Xenococconeis opunohusiensis gen. et sp. nov. and Xenococconeis neocaledonica comb. nov. (Bacillariophyta) from the tropical South Pacific

During a survey of the coral reef diatoms of Moorea Island (Society Archipelago, South Pacific) a small‐sized member of the order Achnanthales was studied using a light microscope (LM) and a scanning electron microscope (SEM). This marine taxon has: a raphe valve (RV) with a non‐crenulate edge; a high cingulum; a sternum valve (SV) often irregularly striated and areolae with concave hymenate pore occlusion; a thick and plain SV valvocopula (SVVC), ring‐shaped, composed of large fused fimbriae, with a central elliptic foramen bordered by the peg‐like edge of the fimbriae. On abvalvar side, the SVVC bears radiate concave and robust transapical ribs, interlinking with short elevated transverse ribs of the RV valvocopula (RVVC). Large marginal fenestrae of the RVVC give access to pseudoloculi. One oblong, unique and striated papilla is located on each RVVC rib. Given this unique set of features, we describe Xenococconeis opunohusiensis gen. et sp. nov. as a new taxon belonging to the Achnanthales. The characteristics of the new taxon are compared with Campyloneis Grunow and Cocconeis Ehrenberg. From New Caledonia, Cocconeis neocaledonica Maillard ex Lange‐Bertalot et Steindorf, a freshwater diatom, was described with two internal septa with marginal pseudoloculi. Based on subsequent SEM illustrations and remarks, we propose the transfer of C. neocaledonica to the new genus, and compare it to the type species, Xenococconeis opunohusiensis.     

Factors controlling the population dynamics of the clonal helophyte Ranunculus lingua

Abstract. Two marginal and two central populations of the pseudo-annual aquatic plant Ranunculus lingua were studied over four years. The main purpose was to quantify potentially influential abiotic and biotic factors and to derive predictions about life-history differences between the populations. Variation in abundance and height of R. lingua ramets at different depths were related to water-level fluctuations, to abundance of other helophyes (emergent macrophytes), and to the occurrence of invertebrate grazing and fungal pathogens. Clear differences between marginal and central populations were shown in the depth distribution of ramet numbers and ramet heights, as well as in the dynamic patterns, where marginal populations had a higher flux of ramets. These patterns and regression analyses indicated that abiotic factors have a greater influence in marginal populations, whereas biotic factors are more important in central populations. It is suggested that marginal habitats for R. lingua would favour life-histories with a high reproductive capacity, whereas a large size of ramet would be the most important life-history feature in central habitats. This was supported by the fact that ramets in marginal populations, in spite of their smaller size, produced higher number of rhizomes than ramets in central populations. Variation in regional abundance was finally related to differences in demographic processes and dispersal potential between the populations.     

High levels of genetic diversity in marginal populations of the marsh orchid Dactylorhiza majalis subsp. majalis

Because of harsh conditions, suboptimal habitat quality and poor connectivity to other populations, plant populations at the margin of a distribution are expected to be less genetically diverse, but to be more divergent from each other than populations in the centre of a distribution. In northern Europe, northern marginal populations may also be younger than populations further to the south, and may have had less time to accumulate genetic diversity by mutation and gene flow. However, orchids have very small seeds, which are easily dispersed long distances by wind, and orchids are therefore expected to show less differentiation between marginal and central populations than other groups of seed plants. Here, we analysed whether Scandinavian populations of the tetraploid marsh orchid Dactylorhiza majalis subsp. majalis differ from central European populations in genetic diversity patterns. A total of 220 plants from eight central European and ten Scandinavian populations was examined for variation at five nuclear microsatellite loci, nuclear ITS and 13 polymorphic sites in noncoding regions of the plastid genome. The total genetic diversity was slightly lower in Scandinavia than in central Europe, both in plastid and nuclear markers, but the differences were small. Also, the Scandinavian populations were less diverse and somewhat more strongly differentiated from each other than the central European ones. Dactylorhiza majalis subsp. majalis has apparently colonized Scandinavia on multiple independent occasions and from different source areas in the south. Seed flow between Scandinavian populations has still not fully erased the patterns imprinted by early colonization. Our results suggest that marginal populations of orchids may be as important as central ones in preserving genetic diversity through Pleistocene glacial cycles. We also predict that orchids with their light seeds are better adapted than many other plants to respond to future climate changes by dispersing into new suitable areas.     

