Pluri-annual study of the reproduction of two Mediterranean Oscarella species (Porifera, Homoscleromorpha): cycle, sex-ratio, reproductive effort and phenology

This study presents the phenology of two common Mediterranean sponges belonging to the genus Oscarella (Porifera, Homoscleromorpha). Oscarella tuberculata and Oscarella lobularis are two sibling species, dwellers of shallow benthic communities which tend to have distinct ecological behavior, respectively, euryecious and rather stenoecious. The comparative study of their reproductive cycle showed that both Oscarella species have a seasonal reproductive cycle with a successive phase duration differing from one species to another. In both species, there is a continuous oogenesis, with new oocytes appearing in spring, whereas the spermatogenesis generally starts later with the early warming of the sea. The embryonic development and the larval release are restricted to the warmest months of the year. We also observed a shift in the period of gametogenesis and larval emission depending on species and differences in their sensitivity to changes in thermal regime. It appears that an increase in seawater temperature can affect sex determination, with mainly a shift toward males in both species. Their reproductive efforts are variable in time, and can be in some cases influenced by the temperature regime. This is especially the case of O. lobularis which seems to be the most thermosensitive, its phenology responding significantly to changes in thermal regime, whereas O. tuberculata seems to be less sensitive and/or reactive. By detecting phenological changes among sponges, this study demonstrated the relevance of such monitoring to assess the possible biological response to climate change.     

Asexual reproduction in homoscleromorph sponges (Porifera; Homoscleromorpha)

Asexual reproduction by external budding in Homoscleromorpha is reported for the first time. Two Mediterranean sponge species were studied, Oscarella lobularis and O. tuberculata. Buds are formed in the marginal basal part of sponge. Budding takes from 1 to 4 days and is defined in three budding stages. First, small irregular protuberances, consisting of external parental tissue, are formed. Second, they elongate and acquire more regular, nipple-like shape. These protuberances are tube like, their internal cavity derived from parental exhalant canal. The wall consists of three layers: (a) external layer is flagellated exopinacoderm, (b) internal one is flagellated endopinacoderm and (c) intermediate one is a thin layer of mesohyl. Third, a spherical bud with a large central cavity is formed. During budding, we did not observe cell proliferation or transdifferentiation either in budding zone or in any special mitotically active region. The bud attached to the substrate is similar to the rhagon developing after larva metamorphosis, it has a syconoid organization. Morphogenetically, budding in Oscarella differes from that in other sponges. Occurring by epithelial morphogenesis, it is similar to morphallaxis during regeneration. The presence in Homoscleromorpha of an epithelial morphogenesis is unique among sponges. This feature is shared by Homoscleromorpha and Eumetazoa.     

Biochemical genetic divergence and systematics in sponges of the genera Corticium and Oscarella (Demospongiae: Homoscleromorpha) in the Mediterranean Sea

The sponge sub-class Homoscleromorpha is generally considered to include just two families, the Oscarellidae (without spicules) and the Plakinidae (with simple spicules). In May 1990, an unusual sponge was found deep inside a submarine cave in the western Mediterranean Sea. On the basis of externally visible characters this sponge appeared indistinguishable from the common plakinid species Corticium candelabrum Schmidt, 1862. However, on closer examination in the laboratory the new sponge proved to be devoid of spicules. Therefore, despite great morphological similarities to C. candelabrum, the new sponge should, by taxonomic convention, have been placed in the Oscarellidae. On the basis of other criteria, the similarities to C. candelabrum were great and the new sponge was at first considered to be conspecific. Thus, the taxonomic position of the new sponge and its relationship to C. candelabrum are highly confusing. It could be an aspiculate morph of C. candelabrum, or a new and undescribed related species or, lacking spicules, it could justifiably be placed in a different family (Oscarellidae). The relationship of the new sponge to C. candelabrum and also to two species of Oscarella (Oscarellidae) was assessed by the use of enzyme electrophoresis to estimate genetic divergence between species. It was found that the new sponge was reproductively isolated from sympatric C. candelabrum, with 6 of 16 loci proving diagnostic. Thus it is clear that the new sponge belongs to a different biological species. Surprisingly it was also found that, although this new species was fairly closely related to C. candelabrum (level of genetic identity, I0.47), the two Oscarella species were similarly closely related to C. candelabrum (I0.31 to 0.41) and rather less closely to the new species (I0.17 to 0.28). Indeed from genetic identity estimates, O. tuberculata is more closely related to C. candelabrum than it is to O. lobularis. It is concluded that all homoscleromorph sponges should be placed in the single family Plakinidae.     

