Associational resistance and shared doom: effects of epibiosis on herbivory

The potential for spatial associations between palatable and unpalatable plant species to reduce herbivore pressure on the palatable species has been described as associational resistance, associational refuge or associational defense for numerous terrestrial and marine communities. One of the closest associations between species-epibiosis-has not been thoroughly investigated in this regard. In this study we evaluated how different associations between host seaweeds and epibiotic plants and animals influenced the movement of an omnivorous sea urchin (Arbacia punctulata) to the host and subsequent feeding on the host. A. punctulata showed clear preferences when given pairwise choices between 12 prey species (3 animals, 9 algae). These preferences were consistent and allowed us to rank the six epibiont species and six host species linearly from least to most preferred by A. punculata. Most host-epibiont associations dramatically changed urchin preference, increasing or decreasing urchin grazing on fouled hosts as compared to clean conspecifics. Herbivory on the host increased when the epibiont was more preferred, and decreased when it was less preferred than the unfouled host alga. Taking the host species as a point of reference, we classified epibiosis-caused decrease in herbivory as associational resistance, while epibiont-caused increases in herbivory were defined as shared doom. These epibiont-host-herbivore interactions could select for hosts that facilitate the growth of certain low preference epibionts on their surfaces in situations where the resulting decreases in herbivory would offset the various negative effects of being fouled. In contrast, in situations where herbivores are common, the negative effects of being fouled by palatable epibionts may be much greater than is generally assumed. In our assays, unpalatable hosts fouled by palatable epibionts became much more attractive to urchins and rose several ranks on the urchins' preference hierarchy.     

Resource Acquisition and Alternative Mating Strategies in Water Striders

Behavioral polymorphisms occur among male and female water striders,Gems remigis, when competing for food and mates. Individualsof both sexes vie for positions in the fastest flowing portionsof streams. Here prey capture rates are highest, as are thoseof swimming and aggression. Only the largest females, and maleswith the largest first appendages, can regularly maintain positionsin these areas. The remaining females are arranged along theflow gradient according to their size with the smallest holdingpositions in pools of slow moving water. For the remaining malesneither overall size, nor the size of the first appendages,appears to determine which males swim near the edge of streams,or which males swim as satellites behind those occupying thefast flowing productive areas. Preliminary data show that matingsuccess of edge and satellite males are about equal, but significantlyless than that of the centrally positioned males with the largestfirst appendages. Thus although it appears that morphologicalphenotype influences male competitive behavior, when the absolutesize of the critical trait is small males adopt behavior afterassessing the actions of others. For these "subordinate" males,behavioral assessment appears to produce an "ideal free" spatialdistribution.     

How does flow recruit epibionts onto brachiopod shells? Insights into reciprocal interactions within the symbiotic framework

Computational fluid dynamics simulations were performed to examine the passive recruitment of epibionts onto Devonian spiriferide brachiopod host shells. Because many planktonic larvae and spores are propulsion-inefficient swimmers, we determined the areas most prone to settlement in terms of inertial impaction and direct interception, which are characteristic of higher and lower pressure, respectively. Simulations on a unique specimen of Paraspirifer with a geopetal structure of broken brachidia suggest that the larva of Aulopora on the shell was transported and had settled onto the shell through inertial impaction after the host was dead and overturned on the sea floor. In the case of an ideal life posture, the spiriferide models received higher pressure on the shell surfaces at the forward and rearward stagnation areas and lower pressure along the shell margins and the anterior part of the sulcus, regardless of whether the ventral or the dorsal valve was facing upstream. Both sites seem to be available for epibionts by way of direct interception or inertial impaction. Our results indicate that the initial recruitment of most epibionts is accidental and passive, whereas the directions and patterns of epibiont growth suggest a biological response to ambient conditions.     

