The polychaete Cirriformia punctata is chemically defended against generalist coral reef predators

The Caribbean cirratulid polychaete, Cirriformia punctata (Grube, 1856), is bright orange and burrows just below the surface of fine carbonate sand with only its filamentous tentacles and gills exposed to potential predators. In addition to its conspicuous coloration, C. punctata lacks obvious structural and morphological defenses. We hypothesized that C. punctata protects itself from predation using secondary metabolites as a chemical defense. Feeding bioassays were performed using whole worms to determine palatability against two generalist coral reef predators: the bluehead wrasse, Thalassoma bifasciatum, and the brown anemone, Aiptasia sp. Additionally, assays were conducted with hermit crabs of the genus Paguristes, but with limited success. In all assays, C. punctata was unpalatable to consumers. The tentacles and body of the worm were separately assayed using T. bifasciatum to determine whether the defensive mechanism was differentially allocated to body regions that are differently exposed to potential predators. Both the tentacles and body of C. punctata were unpalatable to T. bifasciatum, indicating no specific allocation of defenses. Crude organic extracts of whole C. punctata were unpalatable to T. bifasciatum, confirming that the worm defense is chemical rather than morphological. Chemical defenses of Cirriformia spp. appear to be generally effective against taxonomically diverse potential consumers.     

Multiple components in ink of the sea hare Aplysia californica are aversive to the sea anemone Anthopleura sola

Sea hares of the genus Aplysia rely on an array of behavioral and chemical defenses, including the release of ink and opaline, to protect themselves from predation. While many studies have demonstrated that ink and opaline are repellent to predators, very little is known about which components of these secretions are active against predators. Ink was previously shown to facilitate the escape of Aplysia from predatory anemones (Anthopleura) by eliciting tentacle retraction and/or shriveling, and gastrovascular eversion, but the metabolites mediating this interaction were not identified. We investigated the metabolites in Aplysia californica secretions that were aversive to the anemone Anthopleura sola, as demonstrated by tentacle shriveling and/or retraction. We found that ink elicited tentacle shriveling and/or retraction, while opaline elicited a feeding response. The active components in ink do not appear to be diet-dependent, as ink was aversive regardless of diet (natural seaweed diet vs. Gracilaria ferox). Furthermore, metabolites extracted from G. ferox were not aversive, suggesting that the aversive components are produced by the sea hares. We then examined escapin, a protein in ink with antimicrobial properties. Escapin quickly forms reaction products when mixed with the amino acids l-lysine and l-arginine, which would occur when ink and opaline are released into the sea hare mantle cavity. Neither escapin alone nor escapin mixed with its amino acid substrate l-lysine elicited aversive behaviors either immediately before or 2 min before applying to the tentacles. In addition, escapin mixed with opaline and applied to tentacles after 2 min did not elicit a significant aversive response. Using bioassay-guided fractionation, we attempted to isolate the components in A. californica ink that are aversive to A. sola. We determined that multiple components in ink, including both lipophilic and hydrophilic constituents, elicited aversive responses. We hypothesize that these components may facilitate A. californica's escape from A. sola by eliciting tentacle shriveling and/or retraction, which lead to anemones dropping ensnared sea hares.     

Eelgrass patch size and proximity to the patch edge affect predation risk of recently settled age 0 cod (Gadus)

Postsettled age 0 Atlantic cod (Gadus morhua) seek refuge from predation in eelgrass (Zostera marina) habitat within shallow, coastal nurseries. Laboratory and field experiments have demonstrated that predation risk on small fish is reduced in habitats of greater structure compared to less complex or barren environs. To determine if predation risk is linked to the areal extent of eelgrass coverage, we tested the hypothesis that predation risk of age 0 cod decreases with increasing eelgrass patch size. Predation on tethered age 0 cod (G. morhua and G. ogac) was quantified in eelgrass patches (1-80 m²) at three sites in northeastern Newfoundland, Canada, during September and October 1999 and 2000. Based on evidence of edge effects in terrestrial landscapes, we also tested the hypothesis that predation is elevated at ecotones separating eelgrass from adjacent barren mud substrate. We examined predation at the edge (i.e., 0 m) and both 5 and 10 m from this edge into and away from eelgrass cover along an 18 m long barren mud-gravel and eelgrass boundary, at two sites. Logistic regression analysis showed that the risk of predation, as measured by the odds ratio, increased with area over a small range of patch sizes (1-35 m² in 1999). When the study was extended to a wider range of patch sizes (1-80 m²) in 2000, a parabolic relationship emerged, with patches on the order of 25 m² providing the least safety and the largest patches (80 m²) providing the most safety. Predation on tethered cod was highest at the edge of eelgrass patches, compared with barren and eelgrass locations; predation generally decreased with distance from the eelgrass boundary. Our results are consistent with the hypothesis that predators are drawn to large patches of eelgrass because of increased prey numbers, that predators increase their success by searching edges, and that this results in greatest predation risk to prey in isolated patches of intermediate size.     

