Genetic divergence and assortative mating between colour morphs of the sea urchin Paracentrotus gaimardi

Some species of sea urchins feature large variation in pigmentation. This variability may be the result of phenotypic plasticity or it may be associated with genetic divergence between morphs. Paracentrotus gaimardi exhibits five colour morphs (pink, brown, green, grey and black), which often occur side by side on the same rock. We studied genetic divergence between these morphs in three populations on the coast of Brazil. A fragment of the region encoding the mitochondrial ATPase 8 and 6 mitochondrial genes, a fragment of the intron of a nuclear histone and the entire nuclear gene coding for the sperm protein bindin were analysed. Mitochondrial DNA was differentiated between the pink and all other morphs, but the histone intron was similar in all colour morphs. In bindin, nine codons were found to be under positive selection and significant differences of allelic frequencies were observed in almost all pairwise comparisons between colour morphs. Although the molecular differentiation in bindin is not large enough to suggest reproductive isolation, some degree of assortative mating within morphs seems to be occurring in this species.     

Genetic diversity and population structure of the commercially harvested sea urchin Paracentrotus lividus (Echinodermata, Echinoidea)

The population structure of the edible Atlanto-Mediterranean sea urchin Paracentrotus lividus is described by analysing sequence variation in a fragment of the mitochondrial gene cytochrome c oxidase subunit I in 127 individuals from 12 localities across south-west Europe. The study revealed high levels of genetic diversity but low levels of genetic structure, suggesting a large degree of gene flow between populations and panmixis within each, the Mediterranean and Atlantic basins. However, we found significant genetic differentiation between the two basins probably due to restricted gene flow across the geographical boundary imposed by the area of the Strait of Gibraltar. Populations of P. lividus appeared to have experienced a recent demographic expansion in the late Pleistocene. We provide new evidence on the population structure of this commercial species, predicting a healthy stock of this sea urchin on the Mediterranean and Atlantic coasts.     

Gametogenesis correlated with steroid levels during the gonadal cycle of the sea urchin Paracentrotus lividus (Echinodermata: Echinoidea)

The specific mechanism regulating reproduction in invertebrates is a field of topical interest which needs to be explored in detail considering also the intriguing possible comparison with vertebrates. In this paper levels of Testosterone (T) and Estradiol (E2) and their reciprocal ratios were determined in ovaries and testis of the echinoid model species Paracentrotus lividus during the year 2004 by taking into account a putative relationship between steroid levels and reproductive cycle. T levels appeared to significantly vary during male reproductive cycle, thus suggesting a possible role of this hormone in regulation of spermatogenesis as demonstrated for other echinoderms. E2 levels were lower in males with respect to females; consequently E2 involvement in oogenesis is hypothesized. In parallel with steroid levels evaluation, variations in P450-aromatase activity and its possible role on regulation of gametogenesis were also considered. Clear correlations between steroid levels and gonad index (GI), as well as between GI and reproductive cycle were not detected, suggesting that GI alone is not a reliable parameter in describing the reproductive status of the gonads. Altogether the results obtained so far confirm the presence of a relationship between steroid levels and reproductive cycle as suggested by previous results on different echinoderm species.     

The aboral ring and the development of early gonads in the echinoid Paracentrotus lividus (Echinodermata, Echinoidea)

Abstract. The development of the genital apparatus is described for the echinoid Paracentrotus lividus. This apparatus derives from the aboral ring, an annular structure that includes an inconspicuous coelom and, in juveniles, the germinal rachis. The germinal epithelium grows out from the germinal rachis, and the gonadal wall and coelom in early (tubular) gonads share similarities with their equivalents in the aboral ring. The original germinal rachis regresses to form a genital cord one cell wide in late juveniles. A genital cord was observed in a few field-collected adult individuals (>40 mm test diameter).     

