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1.
A valuable approach to understanding the evolution of gender dimorphism involves studies of single species that exhibit intraspecific
variation in sexual systems. Here we survey sex ratios in 35 populations of Wurmbea biglandulosa, previously described as hermaphroditic. We found pronounced intraspecific variation in sexual systems; populations in the
northeastern part of the species' range were hermaphroditic, whereas other populations were gynodioecious and contained 2–44%
females. Populations with lower annual rainfall were more likely to be gynodioecious, supporting the view that gender dimorphism
evolves more frequently in harsher environments. In gynodioecious populations, however, female frequency was not related to
either annual rainfall or habitat, indicating that other factors are important in determining sex ratio variation. Females
had smaller flowers and shorter stems than did hermaphrodites, potentially providing a basis for resource compensation. A
female fecundity advantage may contribute to the maintenance of females in populations because females produced more ovuliferous
flowers and had more ovules per flower than did hermaphrodites.
Received March 2, 2001 Accepted February 25, 2002 相似文献
2.
Ramsey M Vaughton G Peakall R 《Evolution; international journal of organic evolution》2006,60(3):529-537
How females establish in populations of cosexuals is central to understanding the evolution of gender dimorphism in angiosperms. Inbreeding avoidance hypotheses propose that females can establish and be maintained if cosexual fitness is reduced because they self-fertilize, and their progeny express inbreeding depression. Here we assess the role of inbreeding avoidance in maintaining sexual system variation in Wurmbea biglandulosa. We estimated costs of self-pollination, mating patterns, and inbreeding depression in gender monomorphic (cosexuals only) and dimorphic (males and females) populations. Costs of selfing, estimated from seed set of experimentally self- and cross-pollinated flowers, were severe in both males and cosexuals (inbreeding depression, sigma = 0.86). In a field experiment, intact males that could self produced fewer seeds than both emasculated males and females, whereas seed set of intact and emasculated cosexuals did not differ. Thus, pollinator-mediated selfing reduces fitness of males but not cosexuals under natural conditions. Outcrossing rates of males revealed substantial selfing (t = 0.68), whereas females and cosexuals were outcrossed (0.92 and 0.97). For males, progeny inbreeding coefficients exceeded parental coefficients (0.220 vs. 0.009), whereas for females and cosexuals these coefficients did not differ and approached zero. Differences in coefficients between males and their progeny indicate that selfed progeny express severe inbreeding depression (sigma = 0.93). Combined with inbreeding depression for seed set, cumulative sigma = 0.99, indicating that most or all selfed zygotes fail to reach reproductive maturity. We propose that present sexual system variation in W. biglandulosa is maintained by high inbreeding depression coupled with differences in selfing rates among monomorphic and dimorphic populations. 相似文献
3.
4.
J. Caujapé-Castells R. K. Jansen J. Pedrola-Monfort N. Membrives 《Plant Systematics and Evolution》2002,232(1-2):73-88
We examined patterns of cpDNA RFLP variability using 21 restriction endonucleases in 21 populations of Androcymbium that represent 12 endemic species distributed in the winter rainfall areas of South Africa to explore the diversification
of the genus in its area of maximum species diversity. Our results are supportive of a diversification landscape characterized
by continued opportunistic short-range invasion, naturalization, and rapid speciation, in which the selective action of the
different environments where Androcymbium species occur determined their colonization success and subsequent short-range geographic expansion. The historical presence
of fire, the constraint imposed by the low concentration of nutrients throughout southwestern South Africa and the different
reproductive capabilities of Androcymbium species have also likely stimulated species' diversification. Our divergence time estimates bolster the view that speciation
of South African Androcymbium initiated in the late Eocene, intensified in the Oligocene and proceeded more sporadically during the Miocene. These chronological
estimates also substantiate the previous hypothesis that most lineages of Androcymbium in South Africa are much more ancient than their North African relatives, whose diversification began in the late Miocene-early
Pliocene.
Received July 25, 2001 Accepted December 6, 2001 相似文献
5.
