Molecular systematics and radiation of western North American nymphophiline gastropods

Three mitochondrial DNA (mtDNA) markers were used to infer the phylogenetic relationships of the morphologically diverse, species rich, and poorly understood western North American aquatic gastropod genus Pyrgulopsis (Hydrobiidae: Nymphophilinae). Sequences were obtained from 62 of 124 currently recognized species of Pyrgulopsis and representatives of four related genera of North American nymphophilines. Separate and combined analyses of the mtDNA datasets recovered a well supported clade composed of Pyrgulopsis and two other North American nymphophiline genera (Floridobia, Nymphophilus) consistent with the results of a prior study based on a single gene and with anatomical evidence suggesting that these taxa form a monophyletic group. Phylogenetic relationships among lineages of Pyrgulopsis were little resolved in our analyses and provided no obvious basis for splitting this large genus into multiple genera. The little differentiated Mexican genus Nymphophilus was consistently placed within Pyrgulopsis in our trees and is formally synonymized with it herein. Pyrgulopsis was also depicted as paraphyletic with respect to Floridobia in some of our trees while in others the latter was sister to a Nymphophilus + Pyrgulopsis clade. Based on these equivocal results and the morphological and geographical divergence of eastern North American Floridobia relative to Pyrgulopsis, we recommend that the former be maintained as a separate genus. The short, weakly supported branches within Pyrgulopsis and the noncongruence between our molecular phylogenetic hypotheses and geographical groupings of species are attributed to an early rapid diversification of the genus, perhaps triggered by the complex changes in western topography which occurred during the late Tertiary. Our results also indicate that penial morphologies used to define species groups of Pyrgulopsis have been subject to striking convergence throughout the West, suggesting another compelling facet of the radiation of these snails.     

Gynoecium diversity and systematics of the paleoherbs

Gynoecium and ovule structure was compared in representatives of all families of the paleoherbs, including Nymphaeales (Cabombaceae, Nymphaeaceae), Piperales (Saururaceae, Piperaceae), Aristolochiales (Lactoridaceae, Aristolochiaceae), Rafflesiales (Hydnoraceae, Rafflesiaceae) and, in addition, Ceratophyllaceae and Nelumbonaceae, both of which were earlier included in Nymphaeales, but then segregated and with an unestablished position. In all representatives studied, the carpels are closed at anthesis. Carpel closure is attained in three different ways: (1) postgenital fusion of inner surfaces (Piperales, Aristolochiales); (2) occlusion by secretion or mutual appression of inner surfaces without postgenital fusion (Cabombaceae, Ceratophyllaceae, Nelumbonaceae (?) or (3) strong secretion combined with postgenital fusion at the periphery of the carpel (Nymphaeaceae). In Cytinus (Rafflesiaceae), after an earlier developmental stage with apparent postgenital fusion there is strong internal secretion (within the cell walls). Stigma shape tends to be double-crested in the basal taxa of each order: Cabombaceae (Brasenia), Saururaceae, and Lactoridaceae. In some Aristolochiaceae and Cytinus (Rafflesiaceae) they have two lobes in the transverse symmetry plane (i. e. at right angles to the median plane) or, if the carpels are united, the stigmatic lobes are commissural, accordingly. Stigmas are unicellular papillate and secretory in most taxa, but the papillae are uniseriate-pluricellular in some (not basal) Nymphaeaceae, Asaroideae (Aristolochiaceae) and Cytinus (Rafflesiaceae). Ceratophyllaceae have smooth stigmas. Intrusive oil cells in the carpel epidermis were found in Piperales and Aristolochiaceae. Mature ovules vary in length between 0. 2 mm and 2. 5 mm. Mature nucelli vary in breadth between 0. 03 mm and 1. 6 mm. These differences are larger than in the other major magnoliid groups. The outer integument is fully annular (not semiannular) in all taxa with orthotropous ovules (all Piperales and Barclaya of Nymphaeaceae) and also in some with anatropous ovules (some Nymphaeaceae, some Aristolochiaceae). The integuments are variously lobed or unlobed; both integuments tend to exhibit the same behaviour within a family, either both lobed or both unlobed. The results strongly support three pairs of families in sister group relationships, as suggested by studies based on other characters: Cabombaceae-Nymphaeaceae, Saururaceae-Piperaceae, and Lactoridaceae-Aristolochiaceae, and Hydnoraceae-Rafflesiaceae to some extent. Piperales and Aristolochiales are closer to each other than either is to Nymphaeales. Nelumbonaceae is isolated, as is Ceratophyllaceae, but the status of the latter is more difficult to interpret owing to apparent reduction in morphological, anatomical and histological traits.     

