Selective feeding by the echinoid,Evechinus chloroticus,and the removal of plants from subtidal algal stands in Northern New Zealand

Summary Feeding choice of the echinoid Evechinus chloroticus was examined for six fucoid and one laminarian species of algae. Three experiments were conducted to determine the algal choice by echinoids under controlled conditions. In the first experiment, the seven algal species were presented to echinoids in laboratory conditions. The second experiment had replicates of the algal species placed randomly on a subtidal rocky reef where echinoids were abundant and randomly dispersed. For the third experiment, which was also field-based, replicates of one highly-ranked species, Ecklonia radiata, were presented to naturally dispersed Evechinus. In addition, a series of controlled observations was used to examine the order in which echinoids removed algae from mixed species stands on subtidal boulders and to determine if this was related to the experimentally demonstrated choices of algal species.The results of the first two experiments showed that there were differences between algal species in the amount of material grazed by echinoids. Rankings of algal species from the field experiment were not correlated with rankings from the laboratory experiment. The order of removal of algal species from natural stands was correlated with the laboratory-based experimental rankings of algal species, but not with the rankings from the field-based experiment or with algal species availability. There were differences between algal species in their vulnerability to grazing by echinoids, as measured by regression analyses on the amount of material grazed from algal replicates vs. the number of attached echinoids. Within each species, echinoid numbers exerted a non-linear effect on the removal of algal material. In the third experiment, where only one species of algae was presented, the echinoids still distributed themselves non-randomly amongst replicates, aggregating on some samples.Data on the finer scale distribution of algal species over the entire subtidal reef on which these experiments and observations were conducted indicate that Evechinus are not often presented with a choice of adult plants of several different species in natural stands.The evidence from this study supports the conclusion that feeding preferences by echinoids are labile and do not clearly exert the major influence on the removal of plants from natural stands. Preference, as determined from experimental rankings of algal species, is only one of a number of factors which may affect the removal of algae by echinoids. Other important factors are the density of echinoids present, algal susceptibility to removal, and the distribution and abundances of the various algal species and echinoids relative to each other. It is suggested that algal life history characteristics may be unaffected by echinoids and that coevolutionary arguments are not appropriate for describing echinoid-algal interactions.     

Transformation of algal turf by echinoids and scarid fishes on French Polynesian coral reefs

The respective roles of regular echinoids and scarid fishes in the transformation of turf algae, the main food resource for reef herbivores, were investigated on French Polynesian coral reefs. The role of one species of parrotfish (Scarus sordidus) was compared with that of four species of echinoids. The degree and ways of degradation of the algal matter were determined by the organic matter percentage, the composition of the sugar fraction, and the concentration and composition of chlorophylltype pigments as assayed by HPLC analysis. Chemical analyses were performed on anterior and posterior intestines for scarids, intestinal contents and faeces for echinoids, and on fresh algal turf as a control of initial food quality. A decrease in mean percentage of organic matter in gut content was observed from intestine (9.7%) to faeces (7%) in sea urchins, but not in parrotfishes. The total sugar fraction decreased from fresh algal turf (32% of total organic matter) to echinoid (28%) to scarid (18%) gut contents. The ratio of insoluble to soluble sugars (I/S ratios) was higher in echinoids (2.6) than in scarid gut contents (1.0). A decrease in the total pigment concentration was measured from fresh algal turf to echinoid and it was found to be even lower in scarid gut contents. Chromatograms showed that the composition of chlorophyll-type pigments in scarid intestines was very similar to fresh algal turf, with a dominance of native forms, mainly chlorophyll a and b. On the contrary, degraded pigment forms dominated in echinoids. The main degraded products were pheophorbides in sea urchins, and chlorophyllides in parrotfishes. These results provided evidence for differentiation in digestive processes occurring in the two types of grazers. Echinoids released higher degraded algal material than did scarids. Thus, these two types of grazers play different roles in the recycling of organic matter on coral reefs.     

