Impact of nano- and micro-sized polystyrene beads on larval survival and growth of the Pacific oyster Crassostrea gigas

This study successionally monitored how nano- and micro-sized polystyrene beads (MNPs) influence larval mortality, growth, and attachment behavior of the Pacific oyster Crassostrea gigas related to MNP diameter and concentration. D-shaped larvae were sequentially exposed to three-diameter MNPs (0.55, 3.00, 6.00 µm) at five concentrations (0, 0.1, 1.0, 10, 20 μg/mL), and their mortality, growth stages and attachment were observed daily until they die. In addition, MNP intake and accumulation in larvae at each growth stage were determined using fluorescent beads. Deterioration in larval growth and survival was observed under all the exposure conditions, while significant negative effects on the growth parameters were defined with smaller MNPs at lower concentrations. Fluorescent signals were detected in larval digestive tracts at all except D-shaped larval stage, and on the mantle and foot in pediveligers. Therefore, MNP intake adversely affects larval physiological conditions by the synchronal effects of MNP size and concentration. Our findings highlight the implications of MNP characteristics on Pacific oyster larvae, emphasizing the interplay between size, concentration, and physiological responses, crucial for mitigating nanoparticle pollution in marine ecosystems.

Food and light availability induce plastic responses in fire salamander larvae from contrasting environments

Phenotypic plasticity has been proposed as a mechanism facilitating the colonisation and adaptation to novel environments, such as caves. However, phenotypic plasticity in subterranean environments remains largely unexplored. Here, we test for plasticity in growth and development of fire salamander larvae (Salamandra salamandra) from subterranean and surface habitats, in response to contrasting food availability and light conditions. We hypothesized that: (i) low food availability and absence of light decrease larval growth and delay metamorphosis, (ii) light conditions mediate the effects of food availability on growth and time to metamorphosis, and (iii) larval response to contrasting light and food conditions is shaped by the habitat of origin. Our study showed that reduced food availability significantly delayed metamorphosis and slowed total length and body mass growth rates, while exposure to constant darkness slowed body mass growth rate. However, larvae slowed growth rates and increased time to metamorphosis without compromising size at metamorphosis. The effect of food availability on growth and time to metamorphosis did not change under different light conditions. Fire salamanders from subterranean and surface habitats responded differently only in relation to contrasting food availability conditions. Specifically, larvae from the surface habitat grew faster in high food conditions, while growth in larvae from the subterranean habitat was not influenced by food availability. Initial size also appeared to be an influential factor, since larger and heavier larvae grew slower, metamorphosed faster, and the size advantage was maintained in newly-metamorphosed juveniles. Overall, the results of our experiment suggest that plasticity and local adaptation favor the exploitation of aquatic subterranean habitats for breeding by fire salamanders, allowing successful development even under food shortage and day-length constraints, without compromising metamorphic size. Our findings have implications for conservation because they confirm that phenotypic plasticity plays a critical role in allowing fire salamanders to overcome altered environmental conditions.

Evidence of isotopic maternal transmission influence on bluefin tuna (Thunnus thynnus) larval growth

Pre-flexion stages of Atlantic bluefin tuna (Thunnus thynnus) larvae were collected in 2014 during the peak of spawning in the two main spawning areas: Gulf of Mexico (GOM) and Mediterranean Sea (MED). We examined daily growth, otolith biometry, and stable isotopes and found that the GOM grew at a faster rate, had larger otoliths, wider daily increments, and significantly lower values of δ15N when compared to the MED. In addition, an intra-population comparative analysis between slow- and fast-growing individuals (deficient vs. optimal growth groups, respectively) showed that optimal growth groups had significantly lower δ15N within each spawning area, implying a direct relationship between growth potential, development, and maternal transmission of isotopic signatures. A third pre-flexion larval group that was aquaculture-reared also exhibited the same pattern to the wild larval groups. In addition, for the first time, we estimated the maternal trophic niches using models developed with field-captured pre-flexion larvae. The estimated maternal trophic niches for the GOM were narrower than the MED, implying differences in the maternal trophodynamics from each nursery area. Overall, the inter-population (GOM vs. MED) and intra-population growth groups (deficient vs. optimal) grew faster and had narrower maternal niches. This study shows the advantages that larval SIA research can aid in the understanding of the trophodynamics of their breeders by examining the trophic relationship of a spawning stock jointly with the development of growth potential in offspring within the same breeding season.

