A global survey of haplotype frequencies and linkage disequilibrium at the DRD2 locus

A four-site haplotype system at the dopamine D2 receptor locus (DRD2) has been studied in a global sample of 28 distinct populations. The haplotype system spans about 25 kb, encompassing the coding region of the gene. The four individual markers include three TaqI restriction site polymorphisms (RSPs) – TaqI “A”, “B”, and “D” sites – and one dinucleotide short tandem repeat polymorphism (STRP). All four of the marker systems are polymorphic in all regions of the world and in most individual populations. The haplotype system shows the highest average heterozygosity in Africa, a slightly lower average heterozygosity in Europe, and the lowest average heterozygosities in East Asia and the Americas. Across all populations, 20 of the 48 possible haplotypes reached a frequency of at least 5% in at least one population sample. However, no single population had more than six haplotypes reaching that frequency. In general, African populations had more haplotypes present in each population and more haplotypes occurring at a frequency of at least 5% in that population. Permutation tests for significance of overall disequilibrium (all sites considered simultaneously) were highly significant (P<0.001) in all 28 populations. Except for three African samples, the pairwise disequilibrium between the outermost RSP markers, TaqI “B” and “A”, was highly significant with D’ values greater than 0.8; in two of those exceptions the RSP marker was not polymorphic. Except for those same two African populations, the 16-repeat allele at the STRP also showed highly significant disequilibrium with the TaqI “B” site in all populations, with D’ values usually greater than 0.7. Only four haplotypes account for more than 70% of all chromosomes in virtually all non-African populations, and two of those haplotypes account for more than 70% of all chromosomes in most East Asian and Amerindian populations. A new measure of the amount of overall disequilibrium shows least disequilibrium in African populations, somewhat more in European populations, and the greatest amount in East Asian and Amerindian populations. This pattern seems best explained by random genetic drift with low levels of recombination, a low mutation rate at the STRP, and essentially no recurrent mutation at the RSP sites, all in conjunction with an “Out of Africa” model for recent human evolution. Received: 14 January 1998 / Accepted 19 March 1998     

Genetic and clonal diversity in Korean populations ofVitex rotundifolia (Verbenaceae)

Vitex rotundifolia L.f. is a woody perennial and has sexual and asexual modes of reproduction. Allozyme study was conducted on 550 plants in 13 Korean populations. The levels of genetic variability and divergence within and among populations, respectively, are considerably lower and higher than the mean values for woody plants with similar life history tralts. Mean percentage of polymorphic loci (P _P), mean number of alleles per locus (A _P), and mean genetic diversity (He _P) within populations ofV. rotundifolia were: 16.7%, 1.21, and 0.047. On average, about 79% of the total variation inV. rotundifolia was common to all populations (meanG _ST=0.208). In addition, significant differences in allele frequencies among populations were found in all polymorphic loci examined (P<0.001). On the other hand, levels of genotypic diversity within and among populations were moderate. About 44% (18/41) of multilocus genotypes were “local genotypes” (genotypes occurring in only one population), whereas only one “widespread genotype” (genotypes occurring in more than 75% of the populations) were detected. The mean number of multilocus genotypes per population (G) and mean genotypic diversity index (D _G) were 8.4 and 0.74, respectively. Most common multilocus genotypes found in populations were homozygous for five polymorphic loci. The abundance of ramets of these genets is responsible for the low levels of expected heterozygosity within populations. The results indicate that clonal reproduction may act as an enhancer of genetic drift by reducing effective size of local populations ofV. rotundifolia.     