Anatomy and systematics of the minute syrnolopsine gastropods from Lake Tanganyika (Caenogastropoda, Cerithioidea, Paludomidae)

The minute syrnolopsine gastropods endemic to Lake Tanganyika have been allied to a number of freshwater, marine and terrestrial groups as a consequence of superficial conchological similarity. Although early anatomical studies confirmed the cerithioid organization of this clade, their close relationship to other lake species was not consistently recognized. In several recent cladistic analyses based on molecular data, the higher taxonomic placement and sister group relationships of syrnolopsines have been unstable. The present analysis confirms that syrnolopsines possess a spermatophore-forming organ – a synapomorphy of the Paludomidae – corroborating their placement in this family. Consistent with the molecular data, syrnolopsine monophyly is supported by two characters that occur exclusively in this group (salivary gland ducts that bypass the nerve ring and a linear albumen gland). Several characters in Martelia tanganyicensis – the most diminutive syrnolopsine – are only evident in the smallest lake species thus far investigated ( Bridouxia , Stormsia ) namely reduction of ctenidial leaflets, sorting area, intestine length and number of statoconia. These features are interpreted as being correlated with reduction in size. Nevertheless, close examination reveals differences in detail that allow more refined hypotheses of homology and are consistent with their independent origin.     

On the origin of Acochlidia and other enigmatic euthyneuran gastropods,with implications for the systematics of Heterobranchia

Background  

A robust phylogenetic hypothesis of euthyneuran gastropods, as a basis to reconstructing their evolutionary history, is still hindered by several groups of aberrant, more or less worm-like slugs with unclear phylogenetic relationships. As a traditional "order" in the Opisthobranchia, the Acochlidia have a long history of controversial placements, among others influenced by convergent adaptation to the mainly meiofaunal habitats. The present study includes six out of seven acochlidian families in a comprehensive euthyneuran taxon sampling with special focus on minute, aberrant slugs. Since there is no fossil record of tiny, shell-less gastropods, a molecular clock was used to estimate divergence times within Euthyneura.     

Gynoecium diversity and systematics of the Magnoliales and winteroids

Carpel and ovule structure was compared in representatives of all 11 families of the Magnoliales (Annonaceae, Canellaceae, Degeneriaceae, Eupomatiaccae, Himantandraceae, Magnoliaceae, Myristicaceae) and winteroids (Austrobaileyaceae, Illiciaceae, Sehisandraceae, Winteraceae). Special attention was paid to features that are constant at family level. Bisexual flowers are always protogynous. In all representatives studied the carpels are closed at anthesis. Caipel closure is attained in three different ways: (1) postgenital fusion of inner surfaces (Degeneriaceae, Eupomatiaccae. Winteraceae), or (2) occlusion by secretion (Austrobaileyaceae, Sehisandraceae), or (3) a combination of (1) and (2): in Annonaceae, Canellaceae, Myristicaceae there is a conspicuous secretory canal in the innermost part of the ventral slit; in Illiciaceae and Magnoliaceae there is a narrow canal in the innermost part of the ventral slit; and in Himantandraceae the ventral slit is postgenilally fused in the style but completely open in the ovary. In most families the carpels have a double stigmalic crest or they have two tips in the transversal symmetry plane (i.e. at right angles to the median plane). Stigmas are unicellular papillate in most families but the papillae are bi-to multicellular (uniseriate) in Degeneriaceae and Eupomatiaceae. An unusual cryptic exlracarpellary compitum was found in Himantandraceae and Sehisandraceae. Intrusive oil cells were found in the carpel epidermis of Illiciaceae and Sehisandraceae. Mature ovules vary in length between 0.15 and 1.1 mm. The outer integument is fully annular (not semiannular) in Degeneriaceae, Himantandraceae, Canellaceae, Myristicaceae, and Illiciaceae. A rudimentary aril occurs in Canellaceae, and originates at the same site as in arillate Annonaceae and Myristicaceae. The results most strongly support an Annonaceae-Myristicaceae-Canellaceae alliance, to some degree also an Eupomatiaccac-Degeneriaceae-Himantandraceae-Magnoliaceae alliance, and an Illiciaceae-Schisandraceae-Winteraccae-Austrobaileyaceae alliance.     