Within population variation in plant density can affect reproductive success and breeding systems. We examined such effects
in Listera cordata R. Br., a north temperate terrestrial orchid, in a subalpine population in Colorado, USA. Hand pollinations showed that L. cordata was self-compatible as all pollinations produced fruits. Cross-pollinations differed significantly from self-pollinations,
and had a higher number of seeds per capsule and higher % of fertilized ovules. Together they could compensate for the transmission
advantage of self-pollinations. Average number of flowers per inflorescence was 4.2–4.4 and average fruit set was 20.7–23.7%.
By establishing 36 plots with varying plant densities (1, 4, 8 and 16) and emasculating all flowers in target plants of a
set of 20 plots, we estimated density effects on fruit and seed production. Plant density had no effect on the amount of reproduction
except in reduced seed production of highly dispersed plants. Our results suggest that inbreeding depression may be an important
selective factor in L. cordata. Further studies are needed to define its role in the evolution of mating systems in this species.
Received February 21, 2000 Accepted December 26, 2000 相似文献
6.
7.
Little is known about genetic variation in members of the genus Aesculus (Hippocastanaceae), in particular A. flava (yellow buckeye) and A. glabra (Ohio buckeye). Here, three synthetic DNA probes (composed of tandemly repeated, core sequences) that reveal alleles at multiple
variable-number tandem-repeat (VNTR) loci in these two species were used to investigate: 1) levels of genetic variation in
one stand of A. flava and three isolated stands of A. glabra; 2) whether the stands of A. glabra are genetically differentiated from one another; 3) whether there has been selection for more heterozygous individuals through
time in one stand each of A. flava and A. glabra; and 4) whether a possible genetic bottleneck had occurred during the formation of either species of Aesculus.
First, variation of VNTR genetic markers within and among three populations of A. glabra separated by 60–180 km was examined. In each one hectare (ha) population, 22 individuals were randomly sampled. Among the
three populations, the mean number of bands scored per individual was 80.35 and the average number of estimated loci surveyed
was 54.17. Mean similarity and estimated heterozygosity within populations ranged from 0.634 to 0.743 and from 0.342 to 0.486,
respectively. The mean similarity across populations was 0.657, while the mean estimated heterozygosity across populations
was 0.484 for A. glabra. The most isolated site was the most genetically differentiated as indicated by differences in levels of similarity, heterozygosity,
and Fst value comparisons.
In a separate experiment, genetic variation in 22 large (reproductively mature; dbh > 8 cm) individuals was compared with
that in 22 small (not yet reproductive; dbh < 1 cm) individuals collected within one ha stands for both A. flava and A. glabra. Mean similarity values among large versus small individuals of A. flava were 0.665 versus 0.662, while for A. glabra the corresponding values were 0.686 versus 0.691, respectively. Permutation tests of these similarity data detected no evidence
for size class genetic differentiation in either species (both p-values > 0.050). Further, permutation tests for the number
of bands per individual (average band number should be higher in more heterozygous individuals) detected no significant differences
between size classes for either species. Thus, evidence of pronounced inbreeding and/or selection altering population genetics
within small relative to large individuals was not detected.
In addition, comparable similarity and heterozygosity values between these two closely related species (which still maintain
an active zone of hybridization) suggests that either: 1) no extreme genetic bottleneck has accompanied the formation of these
species from a common ancestor; or 2) signs of such a bottleneck have largely been eliminated. These studies demonstrate the
utility of multilocus VNTR DNA probes for investigating genetic variation within and among plant populations, between size
classes within a population, and between closely related species.
Received May 15, 1998 Accepted September 11, 2001 相似文献
8.
