Analysis of the genetic similarities among seven species of Prosopis (Leguminosae:Mimosoideae)

Summary Prosopis (mesquite) is a commercially promising plant genus that has received increased attention lately. Allelic frequencies at 25 enzyme loci in seven species from the section Algarobia were transformed in matrices of genetic distance using three methods. The indices give highly correlated results; only in the cluster Prosopis alba -P. hassleri were minor discrepancies evident. The phenetic relationships observed agree with other biochemical evidence (chromatography of phenol compounds, electrophoresis of seed proteins, etc) but not with morphological groupings. The present data support the hypothesis that the species belonging to the section Algarobia would be equivalent to sub- or semispecies; the community of such sympatric subspecies constitutes a syngameon.     

First Report on RAPDs Patterns Able to Differentiate Some Argentinean Species of Section Algarobia (Prosopis, Leguminosae)

Prosopis species constitute a very important resource in arid and semiarid regions. Some species of section Algarobia hybridise and introgress naturally in areas of sympatry. According to previous isoenzymatic studies these species have high variability within populations. However, the genetic differentiation among species was very low, and these markers failed to provide diagnostic loci for species recognition. Here we analysed by the RAPD technique natural populations of Prosopis alba, P. ruscifolia, P. nigra, P. flexuosa, and P. vinalillo with the purpose of obtaining markers for species and hybrid identification, by analysing the distribution of genetic diversity within and among species. Genetic variability (H = 0.12-0.26) was similar in all populations. Genetic differentiation among populations (FST = 0.39) was highly significant. Hierarchical analysis of genetic structure performed by Wright (1978) method and analysis of molecular variance (AMOVA) indicated that the diversity among populations within species is low (4-13%) and most genetic diversity (54-61%) occurs within populations. The differentiation among species is intermediate (26-42%) between the previous components but highly significant. Five bands provided a tool for identifying any of the species studied, with the exception of P. vinalillo. The difficulty in diagnosing this species is discussed in reference to the hypothesis of its hybrid origin.     

Analysis of the genetic diversity and relationships among and within species of Hippophae (Elaeagnaceae) based on RAPD markers

RAPD markers were used to assess the genetic diversity and inter- and intra-specific relationships of the genus Hippophae L. and to study the correlation between genetic distances and geographic distances among populations of H. rhamnoides ssp. sinensis. The results analyzed by the percentage of polymorphic loci and Shannon information index indicated that a high level of genetic diversity existed both among and within species of the genus Hippophae. In the UPGMA dendrogram, the species or subspecies were clustered into two main groups but not strictly grouped according to sect. Hippophae and sect. Gyantsensis Lian. The multiple regression analysis and Mantel test both indicated a significant correlation between genetic distance and altitude distance among populations of H. rhamnoides ssp. sinensis, and the cluster analysis suggested that the genetic variation among populations of H. rhamnoides ssp. sinensis was linked to their monophyletic origin. Moreover, some degree of genetic differentiation was found among samples collected at different times.     

Consistency of population genetics parameters estimated from isozyme and RAPDs dataset in species of genus <Emphasis Type="Italic">Prosopis</Emphasis> (Leguminosae,Mimosoideae)

Genetic variability, population structure and differentiation among 17 populations of 5 species and 2 natural interspecific hybrids of section Algarobia of genus Prosopis were analyzed from data of 23 isozyme and 28 RAPD loci. Both markers indicated that the studied populations are highly variable. P. alba populations in average showed lower values of genetic variability estimates from isozyme data, but this trend was not observed for RAPD markers. The hierarchical analyses of the distribution of genetic variability showed that the highest proportion of variation occurred within populations, the differentiation among species was intermediate and the lowest component was observed among populations within species. The consistency between results from both dataset implies that they are not biased and reflect the actual genetic structure of the populations analyzed. The matrices of Euclidean distances obtained from the two sets of markers were highly correlated according to Mantel test. In both cases the corresponding phenogram and MDS plot tended to cluster conspecific populations while hybrid populations were not intermediate between putative parents. Some disagreements between isozyme and RAPD phenograms were observed mainly in the affinities of hybrid populations. Such inconsistencies might result from reticular rather than dichotomic evolutionary relationships. The phenetic associations retrieved gave no support to the division of the section Algarobia into series.     