Spatial patterns of morphological diversity across the Indo-Pacific: analyses using strombid gastropods.

Biological diversity can be measured using various metrics, but existing knowledge of spatial patterns of diversity is largely based on species counts. There is increasing evidence that trends in species richness might not match trends in other biodiversity metrics, such as morphological diversity. Here, we use data from a large group of Indo-Pacific gastropods (family Strombidae) to show that the species richness of a region is a poor predictor of the morphological diversity present there. Areas with only a few species can harbour an impressive array of morphologies and, conversely, morphological diversity in the most species-rich regions is no higher than in regions with half their taxonomic diversity. Biological diversity in the Pacific is highly threatened by human activity and our results indicate that, in addition to species richness, morphological diversity metrics need to be incorporated into conservation decisions.     

Pollen diversity and its implications to the systematics of Poecilanthe (Fabaceae,Papilionoideae, Brongniartieae)

The small South-American genus Poecilanthe has a striking morphological diversity in leaf type, inflorescence, seed morphology and chemical composition. Recent phylogenetic work also shows that Poecilanthe is paraphyletic. Despite the importance of palynology to better understand morphological diversity and potentially inform evolutionary analyses, the pollen morphology of Poecilanthe and most of its close relatives is unknown. This study uses light and electronic microscopy to describe the pollen morphology of eight species of Poecilanthe and the four related genera Ormosia, Harpalyce, Clathrotropis and Cyclolobium. We found pollen grains colpate only in four species of Poecilanthe and Harpalyce brasiliana and colporate pollen grains in the other four Poecilanthe species and the other related genera (Ormosia, Clathrotropis and Cyclolobium). An identification key for pollen of all species is provided. Using principal component analyses (PCA) we found that pollen grains of the Poecilanthe have considerable diversity. However, only limited correspondence between the PCA clusters and the Poecilanthe clades was found, suggesting that pollinic characters do not reflect evolutionary history in this group.     

Disulfide bond formation in prokaryotes: History,diversity and design

The formation of structural disulfide bonds is essential for the function and stability of a great number of proteins, particularly those that are secreted. There exists a variety of dedicated cellular catalysts and pathways from archaea to humans that ensure the formation of native disulfide bonds. In this review we describe the initial discoveries of these pathways and report progress in recent years in our understanding of the diversity of these pathways in prokaryotes, including those newly discovered in some archaea. We will also discuss the various successful efforts to achieve laboratory-based evolution and design of synthetic disulfide bond formation machineries in the bacterium Escherichia coli. These latter studies have also led to new more general insights into the redox environment of the cytoplasm and bacterial cell envelope. This article is part of a Special Issue entitled: Thiol-Based Redox Processes.     

A systematics for discovering the fundamental units of bacterial diversity

Bacterial systematists face unique challenges when trying to identify ecologically meaningful units of biological diversity. Whereas plant and animal systematists are guided by a theory-based concept of species, microbiologists have yet to agree upon a set of ecological and evolutionary properties that will serve to define a bacterial species. Advances in molecular techniques have given us a glimpse of the tremendous diversity present within the microbial world, but significant work remains to be done in order to understand the ecological and evolutionary dynamics that can account for the origin, maintenance, and distribution of that diversity. We have developed a conceptual framework that uses ecological and evolutionary theory to identify the DNA sequence clusters most likely corresponding to the fundamental units of bacterial diversity. Taking into account diverse models of bacterial evolution, we argue that bacterial systematics should seek to identify ecologically distinct groups with evidence of a history of coexistence, as based on interpretation of sequence clusters. This would establish a theory-based species unit that holds the dynamic properties broadly attributed to species outside of microbiology.     