Different ecological histories of sea urchins acclimated to reduced pH influence offspring response to multiple stressors

End-of-the-century predictions on carbon dioxide (CO₂) driven ocean acidification and the continuous leakage of pesticides from inland to coastal areas are of concern for potential negative effects on marine species' early life stages which are the most vulnerable to environmental changes. Variations in seawater chemistry related to human activities may interfere with the normal development from embryo to juvenile/adult stage. However, transgenerational studies suggest that the parental generation can influence the offspring phenotype, and thus their performances, based on the environment experienced. Here we compared the transgenerational responses to a multiple stressor scenario in sea urchins (Paracentrotus lividus) that experienced different environments since their settlement: i.e., animals from a highly variable environment, such as the Venice lagoon, versus animals from a coastal area with prevailing oligotrophic conditions in the Northern Adriatic Sea. After long-term maintenance (2 and 6 months) of adult sea urchins at natural and -0.4 units reduced pH, the F1 generations were obtained. Embryos were reared under four experimental conditions: natural and -0.4 pH both in the absence and in the presence of an emerging contaminants' mixture (glyphosate and aminomethylphosphonic acid at environmentally relevant concentrations, 100 μg/L). A significant detrimental effect of both the parental and the filial pH was highlighted, affecting embryo development and growth. Nonetheless, sea urchins from both sites were able to cope with ocean acidification. The 6-months F1 response was better than that of the 2-months F1. Conversely, the F1 response of the sea urchins maintained at natural conditions did not change sensibly after more prolonged parental exposure. An additive but mild negative effect of the mixture was observed, mostly in lagoon offspring. Results suggest that long-term exposure to reduced pH leads to transgenerational acclimation but does not affect susceptibility to the tested pollutants.

Differential effects of microplastic exposure on anuran tadpoles: A still underrated threat to amphibian conservation?

Microplastics (MPs) have been reported to threaten a wide variety of terrestrial, marine, and freshwater organisms. However, knowledge about the effects of MPs on anuran amphibians, one of the most threatened taxa worldwide, is still limited. To assess the effects of MPs on the growth and survival of the Italian agile frog (Rana latastei) and green toad (Bufotes balearicus), we exposed tadpoles to three different concentrations (1, 7, and 50 mg L^-1) of an environmental relevant mixture of microplastics (HPDE, PVC, PS and PES), recording data on their activity level, weight and mortality rates. While the effects of MPs on green toad tadpoles were negligible, Italian agile frog tadpoles were severely affected both in terms of growth and activity level, with high mortality rates even at the lowest MP density (1 mg L^-1). Our results suggest that MP contamination of freshwater habitats may contribute to the ongoing decline of anuran amphibians.

Effects of Ocean Acidification over successive generations decrease larval resilience to Ocean Acidification & Warming but juvenile European sea bass could benefit from higher temperatures in the NE Atlantic