Y-Haplotype X in the Balkans

A total of 2110 unrelated European male subjects were examined for the p49a,f TaqI Y-haplotype X. The results showed a remarkable mean peak of haplotype X frequencies (46.9%) among subjects from Croatia, and similar elevated frequency values were also found in their counterparts from Slovenia (41.5%), Bosnia (40.3%) and ex-Yugoslavia (36.7%). Frequencies of haplotype X decrease towards west (from 41.5% in Slovenia to less than 1% in northern Italy) and south (23.5% in Albania, 15.9% in Serbia, 7.5% in Greece and 2.1% in Crete), but retain relatively high frequencies in Romania (17.9%) and in Bulgaria (16.1%). Historical and genetic evidence allows us to demonstrate that haplotype X originated in Europe among descendants of men who have been associated with the Gravettian culture. During the Last Glacial Maximum the Western Balkan Peninsula constituted a “refuge” for haplotype X, the starting point of an expansion that spread this haplotype around the neighbouring populations in historical times.     

Systematics and genetic variation in commercial shape Kappaphycus and shape Eucheuma (Solieriaceae, Rhodophyta)

The systematics and taxonomy of Kappaphycus and Eucheuma (Solieriaceae) is confused and difficult due to morphological plasticity, lack of adequate characters to identify species and commercial names of convenience. These taxa are geographically widely dispersed through cultivation. Commercial, wild and herbarium sources were analysed; molecular markers provided insights into taxonomy and genetic variation, and where sources of genetic variation may be located. The mitochondrial cox2-3 and plastidal RuBisCo spacers were sequenced. There is a clear genetic distinction between K. alvarezii (“cottonii”) and K. striatum (“sacol”) samples. Kappaphycus alvarezii from Hawaii and some samples from Africa are also genetically distinct. Our data also show that all currently cultivated K. alvarezii from all over the world have a similar mitochondrial haplotype. Within Eucheuma denticulatum (“spinosum”) most African samples are again genetically distinct. Our data also suggest that currently cultivated E. denticulatum may have been “domesticated” several times, whereas this is not evident for the cultivated K. alvarezii. The present markers used do not distinguish all the morpho-types known in cultivation (e.g. var. tambalang, “giant” type) but do suggest that these markers may be useful to assess introductions and species identification in samples.     

Genetic diversity of isolated populations of Nautilus pompilius (Mollusca, Cephalopoda) in the Great Barrier Reef and Coral Sea

Nautilus species are the only remaining cephalopods with an external shell. Targeted heavily by the shell trade across their distribution area, these species have a poorly known population structure and genetics. Molecular techniques have been used to assess levels of inter- and intra-population genetic diversity in isolated populations of Nautilus in the northern sections of the Great Barrier Reef (GBR), Australia and in the Coral Sea. Distinct populations, physically separated by depths in excess of 1,000 m were examined. RAPD analysis of genetic differences showed limited differentiation of the “Northern GBR” populations and the “Coral Sea” populations. Discrimination between the two geographic groups was observed from these data. In addition, partial sequencing of the CoxI gene region, yielded 575 bp of sequence, which was aligned for 43 samples and phylogenetic trees constructed to examine genetic relationships. Two distinct clades were resolved in the resulting trees, representing the “Northern GBR” and “Coral Sea” population groups. Inter- and intra-population relationships are presented and discussed. The differentiation of the Nautilus populations from the Northern section of the Great Barrier Reef and those from the Coral Sea were supported by two distinctly different methodologies and the significance of this separation and the potential evolutionary divergence of these two population groups is discussed.     

Ecological Segregation and Population Structuring of the Cormorant Phalacrocorax carbo in Europe, in Relation to the Recent Introgression of Continental and Marine Subspecies

