Body‐size distribution and biogeographical patterns in non‐marine ostracods (Crustacea: Ostracoda)

The idea that free‐living minute organisms have ubiquitous distributions has been recently revitalized, causing significant controversy. The ubiquitous model predicts that a threshold where ubiquity leaves room to biogeography might exist somewhere along the animal body‐size range. In the present study, such a prediction is tested by analysing body‐size frequency distribution, species distribution, and local‐to‐global species ratio at the scale of biogeographical realms in cypridoidean non‐marine ostracods, a group with a body‐size range in the ubiquity–biogeography (U‐B) boundary. Data were gathered for all described extant cypridoidean ostracod species (N = 1761), with body‐size recorded for 1134 of them. Although local‐to‐global species ratios show significant over‐dispersal of small‐body ostracods for the Palaearctic and the Australasian regions, there are explanations alternative to the ‘Everything is Everywhere’ model that can account for such a result. Indicators of taxonomic structure do not support the hypothesis of a random distribution of cypridoidean species among realms. Nevertheless, the strong biogeography signal occurring at a large scale vanishes at the local scale (country‐level within the Palaearctic), and suggests wide dispersion within biogeographical realms. Additional factors, including inconsistent taxonomic criteria for species recognition, uneven sampling effort, and an excess of ‘single‐report’ occurrences, have been identified too as potential distorters of the observed patterns. Taxonomic harmonization, open databases of biogeographical data, and better ecological information are suggested as critical goals that need to be achieved for further understanding of ostracod global distribution patterns. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 409–423.     

The life-cycle of the asexual ostracod Darwinula stevensoni (Brady & Robertson, 1870) (Crustacea,Ostracoda) in a temporate pond

The life-cycle of the ancient asexual ostracod Darwinula stevensoni was studied during 1 year in a eutrophic pond in Belgium. The reproductive period of this species started in March and was effectively completed by September of the same year. All changes in population structure took place during the spring and summer months and a rapid turnover of the instars was observed. The life-cycle of Darwinula stevensoni appears to take one year or less in Belgium and this is considerably shorter than the 4 years which had been reported previously from subarctic populations. The difference to the present study is most likely temperature-related. Maximal densities of D. stevensoni were observed in June and July and attained 10⁵ ind. m^–2. During winter, densities were lower with a mean of 10⁴ ind. m^–2. Consequently, the calculated population size of each month was high throughout the year. Together with the low mutation rate, such a large population size could effectively counteract the stochastic loss of mutation-free genotypes as predicted by Muller's ratchet. D. stevensoni is a brooder; the maximum number of embryos and juvenile instars (up to third stage) found within a single female was 11.     

Erratic rates of molecular evolution and incongruence of fossil and molecular divergence time estimates in Ostracoda (Crustacea)

Dating evolutionary origins of taxa is essential for understanding rates and timing of evolutionary events, often inciting intense debate when molecular estimates differ from first fossil appearances. For numerous reasons, ostracods present a challenging case study of rates of evolution and congruence of fossil and molecular divergence time estimates. On the one hand, ostracods have one of the densest fossil records of any metazoan group. However, taxonomy of fossil ostracods is controversial, owing at least in part to homoplasy of carapaces, the most commonly fossilized part. In addition, rates of evolution are variable in ostracods. Here, we report evidence of extreme variation in the rate of molecular evolution in different ostracod groups. This rate is significantly elevated in Halocyprid ostracods, a widespread planktonic group, consistent with previous observations that planktonic groups show elevated rates of molecular evolution. At the same time, the rate of molecular evolution is slow in the lineage leading to Manawa staceyi, a relict species that we estimate diverged approximately 500 million years ago from its closest known living relative. We also report multiple cases of significant incongruence between fossil and molecular estimates of divergence times in Ostracoda. Although relaxed clock methods improve the congruence of fossil and molecular divergence estimates over strict clock models, incongruence is present regardless of method. We hypothesize that this observed incongruence is driven largely by problems with taxonomy of fossil Ostracoda. Our results illustrate the difficulty in consistently estimating lineage divergence times, even in the presence of a voluminous fossil record.     

