Antipredator defense and phenotypic plasticity of sclerites from Renilla muelleri, a tropical sea pansy

Calcified sclerites are common in many benthic marine invertebrates, and despite their widespread occurrence, little is known about their ecological roles. Previous studies suggested that the sclerite composition of coral colonies may be altered in response to environmental cues such as predation and water motion. Furthermore, larger sclerites are thought to be more effective than small ones in deterring predators, while small sclerites may provide greater stiffness and resistance to deformation. The present study compared the length of the sclerites of the sea pansy Renilla muelleri from three depths in Guanabara Bay in southeastern Brazil. Our results show that sclerites are larger in deep-water specimens than in those from shallow water. Field assays were conducted in which sclerites from sea pansies at three depths were incorporated into artificial foods and offered to a natural assemblage of fish. These assays demonstrate that sclerites from R. muelleri from all three depths significantly reduced consumption by generalist carnivorous fishes. We conclude that R. muelleri uses skeletal elements not only to give the body its form but also as a defense against biotic threats.     

Patterns of distribution of calcite crystals in soft corals sclerites

The gross morphology of soft coral surface sclerites has been studied for taxonomic purposes for over a century. In contrast, sclerites located deep in the core of colonies have not received attention. Some soft coral groups develop massive colonies, in these organisms tissue depth can limit light penetration and circulation of internal fluids affecting the physiology of coral tissues and their symbiotic algae; such conditions have the potential to create contrasting calcifying conditions. To test this idea, we analyzed the crystal structure of sclerites extracted from different colony regions in selected specimens of zooxanthellate and azooxanthellate soft corals with different colony morphologies, these were: Sarcophyton mililatensis, Sinularia capillosa, Sinularia flexibilis, Dendronephthya sp. and Ceeceenus levis. We found that the crystals that constitute polyp sclerites differ from those forming stalk sclerites. We also observed different crystals in sclerites located at various depths in the stalk including signs of sclerite breakdown in the stalk core region. These results indicate different modes of calcification within each colonial organism analyzed and illustrate the complexity of organisms usually regarded as repetitive morphological and functional units. Our study indicates that soft corals are ideal material to study natural gradients of calcification conditions. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Chancelloriid sclerites from the lowermost Cambrian of North China and discussion of sclerite taxonomy

Chancelloriid sclerites from the lowermost Cambrian Xinji Formation (Series 2, Stage 3), southern margin of the North China platform, are systematically described. Thousands of isolated sclerites from three sections are assigned to three genera and four species, including Chancelloria cf. eros, Allonnia tripodophora, Archiasterella pentactina, and Ar. tetraspina. To accurately document the taxonomic significance of the sclerite structure, modified formulas (m+nC, m+nA, and m+0) are put forward to represent the full series and variation of sclerite forms. Based on the sclerite construction, statistical analysis on the proportions of different sclerite forms in the rock samples and the composition of sclerites in previously described chancelloriid scleritomes, a new scheme for identification and classification of isolated sclerites reconciled within the framework of the complete scleritome, is proposed.     

Intra-specific variation in the morphology and the benefit of large genital sclerites of males in the adzuki bean beetle (Callosobruchus chinensis)

Rapid evolution has led to a large diversity in the sizes and morphology of male genitals across taxa, but the mechanisms driving this evolution remain controversial. In this study, we investigated the function of male genital sclerites in the adzuki bean beetle (Callosobruchus chinensis) and compared the length and morphology of genital sclerites between two populations that vary in their degree of polyandry. We found that the length of male genital sclerites was negatively correlated with copulation duration but positively correlated with the speed of matings with multiple females. Additionally, we found that the average length and number of genital sclerite spines of males from the more polyandrous population were larger than those from the less polyandrous population. We suggest that the genital sclerite of male adzuki bean beetles evolved by sexual selection, and a larger genital sclerite has a selective advantage because it allows for rapid copulations with multiple females.     