Relative importance of predation and intraspecific competition in regulating growth and survival of juveniles of the soft-shell clam, Mya arenaria L., at several spatial scales

Predation appears to be the single most important biotic factor regulating populations of bivalves in estuarine and coastal soft sediments. However, the relative roles of predation and intraspecific competition are rarely investigated simultaneously over different spatial scales, making generalities about these mechanisms difficult. Using juveniles of the soft-shell clam, Mya arenaria (initial mean shell length [SL] ± 95% CI = 12.4 ± 0.13 mm), I tested the interactive effects of predator deterrence and intraspecific density (660 vs. 1320 individuals m^− 2) on growth and survival responses over a 185-day period from May to November 2003 at spatial scales that spanned four orders of magnitude: embayments, sites within embayments, tidal gradients, and blocks that were 10,000's, 1000's, 100's, and 5 m apart, respectively. Replicate field experiments were conducted from May to November 2003 at the upper and lower tidal heights at each of two intertidal mud flats (sites) within each of two embayments (Passamaquoddy Bay [PB] and Cobscook Bay [CB]) in eastern Maine.Mean survival, relative growth, and the abundance of wild recruits each varied significantly over all spatial scales. Predation was the most important factor affecting clam survival, explaining 45% of the total variability, whereas embayment, sites within embayments, tidal gradient, and intraspecific density collectively accounted for less than 10% of the variation. At all four intertidal sites, clam survival in experimental units designed to deter predators averaged 72%, but the degree of enhancement varied between embayments (PB = 61%; CB = 267%). Average survival rate was higher (by 12-16%), but growth was slower (by ca. 50%) in upper vs. lower intertidal blocks; however, the patterns differed for both variables between sites within each embayment. The effect of increasing intraspecific clam density was to lower survival by ca. 17% (56% [660 m^− 2] vs. 48% [1320 m^− 2]) in both embayments, but growth was unaffected. Overall, clams doubled in SL, although mean relative growth was 15% greater in CB than PB. Tidal gradient, sites within embayments, and blocks were the three most important factors explaining 35%, 19%, and 22% of total variation in relative clam growth, respectively. In Maine and the northeast US, juveniles of Mya reach their highest abundance above mean low tide levels. Experimental evidence presented here suggests that differential predation along the tidal gradient is the dominant factor controlling clam abundance and distribution patterns in the intertidal zone.     

Depth-dependant response to light of the reef building coral, Pocillopora verrucosa: Implication of oxidative stress

Several environmental factors have been described to trigger bleaching in cnidarian/dinoflagellate endosymbiosis. However, the molecular mechanisms underlying this process still need more investigations. Symbiosis breakdown is known to result from physiological damage to animal host cells and/or symbionts. Cellular oxidation appears to be an essential player in this damage. Indeed, oxidative stress is a direct consequence of increase in irradiance and temperature, the two main environmental factors involved in bleaching. In this study, we examined the role of irradiance in inducing dissociation and oxidative stress in cnidarians and dinoflagellates. We used the bleaching-sensitive scleractinian coral Pocillopora verrucosa in a field cross-transplantation experiment performed between 5 m and 20 m depth at Grande Glorieuse Island (Indian Ocean), a preserved area subject to minimal anthropogenic influence. Cellular damage and increase in antioxidant defense were correlated with bleaching in upward transplanted samples. Downward transplanted colonies presented no associated alterations similar to the controls. We therefore conclude that increasing light induced bleaching via a prooxidative period. Remarkably, the distribution of Symbiodinium over depth was invariant; all colonies were monomorph for clade C, suggesting that bleaching sensitivity of P. verrucosa might not be associated with clade specificity.     