M. Nepi E. Pacini C. Nencini E. Collavoli G. G. Franchi 《Plant Systematics and Evolution》2003,238(1-4):109-118
We studied nectar characteristics during the long flowering period (late June to end of November) in two populations of Linaria vulgaris (L.) Mill. spontaneously growing in the Botanical Gardens of Siena University (Tuscany, central Italy). The two populations
were close to each other but they differed in blooming period. Plants of population 1 sprouted in May and flowered from the
end of June to the end of September. Population 2 sprouted at the end of August and flowered from September to the end of
November. Differences in nectar production and composition were found between and within populations. Flowers of population
1 produced a very small amount of nectar (not collectable) that remained on the nectary surface. The quantity of nectar increased
in late September, when each flower produced 2–3 μl of nectar that flowed into the spur. Total sugar concentration was 175.8
mg/ml in young flowers. Flowers of population 2 produced 5–8 μl of nectar with a total sugar concentration of 200.9 mg/ml
in the young stage. In bagged senescent flowers nectar volume decreased in both populations and nectar sugar concentration
decreased down to 11.6 mg/ml in population 2 and increased up to 289.6 mg/ml in population 1. For both populations, the decrease
in nectar volume in bagged flowers may have been due to water loss by evaporation. In population 2, the decrease in sugar
concentration may have been due to nectar reabsorption that was never observed in population 1. Nectar variability is discussed
in relation to insect visits and seed set.
Received August 14, 2002; accepted December 17, 2002
Published online: June 2, 2003 相似文献
9.
T. Wendt M. B. F. Canela D. E. Klein R. I. Rios 《Plant Systematics and Evolution》2002,232(3-4):201-212
The reproductive biology of three sympatric species Pitcairnia
flammea, P. corcovadensis and P. albiflos (Bromeliaceae) was studied on Corcovado Mountain in the city of Rio de Janeiro, Brazil. Controlled pollination experiments
were also conducted using plants transplanted to a greenhouse. The three species are self-compatible and interspecifically
cross compatible. Pitcairnia corcovadensis was principally an autonomous self-pollinator, having scarce pollinator activity, anthers and stigmas at the same level,
and absence of nectar. In P. flammea, many flowers opened per day, the stigma and anther were close to each other, and its nectar was regularly consumed by hummingbirds;
all factors that promote geitonogamy in this species. Although fully self-compatible, P. albiflos always opened a few flowers per days showing an adaptation to cross-pollination. Observations during two flowering seasons
showed that despite different times for peak flowering, blooming of these three species overlapped in April. They grow in
mixed clumps that may facilitate promiscuous pollination between them but no intermediate forms were observed under natural
conditions. The absence of temporal isolation, geographic isolation and isolation via post-pollination reproduction suggests
that evolution toward selfing was important to avoid hybridization between these sympatric species.
Received May 10, 2001 Accepted February 25, 2002 相似文献
10.
The flowering of Clutia pulchella was studied in a coastal scarp forest community in southern KwaZulu-Natal, South Africa. Sex dependent differences in the
frequency and magnitude of floral output were recorded, with male individuals producing 4.32 times more flowers per leaf axis
than females. Increased node production, as a manifestation of significantly increased branching, allowed for prolific flower
production in males. Energy investment per flower was marginally greater in females (0.045 J/mg), despite copious pollen production
and glandular secretion in males (0.035 J/mg). Differential flower production, reproductive organ dry mass and an unbalanced
branching ratio revealed that “per plant” expenditure towards flowering was more pronounced in males (♀ flowering × 5.04).
The elevated cost of fruit production (♀ flowering × 5.5), inclusive of imperfect fruit set, resulted in overall reproductive
expense being slightly higher for females. Such sex-dependent reproductive investment was shown to have minimal influence
on the population sex ratio, with sex frequencies and nearest neighbor distances yielding a non-significant male bias of 1.16.
No evidence of spatial asymmetry was found.
Received December 1, 1999 Accepted September 27, 2000 相似文献
11.
