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COMPARISON OF TEMPERATURE AND MOISTURE RESPONSES OF THE SNAIL GENERA POMATIOPSIS AND ONCOMELANIA1 HENRY VANDER ScHALIE AND LowELL L. GETZ Museum of Zoology, University of Michigan, Ann Arbor, and Department of Zoolog)' and Entomology, University of Connecticut, Storrs INTRODUCTION (1948), Abbott (1948), and others stressed the The relationship between amnicolid snails be­ need for basic studies of amnicolid snails and espe­ longing to the American genus Pomatiopsis and cially species in the genus Pomatiopsis. Berry and the Oriental genus Oncomelania has been known Rue ( 1948) found that P. lapidaria could be in­ for a long time. Increased interest in the latter fected with the Chinese strain (personal communi­ group was stimulated when they were recognized cation) of Schistosoma japoniwm; van der Schalie as the hosts for the Oriental blood fluke, S chisto­ and Basch (unpublished data) found development soma japonicum. It was somewhat later that ac­ to the sporocyst stage in one of 25 P. cincinnatien­ tive work on the American Pomatiopsis was ini­ sis, which had been exposed to miracidia of the tiated, particularly at the close of the war when Japanese strain of S. japonicum. Extensive work service men, as well as dogs which had been loaned has been done on Oncomelania in such centers as to the Armed Forces, returned to the continental the 406th Medical General Laboratory in Japan United States from Pacific regions infected with (Hunter III, Ritchie, Williams, et al.), the Philippine 9 team in Palo, Leyte (Pesi­ schistosomiasis. Stunkard ( 1946), Berry and Rue W.H.O. gan, Hairston, et at.), and in other laboratories. 1 This work was sponsored by the Commission of Para­ There is general agreement as to the need better sitic Diseases, Armed Forces Epidemiological Board, and supported by The Office of the Surgeon General, Depart­ to understand the life history and ecology of the ment of The Army. Oncomelania snails. 74 HENRY VANDER SCHALIE AND LOWELL L. GETZ Ecology, Vol. 44, No. 1 Intensive work with both local speciesof Poma- is consideredwith respect to its normal zoogeo- tiopsis (P. lapidaria and P. cincinnatiensis) was graphic range. begun in the laboratory of the senior author about 6 years ago. For referencewe were fortunate in TEMPERATURE RESPONSES havingavailable an excellentstudy of the amnicolid Preferences snails of Michigan by E. G. Berry (1943). In A temperaturegradient was establishedusing addition, some unusually good colonies of both equipment similar to that described by Getz speciesof Pomatiopsisare available in the vicinity ( 1959). The apparatus consisted of a trough of Ann Arbor. With this large reserve of local (made of 1/10 inch tinned-copper) 1 X 1 X 24 material and with facilities for culturing Oncome- inch, with a 1 X 1 X 2 inch water-tight compart- lania (only a few specimensof 0. hupensiswere ment at each end. Each compartmentwas pro- available for use, however), a wide variety of vided with an inlet and an outlet tube. The bot- studies has been possible. Several investigations tom of the trough was covered with wet blotter have centered on P. cincinnatiensis dealing with paper marked into 24 sectionsof 1 inch. A glass its distribution, ecology and life history (van der cover, held in place by a series of flanges, was Schalie and Dundee 1955, van der Schalie and placed 3/8 inch above the floor to keep the snails Getz, in press), its morphology (van der Schalie on the sameplane so as to avoid vertical tempera- and Dundee 1956), its egg-laying habits (van der ture gradients. The top of the trough was covered Schalie and Walter 1957), and the comparative with a piece of plate glass which was in turn difference in moisture requirementsbetween the covered by opaquepaper. Nine thermister ther- young and adults (van der Schalie and Getz mometerswere taped to the bottom of the trough 1961). Likewise, studies of P. lapidaria to date (under sections 1, 3, 6, 9, 12, 15, 18, 21, and 24) centeredon its ecology, morphology and distribu- to determinetemperatures along the trough. The tion (Dundee 1957, van der Schalie and Dundee entire trough was packed in a box of cotton (to 1959). insulate it againsttemperature influences from the Many difficulties were experiencedin culturing outside). species of Oncomelania and Pomatiopsis in the To create a gradient, water heated by passing laboratory. \Vhile efforts were made to duplicate through a coil in a beaker of boiling water was as nearly as possible the conditions observed in circulated through the compartmentat one end, the field for each species, there were no data while water cooled by passagethrough coils in a available to indicate the range of tolerance to chest of crushed ice circulated through the other. variables of such conditions as temperature,mois- The temperature of water going through each ture of air and substrate, or ability to tolerate terminal compartmentwas varied by increasingor drowning or desiccation. It was observedthat the decreasingthe rate of flow through each coil and species varied in their reactions to the environ- compartment until a uniform gradient between mental conditions, but few data were available to suitable extremeswas producedalong the experi- determine the parametersto ecological conditions mental chamber. Once such a gradient was at- for the several species. Without such knowledge tained ( 36-6o C), an experiment was conducted it is difficult to culture certain of the speciesand by placing snails of one species in the 3 central sections. The one cannot interpret behavior in an effort to com- 2 glass covers were then put back in place and the box was pensatefor unfavorable conditions. P. cincinna- darkenedto avoid any possible influence of light. After 6 hours the tiensis proved to be most difficult to maintain; numbers of snails in each section were recorded. hence it received more attention (van der Schalie Two species of Pomatiopsis, P. lapidaria and P. and Getz 1961 and in press). It was found that cincinnatiensis,and 4 speciesof Oncomelania, 0. P. lapidaria was most similar in its responseto quadrasi, 0. nosophora, 0. formosana, and 0. moisture conditions to the 4 species of Oncome- hupensis, were tested. The mean temperatures lania. It is also similar in that it is a biennial preferred by the 6 speciesvaried from 21 oc for species, while P. cincinnatiensis has been shown P. cincinnatiensis and 0. hupensis to 26oC for to be an annual. In the experimentsthat follow, 0. quadrasi (Figure 1). The range of tempera- the data indicate several striking differences be- ture selectionwas mainly between12°C and 30°C tween the ecological tolerancesof the 2 speciesof for most species excepting a few isolated snails Pomatiopsis; it is also evident that each of the in the lower ranges; 0. quadrasi showeda second species of Oncomelania and Pomatiopsis tested peak of distribution at 18°C, probably indicating has rather definite toleranceranges which tend to that the individuals in question were chilled to a identify the species.