Interactive effects of sublethal predation and body size on siphon production of the bivalve Nuttallia olivacea

This paper is intended to reveal effects of siphon cropping on siphon production of a tellinacean bivalve Nuttallia olivacea, an important prey for juvenile stone flounder. We carried out a two-way field experiment in which bivalves of three treatments (3-times siphon removal, 1-time removal, no removal) and four size classes (9-50 mm shell length) were caged and placed in the field for 3 mo. Growth of repeatedly-removed bivalves was inhibited, indicating reduced siphon growth (natural increase of siphon size according to somatic growth). However, siphon production of removed bivalves was larger than non-removed bivalves, possibly because of siphon regeneration. Juveniles (N. olivacea < 20 mm shell length) showed high growth performance. Their siphon growth was greater than their siphon regeneration. In all bivalves except juveniles, siphon regeneration was greater than siphon growth and engendered high siphon production. Siphon growth was dependent on bivalve size and was only slightly reduced by siphon loss, but siphon regeneration seemed to be dependent mostly on the extent of siphon loss. Greater siphon removal enhanced larger siphon production. These results indicate that intensive siphon cropping by juvenile stone flounder induces high siphon production without serious impact on N. olivacea.     

Using experimental ecology to understand stock enhancement: Comparisons of habitat-related predation on wild and hatchery-reared Penaeus plebejus Hess

Marine stock enhancement is often characterized by poor survival of hatchery-reared individuals due to deficiencies in their fitness, such as a diminished capacity to avoid predators. Field experiments were used to examine predation on Penaeus plebejus, a current candidate for stock enhancement in Australia. We compared overall survival of, and rates of predation on, wild P. plebejus juveniles, naïve hatchery-reared juveniles (which represented the state of individuals intended for stock enhancement) and experienced hatchery-reared juveniles (which had been exposed to natural predatory stimuli). Predation was examined in the presence of an ambush predator (Centropogon australis White, 1790) and an active-pursuit predator (Metapenaeus macleayi Haswell) within both complex (artificial macrophyte) and simple (bare sand and mud) habitats. Overall survival was lower and rates of predation were higher in simple habitats compared to complex habitats in the presence of C. australis. However, the three categories of juveniles survived at similar proportions and suffered similar rates of predation within each individual habitat. No differences in survival and rates of predation were detected among habitats or the categories of juveniles when M. macleayi was used as a predator. These results indicate that wild and hatchery-reared P. plebejus juveniles are equally capable of avoiding predators. Furthermore, exposure of hatchery-reared juveniles to wild conditions does not increase their ability to avoid predators, suggesting an innate rather than learned anti-predator response. The lower predation by C. australis in complex habitats was attributed to a reduction in this ambush predator's foraging efficiency due to the presence of structure. Ecological experiments comparing wild and hatchery-reared individuals should precede all stock enhancement programs because they may identify deficits in hatchery-reared animals that could be mitigated to optimize survival. Such studies can also identify weaknesses in wild animals, relative to hatchery-reared individuals, that may lead to the loss of resident populations.     

Post-larval French grunts (Haemulon flavolineatum) distinguish between seagrass, mangrove and coral reef water: Implications for recognition of potential nursery habitats

Environmental cues like sound, magnetic field, oceanic currents, water chemistry or habitat structure are believed to play an important role in the orientation of reef fish towards their settlement habitat. Some species of coral reef fish are known to use seagrass beds and mangroves as juvenile habitats. Once oceanic larvae of these fish have located a coral reef from the open ocean, they still have to find embayments or lagoons harbouring these juvenile habitats. The sensory mechanisms that are used for this are still unknown. In the present study, experiments were conducted to investigate if recruits of the French grunt (Haemulon flavolineatum) respond to habitat differences in water type, as mangrove/seagrass water may differ in biotic and abiotic compounds from coral reef water. Our results show that post-larvae of a reef fish that is highly associated with mangroves and seagrass beds during its juvenile life stage, choose significantly more often for water from mangroves and seagrass beds than for water from the coral reef. These results provide a more detailed insight in the mechanisms that play a role in the detection of these juvenile habitats.     

