Invasion dynamics of two alien Carpobrotus (Aizoaceae) taxa on a Mediterranean island: II. Reproductive strategies

This study compares sexually and asexually produced fruit set, seed production, biomass, germination, and seedling size in Carpobrotus acinaciformis and C. edulis following controlled pollination experiments in order to evaluate the potential role of reproductive traits with respect to the invasive potential of these taxa. C. edulis is slightly agamospermic, completely self-fertile, slightly preferentially self-compatible, experiences no inbreeding depression, and has low hybrid vigour. In contrast, C. acinaciformis does not have reliable agamospermy, is only slightly self-fertile and self-compatible, experiences a slight inbreeding depression, and has a strong hybrid vigour. Both taxa have relatively low, although significantly different germination frequencies, and insignificantly different seedling sizes. Owing to the high performance in hybridisation as compared to all other controlled pollinations in C. acinaciformis, as well as a large amount of previously demonstrated introgression, we refer to the population studied on the island of Bagaud (France) as C. affine acinaciformis. We conclude that both C. edulis and C. affine acinaciformis should be considered as harmful invasive plants in the Mediterranean Basin, the former because of the flexibility of its mating system and high seed production, and the latter because of its strong clonality, high hybrid vigour, and potential for continued introgression from C. edulis genes. These differences require different control strategies, while the avoidance of sympatry is a distinct priority.     

Invasion dynamics of two alien Carpobrotus (Aizoaceae) taxa on a Mediterranean island: I. Genetic diversity and introgression

This study, based on morphological and isozyme analysis, clearly discriminates two invasive Carpobrotus taxa, C. edulis and C. acinaciformis, in the Hyères archipelago off the southeastern coast of France. However, three different allelic combinations demonstrate the presence of intermediate individuals resulting from an introgression of part of the C. edulis genome into that of C. acinaciformis. Both taxa have higher than average genetic (C. edulis: P(0.95)=62.5%, A=2.25+/-0.70, H(o)=0.329+/-0.324; C. acinaciformis: P(0.95)=75%, A=2.38+/-0.42, H(o)=0.645+/-0.109) and clonal diversities (C. edulis: IP=0.37; C. acinaciformis: IP=0.48). Furthermore, C. acinaciformis has an excess of heterozygotes (F=-0.585+/-0.217), probably due to introgression. The relationship between the probability of clonal identity for two individuals and distance indicates that C. acinaciformis relies more on clonal reproduction than on sexual recruitment (seed recruitment/vegetative propagation=u/v=0.027), in contrast to C. edulis, whose probability of clonal identity did not vary with distance. The overwhelming clonal growth and high genetic diversities of C. acinaciformis and the previously recorded invasion potential for C. edulis raises concern for intensified invasion via hybridisation.     

Unexpected insularity effects in invasive plant mating systems: the case of Carpobrotus (Aizoaceae) taxa in the Mediterranean Basin

Although biological invasions are currently recognized as being especially severe on islands, little attention has been given to detecting parameters influencing this pattern. This study tested the common perceptions that uniparental reproductive modes are associated with invasive and/or island plant populations due to a lack of pollinator vectors and/or small initial population sizes, and that pollinator services and biparental seed production modes will subsequently be associated with adjacent mainland sites. Using controlled pollination and germination experiments on invasive Carpobrotus edulis and C.  aff. acinaciformis populations in both island and mainland habitats in south-east France, we found no evidence to support these hypotheses. All significant mean differences found between locations for reproductive indices describing uniparental reproductive modes were significantly smaller in island populations. In contrast, seedling sizes issuing from manual outcrossing and manual hybridization experiments, regardless of taxon, as well as C.  aff.  acinaciformis hybridization indices, were larger in island populations. The presence of significant, though limited, pollinator service was detected for all populations, and stressed the importance of such mutualisms. We suggest that invasive plant reproductive traits could be highly contextual, and that islands may have a potential role in the acceleration of the invasion process through the production of highly variable populations.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 65–79.     

Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in California. I. Morphological evidence

Individuals of the invasive non-native plant species Carpobrotus edulis, its native or naturalized congener C. chilensis, and putative hybrids are found throughout coastal California. This study characterized morphological variation within the genus and assessed the extent of hybridization and direction of introgression between C. edulis and C. chilensis. Twelve randomly selected Carpobrotus individuals from each of 49 sample locations were classified as "C. edulis," "C. chilensis," or one of three intermediate morphotype classes, and compared for clonal, vegetative, and fruit characters. Univariate comparisons showed that C. edulis individuals had deeper mats with more cover within the mat boundary, longer, wider, more serrate leaves, and wider fruits with more carpels than intermediate and C. chilensis morphotype classes. Carpobrotus edulis and intermediates had more lateral branches than did C. chilensis, suggesting that hybrids tend to vary toward C. edulis. Discriminant function analysis (DFA) identified the following characters as discriminating significantly among Carpobrotus groups: leaf length, leaf width, leaf length/width, number of lateral branches, number of carpels, and fruit diameter. Using these characters, DFA correctly classified 98% of apparently pure C. edulis and C. chilensis, but only 76% of all Carpobrotus individuals when putative hybrids were included. Principal components analysis showed that C. edulis and C. chilensis cluster into distinct morphotypes, but that hybrids overlap with both groups, particularly with C. edulis. The genus Carpobrotus in California resembles a large hybrid swarm, with putative hybrids forming a large portion of the overall population and tending to vary toward C. edulis.     

Hybridization and introgression in Carpobrotus spp. (Aizoaceae) in California. II. Allozyme evidence

Morphological evidence has indicated that hybridization and introgression are occurring between Carpobrotus edulis L., a nonindigenous, invasive species in California (Bolus), and its putative native congener, C. chilensis. The identification of allozyme markers has enabled us to quantify hybridization and the extent of introgression between these species. Samples from 20 individuals of each of five morphological types (both parent species and three hybrid phenotypes) were collected from 39 populations along the coast of California from the Mexico to Oregon borders. Ten enzyme systems revealed a total of 17 resolvable loci, eight of which were polymorphic for the genus. Five of the polymorphic loci easily differentiate C. edulis and C. chilensis. Allele frequencies among the morphologically defined types are consistent with estimations of allele frequency changes due to first- and second-generation backcrossing. In comparison to long-lived, herbaceous perennials and widespread species, C. edulis and intermediate types have more variation in their populations (P = 41.73, Ap = 2.11, Ho = 0.246, and P = 38.13, Ap = 2.06, Ho = 0.216, respectively) than C. chilensis (P = 11.76, Ap = 2.00, Ho = 0.082). Indirect estimates of gene flow indicate four of the five morphological types are outcrossing. Gene flow between previously allopatric species may have broad implications if it results in an increase in fitness; further experimentation is needed to determine the ultimate ecological consequences of this phenomenon and its possible threat to limited, remaining natural habitat in California.     

Genetic variation and phylogeographic analyses of two species of Carpobrotus and their hybrids in California

Despite the commonality and study of hybridization in plants, there are few studies between invasive and noninvasive species that examine the genetic variability and gene flow of cytoplasmic DNA. We describe the phylogeographical structure of chloroplast DNA (cpDNA) variation within and among several interspecific populations of the putative native, Carpobrotus chilensis and the introduced, Carpobrotus edulis (Aizoaceae). These species co-occur throughout much of coastal California and form several 'geographical hybrid populations'. Two hundred and thirty-seven individuals were analysed for variation in an approximate 7.0 kb region of the chloroplast genome using PCR-RFLP (polymerase chain reaction - restriction fragment length polymorphism) data. Phylogenetic analyses and cpDNA population differentiation were conducted for all morphotypes. Historic geographical dispersion and the coefficient of ancestry of the haplotypes were determined using nested clade analyses. Two haplotypic groupings (I and II) were represented in C. chilensis and C. edulis, respectively. The variation in cpDNA data is in agreement with the previously reported allozyme and morphological data; this supports relatively limited variation and high population differentiation among C. chilensis and hybrids and more wide-ranging variation in C. edulis and C. edulis populations backcrossed with C. chilensis. C. chilensis disproportionately contributes to the creation of hybrids with the direction of gene flow from C. chilensis into C. edulis. The cpDNA data support C. chilensis as the maternal contributor to the hybrid populations.     

