摘要:

AbstractMating systems of 18 species of homosporous ferns follow a bimodal distribution, similar to that observed for seed plants (Schemske and Lande, 1985). Most species are highly outcrossing, a few are inbreeding, and two species examined to date have mixed mating systems.Equisetum arvenseand several species of lycopods are also highly outcrossing. Several mechanisms, including inbreeding depression, antheridiogen, and ontogenetic sequences that result in effectively unisexual gametophytes, promote outcrossing in homosporous ferns and perhaps other homosporous pteridophytes as well. In some species of homosporous ferns, selection has favored the evolution of inbreeding as an adaptation for colonization. High levels of intra‐ and interpopulational gene flow via spore dispersal, coupled with high levels of intergametophytic crossing, generally lead to genetically homogeneous populations and species of homosporous ferns. However, rock‐dwelling ferns and ferns from xeric habitats may exhibit significant population genetic structure due to physically patchy habitats. Reticulate evolution in homosporous ferns may be enhanced by high levels of intergametophytic cross

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00187.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractPrevious studies on the sequence of the gametangium formation in homosporous fern gametophytes (Masuyama, 1975a, b) suggested that diploid and polyploid taxa may favor gametophytic crossing and gametophytic selfing, respectively. In this view, intraspecific polyploids of three fern species (Phegopteris decursive‐pinnata, Lepisorus thunbergianusandPteris dispar) have been investigated for the amount of genetic load or the rate of gametophytic selfing. As expected, a marked contrast of mating systems is found between diploids and tetraploids; the former predominantly undergo gametophytic crossing and the latter predominantly undergo gametophytic selfing. It seems likely that diploid homosporous pteridophytes favor gametophytic crossing with some exceptions favoring gametophytic selfing as a derived condition, whereas polyploid homosporous pteridophytes favor gametophytic selfing predominantl

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00188.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractFirst, evolutionary theories of selfing of terrestrial plants are reviewed briefly. The evolution of the selfing rate is controlled mainly by (1) the benefit of enhanced genetic relatedness to seeds and (2) the cost of lowered fitness of selfed offspring (inbreeding depression), being modified by (3) fertility assurance under pollen limitation, (4) reduced performance as pollen donor, (5) reduced expenditure to male function, and (6) lowered genetic recombination. Models of the joint evolution of selfing and inbreeding depression predict either strong outcrossing or predominant selfing. Although wind‐pollinated plants fit the prediction, some animal‐pollinated species have intermediate selfing rates, refuting the theory.Second, three resource allocation models are analyzed, in which an individual plant optimally allocates limited resources to outcrossed seeds, selfed seeds, and to energy reserves for the next year. The first model explains how the number of outcrossed and selfed offspring change with plant size when they differ in dispersal distance. The second model predicts that, in a disturbed habitat, the plant is likely to be annual and to produce both selfed and outcrossed seeds; in contrast, in a stable habitat, the plant tends to be perennial and to abort selfed seeds selectively. Hand pollination may increase seed production for perennials but not for annuals. The third model explains the observed difference between animal and wind pollinated plants in the out‐crossing rate pattern by the difference in the way pollen acquisition increases with inves

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00189.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractVariation in mating system in the common wild riceOryza rufipogonwas studied in relation to life‐history traits to examine its effect on the genetic structure of natural populations. Results of general survey in Asian populations and of a detailed population study carried out in Thailand are presented. Estimated outcrossing rates of Asian wild rices ranged from 5 to 60%, though cultivated rices are predominantly selfing. Interpopulational comparison showed mating system is associated with life‐history traits, resulting in the differentiation into two ecotypes; predominantly selfing annuals having high reproductive effort and mixed‐mating perennials having low reproductive effort. Resource allocation to pollen production vs. seed production (pollination effort) proved to be correlated with outcrossing rate. Isozyme study showed that both mating system and reproductive system jointly influence genetic structure of populations such as the level of intrapopulational variability and the extent of interpopulational differentiation. Evolution of selfing in this plant group might have been promoted by selection for seed propagation which was brought by environmental change and/or habitat distur

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00190.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractA survey of 32 populations of the self‐compatible, tristylous, aquatic,Eichhornia paniculata(Pontederiaceae), from N. E. Brazil and Jamaica, was undertaken to examine the role of demographic and reproductive factors on variation in outcrossing rate (t), and to investigate the association betweentand population genetic structure. Multi‐locus outcrossing rates, estimated using isozyme techniques, varied widely (t̂= 0.002–0.960) among populations and were uniformly distributed across the entire range oft. Sixty percent of variation int̂was explained by style morph diversity (E) and the frequency of selfing variants within populations (M). Population size (N) and plant density (d) also accounted for a significant portion of variation int̂, particularly in Jamaica, where variation in style morph diversity was low.Outcrossing rates were significantly correlated with the proportion of loci that were polymorphic (P), the average number of alleles per polymorphic loci (Na), the average observed heterozygosity, (Ho), and the inbreeding coefficient (f̂). A strong regional effect was evident in the association off̂withPandNa. This largely results from the confounding effect of genetic bottleneck(s) and high levels of self‐fertilization associated with the colonization of Jamaica. Comparisons off̂with the equilibrium inbreeding coefficient, (Feq), indicated that outcrossing populations had a significant deficiency of heterozygotes, while selfing populations had an excess. This demonstrates that levels of heterozygosity cannot be accounted for by the mating system alone. Outcrossing rate variation inE. paniculatais controlled by a complex interplay of local demographic and genetic factors. These influences operate within contrasting regional contexts as a result of the different evolutionary histories of populations in N. E. Brazi

