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Physical Factors Influencing Oviposition by the Woodfrog, Rana sylvatica, in Pennsylvania
Dianne B. Seale
Vol. 1982, No. 3 (Aug. 10, 1982), pp. 627-635
Stable URL: http://www.jstor.org/stable/1444663
Page Count: 9
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Observational and experimental studies were conducted to examine patterns of oviposition by the woodfrog, Rana sylvatica, in central Pennsylvania. In eight temporary ponds of varying surface area, observed during 1976-1980, most egg masses were deposited in large communal aggregates, containing up to 963 masses. The locations of major oviposition sites within each pond were fairly repeatable, but significant variations were noted. Air and water temperatures at breeding time, average egg diameter, pond depth at breeding sites, and number of eggs per mass were comparable to previous reports for woodfrogs. There was a repeatable 1:1 correspondence between total number of egg masses deposited and pond surface area. In general, survivorship to metamorphosis was higher in the larger ponds. Pennsylvania woodfrogs apparently gain thermal advantages for developing larvae by: a) clustering masses, b) selecting warmer sites and c) selecting intermediate depths. Temperature elevations inside experimental egg aggregates, compared with the surrounding water, were functions of the number of masses per aggregate and the relative cloud cover. Experiments supported the hypothesis that physical factors, such as black body effects and insulation, contribute to the thermal properties of woodfrog egg masses. Eggs transplanted before oviposition into relatively cool sites in four ponds (from three ponds in which the frogs had bred earlier) failed to attract significant oviposition. Accelerated development is a probable selective force favoring clustered masses, thermal selectivity for oviposition sites, and repeatability in the number of masses deposited, in temporary Pennsylvania ponds.