Phylogeny of Australian Coptotermes (Isoptera: Rhinotermitidae) species inferred from mitochondrial COII sequences

Six Australian species of Coptotermes are traditionally recognized, but recent cuticular hydrocarbon studies suggest that some of these may represent more than one species. An understanding of the phylogenetic diversity of Australian Coptotermes, particularly the pest species, is likely to be important for the improvement of termite management strategies. A study of phylogenetic relationships among species of this genus was performed, based on the mitochondrial cytochrome oxidase (COII) gene, comparing the data with recent data from Asian species. Representatives of the species C. lacteus (Froggatt), C. frenchi Hill and C. michaelseni Silvestri were each found to form closely related monophyletic groups, however representatives of C. acinaciformis (Froggatt) were not. For C. acinaciformis, representatives from northern mound-building populations were found to form a distinct group to southern, tree-nesting forms. Among southern C. acinaciformis, two Western Australian representatives were found to be divergent from other populations. The results suggest that C. acinaciformis probably represents a complex of species rather than one, as has been suggested previously. One unidentified Coptotermes sp. taxon from Melbourne was found to be divergent from other taxa. Notably, some Australian species were more closely related to Asian species than other Australian species.     

Germination and growth responses of hybridizing Carpobrotus species (Aizoaceae) from coastal California to soil salinity

Germination, growth, and physiological responses of hybridizing Carpobrotus from coastal California to soil salinity were studied. Hybrids are presumably the result of hybridization and introgression between the exotic Carpobrotus edulis, a succulent perennial invading coastal habitats, and the native or long-naturalized C. chilensis. Germination responses were investigated at 0, 10, 20, and 50% seawater. Seedling growth and physiology were compared by irrigating seedlings with solutions of the same seawater concentrations and in low and high nutrients. Germination was inhibited in the presence of salt, but recovered after transferring the seeds to fresh water. Seeds exposed to salt had higher final germination rates than control. Growth of Carpobrotus was slightly enhanced by low seawater concentrations but reduced at high salinity at both nutrient regimes. Leaf cell sap osmolarity increased with increasing soil salinity, and taxa did not differ significantly in this physiological adjustment. Leaf carbon isotope ratios (∂¹³C) ranged from −28 to −22‰ and became less negative at higher salinities, indicating an improved water use efficiency in the seedlings at high salt concentrations. In addition, ∂¹³C values were generally less negative at high than at low nutrients. Differences among taxa were generally small. The results show that salinity affects both establishment and growth of hybridizing Carpobrotus. The overall weak species differences in salt tolerance indicate that the exotic C. edulis can occupy the same sites as C. chilensis in terms of salinity. The similarity of hybrids in their response to salinity suggests that they may contribute to the invasion by Carpobrotus.     

Effect of physiological integration in self/non-self genotype recognition on the clonal invader Carpobrotus edulis

Aims Biological invasions represent one of the most important threats to the conservation of biodiversity; however, the mechanisms underlying successful invaders remain unsolved. Many of the most aggressive invaders show clonal growth, and capacity for clonal integration has been pointed out recently as an important trait explaining the success of invasive plants. We aim to determine the role of physiological integration in the capacity for self/non-self genotype recognition in the clonal invader Carpobrotus edulis and the implications of this capacity for the expansion of this aggressive invader.Methods We used connected and severed ramets of identical or different genotype and we determined the capacity for self/non-self recognition by comparing changes in biomass partitioning to avoid competition for resources between pairs of ramets.Important findings Physiological integration allowed self/non-self genotype recognition in the invader C. edulis. Results showed a significant effect of physiological integration on the biomass allocated to roots by genetically identical ramets: older ramets specialize in acquisition of soil-based resources and younger ramets specialize in lateral expansion. This specialization could be considered a form of division of labour, which reduce intra-genotype competition. This is the first evidence that division of labour could be interpreted as a form of self/non-self recognition between genetically identical ramets. Capacity for self/non-self discrimination could contribute to increase the colonization capacity of the aggressive invader C. edulis. This is the first study showing an association between self/non-self recognition and invasiveness in a clonal plant.     

