Evolutionary maintenance of stigma‐height dimorphism in Narcissus papyraceus (Amaryllidaceae)

Abstract

Stigma-height dimorphism is a sexual polymorphism in which plant populations are composed of two floral morphs that differ significantly in style length but not anther position. The morphs exhibit approach and reverse herkogamy, floral designs that in most species typically occur as monomorphic conditions. We investigated the floral biology of stigma-height dimorphism in the Mediterranean geophyte Narcissus papyraceus (Amaryllidaceae) in an effort to understand the evolutionary forces maintaining stylar polymorphism. Our survey of 66 populations in Spain, Portugal, and Morocco indicated that 56% were dimorphic with the long-styled morph at an average frequency of 0.79. The remaining 44% of populations sampled were monomorphic for the long-styled morph. In dimorphic populations there was a significant positive relation between population size and the frequency of the short-styled morph. Controlled pollinations demonstrated that N. papyraceus is self-sterile with no significant differences in female fertility between intra- and intermorph crosses. Prior self-pollination reduced seed set in flowers that were subsequently cross-pollinated. Estimates of mating patterns using allozyme markers in eight populations indicated that N. papyraceus is largely outcrossing (mean t(m) = 0.81) with no significant differences between monomorphic and dimorphic populations or style morphs. Stigma-height dimorphism in N. papyraceus is maintained in populations by insect-mediated cross-pollination with biased morph ratios and stylar monomorphism likely resulting from the combined influence of the inheritance of the polymorphism, morph-specific differences in assortative mating and founder effects.

The evolution of polymorphic sexual systems in daffodils (Narcissus)

“…Second, monomorphic populations of dimorphic species composed of the L-morph are highly outcrossing, so that individuals of this morph seem quite capable of mating with each other (e.g. N. papyraceus, Arroyo et al, 2002). The near absence of populations monomorphic for the S-morph in Narcissus suggests that this morphology is poorly adapted for effective intramorph mating.…”

“…These factors include differences in the pollinator fauna among populations, particularly the presence of short-vs long-tongued pollinators (Arroyo & Dafni, 1995), and the role of the inheritance of style length on morph representation in monomorphic populations following founder effects (Baker et al, 2000b;Arroyo et al, 2002). Interestingly, in several species (N. assoanus in France, Baker et al, 2000c;N.…”

“…Additionally, equilibrium morph ratios could vary considerably among populations, because of the influence of local environmental conditions on both floral phenotypes and insect visitors, with corresponding effects on mating patterns. Indeed, extensive surveys of morph ratios in five Narcissus species with stigmaheight dimorphism have revealed striking variation among populations (Arroyo & Dafni, 1995;Barrett et al, 1996;Baker et al, 2000b;Arroyo et al, 2002;Arroyo, 2002).…”

“…These species are not distylous, because both morphs have anthers in similar positions, and so lack reciprocal herkogamy. Both monomorphic and dimorphic species with the paperwhite morphology are pollinated primarily by Lepidoptera (Sphingidae, Pieridae, Nymphalidae: Vogel & Müller-Doblies, 1975;Arroyo & Dafni, 1995;Arroyo et al ., 2002;Thompson et al ., 2003), which transport pollen on their proboscides or faces. Long-tongued bees also visit these species; however, their tongues are too short to reach the nectar at the base of the tube, so they collect only pollen.…”

Associations between sex‐organ deployment and morph bias in related heterostylous taxa with different stylar polymorphisms

“…In several species of Anchusa , Lithodora, Glandora (Boraginaceae), and Narcissus (Amaryllidaceae) the style morphs are self-incompatible but intramorph compatible-a pattern inconsistent with heteromorphic incompatibility and indicative that they possess distinct self-recognition systems ( Anchusa -Dulberger, 1970 ;Philipp and Schou, 1981 ;Schou and Philipp, 1984 ;Lithodora andGlandora -Ferrero et al, 2011a , 2012 ;Narcissus -Dulberger, 1964 ;Barrett et al, 1997 ;Arroyo et al, 2002 ;Baker et al, 2000b ;Simón-Porcar et al, 2015b ). In Anchusa ( Schou and Philipp, 1983 ) and Narcissus ( Dulberger, 1964 ;Sage et al, 1999 ;Santos-Gally et al, 2015 ;Simón-Porcar et al, 2015b ) self-rejection involves late-acting ovarian incompatibility.…”