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Selected Wurmbea species illustrating diversity in floral morphology, flower colour and inflorescence display. (a) W. monopetala, (b) W. marginata, (c) W. tubulosa female, (d ) W. tubulosa male, (e) W. spicata, ( f ) W. inusta, (g) W. sp. nov., Thomas River WA, (h) W. dioica ssp. dioica (female left, male right), (i) W. pygmaea, ( j) W. dioica ssp. alba (cosexual), (k) W. graniticola, (l ) W. tenella, (m) W. biglandulosa ssp. biglandulosa (female). Species a, b, e and f are African species; species c, d and g-m are Australian species.
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Angiosperms possess diverse sexual systems, often with different combinations of hermaphroditic, pistillate and staminate flowers. Despite this sexual diversity, most populations are either monomorphic or dimorphic with respect to gender strategy, where gender refers to the relative contribution that individuals make to fitness through female and m...
Contexts in source publication
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... contrast to vegetative uniformity, the flowers of Wurmbea species exhibit a wide range of morphological diversity (Fig. 1). They are sessile, actinomorphic and white, cream, pink or purple in colour. Flower number per inflorescence ranges from 1 to ∼40 and most African species possess larger floral displays than Australian species (Fig. 2). Why this difference occurs is unclear. The pollination of Australian species is by flies, small bees and butterflies ...
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... commonly differ in traits other than gender itself (sexual dimorphism), and these traits are referred to as secondary sex characters (Lloyd and Webb 1977;Sakai and Weller 1999). There is considerable variation among Wurmbea species in the nature and degree of dimorphism in secondary sex characters. Sexual dimorphism is most evident in W. tubulosa (Fig. 1c, d) and W. latifolia, where male plants have an erect, open inflorescence but female plants have contracted inflorescences produced at ground level. Differences in flower size and number between females and males have been particularly well documented in W. dioica ( Fig. 1h; Barrett et al. 1999;Jones and Burd 2001;Ramsey and Vaughton ...
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... sex characters. Sexual dimorphism is most evident in W. tubulosa (Fig. 1c, d) and W. latifolia, where male plants have an erect, open inflorescence but female plants have contracted inflorescences produced at ground level. Differences in flower size and number between females and males have been particularly well documented in W. dioica ( Fig. 1h; Barrett et al. 1999;Jones and Burd 2001;Ramsey and Vaughton 2001), where geographical variation in the degree of dimorphism is evident (Barrett 1992). By using pollinator observations and experimental arrays of W. dioica, Vaughton and Ramsey (1998) investigated the consequences of sexual dimorphism for pollination and mating. They ...
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... the polarity of character evolution is critical for distinguishing between these hypotheses. Significantly, nearly half of all African species have larger inflorescences than Australian species (Figs 1 and 2). It is possible that these species have floral mechanisms not present in Australian species (e.g. ...
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... morphology and its effect on pollen capture would also be worth investigating in Wurmbea because of its potential to influence pollinator shifts and the evolution of sexual systems (Case and Barrett 2004a). Flowers of Australian Wurmbea have two distinct types of styles- straight styles with capitate stigmas (e.g. Fig. 1g) and outwardly recurved styles with elongate stigmas (e.g. Fig. 1i). All but two of the gender dimorphic species have recurved styles; most of the monomorphic Australian taxa have straight styles, and no African species bears recurved styles. Style recurvature facilitates selfing by bringing stigmas and anthers of hermaphroditic ...
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... capture would also be worth investigating in Wurmbea because of its potential to influence pollinator shifts and the evolution of sexual systems (Case and Barrett 2004a). Flowers of Australian Wurmbea have two distinct types of styles- straight styles with capitate stigmas (e.g. Fig. 1g) and outwardly recurved styles with elongate stigmas (e.g. Fig. 1i). All but two of the gender dimorphic species have recurved styles; most of the monomorphic Australian taxa have straight styles, and no African species bears recurved styles. Style recurvature facilitates selfing by bringing stigmas and anthers of hermaphroditic flowers closer together. It also brings stigmas closer to the tepal-borne ...