Populations of the “continental” Great Cormorant P. c. sinensis have expanded from north-eastern Europe towards the western part of the range of the “marine” P. c. carbo breeding in the United Kingdom and France. The aim of the study was to test the hypothesis of ecological segregation between subspecies by analysing the structuring of the European populations. Sequencing the mtDNA of 231 birds belonging to 20 colonies revealed 38 haplotypes based on 25 polymorphic sites (5.76% sequence divergence). P. c. sinensis (“S”) was well confirmed, but usual P. c. carbo formed two coastal populations, the real P. c. carbo “C” mainly in the western part of the range (United Kingdom, coastal France), and also in Norway and Sardinia, and “N”, branched to the Japanese Cormorant P. capillatus and probably isolated by glaciations, mainly present in the Nordic range (Norway, but also on the coasts from Sweden to Brittany), we named P. c. norvegicus. In a variable position in the trees but close to C is a group of undetermined origin haplotypes, named U, also present in both traditional ranges. The new tree-nesting colonies in Brittany are clearly a mixture of S and the two clades C and N previously described as P. c. carbo, with a decreasing proportion of C + N between 1993 (67%), 1996 (60%) and 2002 (33%) for the pioneering Grand-Lieu colony. These results confirmed the current introgression of continental populations in the western range, with probable hybridization. Although the subspecies can switch habitats locally due to social behaviour and migrations, the ecological segregation between the two usual subspecies appears to be largely confirmed in Europe.     

Assessment of Gene Flow from Genetically Modified Anthracnose-Resistant Chili Pepper (Capsicum annuum L.) to a Conventional Crop

We conducted a 2-year field assessment of the gene flow from genetically modified (GM) chili pepper (Capsicum annuum L.), containing the PepEST (pepper esterase) gene, to a non-GM control line “WT512” and two commercial hybrid cultivars, “Manidda” and “Cheongpung Myeongwol (CM).” After seeds were collected from the pollen-recipient non-GM plants, hybrids between them and the GM peppers were screened by a hygromycin assay. PCR with the targeting hpt gene was performed to confirm the presence of transgenes in hygromycin-resistant seedlings. Out of 7,071 “WT512” seeds and 6,854 “Manidda” seeds collected in 2006, eight and 12 hybrids, respectively, were detected. In 2007, 33 hybrids from 3,456 “WT512” seeds and 50 hybrids from 3,457 “CM” seeds were found. The highest frequency of gene flow, 6.19%, was observed in that 2007 trial. These results suggest that a limited isolation distance would be sufficient to prevent gene flow from GM to conventionally bred chili peppers.     

Stocking may increase mitochondrial DNA diversity but fails to halt the decline of endangered Atlantic salmon populations

Over the last 50 years, Spanish Atlantic salmon (Salmo salar) populations have been in decline. In order to bolster these populations, rivers were stocked with fish of northern European origin during the period 1974–1996, probably also introducing the furunculosis-inducing pathogen, Aeromonas salmonicida. Here we assess the relative importance of processes influencing mitochondrial (mt)DNA variability in these populations from 1948 to 2002. Genetic material collected over this period from four rivers in northern Spain (Cantabria) was used to detect variability at the mtDNA ND1 gene. Before stocking, a single haplotype was found at high frequency (0.980). Following stocking, haplotype diversity (h) increased in all rivers (mean h before stocking was 0.041, and 0.245 afterwards). These increases were due principally to the dramatic increase in frequency of a previously very low frequency haplotype, reported at higher frequencies in northern European populations proximate to those used to stock Cantabrian rivers. Genetic structuring increased after stocking: among-river differentiation was low before stocking (1950s/1960s Φ _ST = –0.00296–0.00284), increasing considerably at the height of stocking (1980s Φ _ST = 0.18932) and decreasing post-stocking (1990s/2002 Φ _ST = 0.04934–0.03852). Gene flow from stocked fish therefore seems to have had a substantial role in increasing mtDNA variability. Additionally, we found significant differentiation between individuals that had probably died from infectious disease and apparently healthy, angled fish, suggesting a possible role for pathogen-driven selection of mtDNA variation. Our results suggest that stocking with non-native fish may increase genetic diversity in the short term, but may not reverse population declines.     