Bacterial symbionts as an additional cytological marker for identification of sponges without a skeleton

Symbiotic bacteria from six Oscarella species (adults and embryos) collected in the Mediterranean Sea (O. lobularis, O. tuberculata, O. imperialis, O. microlobata, O. viridis) and the Sea of Japan (O. malakhovi) were investigated by scanning electron microscopy and transmission electron microscopy. In most cases, symbionts are rather numerous. Each sponge species has a definite set of bacterial morphological types. All bacteria are extracellular. Symbionts occupy the mesohyl of adult sponges or intercellular space in embryos and are often in contact with mesohylar filaments or cells. Bacteria of some morphotypes have characteristic blebs. Most symbionts are gram-negative, and two types of bacteria have traits of Archaea and one type of bacteria is similar to Planctomycetes. Data on morphology of bacterial symbionts can be a good additional character for identification of Oscarella species, which have no skeleton.     

Evidence of nitrification and denitrification in high and low microbial abundance sponges

Aerobic and anaerobic microbial key processes were quantified and compared to microbial numbers and morphological structure in Mediterranean sponges. Direct counts on histological sections stained with DAPI showed that sponges with high microbial abundances (HMA sponges) have a denser morphological structure with a reduced aquiferous system compared to low microbial abundance (LMA) sponges. In Dysidea avara, the LMA sponge, rates of nitrification and denitrification were higher than in the HMA sponge Chondrosia reniformis, while anaerobic ammonium oxidation and sulfate reduction were below detection in both species. This study shows that LMA sponges may host physiologically similar microbes with comparable or even higher metabolic rates than HMA sponges, and that anaerobic processes such as denitrification can be found both in HMA and LMA sponges. A higher concentration of microorganisms in the mesohyl of HMA compared to LMA sponges may indicate a stronger retention of and, hence, a possible benefit from associated microbes.     

Lack of innate preference for morph and species identity in mate-searching <Emphasis Type="Italic">Enallagma</Emphasis> damselflies

Insect mate recognition is often viewed as stereotypic, innate, and species-specific. However, male damselflies can learn to identify female-specific color morphs as potential mates. A suite of male mimicry hypotheses assume that heteromorphic females, which differ from males in color pattern, are more easily recognized as “female” and thus lack the inherent, anti-harassment advantage that the more male-like signal provides for andromorphs. Using two measures of male preference, we investigated whether naïve males have a preexisting sensory bias for a given morph color in Enallagma civile, a species that appeared to exhibit extreme plasticity in morph expression across generations within a breeding season. E. civile males raised in the absence of females exhibited no preference for either morph, whereas males raised with one female type exhibited a learned sensory bias for that morph. Male Enallagma also lacked a bias toward conspecific females over a congeneric sister species. In a naturally naïve population of Enallagma ebrium, males reacted sexually to both morphs of Enallagma hageni as often as they did to conspecific females, whose thoracic spectra were nearly identical with those of E. hageni. Moreover, despite the similar thoracic spectra of males and andromorphs, both of which reflected UV, males rarely reacted sexually to other males. Our results falsified implicit assumptions of male mimicry hypotheses, supported learned mate recognition, and suggested a scenario for speciation via sexual conflict.     