Phylogeny of the green lacewing Chrysoperla nipponensis species‐complex (Neuroptera: Chrysopidae) in China,based on mitochondrial sequences and AFLP data

Abstract Several studies have indicated that the green lacewing, Chrysoperla nipponensis (Neuroptera: Chrysopidae) may include more than one valid species. We investigated the phylogenetic status of Chrysoperla nipponensis s.l. in China and Japan using mitochondrial sequences and AFLP data. The molecular phylogenetic analyses based on mitochondrial genes showed that the C. nipponensis species‐complex comprises four clades, each having high support values. In addition, the phylogenetic tree based on AFLP data indicates that the species‐complex comprises three groups. These results confirm that C. nipponensis s.l. comprises at least three genetically distinct clades and suggests that two of these clades may be closely related to populations of C. nipponensis in Japan. However, these clades cannot be recognized as species until analysis of their courtship songs has been completed.     

Ultrastructure of the light organ and immunocytochemical localization of luciferase in luminescent marine ostracods (Crustacea: Ostracoda: Cypridinidae)

The ultrastructure of the upper lip, which is the location of the light organ in luminescent ostracods, is described for two species of marine ostracods (Vargula graminicola, and V. tsujii). The light organ contains four primary cell types (here designated A–D) readily identified both by the types of vesicles that they contain and their location. Cell type A, restricted to the center of the light organ, has vesicles that are homogeneous throughout. Cell type B has vesicles with a single electron-dense central area. This cell is most common in the lateral regions but is also found in the tusks. Immunocytochemical experiments revealed that luciferase is found in B cells, but not in any other cells or in control specimens. Cell type C has vesicles containing many electrondense microstructures; this cell type is the least common and is found along with B cells within the lateral margins of the light organ. Cell type D has granulated vesicles and is restricted to the tusks. Metachromatic staining with toluidine blue suggests that the vesicles contain acidic mucosubstances. The cells of the light organ are very long (360–460 μm) and extend through its entire length. The cells found exclusively in the tusks are shorter (ea. 150 μm). All cells possess similar polarity: proximal synthesis, middle transitional, and distal secretory regions. These cells terminate ventrally at nozzles on the anterior portion of the upper lip, and on the tusks. The upper lip and light organ possess two large longitudinal muscles, a central muscle, and several smaller “bridle” muscles that attach onto sclerotized ridges. Various hypotheses for the storage and secretion of light organ materials are suggested relative to these morphological data. © 1993 Wiley-Liss, Inc.     

Recent ostracods (Crustacea,Ostracoda) found in lowland springs of the provinces of Piacenza and Parma (Northern Italy)

The “fontanili” are artificial aquatic ecosystems, typical of the lowland plains of Northern Italy, exploiting natural resurgences of deep groundwater. These habitats are characterized by low variation in hydrologic, hydrochemical and thermal conditions throughout the year. Proper management is required to prevent the spring clogging by biomass accumulation. In spite of their importance as refugia for endangered species, many springs were completely abandoned in the last years and several of them will disappear. We report the results of a study carried out in 2001 on 31 springs of the provinces of Piacenza and Parma, distributed in seven areas defined on hydrological and geological considerations. Physical and chemical variables and parameters of waters were measured and ostracod samples were collected. Most of the springs showed high nitrate concentration, due to a diffuse pollution of agricultural origin. Twelve ostracod species in four families were identified. Ostracod valves were analysed by scanning electron microscopy. Cypria ophtalmica was found in all the springs; other relatively common species were Cyclocypris laevis,Notodromas persica, and Prionocypris zenkeri.The maximum number of species per site was four. Cypridopsis vidua,P. zenkeri, and N. persicashowed a very localized distribution in the study area. The ostracod fauna of the “fontanili” was compared to other species assemblages found in spring habitats and to the available information on recent freshwater ostracods reported for Italy.     

Regional differences in rates of plant speciation and molecular evolution: a comparison between eastern Asia and eastern North America

The eastern Asian (EAS)-eastern North American (ENA) floristic disjunction is one of the best-known biogeographic patterns in the Northern Hemisphere. Recent paleontological and molecular analyses have illuminated the origins of the biogeographic pattern, but subsequent diversification and evolution of the disjunct floras in each of the two continents after isolation remains poorly understood. Although similar in climate and floristic composition, EAS has twice as many species as ENA in genera occurring in both regions. Explaining such differences in species diversity between regions with similar environmental conditions (diversity anomalies) is an important goal of the study of the global patterns of biodiversity. We used a phylogenetic approach to compare rates of net speciation and molecular evolution between the two regions. We first identified EAS-ENA disjunct sister clades from ten genera (Asarum, Buckleya, Carpinus, Carya, Cornus, Hamamelis, Illicium, Panax, Stewartia, and Styrax) that represent diverse angiosperm lineages using phylogenetic analyses of ITS (internal transcribed spacer of nuclear ribosomal DNA) sequence data. Species richness and substitution rate of ITS between sister clades were compared. The results revealed a pattern of greater species diversity in the EAS counterparts. A positive relationship between species diversity and ITS substitution rate was also documented. These results suggest greater net speciation and accelerated molecular evolution in EAS. The data support the idea that a regional difference in net speciation rate related to topographic heterogeneity contributes to the diversity anomaly between EAS and ENA. The close relationship between rates of ITS evolution and species richness further suggests that species production may be directly linked to rate of nucleotide substitution.     

