Phenotypic integration in style dimorphic daffodils (Narcissus, Amaryllidaceae) with different pollinators

Abstract

Different pollinators can exert different selective pressures on floral traits, depending on how they fit with flowers, which should be reflected in the patterns of variation and covariation of traits. Surprisingly, empirical evidence in support of this view is scarce. Here, we have studied whether the variation observed in floral phenotypic integration and covariation of traits in Narcissus species is associated with different groups of pollinators. Phenotypic integration was studied in two style dimorphic species, both with dimorphic populations mostly visited by long-tongued pollinators (close fit with flowers), and monomorphic populations visited by short-tongued insects (loose fit). For N. papyraceus, the patterns of variation and correlation among traits involved in different functions (attraction and fit with pollinators, transfer of pollen) were compared within and between population types. The genetic diversity of populations was also studied to control for possible effects on phenotypic variation. In both species, populations with long-tongued pollinators displayed greater phenotypic integration than those with short-tongued pollinators. Also, the correlations among traits involved in the same function were stronger than across functions. Furthermore, traits involved in the transfer of pollen were consistently more correlated and less variable than traits involved in the attraction of insects, and these differences were larger in dimorphic than monomorphic populations. In addition, population genetic parameters did not correlate with phenotypic integration or variation. Altogether, our results support current views of the role of pollinators in the evolution of floral integration.

Keywords: adaptation; genetic diversity; phenotypic selection; plasticity; pollinator-mediated selection; style dimorphism.

Figure 1.

Floral traits measured in (a) Narcissus papyraceus: flower diameter (1), corona diameter (2) and height (3), flower tube length (4) and width (5), style length (6), upper anther height (7) and lower anther (8) height in long- (L) and short-style (S) flowers, and (b) Narcissus tazetta: flower diameter (1), outer tepal length (2) and width (3), corona diameter (4) and height (5) and flower tube length (6). (Online version in colour.)

Figure 2.

Means and 95% CI of the phenotypic integration index in dimorphic (black bars) and L-monomorphic (white bars) populations with mainly long- and short-tongued pollinators, respectively, in N. papyraceus and N. tazetta.

Figure 3.

Mean and 95% CI of the coefficient of variation of floral traits involved in the pollinator attraction (black bars), pollinator access and fit (grey bars) and in pollen pick-up and deposition (white bars) in dimorphic and L-monomorphic populations of N. papyracueus.

Figure 4.

Mean and 95% CI of the correlation coefficients among traits involved in the attraction of pollinators and traits involved in the pollination function (style length–flower tube length correlation, upper anther height–flower tube correlation and lower anther height–flower tube correlation) in dimorphic and L-monomorphic populations of Narcissus papyraceus.