Larval Size Research Articles

Distribution and Transport of Olympia Oyster Ostrea lurida Larvae in Northern Puget Sound, Washington

As efforts for restoring Olympia oyster Ostrea lurida populations have expanded, there is an increased need to understand local factors that could influence the long-term success of these projects. To address concerns over potential limitations to recruitment at a restoration site in northern Puget Sound, WA, a study was developed to characterize physical processes governing larval transport in conjunction with larval abundance and environmental factors. Larval presence was not associated with tide cycle, season, or a combination of tide cycle and season. In terms of location, larvae were more likely to be present at offshore and intertidal sites versus the estuarine lagoon, where the adult population resides. Larval density was higher during late summer ebbs versus early summer floods. Across sampling dates and locations, larval sizes ranged from 184 to 263 µm, indicating that larvae were released into the water column throughout the reproductive season and retained in the embayment for at least ∼16 days. Throughout different tidal cycles in Skagit Bay, acoustic Doppler current profilers were used to measure current direction and velocities, concurrent with plankton sampling. Surface currents in the study area alternated between a clockwise and a counterclockwise gyre during initial ebb and flood tides, respectively. Larvae exported from the source population during initial to midebbs are swept into a northward gyre and potentially retained at intertidal sites alongshore. These results will provide resource managers attempting to restore native bivalves with the ability to expand populations by identifying optimal areas for habitat enhancement through natural recruitment.

Early life starvation has stronger intra-generational than transgenerational effects on key life-history traits and consumption measures in a sawfly.

Resource availability during development shapes not only adult phenotype but also the phenotype of subsequent offspring. When resources are absent and periods of starvation occur in early life, such developmental stress often influences key life-history traits in a way that benefits individuals and their offspring when facing further bouts of starvation. Here we investigated the impacts of different starvation regimes during larval development on life-history traits and measures of consumption in the turnip sawfly, Athalia rosae (Hymenoptera: Tenthredinidae). We then assessed whether offspring of starved and non-starved parents differed in their own life-history if reared in conditions that either matched that of their parents or were a mismatch. Early life starvation effects were more pronounced within than across generations in A. rosae, with negative impacts on adult body mass and increases in developmental time, but no effects on adult longevity in either generation. We found some evidence of higher growth rates in larvae having experienced starvation, although this did not ameliorate the overall negative effect of larval starvation on adult size. However, further work is necessary to disentangle the effects of larval size and instar from those of starvation treatment. Finally, we found weak evidence for transgenerational effects on larval growth, with intra-generational larval starvation experience being more decisive for life-history traits. Our study demonstrates that intra-generational effects of starvation are stronger than transgenerational effects on life-history traits and consumption measures in A. rosae.

Ionizing radiation reduces larval brain size by inducing premature differentiation of Drosophila neural stem cells

DNA damaging agents, such as ionizing radiation (IR), induce cell cycle arrest, senescence, differentiation, or cell death of stem cells, which may affect tissue homeostasis. The specific response of stem cells upon irradiation seems to vary depending on the cell type and their developmental stages. Drosophila larval brain contains neural stem cells called neuroblasts (NBs) and maintaining an appropriate number of NBs is critical to maintain brain size. Irradiation of larvae at early larval stage results in microcephaly, whereas the DNA damage response of NBs that could explain this small brain size is not clearly understood. We observed that the irradiation of larvae in the second instar retarded brain growth, accompanied by fewer NBs. The IR-induced microcephaly does not seem to result from apoptosis since the irradiated larval brain was not stained with activated Caspase nor was the microcephaly affected by the ectopic expression of the apoptosis inhibitor. When analyzed for the percentage of mitotic cells, irradiated NBs recovered their proliferative potential within 6 h post-irradiation after transient cell cycle arrest. However, IR eventually reduced the proliferation of NBs at later time points and induced the premature differentiation of NBs. In summary, IR-induced microcephaly occurs by NB loss due to premature differentiation, rather than apoptotic cell death.

The enemy of my enemy: multiple interacting selection pressures lead to unexpected anti-predator responses.