Early life-history dynamics of Caribbean coral species on artificial substratum: the importance of competition, growth and variation in life-history strategy

The development of a coral community was monitored for 6 years (1998–2004) on 46 m² of artificial settlement substrate in Curaçao, Netherlands Antilles. Growth and survival of recruits (n=1385) belonging to 16 different species were quantified in relation to characteristics of the benthic community developing around them. The early life history dynamics (i.e. growth rate, growth strategy and survival) of corals differed among species although these differences were small for species occupying similar habitats (i.e. underside versus topside of substratum). In contrast to recruit survival, juvenile growth rates were highly variable and unrelated to benthic community structure, at least at the scale of this study. Competing benthic organisms affected coral recruitment success through space preemption (mainly by macroalgae) or recruit overgrowth (mainly by sponges). The results highlight the small spatial scale (mm–cm) at which the processes responsible for recruitment success or failure occur and emphasize the need to include such small-scale observations in studies of coral early life-phase dynamics.     

Impact of a juvenile hormone analogue on the anatomy and the frontal gland secretion of Prorhinotermes simplex (Isoptera: Rhinotermitidae)

In termites, juvenile hormone plays a key role in soldier differentiation. To better understand the evolutionary origin of the soldiers, we studied the external and inner morphology of pseudergate-soldier intercastes and neotenic-soldier intercastes formed artificially by the application of juvenile hormone analogue in Prorhinotermes simplex. A majority of these intercastes had a soldier phenotype, whereas the inner anatomy had an intermediary form between two castes or a form specific to intercastes. Our experiments showed that traits of neotenics and soldiers can be shared by the same individuals, although such individuals do not exist naturally in P. simplex, and they have not been reported in other species but in some Termopsidae. Our results reinforce the hypothesis that soldiers may have emerged from soldier neotenics during the evolution of termites.     

Occupational strategy of runner reed (Phragmites japonica): Change of growth patterns with developmental aging

The characteristics of P. japonica stands growing along ten transect in an AFP were assessed. Especially those of the reproductive organs in terms of developmental stages were focused. Four consecutive stages were observed based on the existence of reproductive organs (flowers and stolons). Plants in the ‘stolon’ and ‘flower and stolon’ stages played a role as a colonizer by stolonization (the longest length of stolon was more than 9 m) while those in the ‘flower’ stage played a role as an occupant via forming tall and dense shoots on tussocks (more than 2 m and about 20 shoots per tussock including dead standing shoots). Consecutive developmental stages according to changes in growth patterns, particularly in the conversion of reproductive organ from asexual (stolon) to sexual (flower), was the critical strategy of P. japonica for efficient monotypic occupation. This occupational strategy of P. japonica also resulted in a sharp decrease of the plant species richness (two to three including P. japonica) growing in the same area with P. japonica in the mature (‘flower’) stage.     

Nudibranch-sponge feeding dynamics: Benefits of symbiont-containing sponge to Archidoris montereyensis (Cooper, 1862) and recovery of nudibranch feeding scars by Halichondria panicea (Pallas, 1766)

Selected interactions between the encrusting sponge Halichondria panicea and its primary predator, the dorid nudibranch Archidoris montereyensis, were investigated in a high-latitude rocky intertidal community spatially dominated by H. panicea. Feeding experiments were conducted in which A. montereyensis pairs were provided with sponge containing symbiotic zoochlorellae or sponge in which the zoochlorellae population had been reduced or removed by shading. Nudibranchs consuming H. panicea with symbiotic zoochlorellae had higher feeding, growth, and egg production rates than individuals eating aposymbiotic sponge. We simulated A. montereyensis predation on H. panicea by creating typically sized feeding grooves in the sponge. H. panicea's response was high linear growth rates into the experimental feeding grooves, generally recovering most of the groove area within 4 weeks. Overall, the sponge's rapid response to tissue damage minimizes grazing impacts and substrate loss and reduces susceptibility to wave removal.     