Allozyme variability within and divergence among populations of the liverwortConocephalum conicum (Marchantiales: Hepaticae) in Japan

Genetic variation within, and divergence among, populations of the liverwortConocephalum conicum were estimated from the study of 17 populations and 23 putative gene loci. Two additional multilocus genotypes (“T” and “FS”) were detected in Japan, along with the previously reported “J” type. These three multilocus genotypes differed both morphologically and ecologically. All eight populations from western Japan included only the J-type and exhibited low genetic variation within populations: Nei's (1973) average gene diversity (Ĥ)=0.080±0.029. In contrast, co-occurrence of several multilocus genotypes in each population from the Kanto District resulted in much higher levels of genetic variation (Ĥ=0.218±0.037). If the three genotypes are distinguished,Ĥ values are 0.113±0.030 for T-type, 0.107±0.033 for FS-type, and 0.083±0.018 for J-type. UsingC. japonicum, which showed low genetic variation (0.014±0.010) as an outgroup, each genotype formed a monophyletic clade, and the J- and FS-types were more closely related to each other than to the T-type. Populations of western Japan and the Kanto District also differed in the degree of gene diversity among populations, but the reasons for these differences are obscure.     

Population structure of the sailfin sandfish, Arctoscopus japonicus (Trichodontidae), in the Sea of Japan

We analyzed patterns of genetic diversity in the sailfin sandfish (Arctoscopus japonicus), focusing on population subdivisions within the Sea of Japan. We observed 270 specimens from nine sampling sites in 1999–2000, i.e., seven sites in the Sea of Japan and two sites from the Pacific coast of Hokkaido. An additional site (30 specimens) was sampled from eastern Korea in the spawning season of 2004 for comparison. Forty haplotypes, compiled into three haplogroups (A–C), were detected based on the comparison of a 400-bp sequence of the anterior part of the mitochondrial control region. In accordance with previous hypotheses from morphological and molecular analyses, genetic discontinuity between the Sea of Japan and the Pacific coast of Hokkaido was conspicuous. Within the Sea of Japan, eight sampling sites were not genetically uniform, and most of the variations among sites were detected between eastern Korea [the “eastern Korea” (EK) population: distributed from the Korean Peninsula to Mishima, Yamaguchi Prefecture] and the other sites along the coast of Japan [the “western Japan” (WJ) population: from Oki Islands to western Hokkaido] (Φ _CT  = 0.096, P = 0.0183). The WJ population, having lower genetic variability, showed significant departure from neutrality, indicating influences through a recent population expansion. The period of the expansion can be estimated to have begun on the order of 10⁴ years ago. We consider that the present Japan Sea populations have been formed through the invasion of a small ancestral stock to the Sea of Japan and its population expansion during the last glacial period or later. On the other hand, we failed to detect distinct evidence of a population expansion in the EK population. Haplogroup C, detected in a high frequency in this population, was estimated to have mixed with haplogroup A after rapid differentiations of the latter. Therefore, the EK population, strongly influenced by such a mixture, might possess haplogroup C in a higher frequency and a different haplotype composition from the WJ population.     

<Emphasis Type="Italic">MEFV</Emphasis> heterogeneity in Turkish Familial Mediterranean Fever patients