The development of the nervous system in Laevicaudata (Crustacea, Branchiopoda): insights into the evolution and homologies of branchiopod limbs and ‘frontal organs’

We investigated the development of the external morphology and of the nervous system in Lynceus biformis and Lynceus brachyurus (Laevicaudata, Branchiopoda), by using immunohistochemical methods in combination with a confocal laser scanning analysis. In both Lynceus species, a free-swimming nauplius larva, equipped with three appendages, hatches from resting eggs. Despite their close phylogenetic relationship to each other, considerable differences are present in their external morphology. Hatching L. brachyurus larvae are equipped with a large and flattened labrum, where in contrast, the L. biformis larvae possess a smaller labrum with four conspicuous posteriorly directed spines at its margin. Despite these differences, the development of the nervous system is quite similar in both species. The hatching larvae are equipped with a naupliar nervous system, and only in the more advanced stages, the development of the ventral nerve cord starts. Furthermore, our investigation into the nervous system provided insights into architecture and evolution of protocerebral sensory organs, the dorsal setae field and the dorsal frontal organ, only present in Laevicaudata. The identification of frontal filaments with an associated frontal filament organ in Lynceus revealed—after a comprehensive comparison with other branchiopods—that these organs exist throughout Branchiopoda and are comparable to those in other crustaceans. Additionally, our results of the peripheral nervous system analysis showed that the innervation pattern of the naupliar appendages (antenna and mandible) and the trunk appendages could be serially homologized, despite much difference in gross morphology of these. Based on the innervation pattern of limbs, we suggest that the larval uniramous mandibular palp, found in the larvae of all ‘large’ branchiopods, is largely exopodal of nature (contrary to most earlier statements) and that the endopodite of the trunk limbs consists of only one distal endite-like segment (confirming some earlier statements) and not of three as proposed by others.     

Localization of attachment area of the symbiotic Chlorella variabilis of the ciliate Paramecium bursaria during the algal removal and reinfection

Chlorella spp. and ciliate Paramecium bursaria share a mutual symbiosis. However, both alga-removed P. bursaria and isolated symbiotic algae can grow independently. Additionally, mixing them experimentally can cause algal reinfection through host phagocytosis. Although the symbiotic algal localization beneath the host cell cortex is a prerequisite phenomenon for maintenance of the relationship of their endosymbiosis, how and where the algae locate beneath the host cell cortex remains unknown. To elucidate this phenomenon, algal distribution patterns during algal removal and reinfection were observed. During algal removal, algae at the host anterior cortex were easier to remove than at the posterior and ventral or dorsal cortex areas. During algal reinfection, the algae after separation from the host digestive vacuoles tended to localize beneath the host ventral or dorsal cortex more readily than that at other cortices. Algae that reinfected trichocyst-removed paramecia didn’t show this localization. Trichocyst-discharge experiments clarified that trichocysts of the anterior cortex are difficult to remove. In 14 strains of P. bursaria, some of the paramecia lacked their symbiotic algae at the anterior cortex. These observations demonstrate that symbiotic algae of P. bursaria are difficult to localize at the anterior cortex and that they are easy to remove from the area.     

Invertebrate and protozoan epibionts on the velvet swimming crab Liocarcinus puber (Linnaeus, 1767) from Scotland

Invertebrate and ciliate protozoan epibionts of velvet swimming crabs collected near Millport (Scotland) were analysed. The ecdysis peak for male crabs was at the time of collection while that for female crabs was 2 months later. The epibionts were: the polychaetes Pomatoceros triqueter and Hydroides norvegica, the cirriped Balanus crenatus, the entoproct Barentsia matsushimana, the hydroids Leuckartiara sp. and Clytia sp., and the ciliate protozoans Ephelota plana, Ephelota gemmipara, Chilodochona quennerstedti and Cothurnia longipes. The polychaetes, cirripeds, entoprocts and hydroids, all of them with comparatively larger size, were distributed on the carapace, ventral surface of the cephalothorax and the pereiopods; meanwhile the protozoans, with smaller size, were attached also on pleopods, antennae, eyes and buccal appendages. Chilodochona quennerstedti was the epibiont most abundant on the crab, followed by Ephelota plana. Cothurnia longipes was, in contrast, the least abundant epibiont, followed by Barentsia matsushimana. The anatomical unit most colonized was the left third maxilliped, followed by the left first maxilliped and the ventral surface. The less colonized anatomical units were the left antenna and the ocular orbits. Epibionts on this crab have not been described before. Statistical analyses of the epibiont distribution on the crab were carried out. There were significant correlations between right and left appendages in 66.67% of the cases. Males and females differed significantly with respect to the distribution of epibionts on their anatomical units. The comparison analysis indicated a significant differential distribution of each epibiont species on the anatomical units of the crab. Principal component analysis grouped the epibiont species according to their colonization pattern in three clusters: (1) Ephelota plana, Ephelota gemmipara and Chilodochona quennerstedti; (2) Leuckartiara sp., Clytia sp., Barentsia matsushimana and Cothurnia longipes; and (3) Pomatoceros triqueter, Balanus crenatus and Hydroides norvegica. The hierarchical cluster analysis grouped the anatomical units of the crab in relation to their colonization in five clusters.     