Chloroplast population genetics reveals low levels of genetic variation and conformation to the central–marginal hypothesis in Taxus wallichiana var. mairei,an endangered conifer endemic to China

The central–marginal hypothesis predicts that geographically peripheral populations should exhibit reduced genetic diversity and increased genetic differentiation than central populations due to smaller effective population size and stronger geographical isolation. We evaluated these predictions in the endangered conifer Taxus wallichiana var. mairei. Eight plastid simple sequence repeats (cpSSRs) were used to investigate plastid genetic variation in 22 populations of Taxus wallichiana var. mairei, encompassing nearly its entire distribution range. Low levels of plastid genetic variation and differentiation were detected in the populations, and the findings were attributed to low mutation rates, small population sizes, habitat fragmentation and isolation, and effective pollen or seed dispersal. Hunan and Hubei were identified as major refugia based on the number of private haplotypes and species distribution modeling. Trends in plastid genetic diversity and genetic differentiation from central to peripheral populations supported the predictions of the central–marginal hypothesis. In scenarios wherein the future climate becomes warmer, we predict that some peripheral populations will disappear and southern and southeastern regions will become significantly less habitable. Factors that include the levels of precipitation during the driest month, annual precipitation level, and annual temperature range will be decisive in shaping the future distribution of these populations. This study provides a theoretical basis for the conservation of T. wallichiana var. mairei.     

MORPHOLOGICAL AND GENETIC VARIATION IN ECOLOGICALLY CENTRAL AND MARGINAL POPULATIONS OF RUMEX ACETOSELLA L. (POLYGONACEAE)

Six ecologically central (old field) and marginal (strip mine) populations of the hexaploid Rumex acetosella were collected, grown under uniform conditions, and examined for genetic and morphological variation. Extensive electrophoretic variation was found in alcohol dehydrogenase and phosphoglucose isomerase, while other enzymes surveyed showed little or no variation. Hedrick's genotypic measure of identity revealed mean values of 0.506 for central populations, 0.836 for marginal populations, and 0.633 for comparisons of central with marginal populations. Alcohol dehydrogenase phenotypes had significantly fewer electromorphs per individual in marginal populations. Clones of individuals from both environments were subjected to different watering regimes. No significant differences in root/shoot ratio, leaf number, total leaf area, or relative growth rate were found between strip mine and old-field individuals within each watering treatment, although significant differences were found between watering treatments. There are small, but significant amounts of isozyme differentiation between central and marginal populations, while there was no such differentation for morphological characters.     

Morphologic variation in northern marginal Juniperus oxycedrus L. subsp. oxycedrus populations in Istria

Marginal tree populations are believed to be more differentiated and host less variation than central tree populations. The aim of this study was to perform a detailed morphometric study of J. oxycedrus L. subsp. oxycedrus in northern marginal populations in order to establish its phenotypic variation and geographical differentiation and to examine the eventual presence of putative species J. deltoides in Istria. Morphologic variation was studied in 16 northern marginal populations in Istria. Nine morphological traits from a minimum of 50 leaves from each of 206 individuals and two morphological traits from 30 to 50 seed cones in each of 103 females were measured. Phenotypic variation in Istrian populations was high and of a similar magnitude to that found in the centre of the distribution area. Gender dimorphism in leaf morphology was detected, but the study failed to confirm its uniform distribution pattern. Significant and surprisingly high among-population differentiation (8–30%) was revealed. Average leaf shape in the study area is clearly “delta-shaped” characterised by a relatively wide leaf base. However, no significant differences in any of the studied traits were found between the marginal Istrian populations and the more central populations analysed in our earlier studies.     

