Hidden diversity and endemism on seamounts: focus on poorly dispersive neogastropods

The seamounts chain offers a set of fragmented habitats in which species with poor dispersive ability may undergo divergence in allopatry. Such a scenario may explain the endemism often described on seamounts. In gastropods, it is possible to infer the mode of development of a species from the morphology of its larval shell. Accordingly, we examine the population genetics of several caenogastropods from the Norfolk and Lord Howe seamounts (south‐west Pacific) with contrasting modes of larval development. A prerequisite to our study was to clarify the taxonomic framework. The species delimitation was ruled using an integrative approach, based on both morphological and molecular evidence. Molecular data indicate an unexpected taxonomic diversity within the existing species names. Both the clarification of the taxonomic framework and the importance of the sampling effort allow us to confidently detect cryptic diversity and micro‐endemism. These results are discussed in relation to the dispersive capacities of the organisms. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 420–438.     

An integrative approach to species delimitation in Benthomangelia (Mollusca: Conoidea)

DNA sequences are currently used to propose primary hypotheses of species delimitation, especially when morphological variability is difficult to assess. In an integrative taxonomy framework, these hypotheses are then compared with other characters, such as morphology or geography, to produce robust species delimitations. For this purpose, the cytochrome oxidase subunit I (COI) gene has been sequenced for almost 50 specimens of the genus Benthomangelia , a deep-sea marine gastropod genus, collected in the South-West Pacific. Five genetic groups, displaying low and high genetic distances respectively within and between groups, were defined. COI hypotheses were compared with both the results obtained with the independent nuclear 28S gene and with an elliptic Fourier analysis of the shape of the last whorl of the shell. 28S gene analysis confirmed the same well-supported groups as COI, and elliptic Fourier analysis identified several morphological characters that vary similarly to genetic variability.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 696–708.     

MORPHOLOGICAL STUDIES OF LYMNAEID SNAILS FROM THE HUMAN FASCIOLIASIS ENDEMIC ZONE OF BOLIVIA

The taxonomic position of the Lymnaeidae from the BolivianAltiplano has been unclear. On the basis of conchological characters,some authors reported two species from this area, Lymnaea viatrix andL. cubensis while others, considering also anatomical characters,considered L. viatrix as a synonym of L. cubensis. More recentstudies demonstrated genetic identity between the Bolivian lymnaeidsand L. truncatula from the Iberian Peninsula. Populations recognizedas L. cubensis correspond to a distinct genetic group, but geneticinformation was not available for L. viatrix. In the light ofthese genetic results, a morphometric study of both the shell (usingRaupian parameters) and male reproductive system was carried outof L. cubensis from Cuba (type locality), Dominican Republic,Guadeloupe and Venezuela, and of L. truncatula from Bolivia,France, Portugal, Spain and Morocco. Syntypes of L. viatrixfrom Argentina (var. A. ventricosa) and specimens of L. viatrix(var. B. elongata) from the type locality, Peru, were also studied(conchological characters only). The conchological study showedthe presence of a large amount of variability between populations.This variability was not congruent with genetic results. Alarge amount of variability was also found using anatomicalcharacters of the male reproductive system and all of them clearlyseparate L. cubensis from L. truncatula independently from geographicalorigin. Thus anatomical characters, unlike conchological parameters,do differentiate taxonomic species inferred from genetic studies. (Received 11 September 1997; accepted 5 March 1999)     

Effects of landscape features and demographic history on the genetic structure of Testudo marginata populations in the southern Peloponnese and Sardinia

Testudo marginata, the largest European land tortoise, is suffering habitat degradation and destruction. Some populations, in markedly degraded habitats, are characterized by divergent morphotypes. However, the evolutionary significance of these morphotypes is of debate. Using 11 polymorphic microsatellites, we studied: (1) marginated tortoises from Sardinia that display a divergent morphotype – this population was potentially introduced from Greece; and (2) an area in the southern Peloponnese that includes a small and degraded zone in which marginated tortoises are dwarf. Genetic analyses run without any a priori assignment clearly acknowledge the specimens sampled in the territory of the dwarf form as a single group whilst Sardinian specimens are clustered with other specimens from the northern part of the area sampled in Greece. Demographic analyses suggest that Sardinian tortoises originated recently from some of the populations sampled in the northern part of the area sampled in Greece. Over locations sampled in Greece, a landscape‐genetic analysis allowed us to detect potential landscape features that may reduce gene flow between the dwarf form territory and surrounding areas. Our results suggest that the territory of the dwarf form is particularly propitious for marginated tortoises and that conservation regulations in Greece should be reinforced to protect this area from increasing impact of human activities changing from traditional agriculture to mechanization and extensive use of chemicals. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 591–606.     