Morphology of the elytral base sclerites

The elytral base sclerites (= sclerites located at the articular region between the forewing and thorax in Coleoptera) of selected taxa were examined and homologized. Although the elytral base sclerites are highly modified compared to the wing base sclerites of the other neopterans, they can be homologized by using the conservative wing flapping and folding lines as landmarks. A reduction of the first axillary sclerite was identified as a general trend of the elytral base sclerites, although the sclerite usually has a very important function to mediate flight power from the notum to the wing. This result indicates that the functional constraint against the basal sclerites is relaxed because of the lack of an ability to produce flight power by elytra. In contrast, the elytral folding system formed by the basal sclerites is well retained, which probably occurs because proper wing folding is a key for the shelter function of the elytra. The elytral base sclerites apparently contain more homoplasies than the serially homologous hindwing base sclerites of Coleoptera, which suggests that the structure is less useful for higher-level systematics. However, the faster evolutionary rate of the elytral base sclerites suggests there is potential for studying the lower-level phylogeny of Coleoptera.     

Effects of a submarine discharge of urban waste on octocoral (Octocorallia: Alcyonacea) communities in Cuba

The composition and structure of octocoral communities on coral reefs close to a submarine outfall were studied at Reparto Flores, west of Havana City, Cuba. Octocoral community changes after the deployment of the submarine outfall in 2000 were monitored from June 2002 to September 2005, taking as baseline the data existing before its construction. The area also receives the influence of the polluted river Quibú that passes through a great part of the west side of the City. Sampling was done by means of SCUBA diving, counting and identifying colonies in situ within a 1 m2 frame that was randomly placed as many times as to warrant stabilized values of Shannon and Weaver's heterogeneity index H'. In agreement with the available hydrochemical information, changes in the diversity indexes (Shannon and Weaver's heterogeneity index H', Pielou's equitability index J', and Margalef's species richness index R1), the Herrera-Moreno's comparative pollution index (ICC), and density of some octocoral species at a depth of 10 m suggest a decrease in the influence of polluters from 1989 to 2005. Nevertheless, these indicators were affected in 2004 by a sudden intense but brief colonization of Briareum asbestinum, a species that is not typical of polluted places. At a depth of 20 m, a co-dominance of Plexaura kuekenthali and Eunicea clavigera (resistant and non resistant to pollution, respectively) and an increase of the comparative pollution index (ICC) was observed. The increase of P. kuekenthali, a pollution indicator, suggests a rise in the pollution effect 20 m in depth, because of the recent impact caused by the greater closeness of the outfall mouth 50 m deep. Results corroborate the hypothesis about the pollution indicator character of P. kuekenthali. However, this could not be explored for Eunicea flexuosa (also considered a pollution-indicator) due to an intensive illegal selective extraction for lucrative handicraft purposes, which led to a remarkable decrease in its density. B. asbestinum and E. clavigera were outlined as poorly resistant to pollution.     

Selection against Aerial Dispersal in Ants: Two Non-Flying Queen Phenotypes in Pogonomyrmex laticeps

The South American seed-harvester ant Pogonomyrmex laticeps has dimorphic queens: ergatoid (permanently wingless) and brachypterous (short, non-functional wings). Surveys in western Argentina indicated that colonies near Chilecito, La Rioja Province, produced only ergatoid queens, while those near Punta Balasto, Catamarca Province (263 km away), produced only brachypterous queens. Brachypterous queens were significantly larger than ergatoid queens for 10 of 11 external characters, but both phenotypes had comparable reproductive potential, i.e., a spermatheca and a similar number of ovarioles. Using normal winged queens of the closely related P. uruguayensis for comparison, we determined that both queen phenotypes in P. laticeps had a full set of dorsal thoracic sclerites, albeit each sclerite was much reduced, whereas workers had a thorax without distinct dorsal sclerites. Sclerites were fused and immobile in ergatoid queens, while they were separable and fully articulated in brachypterous queens. Both phenotypes lacked the big indirect flight muscles, but brachypterous queens retained the tiny direct flight muscles. Overall, this dimorphism across populations indicates that there are alternative solutions to selective pressures against flying queens. We lack field data about colony founding strategy (independent or dependent) for either queen phenotype, but colonies at both sites produced numerous gynes, and we infer that all foundresses initiate colonies independently and are obligate foragers.     

