摘要:

Clones ofSpartina patenswere collected from 19 locations throughout Gulf coast marshes of Texas, Louisiana, and Florida. Following three vegetative generations of de‐acclimation from field conditions, genotypes were subjected to a salinity screening protocol in which salinity was increased in weekly increments of 5‰ (gram salt/kilogram solution). Plants were harvested when there was 50% death of aboveground tissue, which we defined as the lethal salinity level. The genotypes displayed highly significant intraspecific variation in lethal salinity level, which ranged from 63‰ to 93‰. Significant intraspecific variation was also observed in all plant morphological variables, as well as leaf rolling, leaf expansion rates at 2‰ and 20‰ salinity, aboveground, belowground, and total biomass, and belowground‐to‐aboveground biomass ratio. An ANOVA of principal component scores from a PCA of lethal salinity level and covariable‐adjusted total plant dry mass further illustrated intraspecific variation within this species in these two traits expressed as one principal component. Correlation analysis revealed that intraspecific variation in salt tolerance was not strongly associated with intraspecific variation in plant morphological traits, leaf rolling, or leaf expansion rates.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12811.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Floral ontogeny is described and compared in five species and four genera of the hypothetically basal proteaceous subfamily Persoonioideae sensu Johnson and Briggs. The hypotheses surrounding the origin of the peculiar proteaceous flower and homologous structures within the flowers are examined using ontogenetic morphological techniques. Ontogenetic evidence reveals that the proteaceous flower is simple, composed of four tepals, each tepal initiated successively with the lateral tepals being initiated first and second followed by the successive initiation of the sagittal tepals. Each of four stamens is initiated opposite a tepal in a similar sequence to tepal initiation. A single carpel develops terminally from the remaining floral meristem. In taxa of Persoonieae, nectaries are initiated from a broadened receptacle in alternistamenous sites after zonal growth beneath and between the tepals and stamens has begun. The nectaries are interpreted as secondary organs, not reduced homologues of a “lost” petal or stamen series. Developmental variation is present among the examined taxa in several forms including the development of a Vorlaüferspitze (spine) on the upper portion of the tepals, adnation between the anthers and tepals, and formation of the carpel. InPlacospermumthe early formation of the carpel cleft extends to the floral receptacle and in the other taxa, the carpel cleft is distinctly above the receptacle. Different developmental pathways result in similar mature morphologies of the carpel inPersoonia falcataandPlacospermum coriaceum. Bellendena montanais unique relative to the other taxa in having free stamens, a punctate stigma, reduced (not lost) floral bracts, and the floral and bract primordia are initiated from a common meristem. This study provides a foundation for future studies of the developmental basis of floral diversity within Proteaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12812.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The origins of the genomes of allotetraploid speciesTriticum biunciale, T. ovatum, T. neglectum, andT. columnare, and allohexaploidT. rectumwere investigated by examining the presence of specific restriction fragments of repeated nucleotide sequences in DNAs of the polyploid species. The restriction fragments were detectable either in a single diploidTriticumspecies (unique characters) or a group of diploid species (unique shared characters). The analysis showed thatTriticum biuncialeand T.ovatumare closely related. In both species, one pair of genomes is closely related to the genome ofT. umbellulatumand the other is a modified genome ofT. comosum.The same genome formula, UUM°M°, is proposed forT. biuncialeandT. ovatum.Potential reasons for the modification of the M° genome are discussed.Triticum neglectumandT. columnareare also closely related to each other and have the same genomes. They share the U genome withT. biuncialeandT. ovatum, but their second pair of genomes is unrelated to the M° genome. No relationship was found of this genome to a genome of any extant diploid species ofTriticumor any phylogenetic lineage leading to the extant diploid species. This unknown genome is designated X'.∗∗∗ The proposed genome formula forT. neglectumandT. columnareis UUX'X'∗∗∗. HexaploidT. rectumoriginated from hybridization of one of the tetraploid species with the formula UUX'X', likelyT. neglectum, withT. uniaristatum(genome N), and its genome formula is UUX'X'NN.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12813.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Cabbage palms(Sabal palmetto)go through an establishment phase during which the stem grows downward for a period of time before growing upward. We estimated the duration of this phase for cabbage palms growing in coastal forest in Florida using a matrix model approach. All data were collected over a 2‐yr period (1993‐1995) in coastal forest at Waccasassa∗∗∗ Bay, Florida. The minimum time projected by the model for a plant to develop an aboveground trunk was 14 yr. We estimate that the fastest growing 1, 10, and 50% of plants would develop an aboveground trunk in 33, 42, and 59 yr, respectively. The projected duration of the trunkless phase is surprisingly long but not unlike other palms with similar types of establishment growth. Our estimates are much longer than anecdotal estimates for cabbage palms grown under nursery conditions but are similar to anecdotal estimates for plants grown in field conditions. Management practices that remove cabbage palms with aboveground stems usually leave a population of palms without aboveground stems that serves as temporary reserve for relatively rapid recovery of the palm stand. This may foster the perception by many that cabbage palms are fast growing.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12814.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Tropical plant species have been the focus of considerable attention in regard to their potential economic and social importance in the face of rapidly diminishing biodiversity in the tropics. Pacific Island species represent an even more fragile resource because different island populations are widely scattered and overall population sizes are small. We examined the distribution of genetic variation inCampnosperma brevipetiolata(Anacardiaceae), an upland rainforest tree species that is of potential use for both lumber and reforestation efforts in the Federated States of Micronesia (FSM). Seeds were collected from multiple populations on four island groups in the Caroline Islands (Kosrae, Pohnpei, and Yap in the FSM; and the Republic of Palau) and subjected to an electrophoretic analysis involving four polymorphic genetic loci. We hypothesized that variation on these islands would decrease with increasing distance from the presumed Indo‐Malayan source of these island floras. Indeed, we found a trend of decreasing variation from west to east indicated by the mean number of alleles per locus(A =1.50‐1.33), effective number of alleles per locus(Ae=1.14‐1.12) and mean genetic diversity(He=0.123‐0.107). We also found little genetic differentiation among the islands (Fpt= 0.174) and among subpopulations within islands (Fsp= 0.047), indicating that either there are high levels of gene flow among the islands by seed dispersal or that these populations have not been established long enough for divergence to have occurred. The lack of divergence among islands observed forCampnosperma brevipetiolatasuggests that germplasm sampled from any one island population would be a suitable starting point for plant breeding or reforestation efforts.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12815.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Enzyme electrophoresis of pollinia and seeds was used to identify pollinia on pollinators, interspecific pollinations, and hybrid seed production in sympatric populations ofAsclepias exaltataandA. syriaca.The frequency of mixed pollinia loads on pollinators was low. Only 4.1%(N=169 pollinia) and 8%(N=244 pollinia) of the pollinia collected from pollinators ofA. syriacaandA. exaltata, respectively, were identified as pollinia from the other species. Natural levels of interspecific pollination, 3.6% (N= 166 pollinia) onA. syriacaand 3.1%(N =228 pollinia) onA. exaltata, were typically lower than the number of foreign pollinia carried by pollinators. Hybrid seeds were identified in only two of 208A. syriacafruits and one of 178A. exaltatafruits. Hybrid seeds were largely underdeveloped in the singleA. exaltatafruit. High fruit set (34.7%) and near normal seed set following hand‐pollination ofA. syriacawithA. exaltatapollinia suggest that hybridization is more likely between these taxa whenA. syriacais the maternal parent. Our findings indicate that the likelihood of hybridization betweenA. exaltataandA. syriacais remote. Nevertheless, introgressive hybridization has been documented in these species, which suggests that hybridization remains a strong evolutionary force even for species that infrequently interbreed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12816.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