THE GENUS THALASSIOSIRA (BACILLARIOPHYCEAE): MORPHOLOGY OF HETEROVALVATE RESTING SPORES OF T. SCOTIA

Resting spores of Thalassiosira scotia Fryx. et Hoban were abundant in phytoplankton net hauls collected from the Scotia Sea south of South Georgia in December 1981. Primary valves are distinguished from secondary valves by the presence of marginal striae with rounded, shoelike protrusions, villi surrounding marginal areolae and marginal striae, greater numbers of central strutted processes, and differences in structure of occluded processes. Densities of marginal strutted processes also tend to differ, though ranges overlap. Thalassiosira scotia is most closely related to T. antarctica, differing from that taxon by having coarser areolation, heavier silicification, and more prominent occluded processes. Rudimentary valves of T. scotia differ from those of T. antarctica.     

Large‐scale patterns in genetic variation,gene flow and differentiation in five species of European Coenagrionid damselfly provide mixed support for the central‐marginal hypothesis

Recently, an increased effort has been directed towards understanding the distribution of genetic variation within and between populations, particularly at central and marginal areas of a species’ distribution. Much of this research is centred on the central‐marginal hypothesis, which posits that populations at range margins are sparse, small and genetically diminished compared to those at the centre of a species’ distribution range. We tested predictions derived from the central‐marginal hypothesis for the distribution of genetic variation and population differentiation in five European Coenagrionid damselfly species. We screened genetic variation (microsatellites) in populations sampled in the centre and margins of the species’ latitudinal ranges, assessed genetic diversity (H_S) in the populations and the distribution of this genetic diversity between populations (F_ST). We further assessed genetic substructure and migration with Bayesian assignment methods, and tested for significant associations between genetic substructure and bioclimatic and spatial (altitude and latitude) variables, using general linearized models. We found no general adherence to the central‐marginal hypothesis; instead we found that other factors such as historical or current ecological factors often better explain the patterns uncovered. This was illustrated in Coenagrion mercuriale whose colonisation history and behaviour most likely led to the observation of a high genetic diversity in the south and lower genetic diversity with increasing latitude, and in C. armatum and C. pulchellum whose patterns of low genetic diversity coupled with the weakest genetic differentiation at one of their range margins suggested, respectively, possible range shifts and recent, strong selection pressure.     

PORGUENIA PERUVIANA GEN. ET SP. NOV., A MARINE CENTRIC DIATOM WITH AN UNUSUAL OCELLUS1

A new diatom genus and species, Porguenia peruviana Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The valve outline is circular and the areolation is best described as pseudoloculate; spines of any type are lacking. A ring of elongated, densely packed rimoportulae is situated on the secondary marginal ridge. Externally, each rimoportula consists of a long, flattened, fluted upper portion supported by a shorter cylindrical stalk. The processes are winged and exhibit various degrees of curvature of the major axis. Typically, six reniform ocelli of unusual structure are situated centrifugally to the ring of rimoportulae and interrupt the true marginal ridge. Because the perforation plate differs from that of all other ocellus-bearing diatoms, a new term has been introduced for this structure, the diaphoron. The placement and structure of this newly discovered “perforation plate” do not allow Porguenia to be placed in any circumscribed family, although the Triceratiaceae would appear at present to be the most closely related family.     

STRUCTURE,LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). V. INITIAL CELL AND SIZE REDUCTION IN RH. CURVATA AND A DESCRIPTION OF THE RHOICOSPHENIACEAE FAM. NOV.1

The initial epivalve of Rhoicosphenia curvata (Kütz.) Grun. differs from vegetative valves in having a strongly arched section, a wide hyaline marginal strip, no pseudosepta, an unthickened margin, and a terminal raphe fissure at the head pole. The initial epivalve is of the D type, with short raphe fissures. The epicingulum consists of three bands as usual, but they are narrower and more delicate than those of vegetative cells. The initial hypovalve and hypocingulum are similar in every way to those of vegetative cells, except for the rounded section of the hypovalve. During size reduction the almost isopolar outline of the initial valves and their immediate descendants gives way to an increasingly strong heteropolarity, and this is accompanied by changes in the relative lengths of the raphe slits and the shape of the central area. Different populations have different gametangium and initial cell sizes, suggesting the presence of races within the species. The structure of the initial cell indicates that Rhoicosphenia is less closely related to the monoraphid genera than to the gomphocymbelloid genera, confirming conclusions reached from studies of the vegetative cell and auxospore formation. Rhoicosphenia should therefore be separated into a new family, the Rhoicospheniaceae, which is described.     