Sclerites in different tissues of Mediterranean Echinodermata

The presence of sclerites in different mesodermal tissues was studied in thirteen species of Mediterranean echinoderms representing the five living classes. In the species of Asteroidea and Crinoidea examined, sclerites were present only in specific tissues. In the species of Ophiuroidea and, especially, Echinoidea and Holothuroidea examined, sclerites were present in almost every tissue, but with considerable variation among species and tissues. Data on sclerite shape, size, and relative abundance (measured as tissue abundance) are presented. The data support the possible functional role of sclerites as reinforcing structures, as well as their possible use as taxonomic characters. Finally, the need of more studies to elucidate the ontogenetic and phylogenetic implications of sclerites is discussed.     

Pyritized preservation of chancelloriids from the Cambrian Stage 3 of South China and implications for biomineralization

The enigmatic Cambrian animal chancelloriids were discovered in a wide range of taphonomic settings; however, preservation of biomineralized sclerite microstructure was solely known from secondarily phosphatized skeletal remains. Here, we investigate a uniquely pyritized chancelloriid from the lower Cambrian Guojiaba Formation in southern Shaanxi Province, China, using a combination of advanced analytic techniques. Results of the energy dispersive spectroscopy (EDS), X-Ray Fluorescence (XRF), and Raman spectrum show that the sclerites and scleritomes are preserved as pyritized internal moulds with a calcitic outer layer. The outer layer enveloping the internal moulds likely represents the recrystallized counterpart of the original biomineralized sclerite wall. Distinctive fibrous microstructures are discovered in the sclerites, which echo the features seen in the phosphatized fossils of chancelloriids. The typical microstructure, along with the recrystallized calcite, corroborate the interpretation that chancelloriid sclerites were originally constructed by fibrous aragonite. The stability of the microstructure and mineral composition in both carbonate and siliciclastic backgrounds indicate that chancelloriids were adapted to exploit aragonitic fibres to build their skeletons regardless of the change of their living environments.     

SKELETAL MICROSTRUCTURE INDICATES CHANCELLORIIDS AND HALKIERIIDS ARE CLOSELY RELATED

Abstract: Chancelloriids are problematic, sac‐like animals whose sclerites are common in Cambrian fossil assemblages. They look like sponges, but were united with the slug‐like halkieriids in the group Coeloscleritophora Bengtson and Missarzhevsky, 1981 based on a unique mode of sclerite construction. Because their body plans are so different, this proposal has never been well accepted, but detailed study of their sclerite microstructure presented here provides additional support for this grouping. Both taxa possess walls composed of a thin, probably organic, sheet overlying a single layer of aragonite fibres orientated parallel to the long axis of the sclerite. In all halkieriids and in the chancelloriid genus Archiasterella Sdzuy, 1969 , bundles of these fibres form inclined projections on the upper surface of the sclerite giving it a scaly appearance. On the lower surface of the sclerite, the projections are absent. This microstructure appears to be unique to chancelloriids, halkieriids, and their relatives, siphogonuchitids and sachitids. (The sclerites of another putative halkieriid relative, Wiwaxia Walcott, 1911 , are unmineralized, making direct comparisons impossible.) Thus, similarity both at the level of sclerite construction and the level of sclerite microstructure suggests that chancelloriid, halkieriid, sachitid, and siphogonuchitid sclerites are homologous. The difference in chancelloriid and halkieriid body plans can be resolved in two ways. Chancelloriids either represent a derived condition exhibiting complete loss of bilaterian characters or they represent the ancestral condition from which the bilaterally symmetric halkieriids, and the Bilateria as a whole, derived. The latter interpretation, proposed by Bengtson (2005) , implies that coeloscleritophoran sclerites (‘coelosclerites’) are a plesiomorphy of the Bilateria, lost or transformed in descendent lineages. Given that mineralized coelosclerites appear in the fossil record no earlier than c. 542 Ma, this in turn implies either that the Ediacaran record of bilaterians has been misinterpreted or that coelosclerite preservability increased at the beginning of the Cambrian Period. The former is difficult to reconcile with Ediacaran trace and body fossil evidence, but the latter may be possible, reflecting either independent mineralization of organic‐walled sclerites in chancelloriids and halkieriids or the opening of a taphonomic window that favours coelosclerite preservation.     