Diversity of Cenozoic marsupiate echinoids as an environmental indicator

McNamara, K.J. 1994 10 15: Diversity of Cenozoic marsupiate echinoids as an environmental indicator. Marsupiate echinoids are today largely confined to the seas around Antarctica. Consequently, it has often been inferred that the presence of marsupiate echinoids in the fossil record is indicative of the former existence of low oceanic temperatures. In this study the distribution of marsupiate echinoids through the Cenozoic succession of southern Australia is compared with palaeo-temperature data to test this assumption. The analysis reveals that there is no positive correlation between high marsupiate echinoid diversity during the Cenozoic and low oceanic temperatures. An alternative hypothesis, based on life-history strategies, is investigated. This reveals that marsupiate echinoids show many characteristics typical of organisms with slow growth, long life spans and production of few, large offspring. It is suggested that the northward migration of Australia during the Cenozoic from an original high-latitude location in the early Cenozoic was accompanied by an increase in environmental instability in the southern Australian region in the late Cenozoic. This led to a consequent decrease in marsupiate echinoid diversity. During the Pliocene these direct brooding echinoids were replaced by non-brooders with pelagic lecithotrophic larvae, which dominate the southern coastal echinoid fauna of Australia today. The environmental stability experienced in southern Australia in the early Cenozoic persisted throughout the Cenozoic in the Antarctic region, particularly with regard to predictability of nutrient supply. The result has been the dominance of marsupiate echinoids in that region today. Temporal changes in the diversity of marsupiate echinoids in southern Australia therefore supports the view that their spatial and temporal distribution may be more closely correlated with aspects of their life-history strategy and environmental stability than with low temperature. Echinoidea, evolution, diversity, life-history strategy, Cenozoic.     

Lateral variations of size-frequency distribution in a fossil echinoid community and their palaeoecological significance

The analysis of size-frequency spatial distribution of three species of Cenomanian echinoids in a single fossil assemblage shows both intraspecific and interspecific horizontal segregation of the individuals parallel to the variations in silt and organic matter levels of the substrate. The exceptional preservation of echinoids. fossilized in the living position with part of their spines. and their multimodal size-frequency distribution, with no evidence of physical transportation. suggest that a catastrophic event resulted in the fossilization of the demographic structure of the populations. The assemblage. being the result of mass mortality of a community, corresponds to a census assemblage. Thus the patchy segregation of echinoids could not primarily be influenced by size-selective taphonomy (current winnowing, biological or mechanical destruction) but more likely determined by biological phcnomena like mortality and recruitment patterns, high juvenile growth, substrate selection and herd mode of life. Recent examples of spatial separation of adults and juveniles. given for different species of echinoids. show that these patchy distributions are widespread, and therefore may be a privileged source of fossil preservation of cohort's size-frequency distribution in catastrophic mortality. □ Palaeoecology, size-frequency distribution, demography, echinoids. spatangoids, cassiduloids, M ecaster , C atopygus , N ucleopygus .     

Systematic assessment of the Atelostomata (Spatangoida and Holasteroida; irregular echinoids) based on spine microstructure

Spines of irregular echinoids occur in very high abundance in each specimen, and display distinct architecture as a result of the specialized functions of the spines; however, studies on spine microstructure in atelostomate echinoids have rarely been carried out. Accordingly, little is known about their specific morphology. This work aims to elaborate differences in the spine morphology of selected Atelostomata (Spatangoida and Holasteroida) in detail, and to discuss spine microstructure for its potential systematic value. Based on 82 atelostomate species (56 spatangoids and 26 holasteroids), we show that the perforation pattern in the internal cylinder of the spine (helicoidal versus horizontal pattern) provides a safe distinction between the Spatangoida and Holasteroida. According to this character we discuss the geological history of atelostomate echinoids, in particular their migration into the deep sea, based on well‐preserved records of fossil spines. © 2015 The Linnean Society of London     

The evolution of pedicellariae in echinoids: an arms race against pests and parasites

Coppard, S.E., Kroh, A. and Smith, A.B. (2010). The evolution of pedicellariae in echinoids: an arms race against pests and parasites. —Acta Zoologica (Stockholm) 00 :1–24. Sea urchins (Echinoidea) have evolved a diverse array of jawed appendages termed pedicellariae to deter pests and predators. Pedicellarial structure and function are reviewed and their distribution mapped in 75 extant genera. Using a phylogeny of echinoids at family level constructed from 353 skeletal characters scored across 162 extant and fossil taxa, the evolution of pedicellarial form and function is reconstructed. For much of the Palaeozoic echinoids possessed a very restricted pedicellarial armament. By the early Mesozoic a diverse array of pedicellarial types had become established, implying that the threat from predators and pests markedly increased at this time. Since the Triassic, echinoids have continued to improve their defensive capability by evolving more effective venom delivery in globiferous pedicellariae, developing spatulate‐tips and curved blades for a more efficient grab in tridentate pedicellariae, and stouter, more robust valves with a stronger bite in ophicephalous pedicellariae to disable and remove ectoparasites. However, pedicellarial types are shown to be particularly prone to subsequent secondary loss, especially among infaunal echinoids, and thus have higher homoplasy levels than other phylogenetically useful skeletal structures.     