Despite being a major selective force, predation can induce puzzling variability in anti-predator responses-from lack of predator aversion to lifelong predator-induced fear. This variability is hypothesised to result from variation in the trade-offs associated with avoiding predators. But critical information on fitness outcomes of these trade-offs associated with anti-predator behaviours is lacking. We tested this trade-off hypothesis in Aedes aegypti, by examining oviposition site selection decisions in response towards larval predation risk and comprehensively measuring the fitness implications of trade-offs of avoiding larval predators, using three fitness measures: larval survival, development time and size. In a field study, we find that adult females show a surprisingly variable response to predators, ranging from attraction to avoidance. This variation is explained by fitness outcomes of oviposition along a predation-risk gradient that we measured in the laboratory. We show that ovipositing females could gain fitness benefits from ovipositing in pools with a low density of predators, rather than in predator-free pools, as predators provide a release from negative density effects of conspecific larvae that might co-occur in a pool. Interacting selection pressures may thus explain diverse prey responses. We suggest other systems in which similarly unexpected prey behaviour is likely to occur.

Gut microbiota metabolic potential correlates with body size between mulberry-feeding lepidopteran pest species.

Many insect pests rely on microbial symbionts to obtain nutrients or for defence, thereby allowing them to exploit novel food sources and degrade environmental xenobiotics, including pesticides. Although Lepidoptera is one of the most diverse insect taxa and includes important agricultural pests, lepidopteran microbiotas, particularly functional traits, have not been studied widely. Here, we provide a comprehensive characterization of the gut microbiota across multiple mulberry-feeding lepidopteran species, resolving both community structure and metabolic potential. Our results indicate abundant bacteria inside the gut of larval Lepidoptera. However, even though they were fed the same diet, the structures of the bacterial communities differed in four major mulberry pest species, suggesting host-specific effects on microbial associations. Community-level metabolic reconstructions further showed that although taxonomic composition varied greatly, carbohydrate and amino acid metabolism and membrane transporter were key functional capabilities of the gut bacteria in all samples, which may play basic roles in the larval gut. In addition, principal coordinate analysis (PCoA) of gut bacterial-predicted gene ontologies revealed specialized features of the microbiota associated with these mulberry pests, which were divided into two distinct clusters (macrolepidopterans and microlepidopterans). This pattern became even more prominent when further Lepidoptera species were involved. A suite of gut microbiota metabolic functions significantly correlated with larval size; the metabolism of terpenoids and polyketides, xenobiotics biodegradation and metabolism were specifically enriched in large species, while small larvae had enhanced nucleotide metabolism. Our report paves the way for uncovering the correlation between host phenotype and microbial symbiosis in this notorious insect pest group. © 2019 Society of Chemical Industry.

The anatomy of the miniature predator Trigonulina ornata d’Orbigny, 1853 (Bivalvia: Anomalodesmata: Verticordiidae) from continental shelf waters off Brazil

The anatomy of one of the smallest non-septate carnivorous bivalves is described herein and is the first anatomical study of a member of the genus Trigonulina. This paper shows that similar to other verticordiids, Trigonulina ornata d’Orbigny, 1853 possesses a suite of anatomical features that include a prey-capturing inhalant siphon, a septum, an absence of labial palps and capacious mouth, which characterize it as a carnivorous marine bivalve. A discussion about the origin of the septibranch septum is provided showing that the condition seen in T. ornata could be representative of the transition within the Anomalodesmata between suspension-feeding type E ctenidia and the non-filamentar septibranch condition. Finally, fertilized and encapsulated eggs within the visceral mass, the presence of hypobranchial glands plus larval prodissoconch size collectively suggest self-fertilization and the possible early brooding behaviour by T. ornata.

Ontogeny of larval swimming abilities in three species of coral reef fishes and a hypothesis for their impact on the spatial scale of dispersal

The late-stage larvae of many reef fishes possess strong swimming abilities that may allow them to influence their dispersal. However, due to the challenges associated with directly measuring patterns of larval dispersal, determining how swimming abilities relate to dispersal outcomes remains a critical gap in our knowledge of the mechanisms that shape dispersal patterns. In this study, we first investigated the ontogeny of swimming speed and endurance in lab-reared larvae of the clown anemonefish (Amphiprion percula), and neon gobies (Elacatinus lori and E. colini). In general, the swimming speed and endurance of larvae improved with age. The congeners, E. lori and E. colini, possessed similar swimming speed and endurance, while A. percula was capable of swimming nearly twice as fast and 322 times longer than either Elacatinus. Second, to relate swimming abilities and other larval traits with patterns of dispersal, we searched the literature for all species in which the dispersal kernel, swimming speed, larval body size and pelagic larval duration have been measured. We found complete datasets for three species: A. percula, E. lori and Plectropomus leopardus. For these species, maximum swimming speed was a better predictor of long-distance dispersal than other larval traits. Thus, we propose the testable hypothesis that swimming abilities may play an important role in determining the extent of long-distance dispersal. Testing this hypothesis, and the alternatives, will require measuring the dispersal kernel, swimming speed, and other dispersal-related larval traits of multiple species in the same seascape.