Newly created ponds complement natural waterbodies for restoration of macroinvertebrate assemblages

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Density dependent shifts in attachment site by the ectosymbiotic chironomid Nanocladius asiaticus on its megalopteran host Protohermes grandis

Intraspecific interactions among ectosymbionts may occur when suitable attachment sites are limited to specific parts of their hosts. In this study, we examined attachment site selection by the ectosymbiotic chironomid Nanocladius (Plecopteracoluthus) asiaticus. Larvae and pupae of this chironomid attach to larvae of the megalopteran Protohermes grandis: they feed on algae and detrital materials caught on the chironomid's silken nets and on the body surface of the host. Sampling at approximately monthly intervals in central Japan revealed that the proportion of hosts with chironomids was relatively high and stable during the 2 year study period. When attached singly, larvae were usually found on the ventral side of the host's mesothorax. However, when two or more larvae were attached to a host, the mesothorax was occupied by only one larva (usually a large individual) and the other(s) were attached to the ventral side of the abdomen. Density dependent shifts in attachment sites were confirmed by a reattachment experiment in which a larva was removed from its host and released onto a new host with or without symbiosis by another individual. All of the larvae released singly on a host devoid of symbionts attached to the thoracic region and survived, whereas those released in pairs and not occupying this site were frequently lost. Thus, the thorax (particularly the mesothorax) is the most suitable attachment site, and there is a possibility that chironomid larvae compete for this site.     

Effects of submerged plants on water quality and biota in large-scale experimental ponds

We quantitatively studied the effect of submerged plants on water quality and biota under fish-free conditions for 3 weeks in four large freshwater experimental ponds (533 m³ per pond) at the Aqua Restoration Research Center, Japan. Two artificially harvested ponds with scant vegetation were used as “harvested ponds” (H1, H2), and the other two ponds, which were naturally dominated by Hydrilla verticillata, were used as “vegetated ponds” (V1, V2). The PVI (percent water volume infested with macrophytes) was employed as an index of vegetation abundance. Vegetated ponds had much clearer water than harvested ponds. The water quality in H2 (PVI 10%) was better than in H1 (PVI 3%), whereas the water quality did not differ significantly between the two vegetated ponds (V1, PVI 38% and V2, PVI 84%). Therefore, the threshold between clear water and turbidity was between 10 and 38% in PVI. Our result also showed that a turbid water state was created shortly after harvest. Green algae were abundant in the harvested ponds, and diatoms were dominant in the vegetated ponds. Rotifers were stably dominant in the harvested ponds. Aquatic worms were more abundant in the harvested ponds than in the vegetated ponds. Unexpectedly, zooplanktons were much less abundant in the vegetated ponds; therefore, zooplankton grazing was not the main mechanism behind the cleaner water in our experiment. These results are physical evidence that the presence of dense macrophytes was the main factor in the creation of a clear water state.     

Water quality of rural ponds in the extensive agricultural landscape of the Cerrado (Brazil)

The Brazilian Cerrado, one of the world’s 34 biodiversity hotspots, is today under increasing pressure from the intensification of agriculture, with the replacement of traditional extensive pastures by arable crops. Manmade ponds are currently widespread in rural areas of the Cerrado and provide many ecosystem services such as cattle watering, fish production, irrigation and erosion protection. As in other parts of the world, ponds are also likely to play a critical role in the conservation of freshwater biodiversity, although in the Cerrado there is still very little known about their biota. Good water quality, in particular the level of eutrophication, is a key factor in maintaining aquatic biodiversity at the regional scale. Therefore, we aimed here to assess the water quality of ponds in the Cerrado. We also assessed whether the main types of socioeconomic pond uses have an impact on their water quality. We focused on measures of primary production and conducted socioeconomic inquiries for 56 waterbodies in the Goiânia Cerrado region (GO, Brazil) at the beginning of the 2012 dry season. Overall, differences in water quality appeared to be linked to the type of pond use. The trophic level, as indicated by the chlorophyll concentration and conductivity, was greater in fish ponds and seemed to be related to management practices such as fish feeding and the type of water supply, in particular relatively low inflow volume. This contrasted with ponds used for cattle watering in extensive agricultural landscapes characterized by a low trophic level potentially beneficial for regional biodiversity. Good water quality in pasture ponds may be maintained by spring water inflow or heavy precipitation. Overall, the water quality of the Cerrado ponds was good compared with the same type of waterbodies in other regions of the world. These results highlight the high potential of the Cerrado ponds in extensive agricultural landscapes to provide an important habitat for aquatic biodiversity. Biodiversity inventories and assessments are now needed to increase our knowledge of these waterbodies and inform management activities at the local and regional scale.     

Nanocladius (Plecopteracoluthus) asiaticus sp. n. (Diptera: Chironomidae) Phoretic on Dobsonfly and Fishfly Larvae (Megaloptera: Corydalidae)

The adult male, adult female, pupa, and larva of Nanocladius (Plecopteracoluthus) asiaticus sp. n. (Diptera: Chironomidae) are described and illustrated. Larvae live in coarse silken nets which usually are attached to the ventral side of the mesothorax of larval dobsonflies and fishflies (Megaloptera: Corydalidae) dwelling in stream riffles. The host species are Protohermes grandis and Parachauliodes continentalis in Japan, Protohermes costalis and Neochauliodes sinensis in Taiwan, and Neurhermes maculipennis in the Malay Peninsula. Larvae are not parasitic but may have a commensal relationship with their hosts; they feed on algae and detrital material caught on their silken nets, or on the body surface of their hosts. Pupation occurs in the fine silken net fixed to the lateral side of host thoracic regions, or occasionally to the undersides of hind legs.     

Effects of epibiosis on consumer–prey interactions

In many benthic communities predators play a crucialrole in the population dynamics of their prey. Surfacecharacteristics of the prey are important forrecognition and handling by the predator. Because theestablishment of an epibiotic assemblage on thesurface of a basibiont species creates a new interfacebetween the epibiotized organism and its environment,we hypothesised that epibiosis should have an impacton consumer–prey interactions. In separateinvestigations, we assessed how epibionts onmacroalgae affected the susceptibility of the latterto herbivory by the urchin Arbacia punctulataand how epibionts on the blue mussel Mytilusedulis affected its susceptibility to predation bythe shore crab Carcinus maenas.Some epibionts strongly affected consumer feedingbehavior. When epibionts were more attractive thantheir host, consumer pressure increased. Whenepibionts were less attractive than their host or whenthey were repellent, consumer pressure decreased. Insystems that are controlled from the top-down,epibiosis can strongly influence community dynamics.For the Carcinus/Mytilus system that westudied, the in situ distribution of epibiontson mussels reflected the epibiosis-determinedpreferences of the predator. Both direct and indirecteffects are involved in determining theseepibiont-prey–consumer interactions.     

The distribution of pond snail communities across a landscape: separating out the influence of spatial position from local habitat quality for ponds in south-east Northumberland,UK

Ponds support a rich biodiversity because the heterogeneity of individual ponds creates, at the landscape scale, a diversity of habitats for wildlife. The distribution of pond animals and plants will be influenced by both the local conditions within a pond and the spatial distribution of ponds across the landscape. Separating out the local from the spatial is difficult because the two are often linked. Pond snails are likely to be affected by both local conditions, e.g. water hardness, and spatial patterns, e.g. distance between ponds, but studies of snail communities struggle distinguishing between the two. In this study, communities of snails were recorded from 52 ponds in a biogeographically coherent landscape in north-east England. The distribution of snail communities was compared to local environments characterised by the macrophyte communities within each pond and to the spatial pattern of ponds throughout the landscape. Mantel tests were used to partial out the local versus the landscape respective influences. Snail communities became more similar in ponds that were closer together and in ponds with similar macrophyte communities as both the local and the landscape scale were important for this group of animals. Data were collected from several types of ponds, including those created on nature reserves specifically for wildlife, old field ponds (at least 150 years old) primarily created for watering livestock and subsidence ponds outside protected areas or amongst coastal dunes. No one pond type supported all the species. Larger, deeper ponds on nature reserves had the highest numbers of species within individual ponds but shallow, temporary sites on farm land supported a distinct temporary water fauna. The conservation of pond snails in this region requires a diversity of pond types rather than one idealised type and ponds scattered throughout the area at a variety of sites, not just concentrated on nature reserves. Handling editor: B. Oertli     

Surgical generation of supernumerary appendages for studying neuronal specificity in Drosophila melanogaster

The ability of sensory neurons to establish specific synaptic contacts in the central nervous system (CNS) can be studied by changing the spatial relationship between the periphery and the CNS. In contrast to the genetic displacement of appendages by homoeotic mutations, the surgical approach used in this study allows one to place homologous as well as heterologous appendages to the same site on the body surface. Using an improved technique of “surface transplantation,” we generated supernumerary appendages of any desired type in a particular abdominal position. The sensory axons originating from these grafts enter the CNS through the main abdominal nerve and arborize in the fused abdominal ganglia; many fibers extend also into thoracic centers. In the abdominal ganglia, terminals from dorsal transplants (wings and halteres) stay on the ipsilateral side, whereas terminals from ventral transplants (legs and antennae) distribute ipsi- and contralaterally. The same preference holds true for dorsal and ventral abdominal bristles, respectively, whose projection patterns served as a reference. In thoracic ganglia, axons from dorsal and ventral grafts yield completely different terminal patterns. Dorsal grafts project into the ipsilateral wing center, even in the mutant wingless, in which normal wing afferents are suppressed. In contrast, fibers from ventral grafts often extend along the thoracic midline. These data indicate that sensory axons of homologous appendages on the one hand, and their central targets on the other, share serially repeated surface markers. This may enable sensory fibers to recognize centers of homologous appendages.     

Surface structures and sense organs of the cypris larva of Balanus balanoides as seen by scanning and transmission electron microscopy.

Various features of the settlement stage larva (cyprid) of the barnacle, Balanus balanoides (L.), were studied using scanning and transmission electron microscopy. The cuticle of the valves is pitted and in section has a characteristic ultrastructure. Small sensory setae protrode from the surface of this cuticle and are probably mechanoreceptors able to sense water movement around the larva. Each of the pair of caudla appendages which protrude from between the larval valves posteriorly, is made up of several sensory setae. These appendages are able to sense settlement surface topography. Certain other features of the larva are alos described and their roles discussed; such features include the frontal filaments, antennules and thoracic limbs.     

Effects of epibiotic algae on the survival, biomass and recruitment of mussels, Mytilus L. (Bivalvia: Mollusca)

Habitats composed of living ‘ecosystem engineers’, such as mussels, are subject to direct and indirect interactions with organisms that live among them. These interactions may affect the presence and structure of habitat, and hence, the associated taxa. We examined the direct effects of epibiotic algae on the survival, biomass and recruitment of mussels (Mytilus L.) on the west coast of Ireland. A field experiment showed that the presence of epibiotic fucoid algae reduced the likelihood of survival of mussels during storms. We also found that the strength of attachment of mussels did not increase in the presence of epibionts. Another in situ experiment revealed that the presence of ephemeral epibiotic algal mats had no effect on the biomass of host mussels, suggesting no effect on mussel growth or production. The abundance of small mussels (< 5 mm) covaried with cover of epibiotic algae at one location, but experimental results suggest no direct effect of the algae on recruitment unless through the action of chemical cues which linger after the removal of algae. We have identified a negative direct interaction between epibiotic algae and mussels on exposed rocky shores, which may often be characterised by bottom-up regulation. It is thought that positive interactions may be more important on more sheltered or sedimentary shores where top-down processes are more likely to dominate.     

Calcified epibionts as palaeoecological tools: examples from the Recent and Pleistocene reefs of Barbados

Calcified epibionts (crustose coralline algae, bryozoans, foraminiferans and serpulid worms) which colinize primary framebuilders of Recent Barbados reefs exhibit a well-defined zonation of species and morphological growth forms in response to environmental factors such as water turbulence and light. Exposed environments are characterized by thick crusts of coralline algae whereas cryptic environments are dominated by thin crusts of algae, bryozoans, foraminiferans and serpulid worms. A model, based on this zonation, was used to decipher the environments of growth and early burial of Pleistocene reefs. Lagoonal corals possess an assemblage of encrusters which document prolonged growth in a uniform environment. Reef crest corals support a mixed succession of shallow water encrusters which record a gradual decrease in light as substrates are smothered by accumulating debris. Sequences such as these represent growth under stable conditions. The model can also be used to interpret sequences formed by catastrophic events and fluctuations in sea level.     

Prevalence of Colacium vesiculosum (Colaciales: Euglenophyceae) on planktonic crustaceans in a subtropical shallow lake of Argentina

Colacium vesiculosum (Euglenophyceae) is an epibiont common on planktonic microcrustaceans of continental waters. The interaction between epibionts and substrate organisms is not very well known, particularly in subtropical environments of South America. In the present work, we analyzed the prevalence, density, biomass and attachment sites of C. vesiculosum on planktonic microcrustaceans from Paiva Lake, a subtropical lake of Argentina. With the aim to evaluate whether epibionts affect the filtering rates of Notodiaptomus spiniger, the dominant planktonic crustacean, we carried out bioassays using phytoplankton < 53 microm. Crustaceans were sampled using a PVC tube (1.2m long and 10cm in diameter), filtering 50L of water through a 53 microm-mesh. Microcrustaceans were counted in Bogorov chambers under a stereoscopic microscope. The infested organisms were separated and observed with a photonic microscope to determine density and biovolume of epibionts, by analyzing their distribution on the exoskeleton. The prevalence of C. vesiculosum was higher in adult crustaceans than in their larvae and juveniles. The most infested group was that of calanoid copepods, related to their high density. The attachment sites on the exoskeleton were found to be the portions of the body which have a higher probability of encounter with epibionts during locomotion and feeding, i.e., antennae and thoracic legs in copepods, and thoracic legs and postabdomen in cladocerans. The similar values found in the filtering rate of infested and uninfested individuals of N. spiniger and the constant prevalence (< 40%) of epibiont algae, suggest that C. vesiculosum does not condition the life of planktonic crustaceans of Paiva Lake.     

Antennule shape and body size of <Emphasis Type="Italic">Bosmina</Emphasis>: key factors determining its vulnerability to predacious Copepoda

Cyclopoid copepods are common in lakes and ponds, and they have a significant predation impact on the communities of the small zooplankton species. To reduce the predation risk, some cladoceran zooplankters develop protuberant (defensive) morphologies in the presence of the copepods. In the case of the small cladoceran Bosmina, they elongate their appendages (antennule and mucrone) and change the antennule morphotype. However, information about the effectiveness of these defensive devices against copepod predation is still insufficient. In our study, to find the compositive effects of these appendages on the vulnerability of Bosmina, we exposed two bosminid species (B. longirostris and B. fatalis) of different body sizes and with appendages of different lengths and shapes to copepod (Mesocyclops) predation. The experiment revealed that the shape of the antennule is a main factor determining the bosminid’s vulnerability to copepod predation and indicated that the protection of the opened ventral carapace must be a key strategy by which Bosmina avoids copepod predation.     

On the move: sloths and their epibionts as model mobile ecosystems

Sloths are unusual mobile ecosystems, containing a high diversity of epibionts living and growing in their fur as they climb slowly through the canopies of tropical forests. These epibionts include poorly studied algae, arthropods, fungi, and bacteria, making sloths likely reservoirs of unexplored biodiversity. This review aims to identify gaps and eliminate misconceptions in our knowledge of sloths and their epibionts, and to identify key questions to stimulate future research into the functions and roles of sloths within a broader ecological and evolutionary context. This review also seeks to position the sloth fur ecosystem as a model for addressing fundamental questions in metacommunity and movement ecology. The conceptual and evidence-based foundation of this review aims to serve as a guide for future hypothesis-driven research into sloths, their microbiota, sloth health and conservation, and the coevolution of symbioses in general.