CHARACTERIZATION OF SCHIZOSERIS CONDENSATA,SCHIZOSERIDEAE TRIB. NOV. (DELESSERIACEAE,RHODOPHYTA)1

The Myriogramme group of Kylin contains two distinct clusters of genera that merit recognition at the tribal level. We previously established the tribe Myriogrammeae, and in this paper we erect the Schizoserideae based on a study of the type species of Schizoseris, S. laciniata (=S. condensata), from the southern hemisphere. The Schizoserideae is characterized by 1) marginal and diffuse intercalary meristems; 2) nuclei initially arranged in a plate in the median plane in meristematic and mature cells; 3) chloroplasts one to few, lobed or dissected; 4) microscopic veins absent; 5) procarps scattered, formed singly on either side of the blade with cover cells absent and consisting of a one- to two-celled lateral sterile group, a one- to two-celled basal sterile group, and a four-celled carpogonial branch in which the trichogyne passes beneath the lateral sterile group and emerges anterior to it; 6) auxiliary cell diploidized by a connecting cell cut off posteriolaterally from the fertilized carpogonium; 7) gonimoblast initial cut off laterally from one side of the auxiliary cell and giving rise to unilaterally branched gonimoblast filaments bearing carposporangia in branched chains; 8) gonimoblast fusion cell highly branched, candelabra-like, incorporating all but the basalmost cells of the carposporangial chains and radiating through the central cells in the floor of the cystocarp; 9) spermatangial and tetrasporangial sori formed from surface cells in both monostromatic and polystromatic portions on both sides of the blade; and 10) tetrasporangia formed primarily from cortical rather than from central cells. The Schizoserideae presently includes Schizoseris Kylin, Neuroglossum Kützing, Abroteia J. Agardh, and Polycoryne Skottsberg in Kylin and Skottsberg.     

Systematic revision of the genus Phycodrys (Delesseriaceae,Rhodophyta) from New Zealand,with the descriptions of three new species,P. novae-zelandiae sp. nov., P. franiae sp. nov. and P. adamsiae sp. nov.

Two species of Phycodrys, Phycodrys quercifolia (Bory) Skottsberg and Phycodrys profunda E.Y.Dawson were previously recorded from New Zealand. However, an examination of Phycodrys collections from the New Zealand region showed that all were morphologically different from P. quercifolia (Type locality: the Falkland Islands) and P. profunda (Type locality: CA, USA). RbcL sequence analyses established that the New Zealand Phycodrys species formed a natural assemblage within the genus, consisting of three new species: P. novae-zelandiae sp. nov., P. franiae sp. nov. and P. adamsiae sp. nov. Phycodrys novae-zelandiae is the largest of the three, up to 20 cm in height, with a distinct midrib and multicellular, opposite to subopposite lateral macroscopic veins. It has entirely monostromatic blades except near the midrib and veins, and its procarp contains a three-celled sterile group one (st1) and a one-celled sterile group two (st2). Phycodrys franiae was previously treated as a cryptic species among herbarium collections of P. ‘quercifolia’. It is smaller (4–11 cm high) with weakly developed midribs and veins, the blade is tristromatic throughout, except at the growing margins, and the procarp consists of a four-celled st1 and a two–three-celled st2. Phycodrys adamsiae, previously reported as P. profunda, is a small decumbent or prostrate plant, 1–8 cm long, with a midrib and inconspicuous lateral veins. The blades are tristromatic with serrated margins, two–four-celled surface spines and multicellular marginal holdfasts that differ from those of Californian specimens. The tetrasporangia are borne on marginal bladelets. Phylogenetic analyses place the New Zealand species in a separate group that is distantly removed from most other Phycodrys species.     

