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Tsuyoshi Uehara - One of the best experts on this subject based on the ideXlab platform.
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Effect of temperature on interactions between eggs and spermatozoa in four closely related species of sea urchins of the genus Echinometra
Invertebrate Reproduction & Development, 2020Co-Authors: Masatoshi Mita, Tsuyoshi Uehara, Masaru NakamuraAbstract:Summary Sea urchins of the genus Echinometra are abundant on reef flats in southern Japan. The Okinawan Echinometra is divided into four sympatric and closely related species, Echinometra tsumajiroi (Ea), Echinometra mathaei (Eb), Echinometra ryukyuensis (Ec), and Echinometra oblonga (Ed). To obtain further information of these four species, this study examined the effect of temperature on the interactions between eggs and spermatozoa. Fertilization in all four Echinometra species showed marked temperature dependence. Temperatures above 15°C were required for fertilization and fertilization was virtually zero at temperatures below 10°. Furthermore, the acrosome reaction of spermatozoa in Ea, Eb, Ec and Ed induced by egg-jelly was influenced by temperature. The acrosome reaction hardly occurred at 0°C in the four species, and the proportion of reactive spermatozoa treated with sea water containing egg-jelly increased with temperature to a maximum at 20° but was lower at 30°. The study did not reveal any su...
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effects of delayed metamorphosis on larval survival metamorphosis and juvenile performance of four closely related species of tropical sea urchins genus Echinometra
The Scientific World Journal, 2014Co-Authors: Aminur M Rahman, Fatimah Md Yusoff, Aziz Arshad, Tsuyoshi UeharaAbstract:We report here, the effects of extended competency on larval survival, metamorphosis, and postlarval juvenile growth of four closely related species of tropical sea urchins, Echinometra sp. A (Ea), E. mathaei (Em), Echinometra sp. C (Ec), and E. oblonga (Eo). Planktotrophic larvae of all four species fed on cultured phytoplankton (Chaetoceros gracilis) attained metamorphic competence within 22–24 days after fertilization. Competent larvae were forced to delay metamorphosis for up to 5 months by preventing them from settling in culture bottles with continuous stirring on a set of 10 rpm rotating rollers and larval survival per monthly intervals was recorded. Larval survival was highest at 24 days, when competence was attained (0 delayed period), and there were no significant differences among the four species. Larvae that had experienced a prolonged delay had reduced survival rate, metamorphosis success, and juvenile survival, but among older larvae, Em had the highest success followed by Ea, Eo, and Ec. Juveniles from larvae of all four species that metamorphosed soon after becoming competent tended to have higher growth rates (test diameter and length of spines) than juveniles from larvae that metamorphosed after a prolonged period of competence with progressively slower growth the longer the prolonged period. Despite the adverse effects of delaying metamorphosis on growth parameters, competent larvae of all four species were able to survive up to 5 months and after metamorphosis grew into 1-month-old juveniles in lab condition. Overall, delayed larvae of Em showed significantly higher larval survival, metamorphosis, and juvenile survival than Ea and Eo, while Ec showed the lowest values in these performances. Em has the most widespread distribution of these species ranging from Africa to Hawaii, while Ec probably has the most restricted distribution. Consequently, differences in distribution may be related to differences in the ability to delay metamorphosis.
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feeding rates and absorption efficiencies of four species of sea urchins genus Echinometra fed a prepared diet
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2007Co-Authors: Yuji Hiratsuka, Tsuyoshi UeharaAbstract:Abstract Four closely related species of sea urchins belonging to the genus Echinometra , Echinometra sp. A (Ea), E. mathaei (Em), E. sp. C (Ec), and E. oblonga (Eo), occur sympatrically but in different microhabitats on Okinawan coral reefs. Feeding rates and absorption efficiencies of the four species were investigated in the laboratory by feeding sea urchins ad libitum a diet prepared from turf algae and agar over a 7-day period. Feeding rates differed significantly among the four species of Echinometra (Ea > Em ≈ Ec > Eo). Absorption efficiencies of protein and lipid did not differ significantly among the four species. Carbohydrate, a major nutrient component in the diet, was absorbed by the four species at significantly different efficiencies (Eo > Ec ≈ Em > Ea), which resulted in similar interspecific differences in absorption efficiencies of dry matter, total organic matter, and energy. The amount of nutrients absorbed from the diet was directly related to the feeding rate, indicating that the increase in absorption efficiency was not sufficient to completely compensate for low feeding rate. The interspecific difference in physiological performance in relation to feeding and absorption is consistent with taxonomic differentiation among the four species.
