Cytogeography and genome size variation in the Claytonia perfoliata (Portulacaceae) polyploid complex

Background and Aims

Genome duplication is a central process in plant evolution and contributes to patterns of variation in genome size within and among lineages. Studies that combine cytogeography with genome size measurements contribute to our basic knowledge of cytotype distributions and their associations with variation in genome size.

Methods

Ploidy and genome size were assessed with direct chromosome counts and flow cytometry for 78 populations within the Claytonia perfoliata complex, comprised of three diploid taxa with numerous polyploids that range to the decaploid level. The relationship between genome size and temperature and precipitation was investigated within and across cytotypes to test for associations between environmental factors and nuclear DNA content.

Key Results

A euploid series (n = 6) of diploids to octoploids was documented through chromosome counts, and decaploids were suggested by flow cytometry. Increased variation in genome size among populations was found at higher ploidy levels, potentially associated with differential contributions of diploid parental genomes, variation in rates of genomic loss or gain, or undetected hybridization. Several accessions were detected with atypical genome sizes, including a diploid population of C. parviflora ssp. grandiflora with an 18 % smaller genome than typical, and hexaploids of C. perfoliata and C. parviflora with genomes 30 % larger than typical. There was a slight but significant association of larger genome sizes with colder winter temperature across the C. perfoliata complex as a whole, and a strong association between lower winter temperatures and large genome size for tetraploid C. parviflora.

Conclusions

The C. perfoliata complex is characterized by polyploids ranging from tetraploid to decaploid, with large magnitude variation in genome size at higher ploidy levels, associated in part with environmental variation in temperature.     

Female fertility per flower and trade-offs between size and number in Claytonia virginica (Portulacaceae)

A consistent and paradoxical feature in flowering plants is the production of many more flowers than appear required for female fertility through fruit and seed production. Many mechanistic hypotheses for this observation share key assumptions about (1) limited resources available for reproduction and (b) greater female fertility benefits from larger flowering-time investment. Here I investigate these assumptions in two populations of Claytonia virginica. I also test predictions from theoretical analyses, comparing patterns of flowering allocation and fertility per flower in 18 populations of C. virginica. Results support the assumption that larger benefits accrue from greater flowering-time investment. The between-population pattern of flowering allocation and fertility per flower is also consistent with theoretical expectation, although not statistically significant. Not supported is the assumption that reproduction occurs under strong resource constraint. Possible reasons for this discrepancy are discussed.     

Opposing natural selection from herbivores and pathogens may maintain floral-color variation in Claytonia virginica (Portulacaceae)

The maintenance of floral-color variation within natural populations is enigmatic because directional selection through pollinator preferences combined with random genetic drift should lead to the rapid loss of such variation. Fluctuating, balancing, and negative frequency-dependent selection mediated through pollinators have been identified as factors that may contribute to the maintenance of floral-color variation, and recently it has been suggested that indirect responses to selection on correlated characters through agents of selection other than pollinators may substantially shape the evolution of floral traits. Here, I provide empirical support for this latter view in Claytonia virginica (Portulacaceae) through a multiseason field study, a pollen supplementation study, and an artificial herbivory experiment. These studies show that most individuals fall into one of four discrete color classes, and suggest pollinator-mediated selection for increased floral redness in concurrent years. Floral color is also an indirect target of opposing directional selection via herbivores and pathogens that fluctuates through time. Taken together, these data suggest a novel mechanism by which floral-color variation may be maintained, and illustrate the importance of an inclusive, pluralistic view of selection when investigating the evolution of complex phenotypes.     

Systematics of the calyptridium umbellatum complex (Portulacaceae)

TheCalyptridium umbellatum complex (Portulacaceae), which has been treated as including from one to nine species, is shown to comprise three morphologically distinctive species. Two of these are common, wide-ranging, montane perennial herbs—C. umbellatum, which occurs over a large part of western North America, andC. monospermum, which largely replacesC. umbellatum in cismontane California. The third member of the complex is the rare or possibly extinctC. pulchellum. The perennial members of this complex are accorded the status of a separate genus,Spraguea, by most authors, but a comparative study of the morphology and karyology of all species ofCalyptridium shows this separation to be unwarranted. Chromosome numbers ofn = 22, obtained from eight populations ofC. umbellatum and six ofC. monospermum, constitute the first reported counts for these species. Hybridization studies involvingC. umbellatum andC. monospermum indicate that they are isolated by an incomplete noncrossability barrier.     