Improving scallop (Pecten maximus and Placopecten magellanicus) spat production by initial larvae size and hydrodynamic cues used in nursery system

There are several factors affecting scallops during the metamorphosis process that could explain the relatively low post-larvae yield observed in hatcheries. Competent bivalve larvae respond to different settlement cues to undergo metamorphosis and without adequate cues, larvae delay their metamorphosis. The objective of this study is to improve the settlement ratio of the two scallop species, Placopecten magellanicus and Pecten maximus by physical cues associated with hydrodynamic conditions, stocking density in settlement units and larval size at time of transfer to settling units. For each treatment, physiological condition was determined by fatty acid analysis to determine the energetic reserves and structural lipids. We observed similar results for the two important commercial pectinid species and validate the hypothesis on the positive effect of increased flow rate and larval size after transfer to settlement systems on settlement success. Increasing flow rate also affects positively the physiological condition of settled post-larvae by a higher accumulation of total fatty acids in neutral lipid fractions. Furthermore, no effect of larval stocking density until 90 larvae cm−2 in the downwelling sieves was observed. To our knowledge this study is the first to characterize the effect of seawater flow rate on settlement success of different pectinid species cultured under similar conditions. The experiments were performed in a close to commercial scale and thus are relevant to industry situations.

Appearance before performance? Nutritional constraints on life-history traits, but not warning signal expression in aposematic moths.

Trade‐offs have been shown to play an important role in the divergence of mating strategies and sexual ornamentation, but their importance in explaining warning signal diversity has received less attention. In aposematic organisms, allocation costs of producing the conspicuous warning signal pigmentation under nutritional stress could potentially trade‐off with life‐history traits and maintain variation in warning coloration.We studied this with an aposematic herbivore Arctia plantaginis (Arctiidae), whose larvae and adults show extensive variation in aposematic coloration. In larvae, less melanic coloration (i.e. larger orange patterns) produces a more efficient warning signal against predators, whereas high amounts of melanism (smaller orange pattern) enhance thermoregulation, correlate with better immunity and make individuals harder to detect for naïve predators.We conducted a factorial rearing experiment with larvae originating from lines selected for either small or large orange signal size, which were reared on an artificial diet that had either low or high protein content. Protein content of the diet is critical for melanin production. We measured the effects of diet on individual coloration, life‐history traits, immune defence and reproductive output. We also compared the responses to dietary conditions between the small and large larval signal genotypes.Protein content of the diet did not affect warning coloration in the larval stage, but larval signal sizes differed significantly among selection lines, confirming that its variation is mainly genetically determined. In adults, signal line or diet did not affect coloration in hindwings, but males' forewings had more melanin on the high than on low protein diet. Contrary to coloration, diet quality had a stronger impact on life‐history traits: individuals developed for longer had smaller hindwing sizes in females and lower immune defence on the low protein content diet compared with the high. These costs were higher for more melanic larval signal genotypes in terms of development time and female hindwing size.We conclude that low plasticity in warning signal characteristics makes signal expression robust under varying dietary conditions. Therefore, variation in diet quality is not likely to constrain signal expression, but can have a bigger impact on performance.

Prey size and predator density modify impacts by natural enemies towards mosquitoes

