Repeated Evolution of Dioecy from Monoecy in Siparunaceae (Laurales)

Abstract

Abstract.-Siparunaceae comprise Glossocalyx with one species in West Africa and Siparuna with 65 species in the neotropics; all have unisexual owers, and 15 species are monoecious, 50 dioecious. Parsimony and maximum likelihood analyses of combined nuclear ribosomal ITS and chloroplast trnL-trnF intergenic spacer sequences yielded almost identical topologies, which were used to trace the evolution of the two sexual systems. The African species, which is dioecious, was sister to all neotropical species, and the monoecious species formed a grade basal to a large dioecious Andean clade. Dioecy evolved a second time within the monoecious grade. Geographical mapping of 6,496 herbarium collections from all species sorted by sexual system showed that monoecy is con ned to low-lying areas (altitude < 700 m) in the Amazon basin and southern Central America. The only morphological trait with a strong phylogenetic signal is leaf margin shape (entire or toothed), although this character also correlates with altitude, probably re ecting selection on leaf shapes by temperature and rainfall regimes. The data do not reject the molecular clock, and branch lengths suggest that the shift to dioecy in the lowlands occurred many million years after the shift to dioecy in the ancestor of the Andean clade. [Altitudinal distribution of sexual systems; dioecy; molecular clock; monoecy; sexual system evolution.] About 6% (14,620 of 240,000) of the species of owering plants are dioecious, and about 7% (959 of 13,500) of the genera are completely or partly dioecious (Renner and Ricklefs, 1995). Comparative evidence suggests that dioecy has evolved many times from perfect-owered (monoclinous) or monoecious (with diclinous owers on each plant) ancestors (Lewis, 1942;Charlesworth and Charlesworth, 1978;Lloyd, 1980). Here we study a small tropical family with diclinous owers and monoecious or dioecious species, using a phylogeny to infer the frequency of shifts between these sexual systems. We also address the possible relation between an ecological factor (altitude) and switches in sexual system and discuss differences between some major evolutionary pathways to dioecy. Two key terms, paradioecy and gynodioecy, need to be de ned at the outset. Paradioecy is the inconstant presence of male or female owers in the males and females of dioecious species, with the inconstancies being of similar magnitude in both sexes (Lloyd, 1972a). Gynodioecy is the regular coexistence of perfect-owered and pistillate individuals (

Embryology of Siparunaceae (Laurales): characteristics and character evolution

“…65 spp.) distributed in Central and South America (Renner and Hausner 1997;Renner and Won 2001) are poorly understood embryologically. In a previous paper (Kimoto and Tobe 2001), we presented a literature review of embryological features of Laurales (comprising seven families including Siparunaceae), and suggested that 16 embryological characters (e.g., mode of cytokinesis in the microspore mother cell, anther dehiscing mode, number of integuments) are diversified within the order and are likely to be useful in discussion of morphology-based relationships among and within the seven lauralean families.…”

The evolution of unisexual flowers: morphological and functional convergence results from diverse developmental transitions

“…Empirical and theoretical studies also have identified possible evolutionary pathways to dioecy under these selective forces (reviewed in Barrett, 2002). Transitions to dioecy from distyly (e.g., Darwin, 1877; Barrett and Shore, 1987;Barrett, 1990), from monoecy (e.g., Lloyd, 1980;Renner and Ricklefs, 1995;Renner and Won, 2001;Dorken and Barrett, 2004), and from gynodioecy (e.g., Charlesworth and Charlesworth, 1978a;Ashman, 1999;Charlesworth, 1999;Delph, 2003) have been explored. Despite multiple evolutionary forces and diverse intermediates, these evolutionary transitions all have the same end result-functionally unisexual individuals.…”

A Phylogenetic Study of Evolutionary Transitions in Sexual Systems in AustralasianWurmbea(Colchicaceae)

“…Previous phylogenetic analyses of the evolution of gender strategies have been aimed at identifying independent transitions to evaluate the selective mechanisms responsible for gender dimorphism (e.g., Hart 1985;Wagner et al 1995;Weller et al 1995;Soltis et al 1996;Sakai et al 1997;Renner and Won 2001;Levin and Miller 2005). These findings, in conjunction with population-level studies, can support hypotheses that specific ecological factors favor transitions from gender monomorphism to dimorphism (reviewed in Ashman 2006; Barrett and Case 2006).…”

“…A number of studies have employed phylogenies to investigate evolutionary transitions in plant reproductive characters (e.g., Weller and Sakai 1999 and references therein; Weiblen et al 2000;Renner and Won 2001;Krahenbuhl et al 2002;Miller 2002;Vamosi et al 2003;Graham and Barrett 2004;Givnish et al 2005;Gleiser and Verdú 2005;Levin and Miller 2005). These studies are primarily aimed at estimating the number of times particular traits arose and/or the ecological or morphological context in which traits may have evolved, which provide indirect evidence of the proximate mechanisms responsible for phenotypic change and the adaptive significance of trait transitions.…”