Turkey is one of the few countries in the world where Familial Mediterranean Fever (FMF), an autoinflammatory disease caused by mutations in MEFV, the gene encoding pyrin, is not rare. Many interesting studies regarding the genetics of Familial Mediterranean Fever in Turkey have been already published. Despite that different MEFV genetic profiles have been revealed for Turkish FMF patients, deriving from different regions of Turkey, a systematic population genetics analysis has not been carried out yet. The present study aims to investigate the population genetics of MEFV in Turkish FMF patients so as to additionally facilitate the clinical interpretation of individualized genetic data. All relevant studies have been recruited by searching PubMed with the terms “MEFV”, “FMF”, and “Turkey”. Seven of them, including 3,061 FMF patients, contained all necessary data concerning allelic and genotypic frequencies of the 4 commonest MEFV mutations in Turkey (M694V, V726A, M680I, E148Q). From all 6,122 MEFV alleles analyzed, the M694V mutation was recognized in 15.6–52.2% (mean 29.3%), the V726A in 1.5–9.7% (mean 4.8%), the M680I in 1.5–15.5% (mean 7.6%), and the E148Q in 3.2–13.9% (mean 5.5%). Unidentified mutations ranged from 0–42.9% (mean 16.8%). No mutations were found in 0–54.5% (mean 36.0%) of the patients. The allelic and genotypic frequencies of the most frequent mutation (M694V) showed aberration of the Hardy–Weinberg law for all 7 populations studied. By application of the Arlequin 2.0 population genetics software, the Fixation index (F _ST) was found to be 0.09994, thus demonstrating that the observed variability is mainly within (90.006%) and not among (9.994%) populations (P < 0.00001). Moreover, the global test of differentiation demonstrated that every population differs from each other (P < 0.00325). Finally, the Ewens–Watterson test of selective neutrality yielded to statistical significance in only 3 populations. In conclusion, Turkish FMF patients are characterized by an increased genetic heterogeneity, explained by the intrapopulation differentiation. Thus, the regional origin should be regarded as a determining factor in the diagnosis of FMF in Turkish patients.     

Variability and structure of natural populations of Elymus caninus (L.) L. and their possible relationship with Hordelymus europaeus (L.) Jess. ex Harz as revealed by AFLP analysis

The AFLP method was used to study the inter-population variability of eight populations of Elymus caninus (L.) L. as well as three populations of Hordelymus europaeus (L.) Jess. ex Harz. In these studies a clear distinction was found between two phenotypes of E. caninus collected in the same locality. It also appeared that two populations of E. caninus representing the “pauciflorum” morphotype were clustered together, similarly as two populations of E. caninus exhibiting morphotype “caninus”. Additionally, the populations of the “pauciflorum” type were clustered together with all samples of H. europaeus. Furthermore, the same approach was applied to analyze the intra-population variability of E. caninus. The populations ranged from nearly uniform to as diverse as the samples collected from different localities. In some populations of this species the presence of off-type plants was revealed. Our data indicate the predominantly self-pollinating character of E. caninus and the possible genetic relationship between of E. caninus and H. europaeus. It is the second paper from the series: Biodiversity of wild Triticeae (Poaceae) in Poland, the first is: Mizianty M. 2005. Variability and structure of natural populations of Elymus caninus (l.) L. based on morphology. Pl. Syst. Evol. 251: 199–216.     

Protein variation,taxonomy and differentiation in five species of marmosets (genusCallithrix Erxleben, 1777)

The electrophoretic patterns of 15 protein systems codified for 20 genetic loci were investigated using horizontal electrophoresis. A total of 150 blood samples, from five species of the genusCallithrix were analyzed. Polymorphic variation was observed in 10 out 20 loci analyzed. The genotypic distributions are in Hardy-Weinberg equilibrium. The average heterozygosity (H) varied from 1% to 5%, similar to those observed for other Neotropical primates. The genetic distance coefficients revealed a phylogenetic separation of these species into two groups: (1) “argentata” (C. humeralifer andC. emiliae); (2) “jacchus” (C. jacchus, C. penicillata, andC. geoffroyi). This arrangement is according to the taxonomic arrangement proposed byHershkovitz (1977),de Vivo (1988), andMittermeier et al. (1988). The results in each group are compatible with the subspecies values recorded for the Platyrrhini. These values showed that:C. humeralifer andC. emiliae are subspecies ofC. argentata;C. jacchus, C. penicillata, andC. geoffroyi are subspecies ofC. jacchus. These results also suggest thatC. j. geoffroyi is the “jacchus” group taxon, most similar genetically to the “argentata” group.     