European sea bass (Dicentrarchus labrax) is a large, economically important fish species with a long generation time whose long-term resilience to ocean acidification (OA) and warming (OW) is not clear. We incubated sea bass from Brittany (France) for two generations (>5 years in total) under ambient and predicted OA conditions (PCO2: 650 and 1700 µatm) crossed with ambient and predicted ocean OW conditions in F1 (temperature: 15-18°C and 20-23°C) to investigate the effects of climate change on larval and juvenile growth and metabolic rate. We found that in F1, OA as single stressor at ambient temperature did not affect larval or juvenile growth and OW increased developmental time and growth rates, but OAW decreased larval size at metamorphosis. Larval routine and juvenile standard metabolic rates were significantly lower in cold compared to warm conditioned fish and also lower in F0 compared to F1 fish. We did not find any effect of OA as a single stressor on metabolic rates. Juvenile PO2crit was not affected by OA or OAW in both generations. We discuss the potential underlying mechanisms resulting in the resilience of F0 and F1 larvae and juveniles to OA and in the beneficial effects of OW on F1 larval growth and metabolic rate, but on the other hand in the vulnerability of F1, but not F0 larvae to OAW. With regard to the ecological perspective, we conclude that recruitment of larvae and early juveniles to nursery areas might decrease under OAW conditions but individuals reaching juvenile phase might benefit from increased performance at higher temperatures.

Effect of Blue Light on the Growth of the Red Swamp Crayfish Procambraus clarkii Larvae -Seasonal and Sexual Differences

Organisms have the ability to adapt their behavior and physiology in response to seasonal changes in their habitat's environments. Although it is known that a specific light wavelength affects growth and reproduction in various animal taxa, its effect on sexual and seasonal differences in year-round breeding animals remains unclear. Here, we demonstrate that a blue light stimulus promotes or suppresses larval growth in the red swamp crayfish Procambarus clarkia depending on the season. During the spawning season (natural growing period), blue light irradiation accelerates female growth faster than in males, but suppresses growth in both females and males in the overwintering season. Moreover, these seasonal plastic effects of blue light show apparent sexual differences, with female juveniles exhibiting the greatest sensitivity. Our findings provide an opportunity to research how the red swamp crayfish can adapt to various habitable niches from the point of view of light color perception, and can be applied for the development of a more effective aquaculture system, not only for crayfish, but also for other commercially available decapod crustaceans using a specific light environment.

Probiotic supplementation mitigates the developmental toxicity of perfluorobutanesulfonate in zebrafish larvae

Perfluorobutanesulfonate (PFBS) is an emerging pollutant of international concern, which is found to impair the early embryonic development of fishes. In the context of ubiquitous and persistent pollution, it is necessary to explore mitigatory strategies against the developmental toxicity of PFBS. In this study, zebrafish larvae were acutely exposed to 0, 1, 3.3 and 10 mg/L of PFBS till 168 h post-fertilization (hpf), during which probiotic Lactobacillus rhamnosus bacteria were administered via the exposure media. After the singular or combined exposure, interaction between PFBS and probiotics on the growth of zebrafish larvae was measured. PFBS exposure significantly decreased the larval body weight, weight gain and specific growth rate, while probiotic supplementation efficiently inhibited the growth retardation caused by PFBS. Furthermore, PFBS and probiotic combinations remarkably activated the antioxidant capacity to timely scavenge the reactive oxidative species and protect the larvae from lipid peroxidation. Biochemical assay and fluorescent staining verified that PFBS exposure significantly promoted the production of bile acids, which were further enhanced by the probiotics. In coexposed zebrafish larvae, up-regulation of peroxisome proliferator-activated receptor (PPARb) would enhance the β-oxidation of fatty acids to meet the energy demand from larval growth, subsequently decreasing fatty acid concentrations. In addition, probiotic supplements masked the dysbiosis of PFBS and potently shaped the gut microbiota, which closely modulated the production of bile acids. Overall, the present findings underline the beneficial effects of probiotics to protect the developing larvae from the aquatic toxicities of PFBS, thus highlighting the potential application values of probiotic recipe in aquaculture and ecological reservation.

