Effects of temperature on oocyte growth in the Mediterranean Terebellid Eupolymnia nebulosa (Annelida: Polychaeta

7 páginas, 4 figuras, 1 tabla.Eupolymnia nebulosa (Montagu) is a widely distributed terebellid polychaete that builds its tubes on the coastal shelf in areas with mixed soft and hard bottoms. From a long-term survey in the Bay of Ban- yuls, France (NW Mediterranean), we found an ad- vancement of the timing of the spawning period coin- cident with a delayed breakdown of the thermocline. We postulate that persistent high temperatures can in¯uence gamete development by stimulating oocyte growth, re- sulting in earlier spawning. During 1992 and 1993, we used a between-individuals experimental approach to assess the possible e ect of temperature on oocyte growth based on: (1) determination of the growing fraction of the oocyte population (i.e. oocyte net growth); (2) identi®cation of di erences in oocyte growth-rate among females; (3) comparison of non-sig- ni®cantly di erent size-distributions of the growing oocyte fraction (net oocyte size-distributions) at the beginning of the experiments with those at the end. No e ect of temperature on oocyte growth was detectable at the population level, but a positive individual response to prolonged high temperature was evident. Thus, the lack of a signi®cant response by the population to prolonged high temperature does not imply a lack of individual response. We propose a model of oocyte-growth dy- namics based on temperature that incorporates previous observations of extended oogenesis and oocyte growth during periods of both increasing and decreasing tem- perature and on the scattered pattern of oocyte size- distributions at the onset of spawning.This paper is a contribution to the French National Program on Re- cruitment Determinants (P.N.D.R.±G.L.O.B.E.C.), to the Marine Sciences A.E.L. and to the research project AMB94-0746 of the C.I.C.Y.T. of Spain. The ®rst and third authors were supported by grants of the C.N.R.S. and I.F.R.E.M.E.R. of France. The second author bene®ted from a fellowship of the M.E.C. of Spain (Ref. fr93 46037786) and a research contract of the C.S.I.C. of Spain.Peer reviewe

Description of a new species of Mesochaetopterus (Annelida, Polychaeta, Chaetopteridae), with re-description of M. xerecus and an approach to the phylogeny of the family.

A large chaetopterid polychaete, Mesochaetopterus rogeri sp. nov. is described as new from the Mediterranean Sea. The analyses of partial sequences from the nuclear 18S rRNA (643bp) and the mitochondrial Cytochrome Oxidase I (577bp) genes of representative individuals of all known chaetopterid genera indicated the initial assignment of the new species into Mesochaetopterus. These analyses also supported the monophyly of the family and revealed two well-supported clades: Chaetopterus / Mesochaetopterus and Spiochaetopterus / ,Phyllochaetopterus. Mesochaetopterus rogeri sp. nov. was close to M. xerecus, here re-described from newly collected material. Mesochaetopterus rogeri sp. nov. was characterized by: 1) two long tentacles with dorsal transversal black bands with alternating widths (sometimes with two additional longitudinal light-brown bands); 2) A region with nine chaetigers (up to 12), with 13 - 19 modified chaetae in the 4th; 3) B region with three flat segments, with accessory feeding organs in the 2nd and 3rd; 4) sandy straight tubes, 2.5 m long or more, vertically embedded in the sand. In the Bay of Blanes, M. rogeri sp. nov. occurs between 6 and 9 (up to 30) m deep, with a patchy distribution (< 1 ind. m-2), maximum densities in April/June (likely due to recruitment events) and minimum in September/November (likely a behavioural response to increasing sediment dynamics). Although it was originally thought that M. rogeri sp. nov. could be an introduced species, we argue that it is probably a native of the Mediterranean, which has been overlooked by scientists up to now.Peer reviewe

Dinoflagellate chromosome behaviour during stages of replication

In most dinoflagellate species, chromosomes are characterized by an almost continuous condensation of the nucleofilaments throughout the cell cycle and the absence of longitudinal differentiation as Q, G, or C banding. Their supercoiled architecture is maintained by divalent cations and structural RNAs. Their chromatin is devoid of histones and nucleosomes and their DNA composition is distinctive: in several species, more than 60% of thymines are replaced by a rare base, hydroxymethyluracil. We report here an immunofluorescence (conventional and confocal laser scanning microscopy, CLSM) and immunogold transmission electron microscopy (TEM) analysis of some stages of the early replication process in Prorocentrum micans dinoflagellate cells, after long pulse incorporation (3, 6 or 9 days) with 50 μg/ml bromodeoxyuridine (BrdU) in the presence of 5-fluoro-2´- deoxyuridine (FUdR) and BrdU antibody technique (BAT) detection. The large DNA content (45 pg per nucleus) of P. micans cells is compacted on 100 chromosomes, 10 μm in length. In early S-phase, DNA replication sites are revealed as fluorescent domains organized in clusters, which appear in the periphery of the nucleus unlike other eukaryotes. In late S-phase, the number of labelled clusters increased; helically distributed, they did not appear synchronously in the whole chromosome. Under TEM, spherical domains of equivalent diameter appeared located all along the chromosomes after 6 days BrdU pulse. Replication occurs, but in our experimental conditions, segregation of daughter chromosomes was never observed. The blockade of the cell cycle after BrdU incorporation intervening just before the segregation of daughter chromosomes is discussed