A combined morphological and molecular phylogeny of the genus Chironius Fitzinger, 1826 (Serpentes: Colubridae)

Chironius is one of the most speciose genera of the South American colubrid snakes. Although the genus represents a well‐known radiation of diurnal racers, its monophyly, affinities with other Neotropical colubrid genera, and intrageneric relationships are open questions. Here, we present a phylogenetic analysis of Chironius based on a data matrix that combines one nuclear (c‐mos) and two mitochondrial (12S and 16S rRNA) genes with 37 morphological characters derived from scutellation, skull, and hemipenial features. Phylogenetic relationships were inferred using maximum parsimony (MP) and maximum likelihood (ML). Our combined morphological and molecular analyses strongly support the monophyly of the genus Chironius and its sister‐group relationship with a clade formed by the genera Dendrophidion and Drymobius. Phylogenetic relationships within the genus Chironius is still controversial, although five clades are retrieved with medium to strong support. © 2014 The Linnean Society of London     

Variation in allocation to sexual and asexual reproduction among clones of cyclically parthenogenetic Daphnia pulex (Crustacea: Gladocera)

Organisms reproducing by cyclical parthenogenesis combine the benefits of both sexual and asexual reproduction within the same life cycle. Few studies have examined the evolution of variation in the pattern of investment in parthenogenetic compared to sexual reproduction. Seven clones of Daphnia pulex (Crustacea: Cladocera) varying in allocation to sexual reproduction, as measured by the production of males, were raised in isolation and together in a microcosm to study the pattern of sexual reproduction and the effect of this variation on clone fitness. Sex allocation for clones raised together a microcosm was similar to their allocation when raised in isolation, suggesting a genetic basis to the variation. Three clones showed a cost of producing males that lead to their extinction after about 30 days due to the lack of females required for the clones to persist by parthenogenetic reproduction. The remaining four clones persisted until the end of the 72-day experiment. Clones with little or no allocation to males showed no increased allocation to sexual females. The seven clones showed a greater variation in estimated fitness through male and female function than in total estimated fitness. The clone with the greatest total fitness gained most of its fitness through male function but also had a relatively high fitness through female function. Although one clone produced only females it had the next highest fitness. The three clones that went extinct because of a high investment in males had estimated fitness as high as some clones that persisted in the microcosm because of a higher investment in parthenogenetic reproduction. The similarity in total fitness among clones suggests that Daphnia pulex populations in temporary habitats maintain a sex polymorphism where different genotypes vary-in functional gender ranging from female to primarily male.     

A molecular phylogenetic framework for the evolution of parasitic strategies in cymothoid isopods (Crustacea)

The parasitic isopods belonging to the family Cymothoidae attach under the scales, in the gills or on the tongue of their fish hosts, exhibiting distinctive life-histories and morphological modifications. According to conventional views, the three parasitic types (scale-, gill-, and mouth-dwellers) correspond to three distinct lineages. In this study, we have used fragments of two mitochondrial genes (large ribosomal DNA subunit, 16S rRNA, and cytochrome oxidase I) and two species for each of the three parasitic habits to present a preliminary hypothesis on the evolutionary history of the family. Our molecular data support the monophyly of the family but suggest that – contrary to what was previously believed – the more specialized mouth- and gill-inhabiting species are not necessarily derived from scale-dwelling ones.     

Structure and distribution of pelagic ostracods (Ostracoda: Myodocopa) in the Arctic Ocean

The study of the pelagic ostracod fauna of the Arctic Ocean based on materials collected by numerous Russian expeditions (1929–1993) and data from the literature showed the extreme poorness of the Arctic pelagic ostracod fauna, its mainly North Atlantic genesis and complete isolation from the Pacific fauna. Maximum ostracod abundance was observed in the epipelagic zone, and the greatest species diversity occurred in the relatively warm deep Atlantic layer throughout the year. To the north, east, and west of Franz Josef Land and Spitsbergen, the number of species and abundance indices of pelagic ostracods were decreased. In superficial water layers of the Central Arctic, maximum ostracod density and biomass were recorded in June and September. The best bioindicator of warm Atlantic water in the Arctic basin is Obtusoecia obtusata; and of cold polar water in the North Atlantic, Boroecia maxima.     

