Plastid-bearing sea slugs fix CO2 in the light but do not require photosynthesis to survive

Several sacoglossan sea slugs (Plakobranchoidea) feed upon plastids of large unicellular algae. Four species—called long-term retention (LtR) species—are known to sequester ingested plastids within specialized cells of the digestive gland. There, the stolen plastids (kleptoplasts) remain photosynthetically active for several months, during which time LtR species can survive without additional food uptake. Kleptoplast longevity has long been puzzling, because the slugs do not sequester algal nuclei that could support photosystem maintenance. It is widely assumed that the slugs survive starvation by means of kleptoplast photosynthesis, yet direct evidence to support that view is lacking. We show that two LtR plakobranchids, Elysia timida and Plakobranchus ocellatus, incorporate ¹⁴CO₂ into acid-stable products 60- and 64-fold more rapidly in the light than in the dark, respectively. Despite this light-dependent CO₂ fixation ability, light is, surprisingly, not essential for the slugs to survive starvation. LtR animals survived several months of starvation (i) in complete darkness and (ii) in the light in the presence of the photosynthesis inhibitor monolinuron, all while not losing weight faster than the control animals. Contrary to current views, sacoglossan kleptoplasts seem to be slowly digested food reserves, not a source of solar power.     

The influence of temperature on life history traits in the Iberian slug,Arion lusitanicus

The slug Arion lusitanicus is an invasive species which has recently become established in many European countries and is considered a serious pest, both in agriculture and private gardens. The effect of temperature on growth rate, survival, egg developmental time and hatchability of the slug are reported. The growth rate was positively correlated with temperatures up to 20°C and A. lusitanicus continued (on average) to grow until they die. A model describing how growth depends on temperature was developed, and a field survey found that the predicted growth matched the observed with reasonable accuracy. This study confirms the assumption that A. lusitanicus die after egg laying. Free‐ranging A. lusitanicus has an annual life cycle, but our data show that slugs also possess the ability to live for up to 3 years. The egg developmental time was, like growth, positively correlated with temperature and was shortest at 20°C, but the optimum temperature for egg development, when regarded as the temperature with highest hatchability was found to be 10°C. In conclusion, this study has shown that growth and the life‐history traits, egg developmental time and hatchability, of A. lusitanicus are highly influenced by temperature. However, data also show that temperatures within the range 2–20°C did not influence survival rates to any large degree, and that A. lusitanicus can quickly adjust to changes in temperature. The study provides a number of basic parameters which contribute to the understanding of the population dynamics of A. lusitanicus.     

DNA barcodes and phylogenetic affinities of the terrestrial slugs Arion gilvus and A. ponsi (Gastropoda,?Pulmonata,Arionidae)

The Iberian Peninsula is a region with a high endemicity of species of the terrestrial slug subgenus Mesarion. Many of these species have been described mainly on subtle differences in their proximal genitalia. It therefore remains to be investigated 1) whether these locally diverged taxa also represent different species under a phylogenetic species concept as has been shown for other Mesarion species outside the Iberian Peninsula, and 2) how these taxa are phylogenetically related. Here, we analysed DNA sequence data of two mitochondrial (COI and 16S) genes, and of the nuclear ITS1 region, to explore the phylogenetic affinities of two of these endemic taxa, viz. Arion gilvus Torres Mínguez, 1925 and A. ponsi Quintana Cardona, 2007. We also evaluated the use of these DNA sequence data as DNA barcodes for both species. Our results showed that ITS did not allow to differentiate among most of the Mesarion molecular operational taxonomic units (MOTUs) / morphospecies in Mesarion. Yet, the overall mean p-distance among the Mesarion MOTUs / morphospecies for both mtDNA fragments (16.7% for COI, 13% for 16S) was comparable to that between A. ponsi and its closest relative A. molinae (COI: 14.2%; 16S: 16.2%) and to that between A. gilvus and its closest relative A. urbiae (COI: 14.4%; 16S: 13.4%). Hence, with respect to mtDNA divergence, both A. ponsi and A. gilvus, behave as other Mesarion species or putative species-level MOTUs and thus are confirmed as distinct ‘species’.     