Larval Performance of Amphidromous and Landlocked Atyid Shrimp Species in the Genus Paratya Under Different Temperature and Salinity Conditions

Freshwater shrimps in the family Atyidae exhibit one of two life history traits: amphidromy, in which planktonic larvae develop in the sea; and landlocked, in which lecithotrophic larvae develop in freshwater. Temperature and salinity are the most important environmental factors that affect the survival, duration, and growth of decapod crustacean larvae. Larvae of landlocked shrimps are known to retain the ancestral habit of amphidromy, i.e., the ability to develop to the juvenile stage in saline water. Faster development exhibited by large larvae of landlocked shrimps is considered an adaptation that allows the larvae to stay in or near parental habitats. Therefore, information on larval performance under different temperature and salinity conditions is essential to obtain a better understanding of population connectivity through marine larval dispersal in amphidromous shrimps as well as larval adaptation to freshwater environments in landlocked shrimps. We examined the effects of temperature and salinity on the larval performance of two closely related atyid shrimps in the genus Paratya: the amphidromous P. compressa and the landlocked P. improvisa. Larvae were reared under the 25 combinations of five different temperatures (20, 23, 26, 29, and 32°C) and salinity levels (4.25, 8.5, 17, 25.5, and 34 ppt). In P. compressa, the rate of larvae that survived into the juvenile stage decreased linearly with increasing temperature and the larvae adapted to a wider range of salinity (8.5-34 ppt), though larval mortality increased at the high salinity (34 ppt) under the higher temperature conditions. In P. improvisa, larval survival rates were higher under a wider range of temperatures (20-29°C) in brackish water (4.25-17 ppt). Thus, P. compressa larvae may disperse broadly under the high salinity conditions of the open sea, but oceanic currents with high temperature and high salinity conditions may act as a barrier to restrict larval dispersion northwards from the southern islands. Paratya improvisa larvae adapted to a wider range of temperatures in natural freshwater environments and larval duration was shorter in P. improvisa than in P. compressa under the wide range of temperature and salinity conditions. Our results also highlight the retention strategy by which landlocked P. improvisa larvae stay in or near parental habitats.

Impact of 2,4-D and fipronil on the tropical midge Chironomus sancticaroli (Diptera: Chironomidae)

Increased use of pesticides in conventional agriculture implies potential risks to the environment. In aquatic ecosystems, benthic organisms may be exposed to pesticides via contaminated water and sediment, leading to several potential cascading effects on the food web. The aim of this study was to assess the functional implications of environmental realistic concentrations of the herbicide 2,4-D and the insecticide fipronil (alone and in combination) to the native tropical chironomid Chironomus sancticaroli. These two pesticides are widely applied to different crops and have frequently been detected (together) in surface water bodies in Brazil and elsewhere. Commercial products containing fipronil (Regent® 800WG) and 2,4-D (DMA® 806BR) were evaluated in 8-day toxicity tests for their effects on larval survival, growth (body length and biomass), head capsule width, development, and mentum deformities. Fipronil decreased the larval survival at the highest test concentration and the effective concentrations (EC) after eight days of exposure were: EC₁₀ = 0.48 µg L^-1 (0.395-0.565), EC₂₀ = 1.06 µg L^-1 (0.607-1.513), and EC₅₀ = 3.70 µg L^-1 (1.664-5.736). All sublethal test concentrations of fipronil decreased the larval growth, causing reductions in biomass up to 72%. The two highest test concentrations of fipronil decreased the head capsule width and after exposure to 3.7 µg fipronil L^-1, only half of the larvae reached the fourth instar. The incidence of deformities was increased by fipronil in a concentration dependent manner with an increase ranging from 23% to 75%. The highest test concentration of 2.4-D (426 µg L^-1) decreased the head capsule width, but larval development was unaffected at all concentrations evaluated. In the mixture tests, antagonism was observed at lower fipronil concentrations and synergism at higher fipronil concentrations for growth. The incidence of deformities rose with increasing fipronil concentrations. The results showed that environmental realistic concentrations of fipronil may have serious ecological implications for C. sancticaroli populations and that a mixture with the herbicide 2,4-D can have synergistic effects, potentiating the risks to the aquatic ecosystem.