Local adaptations to frost in marginal and central populations of the dominant forest tree Fagus sylvatica L. as affected by temperature and extreme drought in common garden experiments

Local adaptations to environmental conditions are of high ecological importance as they determine distribution ranges and likely affect species responses to climate change. Increased environmental stress (warming, extreme drought) due to climate change in combination with decreased genetic mixing due to isolation may lead to stronger local adaptations of geographically marginal than central populations. We experimentally observed local adaptations of three marginal and four central populations of Fagus sylvatica L., the dominant native forest tree, to frost over winter and in spring (late frost). We determined frost hardiness of buds and roots by the relative electrolyte leakage in two common garden experiments. The experiment at the cold site included a continuous warming treatment; the experiment at the warm site included a preceding summer drought manipulation. In both experiments, we found evidence for local adaptation to frost, with stronger signs of local adaptation in marginal populations. Winter frost killed many of the potted individuals at the cold site, with higher survival in the warming treatment and in those populations originating from colder environments. However, we found no difference in winter frost tolerance of buds among populations, implying that bud survival was not the main cue for mortality. Bud late frost tolerance in April differed between populations at the warm site, mainly because of phenological differences in bud break. Increased spring frost tolerance of plants which had experienced drought stress in the preceding summer could also be explained by shifts in phenology. Stronger local adaptations to climate in geographically marginal than central populations imply the potential for adaptation to climate at range edges. In times of climate change, however, it needs to be tested whether locally adapted populations at range margins can successfully adapt further to changing conditions.     

Grimmia serrana (Bryopsida,Grimmiaceae), a new species from California,U.S.A.

Abstract

Grimmia serrana, a new endemic species for California, is described and illustrated. The new species is readily distinguished by the presence of multi-stratose marginal bands that are rounded in cross-section. The leaf morphology displayed by Grimmia serrana is unique within the genus. The distribution of Grimmia serrana is along the western foothills of the Sierra Nevada and in the northern Coast Range.     

Morphology and taxonomy of Cyclotella tasmanica spec. nov,a newly described diatom from Tasmanian lakes

A species of Cyclotella with an elliptical valve outline has been found in several Tasmanian lakes and is herein described and named C. tasmanica nov. sp. Morphologically, it is similar to C. stelligera and, to a lesser extent, to C. radiosa. The valve has coarse, clearly alveolate, marginal striae and a central rosette. Unlike other elliptical forms, the central area is always more or less circular. The nearest similar species is C. rhomboideo-elliptica.     

Developmental origins of complex radular characters in the Muricidae: the bifid rachidian edge

Muricid gastropod radulae are more complex than those of most other neogastropods, especially in the number and variety of cusps, denticles, and interlocking mechanisms. How this complexity evolved, however, is unknown. Morphological gaps between higher taxa within the Muricidae are substantial, and there are few unambiguous intermediates. Here, we use developmental data from the Patagonian trophonine muricid Trophon geversianus to investigate the evolution of an unusual condition in which there are two marginal cusps at each end of each central rachidian tooth, rather than one or none as in most muricids. Trophon geversianus begins ontogeny with one marginal cusp (the inner marginal cusp), but a second (the outer marginal cusp) appears later, arising from separation of the rachidian base edge from the radular membrane rather than through bifurcation or lateral migration of pre‐existing cusps. Truncation of development (i.e., paedomorphosis) at this second developmental phase in a trophonine ancestor provides an explanation for the lack of transitional forms between most adult trophonine muricids, which have the plesiomorphic condition of one marginal cusp, and sister group ocenebrine muricids, which have the derived condition of two marginal cusps.     

PORGUENIA PERUVIANA GEN. ET SP. NOV., A MARINE CENTRIC DIATOM WITH AN UNUSUAL OCELLUS1

A new diatom genus and species, Porguenia peruviana Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The value outline is circular and the areolation is best described as pseudoloculate; spines of any type are lacking. A ring of elongated, densely packed rimoportulae is situated on the secondary marginal ridge. Externally, each rimoportula consists of a long, flattened, fluted upper portion supported by a shorter cylindrical stalk. The processes are winged and exhibit various degrees of curvature of the major axis. Typically, six reniform ocelli of unusual structure are situated centrifugally to the ring of rimoportulae and interrupt the true marginal ridge. Because the perforation plate differs from that of all other ocellus-bearing diatoms, a new term has been introduced for this structure, the diaphoron. The placement and structure of this newly discovered “perforation plate” do not allow Porguenia to be placed in any circumscribed family, although the Triceratiaceae would appear at present to be the most closely related family.     