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interspecific and intraspecific variations in sibling species of sea urchin Echinometra
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2004Co-Authors: Sk Mustafizur Rahman, Tsuyoshi UeharaAbstract:Interspecific and intraspecific morphological and fertilization variations were studied in three sibling species of Echinometra (known as sp. B, C and D) found off the coast of Okinawa, Japan. Eggs from C and D were readily fertilized by sperm from all three color morphs of B when the sperm concentrations were high, but no fertilization was observed when sperm of the former were mixed with eggs from the latter. Under limiting sperm concentrations, however, both C and D were incapable to fertilize reciprocally with B. In contrast, crossing between C and D produced fertilization membrane at high and limiting sperm concentrations in both directions. Interspecific crosses between B vs. C and B vs. D clearly showed that these combinations were reproductively isolated in contrast to that observed for crossing between C and D. Interestingly, intraspecific fertilization of B showed considerable morphological variation in addition to variability in fertilization success. Intraspecific fertilization and morphological variations may occur due to a number of genetic and/or non-genetic factors. While the underlying cause(s) remain to be elucidated, the results of the present study suggest that B is now speciating very slowly.
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speciation in four closely related species of sea urchins genus Echinometra with special reference to the acrosome reaction
Invertebrate Reproduction & Development, 2004Co-Authors: Masatoshi Mita, Tsuyoshi Uehara, Masaru NakamuraAbstract:Summary Sea urchins of the genus Echinometra are abundant on Okinawa reef flats in southern Japan. The Okinawan Echinometra is subdivided into four sympatric and closely related species (Ea, Eb, Ec, and Ed). To elucidate the relationships between them, we have examined the effect of egg jelly on the acrosome reaction, a process sea urchin spermatozoa undergo before fertilization. When Echinometra spermatozoa were treated with egg jelly, the acrosome reaction in each species was, as expected, effectively induced by jelly from the same species. The acrosome reaction in Ed spermatozoa was induced by egg jelly regardless of species, whereas the acrosome reaction of Eb spermatozoa took place only when it was treated with Eb egg jelly. The acrosome reaction of Ea spermatozoa was induced by jelly from species Ea or Eb, while Ec spermatozoa responded to egg jelly from Ea, Ec, or Ed. These results suggest that the separation of these four species of Okinawan Echinometra has taken place quite recently. An additiona...
Robyn Cumming - One of the best experts on this subject based on the ideXlab platform.
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variation in abundance and spatial distribution of ecomorphs of the sea urchins Echinometra sp nov a and e sp nov c on a fijian reef
Hydrobiologia, 2004Co-Authors: Subhash Appana, Veikila C Vuki, Robyn CummingAbstract:This paper presents novel spatial distribution and abundance patterns of ecomorphs of Echinometra sp. nov A andE. sp. nov C (hereafter referred to as E. sp. A and E. sp. C, and collectively as Echinometra spp.). Echinometraspp. were surveyed on the Nukubuco Reef, to determine the within-reef variations in size-frequency and density atseveral spatial scales [between positions (east versus west), zones (crest versus flat), sites and quadrats]. The scalesof variation were greatest for both species between positions and zones. Echinometra sp. A was more readily foundon the calmer flats while E. sp. C preferred the high-energy crests. The distribution of ecomorphs of Echinometraspp. varied between habitats (position x zone). Echinometra sp. A ecomorphs were more abundant on all locationsand showed different size-class distributions compared with E. sp. C. Greater urchin numbers were observed onboth zones of the eastern position than the western position. Echinometra sp. A showed marginal aggregationpattern while E. sp. C showed a stronger tendency to cluster.
Sönke Johnsen - One of the best experts on this subject based on the ideXlab platform.
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Spatial vision in the echinoid genus Echinometra.
The Journal of experimental biology, 2020Co-Authors: Erin Blevins, Sönke JohnsenAbstract:Although eyes are generally considered necessary for image resolution, a diffuse photoreceptive system with directional sensitivity may also have this ability. Two species of the echinoid genus Echinometra were tested for spatial vision by examining their ability to locate and move towards targets of different sizes. The echinoids were significantly oriented (P
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spatial vision in the echinoid genus Echinometra
The Journal of Experimental Biology, 2004Co-Authors: Erin Blevins, Sönke JohnsenAbstract:SUMMARY Although eyes are generally considered necessary for image resolution, a diffuse photoreceptive system with directional sensitivity may also have this ability. Two species of the echinoid genus Echinometra were tested for spatial vision by examining their ability to locate and move towards targets of different sizes. The echinoids were significantly oriented ( P <0.0001) towards a target with an angular width of 33° (0.3 sr) but were not oriented to targets with angular widths of 26° and 16°. This ability is probably due to the blocking of off-angle light by the spines, which have approximately the correct spacing for the observed resolution. Spatial vision is advantageous for echinoids of this genus because they leave and return to small dark shelters. This first demonstration of spatial vision in an echinoderm sheds further light on the complex optical structures and photobehaviors found in this phylum.