Phagostimulation of Lytechinus variegatus (Lamarck) (Echinodermata: Echinoidea)

Artificial agarose foods containing either starch, glycogen, carragheenan, alginate, casein, gelatin, albumin, or peptones at a concentration of 1% dry weight were not phagostimulatory. Artificial foods containing sugars, especially galactose, at a concentration of 0.005 M were phagostimulatory. Of the common amino acids, only L‐phenylalanine was phagostimulatory at this concentration. The initiation of feeding postures (movement of the spines, tube feet, peristome, and Aristotle's lantern) of Lytechinus variegatus was little affected by the concentration of plant extracts. Many aspects of this behavior were attributable to physical rather than chemical stimulation. Feeding rates of L. variegatus upon artificial agarose foods containing either Thalassia testudinum or Gracilaria verrucosa were directly dependent upon plant tissue concentration. All artificial agarose food‐items were initially moved to the mouth and fed upon, however the time spent feeding was directly dependent upon plant type and tissue concentration. Retention of the artificial food‐items upon the test after feeding was not influenced by plant type or tissue concentration. Differences in consumption of foods by L. variegatus are determined by the degree of persistence in feeding upon encountered items and not be selection before initiating feeding or by retention of food‐items for subsequent feedings.     

Ultrastructure and cytochemistry of the early calcification site and of its mineralization organic matrix in Paracentrotus lividus (Echinodermata: Echinoidea)

 The ultrastructure and cytochemistry of skeleton formation sites prior to mineralization are described for the first time in echinoderms. These early sites are intracellular vacuoles located in syncytial pseudopodia of skeleteton-forming cells. They contain a mineralization organic matrix, which shows a calcium-binding ability and is framed in a tridimensional structure made of concentric layers bridged by radial threads. This organic matrix presents repetitive structures which could be implicated in mineralization control. Both the tridimensional organization of the organic matrix and its framing, before mineralization starts, question the current theories which suggest that the echinoderm organic matrix is soluble at the onset of mineralization and adsorbs on the forming crystal. Accepted: 19 March 1998     

Gonadal growth and reproduction in the commercial sea urchin Paracentrotus lividus (Lamarck, 1816) (Echinodermata: Echinoidea) from southern Spain

The reproductive state of six populations of the commercial sea urchin P. lividus was investigated. Specimens were sampled monthly from six sites of southern Spain. The development of the gonad during the period of study was measured using histological methods and categorised by four stages for females and two for male specimens. A Gonadosomatic Index was also established. The six populations exhibited similar reproductive patterns, having mature gonads during almost all months while reconstitution and spent were present mainly in autumn. The population from Sancti Petri had the highest Gonadosomatic Index value. Higher food availability may explain this difference.     

Echinoids (Echinodermata: Echinoidea) from the Gulf of Mexico

The echinoid fauna of the Gulf of Mexico collected during three research cruises (20-1260 m depth) was surveyed from samples were taken at 43 stations. A total of 190 individuals were identified (eight orders, 11 families, 15 genera and 18 species). Six species are new records for the Gulf of Mexico: Stylocidaris lineata, Phormosoma placenta placenta, Plesiodiadema antillarum, Plethotaenia spatangoides, Brissopsis atlantica and Hypselaster limicolus. This adds to the little information available on the echinoid fauna of Tamaulipas, Veracruz, Tabasco, Campeche and Yucatan states in Mexico.     

First Insights into the Biochemistry of Tube Foot Adhesive from the Sea Urchin Paracentrotus lividus (Echinoidea, Echinodermata)

Sea urchins are common inhabitants of wave-swept shores. To withstand the action of waves, they rely on highly specialized independent adhesive organs, the adoral tube feet. The latter are extremely well-designed for temporary adhesion being composed by two functional subunits: (1) an apical disc that produces an adhesive secretion to fasten the sea urchin to the substratum, as well as a deadhesive secretion to allow the animal to move and (2) a stem that bears the tensions placed on the animal by hydrodynamism. Despite their technological potential for the development of new biomimetic underwater adhesives, very little is known about the biochemical composition of sea urchin adhesives. A characterization of sea urchin adhesives is presented using footprints. The latter contain inorganic residues (45.5%), proteins (6.4%), neutral sugars (1.2%), and lipids (2.5%). Moreover, the amino acid composition of the soluble protein fraction revealed a bias toward six amino acids: glycine, alanine, valine, serine, threonine, and asparagine/aspartic acid, which comprise 56.8% of the total residues. In addition, it also presents higher levels of proline (6.8%) and half-cystine (2.6%) than average eukaryotic proteins. Footprint insolubility was partially overcome using strong denaturing and reducing buffers, enabling the visualization of 13 proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The conjugation of mass spectrometry with homology–database search allowed the identification of six proteins: alpha and beta tubulin, actin, and histones H2B, H3, H2A, and H4, whose location and function in the adhesive are discussed but require further investigation. For the remaining unidentified proteins, five de novo-generated peptide sequences were found that were not present in the available protein databases, suggesting that they might be novel or modified proteins.     