The tensor-based model of plant growth applied to leaves of Arabidopsis thaliana: A two-dimensional computer model

Plant organs grow in coordinated and continuous way. Such growth is of a tensor nature, hence there is an infinite number of different directions of growth rate in each point of the growing organ. Three mutually orthogonal directions of growth can be recognized in which growth achieves extreme values (principal directions of growth [PDGs]). Models based on the growth tensor have already been successfully applied to the root and shoot apex. This paper presents the 2D model of growth applied to the arabidopsis leaf. The model employs the growth tensor method with a non-stationary velocity field. The postulated velocity functions are confirmed by growth measurements with the aid of the replica method.     

Mob as tumor suppressor is activated at the cell membrane to control tissue growth and organ size in Drosophila

Growth inhibition mediated by Hippo (Hpo) signaling is essential for tissue growth and organ size control in Drosophila. However, the cellular mechanism by which the core components like Mob as tumor suppressor (Mats) and Warts (Wts) protein kinase are activated is poorly understood. In this work, we found that the endogenous Mats is located at the plasma membrane in developing tissues. Membrane targeting constitutively activates Mats to promote apoptosis and reduce cell proliferation, which leads to reduced tissue growth and organ size. Moreover, the ability of membrane-targeted Mats to inhibit tissue growth required the wts gene activity and Wts kinase activity was increased by the activated Mats in developing tissues. Consistent with the idea that Mats is a key component of the Hpo pathway, Mats is required and sufficient to regulate Yki nuclear localization. These results support a model in which the plasma membrane is an important site of action for Mats tumor suppressor to control tissue growth and organ size.     

林窗大小对杉木林内南方红豆杉生长与形质的影响

为明确林窗大小对南方红豆杉生长、形质的影响以及珍贵用材培育成效,测定福建省明溪杉木林中25个林窗样地的南方红豆杉的生长、干形和分枝等指标,分析林窗大小与生长、干形和分枝情况之间的关系,将25个林窗样地按不同面积划分为25～50 m² (Ⅰ)、50～75 m² (Ⅱ)、75～100 m² (Ⅲ)、100～125 m² (Ⅳ)、125～150 m² (Ⅴ)5种林窗类型,运用层次分析法构建了珍贵用材评价指标体系,采用多目标决策法评价5种林窗类型的综合效果.结果表明: 林窗大小显著影响南方红豆杉树高、胸径、冠幅、杈干率、通直度、圆满度、尖削度、径高比、枝下高、枝间距、最大侧枝直径等11个生长和形质指标以及综合评价值. 林窗Ⅰ、Ⅱ类型显著促进南方红豆杉的树高、胸径、冠幅的生长.在干形指标方面,林窗Ⅰ、Ⅱ类型显著抑制分杈率和尖削度,提高通直度;林窗Ⅱ类型显著提高圆满度和径高比.林窗Ⅰ、Ⅱ类型显著提高枝下高,降低最大侧枝直径;林窗Ⅰ类型显著提高枝间距. 林窗Ⅰ、Ⅱ类型显著提高珍贵用材综合评价值.在杉木林内南方红豆杉的培育过程中,控制采伐强度、创建面积25～75 m²的林窗可提高培育效果.     

Recruitment, early survival and growth of the Mediterranean red coral Corallium rubrum (L 1758), a 4-year study

Recruitment, early survival and growth rates of the precious Mediterranean red coral Corallium rubrum (L 1758) are poorly known. We examined these life history traits by means of artificial long-term settlement plates. Eighteen marble tiles placed off the coast of Leghorn (Tuscany, Italy) at two depths (25 and 35 m) were photographed monthly over the 4-year period from 1998 to 2002. Overall, 864 transparencies were examined to follow the individual life histories of red coral colonies belonging to four successive cohorts. Red coral planulae settled on tiles each year between July and September. Overall, 388 settlers colonized the tiles (244 at 25 m and 144 at 35 m), and their respective densities varied between 12.37±6.1 and 2.75±2.4 dm⁻². Heavy mortality affected these colonies (−24.35±9.12 colonies % y⁻¹), but, after 4 years, the tiles still harboured a persistent population (19±4.97 and 9.75±2.87 colonies dm⁻², respectively, at 25 and 35 m) with positive net recruitment rates. Only in 1999 did the net recruitment rate show a negative trend, although only at the shallower depth. At the same time (late summer 1999), a thermal anomaly affected several epibenthic communities in the Ligurian Sea. After 4 years, the tiles were removed, and the colonies that settled on them were measured. The average annual growth rate of colonies was low (0.62±0.19 mm y⁻¹ in diameter), and a marked reduction in growth with age was observed. Our findings suggest that the populations of this slow-growing long-lived octocoral exhibit a high capacity for colonization and seem to be quite resilient to environmental variability.     

