Functional modularity in a forcible flower mechanism: relationships among morphology, biomechanical features and fitness

Abstract

Flowers may be interpreted as complex combinations of organs functionally coordinated to attract pollinators and to mechanically interact with the pollinator's body, particularly when flower mechanisms are actively handled by pollinators. Thus, a functional modularity of traits in keel flowers (Fabaceae) was expected because of a compartmentalization between attraction and mechanical functions. To test this hypothesis, we used Collaea argentina, a Fabaceae that exhibits typical keel flowers. The force needed to open keels, the keel displacement angle and floral morphometric traits in 100 plants from a natural population were measured to detect floral characters correlated with the biomechanical variables. Furthermore, we examined the relationships among this functional module, biomechanical variables and female reproductive success to explore whether these traits are the targets of pollinator-mediated phenotypic selection, and used path analysis to examine the causal relationship among these variables. A functional module formed by two morphometric traits of the petals directly involved in the floral mechanism (keel and wings) was found, but no flag trait was involved in this module. Even though the functional module had a positive effect on force and there were significant relationships between the displacement angle and fruit set, no significant effect of force on female reproductive success was detected. These results question whether selection currently plays a role favouring the integration of this module, but this may be consistent with a past stabilizing selection on the force needed to open the keel.

A stable pollination environment limits current but not potential evolution of floral traits

“…This does contrast with the fact that there is a significant phenotypic correlation between the two traits, but as suggested by previous studies, phenotypic correlations are not always good predictors of genetic correlations, even in highly integrated organs as flowers (Gómez et al 2009). Again, this is consistent with the decoupling of petals found in a related species with keel flowers (Córdoba et al 2015). It is thus possible that the phenotypic correlation is caused by shared environmental factors that affect both traits in Ulex flowers, further confirming the importance of studying evolutionary potential in field realistic conditions.…”

“…We found that flower size shows significant heritability, but no detectable heritability in the standard petal area. Comparing petals in papilionoid flowers, Herrera (2001) found that the standard had higher phenotypic variance than other petals across Genisteae, and argued that its role in pollination was smaller than for the keel petals, in a similar way as Córdoba et al (2015). This and our results suggest that this petal might be prone to high environmentally-induced variation, which increases the exposure to stabilising selection, but does not lead to evolutionary change.…”

An analysis of the energetic reward offered by field bean (Vicia faba) flowers: Nectar, pollen, and operative force

“…For example, the flowers of many members of the legume family (Fabaceae) require pollinators to apply force to access their reward. In some species, such as Spartium junceum, the force required is considerable and exceeds the strength of the honeybee Apis mellifera (Córdoba, Benitez-Vieyra, & Cocucci, 2015;Córdoba & Cocucci, 2011). For accessible rewards, flowers with larger quantities (e.g.…”

Who can open the flower? Assessment of the flower opening force of mammal‐pollinated Mucuna macrocarpa

“…Thus, the force of the pollinator is stronger than the force of petals for opening (termed the operative force), with hypotheses existing on how the operative force has adapted to the pollinator (Córdoba & Cocucci ; Córdoba et al . ; Córdoba & Cocucci ). However, the operative force might be related to factors other than the pollinator.…”

“…Under these circumstances, only a specific animal with sufficient force to open the petals may pollinate the plant (Brantjes 1981;Claβen-Bockhoff et al 2004;Córdoba & Cocucci 2011). Thus, the force of the pollinator is stronger than the force of petals for opening (termed the operative force), with hypotheses existing on how the operative force has adapted to the pollinator (Córdoba & Cocucci 2011;Córdoba et al 2015;Córdoba & Cocucci 2017). However, the operative force might be related to factors other than the pollinator.…”