Contrasting rates of nucleotide substitution in the X-Linked and Y-Linked zinc finger genes

We have sequenced the entire exon (1,180 bp) encoding the zinc finger domain of the X-linked and Y-linked zinc finger genes (ZFX and ZFY, respectively) in the orangutan, the baboon, the squirrel monkey, and the rat; a total of 9,442 by were sequenced. The ratio of the rates of synonymous substitution in the ZFY and ZFX genes is estimated to be 2.1 in primates. This is close to the ratio of 2.3 estimated from primate ZFY and ZFX intron sequences and supports the view that the male-to-female ratio of mutation rate in humans is considerably higher than 1 but not extremely large. The ratio of synonymous substitution rates in ZFY and ZFX is estimated to be 1.3 in the rat lineage but 4.2 in the mouse lineage. The former is close to the estimate (1.4) from introns. The much higher ratio in the mouse lineage (not statistically significant) might have arisen from relaxation of selective constraints. The synonymous divergence between mouse and rat ZFX is considerably lower than that between mouse and rat autosomal genes, agreeing with previous observations and providing some evidence for stronger selective constraints on synonymous changes in X-linked genes than in autosomal genes. At the protein level ZFX has been highly conserved in all placental mammals studied while ZFY has been well conserved in primates and foxes but has evolved rapidly in mice and rats, possibly due to relaxation of functional constraints as a result of the development of X-inactivation of ZFX in rodents. The long persistence of the ZFY-ZFX gene pair in mammals provides some insight into the process of degeneration of Y-linked genes.Correspondence to: W.-H. Li     

Genetic diversity of the dung beetle,Copris tripartitus (Coleoptera: Scarabaeidae), that is endangered in Korea

The dung beetle, Copris tripartitus (Coleoptera: Scarabaeidae), is an endangered insect in Korea. In order to establish a conservation strategy, a preliminary investigation on the genetic diversity of Korean populations was performed using mitochondrial COI (658 bp), CytB (433 bp), and nuclear ITS2 (411 nucleotide positions). Sequencing of 69 individuals collected from five localities showed substantially higher variability (5.02% for COI, 4.62% for CytB, and 8.03% for ITS2). The resulting networks for mitochondrial DNA (mtDNA) haplotypes exhibited two star‐like phylogenies, which might indicate that Korean populations have recently expended from two small populations. The ITS2 network, which was presented in the form of a star‐like phylogeny, confirmed that a recent population expansion occurred. Considering the high genetic diversity and gene flow in C. tripartitus populations, one issue regarding conservation seems to be the recovery of previous habitats.     

Cryptic species within the Chydorus sphaericus species complex (Crustacea: Cladocera) revealed by molecular markers and sexual stage morphology

The cosmopolitanism paradigm in the biogeography of freshwater invertebrates is currently being replaced by non-cosmopolitanism or continental endemism. Benthic water fleas (Cladocera) from the family Chydoridae were the first group of freshwater invertebrates for which non-cosmopolitanism and cryptic diversity was substantiated by morphological studies. Yet, little is known about genetic differentiation and evolutionary history of chydorid species complexes. Here we present the first analysis of the genetic versus morphological differentiation in a benthic cladoceran species complex—Chydorus sphaericus s. str. using sequence variation in a nuclear (ribosomal internal transcribed spacer 2, ITS-2) and a mitochondrial (cytochrome c oxidase subunit I, COI) genes in 50 Holarctic localities. We tested for continental endemism and cryptic diversity predicted by previous morphological studies. We found evidence for the presence of at least seven putative regional species in the Holarctic, at least three of them being distributed beyond a single continent. While the molecular and sexual stage characters showed general concordance on species lineages, parthenogenetic female characters lacked resolution or were unassociated with molecular lineages. We conclude that cryptic regional lineages of benthic cladocerans are apparent and that the sexual stages represent the most informative morphological source of species characters for this environmental indicator group.     

传粉和非传粉榕小蜂线粒体基因组进化差异

[目的]目前关于榕小蜂类群的线粒体基因组报道很少,本研究旨在探讨传粉和非传粉榕小蜂两个群体的线粒体基因组的进化差异.[方法]以15种榕小蜂的线粒体基因组(其中11种的线粒体基因组为新测定)数据为基础,采用比较线粒体基因组学方法,分析榕小蜂的线粒体基因组序列和进化特征.[结果]本研究新测定的11个榕小蜂物种的近全长线粒体...     