Structural Changes in the Relationships of Body Dimensions of Four Species of Pulmonate Slugs (Mollusca : Gastropoda : Pulmonata)

Four species of pulmonate slugs viz. Milax rusticus, Milax sowerbyi, Milax gagates and Limax tenellus are colonised along the north eastern region of Libya. These slugs are homogeneous in character since they belong to the same class and order. However, their body dimensions were significantly different. Significant positive relationships existed on most of the body dimensions of each species and these relationships were found to be heterogeneous among the four species studied.     

An improved bioassay for screening bacteria for biocontrol activity against slugs that avoids volatile-induced slug mortality

A strain of Stenotrophomonas maltophila previously thought to have molluscicidal activity was tested using a standard bioassay. Initial results on host range and dose response were promising. However, slug mortality was induced by volatile compounds released from the decaying food rather than by infection. We propose a modification of the bioassay that avoids this problem.     

Post-dispersal seed predation of three grassland species in a plant diversity experiment

Aims Post-dispersal seed predation is an important ecosystem process because it can influence the seed's fate after the initial dispersal from the mother plant and subsequently transform communities. Even at small scales, post-dispersal seed predation can vary greatly depending on seed identity, granivorous taxa or microhabitat structure. However, little is known about the role of plant species richness and functional group richness in post-dispersal seed predation. The overall aim of this study was to test whether increasing plant species richness or plant functional group richness affects the rate and variability of post-dispersal seed predation. We additionally investigated the influence of vegetation structure and seed species identity on the rate and variability of post-dispersal seed predation and whether the influence of different granivorous taxa changed with increasing plant species richness.Methods We conducted seed removal experiments along a long-term experimental plant diversity gradient, comprising plots with monocultures to 60 species mixtures of common grassland species in Jena, Germany, in August 2011. We studied seeds of Onobrychis viciifolia, Pastinaca sativa and Trifolium pratense in exclusion experiments (seed cafeterias), an experimental setup that allowed access either for arthropods or slugs or for all granivorous taxa. Traditionally, seeds removed from seed cafeterias were classified as consumed but we used traceable fluorescent-coloured seeds to obtain more accurate predation rates by subtracting recovered seeds from overall removed seeds. The effect of multiple vegetation variables on mean and variability of seed predation rates was analysed using generalized mixed-effect models and linear regressions, respectively.Important findings Rates of recovered seeds were low but contributed to significant differences between seed predation rates and removal rates of seeds in some treatments. Seed predation rates were not directly correlated with increasing plant species richness or plant functional group richness but were influenced byseed species identity and granivorous taxa. Vegetation variables such as vegetation height and cover were significantly associated with seed predation rates. Depending on the seed species and/or the granivorous taxa, different vegetation variables correlated with seed predation rates. Our results indicate that effects of plant functional group richness and multiple vegetation variables on the magnitude of post-dispersal seed predation varied with seed identity and seed predator taxa. A direct effect of plant species and plant functional group richness could be shown on the variability of post-dispersal seed predation for some seed species and their respective predators. Thus, the changes in magnitude of post-dispersal seed predation with increasing plant species richness could potentially impact the fitness of some plant species and thereby influence plant community structure.     

Ecological Restoration and Large-Scale Ecological Disturbance: The Effects of Drought on the Response by Fish to a Habitat Restoration Experiment

