Population‐level variation in the expression of heterostyly in three species of Rubiaceae: does reciprocal placement of anthers and stigmas characterize heterostyly?

Abstract

Heterostyly (i.e., reciprocal placement of anthers and stigmas between two or three floral morphs) is hypothesized to enhance outcrossing and reduce selfing. However, few studies have documented reciprocity among individual plants; instead, mean anther and stigma heights for floral morphs are usually reported, masking interindividual variation. We measured eight floral dimensions for individuals in five populations of three heterostylous Rubiaceae. The three methods used to quantify reciprocity yielded different conclusions regarding the degree to which populations conformed to expectations for heterostylous plants. Only Psychotria poeppigiana had stigma and, to a lesser degree, anther heights in discrete classes. Variation among plants of Bouvardia ternifolia and Psychotria chiapensis yielded a continuum of anther and stigma heights across populations. Comparison of distances between stigma and anthers indicated that only flowers of B. ternifolia had, as expected, a constant value for this distance. Finally, regression relationships between anther and stigma heights and corolla length showed that only in one population each of B. ternifolia and P. poeppigiana, and in P. chiapensis, was distance between anthers and stigmas the same across the range of corolla sizes for both floral morphs. Variation among these species in expression of heterostyly was not clearly linked to phylogenetic relationship or pollinator syndromes. Two approach herkogamous (AH) species were studied for comparison. Flowers of Psychotria brachiata were consistently AH, but flowers of P. pittieri were highly variable. Determining fitness consequences of population-level variation in sexual systems requires studies linking floral morphology to pollinator behavior and pollen transfer.

Distyly and variation in floral traits in natural populations of Psychotria ipecacuanha (Brot.) Stokes (Rubiaceae)

“…Such studies took into consideration a great number of individuals from a number of populations and revealed that variation of floral traits associated with distyly may exhibit overlapping of values. Pailler & Thompson (1997) and Faivre & McDade (2001) found variations among flowers of the same individual, among individuals of the same population and among populations of the same species. As pointed out by Barrett & Shore (1987), investigation in floral trait variation among populations may provide important information about the evolution, maintenance and/or loss of heterostyly.…”

“…However, several studies have shown that the morphological components of distyly can display some flexibility (Richards & Koptur 1993, Faivre & McDade 2001. Such studies took into consideration a great number of individuals from a number of populations and revealed that variation of floral traits associated with distyly may exhibit overlapping of values.…”

Variação floral e biologia reprodutiva de Manettia cordifolia Mart. (Rubiaceae)

“…As espécies são consideradas heterostílicas quando os indivíduos podem ser divididos em duas classes morfológicas distintas (longistilas e brevistilas) com uma severa hercogamia recíproca entre os morfos (Faivre & McDade 2001). Com base nessas condições estruturais, a espécie apresentou características morfológicas de monomorfismo longistílico (Barrett 1992, Hamilton 1990) e "approach herkogamy" (disposição morfológica do complexo estigma-antera, com o estigma localizando-se sempre acima das anteras).…”

“…Rubiaceae contém o maior número de espécies distílicas dentre todas as famílias nas quais tal dimorfismo é conhecido, sendo encontrada em 416 espécies distribuídas em 91 gêneros (Ganders 1979, Barrett & Richards 1990, Passos & Sazima 1995. A ocorrência de variações na apresentação da distilia é comum na família, sendo demonstrada para espécies de Psychotria, Palicourea, Bouvardia e Guetarda (Sobrevila et al 1983, Hamilton 1990, Richards & Koptur 1993, Faivre & McDade 2001, Coelho & Barbosa 2003.…”

Biologia reprodutiva de Psychotria spectabilis Steyrm. e Palicourea cf. virens (Poepp & Endl.) Standl. (Rubiaceae) em uma floresta tropical úmida na região de Manaus, AM, Brasil

“…A heterostilia é bastante comum nos representantes estudados da família Rubiaceae, principalmente no gênero Psychotria (Hamilton 1990;Faivre & McDade 2001;Lau & Bosque 2003;Castro & Araújo 2004). Psychotria spectabilis apresentou diferenças na fecundidade entre os morfos florais, sendo esta maior nas flores brevistilas.…”