Effects of pyrrolizidine alkaloids and sesquiterpenes on snail feeding

Summary We determined in the laboratory the feeding response of two populations of the generalist herbivorous snail Arianta arbustorum (Helicidae) towards the composite Adenostyles alliariae and towards various allelochemicals. These were: a pyrrolizidine alkaloid (PA) extract of Adenostyles leaves; senecionine (a PA present in Adenostyles); retrorsine (a PA not present in Adenostyles) and two sesquiterpene (ST) fractions from Adenostyles: a mixture of the STs adenostylone and neoadenostylone, and deacyladenostylone. Tertiary PAs and PA N-oxides were tested separately. For each allelochemical, we tested whether it was deterrent or whether it induced changes of feeding behaviour (i.e. whether it had pre- or postingestive effects), and whether the effects were more pronounced with younger (smaller) snails. The tertiary PA extract from Adenostyles was deterrent, especially for young snails, but did not induce changes of feeding behaviour. Tertiary PA senecionine was deterrent for young snails only and induced changes of feeding behaviour. Also, consumption of untreated Petasites was higher after this treatment. Tertiary PA retrorsine was not deterrent, but induced changes of feeding behaviour. The PA N-oxides showed no activity against the snails. The mixture of adenostylone and neoadenostylone was deterrent and induced feeding aversions. Deacyladenostylone was highly deterrent, but did not induce changes of feeding behaviour. At the Jura site, PA content of Adenostyles was lower than at the Black Forest site. The snails from Jura consumed much less Adenostyles than the snails from Black Forest, and also ate a little less of the treated leaf discs. The PAs which are encountered by the snails in their natural food plants (PA extract and senecionine) were more deterrent than retrorsine (a novel compound). This suggests that the snails have mechanisms for the rejection of allelochemicals which they encounter in their natural food plants, but not for novel allelochemicals. The results suggest two hypotheses regarding the function of the allelochemicals in Adenostyles: (1) The allelochemicals act mainly on very young snails. (2) PAs render Adenostyles toxic, while STs act as feeding deterrents.     

A new octocoral genus (Cnidaria: Anthozoa) from Antarctic waters

Sphaeralcyon weddellensis gen. nov. et sp. nov. is described and illustrated from three colonies collected in the eastern Weddell Sea on the Polarstern cruises ANT V/3 and ANT VI/3. The new genus is compared with three closely related alcyoniid genera, all having capitate or mushroom-shaped colonies and dimorphic polyps. Sphaeralcyon is readily distinguishable from Malacacanthus by the presence of sclerites (absent in the latter genus), and from Anthomastus by sclerite shape, mainly in the form of tuberculate spheroids, and by the horny periderm on the stalk (absent in Anthomastus). Sphaeralcyon also differs from Verseveldtia in the set of sclerites, which are elongate spiny rods and a different type of tuberculate spheroid, and in the presence of eight-points as anthocodial armature (absent in Verseveldtia). The discovery of this new genus lends further support to the notion that diversity in benthic communities in Antarctica is higher than suggested by previous studies. Accepted: 6 December 1999     

A comparative study of Lower Cambrian Halkieria and Middle Cambrian Wiwaxia

Two Cambrian lepidote metazoans known from different respective types of preservation have been compared in order to elucidate their biology and affinities. The widely distributed Lower Cambrian Halkieria is represented by isolated hollow sclerites, probably of originally calcareous composition. The Middle Cambrian Wiwaxia is known from the Burgess Shale as isolated sclerites (scales and spines) and as more or less complete individuals. Although Halkieria sclerites were mineralized and those of Wiwaxia were probably not, there are fundamental structural and morphological similarities between the two. Both bad an imbricating scaly and spiny armour consisting of hollow sclerites with a longitudinally fibrous structure. The sclerites did not grow, but were probably moulted during the course of ontogenetic growth. Halkieria and Wiwaxia are regarded as closely related. Both are referred to the Order Sachitida He 1980. The sclerite armour of Halkieria is reconstructed on the template provided by Wiwaxia. The interpretation of sachitid sclerites as protective armour is an alternative to the interpretation by Jell (1981, Alcheringa 5 )that sachitid sclerites were respiratory organs in an animal of probable annelid affinities. Sachitids are interpreted as sluggish, benthic deposit feeders that do not belong to any recognized phylum.     