Genetic connectivity among color morphs and Pacific archipelagos for the flame angelfish, <Emphasis Type="Italic">Centropyge loriculus</Emphasis>

Color variation is used in taxonomic classification of reef fishes, but it may not reliably indicate evolutionary divergence. In the central Pacific, there are three color morphs of the flame angelfish, Centropyge loriculus: a red morph that occurs primarily in the Hawaiian archipelago, the endemic Marquesan color morph with reduced black markings, and an orange morph that occurs throughout the rest of Oceania. The red and orange morphs co-occur at Johnston Atoll (1,300 km south of Hawai’i), but intermediate forms have not been reported. To determine whether the three color morphs represent distinct evolutionary lineages, we compared 641 base pairs of mitochondrial cytochrome b. Forty-one closely related haplotypes were observed in 116 individuals. Analysis of molecular variance (AMOVA) indicated no significant genetic structure among color morphs (Φ_ST = 0.011, P = 0.147). Likewise, there was no significant pairwise structure between sampling locations, separated by up to 5,700 km, after a Bonferroni correction (Φ_ST = 0.000–0.080, P = 0.0130–0.999). Genetic studies in conjunction with larval distribution data indicate that Centropyge species are highly dispersive. While there is a strong geographic component to the distribution of color morphs in C. loriculus, we find no evidence for corresponding genetic partitioning. We do not rule out an adaptive role for color differentiation, but our data do not support emerging species.     

The hydrozoan coral<Emphasis Type="Italic"> Millepora dichotoma</Emphasis>: speciation or phenotypic plasticity?

This article describes ecological and biological differences between two morphs of the Red Sea fire coral Millepora dichotoma. The species is divided into two main morphs: branching and encrusting, which were found to differ both in color and morphology. Each morph has two or more sub-morphs. A total of 372 M. dichotoma colonies were examined in a census at two study sites in the Gulf of Elat. Colony size and abundance of the two morphs were found to differ significantly between sites. Experimental examination of each morph's morphological plasticity revealed different growth rates and difference in growth plasticity between the branching and the encrusting morph. Most of the fragments from the branching colonies (94%) attached to experimentally placed Plexiglas substrate, compared with much less attachment by the encrusting fragments (11%). The growth form of the branching morph on the Plexiglas switched to encrusting, spreading over and covering the substrate. When the new encrusting colony reached the edge of this substrate, it started to produce tips, and returned to growth in the classic branching form. The encrusting morph did not change its growth form. Following attachment of the original fragments of the branching morph to the substrate, 8.1% of them produced new tips. When the original branches were removed, after converting to encrusting growth form, 19% of the fragments produced new tips. The capsule size of nematocysts of the two morphs was also significantly different (t-test, P<0.05). Molecular data (ITS region) clearly demonstrate that these two M. dichotoma morphs differ considerably. Molecular evidence (srRNA) from the symbiotic zooxanthellae also shows a different pattern of clades in the hosts. The ecological, biological and molecular data thus attest to the two morphs being distinguishable. Contrary to previous reports, we consequently suggest that the two morphs of M. dichotoma found in the Gulf of Elat are actually two distinct species.Communicated by O. Kinne, Oldendorf/Luhe     

Color patterns of the shrimps Heptacarpus pictus and H. paludicola (Caridea: Hippolytidae)

Color patterns of the shallow-water shrimps Heptacarpus pictus and H. paludicola are formed by chromatosomes (usually termed chromatophores) located beneath the translucent exoskeleton. Development of color patterns is related to size (age) and sex. The color expressed is determined by the chromatosome pigment dispersion, arrangement, and density. In populations with well-developed coloration (H. pictus from Cayucos, California, 1976–1978, H. paludicola from Argyle Channel, San Juan Island, Washington, June–July, 1978), prominent coloration was a characteristic of maturing females, breeding females, and some of the larger males. In the Morro Bay, California, population of H. paludicola (sampled 1976–1978), color patterns were poorly developed except in a few large females. In both species, most shrimp lose color at night because of pigment retraction in certain chromatosomes. In both species, there are 5 basic morphs: 1 transparent and 4 colored morphs. In the colored morphs, the color patterns are composed of bands, stripes, and spots which appear to disrupt the body outline. Each color morph also has a common environmental color in its color pattern, e.g the green of green algae, the whites and pinks of dead and living coralline algae, and various shades of tidepool litter. These shrimps are apparently under heavy predation pressure by fish, and it is suggested that the color patterns are camouflage against such visually-hunting predators.     

