Larval Ecology Research Articles

Saproxylic breeding sites for hoverflies (Diptera: Syrphidae): from artificial design to natural habitat management

This paper introduces the importance of veteran trees, tree related microhabitats (TreMs) and their associated hoverfly (Diptera, Syrphidae) fauna. A broader perspective of creating larval habitat is discussed, based on published and novel insights. It focuses on hoverflies that specialise on veteran trees and reflects upon protection and management regimes to conserve veteran trees, TreMs and associated woody habitats. The lack of veteran trees breeding sites can be resolved by tree veteranisation or by using artificial breeding boxes. Whilst protection of veteran trees is essential, enhancement of open areas with flower resources is also vitally important for the survival of saproxylic hoverflies. The larval and adult ecology of only three out of the 134 known European saproxylic species are properly understood. Thus several suggestions are offered for future research aimed at a thorough understanding of the natural history of this unknown and ecologically relevant group of species. The list includes faunistic surveys and investigations into population dynamics, dispersal capacity and habitat preferences. Alongside this research there is a need to investigate the creation of breeding sites including veteranisation techniques and the use of breeding boxes.

Fish larvae dynamics in temperate estuaries: A review on processes, patterns and factors that determine recruitment

AbstractEarly life stages of fish (eggs and larvae) are particularly vulnerable with mortality rates of up to 99% recorded for a large number of species. High mortality rates result from the limited swimming ability of larvae preventing them from escaping sub‐optimal environmental conditions, predators or low prey density areas. In this context, estuaries are key nursery areas for larval and juvenile fish. Estuarine habitats offer environmental conditions favourable to the survival and growth of early stages, through abundant good‐quality prey and protection from predators. A vast literature on larvae occurring in temperate estuaries exists, but an overall perspective is lacking. The occurrence of fish larvae in temperate estuaries depends on several factors. First, the choice of spawning time and location is primordial, as they have evolved to optimise the entry and the retention of larvae in the estuary as well as the conditions experienced by young stages. Secondly, larval growth and survival depend on key environmental factors (e.g. salinity, water temperature, freshwater inputs, turbidity and dissolved oxygen concentration). Knowledge of the larval dynamics in temperate estuaries is scarce for some topics and biased towards some species or geographical areas. The main goal of the present literature review is to synthesise existing knowledge regarding spawning timing and location and larval ecology for fish species occurring in coasts and estuaries, identifying the main patterns, consensus or conflicting hypotheses and highlighting major gaps. Research needs and future perspectives were outlined.

Tadpole morphology of Jerdon’s Narrow-mouthed Frog Uperodon montanus (Jerdon, 1853) with a range and elevation extension report from Western Ghats, India

The study discusses about the new data on larval description, morphological features, larval ecology of stage 25–40 of the Jerdon’s Narrow-mouthed Frog Uperodon montanus (Jerdon, 1853). Tadpoles were identified up to family and genus level based on the historical literature and the species level confirmation was done with molecular studies. We also present a new northern limit record of this species from the Pushpagiri hill ranges in Karnataka (12.669 N, 75.717 E) and a new highest elevation record of 1,916 m at Vaguvarai, Idukki, Kerala which are outside its currently known distribution and elevation ranges. As per the present work, the distribution range of U. montanus has extended northwards by 130 km and upwards by 216 m. Additionally, the IUCN Red List status for the species is also discussed based on the area of occupancy and extent of occurrence redone considering the new range envelope.

