Asteraceae brasileiras com mais flores por capítulo apresentam maior razão pólen-óvulo

Abstract

The pollen-ovule ratio (P:O) is considered a good indicator of the breeding system of plants. While species that favor self-fertilization tend to have lower pollen-ovule ratio, plants that favor cross-fertilization tend to have higher pollen-ovule ratio. Species of the Asteraceae family have inflorescences consisting of a few to hundreds of flowers that mimic flowers and function to attract pollinators. In this study, we investigated how the number of flowers per capitulum is related to the pollen-ovule ratio in Asteraceae. We expected that species with more flowers per capitulum would have a higher investment in pollen relative to ovules due to more intense male-male competition. This study analyzed data from 78 Brazilian species of Asteraceae deposited in the herbarium of the Federal University of Rio Grande do Norte (UFRN). We tested: (i) the allometric relationships between the number of flowers per capitulum (log10) and the number of pollen grains and ovules per capitulum (log10); (ii) the relationship between the number of pollen grains and ovules per capitulum; and (iii) the influence of phylogenetic signal on the number of flowers and pollen grains per capitulum. Our results showed a positive allometric relationship between the number of pollen grains (β = 1.532, P < 0.00001) and the number of flowers per capitulum. In contrast, we found an isometry between the number of ovules ((β = 0.998, P = 0.832) and the number of flowersper capitulum. Furthermore, the phylogenetic signal of all floral variables was weak. Thus, Asteraceae species with a higher number of flowers percapitula have a greater investment in the male function.