Disassortative mating prevails in style-dimorphicNarcissus papyraceusdespite low reciprocity and compatibility of morphs

Abstract

Evolution to reduce inbreeding can favor disassortative (inter-morph) over assortative (intramorph) mating in hermaphroditic sexually polymorphic plant species. Heterostyly enhances disassortative pollination through reciprocal placement of stigmas and anthers of morphs and appropriate pollinators. Stylar dimorphism in which there is not reciprocal anther placement may compromise disassortative mating, particularly when there is not intra-morph incompatibility. Variable rates of disassortative mating along with differential female fecundity or siring success among floral morphs could lead to variation in morph ratio. We investigated mating patterns, female fecundity and siring success of style-length morphs in Narcissus papyraceus, a self-incompatible but morph-compatible species with dimorphic (long-and short-styled) and monomorphic (long-styled) populations in central and north regions of its range respectively. We established experimental populations in both regions and exposed them to ambient pollinators. Using paternity analysis, we found similar siring success of morphs and high disassortative mating in most populations. Female fecundity of morphs was similar in all populations. Although these results could not completely explain the loss of dimorphism in the species' northern range, they provided evidence for the evolutionary stability of stylar dimorphism in N. papyraceus in at least some populations. Our findings support the hypothesis that prevailing inter-morph mating is key for the maintenance of stylar dimorphism.

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

“…3G ). Elsewhere among heteromorphic plants, high levels of disassortative mating resulting in equal morph ratios have been reported in self-compatible, tristylous Eichhornia paniculata ( Barrett et al, 1987 ;Kohn and Barrett, 1992 ) and in stylar dimorphic Narcissus papyraceus ( Simón-Porcar et al, 2014, 2015a. We observed abundant pollinator visitation by long-tongued bees in distylous Glandora and Lithodora populations ( Ferrero et al, 2011b ) and these insects probably play a key role in promoting disassortative mating and causing isoplethic morph ratios.…”

“…For example, if style morphs in a population diff er in rates of disassortative and assortative mating, various L-morph and S-morph biased anisoplethic equilibria are possible. Indeed, there is empirical evidence of biased morph ratios in species in which enforced disassortative mating does not occur because of the absence of heteromorphic incompatibility ( Ganders, 1975 ;Ray and Chisaki, 1957 ;Barrett et al, 1996Barrett et al, , 2004Baker et al, 2000a , b ;Pérez-Barrales and Arroyo, 2010 ;Simón-Porcar et al, 2015a ). In such cases, fl oral morphology plays a more signifi cant role in governing patterns of pollen transfer and mating than in the species envisioned by Haldane, in which illegitimate unions were prevented by physiological incompatibility.…”

“…However, stigma-height dimorphism is clearly a stable polymorphism in each of these taxa because it is reported from a signifi cant number of species. Moreover, at least in Narcissus , there is experimental evidence that despite incomplete sexorgan reciprocity and intramorph compatibility, disassortative mating is promoted by stigma-height dimorphism ( Simón-Porcar et al, 2014, 2015a, and the stylar morphs are subject to frequencydependent selection ( Th ompson et al, 2003 ) in the same manner as in distylous populations.…”

The measure and mismeasure of reciprocity in heterostylous flowers

“…Reciprocal herkogamy (morph reciprocity) can be viewed as an adaptation promoting compatible pollination and reproductive fitness, as Darwin and most authors since have argued (see, for example, Simón‐Porcar et al ., ; Zhou et al ., ). This means that the reproductive fitness of individuals with any particular anther position is determined by the distribution of stigma positions among its potential mates, weighted by its fitness in relation to each, and vice versa for stigma positions.…”

The function of the floral corona in the pollination of a Mediterranean style dimorphic daffodil

“…Here we provided a mechanistic explanation to former results on the contribution of contrasting pollinator groups to female fitness (Pérez‐Barrales & Arroyo ; Simón‐Porcar et al . ).…”