the Snail's Pace.
• I summarized twenty years of research on the reproductive biology of Physa acuta in my post of 5Nov18, "Albinism and Sex Allocation in Physa."
• In my blog post of 9June22 I reviewed the stunning discovery by Patrice David and his colleagues (2022), Cytoplasmic male sterility in Physa!   Amy Wethington and I almost had it way back in 2004 [pdf].

> References

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virgata in response to the crayfish Procambarus simulans.  Oecologia 87:435-442.
Arendt, J. (2015) Why get big in the cold? Size-fecundity relationships explain the temperature-size rule in a pulmonate snail (Physa). Journal of Evolutionary Biology 28: 169-178.
Auld J., and R. Relyea (2011)  Adaptive plasticity in predator-induced defenses in a common freshwater snail: altered selection and mode of predation due to prey phenotype. Evolutionary Ecology 25: 189-202.
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.
Bousset, L., J-P. Pointier, P. David, and P. Jarne (2014) Neither variation loss, nor change in selfing rate is associated with the worldwide invasion of Physa acuta from its native North America. Biological Invasions 16: 1769-1783.
Britton, D.K. and R.F. McMahon (2004)  Environmentally and genetically induced shell-shape variation in the freshwater pond snail Physa (Physella) virgata (Gould 1855).  American Malacological Bulletin 19: 93 – 100.
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