Genetic differentiation between morphotypes of the marine sponge Suberites ficus (Demospongiae: Hadromerida)

Sponges of three morphotypes of Suberites ficus (Johnston, 1842) were collected during February and March 1985 off the south-west of the Isle of Man, and were compared by using spicule size distributions and genetic allele frequencies of isozyme loci. The populations did not show any significant differences of spicule size or type, but could be easily differentiated into three separate species based on isozyme patterns. Samples of pale orange S. ficus growing on gastropod shells inhabited by hermit crabs (Pagurus spp.) were reproductively isolated from the redorange and the pale yellow colour morphs encrusting the bivalve Chlamys opercularis. These latter two colour morphs were genetically similar, but significant differences were observed at two of the 19 gene loci assayed. All the sponges studied were sympatric, and therefore the genetic differences, indicating reproductive isolation, are strong evidence for separate gene pools and, hence, that they are different species. The genetic identity between the two colour morphs of S. ficus on C. opercularis shells was 0.977, whilst between each of these and S. ficus on hermit crabs it was about 0.65. In all three species genetic variability was high, with mean expected and observed heterozygosity values per locus ranging from 0.17 to 0.36.     

Evolution, radiation and chemotaxonomy of Lamellodysidea, a demosponge genus with anti-plasmodial metabolites

Sponges of the family Dysideidae (Dictyoceratida) are renowned for their diversity of secondary metabolites, and its genus Lamellodysidea, particularly Lamellodysidea herbacea, is the most studied taxon biochemically. Despite its importance, the taxonomic status of L. herbacea—whether it is a distinct species or a species complex—has never been assessed. Recent biochemical profiling revealed anti-plasmodial activity of brominated compounds in Lamellodysidea of the Pacific. Here, we present a comparative chemotaxonomic and molecular analysis of selected Dysideidae from the Pacific and the Indian Ocean (New Caledonia, Great Barrier Reef, Fiji, Mayotte, Guam, Palau). We investigated the phylogenetic relationships between the populations and assessed their bioactive (PBDE) compounds in order to unravel the taxonomic status of this commercially important group of sponges and assessed patterns of dispersal and biochemical variation. The molecular phylogeny was based on the internal transcribed ribosomal spacer and compared against a PBDE phylogeny for several specimens. Molecular data revealed a diversity of Indo-Pacific L. herbacea populations, also reflected by different PBDE compound profiles. Molecular and biochemical data also revealed a Lamellodysidea species new to science. Several specimens misidentified as Lamellodysidea were detected based on their position on different clades in the molecular phylogeny and their production of different halogenated compounds (brominated vs. chlorinated). The direct comparison of molecular and biochemical data also provided evidence for the occurrence of a host switch event and support for the theory that abiotic factors, such as sedimentation, affect the chemical constituents produced in L. herbacea.     

Tale of two colors: <Emphasis Type="Italic">Cladopsammia gracilis</Emphasis> (Dendrophylliidae) color morphs distinguished also by their genetics and ecology

Cladopsammia gracilis (Dendrophylliidae), an ahermatypic coral inhabits the northern Red Sea. Two color morphs (pink and orange) are found aggregated in caves devoid of hermatypic corals, associated with crustose coralline algae (CCA). Sequencing the rDNA ITS region revealed a separate clustering of members of each color morph. Both morphs grow in shallow waters, with orange corals limited to the upper 4 m, while some pink coral aggregates thrive deeper than 30 m. Planulae were released between June and December. Pink planulae treated with antibiotics and exposed at different intervals to CCA, were competent and metamorphosed even 110 days after release. Maximal competency period for orange planulae was 70 days. All planulae were enhanced to metamorphose in presence of CCA. The mean age at metamorphosis of pink and orange planulae treated with CCA differed significantly. Most orange planulae settled directly on the CCA while most pink planulae settled on the wall of the experiment vial. The morphs differed significantly in the calyx cross-section area of primary polyps. Despite being considered a single species according to skeletal based taxonomy, the significant ecological and molecular differences between pink and orange C. gracilis specimens suggest that they may belong to separate species.     