Phylogenetic and chemotaxonomic significance of diterpenes in some Portulaca species (Portulacaceae)

An instance is presented in which skeletal features of chemical constituents provide valuable information on the phylogenetic relationship in plant species. A close examination of diterpenoid constituents was carried out on three Portulaca species, each of which has a different basic chromosome number. Major diterpenoid constituents in P. cv. Jewel, P. pilosa and P. grandiflora were found to be, respectively, of the clerodane ([6.6]-fused ring), prinziane ([7.6]-fused ring) and portulane ([7.5]-fused ring) types. From a biosynthetic viewpoint, a linear evolutionary relationship among the Portulaca plants in question would be assumed. All the diterpenoids found in the above three species have 1,4-dihydroxy-2-buten-2-ylethyl side chains and the relevance of this feature for chemical systematics of Portulaca plants is pointed out.     

Rarity associated with specific ecological niches in the bacterial world: the 'Synergistes' example

The 'Synergistes' group, which apparently represents an as yet unnamed division of the bacteria, was explored in 93 anaerobic environments (guts, soils, digestors, etc.). From 16S rDNA gene-targeted polymerase chain reaction (PCR) assays, this group appeared to be present in 90% of the anaerobic microbial ecosystems analysed. The phylogeny of 103 16S rDNA sequences from 30 ecosystems showed a strong link between 16S rDNA sequences and given ecosystems. 'Synergistes' 16S rDNA sequences from animal sources (termites, guinea pigs, pigs, birds, etc.) formed clustered phylogenetical groups. 'Synergistes' groups were also associated either with anaerobic digestors and soils or with thermophilic conditions. Sequences available from the DNA database were consistent with the results. These results show the wide diversity of the 'Synergistes' division as well as the specific ecological niche of each 16S rDNA sequences.     

NicheA: creating virtual species and ecological niches in multivariate environmental scenarios

Robust methods by which to generate virtual species are needed urgently in the emerging field of distributional ecology to evaluate performance of techniques for modeling ecological niches and species distributions and to generate new questions in biogeography. Virtual species provide the opportunity to test hypotheses and methods based on known and unbiased distributions. We present Niche Analyst (NicheA), a toolkit developed to generate virtual species following the Hutchinsonian approach of an n‐multidimensional space occupied by the species. Ecological niche models are generated, analyzed, and visualized in an environmental space, and then projected to the geographic space in the form of continuous or binary species distribution models. NicheA is implemented in a stable and user‐friendly Java platform. The software, online manual, and user support are freely available at < http://nichea.sourceforge.net >.     

Floral ontogeny of five species ofTalinum and of related taxa (Portulacaceae)

The floral development of five species ofTalinum is studied. Each flower is surrounded by two involucral bracts. The perianth consists of five tepals initiated in a 2/5 phyllotaxis. In all species studied a first whorl of 10–13 stamens is initiated, except inT. napiforme where this whorl is reduced to five stamens. In multistaminate androecia, additional whorls develop centrifugally. InT. paniculatum, T. portulacifolium andT. napiforme the first stamens are initiated in pairs opposite the outer tepals. In several flowers ofT. paniculatum andT. portulacifolium ten stamens are incepted in spiral sequence resembling diplostemony. Similar ontogenetic patterns are present in several species ofPhytolacca. However, within the genusTalinum the ontogenetic pattern of the firstly initiated stamens is not consistent with traditional diplostemony. InT. triangulare the firstly initiated stamens are incepted in sectors on a ring meristem, resembling the early inception in several species ofAnacampseros andPortulaca. The nectaries are associated with the filament bases and can be defined as caducous nectaries of the staminal type. The development of the tricarpellate, syncarpous gynoecium is very similar in all species studied; it is characterised by a leptate carpel-form.     

Integrating coalescent-based species delimitation with ecological niche modeling delimited two species within the Stewartia sinensis complex (Theaceae)

Accurate species delimitation is the key to precise estimation of species diversity and is fundamental to most branches of biology. Unclear species boundaries within species complexes could lead to the underestimation of species diversity. However, species delimitation of species complexes remains challenging due to the continuum of phenotypic variations. To robustly examine species boundaries within a species complex, integrative approaches in phylogeny, ecology, and morphology were applied to the Stewartia sinensis complex (Theaceae) endemic to China. Multispecies coalescent-based species delimitation using 572 nuclear ortholog sequences (anchored enrichment) supported reciprocal phylogenetic monophyly of the northern lineage (NL) and southern lineage (SL), which were not sister clades. Niche equivalency and similarity tests demonstrated significant climatic niche differentiation between NL and SL with observed Warren et al.'s I = 0.0073 and Schoener's D = 0.0021. Species distribution modeling also separated their potential distribution. Morphometric analyses suggested significant interlineage differentiation of multiple traits including the ratio of length and width, leaf width, and pedicel length, although overall similarity did not differ. Based on the integrative species concept, two distinct species were proposed with legitimate names of Stewartia gemmata for SL and S. sinensis for NL. Our empirical study of the S. sinensis complex highlights the importance of applying multiple species criteria, in particular the underappreciated niche differentiation, to species delimitation in species complexes pervasive in plants.     

