Sexual Dimorphism and Gynoecium Size Variation in the Andromonoecious Shrub Caesalpinia gilliesii

Abstract

The degree of sexual dimorphism in flowers and inflorescences can be evaluated early in flower development through the study of floral organ size co-variation. In the present work, the gynoecium-androecium size relationship was studied to assess the degree of sexual expression in flowers and inflorescences of the andromonoecious shrub Caesalpinia gilliesii. The co-variation pattern of floral organ sizes was compared between small and large inflorescences, under the hypothesis that inflorescence size reflected differential resource availability. Also, staminate and perfect flowers were collected from three populations and compared on the basis of gynoecium, ovule length, filament length, pollen size and number. The obtained results indicated that staminate and perfect flowers differed only in the gynoecium and ovule length, whereas filament length, pollen size, and number varied across populations. The gynoecium size was smaller and its variability was much higher in staminate than in perfect flowers, as explained by a recent hypothesis about pollinator-mediated gynoecium size selection acting upon perfect flowers. The analysis of the gynoecium-androecium size relationship during flower development, revealed a dissociation of gynoecium growth relative to other floral structures in some buds. Lower gynoecium-androecium regression slopes and smaller gynoecia length characterized smaller inflorescences, thus reflecting the fact that sexual expression was more male-biased. This trend is in agreement with a differential resource-related response at the inflorescence level, however, post-mating resource allocation and the inclusion of other modular levels may also help us to understand the variation in sexual dimorphism in this species.

Variation in sexual expression in relation to plant height and local density in the andromonoecious shrub Caesalpinia gilliesii (Fabaceae)

“…The vegetation in the region corresponds to Bosque Serrano woodlands (Luti et al 1979) within the Chaco phytogeographical province (Cabrera 1994). C. gilliesii grows sparsely beneath the canopy of dominant trees, such as Lithraea molleoides and Prosopis spp., or forms pure patches in canopy gaps.…”

Specialized use of pollen vectors by Caesalpinia gilliesii, a legume species with brush-type flowers

“…gilliesii is considered endemic to Argentina (Burkart, 1936). Plants are andromonoecious and show variability in the production of staminate and perfect flowers in relation to plant and inflorescence size (Cocucci, Galetto & Sérsic, 1992; Calviño & Carrizo García, 2005). The fragrant flowers have dark‐red, exserted styles and stamens that contrast with the light‐yellow, highly reflective petals (Moré et al ., 2003).…”

Effects of ovule and seed abortion on brood size and fruit costs in the leguminous shrub Caesalpinia gilliesii (Wall. ex Hook.) D. Dietr

“…Because our study was based on a fruit sample, the positional variability attributable to plasticity in fruiting success or architecture alone cannot be distinguished (Diggle 2003). However, ovule number per ovary was similar when bud position was controlled for in fruitless inflorescences (Calviño & Carrizo García 2005) in favor of fruiting success as the main source of variability in ovule number. In addition, some features indicate that the influence of a predictable pollination environment would be the main source of position-dependent variation in ovule abortion in C. gilliesii.…”