Shell Structure And Inferred Growth, Functions And Affinities Of The Sclerites Of The Problematic Micrina

The stratiform laminae of Micrina sclerites originally consisted of rheomorphic successions of monolayers of micrometric–sized, apatitic tablets, presumably interleaved with chitin and glycosaminoglycans (GAGs). Paired laminae enclose slot–like chambers swelling into lobes distally that originally contained GAGs and deposits of spherulitic and prismatic apatite. The laminae are pervaded by apatitic tubes, apparently secreted by microvillous setoblasts and containing, at the surface, chitinous setae. Internal markings suggest that the triangular (sellate) sclerite supported a pair of muscles and the planospiral (mitral) sclerite, a medial muscle and gonadal sacs flanked by a pair of crescentic muscle bases. Both sclerites were secreted by a mantle with a circumferential fold. The sellate and mitral sclerites are homologized with the anterior and posterior shells of Halkieria and could have become the dorsal and ventral valves of the ancestral brachiopod by a sequence of transformations. These include: the folding of the halkieriid body axis; accelerated mixoperipheral growth of the anterior (dorsal) shell to enclose, with the posterior (ventral) shell, a mantle cavity lined with modified ciliated epithelium of the foot; reduction of sclerite–secreting epithelium to the locus of the brachiopod pedicle epithelium; and the anterior (dorsal) spread of gonadal lamellae.     

Chemical and physical defenses of Singapore gorgonians (Octocorallia: Gorgonacea)

Gorgonians are abundant in tropical waters and their polyps are seldom predated on. This study investigates how gorgonians defend themselves chemically and physically against fish predation. Gorgonian extracts and sclerites were incorporated into fish feed and tested on reef fishes. Laboratory bioassays using Greyhead wrasses, Halichoeres purpurescens, as well as field bioassays showed five gorgonian species from the family Ellisellidae and three from the family Plexauridae collected from Singapore reefs to be deterrent towards fishes. Bioassays of fractions obtained from subsequent fractionation suggested synergistic or additive effects between compounds present in gorgonians. Sclerites incorporated into fish feed in their natural concentrations were also tested for fish deterrence and were positive for only two gorgonian species from the family Ellisellidae.     

Frequent Failure of Male Monopolization Strategies as a Cost of Female Choice in the Black Widow Spider Latrodectus tredecimguttatus

In many mating systems, males strive for securing paternity through monopolizing females. As male monopolization attempts often contradict female interests, this conflict may fuel an evolutionary arms race. In the widow spider genus Latrodectus, females are commonly polyandrous, whereas males are monogynous, hence restricted to mate with a single female, making paternity protection particularly important. Potential mating plugs (specialized embolus sclerites of male copulatory organs) have been discovered in the complex female genital tracts of several Latrodectus species. In this study, we investigated mating strategies in the Mediterranean black widow spider Latrodectus tredecimguttatus and tested the adaptive value of female attacks against male monopolization efforts. In a double mating experiment, we manipulated the number of insertions (=copulations) for first and second males to assess female behaviour and male embolus sclerite placement success. Our results indicate that first males′ embolus sclerites inside the females′ sperm stores physically block sclerites of subsequent males. While female attacks did not affect the deposition of potential mating plugs, they significantly reduced copulation duration. Irrespective of female aggression, male sclerite placement failure occurred frequently, but large males were more successful than smaller competitors. We suggest that the complex genital morphology in both sexes may have co‐evolved antagonistically and female morphology could serve to favour large males for fertilization.     