Evolution of seasonal ecological niches in the Passerina buntings (Aves: Cardinalidae)

The evolution of migration has long been considered complex and recent work has demonstrated additional complexity: some species follow the same ecological conditions throughout the year, whereas others 'switch niches' between breeding and wintering ranges. Hypotheses regarding the evolution of migration would generally predict niche-following as primitive, and niche-switching as derived. However, no test has, to our knowledge, yet determined the directionality of evolution of these states within a lineage. We present an analysis of phylogenetic dimensions of seasonal niches in the Passerina buntings that indicates greater evolutionary change in the niches of breeding populations than among those of wintering populations. These results are consistent with hypotheses of (i) niche conservatism (in winter, at least) across a recently speciated lineage; and (ii) the derived state of the breeding (rather than winter) ecological niches of each species.     

同地共栖四种蝙蝠食性和回声定位信号的差异及其生态位分化

本研究于 2 0 0 2年 5月初至 2 0 0 3年 9月中旬在北京房山区霞云岭四合村蝙蝠洞进行 ,分析了共栖同一山洞四种蝙蝠的形态特征、食性和回声定位信号。大足鼠耳蝠食谱中以宽鳍等三种鱼为主 (体积百分比为5 3% ) ,回声定位主频 4 1 87± 1 0 7kHz;马铁菊头蝠主要掠捕鳞翅目昆虫 (73% ) ,恒频叫声主频 74 70± 0 13kHz ;中华鼠耳蝠以近地面或在地表活动的鞘翅目昆虫步甲类和埋葬甲类为主要食物 (6 5 4 % ) ,声脉冲主频较低 35 73± 0 92kHz;白腹管鼻蝠捕食花萤总科和瓢虫科等鞘翅目昆虫 (90 % ) ,回声定位信号主频为 5 9 4 7±1 5 0kHz。结果证实同地共栖四种蝙蝠种属特异的回声定位叫声和形态结构的差异 ,以及不同的捕食生境和捕食策略 ,导致取食生态位分离是四种蝙蝠同地共栖的原因     

Stomatogenesis in the genus Portulaca L. (Portulacaceae)

The stomata in the six Indian species of Portulaca L. are paracytic and predominantly dicyclic, completely enclosed at their polar ends by the subsidiaries, and mesogenous dolabrate and basipetal in differentiation except in P. oleracea , where they are diffuse in origin. The subsidiaries of the outer cycle develop directly from the stomatal meristemoids. The leaves are amphistomatic except in P. quadrifida , where they are epistomatic. The stomata are mostly orientated at c. 90^o to the midrib of the leaf, but in P. oleracea they are irregularly orientated. The origin of the stomatal orientation appears to be genetically regulated rather than epigenetic. In Portulaca , as in some other angiosperms, the epidermal pattern of the costae is similar to that of the interstices, i.e. stomatiferous with nearly isodiametric cells. This is considered to be due to prevention by the thick chlorenchyma, characteristic of these plants, of the stomatal inhibitory stimuli originating in the vascular tissues from reaching the epidermis.     

Plasticity in the degree of CAM-cycling and its relationship to drought stress in five species of Talinum (Portulacaceae)

Summary The degree of CAM-cycling was examined in plants from 23 populations representing five morphologically similar species of Talinum to determine how CAM-cycling correlates with site aridity and drought stress. In the field, CAM-cycling, as indicated by the amount of malic acid accumulated in plant tissues overnight, and stable carbon isotope ratio (¹³C) were positively correlated with an index of site aridity. The relative levels of CAM-cycling and ¹³C values among populations in the field reversed when plants were grown under less arid conditions in a growth chamber such that populations with the highest average CAM-cycling and ¹³C in the field had the lowest averages in the growth chamber. In both cases, plants from all populations showed significantly higher levels of CAM-cycling under drought-stressed conditions relative to conditions known or predicted to be less arid. CAM-cycling was also positively correlated with tissue water content in both well-watered and drought-stressed plants, possibly reflecting greater water conservation associated with reductions in stomatal conductance. Biomass accumulation in plants exhibiting the greatest degree of CAM-cycling in the growth chamber was suppressed by drought stress to a similar degree as in the other plants, yet reproductive biomass of these plants was inhibited to a smaller degree. Thus, the importance of CAM-cycling increases in these species of Talinum during drought stress, due to increased malic acid accumulation overnight, potentially enhancing their water status, survival, and reproduction.     