Phase determination from direct sequencing of length‐variable DNA regions

For diploid organisms, haplotype determination usually requires sequencing cloned polymerase chain reaction (PCR) products or comparing the genotypes of several individuals. We found out that phase could be reconstructed from direct sequencing of mixed PCR products by combining for each individual the complementary information contained in its forward and reverse chromatograms, provided these products had different lengths. When applied to the internal transcribed spacer 2 (ITS2) from corals of the genus Pocillopora, this new method allowed us to identify two dominant sequence types in some specimens; however, sequencing cloned PCR products from the same specimens yielded more variants, including possible PCR‐generated recombination artifacts.     

Isolation and characterization of eight microsatellite loci for the study of gene flow between Testudo marginata and Testudo weissingeri (Testudines: Testudinidae)

The taxonomic status of the Greek Testudo species, marginated tortoise (Testudo marginata Schoepff, 1793) and dwarf marginated tortoise (Testudo weissingeri Bour, 1995), is controversed. In order to study the gene flow among these Greek Testudo species, eight polymorphic microsatellite markers were characterized and screened for 32 individuals. The number of alleles observed per locus ranged from two to 19. Observed heterozygosities varied from 0.235 to 0.830. These microsatellite loci were also successfully tested on seven closely related species of Testudinidae. This set of microsatellites offers an efficient tool to investigate genetic differentiation among testudinid species.     

Species: towards new, well-grounded practices

Velasco recently criticized our formal definition of the species concept, arguing for its inappropriateness both in fundamental and practical aspects [Velasco JD (2008) Biological Journal of the Linnean Society , 93 , 865–869]. Here, we clarify some misunderstandings that are at the basis of Velasco's paper. First, we show why and how the definition of the species concept can be grounded in the theory of evolution and what that implies. Then, we explain why Velasco's formal criticisms are unjustified. Finally, we point out the practical and methodological consequences of a rigorous conceptual framework for species study, and we show that today's development of species delimitation methods fully agrees with our proposal.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 217–222.     

Density and variability of dinucleotide microsatellites in the parthenogenetic polyploid snail Melanoides tuberculata

Characterization of microsatellites in the parthenogenetic polyploid snail Melanoides tuberculata revealed an unusual high density of dinucleotide repeats. Multiple banding patterns were obtained at these loci, and interpreted as a consequence of polyploidy. Microsatellite variability was low within, but high between, shell morphotypes. Genotypes were wholly transmitted from mothers to offspring. These results suggest that reproduction is strictly apomictic, and that shell morphotypes are genetic clones.     

The tree, the network, and the species

To enrich the Hennigian internodal conception of species, a new formalization of the definition of the species concept is proposed. This rigorous definition allows for considerable unification of the various, and sometimes conflicting, techniques of species delimitation used in practice. First, the domain of such a definition is set out, namely, the set of all organisms on Earth, past, present, and future. Next, the focus is on the genealogical relationship among organisms, which provides the key to analysing the giant or global genealogical network (GGN) connecting all these organisms. This leads to the construction of an algorithm revealing the topological structure of the GGN, from families to lineages, ending up with a definition of species as equivalence classes of organisms corresponding to branches of the 'tree of life'. Such a theoretical definition of the species concept must be accompanied by various recognition criteria to be operational. These criteria are, for example, the ill-named 'biological species concepts', 'phylogenetic species concepts', etc., usually, but wrongly, presented as definitions of the species concept. Besides clarifying this disputed point, the definition in the present study displays the huge diversity of the scales (time-scale and population size) involved in actual species, thus explaining away the classical problems raised by previous attempts at defining the species concept (uniparental reproduction, temporal depth of species, and hybridization).  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 509–521.     

Characterization of seven polymorphic microsatellites for the study of two Ranunculaceae: Ranunculus nodiflorus L., a rare endangered species and Ranunculus flammula L., a common closely related species

Ranunculus nodiflorus and Ranunculus flammula are two closely related Ranunculaceae. In France, the first one is rare and endangered, whereas the second is common. To compare their population genetic structure, seven polymorphic microsatellite markers were characterized. We found no polymorphism in R. nodiflorus, whereas R. flammula was polymorphic at each locus. The total number of alleles per locus varied from three to eight. Observed heterozygosities ranged from 0 to 0.261. This set of microsatellites offers an efficient tool to study population genetic structure and to compare the results between closely related endangered and common species.