Wrapping culture plates with Parafilm M® increases Caenorhabditis elegans growth

OBJECTIVE

Parafilm M® is a moisture-resistant thermoplastic commonly used to seal Nematode Growth Media (NGM) agar plates on which the nematode Caenorhabditis elegans is cultured. This practice reduces media dehydration and microbial contamination. However, the effects on C. elegans individuals of placing this barrier between the external environment and the interior of the NGM plate are currently unknown. Our research aims to determine if this common practice engenders developmental changes, such as growth, that could subsequently and unintentionally alter experimental data. We compared the larval growth over 48 h of animals cultured on Parafilm-wrapped and unwrapped control NGM plates.

RESULTS

Wrapping culture plates with Parafilm significantly accelerated and increased larval growth, with a 0.87 μm/h increase in growth rate (~ 6%) and a 37.90 μm increase in the change in growth (Δgrowth; ~ 5%) over 48 h. Therefore, C. elegans investigators should be aware that wrapping their experimental cultures with Parafilm may result in statistically detectable changes in worm growth and possibly other developmental processes.

Low adaptive potential for tolerance to ethynylestradiol, but also low toxicity, in a grayling population (Thymallus thymallus)

BACKGROUND

The presence of a novel pollutant can induce rapid evolution if there is additive genetic variance for the tolerance to the stressor. Continuous selection over some generations can then reduce the toxicity of the pollutant but also deplete the additive genetic variance for the tolerance and thereby slow down adaptation. One common pollutant that has been ecologically relevant for some time is 17alpha-ethynylestradiol (EE2), a synthetic compound of oral contraceptives since their market launch in the 1960s. EE2 is typically found in higher concentrations in rivers than in lakes. Recent experimental work revealed significant genetic variance for the tolerance to EE2 in two lake-spawning salmonid species but no such variance in river-spawning brown trout. We used another river-spawning salmonid, the European grayling Thymallus thymallus, to study the toxicity of an ecologically relevant concentration of EE2. We also used a full-factorial in vitro breeding design and singly rearing of 1555 embryos and larvae of 40 sib groups to test whether there is additive genetic variance for the tolerance to this pollutant.

RESULTS

We found that exposure to EE2 reduced larval growth after hatching, but contrary to what has been found in the other salmonids, there were no significant effects of EE2 on embryo growth and survival. We found additive genetic variance for embryo viability, i.e. heritability for fitness. However, there was no significant additive variance for the tolerance to EE2.

CONCLUSIONS

Our findings support the hypothesis that continuous selection has reduced the toxicity of EE2 and depleted genetic variance for tolerance to this synthetic stressor.

Antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae under methylmercury exposure

Methylmercury (MeHg) is a highly toxic contaminant in coastal environments and poses threats to marine fish in early life stages (ELSs). However, MeHg toxicity to fish embryos and larvae is not well investigated. This study investigated the antioxidant defenses and immune responses of flounder Paralichthys olivaceus larvae exposed to waterborne MeHg (0, 0.1, 1.0 and 10.0 μg L^-1) for 35 days, from embryogenesis to settlement. The results revealed that metal accumulation in the larvae was positively correlated with MeHg concentration, reduced larval growth and survival. The activities of catalase and glutathione reductase were significantly increased at 10.0 μg L^-1, while glutathione peroxidase activity and lipid peroxidation level were significantly increased at concentrations over 1.0 μg L^-1. The corresponding antioxidant-related genes were upregulated under MeHg exposure (cat and gpx at 10.0 μg L^-1; gr over 1.0 μg L^-1). Lysozyme content was significantly increased, but immunoglobulin M content was significantly decreased at 10.0 μg L^-1. The immune-related genes were significantly upregulated (hsp70 at 0.1 and 10.0 μg L^-1; lzm and il-1β over 1.0 μg L^-1; tnf-α and il-6 at 10.0 μg L^-1) or downregulated (igm, over 0.1 μg L^-1). Overall, MeHg exposure induced oxidative stress and caused immunotoxicity at concentrations over 1.0 μg L^-1 and 10.0 μg L^-1, respectively. The transcription of selected genes correlated with the corresponding biochemical markers in response to MeHg toxicity. These findings improve our knowledge to better understand the mechanisms by which marine fish at ELSs cope with oxidative stress and immunotoxicity induced by MeHg.