Behavioral ecology of Strongylocentrotus droebachiensis (Muller) (Echinodermata: Echinoidea)

Summary Field observation indicated that extensive aggregation behavior occurs in Strongylocentrotus droebachiensis, an important echinoid herbivore in rocky subtidal zones of northern New England. The relationship of this behavior to the behavioral ecology of this species was investigated. Laboratory studies indicated that urchins are chemically sensitive to the stimuli of food and other urchins. Quantitative field experiments with tagged animals and transects showed the existence of two types of aggregations: feeding and nonfeeding, which appear to be pervasive phenomena in the biology of S. droebachiensis.It is concluded that, depending upon their hunger state, urchins shuttle between feeding aggregations in exposed locations and non-feeding aggregations located in relatively sheltered areas (where they spend most of their time). Individuals of S. droebachiensis aggregate actively through response to other urchins in the form of chemotaxis. The aggregative behavior may be maintained for its selective value in terms of defense from predation and, to lesser extents, facilitation of feeding and breeding.     

Phylogeography and genetic structure of the edible sea urchin Paracentrotus lividus (Echinodermata: Echinoidea) inferred from the mitochondrial cytochrome b gene

Phylogeographical analysis of Paracentrotus lividus was carried out by means of sequencing the mitochondrial cytochrome b gene (1143 bp) of 260 individuals collected at 22 Mediterranean and four Atlantic localities. Against a background of high haplotype diversity and shallow genetic structuring, we observed significant genetic divergence between the Adriatic Sea and the rest of the Mediterranean, as well as between the Mediterranean and the Atlantic sample groups. Furthermore, on the largest spatial scale, isolation by distance was detected. Three main haplogroups were identified by network and Bayesian assignment analyses. The relative proportions of haplogroups were different in the four regions considered, with the exception of Western and Eastern Mediterranean that showed a similar pattern. This result together with the outcome of S_nn statistics, analysis of molecular variance and network analyses allowed to identify three weakly differentiated populations corresponding to the Atlantic, Western + Eastern Mediterranean, and Adriatic seas. Analyses of mismatch distribution and neutrality tests were consistent with the presence of genetic structuring and past demographic expansion(s). From a fisheries perspective, the results obtained in the present study are consistent with genetic sustainability of current exploitation; local depleted stocks are recurrently replenished by recruits that may have originated from nonharvested areas. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 910–923.     

Siphons and siphonal grooves in the digestive systems of the Echinoidea (Echinodermata)

Here we use histological sections and, to a limited extent, scanning electron microscopy to ascertain whether siphons or siphonal grooves parallel the stomach of five sea urchin species representing five higher taxa in the Echinoidea. We find a siphonal groove in Centrostephanus coronatus of the Diadematidae and in Caenopedina diomedeae of the Pedinidae; we find a siphon in Tromikosoma panamense of the Echinothurioida and in Strongylocentrotus purpuratus of the Camarodonta; and we find a hemisiphon in Aspidodiadema hawaiiense of the Aspidodiadematidae (it is currently unsettled whether this last group belongs in the Pedinoida or the Diadematoida). Several recent accounts of echinoid gut anatomy have claimed that species in the Echinothurioida have a siphonal groove instead of a siphon and that species in the Diadematidae and Pedinidae have siphons instead of siphonal grooves. The present work shows that these claims are mistakes and confirms that Holland and Ghiselin (1970) correctly described the distribution of siphons and siphonal grooves in the Echinoidea.     