Presence of Hemitragus aff. cedrensis (Mammalia, Bovidae) in the Iberian Peninsula: Biochronological and biogeographical implications of its discovery at Bolomor Cave (Valencia, Spain)

The discovery of new material in Late Pleistocene levels at Bolomor Cave (Valencia, Spain) raises some questions about the presence of the most ancient record of Hemitragus cedrensis in the peninsula, and its dispersal out of Provence. The morphology and dimensions of some lower teeth confirm the identification of H. aff. cedrensis. Moreover, it presents strong similarities, both morphological and metrical, with the specimens from Caune de l’Arago and bau de l’Aubesier (end of OIS 7 to OIS 5e) rather than with the population from the eponymous locality. The data suggest a dispersal event out of Provence towards the Iberian Peninsula during the Eemian. This dispersal was not stopped by natural barriers such as large rivers, or mountains. The results presented here confirm the biochronological interest of the genus Hemitragus for the Late Pleistocene in Mediterranean Europe.     

The evolutionary potential of invasive Carpobrotus (Aizoaceae) taxa: are pollen-mediated gene flow potential and hybrid vigor levels connected?

Few studies have addressed the importance of native pollinators in shaping the breeding systems and evolutionary potential of invasive plants. We examined the pollination and gamete production of Carpobrotus affine acinaciformis (L.) L. Bol. and C. edulis (L.) N. E. Br. invading the coasts of southeast France (Provence), and found preliminary evidence that the pollen-mediated gene flow potential (PMGFP) within the four studied populations is positively correlated with their Relative Performance in Hybridization indices (RP_H), suggesting a link between pollinator services, gene flow, and Carpobrotus hybridization. Flower density (FD) may be a driver behind pollinator abundance and visitation patterns since it shows a significant, positive relationship with relative pollinator abundance (FR) and a significant negative relationship with per flower visit frequencies (FR/F). In the populations with the highest RP_H indices, and therefore high hybrid vigor, both taxa produce similar quantities of ovules and pollen per flower, whose ratios further indicate (facultative) xenogamy. Pollen diameter distributions include ∼25% micro-pollen, and overall viability is less than one half. Viable pollen profiles consist of 3.5% micro, 85.5% normal and 10.9% macro pollen (considered as diplogametes) on average per flower for C. affine acinaciformis, and 0.7% micro, 73.0% normal and 26.2% macro pollen for C. edulis. Given the co-occurrence of (1) (facultative) xenogamic breeding strategies, (2) a significant, positive relationship between RP_H and PMGFP, and (3) frequent pollen abnormalities, it is probable that hybrid dysgenesis mediated by the local pollinators occurs in these populations. Furthermore, the unusually high frequency of potentially viable, diploid macro-pollen underlines the evolutionary/polyploid potential of these invasive, introgressed populations. Native pollinator interactions may greatly affect the taxonomic status and evolutionary potential of invasive plant complexes.     

Are some communities of the coastal dune zonation more susceptible to alien plant invasion?

Aims Coastal areas, and in particular coastal dunes, are ecosystems strongly affected by the invasion of alien plants. However, few attempts have ever been made to quantify alien species incidence in different communities along the coastal zonation. This work aims to analyze the distribution of alien plants along the coastal zonation of sandy shores on the Tyrrhenian coast, addressing specifically differences among plant communities in abundance of alien plants.Methods The study was performed on recent dunes (Holocene) of the central western coast of Italy. We selected dune landscapes where invasion processes were particularly evident. Vegetation plots were randomly sampled and through cluster analysis, we identified six plant communities corresponding to the typical zonation described for the Tyrrhenian sandy coast of Central Italy. We evaluated and compared frequency and abundance of invasion in these different communities. Further, we investigated how propagule pressure (measured using as proxy human structures) contributed to the observed invasion patterns.Important findings We found a relatively low total number of aliens but also a differential distribution pattern and strong abundance of some of the aliens in specific sectors of the vegetation zonation. The perennial community of transition dunes appears most affected by invasion processes, related almost exclusively to the frequent and widespread Carpobrotus aff. acinaciformis. This alien species reaches high cover values, apparently lowering cover of native species of transition dune plant communities. Higher levels of invasion in the transition dune can be partially explained because of greater propagule pressure in this section of the dune profile. Our findings thus have important conservation and management implications since transition dune communities with Crucianella maritima are rare and protected (sensu Habitat 92/43/EEC Directive) along the entire Italian coast.     