Oxygen dynamics and transport in the Mediterranean sponge Aplysina aerophoba

The Mediterranean sponge Aplysina aerophoba kept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumping A. aerophoba specimens with Clark-type oxygen microelectrodes (tip diameters 18–30 μm). Total oxygen consumption rates of whole sponges were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model. Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows total oxygen consumption rates of 6–12 μmol cm⁻³ sponge day⁻¹. Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios. In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm⁻³ sponge day⁻¹, and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system of A. aerophoba thus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated microbial lineages and improve our understanding of the sponge-microbe-system.     

Genetic and color morph differentiation in the Caribbean sea anemone<Emphasis Type="Italic"> Condylactis gigantea</Emphasis>

The distribution of phenotypic and genetic variation across environments can provide insights into local adaptation. The tropical sea anemone Condylactis gigantea inhabits a broad spectrum of coral-reef habitats and displays a variety of phenotypes, particularly with respect to color. At the coast of Discovery Bay, Jamaica, individuals with either pink or green tentacle tips show distinct distributions. Pink morphs are more abundant in the lagoon and in deeper areas, while green morphs are more abundant in the forereef and in shallower areas. We use DNA sequence data (ITS1-5.8S) to investigate if variation in color is associated with genetic differentiation in lagoon and forereef habitats about 5 km apart. Population genetic analyses reveal two distinct ITS1-5.8S variants, which differ in relative frequency. The two variants are present in both habitats, but a dearth of intermediates suggests reduced gene flow. In the lagoon, but not the forereef, ITS variants show an association with color. In order to address the potential ecological significance of color, we study UV absorbance and UV acclimatization capacities of pink and green color morphs in the lagoon. Color morphs differed significantly in UV-B absorbance. These results suggest genetic and ecological differentiation in the face of gene flow over short distances.Communicated by O. Kinne, Oldendorf/Luhe     

Poecilogony in Polydora hoplura (Polychaeta: Spionidae) from commercially important molluscs in South Africa

Females of the polychaete Polydora hoplura (Claparède 1869) that produced planktotrophic and adelphophagic larvae were compared genetically to determine whether the different reproductive morphs represented sibling species or poecilogony. Worms were collected from Saldanha Bay, South Africa (33°0′37.71S, 17°56′59.74E), and cultured in a laboratory setting from November 2012 to April 2013. The results based on mitochondrial and nuclear DNA (Cyt b and ATPSα, respectively) showed shared haplotypes between reproductive morphs for both markers. Additionally, variation in mtDNA sequences was significantly higher within morphs than between morphs (95.8 and 4.2 %, respectively). A comparison of developmental modes found that broods of planktotrophic larvae were larger than broods of adelphophagic larvae, while the latter had larger eggs and larvae at hatching. Developmental time from oviposition to settlement for planktotrophic and adelphophagic larvae was 40.2 and 16.6 days, respectively. Polydora hoplura represents the fifth confirmed case of poecilogony in the Spionidae.     

Cadmium kinetics in oysters — a comparative study of Crassostrea gigas and Ostrea edulis

