Free-floating Ulva in the southwest Netherlands: species or morphotypes? a morphological,molecular and ecological comparison

Free-floating Ulva L. biomass in the eutrophic brackish ‘Veerse Meer’ lagoon (southwest Netherlands) consists of four morphologically identified species: U. curvata (Kützing) De Toni, U. lactuca L., U. rigida C. Agardh and U. scandinavica Bliding. U. curvata could be recognized easily because of the characteristic central cavity in the holdfast of the attached plants, the arrangement of cells in rows and the single pyrenoid in each cell. U. rigida was distinguished by the thick thallus and the large number of pyrenoids. The Veerse Meer isolate, however, was slightly different from the isolate from the Oosterschelde estuary (the Netherlands). U. lactuca and U. scandinavica showed a high degree of overlap in thallus thickness and cell size, but U. scandinavica usually possessed more pyrenoids. However, doubts have frequently been expressed about the use of some morphological characters in Ulva taxonomy. To determine the validity of such characters in the identification of Ulva species, the morphological variation within and between morphological species was recorded and a molecular data set generated. To detect possible ecophysiological differences between species, optimum temperatures and salinities for growth were determined experimentally. The sequences of the nuclear ribosomal DNA internal transcribed spacer 2 (ITS2) and flanking regions of U. lactuca, U. rigida and U. scandinavica from the Veerse Meer were all identical, but differed from that of U. rigida from the Oosterschelde estuary. Ulva species from the Veerse Meer were most closely related to U. armoricana and U. rigida from Brittany (2.9% and 3.5% divergence respectively); the difference between U. rigida from the Veerse Meer and from the Oosterschelde estuary was 7.5%. Rooted trees, based on a comparison of these sequences with sequences of other Ulva and Enteromorpha species obtained from the literature, using Monostroma arcticum as outgroup, suggested that Ulva is paraphyletic with respect to Enteromorpha. The optimum temperature for growth of U. curvata was 25?°C; for all other species it was 10?°C. The optimum salinity for growth was 30?°C for all isolates. It is concluded that U. lactuca, U rigida and U. scandinavica from the Veerse Meer are all members of one highly polymorphic species.     

Obesity and hypertension: two epidemics or one?

The association between obesity and hypertension is well documented, although the exact nature of this relation remains unclear. Sympathetic nervous and renin-angiotensin-aldosterone system activation appear to play an important role in the sodium and water retention, rightward shift in the pressure-natriuresis, and blood pressure elevation observed in obese individuals. Visceral obesity and the ectopic deposition of adipose tissue may be important in the activation of these systems and in the target organ damage that ensues. Weight loss is critical in the effective management of obesity hypertension and the accompanying target organ damage, although recidivism rates are high. However, prevention of weight gain should be the major priority for combating hypertension and its consequences in the future. The present review will provide an overview of our understanding of the etiology, pathophysiology, and treatment of obesity hypertension. Our focus is on the state of knowledge in humans. The potential role of abdominal obesity is considered throughout our review. We refer to relevant animal literature for supportive evidence and where little or no data in humans are available.     

A morphological and molecular perspective of Trichoderma viride: is it one or two species?

Trichoderma (Ascomycetes, Hypocreales) strains that have warted conidia are traditionally identified as T. viride, the type species of Trichoderma. However, two morphologically distinct types of conidial warts (I and II) have been found. Because each type corresponds to a unique mitochondrial DNA pattern, it has been questioned whether T. viride comprises more than one species. Combined molecular data (sequences of the internal transcribed spacer 1 [ITS-1] and ITS-2 regions and of part of the 28S rRNA gene along with results of restriction fragment length polymorphism analysis of the endochitinase gene and PCR fingerprinting), morphology, physiology, and colony characteristics distinguish type I and type II as different species. Type I corresponds to "true" T. viride, the anamorph of Hypocrea rufa. Type II represents a new species, T. asperellum, which is, in terms of molecular characteristics, close to the neotype of T. hamatum.     

Sympatric morphotypes of the restricted-range Tashan Cave Garra: distinct species or a case of phenotypic plasticity?

Environmental Biology of Fishes - Among Tashan cave barb Garra tashanensis inhabiting a small cave in southwest Iran, two mental disc (sucking mouth disc) forms were observed. To assess their...     

Reactive oxygen and nitrogen species: Friends or foes?