High molecular and phenotypic diversity in the Merodon avidus complex (Diptera,Syrphidae): cryptic speciation in a diverse insect taxon

This paper examines molecular and phenotypic variability in the widely spread European hoverfly species complex Merodon avidus. Herein, based on the mitochondrial DNA (mtDNA) sequences of the cytochrome c oxidase subunit I (COI) and morphometric wing parameters, M. avidus is shown to comprise a complex of cryptic species, and one variety is redefined as a valid species: M. bicolor Gil Collado, 1930 (as var. of spinipes). The species M. bicolor, M. avidus A, and M. avidus B were clearly delimited based on their wing size. A total of 29 M. avidus and M. bicolor individuals presented 20 mtDNA haplotypes, four of which were shared by M. avidus A and M. avidus B, three were confined to M. bicolor, seven to M. avidus A, and six to M. avidus B. Sequence divergences between lineages occurring in the Balkan and in Spain ranged from 4.93 to 6.0 (uncorrected p in %) whereas divergences between M. avidus A and M. avidus B were 0.26 to 1.56. Divergence among morphologically identified individuals of M. avidus A and M. avidus B species ranged from 0.13 to 1.58, and from 0.13 to 0.52, respectively. The phenotypic substructuring and observed genetic uniqueness of populations in spatially and temporally fragmented M. avidus taxa were used to identify genetic units. The early split of two allopatric lineages, Spanish M. bicolor and Balkan M. avidus, was followed by diversification in each lineage. Present‐day morphological uniformity masks much of the genetic complexity of lineages within the M. avidus complex. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 819–833.     

Genetic relationships between Mt. Halla and Mongolian populations of Hipparchia autonoe (Lepidoptera: Nymphalidae)

Hipparchia autonoe belongs to the family Nymphalidae (Lepidoptera) and is designated as an endangered insect and national monument in Korea. It only inhabits a very restricted area on Mt. Halla but is widely distributed in several Asian countries including Mongolia. A previous study conducted to understand the genetic relationship between Mt. Halla and Mongolian H. autonoe for conservation purposes suffered from a limited number of samples. Therefore, we sequenced the DNA barcode region of an additional 36 H. autonoe individuals, combined them with previous data from 19 individuals, and performed phylogenetic and population genetic analyses. Furthermore, the internal transcribed spacer 2 (ITS2) region was also sequenced from the 36 samples as a nuclear DNA marker. The existence of independent haplotypes, sequence types, and significant F_ST estimates (P < 0.05) between Mt. Halla and Mongolian populations indicated hampered gene flow between the populations. Nevertheless, an absence of a reciprocal monophyletic group in Mt. Halla and Mongolian populations by cytochrome oxidase subunit I gene‐ and ITS2‐based phylogeny suggests that the genetic isolation of the Mt. Halla population from the Mongolian populations seemed not large enough to consider them independent genetic entities.     

The limits of cryptic diversity in groundwater: phylogeography of the cave shrimp Troglocaris anophthalmus (Crustacea: Decapoda: Atyidae)

Recent studies have revealed high local diversity and endemism in groundwaters, and showed that species with large ranges are extremely rare. One of such species is the cave shrimp Troglocaris anophthalmus from the Dinaric Karst on the western Balkan Peninsula, apparently uniform across a range of more than 500 kilometres. As such it contradicts the paradigm that subterranean organisms form localized, long-term stable populations that cannot disperse over long distances. We tested it for possible cryptic diversity and/or unexpected evolutionary processes, analysing mitochondrial (COI, 16S rRNA) and nuclear (ITS2) genes of 232 specimens from the entire range. The results of an array of phylogeographical procedures congruently suggested that the picture of a widespread, continuously distributed and homogenous T. anophthalmus was wrong. The taxon is composed of four or possibly five monophyletic, geographically defined phylogroups that meet several species delimitation criteria, two of them showing evidence of biological reproductive isolation in sympatry. COI genetic distances between phylogroups turned out to be a poor predictor, as they were much lower than the sometimes suggested crustacean threshold value of 0.16 substitutions per site. Most results confirmed the nondispersal hypothesis of subterranean fauna, but the southern Adriatic phylogroup displayed a paradoxical pattern of recent dispersal across 300 kilometres of hydrographically fragmented karst terrain. We suggest a model of migration under extreme water-level conditions, when flooded poljes could act as stepping-stones. In the north of the range (Slovenia), the results confirmed the existence of a zone of unique biogeographical conflict, where surface fauna is concordant with the current watershed, and subterranean fauna is not.