Cloning, characterization and chromosomal localization of a repeated sequence in Crypthecodinium cohnii, a marine dinoflagellate

Genomic DNA of Crypthecodinium cohnii has been extracted in the presence of cetylmethylammonium bromide and hydrolysed by 13 restriction enzymes. No typical ladder-like pattern or isolated band of satellite sequences were found with any of these enzymes. A “mini” genomic DNA library had been made and screened by reverse hybridization to isolate highly repeated sequences. Seven such DNA fragments were sequenced. The copy number of one of them (Cc18), 226 bp long, was estimated at around 25,000, representing 0.06% of the total genome. Cc18 was found to be included in a higher fragment of 3.0 kb by Southern blot analysis after cleavage by PstI. This higher molecular weight fragment could be composed either of tandemly repeated Cc18 sequences, or by only one or a very low copy number of Cc18. In this latter case, these fragments, also repeated 25,000 times would represent 1 to 2% of the total genome. Genomic localization of Cc18 by in situ hybridization on squashed C. cohnii cells showed that it was widely distributed on the different chromosomes. All the chromosomes observed displayed Cc18 labeling, which appeared homogeneously distributed. The ability of Cc18 to be a specific molecular marker to distinguish sibling C. cohnii species is discussed

Reproductive biology of Diopatra neapolitana (Annelida, Onuphidae), an exploited natural resource in Ria de Aveiro (Northwestern Portugal)

Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is an important economic natural resource in Ria de Aveiro (northwestern coast of Portugal) and throughout Europe. The species is intensively harvested for use as fresh bait. However, there is only limited knowledge about its life cycle derived from a previous study in Mediterranean Sea. Reproduction and development patterns are known to vary biogeographically, making it important to base management decisions on locally appropriate information. This work examines reproduction patterns for populations from the Eastern Atlantic, which have not previously been assessed, with an eye towards drawing Atlantic–Mediterranean comparisons and informing local management strategies. The study was conducted from May 2007 to April 2009 in Ria de Aveiro. The reproductive biology of D. neapolitana was described from the proportional variation of worms with gametes in the coelom and from the progression of the oocyte diameter. Individuals with gametes inside the coelom were found all year round, but the peak reproductive period occurred between May and August, when almost all individuals had gametes in the coelom and females contained more oocytes than at any other time of the year. The overall male:female ratio was close to 1:1 and the oocyte diameter ranged from 40 to 240 μm. In vitro fertilization was performed and the results compared to other studies. Based on the present results, some protection measures are suggested to implement a sustainable exploitation of the species

A Tri-Oceanic Perspective: DNA Barcoding Reveals Geographic Structure and Cryptic Diversity in Canadian Polychaetes

Although polychaetes are one of the dominant taxa in marine communities, their distributions and taxonomic diversity are poorly understood. Recent studies have shown that many species thought to have broad distributions are actually a complex of allied species. In Canada, 12% of polychaete species are thought to occur in Atlantic, Arctic, and Pacific Oceans, but the extent of gene flow among their populations has not been tested.Sequence variation in a segment of the mitochondrial cytochrome c oxidase I (COI) gene was employed to compare morphological versus molecular diversity estimates, to examine gene flow among populations of widespread species, and to explore connectivity patterns among Canada's three oceans. Analysis of 1876 specimens, representing 333 provisional species, revealed 40 times more sequence divergence between than within species (16.5% versus 0.38%). Genetic data suggest that one quarter of previously recognized species actually include two or more divergent lineages, indicating that richness in this region is currently underestimated. Few species with a tri-oceanic distribution showed genetic cohesion. Instead, large genetic breaks occur between Pacific and Atlantic-Arctic lineages, suggesting their long-term separation. High connectivity among Arctic and Atlantic regions and low connectivity with the Pacific further supports the conclusion that Canadian polychaetes are partitioned into two distinct faunas.Results of this study confirm that COI sequences are an effective tool for species identification in polychaetes, and suggest that DNA barcoding will aid the recognition of species overlooked by the current taxonomic system. The consistent geographic structuring within presumed widespread species suggests that historical range fragmentation during the Pleistocene ultimately increased Canadian polychaete diversity and that the coastal British Columbia fauna played a minor role in Arctic recolonization following deglaciation. This study highlights the value of DNA barcoding for providing rapid insights into species distributions and biogeographic patterns in understudied groups