Temperature and sperm incorporation in polyploid salamanders.

Although most animals reproduce sexually, a number of all-female groups exist. Triploid hybrid salamanders appear to maintain themselves by using a male's sperm to activate their eggs, after which the sperm nucleus is eliminated (gynogenesis). The incidence of sperm nuclear incorporation in eggs of these salamanders depends on temperature. Triploid offspring derived gynogenetically are more frequent at lower temperature, whereas tetraploid offspring derived sexually are far more frequent at higher temperatures. Temperature-dependent variability in sperm nuclear incorporation helps explain the variability in reproductive modes reported for hybrid salamanders.

Reproduction and the origin of polyploids in hybrid salamanders of the genus Ambystoma.

Eggs and larvae produced by diploid, triploid, and tetraploid females collected from breeding ponds on Pelee Island in Lake Erie were studied to examine the reproductive mechanism. No instance of parthenogenesis was found as all examined females required sperm to produce viable progeny. Diploid females produced diploid and triploid larvae, triploid females produced triploid and tetraploid larvae, and tetraploid females produced triploid and tetraploid larvae. The majority of the eggs produced by hybrid females do not develop or do not complete embryogenesis. Electrophoretic examination of females and their offspring demonstrate that the male genome is being incorporated in reduced as well as unreduced eggs produced by all three ploidy classes of females. The elevation of ploidy among Pelee Island Ambystoma is attributed to sperm incorporation in unreduced eggs. Triploid as well as tetraploid individuals are constantly being produced. A critical examination of the literature on parthenogenetic or gynogenetic modes of reproduction in North America Ambystoma hybrids shows no conclusive evidence supporting these modes and it is suggested that the reproductive mechanism found among Pelee Island female hybrids may be more generally applied to other hybrid Ambystoma populations.

Uptake of 14C DDT by wood frog embryos after short term exposure.

Wood frog embryos at four different developmental stages and three temperatures were subjected to 0.025 ppm 14C DDT for 24 hr. Embryos within jelly capsules at stages 13, 16 and 18 accumulated about 0.16 ppm at 9, 15 and 21 degrees C. The protective jelly envelopes around embryos in stages 13, 16 and 18 contained about 0.014 ppm at all temperatures. Jelly-free hatching embryos in stage 20 accumulated about 6-10 times the level of earlier stages and showed effects of DDT poisoning. Jelly capsules around amphibian eggs restrict DDT uptake.