Karyology, generic delineation and dysploidy in the genera Carduncellus, Carthamus and Phonus (Asteraceae)

Within the Mediterranean complex Carduncellus Carthamus Phonus , taxonomic classification has proven problematical. A recent molecular analysis has clarified the generic delineation, while a revision of the abundant karyological data has suggested that correlation of taxonomic classification and karyology would be of great interest. In this paper, a confirmation of chromosome numbers in the complex is offered, with 44 populations of 30 taxa studied. Six of the counts are new. A short analysis of the correlation between base chromosome numbers and generic classification follows. The main conclusion is that descending dysploidy is the main mechanism of karyological evolution in the complex, as has been the case in other genera of the subtribe.     

Speciation by host-switching in pinyon Cinara (Insecta: Hemiptera: Aphididae)

Parasite-host cospeciation has received much attention as an important mechanism in the diversification of phytophagous insects. However, studies have shown that for certain taxa, it is not host fidelity but host-switching that plays the critical role in speciation. Cinara are aphids (Insecta: Hemiptera: Aphididae: Lachninae) that feed exclusively on the woody parts of conifers of the Cupressaceae and Pinaceae. They are unusual aphids because most Pinaceae play host to several species of Cinara. The aphids show relatively strong host fidelity, and as a consequence historically have been treated based on the taxonomy of their hosts. The historical paradigm of aphid evolution implies that Cinara species have radiated to different parts of the same host species and/or speciated with their host. Using mitochondrial cytochrome oxidase 1 and nuclear elongation factor 1-alpha DNA sequences, we performed molecular phylogenetic analysis of Cinara species, concentrating on those associated with pinyon pines in the southwestern USA. We determined that switching hosts has played a key role in the speciation of the genus, reflected in the polyphyly of pinyon-feeding Cinara. Furthermore, species sharing a common feeding site on different hosts were more closely related to each other than to those sharing the same host but at different feeding sites, suggesting that feeding site fidelity plays a more important role in speciation than does host fidelity in general. This study also elucidated the primary taxonomy of various species: it suggested that Cinara rustica Hottes is a junior synonym of C. edulis (Wilson) and that C. wahtolca Hottes represents two species on the two different pinyon pine species, Pinus edulis Englem. and P. monophylla Torr. & Frem.     

Systematic significance of cytology in Cyananthus (Campanulaceae) endemic to the Sino-Himalayan region

Chromosome numbers and the morphology of members of 24 populations representing 15 species of the Sino-Himalayan endemic genus Cyananthus(Campanulaceae) were studied using karyological and numerical taxonomic techniques. The chromosome numbers of these taxa are 2n = 10, 12, 14, 24, 28, and the basic chromosome numbers for the genus are x = 5, 6, 7. All species except C. inflatus Hook. f. & Thoms. and C. microphyllus Edgew. were examined for the first time and a new ploidy level (tetraploidy) is reported in the genus. Chromosome measurement data were analyzed using cluster analysis. The relationships between three sections within Cyananthus and evolutionary trends within the genus are discussed in the light of karyological data. The cytological data suggest that Cyananthus is a relatively primitive genus in Campanulaceae and there is significant division within the genus, and polyploidization may have played an important role in the chromosome evolution and speciation of Cyananthus in the Himalayan–Hengduan Mountains.     

A new species of Cardamine subgen. Dentaria (Cruciferae), apoendemic in Calabria (Southern Italy)

ABSTRACT

Cardamine battagliae Cesca & Peruzzi sp. nova is related to Cardamine heptaphylla (Vill.) O. E. Schulz. (2n = 48). On the other hand, the new species is well distinguished both from a morphological and karyological point of view. Because of its distribution and high ploidy level (2n = ca. 160) C. battagliae can be considered as a new apoendemic taxon. Morphological and karyological data are presented and discussed.     