Effects of ocean warming and acidification on fertilization success and early larval development in the green sea urchin Lytechinus variegatus

Ocean acidification and warming are predicted to affect the early life of many marine organisms, but their effects can be synergistic or antagonistic. This study assessed the combined effects of near-future (2100) ocean acidification (pH 7.8) and warming (+3 °C) on the fertilization, larval development and growth of the green sea urchin, Lytechinus variegatus, common in tropical reefs of Florida and the Caribbean. Acidification had no effect on fertilization, but delayed larval development, stunted growth, and increased asymmetry. Warming decreased fertilization success when the sperm:egg ratio was higher (1847:1), accelerated larval development, but had no effect on growth. When exposed to both acidification and warming, fertilization rates decreased, larval development accelerated (due to increased respiration/metabolism), but larvae were smaller and more asymmetric, meaning acidification and warming had additive effects. Thus, climate change is expected to decrease the abundance of this important herbivore, exacerbating macroalgal growth and dominance on coral reefs.

Patterns of selective predation change with ontogeny but not density in a marine fish

Phenotypic variation is prevalent in the early life-history stages of many organisms and provides the basis for selective mortality on size and growth-related traits of older life stages. Densities of organisms can vary widely at important life-history transitions, raising additional questions about the interplay between selection and density-dependent processes. We evaluate density dependence in patterns of selective mortality for a temperate reef fish. Specifically, we exposed pre-settlement and post-settlement stages of the common triplefin (Forsterygion lapillum) to a natural predator and evaluated patterns of selective mortality on early life-history traits as a function of ontogenetic stage and density. We used otoliths to reconstruct the traits of fish that survived versus fish that were consumed (i.e., we recovered otoliths from the guts of predators), and we estimated selection by analysing the relationship between absolute fitness and standardised traits. Absolute fitness was negatively correlated with size and larval growth rate for pre-settlement fish (i.e., larger and faster growing individuals were more likely to be consumed by predators), and this was consistent across the range of densities evaluated. Post-settlement fish experienced no selective mortality. Additionally, absolute fitness was equal across density treatments, suggesting mortality was density-independent. Collectively, these results suggest that patterns of selection change with ontogeny, but may be stable across densities when mortality is density-independent. Shifts in selective mortality for species with distinct life-stages can mask and complicate relationships between traits and fitness, and the importance of such traits may be underappreciated for earlier life stages.

Allometric growth and development of organs in ballan wrasse (Labrus bergylta Ascanius, 1767) larvae in relation to different live prey diets and growth rates

Small fish larvae grow allometrically, but little is known about how this growth pattern may be affected by different growth rates and early diet quality. The present study investigates how different growth rates, caused by start-feeding with copepods or rotifers the first 30 days post-hatch (dph), affect allometric growth and development of nine major organs in ballan wrasse (Labrus bergylta) larvae up to experimental end at 60 dph. Feeding with cultivated copepod nauplii led to both increased larval somatic growth and faster development and growth of organ systems than feeding with rotifers. Of the organs studied, the digestive and respiratory organs increased the most in size between 4 and 8 dph, having a daily specific growth rate (SGR) between 30 and 40% in larvae fed copepods compared with 20% or less for rotifer-fed larvae. Muscle growth was prioritised from flexion stage and onwards, with a daily SGR close to 30% between 21 and 33 dph regardless of treatment. All larvae demonstrated a positive linear correlation between larval standard length (SL) and increase in total tissue volume, and no difference in allometric growth pattern was found between the larval treatments. A change from positive allometric to isometric growth was observed at a SL close to 6.0 mm, a sign associated with the start of metamorphosis. This was also where the larvae reached postflexion stage, and was accompanied by a change in growth pattern for most of the major organ systems. The first sign of a developing hepatopancreas was, however, first observed in the largest larva (17.4 mm SL, 55 dph), indicating that the metamorphosis in ballan wrasse is a gradual process lasting from 6.0 to at least 15-17 mm SL.