Chemical and physiological functions of molecular oxygen and reactive oxygen species (ROS)and existing equilibrium between pools of pro-oxidants and anti-oxidants providing steady state ROS level vital for normal mitochondrial and cell functioning are reviewed. The presence of intracellular oxygen and ROS sensors is postulated and few candidates for this role are suggested. Possible involvement of ROS in the process of fragmentation of mitochondrial reticulum made of long mitochondrial filaments serving in the cell as electric cables, as well as the role of ROS in apoptosis and programmed mitochondrial destruction (mitoptosis) are reviewed. The critical role of ROS in destructive processes under ischemia/reoxygenation and ischemic preconditioning is discussed. Mitochondrial permeability transition gets special consideration as a possible component of the apoptotic cascade, resulting in excessive ROS induced ROS release.Translated from Biokhimiya, Vol. 70, No. 2, 2005, pp. 265–272.Original Russian Text Copyright ¢ 2005 by Zorov, Bannikova, Belousov, Vyssokikh, Zorova, Isaev, Krasnikov, Plotnikov.This revised version was published online in April 2005 with corrections to the post codes.     

Keystone species and vulnerable species in ecological communities: strong or weak interactors?

The loss of a species from an ecological community can trigger a cascade of secondary extinctions. The probability of secondary extinction to take place and the number of secondary extinctions are likely to depend on the characteristics of the species that is lost--the strength of its interactions with other species--as well as on the distribution of interaction strengths in the whole community. Analysing the effects of species loss in model communities we found that removal of the following species categories triggered, on average, the largest number of secondary extinctions: (a) rare species interacting strongly with many consumers, (b) abundant basal species interacting weakly with their consumers and (c) abundant intermediate species interacting strongly with many resources. We also found that the keystone status of a species with given characteristics was context dependent, that is, dependent on the structure of the community where it was embedded. Species vulnerable to secondary extinctions were mainly species interacting weakly with their resources and species interacting strongly with their consumers.     

Diet divergence in two sympatric congeneric butterflies: Community or species level phenomenon?

Summary Two species ofEuphydryas butterflies were studied in California, USA, and showed considerable diet overlap at the species level. They utilize many of the same plant genera for oviposition. However,E. editha is less likely to use woody perennials than isE. chalcedona.Both butterfly species are known to specialize on different host plants in different populations, so species level divergence may not be a good predictor of community level divergence. Within five communities,E. editha andE. chalcedona showed no dietary overlap. A major component of the niche ofE. editha in one community was occupied byE. chalcedona in a second community, even though both butterfly species occupied both communities. These resource use patterns indicate that community level interactions may affect diet divergence. The degree to which divergence within communities is greater (or less) than expected from a species level comparison may be used to provide a measure of community organization. Equations are given in the Appendix for calculating overlap probabilities from presence/absence types of data; in this study, presence is oviposition on a particular plant species, absence is no oviposition on that plant species. Given the various assumptions of the model,E. editha andE. chalcedona show significant community level components of their dietary divergence in the areas studied. However, in some other communitiesE. editha andE. chalcedona do share host plant species. Therefore, we could not demonstrate community level divergence conclusively, nor has this been demonstrated for any other pair of insect herbivore species. We do not know whether this is because the phenomenon is truly rare or just very hard to demonstrate.     

Paracorethrura Melichar, 1915 (Hemiptera: Lophopidae): two distinct species or sexual dimorphism in a species?

A taxonomic update is provided for Paracorethrura Melichar, 1915. P. arrhen n. sp. is described from Vietnam and brings up the number of species to two for the genus: P. iocnemis (Jacobi, 1905) being known only by female specimens and P. arrhen only by males, CO1 sequences are provided in order to check if they are truly two different species or if we are witnessing some sexual dimorphism.     

Invasive species: reality or myth?

In view of the recent debate on the future of invasion biology, we argue that species could be regarded as invasive only when after adaptation in non-native habitats they reach yet another fitness maximum. We suggest that invasion biologists need to unambiguously clarify what constitutes being “invasive” to refute those who call for an end to invasion biology.     

Entamoeba, giardia and toxoplasma: clones or cryptic species?

The availability of molecular markers has renewed interest in the taxonomy of parasitic protozoa at the subspecific and specific levels. Nevertheless, the conclusions reached are heavily dependent upon the way the data are analyzed. Some authors have emphasized the value of genetic distances to propose the creation o f new species, while others have rather favoured a population genetic approach to account for the intraspecific variability of parasites. In this article, using three illustrative cases, Michel Tibayrenc shows that dissimilar taxonomic approaches can be built from quite comparable sets of data.     