Variation of DNA amount in 47 populations of the subtribe Artemisiinae and related taxa (Asteraceae, Anthemideae): karyological, ecological, and systematic implications.

Genome size has been estimated by flow cytometry in 47 populations of 40 species of the tribe Anthemideae (Asteraceae), mainly from Artemisia and other genera of the subtribe Artemisiinae and related taxa. A range of 2C values from 3.54 to 21.22 pg was found. DNA amount per basic chromosome set ranged from 1.77 to 7.70 pg. First genome size estimates are provided for one subtribe, 10 genera, 32 species, and two subspecies. Nuclear DNA amount correlated well with some karyological, physiological and environmental characters, and has been demonstrated as a useful tool in the interpretation of evolutionary relationships within Artemisia and its close relatives.     

Contributions to the karyological study of the genus Ranunculus L. subgenus Batrachium (DC.) A Gray from the Iberian Peninsula

DIOSDADO. J. C, PASTOR, J. E. & VALDÉS, B. 1993. Contributions to the karyological study of the genus Ranunculus L. subgenus Batrachium (DC.) A. Gray from the Iberian Peninsula. The somatic and gametic chromosome numbers and detailed chromosome morphology are presented for eight taxa of aquatic ranunculi from the Iberian Peninsula. Within the subgenus Batrachium diploid and tetraploid levels have been observed (2 n = 16, 32) the commoner of which is the diploid. From the karyological data relationships have been established between the subgenus Batrachium and subgenus Ranunculus.     

Ranunculus cacuminis andR. crenatus,representatives of theR. alpestris-group (Ranunculaceae) on the Balkan Peninsula

Morphological and karyological investigations as well as crossing experiments were carried out withR. cacuminis, R. crenatus, andR. alpestris. A key is presented including all 6 taxa of theR. alpestris-group. Ecological and geographical data for the Balkan Peninsula are also presented.R. cacuminis is diploid with 2n = 16 chromosomes as all taxa of the group, its karyotype exhibits no statistically significant differences to those from the 5 other taxa. In crossing experiments betweenR. cacuminis andR. alpestris, no hybrids could be obtained, whereas those betweenR. cacuminis andR. crenatus were slightly successful. According to its morphology, geographical distribution, and crossing behaviour,R. cacuminis is closely related toR. crenatus, and probably has originated fromR. crenatus by quantum speciation.     

Evidence of functional and structural changes in the microbial community beneath a succulent invasive plant in coastal dunes

海岸沙地肉质入侵植物对微生物群落功能与结构变化的影响 海岸沙地提供了诸多宝贵的生态系统服务，例如耕地保护、水分供应和生物多样性保护，因此海岸沙地代表了重要的栖息地保护区。因为海岸沙地环境恶劣、水资源匮乏、养分贫瘠，所以土壤微生物群落对维持植物多样性至关重要。就海岸沙地的生态系统保护而言，外来入侵植物是主要威胁。本文探讨了沿海地区入侵植物食用日中花(Carpobrotus edulis)对细菌群落功能及结构的各种影响。沙地中土壤有机质含量低，微生物活性有限，所以沙地是一种颇具挑战性的底物。因此，在评估食用日中花对生态系统的影响之前需要对细菌提取进行优化，并开展功能评估。本文首先从群落水平生理特征(CLPP)的角度，比较了采用不同土壤储量、样品量、提取液等12种提取方法对沙地群落功能活性的影响，然后又探讨了食用日中花入侵的沙地菌落功能(利用Biolog Ecoplates)与结构变化(利用PCR-DGGE)。血细胞计数发现盐溶液持续增殖了细菌细胞(P ≤ 0.001)。主成分分析(PCA)结果显示，在有限时间框架(0–24 h)内，碳底物消耗没有显著变化。通过对比天然区与非天然区(种间)及天然区(种内)之间食用日中花入侵后的变化，发现了一种与众不同的碳底物利用模式，食用日中花入侵对群落功能的影响因地而异，而与之相辅相成的是，PCR-DGGE结果表明原沙地的菌落结构不同于食用日中花入侵后沙地的菌落结构。