1. Interactions between multiple predators can modify prey risk and profoundly alter ecological community dynamics. Further, ontogenic prey size changes are known to mediate prey risk through refuge effects. Understandings of these biotic factors is important for robust quantifications of natural enemy effects on target species, yet their combined influence lacks investigation.2. Functional responses were used to quantify the predatory impacts ofNotonecta glauca(water boatman;Ng) andGammarus pulex(river shrimp;Gp) towards four different larval instars ofCulex pipiensin container‐style habitats. Using conspecific pairs of predators, multiple predator effects (MPEs) of both predator species were examined across larval prey sizes, and prey preference tests were applied to examine prey selectivity across predator–prey body size ratios.3. Both predators were able to feed onC. pipiensacross their larval ontogeny; however,Ngconsumed significantly more larvae thanGp. Functional responses ofNgwere typically Type IIs, whereasGptrended towards sigmoidal Type IIIs. Predation by pairs ofNgandGpshowed independent MPEs towards first‐, third‐, and fourth‐instar stages (except predation byGpat higher densities of fourth‐instar) stages, whereas, for second‐instar stages,Ngshowed synergistic MPEs andGpshowed antagonistic MPEs. Both predators preferred late instar mosquitoes (Ng: fourth instar;Gp: third instar). These preferences reflected predator:prey weight–length ratios, showing that relative sizes of predators and prey are important factors in prey selectivity.4. The results obtained in the present study demonstrate that MPEs, combined with intraspecific prey preferences, may modulate trophic interactions within ecosystems. Therefore, such effects should be increasingly considered to further the understanding of agent efficacies.

The Effects of Conspecific Alarm Cues on Larval Cane Toads (Rhinella marina)

Many aquatic organisms detect and avoid damage-released cues from conspecifics, but the chemical basis of such responses, and the effects of prolonged exposure to such cues, remain poorly understood. Injured tadpoles of the cane toad (Rhinella marina) produce chemical cues that induce avoidance by conspecific tadpoles; and chronic exposure to those cues decreases rates of tadpole survival and growth, and reduces body size at metamorphosis. Such effects suggest that we might be able to use the cane toads' alarm cue for biocontrol of invasive populations in Australia. In the present study, we examined behavioral and ecological effects of compounds that are present in cane toad tadpoles and thus, might trigger avoidance of crushed conspecifics. Four chemicals (L-Arg, L-Leu-L-Leu-OH, L-Leu-L-Ile-OH and suberic acid) induced behavioral avoidance in toad tadpoles at some (but not all) dosage levels, so we then exposed toad larvae to these chemicals over the entire period of larval development. Larval survival and size at metamorphosis were decreased by chronic exposure to crushed conspecifics (consistent with earlier studies), but not by exposure to any of the four chemicals. Indeed, L-Arg increased body size at metamorphosis. We conclude that the behavioral response to crushed conspecifics by cane toad tadpoles can be elicited by a variety of chemical cues, but that consistent exposure to these individual chemical cues does not affect tadpole viability or developmental trajectory. The optimal behavioral tactic of a tadpole may be to flee if it encounters even a single chemical cue likely to have come from an injured conspecific (indicative of predation risk), whereas the continuing presence of that single chemical (but no others) provides a less reliable signal of predation risk. Our data are consistent with results from studies on fish, that suggest a role for multiple chemicals in initiating alarm responses to damage-released cues.

Testing adaptive hypotheses on the evolution of larval life history in acorn and stalked barnacles.

Despite strong selective pressure to optimize larval life history in marine environments, there is a wide diversity with regard to developmental mode, size, and time larvae spend in the plankton. In the present study, we assessed if adaptive hypotheses explain the distribution of the larval life history of thoracican barnacles within a strict phylogenetic framework. We collected environmental and larval trait data for 170 species from the literature, and utilized a complete thoracican synthesis tree to account for phylogenetic nonindependence. In accordance with Thorson's rule, the fraction of species with planktonic‐feeding larvae declined with water depth and increased with water temperature, while the fraction of brooding species exhibited the reverse pattern. Species with planktonic‐nonfeeding larvae were overall rare, following no apparent trend. In agreement with the “size advantage” hypothesis proposed by Strathmann in 1977, egg and larval size were closely correlated. Settlement‐competent cypris larvae were larger in cold water, indicative of advantages for large juveniles when growth is slowed. Planktonic larval duration, on the other hand, was uncorrelated to environmental variables. We conclude that different selective pressures appear to shape the evolution of larval life history in barnacles.

Supply and larval traits at metamorphosis of a coastal marine invertebrate with a bi-phasic life cycle under contrasting oceanographic conditions