Global diversity of gastropods (Gastropoda; Mollusca) in freshwater

The world’s gastropod fauna from continental waters comprises ∼4,000 valid described species and a minimum of 33–38 independent lineages of Recent Neritimorpha, Caenogastropoda and Heterobranchia (including the Pulmonata). The caenogastropod component dominates in terms of species richness and diversity of morphology, physiology, life and reproductive modes and has produced several highly speciose endemic radiations. Ancient oligotrophic lakes (e.g., Baikal, Ohrid, Tanganyika) are key hotspots of gastropod diversity; also noteworthy are a number of lower river basins (e.g., Congo, Mekong, Mobile Bay). But unlike many other invertebrates, small streams, springs and groundwater systems have produced the most speciose associations of freshwater gastropods. Despite their ecological importance in many aquatic ecosystems, understanding of even their systematics is discouragingly incomplete. The world’s freshwater gastropod fauna faces unprecedented threats from habitat loss and degradation and introduced fishes and other pests. Unsustainable use of ground water, landscape modification and stock damage are destroying many streams and springs in rural/pastoral areas, and pose the most significant threats to the large diversity of narrow range endemics in springs and ground water. Despite comprising only ∼5% of the world’s gastropod fauna, freshwater gastropods account for ∼20% of recorded mollusc extinctions. However, the status of the great majority of taxa is unknown, a situation that is exacerbated by a lack of experts and critical baseline data relating to distribution, abundance, basic life history, physiology, morphology and diet. Thus, the already considerable magnitude of extinction and high levels of threat indicated by the IUCN Red List of Threatened Species is certainly a significant underestimate. Guest editors: E. V. Balian, C. Lévêque, H. Segers and K. Martens Freshwater Animal Diversity Assessment     

History and diversity: explorations at the intersection of ecology and evolution

Phylogenetic analysis provides an important tool for assessing the influence of historical and evolutionary processes on the structure of contemporary ecological systems. Patterns of diversity, for example, represent the regional buildup of species through immigration and diversification, their loss through extinction, and the sorting of species ecologically within the region. Colonization-extinction dynamics on islands can be inferred from lineage accumulation through time. Lineage branching within clades can be used to estimate rates of speciation and extinction. However, simulations of these processes show potential ambiguities in the interpretation of data. Clade size is unrelated to age in many studies, suggesting that speciation and extinction might be in long-term equilibrium and raising questions about unobserved past diversity. Among passerine birds and other groups, the size of similar-aged clades is positively related to the size of the region within which they have diversified, and it is greater in tropical than in temperate regions. There is no consensus on the causes of these patterns. Finally, the ecological interactions between populations within regions brings the timescale of species sorting and species production close to each other and emphasizes the important interaction of ecological and evolutionary processes in shaping ecological systems.     

Latitudinal changes in the diversity of freshwater gastropods (Mollusca: Gastropoda) in waterbodies of western Siberia

The patterns of spatial variation in gastropod diversity in the waterbodies of western Siberia have been revealed. The highest species and generic diversity of freshwater gastropods is found in the waterbodies of the forest-steppe zone; from there, these parameters significantly decrease northwards, reaching their minimum beyond the polar circle. The proportion of gastropods of non-European origin increases in the same direction. The possible reasons for these changes in the spatial diversity of aquatic gastropods and the likely connections between the latitudinal variation of their diversity and the geological history and features of the relief of western Siberia are discussed. It is assumed that the forest-steppe zone of western Siberia is a local center of aquatic gastropod diversity.     

Population systematics of Russell's viper: a multivariate study

A multivariate analysis of the population systematics of Russell's viper, based on scalation and colour pattern characters, reveals that the populations of this viper constitute two well-defined taxa: a western form, comprising all populations from the Indian subcontinent, and an eastern form, comprising all populations from east of the Bay of Bengal. The two forms could be considered either as subspecies of one species, or as two separate species, depending on the species concept used. Within the western form, there is no clear pattern of geographic variation. Within the eastern form, the populations from the Lesser Sunda Islands are clearly divergent from the populations of mainland Asia and Java. The conventionally recognized subspecies of Vipera russelli fail to portray this pattern of geographic variation. There is no clear relationship between the pattern of geographic variation in morphology and the pattern of geographic variation in the clinical effects of the venom in human bite victims: some populations with considerable differences in venom effects are equally distinct morphologically, whereas other populations with equally strong venom differences are morphologically very similar. The distribution of Russell's viper can be attributed to Pleistocene changes in climate and sea level, coupled with the viper's ecological requirements, which appear to include a seasonally dry climate.