Do major species concepts support one, two or more species within Cryptococcus neoformans?

Cryptococcus neoformans, the agent of cryptococcosis, had been considered a homogeneous species until 1949 when the existence of four serotypes was revealed based on the antigenic properties of its polysaccharide capsule. Such heterogeneity of the species, however, remained obscure until the two morphologically distinct teleomorphs of C. neoformans were discovered during the mid 1970s. The teleomorph Filobasidiella neoformans was found to be produced by strains of serotype A and D, and Filobasidiella bacillispora was found to be produced by strains of serotype B and C. Ensuing studies revealed numerous differences between the anamorphs of the two Filobasidiella species with regard to their ecology, epidemiology, pathobiology, biochemistry and genetics. At present, the etiologic agent of cryptococcosis is classified into two species, C. neoformans (serotypes A and D) and Cryptococcus gattii (serotypes B and C). Intraspecific genetic diversity has also been revealed as more genotyping methods have been applied for each serotype. As a result, the number of scientifically valid species within C. neoformans has become a controversial issue because of the differing opinions among taxonomists as to the appropriate definition of a species. There are three major species concepts that govern classification of organisms: phenetic (morphologic, phenotypic), biologic (interbreeding) and cladistic (evolutionary, phylogenetic). Classification of the two C. neoformans species has been based on the phenetic as well as the biologic species concept, which is also supported by the cladistic species concept. In this paper, we review and attest to the validity of the current two-species system in light of the three major species concepts.     

Genetic structure and gene flow in French populations of two Ostrinia taxa: host races or sibling species?

Most models of ecological speciation concern phytophagous insects in which speciation is thought to be driven by host shifts and subsequent adaptations of populations. Despite the ever-increasing number of studies, the current evolutionary status of most models remains incompletely resolved, as estimates of gene flow between taxa remain extremely rare. We studied the population genetics of two taxa of the Ostrinia genus--one feeding mainly on maize and the other on mugwort and hop--occurring in sympatry throughout France. The actual level of divergence of these taxa was unknown because the genetic structure of populations had been investigated over a limited geographical area and the magnitude of gene flow between populations had not been estimated. We used 11 microsatellite markers to investigate the genetic structure of populations throughout France and the extent of gene flow between the two Ostrinia taxa at several sites at which they are sympatric. We observed clear genetic differentiation between most populations collected on the typical respective hosts of each taxon. However, populations displaying intermediate allelic frequencies were found on hop plants in southern France. Individual assignments revealed that this result could be accounted for by the presence of both taxa on the same host. Gene flow, estimated by determining the proportion of hybrids detected, was low: probably<1% per generation, regardless of site. This indicates that the two Ostrinia taxa have reached a high level of genetic divergence and should be considered sibling species rather than host races.     

Phagocyte-derived reactive species: salvation or suicide?

Activated phagocytes produce "reactive oxygen, halogen and nitrogen species" that help to kill some types of microorganism. How these species destroy microorganisms remains, however, an enigma: both direct oxidative damage and indirect damage (whereby reactive species promote the actions of other antibacterial agents) are involved, and no single mechanism is likely to account for the killing of all microorganisms. Phagocyte-derived reactive species are known to injure human tissues and to contribute to inflammation. Recently, however, we have learned that they can also be anti-inflammatory by modulating the immune response. These data have implications for the proposed use of antioxidants to treat inflammation.     

Metazoan parasite species richness and genetic variation among freshwater fish species: cause or consequence?

The factors responsible for the maintenance of genetic variation among natural populations remain a mystery. Recent models of host-parasite co-evolution assume that parasites exert frequency-dependent selection on their hosts by favouring rare alleles that may confer resistance against infection. We tested this prediction in a comparative analysis that sought relationships between levels of genetic variation and the number of metazoan parasite species exploiting each host species. We used data on 40 species of North American freshwater fishes. After controlling for sampling effort and phylogenetic influences, we found no relationship between genetic polymorphism and parasite species richness among fish species. However, we found a marginal negative correlation between parasite species richness and heterozygosity. This result goes against the prediction that increased selective pressure by parasites should be associated with higher levels of genetic variation. Instead, it suggests that parasites may be colonising host species showing low levels of genetic variation with greater success than genetically more variable host species.