Phylogeny of Early Cretaceous spatangoids (Echinodermata: Echinoidea) and taxonomic implications

A phylogenetic analysis of 36 species provides a test for the taxonomy and the history of Early Cretaceous spatangoids. Most taxonomic units from genera to suborders are consistent with the proposed phylogenetic framework. We retain Hemiasterina, Micrasterina, Hemiasteridae, Schizasteridae, Hemiaster , Heteraster , Mecaster , and Periaster as original monophyletic groups. However, all of these clades originate without the classical apomorphies normally ascribed to them. We suggest a revision of their diagnoses and of the generic attributions of basal species. Some ill-defined, 'primitive', and paraphyletic taxa are recognised: Toxaster , Epiaster , Palhemiaster , and Toxasteridae. Even if they do not have phylogenetic meaning, they are retained here, pending a more complete revision.     

Fine structure of the axial complex of Sphaerechinus granularis (Lam.) (Echinodermata: Echinoidea)

Summary Three regions of the axial complex in Sphaerechinus granularis can be distinguished: 1) The axial organ which protrudes from one side of the axial sinus; the sinus septum which separates the sinus from the body cavity and encloses the stone canal; the pulsating vessel which runs along the inside of the axial organ. 2) The blindly-ending terminal sinus in which the pulsating vessel broadens out to the contractile terminal process. 3) The ampulla of the stone canal which connects the axocoel and water vascular system and which opens out through the madreporite.A single-layered, monociliated coelomic epithelium surrounds all regions of the axial complex. This epithelium contains smooth muscle cells at the contractile areas. Canaliculi, surrounded by basal lamina, are formed through infolding of epithelia; they end blindly in the fluid and connective tissue -matrix of the inner structures.The lacunae of the dorso-ventral mesentery connect the periesophageal and the perianal haemal ring with the axial organ. The axial organ contains many coelomocytes rich in pigment and granules. These coelomocytes are separated into compartments by elastic fibres. Phagocytosis of whole cells and transformational stages of coelomocytes suggest storage and degradation functions. An excretory function via the water vascular system is also suggested.     

Histology of the globiferous pedicellariae of Psammechinus miliaris (Echinodermata: Echinoidea)

The general morphology, function and histology of the globiferous pedicallariae of the regular sea-urchin, Psammechinus miliaris are described. There is a ganglion under the sensory epidermis on the inner surface of each jaw. This is the first discovery of a ganglion in any echinoid.
The regeneration of globiferous pedicellariae in laboratory conditions takes 25 to 40 days.     

Phylogeny of Cidaroida (Echinodermata: Echinoidea) based on mitochondrial and nuclear markers

We present the first molecular phylogeny of Cidaroida, one of the most problematic groups within the echinoids. Two genes??the nuclear ribosomal gene 28?S rRNA and the mitochondrial protein-encoding gene COI??were obtained from 21 specimens representing 17 genera and 20 species, among which 13 species belong to Cidaroida. Phylogenetic analyses of the combined molecular data using parsimony and maximum likelihood optimality criteria resulted in a well-resolved phylogeny. Our results are broadly compatible (with the notable exception of Cidaris cidaris) with previous results obtained from morphological data. We find that Cidaroida represent a monophyletic group sister to the non-cidaroid Echinoidea. The family Cidaridae sensu Mortensen (1928) and Fell (1966) is paraphyletic because of the placement of Psychocidaris ohshimai as sister-group to Histocidaris elegans. Inside the Stylocidarina, we show that the two Atlantic species Stylocidaris affinis and Stylocidaris lineata constitute a well-supported clade. However, these two taxa could also represent two morphotypes within a single species showing high morphological variation.     