Development of the nervous system in the brittle star Amphipholis kochii

There are several studies of neural development in various echinoderms, but few on ophiuroids, which develop indirectly via the production of pluteus larvae, as do echinoids. To determine the extent of similarity of neuroanatomy and neural development in the ophiuroids with other echinoderm larvae, we investigated the development of the nervous system in the brittle star Amphipholis kochii (Echinodermata: Ophiuroidea) by immunohistochemistry. Immunoreactive cells first appeared bilaterally in the animal pole at the late gastrula stage, and there was little migration of the neural precursors during A. kochii ontogeny, as is also the case in echinoids and holothuroids. On the other hand, neural specification in the presumptive ciliary band near the base of the arms does occur in ophiuroid larvae and is a feature they share with echinoids and ophiuroids. The ophiopluteus larval nervous system is similar to that of auricularia larvae on the whole, including the lack of a fine network of neurites in the epidermis and the presence of neural connections across the oral epidermis. Ophioplutei possess a pair of bilateral apical organs that differ from those of echinoid echinoplutei in terms of relative position. They also possess coiled cilia, which may possess a sensory function, but in the same location as the serotonergic apical ganglia. These coiled cilia are thought to be a derived structure in pluteus-like larvae. Our results suggest that the neural specification in the animal plate in ophiuroids, holothuroids, and echinoids is a plesiomorphic feature of the Ambulacraria, whereas neural specification at the base of the larval arms may be a more derived state restricted to pluteus-like larvae.     

Echinoids,epizootics and ecological stability in the rocky subtidal off Nova Scotia,Canada

Mass mortalities ofStrongylocentrotus droebachiensis, attributed to disease, have occurred along the Atlantic coast of Nova Scotia from 1980 to 1982. An amoeboid protist has been tentatively identified as the pathogenic agent. Temperature appears to play an important role in triggering epizootics and determining the extent of mortality. Epizootics have occurred in the autumn of each year during months of record high temperatures. The virtual elimination of echinoids over a large area of coast has enabled regeneration of kelp beds. Disease may play a key role in determining the structure and stability of benthic communities off Nova Scotia and elsewhere by controlling echinoid abundance.     

Resolving phylogenetic signal from noise when divergence is rapid: a new look at the old problem of echinoderm class relationships

Resolving evolutionary relationships in groups that underwent fast radiation in deep time is a problem for molecular phylogeny, as the scant phylogenetic signal that characterises short internal branches is generally swamped by more recent substitutions. We implement an approach, that maps how the support for rival phylogenies changes when analysing subsets of sites with either faster and more heterogeneous rates or slower and more homogeneous rates, to address a long-standing problem in deuterostome phylogeny - the interrelationships of the eleutherozoan echinoderm classes. We show that miRNA genes are phylogenetically uninformative as to the relationships of asteroids, echinoids and ophiuroids, consistent with a rapid radiation of these groups as suggested by their fossil record. Using three nuclear rRNAs and seven nuclear housekeeping genes, we map the support for the three possible phylogenetic arrangements of asteroids, ophiuroids and echinoids when moving between subsets of the data with very similar or very different rates of evolution. Only one of the three possible topologies (asteroids (ophiuroids + echinoids)) strengthens when the most rate-homogeneous subset of data are analysed. The other two possible pairings become stronger in a less reliable data subset, which includes the fastest and thus homoplasy-rich data in our alignment. Thus, while superficial analysis of our concatenated alignment identifies asteroids and ophiuroids as sister taxa, more thorough analyses suggest that ophiuroids may be more closely related to echinoids. Divergence of these echinoderm groups, using a relaxed molecular clock, is estimated to have occurred within ∼5 million years. Our results illustrate that the analytic approach of phylogenetic signal dissection can be a powerful tool to investigate rapid radiations in deep geologic time.     