Patterns of larval supply and larval condition at metamorphosis play key roles in the structure and dynamics of marine populations. Hence, biological and environmental conditions driving the dispersion of larval individuals, shape early life phenotypes, and influence their survival and post-settlement success. We performed a study over two consecutive years at Ria de Aveiro (Portugal), a coastal lagoon influenced by upwelling regimens in the North-eastern Atlantic. This study assessed the effect of contrasting oceanographic conditions on larval supply and larval traits at metamorphosis of the green crab Carcinus maenas. Crab megalopae were daily sampled and monitored in the laboratory until metamorphosis. Environmental conditions experienced by larvae in the field were estimated considering their expected planktonic larval duration, which was calculated for each individual using the size at metamorphosis and the average water temperature during larval development. Presence/absence, megalopa supply, and larval size were posteriorly modelled using generalized linear mixed models. The analysis of the two consecutive years showed haphazard patterns, revealing that both larval supply and phenotypic traits changed during and between supply seasons. The lunar cycle and environmental conditions were identified as drivers of the presence and supply of megalopae. Settlement events with weak upwelling index were influenced by sea temperature, while intense and constant upwelling events conditioned megalopa supply and performance at metamorphosis. In 2013, megalopae invaded the coastal lagoon in a more advanced physiological stage than in 2012 and/or under better nutritional conditions, probably due to stronger and more constant upwelling events during their pelagic larval life. Our results show that oceanographic processes stimulating upwelling and secondary production are sources of phenotypic variation at settlement, influencing both early benthic performance and adult population dynamics of marine organisms with bi-phasic life cycles.

Chrysodeixis includens nucleopolyhedrovirus (ChinNPV) Affects on Immature Stages of Chrysodeixis includens (Lepidoptera: Noctuidae)

Soybean looper (Chrysodeixis includens) is an important defoliating pest, which has caused significant losses in Brazilian soybean crops. The present study evaluated the foliar consumption, feeding period and mortality of small (< 1.0 cm), medium (1.0 to 2.0 cm) and large (> 2.0 cm) C. includens larvae after infection by the virus Chrysodeixis includens nucleopolyhedrovirus (ChinNPV), isolate Chin-IA (I-A). The bioassay was performed in a completely randomized design organized in a 3 × 2 factorial combination (three size of larvae fed on soybean leaf discs, either treated or not with 4.0 × 1011 PIB ha-1 suspension of virus) with ten replicates per treatment. The average consumption of all three sizes C. includens larvae were significantly reduced after ingestion of soybean discs treated with virus, compared to the larvae from control treatment. The total consumption reduction was 95.6%, 69.4% and 45.9% for the small, medium and large larvae, respectively. Feeding period was significatively reduced for small and medium larvae infected by the virus, but not for large larvae. The corrected mortality level of soybean loopers ranged from 70 to 90% and was not significant different between the three larval sizes. The behavior and physiological alterations of larvae started on the third day, and the mortality occurred between fifth and sixth day after ingestion of infective particles of virus, therefore reducing their damage abilities. Based on the results obtained, ChinNPV can be considered as an important tool within integrate management to control C. includens, mainly when small larvae were predominant in soybean crops.

Crab Larvae Counter Using Image Processing

Very small larval size, high mortality rate of crab larvae, the absence of an accurate crab larva counter at affordable price, the density of larvae that are not known accurately, the ratio of feed that not in accordance with the number of larvae to damage water quality and cannibalism, water quality can not be adjusted to the density of distribution, and economically unprofitable both in terms of feed efficiency and buying and selling transactions. By knowing the number of crab larvae accurately the survival rate of crab larvae increases and is economically beneficial. In this study larvae counters were designed and developed. This tool uses digital imagery to detect and count the crab larvae zoea-1 phase. The accuracy of crab larva counter is 89,8%.

Operational sex ratio does not influence the evolution of male mate choice in the Indian meal moth

The strength of mate choice, pre-copulatory sexual selection more generally, is predicted to vary according to a range of social and demographic factors, including the operational sex ratio (OSR). The OSR influences the number of mating opportunities available to each sex, and can, therefore, strongly influence the degree of intrasexual competition and the cost of mate choice. Accordingly, many animals show short-term plasticity in the strength of mate choice in relation to changes in the OSR. However, whether such change persists over evolutionary time has rarely been tested experimentally. In this study, we examined how female mating success in relation to larval food level and body size differs according to the evolutionary history of their mates, in the Indian meal moth Plodia interpunctella. We used males from populations that have been reared at different adult sex ratios (and, therefore, OSRs) for 130 + generations. We found that small females were more likely to mate compared to large females; however, this effect could not be attributed exclusively to male mate choice. Larval food level also did not influence female mating success. Further, males from different sex ratio regimes did not differ in their likelihood of mating with small females, or those from high-food populations. We suggest that male post-copulatory choice is potentially more important than pre-copulatory choice in this species.