Comparative morphology of the postmentum of bees (Hymenoptera: Apoidea) with special remarks on the evolution of the lorum

A comparative morphological study of the basal sclerites of the bee labium was undertaken. The term postmentum was applied to the basal sclerite of the bee labium. In contrast to recent interpretations, the undivided postmentum was found to be ancestral for bees and homologous with the single postmental sclerite of other Hymenoptera. This sclerite has previously been incorrectly indentified as two separate sclerites, usually termed mentum and lorum (= submentum), for many short-tongued bees (Colletidae, Halictidae, Andrenidae, Melittidae) and for the long-tongued families of bees (Anthophoridae, Fideliidae Megachilidae) excepting most members of the Apidae. The postmentum, divided into a true mentum and lorum, was found only in certain members of the Apidae. A phylogenetic implication resulting from this study shows that the Andrenidae may be the sister group to the MCL-T group (Melittidae, Ctenoplectridae and long-tongued families of bees). In addition, it is proposed that the Euglossinae should be the sister group to the Apinae (Meliponini, Apini and Bombini). This means that eusociality may be considered a synapomorphy for the Apinae.     

Population Structure of Montastraea cavernosa on Shallow versus Mesophotic Reefs in Bermuda

Mesophotic coral reef ecosystems remain largely unexplored with only limited information available on taxonomic composition, abundance and distribution. Yet, mesophotic reefs may serve as potential refugia for shallow-water species and thus understanding biodiversity, ecology and connectivity of deep reef communities is integral for resource management and conservation. The Caribbean coral, Montastraea cavernosa, is considered a depth generalist and is commonly found at mesophotic depths. We surveyed abundance and size-frequency of M. cavernosa populations at six shallow (10m) and six upper mesophotic (45m) sites in Bermuda and found population structure was depth dependent. The mean surface area of colonies at mesophotic sites was significantly smaller than at shallow sites, suggesting that growth rates and maximum colony surface area are limited on mesophotic reefs. Colony density was significantly higher at mesophotic sites, however, resulting in equal contributions to overall percent cover. Size-frequency distributions between shallow and mesophotic sites were also significantly different with populations at mesophotic reefs skewed towards smaller individuals. Overall, the results of this study provide valuable baseline data on population structure, which indicate that the mesophotic reefs of Bermuda support an established population of M. cavernosa.     

Scleritome construction,biofacies, biostratigraphy and systematics of the tommotiid Eccentrotheca helenia sp. nov. from the Early Cambrian of South Australia

Abstract: Large collections of Eccentrotheca helenia sp. nov. from the lower Cambrian Wilkawillina and Ajax limestones in the Arrowie Basin, South Australia, contain abundant low, cap‐shaped and high, laterally compressed isolated sclerites in addition to partially articulated tubular specimens. The scleritome of Eccentrotheca helenia sp. nov. is fully described for the first time and shown to be formed by ontogenetic fusion of sclerites into successively stacked sclerite rings, forming a larger, tubular structure. The apical termination of the tube is highly variable, but is primarily constructed by low, cap‐shaped sclerites and characterised by a central aperture of variable inclination. The adapical portion of the tube is predominantly constructed by high, laterally compressed sclerites, but individual sclerite rings can contain both cap‐shaped and laterally compressed sclerites along with sclerites of intermediate morphology. The apical aperture presumably housed organic structures for attachment to a hard substrate, but the scleritome also occasionally preserves small lateral perforations between fused sclerites, which may have served to stabilise the scleritome by providing additional points of anchorage. In the Arrowie Basin, E. helenia is found in association with archaeocyath‐microbial‐spongiomorph‐dominated bioherms and most likely inhabited pendant or cryptic habitats within these bioherms. Eccentrotheca‐like sclerites form an integral part of the scleritomes of many tommotiids which may confuse taxonomic analysis. Sclerites previously assigned to ‘E.’guano, consistently occur together with sclerites of Kulparina rostrata in stratigraphic intervals consistently older than strata hosting E. helenia. Rare fused specimens indicate that the sclerites of K. rostrata and ‘E.’guano belong to the same scleritome.