Antarctic echinoids and climate change: a major impact on the brooding forms

Ocean acidification (OA) and the accompanying changes to carbonate concentrations are predicted to have especially negative impacts in the Southern Ocean where, as a result of colder temperatures, there will be shallowing of both the aragonite (ASH) and calcite saturation horizons (CSH). Echinoids are a dominant group of the Antarctic macrofauna which, because of their high‐Mg calcite skeleton, are particularly susceptible to changes in the ASH. Using published information on the bathymetric distributions of Antarctic echinoids, we show that the majority of heavily calcified echinoids have their lower bathymetric limit above a depth of ca. 3000 m, approximately the current depth of the CSH. Echinoids whose depth range extends below 3000 m generally have thin, weakly calcified tests and include species from the Order Holasteroida, and the Families Cidaridae and Schizasteridae. Examination of the reproductive mode of Antarctic echinoids shows that brooding, where calcification of the young occurs in the same CaCO₃ environment as the mother, is primarily found at a depth above 3000 m. The predicted shallowing of the ASH and CSH under OA conditions is likely to negatively impact growth and reproduction of heavily calcified brooders in the Family Cidaridae, which may result in changes to bathymetric ranges, local population extinction, and associated losses in macrofaunal biodiversity. As with other calcified deep sea invertebrates, echinoids may be particularly vulnerable to the impacts of increased CO₂ and OA in the Southern Ocean.     

Comparative Morphology of Echinoderm Sperm and Possible Phylogenetic Implications

The sperm morphology of at least 7 crinoids, 11 ophiuroids,23 asteroids, 23 holothuroids, and 37 echinoids is known. Forall the known crinoids, ophiuroids, and asteroids, the spermare spherical, while those of echinoids are conical. Holothuroidsperm are basically spherical, with two exceptions: cylindricalin Cucumaria lubrica and tabloid in Cucumaria pseudocurata.The possible implications of sperm morphology in the mode offertilization and in echinoderm phylogeny are discussed.     

Larval ectoderm, organizational homology, and the origins of evolutionary novelty

Comprehending the origin of marine invertebrate larvae remains a key domain of research for evolutionary biologists, including the repeated origin of direct developmental modes in echinoids. In order to address the latter question, we surveyed existing evidence on relationships of homology between the ectoderm territories of two closely related sea urchin species in the genus Heliocidaris that differ in their developmental mode. Additionally, we explored a recently articulated idea about homology called 'organizational homology' (Müller 2003. In: Müller GB, Newman SA, editors. Origination of organismal form: beyond the gene in developmental and evolutionary biology. Cambridge, MA: A Bradford Book, The MIT Press. p 51-69. ) in the context of this specific empirical case study. Applying the perspective of organizational homology to our experimental system of congeneric echinoids has led us to a new hypothesis concerning the ectoderm evolution in these species. The extravestibular ectoderm of the direct developer Heliocidaris erythrogramma is a novel developmental territory that arose as a fusion of the oral and aboral ectoderm territories found in indirect developing echinoids such as Heliocidaris tuberculata. This hypothesis instantiates a theoretical principle concerning the origin of developmental modules, 'integration', which has been neglected because the opposite theoretical principle, 'parcellation', is more readily observable in events such as gene duplication and divergence (Wagner 1996. Am Zool 36:36-43).     

Evolutionary Modification of Echinoid Sperm Correlates with Developmental Mode

A significant fraction of living sea urchin species have completely or partially eliminated the pluteus larval stage and instead develop directly from embryo to adult. Direct developing sea urchins develop from large buoyant eggs. We present data to show that evolution of these large eggs is accompanied by the evolution of spermatozoa with elogate heads, in contrast with the conical sperm heads typical of most echinoids. Two congeneric Australian species, Heliocidaris tuberculata , which develops via a pluteus, and H. erythogramma , a direct developer, were investigated in detail. The sperm of H. erythrogramma have an elongate head (11 μm in length) as compared to the conical sperm head (5.6 μm) of H. tuberculata . Electrophoretic analysis of the sperm histones indicates that no unusual histones or protamines are associated with modified head morphology. Genome sizes were determined by flow cytometry. H. erythrogramma has a haploid genome size of 1.3 pg as compared to a haploid genome size of 0.95 pg for H. tuberculata . Other direct developing echinoids have elongate sperm heads, and co-evolution of gametes is indicated as a common feature of evolution of direct development in echinoids. The most extreme case, the direct developing cidaroid sea urchin, Phyllacanthus parvispinus , possesses the longest and narrowest sperm head (20 μm × 1 μm) ever observed in an echinoid.     

Grazing bioerosion in Jurassic seas: a neglected factor in the Mesozoic marine revolution?