Effect of light environment on prey consumption in two species of larval stomatopods, Gonodactylaceus falcatus (Forskål, 1775) and Gonodactylellus sp. (Stomatopoda: Gonodactylidae)

Abstract While adult stomatopod crustaceans are relatively well studied, understanding of larval stomatopod ecology is lacking, largely due to difficulties studying larvae in their natural habitat. This study investigated how light environment (i.e., spectral composition) and time of day affected prey consumption in two species of larval stomatopod, Gonodactylaceus falcatus (Forskål, 1775) and Gonodactylellus sp. Individual larvae were placed with 20 Artemia nauplii prey in feeding chambers treated to produce different light environments with respect to ultraviolet (UV) light: full spectrum light UV+, full spectrum UV–, and a dark control. Chambers were lowered to a depth of 3 m for 2 hours at three times of day (noon, twilight, and night) to test 1) if larval feeding rates changed at different times of day and 2) if UV vision was involved in prey capture. We found that light was important for successful feeding, with both species eating significantly more in lighted treatments than the dark controls during daytime experiments. Gonodactylellus sp. also had a significantly higher feeding rate at twilight in the UV+ treatment than in the dark control. Both species showed decreased consumption at night compared to daytime rates, and decreased consumption in all dark controls. This study is one of the first to examine how ecological conditions affect feeding behavior in larval stomatopods. Our results suggest that light is important for larval stomatopod feeding, with differences between species in daily feeding activity periods. There was also a difference in total consumption between the two species, with the slightly larger Gonodactylaceus falcatus consuming nearly double the prey items as Gonodactylellus sp. at peak feeding times. Follow up studies should incorporate a variety of prey types to test how feeding changes based on food source and density.

Encapsulation of silver nano crystals using Salvinia molesta against the Anopheles stephensi and oxidative stress enzyme activity of larvivorous fish

Anopheles mosquitoes, which are the main carriers of the disease throughout India, Asia, and the Middle East, are the ones that cause malaria. The role of water predators in mosquito aquatic stage regulation is still recognized. With the use of synthetic insecticides, the environment became contaminated and insects developed high resistance to chemical pesticides. Based on our outline, we anticipated an innovative technique of bioencapsulated silver nanoparticles (AgNPs) using Salvinia molesta, which would perform as a reducing and stabilizing agent. Bioencapsulated-AgNPs existed and were classified using a variety of physiochemical techniques. In bioassays, the LC50 values of S. molesta aqueous extract against Anopheles stephensi range from 240.247 (1st instar larvae) - 428.851 ppm (pupae), LC50 of S. molesta-encapsulated AgNPs ranges from 20.010 (1st instar larvae) to 35.676 ppm (pupae). An experiment with S. molesta extract and encapsulated AgNPs was conducted in the open environment, and the larval reduction of mosquitoes was 100% after 72 h. In the ovicidal activity of An. stephensi, hatched eggs were reduced by 100% when treated with 40 ppm of encapsulated AgNPs and 500 ppm of S. molesta extract and encapsulated AgNPs, which significantly reduced the life span of malarial mosquito adults. Furthermore, we investigated the predatory ability of the larvivorous fish Aplocheilus blockii against third and fourth instar larvae of An. stephensi in laboratory conditions using ultra-low doses of bioencapsulated-AgNPs. Regarding non-target impact, in a conventional laboratory environment, the predation efficacy of the larvivorous fish A. blockii, was 58.58% and 54.78% against the 3rd and 4th instar larvae of An. stephensi, respectively. In bioencapsulated AgNPs-contaminated circumstances, fish predation was amplified to 78.18% and 75.54%, respectively. A. blockii was exposed to sublethal concentrations of AgNPs, namely 5, 10, and 15 g/ml, in enzymatic assays to assess changes in GST and AChE activity after 16 days. This study advances our understanding of the contagiousness of water-floating fern-conveyed insecticides and bioencapsulated AgNPs against therapeutically important insects, allowing us to recommend the proven materials as effective candidates to evolve the most recent and cost-effective pest management tools, and the long-term use of this larvivorous fish during wetlands and associated An. stephensi larval ecologies in various parts of the country is proposed.

A first glimpse of larval ecology of halibut species in the Gulf of St. Lawrence, Canada.

