Species with mixed mating systems often demonstrate variable expression of breeding system characteristics and thus represent the opportunity to understand the factors and mechanisms that promote both outcrossed and selfed seed production. Here, we investigate variation in levels of herkogamy (variation in stigma-anther separation distance) in a Puerto Rican population of hummingbird pollinated Gesneria citrina Urban. There is significant variation in herkogamy levels among individuals of this species and stigma-anther separation is negatively associated with the ability to set fruits and seeds in the absence of pollinators. The variation in levels of herkogamy may represent a mechanism to ensure the production of some self-fertilized progeny in the absence of hummingbird pollinators. We also describe a novel breeding system in G. citrina, where stamens elongate over time to reach stigma height, but stamen elongation is accelerated by pollination. These results suggest that once the flowers are pollinated, stamen elongation may favor increased pollen removal and siring success, while the reduction in stigma-anther distance no longer imposes the risk of interference between male and female functions. We discuss our findings of breeding system variation in the context of pollination system evolution in an island setting (Antillean islands).
Xin-Sheng ChenSilvana Marten-RodriguezQing-Jun LiCharles B. Fenster
Current understanding of the classical ABC model of floral development has provided a new set of characters to evaluate floral evolution. However, what is still lacking is a clear assessment of this genetic program across monocots. Here, to investigate the evolution of members of class A and B genes in monocots, we report the sequence characteristic and transcript expression of three new MADS-box genes in Alpinia oblongifolia Hayata. Sequence and phylogenetic analysis reveals that these genes are FUL-like and AP3-like. Therefore, they were termed AoFL1, AoFL2 and AoAP3. AoFL1 contains the FUL motif, but AoFL2 lacks this motif. Their expression revealed by in situ hybridization may reflect the ancestral function of FUL-like genes in the specification of inflorescence and floral meristems. The AoAP3 gene contains two conserved motifs, the PI-derived and paleoAP3 motifs. The AoAP3 transcripts located to the corolla and stamen, and hybridization signals were detected in the central whorl. These expression patterns suggest that the functions of homologous organ identity genes are diversified in A. oblongifolia. The implications of these findings on the conservation of homologous gene function are discussed.