Grazing bioerosion, notably by chitons, gastropods and regular echinoids, is a powerful destructive force in many recent shallow-marine environments and impacts significantly on sessile epibionts through grazing predation and/or unselective dislodgement. Grazing bioerosion was an important component of a major phase of biotic escalation; the Mesozoic marine revolution. Recent investigations of hard substrates in southern British Jurassic marine formations have identified widespread ichnofossils attributable to grazing activity by gastropods and/or chitons, and regular echinoids. The co-occurring benthic macrofaunas include groups that would have been vulnerable to grazing disturbance and dislodgement; notably articulate brachiopods. The emerging ichnological evidence strengthens the argument for grazing bioerosion as a significant contributor to the Mesozoic–Cenozoic decline of the articulate brachiopods, and their retreat to deep-water and/or cryptic refugia.     

IRREGULAR ECHINOIDS—AN INSUFFICIENTLY KNOWN GROUP

Some aspects of echinoid evolution from an endocyclic towards an exocyclic apical system, in the light of embryological and palaeontological data, are discussed. A primitive feature—imbrication of interamhulacral plates in Jurassic irregular echinoids, recently described—proves once more that this group is insufficiently known. Every revision of taxonomic or phylogenetic concepts concerning this group of echinoids should be preceded by careful morphological analysis of the material.     

250 million years of bindin evolution

Bindin plays a central role in sperm-egg attachment and fusion in sea urchins (echinoids). Previous studies determined the DNA sequence of bindin in two orders of the class Echinoidea, representing 10% of all echinoid species. We report sequences of mature bindin from five additional genera, representing four new orders, including the distantly related sand dollars, heart urchins, and pencil urchins. The six orders in which bindin is now known include 70% of all echinoids, and indicate that bindin was present in the common ancestor of all extant sea urchins more than 250 million years ago. Over this span of evolutionary time there has been (1). remarkable conservation in the core region of bindin, particularly in a stretch of 29 amino acids that has not changed at all; (2). conservation of a motif of basic amino acids at the cleavage site between preprobindin and mature bindin; (3). more than a twofold change in length of mature bindin; and (4). emergence of high variation in the sequences outside the core, including the insertion of glycine-rich repeats in the bindins of some orders, but not others.     

PRESENCE OF 1-METHYLADENINE IN SEA URCHIN GONAD AND ITS RELATION TO OOCYTE MATURATION

A water extract of sea urchin ovary was found to induce maturation of starfish oocytes in vitro . The presence of the active substance was demonstrated in ovaries of the sea urchins, Pseudocentrotus depressus, Anthocidaris crassispina and Hemicentrotus pulcherrimus , and the sand dollars, Clypeaster japonicus and Peronella japonica . The active substance was also contained in the testes of these echinoids. That the content of this substance increases during the reproductive season was demonstrated with Anthocidaris gonads. The active substance present in ovary or testis of the sea urchins was successfully extracted with 85% ethanol and purified with gel-filtrations on Sephadex G-15 columns after washing with chloroform and ether. The purified active substances were the same and were identified as 1-1-methyladenine by thin layer chromatography. 1-Methyladenine was found to be effective in inducing oocyte maturation in Anthocidaris crassispina in vitro . Therefore, 1-methyladenine seems to play an important role in oocyte maturation in echinoids as well as in asteroids.     

Phosphagen kinase evolution. Expression in echinoderms

Arginine kinase and creatine kinase that catalyze the transfer of a phosphate group between ATP and arginine and creatine, respectively, play an important role in cellular energetics. In contrast to most animals which exhibit a single phosphagen kinase activity (creatine kinase in chordates and arginine kinase in protostomians), echinoderms exhibit both arginine kinase and creatine kinase activities, sometimes in the same tissue. In contrast to chordates in which creatine kinases are dimers (consisting of two subunits of 40 kDa) and protostomians in which arginine kinases are usually monomers (40 kDa), echinoids contain specific phosphagen kinases: a dimeric arginine kinase (consisting of two subunits of 42 kDa) in eggs and a monomeric creatine kinase (145 kDa) in sperm. We have examined echinoderms from the five existing classes (echinoids, asteroids, ophiuroids, holothurians and crinoids) for the expression of these specific phosphagen kinases in different tissues. Gel filtration was used to determine the molecular masses of the native enzymes. Antibodies specific for arginine kinase or for creatine kinase were used to characterize the subunit composition of arginine kinase and creatine kinase after SDS/PAGE and transfer. In all echinoderms analyzed, arginine kinase always occurred as an enzyme of about 81 kDa consisting of two subunits of 42 kDa and creatine kinase as a monomeric enzyme of 140-155 kDa. The occurrence in echinoderms of both phosphagen kinases with distinct specificities and specific molecular structures is discussed from both a developmental and evolutionary point of view.