Knowledge of the larval ecology of winter-spawning fish from the Estuary and Gulf of St. Lawrence, Canada, remains scarce due to the seasonal ice cover that prevents ichthyoplankton sampling using conventional methods. Two winter-spawning species, Atlantic halibut (AH, Hippoglossus hippoglossus) and Greenland halibut (GH, Reinhardtius hippoglossoides), support the most important groundfish fisheries of this area. In March 2020, the authors captured 10 halibut larvae ranging in size from 5 to 14 mm during an opportunistic survey in the GSL onboard an icebreaking vessel. Of these, eight were AH and two GH. Judging by their very small size, the larvae were only a few days old, suggesting that the spawning grounds are close to the capture sites. This effort constitutes a first step in validating the putative spawning areas for these two important GSL stocks. This knowledge is important for the conservation and sustainable management of these fisheries.

Spatial distribution of Munida gregaria (Decapoda, Munididae) larvae in the silled Beagle Channel: Insights from spring and autumn surveys

The squat lobster Munida gregaria is an ecologically relevant species in southern South American waters. Nonetheless, fundamental topics regarding its larval ecology remain poorly studied, especially at the southern limit of its distribution area. Here, we investigated the abundance, size, and spatial distribution of M. gregaria larval stages (zoeae I-V and megalopa) in the Beagle Channel, during spring and autumn, and explored their relationships with variations in bathymetry and seawater physico-chemical properties at both sides of the Mackinlay pass sill. Plankton samples were collected from the inner sector of the channel, a fresh water-influenced and semi-enclosed system, to its mouth towards the Atlantic Ocean during four oceanographic cruises (springs of 2014 and 2015 and autumns of 2016 and 2017). Zoeae occurred throughout the study area in both seasons, with lower densities in autumn, whereas megalopae were detected exclusively in spring. The highest larval abundances and all developmental stages were found in the outer sector, where juveniles and adults also occurred. These spatial patterns were consistently observed across the different sampling dates. Contrary to previous reports, the coexistence of zoeae I-V during autumn would indicate that, at least in the outer sector, larvae that hatch late in the summer are able to reach advanced developmental stages. However, it remains unknown whether they fully develop in subsequent months. Significant associations among larval distribution patterns and environmental variables were detected, especially for late stages, which occurred mainly in the westernmost and shallowest part of the outer sector, characterized by highly stratified waters with the warmest bottom temperatures. All together, these results may reflect the effects of variations in local environmental conditions along the channel, related to bottom topography and degree of freshwater/oceanic influence, on larval cohort dynamics, adult reproduction, or both. Larvae hatched in spring were larger than those hatched in summer/autumn for all zoeal stages. Possible explanations for this finding are discussed. This study contributes to our knowledge of M. gregaria larval ecology, which is essential to understand its complex population dynamics in an environmentally complex geographical area, and to better predict its responses to climate change. • Zoeal stages I-V occurred in both spring and autumn. • Larval abundance and stage structure differed west and east of the Mackinlay sill. • Higher larval abundances and all larval stages occurred in the outer sector. • Advanced stages occurred mainly in shallow and highly stratified waters. • Larvae hatched in spring were larger than those hatched in summer-autumn.

Anopheles gambiae s.l. larval habitats and resistance mechanisms in Kribi, Cameroon

The effectiveness of Long-Lasting Insecticidal Nets (LLINs) and indoor residual spraying (IRS) in controlling malaria vectors is hampered by the resistance of anopheles to insecticides. A good knowledge of the breeding sites and of the resistance profile of the vectors could facilitate the development of an appropriate control strategy. This study looks at the larval ecology and the susceptibility profile of An. gambiae s.l. to insecticides in urban and rural areas in Kribi, South Region of Cameroon. Mosquito breeding sites were categorized and geo-referenced. For each site, larvae were collected and reared and physicochemical parameters were measured in situ. The susceptibility of anopheles to dichlorodiphenyltrichloroethane (DDT), deltamethrin and permethrin, after pre-exposure to piperonyl butoxide (PBO) or not, was evaluated on the reared larvae. The Kdr mutation was detected using the Hot Oligonucleotide Ligation Assay (HOLA). Natural breeding sites of An. gambiae s.l. were tyre tracks (12%, n=10), unbuilt wells (5%, n=4), pools of residual water (57%, n=48), foot and hoof prints, gullies, streams and the banks of the Kienké River (15%, n=13). Artificial breeding sites were abandoned dugouts (11%, n=9). Breeding sites in urban areas were characterized by higher mean values of temperature, conductivity, salinity and turbidity compared to the breeding sites in the rural area. The breeding sites of An. gambiae s.l. in urban Kribi were found to be sunnier than those in rural Kribi. A total of 4320 adults were used for testing, 1 440 mosquitoes from rural Kribi, 1 440 from urban Kribi and 1 440 specimens from the laboratory Kisumu strain. For DDT and deltamethrin, susceptibility tests showed that mortality was lower in a situation of no pre-exposure to PBO than in a situation of pre-exposure to PBO in the two study areas. The frequency of the resistant allele (R) was high for the Kdr West mutation in both urban (0.94) and rural areas in Kribi (0.93). An. gambiae s.l. colonizes a wide range of breeding sites and develops metabolic and mutation resistance to recommended insecticides. The search of alternative molecules for vector control is a necessity.