Habitat selection of juvenile banana prawns, Penaeus merguiensis de Man: Testing the roles of habitat structure, predators, light phase and prawn size

The effects of fish predators, light phase, habitat structure and prawn size on the habitat preferences of juvenile Penaeus (Fenneropenaeus) merguiensis de Man were examined with laboratory experiments. The behaviour of juvenile P. merguiensis within habitats of different structural complexity was also examined. Experiments were carried out in a tank (1.8 m diameter) divided into four habitats representing: bare substratum, leaf litter (little vertical structure), mangrove pneumatophores (regular vertical structure) and mangrove woody debris (heterogeneous vertical structure). The location of 10 prawns was monitored over 270 min (135 min light and 135 min dark), with different prawns five times for each combination of prawn size class, and predator (no predator; Arius graeffei Kner and Steindachner and Lates calcarifer Bloch).In the absence of predators and during the light phase, when observations on prawn behaviour were made, swimming was the most common behaviour (of seven mutually exclusive behavioural categories) with few differences in behaviour between sizes. All size classes of juvenile P. merguiensis selected vertical structure (mangrove debris and pneumatophores) over low vertical structure (leaf litter and bare substratum), in both light and dark conditions and in the presence or absence of predators. When L. calcarifer was present, the selection by prawns of the mangrove-debris habitat increased significantly. This was attributed to an increase in predation risk in the other habitats. L. calcarifer rarely pursued prey amongst the mangrove-debris structure, compared to habitats with less heterogeneous vertical structure (pneumatophores, leaf litter and bare substratum).     

Zooid size and growth rate of the bryozoan Cryptosula pallasiana Moll in relation to temperature, in culture and in its natural environment

The size of cheilostome bryozoan zooids has been widely discussed for its potential in inferring palaeotemperatures, based on correlations between zooid size and temperature. Studies in both the natural environment and under experimental laboratory conditions have shown that an increase in temperature significantly decreases zooid size in a range of bryozoan taxa. In order to test the effect of temperature on zooid size, the cheilostome bryozoan Cryptosula pallasiana was for the first time successfully cultured under laboratory conditions. C. pallasiana was grown at 14 °C and 18 °C using Rhodomonas sp. as a food organism. Zooid size, tentacle number and growth rate were measured over a period of 26 days. For comparison, zooids from colonies of C. pallasiana collected from the natural environment were measured in winter and summer months. Results showed that colonies grown in laboratory culture had significantly longer and wider zooids at 14 °C than at 18 °C. The specific growth rate of C. pallasiana doubled from 14 °C to 18 °C. Comparison of tentacle number in culture showed a significantly higher value at lower temperatures. This may be related to differing food availability, longer polypide life spans, or a shift of energy use at colder temperatures. In nature the zooids were significantly longer in colonies sampled in July than in January, a clear difference from laboratory results. The utility of cheilostome Bryozoa as indicators of environmental change and their potential for studies of paleotemperature are highlighted.     

Sexual size dimorphism in the ontogeny of the solitary predatory wasp Symmorphus allobrogus (Hymenoptera: Vespidae)

Sex-specific patterns of individual growth, resulting in sexual size dimorphism (SSD), are a little studied aspect of the ontogeny related to the evolutionary history and affected by the ecology of a species. We used empirical data on the development of the predatory wasp Symmorphus allobrogus (Hymenoptera, Vespidae) to test the hypotheses that sexual differences of growth resulting in the female-biased SSD embrace the difference in (1) the egg size and the starting size of larva, (2) the larval development duration, and (3) the larval growth rate. We found that eggs developing into males and females have significant differences in size. There was no significant difference between the sexes in the duration of larval development. The relative growth rate and the food assimilation efficiency of female larvae were significantly higher than compared to those of male larvae. Thus, the SSD of S. allobrogus is mediated mainly by sexual differences in egg size and larval growth rate.