The internal transcribed spacers (ITS1 and ITS2) of nuclear ribosomal DNA were amplified and sequenced from 19 samples representing
all species of the genus Mercurialis and two outgroup species, Ricinus communis and Acalypha hispida. The length of ITS1 in the ingroups ranged from 223 to 246 bp and ITS2 from 210 to 218 bp. Sequence divergence between pairs
of species ranged from 1.15% to 25.88% among the ingroup species in the combined data of ITS1 and ITS2. Heuristic phylogenetic
analyses using Fitch parsimony on the combined data of ITS1 and ITS2 with gaps treated as missing generated 45 equally parsimonious
trees. The strict consensus tree was principally concordant with morphological classification. Within the genus, the ITS sequences
recognised two main infrageneric clades: the M. perennis complex including three Eurasian stoloniferous species (M.␣leiocarpa, M. ovata and M. perennis) and the western Mediterranean group including eight both annual and perennial species. Of the western Mediterranean clade,
the annual and perennial species grouped respectively into two different groups, and the annual life form is revealed as a
synapomorphic character derived from perennial, whereas in the Eurasian clade ITS phylogeny suggested M. leiocarpa as basal clade sister to M.␣perennis and M. ovata. ITS phylogeny failed to resolve the relationships among the different cytotypes of M. ovata and M. perennis. ITS phylogeny also suggested rapid karyotypic evolution for the genus. The karyotypic divergence among the perennial species
of western Mediterranean region did not corroborate the nucleotide sequence divergence among the species. Optimisation of
chromosome numbers onto the ITS phylogeny suggested x=8 to be the ancestral basic chromosome number of the genus. ITS phylogeny
confirmed that the androdioecy of M. ambigua is derived from dioecy. The nucleotide heterozygosity and additivity in ITS sequences clearly confirm the interspecific hybridisation
in the genus Mercurialis.
Received December 22, 2001; accepted May 21, 2002?Published online: November 14, 2002
Address of the authors: Martin Kr?henbühl, Yong-Ming Yuan (correspondence) and Philippe Küpfer, Institut de Botanique, Laboratoire
de botanique évolutive, Université de Neuchatel, Emile-Argand 11, CH-2007 Neuchatel, Suisse. (e-mail: yong-ming.yuan@unine.ch) 相似文献
12.
Axial and apical flowers of Cryptantha capituliflora were analyzed with regard to morphology and pollen tube growth to assess the occurrence of cleistogamy. Although intermediate
floral forms do occur, cleistogamous flowers were significantly smaller than chasmogamous flowers, had fewer anthers, and
showed a distinctive stigmatic surface. Chasmogamous flowers can be cross-pollinated. Nevertheless, the growth of self-pollen
tubes in few chasmogamous buds jointly with flower characters suggests that these flowers can probably produce fruits through
autonomous selfing. The mean seed number per fruit did not differ between fruits from chasmogamous and cleistogamous flowers.
Cleistogamous flowers were only observed in axial inflorescences, which are completely covered by the leaf. Other species
of section Cryptantha also show the same trend, with cleistogamous flowers located in the lower half of the stems. This pattern is discussed in
relation to dissimilarities in the outcrossing opportunities between flower types within the plant.
Received May 22, 2002; accepted November 14, 2002 Published online: March 20, 2003 相似文献
13.
M. L. Masierowska 《Plant Systematics and Evolution》2003,238(1-4):97-107
The dynamics and abundance of nectar secretion as well as sugar productivity were studied in flowers of brown mustard (Brassica juncea) cv. Małopolska and white mustard (Sinapis alba) cv. Borowska. Moreover, floral nectaries were examined under LM and SEM. In both cultivars lateral and median pairs of nectaries
secreted nectar. However, differences were found in morphology and activity of these pairs. The lateral nectaries produced
more nectar than the median ones. Nectar secretion started at loose bud and peaked during anther dehiscence. Average amount
of nectarsecreted by 100 flowers of cv. Małopolska and cv. Borowska were 119.9 mg and 134 mg. Mean concentration of nectar
was 26.7% and 23.4%, respectively. One hundred flowers of cv. Małopolska and cv. Borowska secreted 28.4 mg and 24.9 mg of
sugars in nectar. Estimated sugar productivity per 1 ha of crop was 65.5 kg and 71.2 kg, respectively.
Received August 28, 2002; accepted November 2, 2002
Published online: June 2, 2003 相似文献
14.