Does plastic type matter? Insights into non-indigenous marine larvae recruitment under controlled conditions.

Marine plastic debris (MPD) are a global threat to marine ecosystems. Among countless ecosystem impacts, MPD can serve as a vector for marine 'hitchhikers' by facilitating transport and subsequent spread of unwanted pests and pathogens. The transport and spread of these non-indigenous species (NIS) can have substantial impacts on native biodiversity, ecosystem services/functions and hence, important economic consequences. Over the past decade, increasing research interest has been directed towards the characterization of biological communities colonizing plastic debris, the so called Plastisphere. Despite remarkable advances in this field, little is known regarding the recruitment patterns of NIS larvae and propagules on MPD, and the factors influencing these patterns. To address this knowledge gap, we used custom-made bioassay chambers and ran four consecutive bioassays to compare the settlement patterns of four distinct model biofouling organisms' larvae, including the three notorious invaders Crassostrea gigas, Ciona savignyi and Mytilus galloprovincialis, along with one sessile macro-invertebrate Spirobranchus cariniferus, on three different types of polymers, namely Low-Linear Density Polyethylene (LLDPE), Polylactic Acid (PLA), Nylon-6, and a glass control. Control bioassay chambers were included to investigate the microbial community composition colonizing the different substrates using 16S rRNA metabarcoding. We observed species-specific settlement patterns, with larvae aggregating on different locations on the substrates. Furthermore, our results revealed that C. savignyi and S. cariniferus generally favoured Nylon and PLA, whereas no specific preferences were observed for C. gigas and M. galloprovincialis. We did not detect significant differences in bacterial community composition between the tested substrates. Taken together, our results highlight the complexity of interactions between NIS larvae and plastic polymers. We conclude that several factors and their potential interactions influenced the results of this investigation, including: (i) species-specific larval biological traits and ecology; (ii) physical and chemical composition of the substrates; and (iii) biological cues emitted by bacterial biofilm and the level of chemosensitivity of the different NIS larvae. To mitigate the biosecurity risks associated with drifting plastic debris, additional research effort is critical to effectively decipher the mechanisms involved in the recruitment of NIS on MPD.

Coloring coral larvae allows tracking of local dispersal and settlement.

Quantifying patterns of dispersal and settlement in marine benthic invertebrates is challenging, largely due the complexity of life history traits, small sizes of larvae (<1 mm), and potential for large-scale dispersal (>100 km) in the marine environment. Here, we develop a novel method that allows for immediate differentiation and visual tracking of large numbers of coral larvae (106 to 109) from dispersal to settlement. Neutral red and Nile blue stains were extremely effective in coloring larvae, with minimal impacts on survival and settlement following optimization of incubation times and stain concentrations. Field validation to wild-captured larvae from the Great Barrier Reef demonstrates the efficacy of staining across diverse taxa. The method provides a simple, rapid (<60 minutes), low-cost (approximately USD$1 per 105 larva) tool to color coral larvae that facilitates a wide range of de novo laboratory and field studies of larval behavior and ecology with potential applications for conservation planning and understanding patterns of connectivity.