Two new“Meganthropus” mandibles from Java

There are now eleven known mandibular pieces from the Lower and Middle Pleistocene of Java, all but one being from the Sangiran site. All of these have been assigned toHomo erectus by most authorities, while others have suggested as many as four different hominoid taxa. Two of the mandibles, Sangiran 33 (Mandible H) and“Meganthropus”D (no Sangiran number yet assigned), are described here for the first time. The two new mandibles come from the Upper Pucangan Formation and date approximately 1.2–1.4 Myr. They are morphologically compatible with other“Meganthropus” mandibles described from Java. Despite attempts by numerous authorities to place all the Sangiran hominid mandibles in the species,H. erectus, the range of variation in metric and nonmetric features of the“Meganthropus” hominids is clearly beyond the know variation found inH. erectus. “Meganthropus” could represent a speciation from the well-knownH. erectus.     

Genetic diversity of <Emphasis Type="Italic">Salanx ariakensis</Emphasis> (Salangidae) from Korea and Japan inferred from AFLP

The genetic diversity and population structures within and between Korean and Japanese populations of Salanx ariakensis were investigated using AFLP (amplified fragment length polymorphism). Using seven primer pair sets, 411 fragments were amplified from 31 specimens of S. ariakensis, 393 fragments (96%) being polymorphic. The expected heterozygosities were 0.211 and 0.245 for the Japanese and Korean populations, respectively, levels similar to those of other freshwater and diadromous fishes, but lower than those of marine fishes. The difference in genetic diversity between the two populations may result from their different habitat sizes. Principal coordinate analysis using 393 polymorphic fragments resulted in specimens from each population being plotted separated, suggesting an absence (or little if present) gene flow between them since Tsushima Strait has been open. Therefore, each population of S. ariakensis is relevant from the conservation perspective and should at least be treated as a “management unit” for conservation purposes.     

Expression of phytoene synthase gene (Psy) is enhanced during fruit ripening of Cara Cara navel orange (Citrus sinensis Osbeck)

Citrus is an important fruit crop as regards accumulation of carotenoids. In plant carotenoid biosynthesis, phytoene synthase gene (Psy) plays a key role in catalyzing the head-to-head condensation of geranylgeranyl diphosphate molecules to produce colorless phytoene. In the present paper, we reported the phytoene contents determination and characterization of Psy during fruit ripening of “Washington” navel orange and its red-fleshed mutant “Cara Cara”. Results showed that phytoene was exclusively accumulated in peel and pulp of “Cara Cara”. Although phytoene was observed accumulating with fruit ripening of “Cara Cara”, the contents in pulp were 10 times higher than those in peel. The isolated two Psy cDNAs were both 1520 bp in full length, containing 436 deduced amino acid residues, with a different amino acid at 412th. Genomic hybridization results showed that one or two copies might be present in “Cara Cara” and “Washington” genomes. During “Cara Cara” and “Washington” fruit coloration, expression of Psy was observed to be up-regulated, as revealed by tissue specific profiles in the flavedo, albedo, segment membrane and juice sacs. However, Psy expression in albedo of “Cara Cara” was higher than that in “Washington”, as evidenced by phytoene accumulation in the peel.     

Glutathione S-transferase T1 (GSTT1) and M1 (GSTM1) polymorphisms in a sample of the population in Northern Italy

Glutathione S-transferase is a group of multifunctional enzymes important in the metabolism of xenobiotics. GSTT1 and GSTM1 are polymorphic in human populations. Since a relation between polymorphism and cancer susceptibility has been found, their distribution in human populations is of great interest. In the present study the distribution of GSTT1 and GSTM1 genotypes was studied in a total sample of 252 individuals of three localities of northwest Italy (Postua, Cavaglià, and Biella) by PCR test. The frequencies of GSTT1 and GSTM1 “null” genotypes were respectively 7.94 and 34.92%. There are no significant differences between the populations studied in the GSTT1 “null” genotypes. On the other hand, for GSTM1 the frequency of gene deletion in Postua (25.5%) differs significantly (P < 0.01; χ² test) from that of Biella (46.32%), which on the other hand approaches the values indicated by most studies for Europeans (about 50%). The analysis of the frequencies of GSTT1 and GSTM1 polymorphisms among different age groups showed a lower frequency of negative genotypes in the older group, although not statistically confirmed. The text was submitted by the authors in English.     