Citations
... This trade-off between flower size and flower number is thought to be the result of a genetic constraint, with plants making either many small flowers or few large flowers (Herlihy and Delph, 2009;Vasconcelos and Proença, 2015). Moreover, sexual dimorphism is expected to be greater in more arid environments (Barrett and Case, 2006;Herlihy and Delph, 2009), and our finding that a greater number of traits are more sexually dimorphic in plants from Spain relative to plants from Croatia supports this premise. In our study, plants from a region known to experience long periods of high temperatures and drought produced fewer large flowers, and differences in flower number were greater between males than females. ...
Background: Plants in hot and dry climates often flower earlier, make thicker leaves, and produce fewer flowers than conspecifics from relatively wet, cool climates. Silene latifolia, a dioecious, short-lived, flowering perennial, grows in both of these climates in Europe. Question: Is variation in traits seen among populations with divergent climates a result of genetic changes in response to local environmental conditions, differences in the degree of sexual dimorphism, or phenotypic plasticity? Hypothesis: Traits will differ between populations in a common garden as a result of genetic divergence, and exhibit a pattern of variation that is congruent with adaptation to climate. Methods: Morphological and phenological measurements were taken during two flowering seasons on plants growing in Croatia (relatively wet and cool) and Spain (hot and dry). Seeds from both regions were grown to flowering in the greenhouse and several traits were measured. Results: Significant divergence in traits existed between Croatia and Spain that persisted in the common garden (greenhouse), indicating that populations in these two regions likely represent different ecotypes. Plants from Spain flowered earlier in the field, made thicker leaves, and produced fewer flowers than plants from Croatia. Plants from Spain also showed greater sexual dimorphism than those from Croatia.
... Autonomous self-pollination in hermaphroditic species ensures seed production in unpredictable pollination environments (Baker 1955;Eckert et al. 2006) and may alleviate pollen limitation (Larson & Barrett 2000). Under mate limitation, three selfing modes can theoretically provide reproductive assurance if they contribute to ensuring seed production (Goodwillie et al. 2005): (i) autonomous selfing, (ii) pollinator-mediated selfing occurring among flowers within an individual plantgeitonogamy (Harder & Barrett 1996;Eckert 2000;Karron et al. 2004), and (iii) pollinator-mediated selfing occurring within a flowerfacilitated selfing (Goodwillie et al. 2005;Barrett & Case 2006;Vaughton & Ramsey 2010). When pollinator visits are abundant, facilitated selfing may play a key role in reducing mate limitation, particularly in buzz-pollinated species (Buchmann 1983;Larson & Barrett 1999). ...
Plant mating systems are driven by several pre-pollination factors, including pollinator availability, mate availability and reproductive traits. We investigated the relative contributions of these factors to pollination and to realized outcrossing rates in the patchily distributed mass-flowering shrub Rhododendron ferrugineum. We jointly monitored pollen limitation (comparing seed set from intact and pollen-supplemented flowers), reproductive traits (herkogamy, flower size and autofertility) and mating patterns (progeny array analysis) in 28 natural patches varying in the level of pollinator availability (flower visitation rates) and of mate availability (patch floral display estimated as the total number of inflorescences per patch). Our results showed that patch floral display was the strongest determinant of pollination and of the realized outcrossing rates in this mass-flowering species. We found an increase in pollen limitation and in outcrossing rates with increasing patch floral display. Reproductive traits were not significantly related to patch floral display, while autofertility was negatively correlated to outcrossing rates. These findings suggest that mate limitation, arising from high flower visitation rates in small plant patches, resulted in low pollen limitation and high selfing rates, while pollinator limitation, arising from low flower visitation rates in large plant patches, resulted in higher pollen limitation and outcrossing rates. Pollinator-mediated selfing and geitonogamy likely alleviates pollen limitation in the case of reduced mate availability, while reduced pollinator availability (intraspecific competition for pollinator services) may result in the maintenance of high outcrossing rates despite reduced seed production.
... Species can be dioecious or gynodioecious and are insectpollinated (Barrett and Case 2006; Case et al. 2008). In the polyploid W. dioica, which is gynodioecious, individuals with bisexual flowers suffer high levels of selfing (Vaughton and Ramsey 2003). ...