Transgenerational effects of UV-B radiation on egg size, fertilization, hatching and larval size of sea urchins Strongylocentrotus intermedius.

Transgenerational effects are important for phenotypic plasticity and adaptation of marine invertebrates in the changing ocean. Ultraviolet-B (UV-B) radiation is an increasing threat to marine invertebrates. For the first time, we reported positive and negative transgenerational effects of UV-B radiation on egg size, fertilization, hatchability and larval size of a marine invertebrate. Strongylocentrotus intermedius exposed to UV-B radiation showed positive transgenerational effects and adaptation on egg size, hatching rate and post-oral arm length of larvae. Negative transgenerational effects were found in body length, stomach length and stomach width of larvae whose parents were exposed to UV-B radiation. Sires probably play important roles in transgenerational effects of UV-B. The present study provides valuable information into transgenerational effects of UV-B radiation on fitness related traits of sea urchins (at least Strongylocentrotus intermedius).

Prey preferences of notonectids towards larval mosquitoes across prey ontogeny and search area.

Predatory biological control agents can be effective natural means of managing pests, vectors and invasive species. However, the strength of predator-prey interactions can be regulated through context-dependencies that often remain unquantified. In particular, refuge effects can influence the efficacy of biological agents towards target species, and such effects are often driven by prey size and search area differences. In this study, we quantify the prey preferences of two predaceous notonectids, Anisops breddini and Anisops sardeus, towards four different aquatic larval instar stages of the medically important mosquito Culex quinquefasciatus across variations in surface area and water depth. Consumption rates differed significantly among the four larval sizes but not between the notonectids. Search area variations also elicited differences in consumption rates. Both predators tended to prefer second-instar mosquito prey among surface area and water depth variations, while generally avoiding the largest (fourth instar) and smallest (first instar) prey instar stages. For both predators, differential selectivity traits were emergent across surface area variations and water depth, with refuge effects for small prey generally greatest at intermediate-large depths with high surface areas. We thus demonstrate that predatory impacts of notonectids towards mosquito larvae differ significantly according to prey size, and likely peak at intermediate size classes. Different mosquito size classes often coexist and compete, selectivity has important implications for adult mosquito proliferations. Further, in ephemeral aquatic habitats where surface areas and water depths are highly variable spatiotemporally, the efficacy of notonectids in controlling mosquito prey may differ substantially. © 2019 Society of Chemical Industry.

Azadirachtin A inhibits the growth and development of Bactrocera dorsalis larvae by releasing cathepsin in the midgut

Azadirachtin, a botanical insecticide with high potential, has been widely used in pest control. Azadirachtin has shown strong biological activity against Bactrocera dorsalis in toxicological reports, but its mechanism remains unclear. This study finds that azadirachtin A inhibits the growth and development of Bactrocera dorsalis larvae. The larval weights and body sizes of the azadirachtin-treated group were significantly less than those of the control group in a concentration-dependent manner. Further, pathological sections revealed that azadirachtin destroyed the midgut cell structure and intestinal walls, while TUNEL staining showed that azadirachtin could induce apoptosis of midgut cells, and Western blot analysis indicated that Bcl-XL expression was inhibited and cytochrome c (CytC) released into the cytoplasm. The results also imply azadirachtin-induced structural alterations in the Bactrocera dorsalis larvae midgut by activation of apoptosis. RNA-seq analysis of midgut cells found that 482 and 708 unique genes were upregulated and downregulated, respectively. These differentially expressed genes (DEGs) were enriched in apoptotic and lysosomal signaling pathways and included 26 genes of the cathepsin family. qRT-PCR verified the expression patterns of some DEGs, indicating that Cathepsin F was upregulated by 278.47-fold and that Cathepsin L and Cathepsin D were upregulated by 28.06- and 8.97-fold, respectively. Finally, association analysis between DEGs and DEMs (differentially expressed metabolites) revealed that azadirachtin significantly reduced the digestion and absorption of carbohydrates, proteins, fats, vitamins and minerals in the midgut. In conclusion, azadirachtin induces the release of cathepsin from lysosomes, causing apoptosis in the midgut. Ultimately, this leads to reduced digestion and absorption of nutrient metabolites in the midgut and inhibition of the growth and development of Bactrocera dorsalis larvae.

Putting the pieces together: Recent growth, nutritional condition, and mortality of Engraulis anchoita larvae in the Southwest Atlantic

AbstractDynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll‐a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.