Summary: Allometric growth patterns of ballan wrasse were not affected by different diets, and larval functional development was found to be dependent on size and not age or growth rate.

Impact of CO2-driven acidification on the development of the sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea)

We evaluated the impact of ocean acidification on the early development of sea cucumber Apostichopus japonicus. The effect of pH-levels (pH 8.04, 7.85, 7.70 and 7.42) were tested on post-fertilization success, developmental (stage duration) and growth rates. Post-fertilization success decreased linearly with pH leading to a 6% decrease at pH 7.42 as compared to pH 8.1. The impact of pH on developmental time was stage-dependent: (1) stage duration increased linearly with decreasing pH in early-auricularia stage; (2) decreased linearly with decreasing pH in the mid-auricularia stage; but (3) pH decline had no effect on the late-auricularia stage. At the end of the experiment, the size of doliolaria larvae linearly increased with decreasing pH. In conclusion, a 0.62 unit decrease in pH had relatively small effects on A. japonicus early life-history compared to other echinoderms, leading to a maximum of 6% decrease in post-fertilization success and subtle effects on growth and development.

How the pilidium larva grows

BACKGROUND

For animal cells, ciliation and mitosis appear to be mutually exclusive. While uniciliated cells can resorb their cilium to undergo mitosis, multiciliated cells apparently can never divide again. Nevertheless, many multiciliated epithelia in animals must grow or undergo renewal. The larval epidermis in a number of marine invertebrate larvae, such as those of annelids, mollusks and nemerteans, consists wholly or in part of multiciliated epithelial cells, generally organized into a swimming and feeding apparatus. Many of these larvae must grow substantially to reach metamorphosis. Do individual epithelial cells simply expand to accommodate an increase in body size, or are there dividing cells amongst them? If some cells divide, where are they located?

RESULTS

We show that the nemertean pilidium larva, which is almost entirely composed of multiciliated cells, retains pockets of proliferative cells in certain regions of the body. Most of these are found near the larval ciliated band in the recesses between the larval lobes and lappets, which we refer to as axils. Cells in the axils contribute both to the growing larval body and to the imaginal discs that form the juvenile worm inside the pilidium.

CONCLUSIONS

Our findings not only explain how the almost-entirely multiciliated pilidium can grow, but also demonstrate direct coupling of larval and juvenile growth in a maximally-indirect life history.

Superparasitism in Cotesia glomerata does not benefit the host plant by reduction of herbivory caused by Pieris brassicae

Superparasitism occurs in Cotesia glomerata L. (Hymenoptera: Braconidae), a gregarious endoparasitoid of Pieris spp. (Lepidoptera: Pieridae). The responses of Pieris brassicae L. larvae to superparasitism were examined in order to elucidate the ecological significance of this behaviour. Models of tritrophic interactions often imply that attraction of herbivore natural enemies by the plant constitutes a defence. Parasitoid attack on herbivores is assumed to result in a reduction in herbivory and or an increase in plant fitness. Coupled with the active involvement of the plant in producing signals, this can be seen as an indirect mediation of wound induced defence. The results show that superparasitism of P. brassicae by the parasitoid C. glomerata reduced survivorship but increased food consumption and weight growth in P. brassicae larvae. The duration of host larval development was found prolonged as the number of oviposition increased and superparasitized larvae (three to five time parasitized) grew slower than unparasitized larvae or larvae parasitized one or two times.