Harilaos A. Lessios - One of the best experts on this subject based on the ideXlab platform.
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Lack of Character Displacement in the Male Recognition Molecule, Bindin, in Altantic Sea Urchins of the Genus Echinometra
Molecular Biology and Evolution, 2009Co-Authors: Laura B. Geyer, Harilaos A. LessiosAbstract:: Bindin, a protein involved in sea urchin sperm-egg recognition and adhesion, is under positive selection in genera with sympatric species but evolves neutrally in genera in which all species are allopatric. This pattern has led to suggestions that reinforcement may be the source of the observed selection. Reproductive character displacement, or increased divergence of reproductive characters in areas where closely related species overlap, is often a consequence of reinforcement and has been shown to be present in one Indo-Pacific species of the genus Echinometra. In the Atlantic species of the same genus, positive selection has been shown to act on bindin of Echinometra lucunter. To examine whether the source of this selection is reinforcement, we determined variation on the first exon of bindin in E. lucunter in the Caribbean, where it is sympatric with Echinometra viridis, and in the rest of the Atlantic, where E. viridis is absent. There was no differentiation between bindin sequences from the two geographic regions; similar levels of positive selection were found to be acting in both areas. The similarities were not due to gene flow; mitochondrial DNA from the two regions indicates that E. lucunter populations most likely originated in the Atlantic and have not exchanged genes with Caribbean populations for approximately 200,000 years. The lack of evidence of stronger selection on bindin of E. lucunter in areas of sympatry with its sister species suggests that the source of selection is not reinforcement. Processes acting within species, such as sexual selection, sperm competition, or sexual conflict, are more likely to be involved in the evolution of this molecule.
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adaptive evolution of sperm bindin tracks egg incompatibility in neotropical sea urchins of the genus Echinometra
Molecular Biology and Evolution, 2004Co-Authors: Michael A Mccartney, Harilaos A. LessiosAbstract:: Bindin is a gamete recognition protein known to control species-specific sperm-egg adhesion and membrane fusion in sea urchins. Previous analyses have shown that diversifying selection on bindin amino acid sequence is found when gametically incompatible species are compared, but not when species are compatible. The present study analyzes bindin polymorphism and divergence in the three closely related species of Echinometra in Central America: E. lucunter and E. viridis from the Caribbean, and E. vanbrunti from the eastern Pacific. The eggs of E. lucunter have evolved a strong block to fertilization by sperm of its neotropical congeners, whereas those of the other two species have not. As in the Indo-West Pacific (IWP) Echinometra, the neotropical species show high intraspecific bindin polymorphism in the same gene regions as in the IWP species. Maximum likelihood analysis shows that many of the polymorphic codon sites are under mild positive selection. Of the fixed amino acid replacements, most have accumulated along the bindin lineage of E. lucunter. We analyzed the data with maximum likelihood models of variation in positive selection across lineages and codon sites, and with models that consider sites and lineages simultaneously. Our results show that positive selection is concentrated along the E. lucunter bindin lineage, and that codon sites with amino acid replacements fixed in this species show by far the highest signal of positive selection. Lineage-specific positive selection paralleling egg incompatibility provides support that adaptive evolution of sperm proteins acts to maintain recognition of bindin by changing egg receptors. Because both egg incompatibility and bindin divergence are greater between allopatric species than between sympatric species, the hypothesis of selection against hybridization (reinforcement) cannot explain why adaptive evolution has been confined to a single lineage in the American Echinometra. Instead, processes acting to varying degrees within species (e.g., sperm competition, sexual selection, and sexual conflict) are more promising explanations for lineage-specific positive selection on bindin.