THE GENUS ACTINOCYCLUS (BACILLARIOPHYCEAE): FRUSTULE MORPHOLOGY OF A. SAGITTULUS SP. NOV. AND TWO RELATED SPECIES1

Actinocyclus octonarius var. tenellus (Bréb.) Hendey, A. actinochilus (Ehr.) Simonsen and A. sagittulus sp. nov. were examined by light and scanning electron microscopy from field samples and/or culture material. Consistent cingulum patterns of a wide valvocopula and one narrow pleura were found. In A. actinochilus, a small third band was found filling the opening of the pleura and is probably present in the other two taxa. The observed variability of the pseudonodulus, especially in A. actinochilus but also in other members of the genus, was confirmed and our results support the literature definition of Actinocyclus as having: 1) a marginal ring of large labiate processes, laterally expanded internally, 2) no external tubes, 3) essentially radial areolation arranged in fascicles, 4) external cribrum, internal foramen, and 5) a pseudonodulus usually present, but may be absent or difficult to detect on individual valves. On the basis of the present study another characteristic should be added; 6) hyaline bands with a wide valvocopula and at least one pleura. This characteristic appears to extend throughout the family Hemidiscaceae, suggesting a close relationship to those Coscinodiscus species with a single marginal row of large labiate processes and zero or one central labiate processes. In addition, Actinocyclus has been noted to have a thin valve overhang extending outside the valvocopula for as much as one-third of its width.     

New red alga, Acanthopeltis longiramulosa sp. nov. (Gelidiales, Rhodophyta) from Jeju Island, Korea

A new red alga from Jeju Island, Korea is described. The alga is assigned to Acanthopeltis, Gelidiaceae by the characteristics of terete erect axes, sympodial growth, and suborbicular branchlets that are amplexi‐caul at the base. Acanthopeltis longiramulosaY. Lee et Kim is characterized by a discoid holdfast with a few stolons, rhizoids arising from the apex of the branchlet, an erect terete axis diverging into a few branches, longish obpyriform to lanceolate branchlets with smooth surfaces, and tetrasporangial stichidia or sper‐matangial and cystocarps appendages on the marginal region of the branchlet. A. longiramulosa is more closely related to Acanthopeltis japonica than Acanthopeltis hirsuta in terms of thallus morphology. However, A. longiramulosa is easily distinguished from A. japonica, which has suborbicular branchlets with setaceous processes on both surfaces.     

THE GENETICS OF CENTRAL AND MARGINAL POPULATIONS OF DROSOPHILA SERRATA. I. GENETIC VARIATION FOR STRESS RESISTANCE AND SPECIES BORDERS

A selection experiment was used to determine if levels of genetic variance in an ecologically important trait, desiccation resistance, were different in central and marginal populations. Four populations of Drosophila serrata were sampled from central and marginal areas of its distribution, along a 3000-km stretch of Australia's east coast. Rainfall patterns along this stretch of coastline change from a tropical cycle in the north to a temperate cycle in the south. Replicate lines from the four populations underwent selection for desiccation resistance for 14 generations. Realized heritabilities calculated after 10 and 14 generations of selection indicated that the four populations differed significantly in the level of genetic variation for desiccation resistance available to selection. Populations from the more southern marginal areas had lower realized heritabilities than more northern central populations. However, a corresponding increase in mean desiccation resistance toward the margin was not found. A mechanism by which D. serrata seemed to have responded to selection was a reduction in the extent that metabolic rate was increased when flies were exposed to low humidity. This response indicates genetic variation for the control of metabolic rate. In contrast, increased desiccation resistance was not associated with lipid or glycogen levels. Increased resistance to desiccation was accompanied by increased starvation resistance, but radiation resistance was not affected. Selection did not affect the degree that replicate lines or populations had diverged.