Repeated Evolution of Dioecy from Monoecy in Siparunaceae (Laurales)

Repeated Evolution of Dioecy from Monoecy in Siparunaceae (Laurales)

Repeated Evolution of Dioecy from Monoecy in Siparunaceae (Laurales) S US ANNE S . RENNER AND HYOSIG WON Abstract.—Siparunaceae comprise Glossocalyx with one species in West Africa and Siparuna with 65 species in the neotropics; all have unisexual flowers, 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 evolutio n 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 collection s from all species sorted by sexual system showed that monoecy is confined to low-lying areas (altitude < 700 m) in the Amazon basin and southern Central America. The only mor- phological trait with a strong phylogenetic signal is leaf margin shape (entire or toothed), although this character also correlates with altitude, probably reflecting 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 lowland s occurred many million years after the shift to dioecy in the ancestor of the Andean clade. [Altitudina l distribution of sexual systems; dioecy; molecular clock; monoecy; sexual system evolution.] About 6% (14,620 of 240,000 ) of the species have bisexual or unisexual flowers (Lloyd, of flowering plants are dioecious, and about 1980; Barrett, 1998; Sakai and Weller, 1999; 7% (959 of 13,500) of the genera are com- Sarkissian et al., 2001). This broadening pletely or partly dioecious (Renner and of the meaning of gynodioecy affects the Ricklefs, 1995). Comparative evidence sug- debate about two of the evolutionary path- gests that dioecy has evolved many times ways to dioecy—the gynodioecy/dioecy from perfect-flowered (monoclinous) or mo- pathway and the monoecy/paradioecy/ noecious (with diclinous flowers on each dioecy pathway—a point we take up in the plant) ancestors (Lewis, 1942; Charlesworth discussion. and Charlesworth, 1978; Lloyd, 1980). Here Our study system is Siparuna, a genus we study a small tropical family with dicli- with 50 dioecious and 15 monoecious species nous flowers and monoecious or dioecious that do not vary in pollination, seed dis- species, using a phylogeny to infer the fre- persal, or woodiness. All species are gall quency of shifts between these sexual sys- midge–pollinated, animal-dispersed shrubs tems. We also address the possible relation or trees of humid forests (Feil and Renner, between an ecological factor (altitude) and 1991; Feil, 1992; Renner et al., 1997; Schulz- switches in sexual system and discuss dif- Burck, 1997). That monoecy or dioecy (or ferences between some major evolutionary both) might have evolved repeatedly within pathways to dioecy. Two key terms, para- the genus is suggested by the pattern dioecy and gynodioecy, need to be defined at of leaf margin variation (photos of most the outset. Paradioecy is the inconstant pres- leaves appear in Renner and Hausner [1997] ence of male or female flowers in the males at http: www.siparuna.com). All monoe- and females of dioecious species, with the cious species have entire leaf margins, inconstancies being of similar magnitude in whereas all but two dioecious species have both sexes (Lloyd, 1972a). Gynodioecy is the toothed margins. The two dioecious species regular coexistence of perfect-flowered and with entire margins could have originated pistillate individuals (Darwin, 1877; Percival, from entire-margined ancestors, represent- 1965; Lloyd, 1976; Delannay, 1978; Mayer ing a transition from monoecy to dioecy and Charlesworth, 1991; Grant, 1999). Some separate from the one in the toothed clade. times, the term is used more broadly to Leaf margin shape, however, is highly corre- apply to populations composed of female lated with temperature and rainfall (Wolfe, and hermaphroditic individuals, irrespective 1990; Wiemann et al., 1998), the proportion of whether the genetic hermaphrodites of entire-margined leaves in a flora being the best single character for estimating mean an- any other character. The last monograph of nual temperature. Independent evidence is Siparuna (Perkins, 1901), perhaps surpris- therefore needed to test the hypotheses that, ingly, used sexual system as the first crite- in Siparuna, leaf margin shape carries phylo- rion in the arrangement of species, followed genetic signal and that its message (two sex- by indumentum and androecial characters. ual system switches) is trustworthy. Finally, Even when more characters are used, poten- we were interested in estimating the relative tially monophyletic groups and their rela- and absolute times of any switches in sexual tionships are difficult to discern. Therefore, system because simultaneous changes at par- we used nuclear and chloroplast DNA se- ticular times might argue for similar factors quences to construct a phylogenetic hypoth- having selected for them. esis that provides a framework in which to Siparuna is distributed in tropical South discuss the evolution of monoecy and dioecy America and is one of two