Pourtalesiid sea urchins (Echinodermata: Echinoidea) of the northern Mid-Atlantic Ridge

Five species of deep-sea pourtalesiid echinoids were collected by the RV G.O. Sars MAR-ECO expedition to the northern part of the Mid-Atlantic Ridge: Solenocystis imitans new genus, new species, Echinosigra phiale (Thomson, 1872), Echinosigra (Echinogutta) fabrefacta Mironov, 1974, and two unidentified species of Pourtalesia. Three types of plastron plating are distinguished within the family Pourtalesiidae; in Solenocystis new genus the plating is similar to that in Spatagocystis, a genus known only from the deep-sea Antarctic. Each of three groups with distinctive plastron plating shows a continuous morphological gradation from a less elongated test without subanal rostrum to an extraordinarily elongated test with large rostrum and wide subanal fasciole; the ratio width/length of test varies from 0.86 to 0.12. Some morphological characters of the pourtalesiids are regarded as adaptations to burrowing and appear to be correlated with test elongation. The family is represented in the northern Atlantic only by 'advanced' genera (Echinosigra, Pourtalesia and Solenocystis) with very elongated tests.     

FEMALE AND MALE GENETIC EFFECTS ON OFFSPRING PATERNITY: ADDITIVE GENETIC (CO)VARIANCES IN FEMALE EXTRA‐PAIR REPRODUCTION AND MALE PATERNITY SUCCESS IN SONG SPARROWS (MELOSPIZA MELODIA)

Ongoing evolution of polyandry, and consequent extra‐pair reproduction in socially monogamous systems, is hypothesized to be facilitated by indirect selection stemming from cross‐sex genetic covariances with components of male fitness. Specifically, polyandry is hypothesized to create positive genetic covariance with male paternity success due to inevitable assortative reproduction, driving ongoing coevolution. However, it remains unclear whether such covariances could or do emerge within complex polyandrous systems. First, we illustrate that genetic covariances between female extra‐pair reproduction and male within‐pair paternity success might be constrained in socially monogamous systems where female and male additive genetic effects can have opposing impacts on the paternity of jointly reared offspring. Second, we demonstrate nonzero additive genetic variance in female liability for extra‐pair reproduction and male liability for within‐pair paternity success, modeled as direct and associative genetic effects on offspring paternity, respectively, in free‐living song sparrows (Melospiza melodia). The posterior mean additive genetic covariance between these liabilities was slightly positive, but the credible interval was wide and overlapped zero. Therefore, although substantial total additive genetic variance exists, the hypothesis that ongoing evolution of female extra‐pair reproduction is facilitated by genetic covariance with male within‐pair paternity success cannot yet be definitively supported or rejected either conceptually or empirically.     

Abundance of Diadema antillarum (Echinodermata: Echinoidea) in the coasts of Venezuela

Diadema antillarum is a shallow-water sea-urchin from the tropical Atlantic whose populations almost disappeared in 1983-84 because of widespread mortalities which reached 87-100 %. In Venezuela, urchin population densities before the mortality event were comparable to those of other Caribbean regions; however, later abundancies remain unknown. The objectives of this study were to evaluate the recent densities of certain D. antillarum populations along the Venezuelan coasts and compare the densities at the Parque Nacional Mochima before and after the mortality. At each location urchin densities were determined by means of transects using 1 m2-quadrats as sampling units. The highest mean densities were observed at the sites on the central coast: Ensenada de Oricao, 0.28 ind/m2 (2002) and 1.05 ind/m2 (2003), and Chichiriviche de la Costa, 0.84 ind/m2 (2002) and 0.74 ind/m2 (2003). In Mochima, the mean density before the mortality for D. antillarum oscillated between 0.28 and 4 ind/m2, after the mortality event the mean density varied between 0.15 ind/m2 (2000) and 0.47 ind/m2 (2000). The populations of D. antillarum studied at Parque Nacional Morrocoy and Refugio de Fauna Silvestre Cuare showed highest densities at Playuela (0.43 ind/m2) and Cayo Sur (0.95 ind/m2) respectively, whereas other sites showed densities below 0.1 ind/m2. The density registered at Playuela in 2003 is lower than that reported before the mortality event (0.58-3.64 ind/m2). The density for Parque Nacional Archipiélago de Los Roques, specifically for the Arrecife de Herradura remained constant between 2002 and 2003 with values between 0.22-0.23 ind/m2 respectively. To conclude, the sea urchin abundancies observed at most of the Venezuelan coastal sites that we studied were higher than those reported for other areas of the northern Caribbean, even though the values have not yet returned to those preceding the 1984 mass-mortality event, due to the slow recovery of the populations.