Chemically mediated rheotaxis of endangered tri-spine horseshoe crab: potential dispersing mechanism to vegetated nursery habitats along the coast.

An enhanced understanding of larval ecology is fundamental to improve the management of locally depleted horseshoe crab populations in Asia. Recent studies in the northern Beibu Gulf, China demonstrated that nesting sites of Asian horseshoe crabs are typically close to their nursery beaches with high-density juveniles distributed around mangrove, seagrass and other structured habitats. A laboratory Y-maze chamber was used to test whether the dispersal of early-stage juvenile tri-spine horseshoe crab Tachypleus tridentatus is facilitated by chemical cues to approach suitable nursery habitats. The juvenile orientation to either side of the chamber containing controlled seawater or another with various vegetation cues, as well as their movement time, the largest distance and displacement were recorded. The juveniles preferred to orient toward seagrass Halophila beccarii cues when the concentration reached 0.5 g l-1, but ceased at 2 g l-1. The results can be interpreted as a shelter-seeking process to get closer to the preferred settlement habitats. However, the juveniles exhibited avoidance behaviors in the presence of mangrove Avicennia marina and invasive saltmarsh cordgrass Spartina alterniflora at 2 g l-1. The juveniles also spent less time moving in the presence of the A. marina cue, as well as reduced displacement in water containing the S. alterniflora cue at 1 and 2 g l-1. These results may explain the absence of juvenile T. tridentatus within densely vegetated areas, which have generally higher organic matter and hydrogen sulfide. Early-stage juvenile T. tridentatus are capable of detecting and responding to habitat chemical cues, which can help guide them to high-quality settlement habitats. Preserving and restoring seagrass beds in the intertidal areas should be prioritized when formulating habitat conservation and management initiatives for the declining horseshoe crab populations.

Impact of Environmental Modifications on the Ecology, Epidemiology, and Pathogenesis of Plasmodium falciparum and Plasmodium vivax Malaria in East Africa.

Food insecurity, recurrent famine, and poverty threaten the health of millions of African residents. Construction of dams and rural irrigation schemes is key to solving these problems. The sub-Saharan Africa International Center of Excellence for Malaria Research addresses major knowledge gaps and challenges in Plasmodium falciparum and Plasmodium vivax malaria control and elimination in malaria-endemic areas of Kenya and Ethiopia where major investments in water resource development are taking place. This article highlights progress of the International Center of Excellence for Malaria Research in malaria vector ecology and behavior, epidemiology, and pathogenesis since its inception in 2017. Studies conducted in four field sites in Kenya and Ethiopia show that dams and irrigation increased the abundance, stability, and productivity of larval habitats, resulting in increased malaria transmission and a greater disease burden. These field studies, together with hydrological and malaria transmission modeling, enhance the ability to predict the impact of water resource development projects on vector larval ecology and malaria risks, thereby facilitating the development of optimal water and environmental management practices in the context of malaria control efforts. Intersectoral collaborations and community engagement are crucial to develop and implement cost-effective malaria control strategies that meet food security needs while controlling malaria burden in local communities.

Evolutionary rates and shape variation along the anuran vertebral column with attention to phylogeny, body size, and ecology.

The vertebral column is critical to a vertebrate species' flexibility and skeletal support, making vertebrae a clear target for selection. Anurans (frogs and toads) have a unique, truncated vertebral column that appears constrained to provide axial rigidity for efficient jumping. However, no study has examined how presacral vertebrae shape varies among anuran species at the macroevolutionary scale nor how intrinsic (developmental and phylogenetic) and extrinsic (ecological) factors may have influenced vertebrae shape evolution. We used microCT scans and phylogenetic comparative methods to examine the vertebrae of hundreds of anuran species that vary in body size as well as adult and larval ecology. We found variation in shape and evolutionary rates among anuran vertebrae, dispelling any notion that trunk vertebrae evolve uniformly. We discovered the highest evolutionary rates in the cervical vertebrae and in the more caudal trunk vertebrae. We found little evidence for selection pressures related to adult or larval ecology affecting vertebrae evolution, but we did find body size was highly associated with vertebrae shape and microhabitat (mainly burrowing) affected those allometric relationships. Our results provide an interesting comparison to vertebrae evolution in other clades and a jumping-off point for studies of anuran vertebrae evolution and development.