Species of the Metarhizium anisopliae complex with diverse ecological niches display different susceptibilities to antifungal agents

Species of the Metarhizium anisopliae complex are globally ubiquitous soil-inhabiting and predominantly insect-pathogenic fungi. The Metarhizium genus contains species ranging from specialists, such as Metarhizium acridum that only infects acridids, to generalists, such as M. anisopliae, Metarhizium brunneum, and Metarhizium robertsii that infect a broad range of insects and can also colonize plant roots. There is little information available about the susceptibility of Metarhizium species to clinical and non-clinical antifungal agents. We determined the susceptibility of 16 isolates comprising four Metarhizium species with different ecological niches to seven clinical (amphotericin B, ciclopirox olamine, fluconazole, griseofulvin, itraconazole, tebinafine, and voriconazole) and one non-clinical (benomyl) antifungal agents. All isolates of the specialist M. acridum were clearly more susceptible to most antifungals than the isolates of the generalists M. anisopliae sensu lato, M. brunneum, and M. robertsii. All isolates of M. anisopliae, M. brunneum, and M. robertsii were resistant to fluconazole and some were also resistant to amphotericin B. The marked differences in susceptibility between the specialist M. acridum and the generalist Metarhizium species suggest that this characteristic is associated with their different ecological niches, and may assist in devising rational antifungal treatments for the rare cases of mycoses caused by Metarhizium species.     

Assassin bugs of the subfamily Diaspidiinae (Heteroptera: Reduviidae): distribution and potential ecological niches

The prediction and definition of the conditions for the potentially suitable ecological niche of the subfamily Diaspidiinae was the main goal of this study. Our research was based on 283 specimens of all known species of assassin bugs belonging to the subfamily Diaspidiinae stored in European museum collections and a set of 21 environmental variables in the form of a 1 × 1 km grid covering Africa and Madagascar. Based on occurrence localities, as well as a digital elevation model and layer of the tree cover‐continuous fields, information about the distribution of each species is given. Using Maxent software, potentially useful ecological niches were modeled, which allowed for the creation of a map of the potential distribution of the members of this subfamily and for determining their climatic preferences. A jackknife test showed that annual precipitation, annual temperature range and tree cover‐continuous fields were the most important environmental variables affecting the distribution of the subfamily Diaspidiinae. An analysis of climatic preferences suggested that the representatives of the subfamily were linked mainly to the tropical climate. An analysis of environmental variables also showed that the subfamily preferred areas with herbaceous vegetation and some trees, and this preference is probably caused by the food preferences of their prey. On the basis of the museum data on the species occurrence, as well as ecological niche modeling methods, we provided new and valuable information on potentially suitable habitat and the possible range of distribution of the subfamily Diaspidiinae along with its climatic preferences.     

Divergence in coloration and ecological speciation in the Anolis marmoratus species complex

Adaptive divergence in coloration is expected to produce reproductive isolation in species that use colourful signals in mate choice and species recognition. Indeed, many adaptive radiations are characterized by differentiation in colourful signals, suggesting that divergent selection acting on coloration may be an important component of speciation. Populations in the Anolis marmoratus species complex from the Caribbean island of Guadeloupe display striking divergence in the colour and pattern of adult males that occurs over small geographic distances, suggesting strong divergent selection. Here we test the hypothesis that divergence in coloration results in reduced gene flow among populations. We quantify variation in adult male coloration across a habitat gradient between mesic and xeric habitats, use a multilocus coalescent approach to infer historical demographic parameters of divergence, and examine gene flow and population structure using microsatellite variation. We find that colour variation evolved without geographic isolation and in the face of gene flow, consistent with strong divergent selection and that both ecological and sexual selection are implicated. However, we find no significant differentiation at microsatellite loci across populations, suggesting little reproductive isolation and high levels of contemporary gene exchange. Strong divergent selection on loci affecting coloration probably maintains clinal phenotypic variation despite high gene flow at neutral loci, supporting the notion of a porous genome in which adaptive portions of the genome remain fixed whereas neutral portions are homogenized by gene flow and recombination. We discuss the impact of these findings for studies of colour evolution and ecological speciation.