We studied the reproductive behavior of Colletia spinosissima Gmel. at six sites in two regions of Argentina during the 1998–2000 flowering seasons. Flowering takes place in winter. The
flowers are homogamous, fragrant, and entomophilous. There was evidence of self-incompatibility and cross-incompatibility
between nearby partners. Fruit set of open-pollinated flowers (13.3%) seemed pollen-limited, since low fecundity was consistently
associated with small stigmatic pollen loads and with low numbers of successful pollen tubes, and fecundity increased with
abundance of efficient pollinators. Reproductive success (percent ovules becoming viable seeds) was 3.6. It is hypothesized
that homogamy was established in Colletia because in an impoverished pollination environment – such as the one likely prevailing when this lineage evolved – achieving
pollen export and receipt in a single pollinator visit has selective advantages. A large stigma and an extragynoecial compitum
would compensate for the homogamy-driven, increased pollen-stigma interference.
Received March 8, 2001 Accepted July 19, 2001 相似文献
15.
Lens includes L.
culinaris subsp. culinaris (the cultivated lentil) and several wild species distributed from the Mediterranean region to western Asia. We compared sequence
variation in the ITS region among species of Lens in an effort to end persisting uncertainty regarding the phylogeny of the genus. The parsimony analysis revealed a single
minimum-length tree with a topology congruent with patterns derived by previous studies of nuclear and chloroplast DNA RFLPs.
The basal and highly divergent status of the L. nigricans clade is depicted, and the progenitor-derivative relationship between L. culinaris subsp. orientalis and L. culinaris subsp. culinaris is reaffirmed. Resolution in the tree was improved by combining the ITS data set with a pre-existing set of chloroplast DNA
restriction site data obtained from the same group of samples.
Received May 8, 2000 Accepted October 26, 2001 相似文献
16.
Flower development, pollination and breeding system of the high alpine cushion plant, Eritrichium nanum (Boraginaceae), were investigated in nine populations from the European Alps at altitudes of 2700 m–3200 m. Peak flowering
period lasts longer than a month, from mid-June to the end of July. In contrast to statements in the literature that flowers
are protogynous and nutlets remain in their calyx until spring we found a distinct protandry and nutlets being dispersed before
mid-September. Various insects from 12 families, but mostly Diptera, frequently visited E. nanum flowers, with flies from the families Anthomyiidae and Muscidae being the predominant visitors. Under optimal conditions
(max. solar radiation, min. wind force), visitation rates of 200 simultaneously observed flowers reached 32.5–46.7 insects
per hour, i.e. 0.16–0.24 insects per flower per hour. However, the commonly observed Anthomyiidae and Muscidae clearly preferred
the white-yellowish flowers of Saxifraga exarata and Saxifraga bryoides which are abundant at E. nanum sites and which are certainly also pollinated by species of these two fly families. The flowers of these Saxifraga species offer plenty of nectar and may compete for pollinators with E. nanum, when they are flowering in its proximity. However, various other insects like Pontia callidice and Psodos sp. (Lepidoptera) as well as Andrena sp. (Hymenoptera) and especially Eristalis tenax and closely related hoverflies showed a higher degree of flower constancy to E. nanum, often flying from a blue Eritrichium cushion to the next and hence causing outcrossing. The five fornices of E. nanum flowers which obstruct the tube containing stamens and nectar, are a feature which differs distinctly from the syndrome of
fly-pollinated flowers with easily accessible nectar. Consequently pollination by flies in E. nanum seems to be caused mainly by the unfavorable ecological conditions at high altitudes, where flies are the most frequent insects.
Bagging experiments showed that outcrossing and geitonogamy are the prevailing pollination modes, and autogamy, although possible,
plays only a minor role.
Received February 13, 2001 Accepted November 23, 2001 相似文献
17.