The interaction of mating system and nutrient limitation in determining seed production was investigated in the annual, self‐compatible plantLupinus texensis(Fabaceae). Abortion of developing seeds is a major factor limiting seed production in natural populations (17‐28%). Selfing rates are generally low (0.02‐0.21), suggesting that deleterious recessive genes may be maintained at significant levels in natural populations. The average inbreeding depression associated with seed development is δ = 0.24. Nutrient limitation reduced seed output across experimental treatments by a factor of 0.22 through decreased production of inflorescences, flowers, and ovules, and by a factor of 0.29 through increased abortion of fruits and of seeds within fruits. Competition for resources among fruits increased the frequency of seed abortion. Moreover, a greater proportion of selfed seeds were aborted as the overall abortion rate increased. Estimates of genetic load may therefore only be appropriate if undertaken in the field, and inbreeding depression may vary from year to year simply due to changes in environmental conditions rather than to underlying genetic changes in populations. The existence of inbreeding depression and the high frequency of abortions suggest that selective abortion favoring outcrossed progeny occurs in natural populations ofL. texensis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12817.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Two experiments were designed to examine jointly the roles of maternal effect, genetic load, and other genetic variability at nuclear loci in determining offspring fitness inLupinus texensis, an outbreeding annual herb. A diallel crossing design was used to generate seeds in the greenhouse. This design directly compares maternal and paternal contribution to offspring survival, growth, and flowering, and also assesses the role of genetic load because selfs are included in the crossing design. A nested crossing design was used to generate seeds at a field site. This design addresses the contribution of parental plants to their offspring under natural conditions. Maternal effects occur throughout the life cycle, but dominate the early growth of offspring inL. texensis.Inbreeding depression also occurs throughout the life cycle, but primarily affects size and survival of offspring. Overall inbreeding depression is substantial (δ = 0.66), exceeding the twofold threshold required for maintenance of an outcrossing mating system. However, lineages vary in the stages at which inbreeding depression occurs. Moreover, extreme heterogeneity was observed among lineages, with inbreeding depression ranging from negligible (δ = 0.02) to complete (δ = 1.00). This heterogeneity could allow the invasion and maintenance of selfing genotypes in natural populations ofL. texensis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12818.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