Discovery of a life history shift: precocious flowering in an introduced population of Prosopis

The genus Prosopis contains many valuable, long-lived, multi-purpose legume trees, some of which are also invasive species. The time of first flowering is important for increasing production of sweet, protein-rich pods in plantations, especially under short rotations, and affects the rate of spread as a weed. Trees generally begin flowering at 3–5 years of age. However, seedlings from a small seedlot collected from an introduced population in southern Mauritania were observed to begin flowering at 3–4 months after germination. This is unknown in the native range of any Prosopis species, and appears to represent a major evolutionary event triggered after naturalization. This paper reports a detailed investigation with seed collected from Aleg, Brakna region, Mauritania, in 1998 (Prosopis sp. ‘Aleg’). Two experiments were established, in glasshouses at Cirad, Montpellier, France, and Coventry University, UK. Flowering began at the two sites 104 and 169 days after sowing, respectively, and 97.5% of plants had flowered at Coventry after 306 days. Flowers produced abundant pollen with 50–60% viability indicated by FDA staining and 40–50% germination on an artificial medium. No pods were formed. All plants analysed were diploid. Morphologically, these juvenile plants were similar to American species of section Algarobia, and exhibited leaf characters typical of P. pallida. However, due to the large variation in morphology within this section of the genus, further studies are required to confirm the actual species. This is the first record of precocious flowering in Prosopis, and has been found only in a single, introduced population. Implications for genetic improvement of tropical Prosopis, and particularly the spread of these species as invasive weeds, are discussed. Such a life history shift in the increased reproductive ability of a species following introduction, with potentially significant environmental effects, may not be restricted to Prosopis and merits further detailed investigation.     

Inter- and intrapopulation genetic variation in species ofPorphyra (Rhodophyta: Bangiales) from British Columbia and adjacent waters

Starch gel electrophoresis of 17 proteins has provided data on inter- and intrapopulation genetic variation in 20 species ofPorphyra occurring in British Columbia and adjacent areas.P. cuneiformis andP. nereocystis showed no within species variation, even over ranges of more than 1000 km. Populations ofP. abbottae, P. fallax, P. fucicola, P. gardneri andP. schizophylla were characterized by fixation for certain alleles. The number of polymorphic loci in a population ranged from zero to nine, depending on the species. Six species had populations that were polymorphic at just a single locus. Only two species (P. mumfordii andP. pseudolanceolata) had populations that were polymorphic at more than three loci. These levels of genetic variation are lower than those reported for populations of JapanesePorphyra species. Eleven taxa were polymorphic for 6-phosphogluconate dehydrogenase, the most variable enzyme. No within species polymorphisms were detected for bromoperoxidase, lactate dehydrogenase, superoxide dismutase or phycoerythrin. Possible evidence for the chimeric nature of the thallus was observed only inP. mumfordii.     

Chemotaxonomic features of lipophilic components inAdesmia species (Leguminosae)

Studies were performed on GC-MS to assess the lipophilic composition of sixAdesmia species representing two subgenera and three series. Normal fatty acids and hydrocarbons were mainly found, as well as acetylenic compounds, dibasic acids, cyclic hydrocarbons, high molecular weight alcohols and one sterol.     

Critical examination of postulated cladistic relationships among species of flour beetles (genus Tribolium,Tenebrionidae, Coleoptera)

Cytological considerations have led to the hypothesis that Tribolium confusum (CF) evolved from an ancestor similar to T. castaneum (CS) by translocation of an autosome to the X chromsome, and that T. destructor (DEST) was derived from CF. T. brevicornis (BREV) is regarded as the most primitive on morphological grounds. Electrophoretic analyses of 19 strains of CS, 7 of CF, and 1 each of DEST and BREV do not support this postulated evolutionary pathway. CF and CS are much more similar to BREV than they are to each other. (Comparisons of morphological mutations in CS and CF also indicate that the two species are not similar genetically.) DEST and CF are very dissimilar electrophoretically. It is likely that the species evolved independently from an ancestral stock which may be represented by BREV. Recognition of gene homology in different species is the keystone for all attempts at constructing genetically meaningful evolutionary pathways. The difficulties involved in doing so are pointed out.     

Four new Brazilian species of Lonchocarpus (Leguminosae, Papilionoideae, Millettieae)

Lonchocarpus castaneifolius, L. grazielae, L. longiunguiculatus, and L. montanus from Brazil are described and illustrated based on field and herbarium studies. The first species belongs to Lonchocarpus sect. Punctati and is restricted to northeastern Brazil (Bahia state). The other three are included in sect. Laxiflori. Lonchocarpus grazielae is restricted to the southern coastal region (Santa Catarina state), L. montanus is found in northeastern Brazil (Bahia and Piauí states), the west-central region (Goiás and Tocantins states) and the southeast (Minas Gerais state), and L. longiunguiculatus occurs in northeastern (Bahia state) and southeastern (Minas Gerais state) Brazil.     