genera of in Siparunaceae . Siparunaceae , a family of Laurales (Renner, 1999). The other genus is Glossocalyx with MATERI ALS AND MET HOD S a single species in lowland tropical West Taxon Sampling Africa that is dioecious and has toothed leaves (Fouilloy, 1974; an additional species Representatives of Siparunacea e and their is recognized by Fouilloy but is considered outgroups were selected on the basis of ear- a synonym by Renner and Hausner, un- lier morphological and molecular analyses publ. manuscript). A third genus, Bractean- (Perkins, 1901; Renner and Hausner, 1997; thus , is here found nested within Siparuna. Renner et al., 1997). Trees were rooted with The ranges and gross morphology of the Gomortega nitida based on the finding that species studied are known from ongoing monotypic Gomortegaceae and Atherosper- monographic work (Renner and Hausner, mataceae together are the sister group of 1997, 2000). Sexual systems are known Siparunacea e (we did not include Atheros- from fieldwork on 13 dioecious species in permataceae sequences because their highly Ecuador (Feil, 1992) , 6 monoecious species in divergent internal transcribed spacer (ITS) Amazonian Brazil (Schulz-Burck, 1997) , and sequences caused dubious alignments). The herbarium study of all species. More than 21 ingroup taxa (Table 1) consist of 7 of the 8,000 herbarium collections of Siparunaceae 15 monoecious species and 14 of the 50 dioe- have been studied for a monograph of the cious ones. One additional dioecious species, family. Flowers of Siparunacea e are a few S. brasiliensis, was sampled only for trnL-trnF, millimeters in diameter and strictly unisex- which placed it inside the Andean dioecious ual. They are borne in cymes that in monoe- clade. Material of Siparunacea e is difficult cious species usually bear a mixture of male to obtain because many of the 65 species and female flowers, either on the same pe- are restricted to particular mountain ranges duncle or on a nearby peduncle. Because of in Colombia, Ecuador, and Peru, where in- the small size of the reproductive structures, dividuals often grow widely dispersed. Al- herbarium sheets of Siparuna often bear sev- though our sample is thus biased towards eral inflorescences and many flowers, thus widespread species, it does include the allowing the dissection and gender assess- rarely collected Bracteanthus glycycarpus (D ment of flowers. Species represented by suf- Siparuna glycycarpa) and S. sp. nov. aff. monog- ficient herbarium specimens can therefore be yna. Herbarium specimens of Siparuna did identified as either monoecious or dioecious. not yield usable DNA. Siparunacea e are isolated among Lau- rales in the morphology and strict uni- sexuality of their flowers, and molecu- DNA Isolation, Amplification, lar phylogenies show that their closest and Sequencing relative is a clade with bisexual flow- Total DNA was isolated from silica gel– ers, the monotypic Chilean Gomortegaceae dried leaves from single individuals by using and the trans-Antarctic Atherospermataceae DNeasy plant mini kits (QIAGEN, Valencia, (Renner, 1999; Renner et al., 2000). Mor- CA) according to the manufacturer ’s in- phological studies within Siparunacea e have structions. DNA amplification by the poly- provided little insight into the direction of merase chain reaction (PCR) followed stan- evolutionary change in sexual system or dard protocols. The chloroplast trnL-trnF TAB LE 1. Species sequenced for this study with their voucher specimens, geographical and altitudinal ranges, and GenBank accession numbers. Vouchers for silica-dried leaves are in the herbaria listed in parentheses after each collection; for herbarium acronyms see the Index Herbariorum at http://www.nybg.org/bsci/ih/ih.html. trnL-trnF Species Mating systema Voucher specimen Range and altitude spacer ITS Bracteanthus glycycarpus Ducke D M Sothers and Silva 708 Eastern Amazon basin; AF289849 AF289828 Siparuna glycycarpa (Ducke) (INPA, MO) 60–500 m Renner and Hausner, ined. Glossocalyx longicuspis Benth. D Bos 4659 (MO) West Africa, lowlands AF012405 AF289845 Gomortega nitida R. & P. B Rodriguez 3070 (CONC) Chile, lowlands AF012404 AF289846 Siparuna aspera (R. & P.) A. DC. D Madrin˜ a´ n, Renner and Andes from Colombia to AF040695 AF289834 Cortes 1502 (COL) Peru; 350–3,000 m Siparuna bifida (P. & E.) A. DC. D Pereira-Moura 1711 (R) Amazon basin; AF289853 AF289832 85–600(–1,100) m Siparuna brasiliensis (Spreng.) A. DC. D Pignal 309 (MO, P) Southeastern Brazil; 100–1,600 m AF012408 — Siparuna cervicornis Perkins D Renner and Hausner 1 (MO, QCNE) Western Amazon basin; 100–550 m AF289854 AF289833 Siparuna conica Renner and Hausner D Galdames 4325 (PMA) Andes from Panama to AF289855 AF289835 Ecuador; 0–1,860 m Siparuna cuspidata (Tul.) A. DC. M Costa and Assunc¸ a˜ o 373 Amazon basin and South AF289848 AF289826 (INPA, K, MO) Central America; 9–700 m Siparuna cymosa A.

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