An anatomical survey of anthers of the Poaceae and Cyperaceae and two related families, the Restionaceae and Flagellariaceae, was conducted to determine the taxonomic distribution and possible phylogenetic significance of pollen arrangement. An unusual pollen arrangement was known from a small number of taxa in the Poaceae and Cyperaceae, in which a single, uniseriate cylinder of pollen grains is arranged in the anther locule such that each grain is in contact with the tapetum (termed here “peripheral” pollen). This contrasts with the prevailing arrangement in other angiosperms in which the locule contains a relatively large number of pollen grains in no special configuration, with many interior grains that never touch the tapetum (termed here “central” pollen). A total of 48 species in these four families was examined in this study, and observations on pollen arrangement for numerous additional species in these families were gleaned from the literature. We confirm that the peripheral arrangement is predominant in Poaceae and Cyperaceae, although both families also include species with central pollen, whereas only central pollen is found in Restionaceae and Flagellariaceae. In the peripheral arrangement, the pore of the pollen grain or pseudomonad, when observed, is in contact with the tapetum, but it has not been definitively demonstrated that this is always the case. Peripheral pollen in the Poaceae and Cyperaceae is nonhomologous because of the presence of pseudomonads in the latter family. It remains unexplained why peripherally arranged pollen or pseudomonads, with the attendant reduction in the number of pollen grains, should be associated with anemophily in these two families.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12819.x

出版商:Wiley    

年代:1996

数据来源: WILEY

摘要:

Chloroplast DNA (cpDNA) markers were developed that provided markers unique to a species or that delimited a large area within a species. These markers were then followed across two hybrid zones:Iris douglasiana/Iris∗∗∗ innominata, andIris chrysophylla/Iris tenax.In each case the cline in haplotype frequency was compared to the cline for a morphologically based hybrid index. In all three transects across theI.douglasianall. innominatahybrid zone, the cpDNA cline was displaced 1‐2 km relative to the morphologically defined hybrid zone; the displacement was not found in the other hybrid zone. The observed displacement represents introgression of cpDNA from ∗∗∗I.douglasianainto ∗∗∗I.innominata.It may be that theI.douglasiana/I.∗∗∗ innominatahybrid zone has shifted in recent time, leaving the slowly dispersing chloroplast DNA behind. The populations known asIris thompsoniido not form a phylogenetic species and are best viewed as products of hybridization between ∗∗∗I.douglasianaand ∗∗∗I.innominata.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1996.tb12820.x

出版商:Wiley    

年代:1996

数据来源: WILEY