Isoenzyme Variation in Melipona rufiventris (Hymenoptera: Apidae, Meliponina) in Minas Gerais State, Brazil

The stingless bee Melipona rufiventris is an important pollinator in several Brazilian ecosystems. Originally widely distributed in Minas Gerais (MG) state, this species is becoming very rare. Therefore this species was included in the endangered species list of MG. We used isoenzyme data for a better understanding of the genetic structure of several M. rufiventris colonies. Samples of 35 colonies were collected from 12 localities and evaluated by nine enzymatic systems, which yielded 17 loci. M. rufiventris genetic variation was found to be low, typical of an endangered species. The proportion of polymorphic loci was 5.88% in both ecosystems. Only Est-4 was polymorphic in colonies from the Forest and Mdh-1 in colonies from the Cerrado. The expected heterozygosity ranged from 0.0068 in the Cerrado to 0.0078 in the Forest. Despite this, enzyme electrophoretic analyses provided a good idea of the diversity between samples from Cerrado and Forest which reinforce the existence of two different forms of M. rufiventris in MG, one present in the Cerrado and the other in Forest. This information is of great importance for the conservation of, M. rufiventris in MG.     

Distribution of allozyme variation inVicia benghalensis (Leguminosae) suggests the existence of two genepools

InVicia benghalensis two biotypes differing in biochemical and cytological features were identified in previous studies. It was hypothesized that these biotypes could also vary in reproductive behaviour and be genetically isolated. To better understand this issue, 25 distinct samples were studied using allozymes. Nine enzyme systems, accounting for 15 putative loci, were scored. The data obtained were analysed using population diversity parameters; Nei's genetic distance was calculated and used to construct a dendrogram. Principal component analysis was conducted to verify the dendrogram and to determine which alleles had stronger influence on the grouping of populations. The analyses demonstrated that the two previously identified biotypes are genetically different: Nei's distance between the two groups is larger than the distance within each group. Three-dimensional plotting of the first three principal components corroborates this division. Genetic diversity parameters confirm that the two biotypes also differ in outcrossing rates. These results denote the existence of two highly divergent genepools inV. benghalensis and suggest that a speciation process may be acting. The consequence of the present findings on the management of gene bank collections is analysed.     

Isozymes in macroalgae (seaweeds): genetic differentiation,genetic variability and applications in systematics

Use of isozymes (including allozymes) in studies of population genetics and systematics of seaweeds has increased sufficiently in the last decade to allow some generalization. Only a single locus has been observed for about half the enzymes analysed in seaweeds, compared with 29% in vascular plants. Compared with higher plants, macroalgal species generally have low amounts of electrophoretically detectable genetic variation; the lowest levels of genetic variation found in natural populations are those reported for seaweeds. Nonetheless, seaweeds show an association between levels of genetic diversity as revealed by isozymes and species-specific attributes, such as mating system and predominance of asexual versus sexual reproduction. In systematic studies, isozymes have revealed cryptic species and identified pairs of sibling taxa. The quaternary structure of enzymes appears to be conserved at the phylum level. With the current availability of improved techniques for enzyme electrophoresis and for data interpretation, we expect future studies utilizing isozyme electrophoresis to provide further insight into population and evolutionary processes in seaweeds.     

Genome relationships among Lotus species based on random amplified polymorphic DNA (RAPD)

The ability of random amplified polymorphic DNA (RAPD) to distinguish among different taxa of Lotus was evaluated for several geographically dispersed accessions of four diploid Lotus species, L. tennis Waldst. et Kit, L. alpinus Schleich., L. japonicus (Regel) Larsen, and L. uliginosus Schkuhr and for the tetraploid L. corniculatus L., in order to ascertain whether RAPD data could offer additional evidence concerning the origin of the tetraploid L. corniculatus. Clear bands and several polymorphisms were obtained for 20 primers used for each species/accession. The evolutionary pathways among the species/accessions presented in a cladogram were expressed in terms of treelengths giving the most parsimonious reconstructions. Accessions within the same species grouped closely together. It is considered that L. uliginosus which is most distantly related to L. corniculatus, may be excluded as a direct progenitor of L. corniculatus, confirming previous results from isoenzyme studies. Lotus alpinus is grouped with accessions of L. corniculatus, which differs from previous studies. With this exception, these findings are in agreement with previous experimental studies in the L. corniculatus group. The value of the RAPD data to theories on the origin of L. corniculatus is discussed.     

Isozyme variation in Calliandra calothyrsus (Leguminosae): its implications for species delimitation and conservation

Patterns of genetic diversity within and among populations of Calliandra calothyrsus, an important multipurpose tree species, were examined using isozyme analysis. C. calothyrsus is a widespread species distributed throughout Central America and southern Mexico, across a variety of environments. Morphologically and ecologically distinct populations can be identified within this range, but they are currently considered to represent a single species. C. calothyrsus has been introduced to many parts of the tropics, where it is cultivated as a source of fuelwood, animal fodder, green manure, and shade by rural communities. Some of these introductions are known to have originated from Guatemala, but very little is known about the genetic diversity of either the native or naturalized populations. Isozyme electrophoresis of 23 loci across 17 populations of C. calothyrsus indicated that the majority of genetic diversity was partitioned between populations (FST = 0.802) and that within-population heterozygosity was low (mean Ho = 0.057). Naturalized populations had lower than expected heterozygosities and were most similar to material from Santa Maria de Jesus, a natural population in southern Guatemala. Four distinct groups of populations were identified on the basis of Nei's genetic distances and Population Aggregation Analysis (PAA), and correlate with the morphological and ecological differences that can be observed within the species. The results are discussed in relation to species delimitation and conservation.     

