Print PageSexual systems evolve by preventing inbreeding depression and responding to ecological factors that limit fitness, such as rarity. We compared sexual systems in the monophyletic genus Ariocarpus to determine whether biogeographic rarity and reproductive traits were related. Additionally, we compared floral morphology among species to discuss factors that could have driven evolution in Ariocarpus. We hypothesized that punctually distributed, rare species would have mixed mating systems and floral traits that permit self-pollination, since some degree of selfing may be advantageous; in contrast, widespread, common species would be strictly outcrossers and xenogamous. One population per species was studied to evaluate the breeding system through behavior and 12 floral measurements; mating system was determined trough pollination treatments. A discriminant analysis was conducted to recognize floral attributes that best classify flowers into species. Phylogenetic independent contrasts (PIC’s) were obtained to search for correlations between floral traits.
Results/Conclusions
Results showed that Ariocarpus species are strict xenogamous and mainly outcrossers (from 20 to 72% of cross-pollinated flowers set fruit); selfing success varied from 1 to 20%. Supporting our hypothesis, common species produced significantly more gametes than rare species, except for A. kotschoubeyanus, whose floral traits were more similar to the rare species. Main differences among species were based on traits related to the amount of pollen produced; however, PIC’s showed that male and female traits are positively correlated. Melittophily in Ariocarpus supports the evidence that main floral differences among species are related to male fertility. Besides biogeographic rarity, floral evolution in Ariocarpus may be explained by generalist pollination systems that respond to ecological pressures related to pollen export.
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