The accumulation of cadmium was investigated in two species of oysters [Crassostrea gigas (L.) and Ostrea edulis (L.)] from the same environment and in oysters of the same species (O. edulis) from two different environments (contaminated and uncontaminated), under controlled laboratory conditions (33‰ salinity, 10°C, 100 μg Cd l^-1) for up to 111 d in 1982. C. gigas accumulated cadmium twice as fast as O. edulis (1.07 vs 0.52 μg Cd g^-1 wet wt d^-1). Furthermore, O. edulis from an uncontaminated environment accumulated cadmium faster than O. edulis from a metal-contaminated environment (0.52 vs 0.34 μg Cd g^-1 wet wt d^-1). There was no effect of cadmium exposure on total soft-tissue copper and zinc concentrations. Investigation of cytosolic metal-binding using Sephadex G-75 gel-permeation chromatography indicated that binding to very low molecular weight ligands (MW<1000) accounted for>70% of the cytosolic zinc in all oysters and>40% of the cytosolic cadmium in all oysters except O. edulis from Conwy at 83 d. In copper-contaminated oysters, excess copper was also associated with very low molecular weight ligands. Intermediate molecular weight cadmium/copper-binding proteins (similar to metallothionein in molecular weight) were observed in the cytosol and were shown to differ between species in terms of their behavior on Sephadex G-75. Finally, the distribution of accumulated cytosolic cadmium in O. edulis from the contaminated environment was shown to have a unique distribution, i.e., there was no cadmium associated with high molecular weight cytosolic macromolecules. The data indicate that both genetic and environmental factors influence cadmium accumulation in oysters.     

Variable effects of symbiotic snapping shrimps on their sponge hosts

Mutualistic relationships are ubiquitous in tropical coral reefs, but the costs and benefits to partner species are often poorly known. In Caribbean coral reefs, several species of snapping shrimp (Synalpheus spp.) dwell exclusively in marine sponges, which serve as both habitat and food source. A paired experimental design was used to examine the effects of Synalpheus occupancy on predation, morphology, and growth of their sponge host Lissodendoryx colombiensis in Bocas del Toro, Panama (9.351°N, 82.258°W) in June 2009. Shrimp occupancy significantly decreased consumption of sponges by a predatory sea star (Oreaster reticulatus) and also affected sponge morphology; sponges grown without shrimps decreased in canal size, in both the laboratory and the field. Shrimp occupancy had more ambiguous effects on sponge growth. In laboratory experiments, shrimp occupancy benefited sponge growth, although all sponges experienced overall decreases in mass. In field experiments, there were no significant differences in growth between occupied and empty sponges. However, the benefits of shrimp occupancy on sponge growth were negatively correlated with overall increases in sponge size; sponges that decreased in mass during the experiment benefited more from shrimp occupancy than sponges that increased in mass. These costs and benefits suggest that Synalpheus has variable effects on sponges: positive effects on sponges in the presence of predators, and/or when sponges are decreasing in mass (e.g., during periods of physical stress), but a negative effect on sponges during periods of active sponge growth.     

Molecular characterization of symbiotic algae (Symbiodinium spp.) in soritid foraminifera (Sorites orbiculus) and a scleractinian coral (Orbicella annularis) from St John,US Virgin Islands

The exchange of Symbiodinium symbionts among scleractinian and soritid hosts could facilitate acclimatization to changing conditions by establishing novel symbiotic unions better tuned to prevailing conditions. In this study, we compare the communities of Symbiodinium spp. in neighboring populations of Orbicella annularis and Sorites orbiculus from St. John, US Virgin Islands, using operational taxonomic unit (OTU) clustering of cloned internal transcribed spacer 2 (ITS-2) rDNA sequences. We tested for partitioning of Symbiodinium OTUs by host and depth within and between two sites to explore the potential for symbiont exchange between hosts and light-dependent microhabitat specialization. An apparent lack of overlap in Symbiodinium communities (13 OTUs representing 7 clades) hosted by O. annularis and S. orbiculus suggests that exchange among these hosts does not occur. A low number of novel clade G ITS-2 sequences were found in one O. annularis and one S. orbiculus. A phylogenetic analysis of these sequences revealed them to be sub-clade G2 Symbiodinium, which are most commonly hosted by excavating clionid sponges. A permutational MANOVA revealed within host differences in the partitioning of Symbiodinium OTUs by site but not depth. This finding highlights the potential roles of either dissimilar environmental conditions between sites, or at least partial separation between populations, in determining the types of Symbiodinium contained in different hosts on a spatial scale of a few kilometers.     