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dispersal barriers in tropical oceans and speciation in atlantic and eastern pacific sea urchins of the genus Echinometra
Molecular Ecology, 2000Co-Authors: Michael A Mccartney, Gwen P Keller, Harilaos A. LessiosAbstract:Echinometra is a pantropical sea urchin made famous through studies of phylogeny, spe- ciation, and genetic structure of the Indo-West Pacific (IWP) species. We sequenced 630 bp of the cytochrome oxidase I (COI) mitochondrial gene to provide comparable information on the eastern Pacific and Atlantic species, using divergence between those separated by closure of the Isthmus of Panama 3.1 million years ago (Ma) to estimate dates for cladogenic events. Most recently (1.27-1.62 Ma), the Atlantic species E. lucunter and E. viridis diverged from each other, at a time in the Pleistocene that sea levels fell and Caribbean coral speciation and extinction rates were high. An earlier split, assumed to have been coincident with the completion of the Isthmus of Panama, separated the eastern Pacific E. vanbrunti from the Atlantic common ancestor. Transisthmian COI divergence similar to that in the sea urchin genus Eucidaris supports this assumption. The most ancient split in Echinometra occurred between the IWP and the neotropical clades, due to cessation of larval exchange around South Africa or across the Eastern Pacific Barrier. Gene flow within species is generally high; however, there are restrictions to genetic exchange between E. lucunter populations from the Caribbean and those from the rest of the Atlantic. Corre- lation between cladogenic and vicariant events supports E. Mayr's contention that marine species, despite their high dispersal potential, form by means of geographical separation. That sympatric, nonhybridizing E. lucunter and E. viridis were split so recently suggests, however, that perfection of reproductive barriers between marine species with large popula- tions can occur in less than 1.6 million years (Myr).
Yossi Loya - One of the best experts on this subject based on the ideXlab platform.
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photoperiod temperature and food availability as drivers of the annual reproductive cycle of the sea urchin Echinometra sp from the gulf of aqaba red sea
Coral Reefs, 2015Co-Authors: Omri Bronstein, Yossi LoyaAbstract:In spite of the efforts invested in the search for the environmental factors that regulate discrete breeding periods in marine invertebrates, they remain poorly understood. Here, we present the first account of the annual reproductive cycle of the pantropical sea urchin Echinometra sp. from the Gulf of Aqaba/Eilat (Red Sea) and explore some of the main environmental variables that drive echinoid reproduction. Monthly measurements of gonado-somatic indexes and histological observations of 20 specimens revealed a single seasonal reproductive cycle, with gametogenesis in males and females being highly synchronized. Gametogenesis commenced in June and peak spawning occurred between September and October. Gonado-somatic indexes were significantly correlated with seawater temperatures but not with photoperiod. The latter cycle lagged behind the gonado-somatic cycle by two months, suggesting that the onset of gametogenesis corresponds to shortening day length, while spawning may be driven by warming seawater temperatures. Gonads remained quiescent throughout the winter and spring (January through May) when temperatures were at their lowest. Chlorophyll-a concentrations increased significantly in the months following spawning (October through January). These high concentrations are indicative of high phytoplankton abundance and may reflect the increase in food availability for the developing larvae. Of the external test dimensions, length presented the highest correlation to body weight, indicating length as the best predictor for body size in Echinometra. Neither sexual dimorphism nor size differences between males and females were detected, and the sex ratios were approximately 1:1 in three distant Echinometra populations. Environmentally regulated reproduction, as occurs in sea urchins, might face severe outcomes due to anthropogenic disturbances to the marine environment. Consequently, there is a need to deepen our understanding of the mechanisms that drive and regulate this process in broadcast-spawning species.
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the taxonomy and phylogeny of Echinometra camarodonta echinometridae from the red sea and western indian ocean
PLOS ONE, 2013Co-Authors: Omri Bronstein, Yossi LoyaAbstract:The number of valid species in the genus Echinometra (Echinodermata, Echinoidea) and their associated identification keys have been debated in the scientific literature for more than 180 years. As the phylogeny and dispersal patterns of these species have been widely used as a prominent model for marine speciation, new insights into their taxonomy have the potential to deepen our understanding of marine speciation processes. In this study we examine Echinometra taxonomy, combining morphology and molecular tools. We present the taxonomy and phylogeny of Red Sea and Western Indian Ocean Echinometra. The currently available morphological keys were found to be limited in their ability to delineate all species within this genus. Nonetheless, morphological similarities between the Red Sea and Western Indian Ocean populations were high, and delimited them from the other species. These latter populations together formed a monophyletic clade, genetically distant from any of the other Echinometra species by more than 3%. Combining both traditional taxonomy and molecular evidence, we found that these populations were neither Echinometra mathaei nor E. oblonga, as previously considered. The morphological discrepancies of these populations, and their genetic divergence from the other Echinometra species, suggest that they should be considered as a new Echinometra species.