Abstract—
The lily family Colchicaceae consists of geophytic herbs distributed on all continents except the Neotropics. It is particularly diverse in southern Africa, where 80 of the 270 species occur. Colchicaceae exhibit a wide range of ploidy levels, from 2n
= 14 to 2n = 216. To understand where and how this cytogenetic diversity arose, we generated multilocus phylogenies of the Colchicaceae and the Colchicum clade that respectively included 85 or 137 species plus relevant outgroups. To infer the kinds of events that could explain
the observed numbers in the living species (dysploidy, polyploidization, or demi-duplication, i.e. fusion of gametes of different ploidy), we compared a series of likelihood models on phylograms, penalized likelihood ultrametric trees, and relaxed clock chronograms that contained the 58 or
112 species with published chromosome counts. While such models involve simplification and cannot address the processes behind chromosomal rearrangements, they can help frame questions about the direction of change in chromosome numbers in well-sampled groups. The results suggest that dysploidy
played a large role in the Colchicaceae, with the exception of Colchicum itself for which we inferred frequent demi-duplication. While it is known that triploids facilitate the fixation of tetraploidy and that plant species often include individuals of odd ploidy level (triploids, pentaploids),
we hesitate to accept the phylogenetically inferred scenario without molecular-cytogenetic work and data from experimental hybridizations.
... The sexual systems of both groups, with pistillate, staminate and hermaphroditic plants, can be characterized as a transition from dioecious to gynodioecious systems (Barrett and Case 2006). While " pistillate " plants were completely unisexual, the fruit production by " staminate " plants, and the individual with hermaphroditic and homostylous flowers, may represent a reversal in the sterility of the gynoecium, and a transition from unisexual condition to hermaphroditism. ...
In this study we explore morphological and ecological variation in sympatric populations of Pagamea coriacea s.l. - a species complex from white-sand vegetation in the Amazon. A total of 147 trees were sampled and monitored at three nearby sites in Central Amazon, Brazil. Multivariate analyses of morphology indicated two distinct groups (A and B), which also differed in bark type, each containing subgroups associated with sexual dimorphism. However, a single hermaphroditic individual was observed within group B. As expected, all pistillate plants produced fruits, but 23% of the staminate plants of group B, and 5% of group A also produced fruits. This variation suggests that the sexual systems of both groups are between dioecy and gynodioecy. There was an overlap in flowering phases between the two groups, but the pattern of floral maturation differed. Ecologically, plants of group B were found in more shaded habitats and over sandstone bedrocks, while group A was prevalent in deeper sandy soils as canopy plants. The significances of morphological and environmental differences were tested by a multivariate analysis of variance, and a canonical discriminant analysis assessed the importance of variables. The coexistence in sympatry of two discrete morphological groups in the P. coriacea s.l., with different habitat preferences and reproductive behaviors, indicates they represent distinct species.
... This could affect sexual system evolution, such that dioecy is most likely to evolve in low resource environments, while gynodioecy and sub-dioecy are maintained in environments that are less severe (Case and Ashman, 2007). Australian Wurmbea species are diminutive, insectpollinated geophytes that vary in sexual system from cosexual through gynodioecy and sub-dioecy to dioecy (reviewed by Barrett and Case, 2006). Sexual system variation within and between closely related W. biglandulosa (cosexual and gynodioecious populations) and W. dioica (sub-dioecious and putatively dioecious populations) provides unique opportunities to study the evolution of separate sexes. ...
Sexually dimorphic populations are often located in drier habitats than cosexual populations. Gender plasticity (GP), whereby hermaphrodites alter female and male functions depending on resources, and sex-differential plasticity (SDP) between hermaphrodites and unisexuals are predicted to affect sexual system stability. Here, GP and SDP are evaluated in cosexual and gynodioecious Wurmbea biglandulosa and sub-dioecious and dioecious W. dioica.