Dispersal and use of sponges and ascidians as camouflage by Cryptodromia hilgendorfi (Brachyura: Dromiacea)

From May 1977 to February 1979, the use of sponges and ascidians by Cryptodromia hilgendorfi was studied in Moreton Bay, Queensland, Australia. The aim was to investigate patterns of seasonal use, cap making behaviour, cap turnover, the effect of intraspecific interactions on cap life and the effect of movement of crabs between hosts on background matching. C. hilgendorfi uses 12 (of 16 available) species of sponge and 3 species of ascidians to construct caps, which are carried by the crabs using their last two pairs of legs. Cap area increases non-linearly with crab size, and caps are normally two to three times as large as the crabs. Cap making behaviour is described. It occurs during intermoult periods, with females making most of their caps at night. Caps decrease in size with time, but conceal the crabs which commonly occupy exposed sites on sponges. Cap life is independent of crab size, differs between different cap species and is influenced by the presence of other crabs who can dislodge caps through aggressive behaviour. Caps are made from the sponge Suberites carnosus more often than from other available sponges. S. carnosus caps also decay less rapidly than caps made from other sponges. Use of sponge and ascidian species varies seasonally, with Halichondria sp. and S. carnosus being used in all months. C. hilgendorfi exhibits a preference for certain sponges. The majority of crabs carried caps which matched their host sponge or ascidian, but mis-matches varied seasonally with a winter peak following the breeding season. Young C. hilgendorfi settle only on S. carnosus sponges and disperse from this host to other species in the environment. Males and females differ in their rate of discovery of new hosts. Males, despite their greater mobility, find new hosts slower than females. It is hypothesized that males occupy “home ranges” which females do not. Crabs frequently move between sponges, mostly at night. Sponges and ascidian species grow in intimate association with each other, and sponge crabs act a selective asexual propagation mechanism. Depending upon the nature of the interactions between sponge and ascidian species (co-operative or competitive) and whether competitive hierarchies or networks are involved, the sponge crabs may have either stabilizing or destabilizing effects on the sponge community.     

Temporal reproductive isolation and gametic compatibility are evolutionary mechanisms in the<Emphasis Type="Italic"> Acropora humilis</Emphasis> species group (Cnidaria; Scleractinia)

Patterns of interbreeding between individuals are fundamental to the structure and maintenance of evolutionary boundaries between species. In corals, both hybridisation and reproductive isolation appear to be important evolutionary mechanisms. In this study, I examine evolutionary boundaries using morphological, molecular and reproductive criteria within the Acropora humilis species group at Lizard Island on the Great Barrier Reef, Australia. Five species and seven morphs are recognised on the basis of morphological appearance of features traditionally used to identify corals of the genus Acropora. In a molecular phylogenetic analysis, I examine relationships for the mitochondrial DNAs putative control region, using maximum-parsimony and maximum-likelihood methods. The reproductive criteria explore whether species and morphs are reproductively isolated on the basis of temporal or fertilisation barriers. Timing of gamete maturity is surveyed for each species and morph, from the month prior to and 3 months after the mass spawning. Time of spawning is documented at the levels of night and hour of spawning, and time taken for egg-sperm bundles to separate. Laboratory fertilisation experiments tested the potential of species and morphs to interbreed. High levels of intraspecific and extremely low or zero fertilisation levels between the five species indicated that they are valid species. Based on the combined assessment of morphological, molecular and reproductive criteria, A. humilis and A. gemmifera appear to be the most closely related species, which are most closely related to the remaining species in the following order: A. samoensis, A. monticulosa and A. digitifera. Evidence derived from one or more of these criteria suggest that the morphs (1) are at various stages of divergence from the species with which they share morphological characters, and (2) may indicate possible zones of speciation and hybridisation. Identification of morphs avoided the possibility of taxonomic error and was essential for accurate interpretation of evolutionary boundaries. Confirmation of morphology as an informative character of evolutionary boundaries is of great significance because most coral research projects rely on morphology as the primary tool for identification of species.Communicated by M.S. Johnson, Crawley