Cross-compatbility and self-compatbility in trees of Sorbus torminalis (L.) Crantz were evaluated. Degree of mating-compatibility between three trees was determined by means of fluorescence microscope. Self-compatibility evaluated on the basis of the pollen tube germination index showed that one tree is fully self-incompatible and the other two are self-compatible. Observations of pollen tube germination showed full cross-compatibility between trees under investigation.
Experimental crosses with and without risk of sperm competition were performed in the locust Locusta migratoria, an orthopteran species with a certain degree of first male sperm precedence. The results showed that first mating males perform a significantly higher number of matings than non-first ones, which is paralleled to a shorter remating period. Possible explanations of this differential male mating frequency are discussed in the light of current hypotheses on sexual selection theory.
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