GP was evaluated under two resource conditions, compared among sexual systems and assessed as to whether (1) males produced perfect flowers and (2) hermaphrodites altered investment in perfect (female function) and total (male function) flowers. SDP was assessed within sexual systems as differences between sex functions of hermaphrodites vs. unisexuals. Males and hermaphrodites were compared to assess whether size thresholds for female function differed among sexual systems. Plasticity costs were evaluated using correlations between female function and male traits in hermaphrodites, and in W. dioica by comparing hermaphrodite and male regressions between plant size and pollen production.
In dioecious W. dioica no males exhibited GP, whereas 100 % did in gynodioecious and cosexual W. biglandulosa. In sub-dioecious W. dioica, resources affected GP (high, 66 %; low, 42 %). Hermaphrodites in all sexual systems reduced perfect but not total flowers under low resources. Unisexuals were unaffected, demonstrating SDP for female function only. Thresholds for female function were greater in sub-dioecious W. dioica than in W. biglandulosa. Plasticity costs were detected only in sub-dioecious W. dioica.
SDP for female function could assist female establishment in cosexual populations and maintain females in gynodioecious and sub-dioecious populations. Although the absence of male SDP should stabilize sub-dioecy, plasticity costs would render sub-dioecy unstable, favouring canalized males over hermaphrodites. This study highlights the importance of interactions between environmental conditions and hermaphrodite sex expression for the stability of dimorphic sexual systems.
... The new species described here was first collected during unrelated fieldwork by R.J. Chinnock in 1986 and lodged in the South Australian Herbarium (AD), where it was identified as Wurmbea deserticola T.Macfarlane by R.J. Bates in 1994. In 1996 A.L. Case with colleague Bill Cole independently found it at a second location while engaged in field work for a study of sexual systems in Wurmbea (Barrett & Case 2006, Case et al. 2008, immediately recognised it as a new species, and soon after saw the Chinnock specimen at AD. Subsequent field work by T.D. Macfarlane, A.P. Brown and C.J. French has improved our understanding of the species but has not revealed any more populations other than one casually recorded photographically by A.P. Brown and J. Brown in 2006. Plants tall, 15-55 cm tall. ...
Macfarlane, T.D. & Case, A.L. Wurmbea fuviatilis (Colchicaceae), a new riverine species from the Gascoyne region of Western Australia. Nuytsia 21(1): 25-30 (2011). A new species of Wurmbea, W. fuviatilis T.Macfarlane & A.Case, is described and illustrated with photographs and a distribution map. The new species is known from only three populations from the Gascoyne River catchment in the region of Mount Augustus, growing on river banks and beside riverside pools. It is a relatively tall, attractive species with bi-coloured fowers.
... Thus, our results are in agreement with the previous studies (Cameron et al., 2002;Rivadavia et al., 2003) and suggest that the cp DNA in A. vesiculosa has different origins than the nuclear genes. Similar inconsistencies between gene trees based on nuclear and cytoplasmic markers have been explained by chloroplast capture ( Tsitrone et al., 2003), and this phenomenon has been documented in several plant species (Gaskin and Wilson, 2007;Barrett and Case, 2006). ...
Organellar DNA from the widely distributed but rare and critically endangered aquatic carnivorous plant Aldrovanda vesiculosa (Droseraceae) was examined. Six chloroplast intergenic regions (3700 nt in total) were sequenced before analyzing the Southern-RFLP (Restriction Fragment Length Polymorphism) of 2 mt gene flanking regions. Only two different chloroplast haplotypes among 15 A. vesiculosa accessions from Africa, Australia, Europe, and Japan were found, generally distinguishing European and non-European plants, with two exceptions. Genetic variation observed in A. vesiculosa appears to be even lower than in other aquatic species with a similar world-wide distribution. A recent bottleneck followed by long-distance dispersal by water birds or low mutation rates could be responsible for the observed genetic uniformity. Estimation of genetic distances based on six chloroplast intergenic regions led to the conclusion that the chloroplast genome of A. vesiculosa matches more closely to that of Drosera regia than Dionaea muscipula, a sister genus sharing snapping traps. The inconsistency between genetic distance estimates based on nuclear and cytoplasmic markers may reflect a chloroplast capture. In A. vesiculosa, a four amino acids substitution (TGWS) in the amino acid sequence of ATP synthase alpha subunit (ATP1), highly conserved mitochondrial protein, was discovered, unique among all organisms based on current knowledge.