Human‐induced erosion regularly delivers massive quantities of fine sediments into streams and rivers forming large static bodies of sediment known as sand slugs, which smother in‐stream habitat, alter community structure, and decrease biodiversity. Sand slugs are widespread in parts of southeastern Australia as well as in many other parts of the world, and there is now considerable interest in restoring such affected streams. The reintroduction of large timber is widely suggested as a strategy for restoring habitat complexity, but this has rarely been tested in sand slug–affected streams. We examined the response of fish populations to wood addition to two streams in southeastern Australia that have been impacted by sand slugs. Manipulated sites (three per treatment) had either one or four timber structures added, and these sites were compared with (three) unmanipulated (control) sites before and after the manipulation occurred. Despite a supraseasonal drought during the study, we observed short‐term increases in the abundance of Mountain galaxias (Galaxias olidus) at the four‐structure sites, while both the four‐structure and the one‐structure treatments appeared to buffer against drought‐induced declines in two other species, River blackfish (Gadopsis marmoratus) and Southern pygmy perch (Nannoperca australis), relative to controls. However, drought eventually caused the complete loss of surface water from these streams and the loss of fish from both manipulated and unmanipulated sites. Thus, although the study supports the use of timber structures as a means of increasing local fish abundances, these beneficial effects were, in these streams, contingent upon permanency of flow. Because sedimentation has depleted the number of permanent refuge pools in these creeks, recovery rates of the fauna (i.e., resilience) are likely to be slow. We therefore conclude that in streams subjected to frequent disturbance, restoring refugia may be as, if not more, important as restoring what we term residential habitat.     

Invasive slugs as under-appreciated obstacles to rare plant restoration: evidence from the Hawaiian Islands

Introduced slugs have invaded many parts of the world where they were recognized as important pests of gardens and agriculture, but we know little about the effects of introduced slugs on rare plants in natural areas. The Hawaiian Islands have no native slugs, but over a dozen introduced slug species are now established. We reviewed Rare Plant Recovery Plans produced by the U.S. Fish and Wildlife Service for Hawaii and found that introduced slugs were specifically mentioned as threats or potential threats to 59 rare plant species (22% of all endangered and threatened plants), based mainly on anecdotal observations by field biologists. We then initiated an experimental field study to assess the impact of slug herbivory on the growth and survival of two endangered plant species (Cyanea superba, and Schidea obovata), one non-endangered native species (Nestegis sandwicensis) and two co-occurring invasive plant species (Psidium cattleianum and Clidemia hirta). In mesic forest on the Island of Oahu, we tracked the fate of outplanted seedlings in replicated 1 m² plots, with and without slug control. Slugs decreased seedling survival of the endangered species by 51%, on average. Slugs did not significantly affect survival of the non-endangered or invasive plant species. Introduced slugs seem to be under-appreciated as a direct cause of plant endangerment. Invasive slugs may also facilitate the success of some invasive plant species by reducing competition with more palatable, native plant competitors. Slug control measures are relatively inexpensive and could facilitate rare plant establishment and population recovery.     

Gastropod biodiversity at the 'Evolution Canyon' microsite, lower Nahal Oren, Mount Carmel, Israel

Twenty-six species of gastropods (terrestrial, shell-bearing snails and slugs) were recorded at the 'Evolution Canyon' microsite, lower Nahal Oren, Mount Carmel, Israel. Twenty-five species were recorded at the temperate, mesic north-facing slope (NFS) and 20 species at the xeric south-facing slope (SFS). Out of these species, six were NFS specific ( Pilorcula raymondi hebraica , Euchondrus septemdentatus , Monacha crispulata , Pyramidula rupestris hierosolymitana , Truncatellina haasi , and Vitrea contracta ) and one was SFS specific ( Prolimax eustrictus ). The interslope difference was probably partly due to missing forest species at the SFS in comparison with the NFS. Twenty-two species were Levantine endemics (84.6%) and four species were more widely distributed in the Palaearctic region (15.4%). The Levantine species are inhabitants of the mesic and mainly mountainous regions, but four species ( Granopupa granum , Calaxis hierosolymarum , Cecilioides acicula , and Helix engaddensis ) also penetrate the deserts. Seven species ( Buliminus labrosus , H. engaddensis , Levantina spiriplana caesareana , Metafruticicola fourousi , Monacha syriaca , Sphincterochila cariosa , and Xeropicta vestalis joppensis ) were significantly more abundant on the SFS than on the NFS. The local physical microclimatic sharp divergence leads to gastropod adaptive interslope biotic divergence caused by natural selection.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 147–155.