Using AFLP markers for species differentiation and assessment of genetic variability of in vitro-cultured Papaver bracteatum (section Oxytona)

Summary Amplified fragment length polymorphism (AFLP) markers were employed to deteet genetic variation among species of Papever (section Oxytona) and assess genetic fidelity between in vitro cell lines of Papaver bracteatum and mature plants derived from the propagation of their callus cultures. Regenerated plants exhibited morphological and phytochemical characteristics dissimilar to those of their source material. Thebaine, the dominant alkaloid produced by Papaver bracteatum, was not detected in capsules from mature regenerated accessions, indicating that there may have been a loss of genetic uniformity. Instead, the dominant alkaloid produced by the regenerated plant was shown to be isothebaine (by TLC and GC/MS), a metabolic characteristic of P. pseudo-orientale. A Neighbor-Joining tree constructed from AFLP fingerprints distinetly separates the three species of Oxytona while firmly grouping the in vitro-cultured plants with P. pseudo-orientale. Additionally phytochemical data and chromosome counts indicate that the seed used to initiate cultures was of hybrid origin and ihat the loss in genetic uniformity was not due to somaclonal variation occurring during the in vitro culture process. AFLP fingerprinting was therefore able to differentiate Oxytona species and invesgigate allopolyploidy in closely related papaver species.     

Genetic differentiation of theErigeron species (Asteraceae) in the Alps: A case of unusual allozymic uniformity

Allozyme variation was studied in all nine diploidErigeron species known from the Alps:E. alpinus, E. neglectus, E. polymorphus, E. candidus, E. uniflorus, E. atticus, E. gaudinii, E. acer, andE. angulosus. A total of 248 individuals from 24 natural populations was investigated using starch gel electrophoresis. Seven enzymes and 13 loci were assessed. Genetic variation within populations was low with the proportion of polymorphic loci ranging from 0.0–0.385, and average number of alleles per polymorphic locus from 2.0–2.5. In general, 70–100% of the genetic variation was attributed to between population differences. Mean genetic identities for pair-wise comparisons of populations averaged 0.893 within species, and 0.890 among species. Interspecific genetic variation of populations usually did not exceed intraspecific variation. It was concluded that theErigeron species from the Alps may have arisen by recent speciation probably during the epoches of glaciation. Morphological and ecological differences between species seem to be based on few gene loci.     

Allozyme divergence among species ofWolffia (Lemnaceae)

The genusWolffia was surveyed electrophoretically at 14 allozyme loci. A total of 133 clones representing 10 of the 11 recognized species was examined. Genetic identities among most pairs of species are zero, with non-zero values ranging from 0.14 to 0.40.Wolffia angusta and the newly describedW. neglecta show the highest similarity, and the former species has an identity of 0.14 withW. australiana. The next highest similarity (0.34) occurs betweenW. globosa of Southeast Asia andW. cylindracea of southern Africa, which until recently, had generally been viewed as members of the same species. Other species showing some common alleles are members of a complex involvingW. arrhiza, W. columbiana, W. cylindracea, andW. globosa. WithinW. arrhiza, plants from South Africa and Europe are easily distinguished electrophoretically because each contains unique alleles at two loci. Strains from other parts of Africa vary at these loci and are not totally distinct from either the plants from South Africa or from Europe. Species ofWolffia are much more divergent at allozyme loci than the majority of congeners of flowering plants. This suggests that the species are quite old and that the difficulties in distinguishing taxa morphologically are the result of reduction rather than lack of divergence due to recent speciation. Because of the lack of shared alleles between the majority of species pairs inWolffia, enzyme electrophoresis provides limited resolution of species relationships in the genus.     

Isozyme evidence on the genetic diversity, mating system and evolution of Bromus intermedius (Poaceae)

Genetic diversity and differentiation among the B. intermedius accessions of different geographic origin has been studied using isozyme analysis. The mating system was evaluated on the basis of allozyme polymorphism. Outcrossing rate (t) in B. intermedius was mostly 0, except one population with t = 0.16, indicating nearly complete autogamy in this species. Given that B. arvensis and B. intermedius had common allozymes of all isozymes studied, it is suggested that B. intermedius may be a direct autogamous derivative of the outcrosser B. arvensis. Contrary to expectations, the allozyme diversity in B. intermedius was higher than in B. arvensis, 23 and 16 allozymes, respectively. Geographic pattern was found among the accessions of B. intermedius.