Abstract
AbstractPolyploid hybrid salamanders of the genus Ambystoma tend to produce unreduced eggs. At higher temperatures (15°C), the sperm often contributes genetically, leading to tetraploid offspring from triploid mothers and pentaploid offspring from tetraploid mothers. At lower temperatures (5°C), the sperm nucleus usually is lost, and the eggs develop gynogenetically. We examined the cytology of fertilization at 5°C in order to determine the nature of the temperature‐dependent nuclear loss. As in other urodeles, fertilization is polyspermic. The sperm nuclei decondense to form pronuclei, and one sperm pronucleus associates with the egg pronucleus. At metaphase, a clump of chromatin appears along with the chromosomes at the metaphase plate. This chromatin clump fails to segregate at anaphase and is left at the site of the cleavage furrow. The chromatin clump is likely the discarded sperm pronucleus, so its loss is due to its failure to condense properly into chromosomes. © 1992 Wiley‐Liss, Inc.
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