... Such variation complicates inferences on ancestral nodes and the determination of the statistical confidence of character state transitions. A particularly thorny issue came to light from sampling multiple populations of W. dioica and W. biglandulosa, two species that have been the main focus of micro-evolutionary work on the ecological mechanisms driving the evolution of dioecy in Wurmbea (reviewed in Barrett & Case 2006). The interest in these species arises because of their widespread distributions and the fact that they are both polymorphic for sexual-system variation with both hermaphroditic and gender dimorphic populations. ...
Flowering plants display spectacular floral diversity and a bewildering array of reproductive adaptations that promote mating, particularly outbreeding. A striking feature of this diversity is that related species often differ in pollination and mating systems, and intraspecific variation in sexual traits is not unusual, especially among herbaceous plants. This variation provides opportunities for evolutionary biologists to link micro-evolutionary processes to the macro-evolutionary patterns that are evident within lineages. Here, I provide some personal reflections on recent progress in our understanding of the ecology and evolution of plant reproductive diversity. I begin with a brief historical sketch of the major developments in this field and then focus on three of the most significant evolutionary transitions in the reproductive biology of flowering plants: the pathway from outcrossing to predominant self-fertilization, the origin of separate sexes (females and males) from hermaphroditism and the shift from animal pollination to wind pollination. For each evolutionary transition, I consider what we have discovered and some of the problems that still remain unsolved. I conclude by discussing how new approaches might influence future research in plant reproductive biology.
... The polymorphism poses the intriguing question as to the conditions under which male-sterile individuals , which have lost one of their sexual functions, can be maintained with hermaphrodites that possess both. A great deal of theoretical analyses has been performed in addressing this question (e.g., Charlesworth and Ganders 1979; Kohn 1988; Frank 1989; Gouyon et al. 1991; Couvet et al. 1998; Bailey et al. 2003), and the predictions made by these studies have been tested in a wide range of species (e.g., Kohn 1988; Thompson and Tarayre 2000; Barrett 2002; Ramsey and Vaughton 2002; Asikainen and Mutikainen 2003; Ashman et al. 2004; Barrett and Case 2006). ...
Gynodioecy, where females co-occur with hermaphrodites, is a relatively common sexual system in plants that is often the result of a genetic conflict between maternally inherited male sterility genes in the mitochondrial genome and the biparentally inherited male fertility restorer genes in the nucleus. Previous models have shown that nuclear-cytoplasmic gynodioecy can be maintained under certain conditions by negative frequency-dependent selection, but the effect of other evolutionary processes such as genetic drift and population subdivision is only partially understood. Here, we investigate the joint effects of frequency-dependent selection, drift, and migration through either pollen or seeds on the maintenance of nuclear-cytoplasmic gynodioecy in a subdivided population. We find that the combination of drift and selection causes the loss of gynodioecy under scenarios that would maintain it under the influence of selection alone, and that both seed and, more surprisingly, pollen flow can maintain the polymorphism. In particular, although pollen flow could not avoid the loss of cytoplasmic polymorphism within demes, it allowed the maintenance of nuclear-cytoplasmic polymorphism at the metapopulation level.
... Studier av de selektive mekanismene som styrer evolusjon av seksualsystemer følger også i Darwins spor, med fokus på hvilke faktorer som påvirker optimal allokering av ressurser til hannlig og hunnlig funksjon, og på hvordan endringer i grad av kryssbefruktning påvirker innavlsdepresjon. Dette er i dag et saerdeles aktivt forskningsfelt (se for eksempel Barrett & Case 2006). ...
In this year celebrating the bicentenary of Darwin's birth, and the sesquicentennial of the publication of 'On the Origin of Species', our paper aims to review Darwin's history as a plant scientist, and his contribution to current research in plant evolutionary ecology. We start out with a biographical sketch, and continue with an overview of his published books on plants, emphasizing how he used plants as model systems for demonstrating evolution by natural selection. Several of his books have stimulated an extraordinary amount of original research since their publication, and Darwin introduced a multitude of concepts that still constitute core research issues in evolutionary ecology.