Morphological and electrophoretic data were studied to examine species delimitation, patterns of morphological and genetic
variation in three Korean Hepatica including two endemics, H.␣maxima and H. insularis. Based on a phenogram using 15 morphological characters, taxa were distinct; it was consistent with the phenogram based on
genetic distance. In the enzyme electrophoresis study, the genetic identities suggested that three taxa were genetically divergent
enough to be recognized as different species, falling within the range expected␣for congeners. The genetic identity between
H.␣asiatica and H. insularis was higher than the values between these two taxa and H.␣maxima, a restricted endemic of Ulleung Island. The least genetic variation was found in H. maxima and the greatest in widespread H. asiatica. These data are consistent with theoretical expectations that small populations are more likely to be genetically depauperate.
Received November 13, 2001; accepted May 10, 2002 Published online: December 11, 2002 相似文献
18.
In the intermediate zone of the inflorescence of genera of Aroideae one can find flowers with male and female characteristics.
Until now, two types of developmental sequences of atypical bisexual flowers (ABFs) have been recognized: the Philodendron type and the Cercestis type. In the Philodendron type, bisexual flowers generally consist of functional carpels and staminodes inserted on the same whorl. In the Cercestis type, the gynoecium and stamens are inserted on two different whorls. These different ontogenetic patterns represent two
different pathways in the evolution of unisexual flowers in this subfamily. A molecular phylogenetic analysis of 33 genera
of Araceae, based on the chloroplast trnL intron and trnL–F intergenic spacer sequences was carried out. We use this phylogenetic analysis and those published by French et al. (1995)
and Mayo et al. (1997) to examine the distribution of the two types of ABFs in selected genera. Our results suggest that the
two developmental patterns of ABFs in Aroideae sensu Mayo et al. (1997) do not correspond to two separate evolutionary lineages
but rather are more or less consistent within clades. Although this new molecular phylogeny does not include all aroid genera,
it corroborates in general, at the subfamily level, the molecular analysis of French et al. (1995) based on chloroplast DNA
restriction site data and the analysis of Mayo et al. (1997) based on morphological and anatomical data.
Received March 15, 2001 Accepted October 11, 2001 相似文献
19.
A. R. Hagen T. Sæther L. Borgen R. Elven O. E. Stabbetorp C. Brochmann 《Plant Systematics and Evolution》2002,230(3-4):203-219
The high polyploids Cerastium alpinum (8x) and C. nigrescens (12x) were investigated in a mixed population in central Norway to evaluate whether hybridisation has resulted in continuous variation
in morphology and genetic markers, a hypothesis previously proposed to account for the extensive taxonomic confusion in this
species group. Isozyme, fertility, and morphological (37 characters) variation were examined among 347, 265, and 237 plants,
respectively. A PCO analysis based on 23 quantitative morphological characters identified two main groups, corresponding to
C. alpinum and C. nigrescens. The groups were also clearly separated in isozyme markers, several qualitative morphological characters, and chromosome numbers.
Only 20 plants (8.4%) were more or less intermediate in the PCO analysis. These plants had a parental or hybrid isozyme multilocus
phenotype and typically few well-developed anthers, low pollen stainability, and no seed set. Several plants within the C. nigrescens group also had reduced pollen stainability. These results indicate that later-generation hybrids and/or backcrosses towards
C. nigrescens are formed. Thus, interspecific, interploidal gene flow probably occurs, but at rates that are insufficient to break down species integrity.
Received July 5, 2000 Accepted August 2, 2001 相似文献
20.
Immunochemical investigation of the seed storage proteins of some large genera in the tribe Peucedaneae (Umbelliferae) has
clearly demonstrated the heterogeneity of Angelica and Peucedanum and the comparative homogeneity of Ferula. Among the taxa included in Angelica, Ostericum appears to be the most distant from the type species A. sylvestris, and should be treated as an independent genus. On the contrary, Archangelica is serologically similar to Angelica s. str. A rather complicated picture has been revealed within Peucedanum s. l. Serotaxonomical studies show a relationship pattern largely corresponding to the infrageneric classification of Thellung
(1926). The splitting of satellite genera from Peucedanum s. l. is only partially supported.
Received June 25, 2002; accepted October 3, 2002 相似文献