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00191.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractIsland populations ofCampanula microdontaand mainland Honshu populations ofC. punctatahave several different mating systems: self‐incompatible (SI) and therefore obligately outcrossing in mainland Honshu and Oshima Island; self‐compatible (SC) and largely outcrossing in the northern islands of Toshima and Niijima; and SC and predominantly inbreeding southern ones of Miyake and Hachijo. Several features possibly associated with the mating systems are described. A hypothesis is proposed that the mean and variance of pollinator availability together with inbreeding depression could explain the observed patterns of mating system as the results of evolut

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00192.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractSpecies ofTrilliumhave a disjunct distribution occurring in both North America and eastern Asia. In North America all 36 species are diploid. The 11 species of eastern Asia, however, include only a single diploid with all the other species being polyploids. Why do different patterns of speciation develop in North America and in eastern Asia? The breeding systems of populations in the North AmericanT. erectum, T. grandiflorumandT. ovatum, and in AsianT. kamtschaticumwere investigated by estimating the inbreeding coefficient from cold‐induced banding patterns which reveal homozygotes and heterozygotes. From the analyses of the inbreeding coefficients,T. erectum, T. grandiflorumand the Pacific coastal species,T. ovatumare predominantly inbreeding species.T. ovatumpopulations from the Rocky Mountain region are outbreeders. However the Japanese species,T. kamtschaticumhas a mixture of outbreeding and inbreeding among populations. The development of polyploid systems in Asia is possibly the result of the diversity of the breeding systems among the populations. The shift from outbreeding to inbreeding appears to be an important key step in the occurrence of poliploids by hybridization between the different specie

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00193.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe differentiation patterns of reproductive systems, including breeding and pollination systems, and perennation strategies of the genusTrilliumwere critically studied. The pedicellate‐ and sessile‐flowered species with different floral morphologies and ecological distributions exhibited distinct modes of reproductive systems in relation to their habitat conditions. The pedicellate‐flowered species occurring in stable mesic temperate deciduous forests reproduce exclusively by seeds, while sessile‐flowered species growing in the alluvial flood plain habitats depend to a large extent on vegetative reproduction to compensate for the insufficient sexual reproduction under ecologically unstable conditions, e.g., frequent disturbance due to flooding. These sessile‐flowered species are characterized by low ovule numbers, subsequent low seed outputs and low fecundity levels. In contrast to the sessile‐flowered species, the pedicellate‐erect‐flowered species showed very high seed setting rates of over 50%. Breeding experiments for four Japanese species suggest that, although they substantially possess the capability of both inbreeding and outbreeding, the high fecundity levels are maintained by predominant inbreeding system. Furthermore, resource levels in the stock organs of these species obviously determine fecundity levels. As a consequence the amount of reserved food in the rhizomes transferred to the next season is determined, which gurantees a continuous reproductive activity of a given i

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00194.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe evolution of dioecy was studied inSchiedea(Caryophyllaceae), a genus endemic to the Hawaiian Islands. Eight of the 22 species are diclinous, possessing gynodioecious, subdioecious, or dioecious breeding systems. A biogeographic analysis of the genus indicates that the ancestor ofSchiedeacolonized early in the history of the Hawaiian Islands. Subsequently, hermaphroditic species appear to have engaged in inter‐island colonization more frequently than diclinous species. For this reason, single‐island endemism and dicliny are more common on the older Hawaiian Islands. Strong inbreeding depression was detected in three species ofSchiedea, indicating that genetic factors have played a role in the evolution of dicliny. Depending on the level of natural selfing, the expression of inbreeding depressioin may have favored the outcrossed progeny of rare females in populations, and eventually the evolution of dioecy. In contrast to evidence for inbreeding depression, there was very little evidence that resource allocation, sex lability, or habitat partitioning have played an important role in the evolution of dioecy. In subdioeciousS. globosahermaphrodites were largely male in function, and in gynodioeciousS. salicariafemales and hermaphrodites were equivalent in nearly all aspects of female function that could be measured. Variation in breeding systems inSchiedeaand the closely relatedAlsinidendronmay result from the past history of population bottlenecks that have resulted in varying levels of inbreeding depress

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00195.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

AbstractThe process and mechanisms of spatio‐temporal changes in growth, population structure, as well as various yield and reproductive components of a population of an amphicarpic annual,Polygonum thunbergii(Polygonaceae), with two reproductive systems (aerial chasmogamous flowers and subterranean cleistogamous flowers) along an environmental gradient (light, moisture and soil nitrogen levels) were investigated in the field.The results clearly demonstrate that growth and allocation patterns, population structure, and reproductive output of individuals changed sharply along the environmental gradient in response to seasonal and spatial changes in resource availability. Models predicted that light conditions bring about one‐sided competition, whereas nutrient conditions in the soil engender two‐sided competition. As expected, the degree of one‐sided competition was prominent in the case of a planophile,Polygonum thunbergii.Allocation patterns, seed outputs, individual seed size as well as relative energy costs of chasmogamous and cleistogamous seed as affected by light and nutrient levels were also critically analyzed. The most noteworthy finding was that the size of chasmogamous seeds sharply decreased in response to a decrease in the light regime, while cleistogamous seed size remained constant along the gradient. However, relative cost of both chasmogamous and cleistogamous seeds sharply increased with decrease in the light level, reflecting different degrees of environmental stress, biotic interference,

ISSN:0913-557X    

DOI:10.1111/j.1442-1984.1990.tb00196.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY