Associational resistance of fouled blue mussels (<Emphasis Type="Italic">Mytilus edulis</Emphasis>) against starfish (<Emphasis Type="Italic">Asterias rubens</Emphasis>) predation: relative importance of structural and chemical properties of the epibionts

Several epibiotic species reduce starfish (Asterias rubens) preference for the blue mussel Mytilus edulis in the Baltic. The aim of this study was to reveal whether this associational resistance was caused by structural or chemical aspects of the different epibionts. To assess structural epibiont effects, an in situ experiment was conducted with unfouled mussels and mussels equipped with artificial epibionts (dummies) exposed to natural predation by A. rubens. The chemically inert dummies closely matched the structural properties of the locally common epibionts Balanus improvisus (barnacle), Ceramium strictum (red alga), Halichondria panicea (sponge), and Laomedea flexuosa (hydrozoan). Starfish fed indiscriminately in all treatments. Chemical effects of epibionts on the attractiveness of mussels for A. rubens were investigated by incorporating freeze-dried epibionts or mussel tissue into Phytagel pellets at natural concentrations. Starfish were allowed to choose among these structurally similar but chemically different prey items in an in vitro experiment. The predators exhibited significant preferences among the food pellets, which closely matched their preferences for corresponding natural mussel–epibiont associations. Thus, chemical aspects of epibionts appear to play a larger role in this associational resistance than do structural aspects. Implications of these indirect interactions for benthic communities are discussed.Communicated by H.-D. Franke     

Plant defences and the role of epibiosis in mediating within-plant feeding choices of seagrass consumers

Within-plant variation in susceptibility to herbivory can significantly influence the ecological and evolutionary consequences of plant–herbivore interactions. Seagrasses are marine angiosperms characterised by substantial intra-individual differences in multiple traits, such as nutrients, chemical and structural defences and epibiotic load, all of which can strongly influence herbivore preferences. We quantified the within-plant feeding choices of the two main consumers of the temperate seagrass Posidonia oceanica––the fish Sarpa salpa and the sea urchin Paracentrotus lividus––and determined the plant traits that explained their foraging strategies. We found strong within-plant heterogeneity in both seagrass susceptibility to herbivory and chemical composition, but different consumers exhibited contrasting feeding choices. S. salpa preferred the most nutritious and chemically defended younger leaves, suggesting a full adaptation to consuming this macrophyte and a greater impact of this herbivore on the plant. In contrast, P. lividus consistently preferred the older leaves covered by epibionts, probably attenuating the relative impact of this consumer and helping to explain the weak effects usually recorded for this echinoid in undisturbed meadows. Artificial diet experiments showed that morphology and fine-scale structural defences were the primary determinant of urchin feeding choices, with nutrient content and chemical defences being of secondary importance. Epibiosis did not strongly influence fish feeding, but it did have a strong ‘shared-doom’ effect on urchin consumption. This effect was driven by a distinct preference towards a mixed diet that included both host tissues and their epibiotic community.     

The effect of epibionts on the susceptibility of the red seaweed Cryptonemia seminervis to herbivory and fouling

Epibiosis or fouling on living organisms can have direct and indirect detrimental effects, in particular on photosynthetic organisms such as seaweeds. It thus seems reasonable to hypothesize that macroalgae have been selected for the presence or induction of antifouling (AF) defences. The red seaweed Cryptonemia seminervis is usually found in nature with an elevated cover of epibionts. To assess the effect of epibiosis on the susceptibility of this seaweed to herbivory and fouling, the abundance of fouling was evaluated and compared to herbivore consumption (by amphipods and sea urchins) of fouled (bryozoan and sponge) and non-fouled C. seminervis. Attachment of the mussel Perna perna to surfaces treated with extracts from seaweeds with and without epibionts was also assessed. Epibiosis corresponded to ca. 51% of the blade surface of C. seminervis, sometimes covering as much as 90% and up to 51% of the thallus weight, encompassing mainly the bryozoan Membranipora membranacea and an unidentified sponge. Algae colonized by M. membranacea were preferred compared to algae devoid of epibionts, a ‘shared doom’ effect, either by the amphipod Elasmopus brasiliensis or by the urchin Lytechinus variegatus (p < 0.01). Sponge epibiosis also increased consumption by both herbivores (p < 0.001), suggesting that epibionts may act as lures to herbivores, attracting consumers that otherwise would not feed significantly on the seaweed. Foods containing extracts from fouled C. seminervis were preferred by urchins over the alga devoid of epibionts. However, extracts from fouled alga inhibited mussel attachment when compared to epibiont-free alga. Differences might be a direct detrimental effect of the presence of epibionts. On the other hand, epibiosis may induce the production of AF defences in C. seminervis.     

Is palatability of a root-hemiparasitic plant influenced by its host species?

Palatability of parasitic plants may be influenced by their host species, because the parasites take up nutrients and secondary compounds from the hosts. If parasitic plants acquired the full spectrum of secondary compounds from their host, one would expect a correlation between host and parasite palatability. We examined the palatability of leaves of the root-hemiparasite Melampyrum arvense grown with different host plants and the palatability of these host plants for two generalist herbivores, the caterpillar of Spodoptera littoralis and the slug Arion lusitanicus. We used 19 species of host plants from 11 families that are known to contain a wide spectrum of anti-herbivore compounds. Growth of M. arvense was strongly influenced by the host species. The palatability of the individual host species for the two herbivores differed strongly. Both A. lusitanicus and S. littoralis discriminated also between hemiparasites grown with different host plants. There was no correlation between the palatability of a host species and that of the parasites grown on that host, i.e., hemiparasites grown on palatable host species were not more palatable than those grown on unpalatable hosts. We suggest an interacting pattern of specific effects of chemical anti-herbivore defences and indirect effects of the hosts on herbivores through effects on growth and tissue quality of the parasites.     

The effect of epibionts on the susceptibility of the red seaweed Cryptonemia seminervis to herbivory and fouling

Epibiosis or fouling on living organisms can have direct and indirect detrimental effects, in particular on photosynthetic organisms such as seaweeds. It thus seems reasonable to hypothesize that macroalgae have been selected for the presence or induction of antifouling (AF) defences. The red seaweed Cryptonemia seminervis is usually found in nature with an elevated cover of epibionts. To assess the effect of epibiosis on the susceptibility of this seaweed to herbivory and fouling, the abundance of fouling was evaluated and compared to herbivore consumption (by amphipods and sea urchins) of fouled (bryozoan and sponge) and non-fouled C. seminervis. Attachment of the mussel Perna perna to surfaces treated with extracts from seaweeds with and without epibionts was also assessed. Epibiosis corresponded to ca. 51% of the blade surface of C. seminervis, sometimes covering as much as 90% and up to 51% of the thallus weight, encompassing mainly the bryozoan Membranipora membranacea and an unidentified sponge. Algae colonized by M. membranacea were preferred compared to algae devoid of epibionts, a 'shared doom' effect, either by the amphipod Elasmopus brasiliensis or by the urchin Lytechinus variegatus (p < 0.01). Sponge epibiosis also increased consumption by both herbivores (p < 0.001), suggesting that epibionts may act as lures to herbivores, attracting consumers that otherwise would not feed significantly on the seaweed. Foods containing extracts from fouled C. seminervis were preferred by urchins over the alga devoid of epibionts. However, extracts from fouled alga inhibited mussel attachment when compared to epibiont-free alga. Differences might be a direct detrimental effect of the presence of epibionts. On the other hand, epibiosis may induce the production of AF defences in C. seminervis.     

Interactions of plant stress and herbivory: intraspecific variation in the susceptibility of a palatable versus an unpalatable seaweed to sea urchin grazing

Summary Interactions among environmental stresses, plant defensive characteristics, and plant nutrient status may significantly affect an alga's susceptibility to herbivores. Following desiccation, the palatable seaweed Gracilaria tikvahiae was less susceptible to grazing by the sea urchin Arbacia punctulata while the unpalatable alga Padina gymnospora became more susceptible. Increased grazing on desiccated Padina appeared to result from a loss of chemical defenses following desiccation. Palatable plants treated with organic extracts from desiccated Padina plants were consumed at more than twice the rate of plants treated with extracts from undesiccated plants. Increased susceptibility of Padina did not correlate with changes in protein content of the alga; reduced grazing on desiccated Gracilaria was associated with a decrease in protein content. When Padina was grazed by Arbacia or mechanically damaged to mimic urchin grazing, its susceptibility to Arbacia decreased within 1 to 5 days. These results demonstrate that history of physical or biological stress may affect a plant's susceptibility to herbivory. We hypothesize that urchins cue primarily on attractiveness features (e.g. nutrient content) of highpreference algae and deterrent features (e.g. chemical defenses) of low-preference algae. Stresses may therefore increase, decrease, or not affect a plant's susceptibility to herbivory depending upon the primary feeding cues used by the herbivore, the defensive mechanisms used by the plant, and the way these are altered by various environmental stresses.     

Epibionts of Asellus aquaticus(L.) (Crustacea, Isopoda): an SEM study

1. This study presents a qualitative and quantitative survey of epibionts infesting two populations of the freshwater isopod Asellus aquaticus (L.). Using scanning electron microscopy, the prevalence, mean intensity, abundance, spatial preferences and distribution of organisms on various external surfaces were ascertained.
2. A diverse community, consisting primarily of protozoa and rotifers, utilised A. aquaticus as a substrate organism. Every individual A. aquaticus supported some form of epizoic life. Peritrich species comprised 89.2% of all epibionts. Carchesium polypinum, Pseudocarchesium aselli, Pseudocarchesium asellicola, Pseudocarchesium simulans and Opercularia hebes dominated the epifauna.
3. Highest epibiont burdens occurred on the mouthparts, the first few ventral segments and the gills and largely comprised the above peritrich species. Most epibionts exhibited some degree of site preference on the host. A distinct gill epifauna existed. Apart from Acineta tuberosa and Vorticella rotunda , which had equal prevalences on dorsal and ventral surfaces in one culture, most species largely avoided the dorsal surface.
4. Epibionts exhibited varying degrees of adaptation to life on a living substrate. They ranged from facultative species such as A. tuberosa , which are capable of colonising abiotic substrata, to Gymnodinoides aselli whose life cycle relies on interaction with A. aquaticus . Highly specialised species tended to exhibit the most pronounced and consistent site restriction.
5. Asellus aquaticus offers a highly tractable system for further study of substrate species–epibiont relationships.     

Within-plant variation in seaweed palatability and chemical defenses: optimal defense theory versus the growth-differentiation balance hypothesis

Within-plant variation in the concentration of secondary metabolites, nutritive value, toughness, and susceptibility to herbivory was assessed for the brown alga Dictyota ciliolata. When young apices and older tissue from the same plant were offered in equal abundance to the herbivorous amphipod Ampithoe longimana and the sea urchin Arbacia punctulata, young apices were consumed about 2 times more than older tissue. Compared to young apices, the less preferred older tissue had a less palatable lipophilic extract, significantly higher concentrations of two secondary metabolites (another secondary metabolite did not differ significantly), 33% more soluble protein, and was 233% tougher. Higher levels of chemical defenses in older tissues, and not tissue toughness or nutritive value, appear to be responsible for the preference of Ampithoe longimana for young apices. The pattern of lower levels of chemical defenses in young than older tissues of D. ciliolata is the opposite of the pattern observed in coenocytic seaweeds and most vascular terrestrial and marine plants, all of which have translocation systems for moving materials among plant portions. Unlike these other plants, which preferentially allocate chemical defenses to young tissues, D. ciliolata cannot readily translocate secondary metabolites. The growth-differentiation balance hypothesis suggests that actively dividing and expanding cells are less able to produce secondary metabolites. This hypothesis may help explain why older tissues are better defended than young, rapidly growing apices.     

Vegetation shift from deciduous to evergreen dwarf shrubs in response to selective herbivory offsets carbon losses: evidence from 19 years of warming and simulated herbivory in the subarctic tundra

Selective herbivory of palatable plant species provides a competitive advantage for unpalatable plant species, which often have slow growth rates and produce slowly decomposable litter. We hypothesized that through a shift in the vegetation community from palatable, deciduous dwarf shrubs to unpalatable, evergreen dwarf shrubs, selective herbivory may counteract the increased shrub abundance that is otherwise found in tundra ecosystems, in turn interacting with the responses of ecosystem carbon (C) stocks and CO₂ balance to climatic warming. We tested this hypothesis in a 19‐year field experiment with factorial treatments of warming and simulated herbivory on the dominant deciduous dwarf shrub Vaccinium myrtillus. Warming was associated with a significantly increased vegetation abundance, with the strongest effect on deciduous dwarf shrubs, resulting in greater rates of both gross ecosystem production (GEP) and ecosystem respiration (ER) as well as increased C stocks. Simulated herbivory increased the abundance of evergreen dwarf shrubs, most importantly Empetrum nigrum ssp. hermaphroditum, which led to a recent shift in the dominant vegetation from deciduous to evergreen dwarf shrubs. Simulated herbivory caused no effect on GEP and ER or the total ecosystem C stocks, indicating that the vegetation shift counteracted the herbivore‐induced C loss from the system. A larger proportion of the total ecosystem C stock was found aboveground, rather than belowground, in plots treated with simulated herbivory. We conclude that by providing a competitive advantage to unpalatable plant species with slow growth rates and long life spans, selective herbivory may promote aboveground C stocks in a warming tundra ecosystem and, through this mechanism, counteract C losses that result from plant biomass consumption.     

Associational plant refuges: convergent patterns in marine and terrestrial communities result from differing mechanisms

Summary An associational plant refuge occurs when a plant that is susceptible to herbivory gains protection from herbivory when it is associated with another plant. In coastal North Carolina, the abundance of the palatable red alga Gracilaria tikvahiae is positively correlated with the abundance of the unpalatable brown alga Sargassum filipendula during times of increased herbivore activity. To see if grazing by the sea urchin Arbacia punctulata could generate this pattern, controlled experiments were conducted in out-door microcosms and in the laboratory. Gracilaria beneath a canopy of Sargassum was eaten significantly less than Gracilaria alone. When Arbacia were excluded, Gracilaria alone grew significantly more than Gracilaria beneath Sargassum, demonstrating that Sargassum is a competitor of Gracilaria. Experiments investigating Sargassum's deterrent role indicated that Sargassum decreased the foraging range of Arbacia and the rate at which it fed on Gracilaria. Additional experiments with plastic Sargassum mimics indicated that the decreased grazing on Gracilaria was not a result of Sargassum morphology, but was probably attributable to some chemical characteristic of Sargassum. The pattern of increased grazing in monocultures (only Gracilaria present) versus polycultures (both Gracilaria and Sargassum present) demonstrated in this study also has been demonstrated for plant-insect interactions in terrestrial communities. In these communities, insect density is higher in monocultures than in polycultures because insects find and immigrate to monocultures more rapidly, and once in a monoculture, they emigrate from them less often than from polycultures. In this study, urchins did not find and immigrate to monocultures more rapidly, nor did they tend to stay in them once they were found; in fact, they emigrated from monocultures of Gracilaria more rapidly than from Gracilaria and Sargassum polycultures. Increased grazing in Gracilaria monocultures resulted from increased rates of movement and feeding of individual herbivores, not from increased herbivore density as has been reported for terrestrial systems.     

A checklist of epibiotic ciliates (Peritrichia and Suctoria) on the cladoceran crustaceans

Despite the growing awareness of the ecological importance of epibiont-host associations, detailed inventories for planktonic hosts are rare. Here, we provide an updated checklist of the peritrich and suctorian epibiont ciliates (Ciliophora) on the cladocerans (Crustacea: Cladocera). Thirty-nine species of peritrich ciliates (of which 34 are assigned to species) and three species of suctorian ciliates are found to be epibionts on the Cladocera. Fifty-eight cladoceran taxa are known to be hosts of the ciliate epibionts, 33 of these hosts (57%) are planktonic. Seven taxa were determined to the level of genus. Complete species designations were geographically biased (38 of 51 species) towards European sites, suggesting poor taxonomic knowledge beyond Europe. Also, the recently discovered continental endemism of cladoceran hosts could indicate that associated ciliates are more diverse than previously appreciated.     

Effects of artificial epibionts on byssogenesis,attachment strength,and movement in two size classes of the blue mussel,Mytilus edulis

Blue mussels (Mytilus edulis) can alter the strength of byssal attachment and move between and within mussel aggregations on wave‐swept shores, but this movement ability may be limited by epibiont fouling. We quantified the effects of artificial epibiont fouling on the production of byssal threads, attachment strength, and movement in two size classes of blue mussels. In a factorial experiment, large epibiont‐covered mussels produced more functional byssal threads (i.e., those continuous from animal to substrate) after 24 h than large unfouled and small fouled mussels, but not more than small unfouled mussels. Small unfouled mussels formed and released more byssus bundles compared to any other treatment group, which indicates increased movement. Conversely, epibiont fouling resulted in decreased numbers of byssus bundles shed, and therefore reduced movement in small mussels. Epibiont‐covered mussels started producing byssal threads sooner than unfouled mussels, while small mussels began producing byssal threads earlier compared to large mussels. Mean attachment strength from both size classes increased by 9.5% when mussels were artificially fouled, and large mussels had a 34% stronger attachment compared to small mussels. On the other hand, a 2.3% decrease in attachment strength was found with increasing byssus bundles shed. Our results suggest that fouling by artificial epibionts influences byssal thread production and attachment strength in large mussels, whereas epibionts on small mussels impact their ability to move. Mussels are able to respond rapidly to fouling, which carries implications for the dynamics of mussel beds in their intertidal and subtidal habitats, especially in relation to movement of mussels within and among aggregations.     

Choosy mothers pick challenging plants: maternal preference and larval performance of a specialist herbivore are not linked

1. Maternal preference is a dynamic process and interactions between preference and performance are fundamental for understanding evolutionary ecology and host association in insect–plant interactions. In the present study, the hypothesis of preference–performance was tested by offering solanaceous specialist Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) larvae and adult females four plant congeners that ranged in suitability. 2. Larval feeding, development, oviposition, plant glycoalkaloids, and headspace volatiles in the four plant species were analysed to examine the extent of variation, which might explain performance–preference differences. 3. It was found that larval performance was mismatched with adult oviposition preferences. Adults laid more eggs on Solanum immite Dunal plants, which were poor hosts for larval development, feeding, and survival, compared to the other three Solanum species. 4. Chemical plant defenses, in general, did not correlate with performance or preference, but some plant volatiles may have played a role in resolving female choice. Glycoalkaloids such as solanine and chaconine were detected in similar amounts in preferred and non‐preferred hosts, but there was significantly more limonene in the headspace of S. immite than in S. tuberosum L. 5. The present findings suggest that we must consider the risk‐spreading hypothesis in cases where preference and performance are not positively correlated, particularly in specialist herbivores that can feed on a diversity of congener plants and may attempt to expand their exploits to other solanaceae species.     

Variation in multiple traits of vegetative and reproductive seagrass tissues influences plant–herbivore interactions

Plant–herbivore interactions have strong ecological and evolutionary consequences, but have been traditionally overlooked in marine higher plants. Despite recent advances in seagrass ecology that highlight the importance of herbivory, the mechanisms that regulate the feeding behaviour of seagrass consumers remain largely unknown. Herbivores have been shown to reduce the sexual reproductive success of seagrasses through direct consumption of inflorescences and seeds, but we know little about intraspecific variation in susceptibility to grazing of different seagrass tissues. We contrasted the relative palatability of reproductive and vegetative tissues of the temperate seagrass Posidonia oceanica in the field, and we assessed the feeding preferences among these tissues of the main consumers of the plant, the fish Sarpa salpa and the urchin Paracentrotus lividus. Moreover, we identified the plant traits that explained the observed feeding behaviour. We provide strong evidence for herbivore selectivity among seagrass tissues. In the field, 70–90% of inflorescences were damaged by herbivores compared to 3–60% of leaves of similar age. In feeding assays, the urchin P. lividus showed over a twofold preference for reproductive tissue at various stages of development. By contrast, we detected no feeding activity on either leaves or inflorescences from the fish S. salpa, which is known to migrate to deeper waters soon after flowering starts and during the period of fruit maturation. Despite being the preferred food of urchins, inflorescences were chemically defended, had higher levels of phenolics and lower nutrient and calorific content than leaves. We experimentally demonstrated that leaf structural defences are the primary factor in determining urchin feeding preferences. Removal of plant structure results in a drastic shift in urchin selectivity towards the most nutritious and less chemically defended leaf tissue, indicating that multiple mechanisms of defence to herbivory may coexist in seagrasses.     

Ecological implications of parasites in natural <Emphasis Type="Italic">Daphnia</Emphasis> populations

In natural host populations, parasitism is considered to be omnipresent and to play an important role in shaping host life history and population dynamics. Here, we study parasitism in natural populations of the zooplankton host Daphnia magna investigating their individual and population level effects during a 2-year field study. Our results revealed a rich and highly prevalent community of parasites, with eight endoparasite species (four microsporidia, one amoeba, two bacteria and one nematode) and six epibionts (belonging to five different taxa: Chlorophyta, Bacillariophyceae, Ciliata, Fungi and Rotifera). Several of the endoparasites were associated with a severe overall fecundity reduction of the hosts, while such effects were not seen for epibionts. In particular, infections by Pasteuria ramosa, White Fat Cell Disease and Flabelliforma magnivora were strongly associated with a reduction in overall D. magna fecundity. Across the sampling period, average population fecundity of D. magna was negatively associated with overall infection intensity and total endoparasite richness. Population density of D. magna was negatively correlated to overall endoparasite prevalence and positively correlated with epibiont richness. Finally, the reduction in host fecundity caused by different parasite species was negatively correlated to both parasite prevalence and the length of the time period during which the parasite persisted in the host population. Consistent with epidemiological models, these results indicate that parasite mediated host damages influence the population dynamics of both hosts and parasites.     

Wooded habitat edges as refugia from microtine herbivory in tallgrass prairies

Meadow voles, Microtus pennsylvanicus , affect the species composition, distribution, and succession of plants in grassland ecosystems, but the effects of voles on herbaceous plants when grasslands are bordered by wooded edges is not known. We investigated the impact of wooded edges on vole distribution and herbivory of relatively palatable and unpalatable native prairie plant species by studying five reconstructed tallgrass prairies with wooded edges in central Iowa. A 50×50 m trapping grid at each site was established to determine the proportion of voles captured at various distances from the edge. We found that meadow voles were less abundant at wooded edges and, in general, increased in number toward the prairie interior. Seedlings of purple prairie clover ( Dalea purpurea ) and Illinois bundleflower ( Desmanthus illinoensis ), a relatively palatable and unpalatable species, respectively, were transplanted onto simulated gopher mounds 2, 5, 10, 20 and 30 m from the edge. The number of plants grazed per species per mound was determined 1 week and 4 weeks after planting. The amount of herbivory on both species was significantly different by distance, with fewer plants eaten 2 m from the edge. Interestingly, the amount of herbivory on relatively unpalatable plants did not differ from more palatable plants. Herbivory on both plant species also varied by site, such that sites with lower vole density tended to have lower amounts of herbivory. These results indicate that wooded edges do have an effect on meadow vole distribution and native prairie seedling herbivory. Because voles avoid wooded edges, seedlings of any species may experience a small refuge from herbivory along wooded edges.     

When random sampling does not work: standard design falsely indicates maladaptive host preferences in a butterfly

In experiments that investigate species' interactions, individuals are often chosen at random to represent their populations. However, this practice can generate misleading results when individuals of different species do not interact at random. We illustrate this effect by examining oviposition preferences of Euphydryas aurinia butterflies from three populations using three different plant genera. We first offered each insect a randomly chosen member of its own host population and a foreign host ( Succisa pratensis ) not present in the insect's habitat. The butterflies uniformly preferred the foreign Succisa over their own hosts. Preferences were apparently maladaptive because insects wasted time searching for a nonexistent plant. We repeated the experiment using individual hosts that had naturally received eggs in the field. The overall preference for Succisa and the appearance of maladaptation both disappeared. In the original experiments, our random choice of experimental host individuals had combined with strong within-species discrimination by the butterflies and with overlap of acceptability between host species to obscure the true nature of host preference.     

Vestiges of an ancestral host plant: preference and performance in the butterfly Polygonia faunus and its sister species P. c‐album

1. In the study of the evolution of insect–host plant interactions, important information is provided by host ranking correspondences among female preference, offspring preference, and offspring performance. Here, we contrast such patterns in two polyphagous sister species in the butterfly family Nymphalidae, the Nearctic Polygonia faunus, and the Palearctic P. c‐album. 2. These two species have similar host ranges, but according to the literature P. faunus does not use the ancestral host plant clade – the ‘urticalean rosids’. Comparisons of the species can thus test the effects of a change in insect–plant associations over a long time scale. Cage experiments confirmed that P. faunus females avoid laying eggs on Urtica dioica (the preferred host of P. c‐album), instead preferring Salix, Betula, and Ribes. 3. However, newly hatched larvae of both species readily accept and grow well on U. dioica, supporting the general theory that evolutionary changes in host range are initiated through shifts in female host preferences, whereas larvae are more conservative and also can retain the capacity to perform well on ancestral hosts over long time spans. 4. Similar rankings of host plants among female preference, offspring preference, and offspring performance were observed in P. c‐album but not in P. faunus. This is probably a result of vestiges of larval adaptations to the lost ancestral host taxon in the latter species. 5. Female and larval preferences seem to be largely free to evolve independently, and consequently larval preferences warrant more attention.     

Seasonality and edge effect determine herbivory risk according to different plant association models

We report evidence of hierarchical resource selection by large herbivores and plant neighbouring effects in a Mediterranean ecosystem. Plant palatability was assessed according to herbivore foraging decisions. We hypothesize that under natural conditions large herbivores follow a hierarchical foraging pattern, starting at the landscape scale, and then selecting patches and individual plants. A between- and within-patch selection study was carried out in an area formed by scrubland and pasture patches, connected by habitat edges. With regard to between-patch selection, quality-dependent resource selection is reported: herbivores mainly consume pasture in spring and woody plants in winter. Within-patch selection was also observed in scrub habitats, influenced by season, relative patch palatability and edge effect. We defined a Proximity Index (PI) between palatable and unpalatable plants, which allowed verification of neighbouring effects. In spring, when the preferred food resource (i.e. herbs) is abundant, we observed that in habitat edges large herbivores basically select the relatively scarce palatable shrubs, whereas inside scrubland, unpalatable shrub consumption was related to increasing PI. In winter, a very different picture was observed; there was low consumption of palatable species surrounded by unpalatable species in habitat edges, where the latter were more abundant. These outcomes could be explained though different plant associations described in the literature. We conclude that optimal foraging theory provides a conceptual framework behind the observed interactions between plants and large herbivores in Mediterranean ecosystems.     

Epibiotic Bacteria on Several Ciliates from Marine Sediments

ABSTRACT Bacterial epibionts were observed on the surface of the marine sediment ciliate Geleia fossata. Rod-shaped bacteria, from 2-10 X10³ per ciliate, were universally positioned in ciliated grooves, in apparent spatial association with dikinetids. SEM and TEM examination of the ciliates confirmed that a tight affiliation exists between the epibiotic bacteria and ciliate cortex infrastructures. These observations, as well as the distinct bacterial distribution pattern over ciliate surface, suggest that there is a close epibiont/host physiological integration. Epibiotic bacteria were also observed on the surfaces of other sediment ciliates from the genera Loxophyllum, Tracheloraphis, Geleia, Paraspathidium , and Cyclidium. These findings indicate that the bacterial/protozoa associations are widespread in the marine benthic environment. The potential benefits for both epibionts and their hosts are discussed.