Molecular-genetics analysis of natural and stimulated ovulation impairment

The influence of FMR1, INHα1, NAT2, GSTT1 and GSTM1 genes mutations on ovarian function and their association with POF and “poor response” to exogenous GT after ovulation stimulation were investigated. The carriers of Ala257Thr transition predominated in the studied “poor responders” group. In 1.6% POF patients and 2.5% persons from “poor responders” group, but nobody from control group this transition combined with intermediate alleles of FMR1 gene was observed. The frequency of deletion in GSTM1 gene in “poor responders” group was significantly higher (p = 0.01) than in normal ovulatory control group. The frequency of Ser680Ser-Ala307Ala polymorphic genotype (22.2%) in “poor responders” group was significantly higher (p = 0.028) than in normal-ovulatory control group (7.7%). The daily dosage of GT in intermediate alleles of FMR1 gene carriers as well in patients with “slow acetylation” NAT2 genotype was significantly higher in comparison to patients without intermediate alleles and patients with “quick acetylation” NAT2 genotype. Quantity of oocytes after stimulation ovulation in women with INHα1 gene Ala257Thr transition were significantly decreased in comparison to patients without such mutation. Further investigations of these genes can play a major role in POF studying and modulation of ovarian response to exogenous GT. Published in Ukrainian in Tsitologiya i Genetika, 2008, Vol. 42, No. 2, pp. 63–69. The text was translated by the authors.     

Dolichopteryx minuscula, a new species of spookfish (Argentinoidei: Opisthoproctidae) from the Indo-West Pacific

A new species Dolichopteryx minuscula is described on the basis of three specimens [49.4–59.6 mm in standard length (SL)] collected from the Indo-West Pacific. The new species is characterized by pouchlike eyes with a small lens (lens diameter 2.2% SL), an adipose fin, the anal fin base originating posterior to the dorsal fin base, and 16–17 (= 5–6 + 1 + 10–11) gill rakers. Total fecundity was relatively low, only 658 ova being obtained from one specimen, despite the ovary being mature. Ovarian eggs were clearly subdivided into “undeveloped” (0.1–0.7 mm diameter classes, n = 561) and “developed” (1.0–1.3 mm classes, n = 97) groups, based on their frequency distribution. Such relatively low fecundity and frequency distributions of ovarian eggs suggest that Dolichopteryx species spawn iteratively during spawning season.     

Is there a risk to living large? Large size correlates with reduced growth when stressed for knapweed populations

A central hypothesis in ecology is that plant life history evolution is constrained by fundamental “compromises between the conflicting selection pressures resulting from particular combinations of competition, stress, and disturbance”, with stress being defined as abiotic conditions that restrict production. Biogeographic differences among native and non-native ranges of invasive plants may provide unique opportunities for tests of this theory. We conducted a greenhouse experiment with Centaurea stoebe plants from North American and European populations. We compared the total biomass and phenotypic plasticity indices for plants from the native and non-native ranges under stressed and non-stressed conditions. The average size of Centaurea stoebe plants from 13 North American populations was greater than that of plants from 18 European populations regardless of stress treatment. However, when plants from the same populations were exposed to lower resources the differences in biomass between plants from North American and European populations were significantly less, suggesting that large plants were poorer stress tolerators. For all 31 populations the regression slope for the relationship between mean mass for populations in non-stressful conditions and mean mass in stressful conditions was less than 1.0, indicating that populations that produced large plants in good conditions also produced plants that grew disproportionately less in stressful conditions. These findings suggest that Centaurea stoebe may be evolving towards being a good “competitor” (sensu Grime, 1977) in its invasive range, but at the cost of being a good “stress tolerator”.