Male and female selective mechanisms, reproductive success and gene flow

Sammanfattning: In this thesis, I have studied male and female selective mechanisms that can affect plant reproductive success and gene flow. I have focussed on sexually selected traits, mainly pollen competition and maternal sorting mechanisms, for example through non-random ovule abortion. The main question was; what kind of traits can influence the most successful pollen donor or maternal sorting process? I focused on disease resistance (zucchini yellow mosaic virus -ZYMV) in Cucumis sativus as a possible trait that could influence selective processes. Controlling for pollen tube growth, I performed two donor crosses between pollen donors with or without this trait and later genotyped progeny using a molecular marker. I found that in the absence of disease, success could be through either pollen competitive ability or maternal sorting. Though pollen tube growth rate was important, genetic differences between the pollen donors determined the best donor. These genetic differences were however, not based on one resistance quality (ZYMV) but other traits too which were not clear. In presence of the pathogen, selective mechanisms seemed to be based on a secondary level, the pistil nutrient environment which increased in infected recipient plants. This kind of selection favoured the susceptible embryos (maternal selection). In addition, pollen donors performed best in pistils if both came from the same nutrient environments. Since most plants spread their seeds near where they grow, maternal plants could achieve higher fitness by promoting fertilisations by pollen adapted to their growing conditions. I have also studied potential ways in which sexual conflicts can occur between male and female reproductive functions in plants. I studied development of receptivity to different pollen donors in Collinsia heterophylla. I found that some pollen donors could achieve fertilisations soon after flower opening, before the pistil achieved full receptivity. Although this trait varied between donors and among female recipients, potential for conflicts could exist. This is because the female may benefit by enhancing pollen competition (by delaying receptivity) but on the other hand, pollen donors would benefit by achieving as many fertilisations without competition from other donors. Finally, I was able to separate reproductive mechanisms that result from pollen competition or maternal sorting. I did this though reciprocal experiments with hybrids as either pollen or ovule parents. I concluded that in my experiments with Cucumis sativus, pollen competition contributed to high siring success of the Bitter genotype. Regulation of maternal investment to the seed seemed to be governed by time to ovule fertilisation.