Unraveling the Drifting Larval Fish Community in a Large Spawning Ground in the Middle Pearl River Using DNA Barcoding

Simple SummaryDNA barcoding identified 28 species from larvae collected from the Dongta spawning ground. Six invasive species were identified in the larval pool, implying that these species had successfully colonized the middle Pearl River. Several migratory species common in the lower Pearl River were rare or absent in the Dongta spawning ground, suggesting that adverse effects of dam construction posed on these migratory species. Our study provided important reference data for fishery management and conservation in the Pearl River.Resolving the species composition of a larval pool in a spawning ground can provide novel insights into regional fish stocks and can support the development of effective monitoring and conservation policies. However, it is challenging to identify fish larvae to species due to their high diversity and dramatic phenotypic changes over development. In this study, we collected fish larvae in the Dongta spawning ground (Guiping City, Guangxi Province, China) in the middle reaches of the Pearl River between May and August 2018. We used a DNA barcoding approach to determine the species composition of the larval pool. A total of 905 larvae were chosen for molecular identification, of which 750 yielded high-quality barcoding sequences. Of these, 597 (≈79.6%), 151 (≈20.1%)/and 2 (≈0.3%) were assigned to 28 species, 8 genera, and 1 subfamily using the Barcode of Life Data System and GenBank nucleotide databases, respectively. Among the 28 identified species, 21 were cyprinids. Two species (Mugilogobius myxodermus and Pseudolaubuca engraulis) that were present only infrequently in previous adult surveys were abundant in the larval pool. Six invasive species were identified in the larval pool, implying that these species had successfully colonized the studied river section. Several migratory species common in the lower Pearl River were rare or absent in the investigated region, suggesting that dam construction in the Pearl River has had adverse effects on these migratory species. In summary, our study confirmed the applicability of DNA barcoding to studies of fish larval ecology and provided important reference data for fishery management and conservation in the Pearl River.

Spatio-temporal Prediction of the Malaria Transmission Risk in Minab District (Hormozgan Province, Southern Iran)

IntroductionMalaria is the most important parasitic disease in tropical and subtropical regions, with more than 240 million cases reported annually. In Iran, indigenous cases occur in its south-eastern region. The aim of this study is to assess the environmental risk of malaria transmission in an endemic area of southern Iran.MethodsThe study was carried out in Minab district (Hormozgan province, southern Iran), with the aim to assess the environmental risk of malaria, based on a spatio-temporal study, using Growing Degree Days (GDD)-based predictions, larval habitat ecology, MaxEnt spatial predictions and malaria transmission data.ResultsThe Gradient Model Risk index showed the highest malaria transmission risk period to be during January–April and October–December. The ecological conditions of water bodies of larval habitats of the four vector species (Anopheles culicifacies, A. dthali, A. fluviatilis and A. stephensi) were assessed, with A. stephensi being the most prevalent and the most widely distributed species.ConclusionThese findings, together with the MaxEnt Anopheles predictive distribution models, allowed identifying villages in danger of malaria transmission in Minab district. This spatio-temporal prediction of malaria transmission risk should be incorporated in the design of malaria control initiatives towards a local malaria early warning system. Moreover, the proposed transmission risk model can be extrapolated, at local scale, to other malaria endemic areas of tropical and subtropical regions.

Field Comparison of Removed Substrate Sampling and Emergence Traps for Estimating Culicoides Orbivirus Vectors in Northern Florida

The larval ecology of Culicoides (Diptera: Ceratopogonidae) influences their spatial distributions and the pathogens they transmit. These features are of special concern for deer farmers in Florida where epizootic hemorrhagic disease virus (EHDV) is a major source of mortality in captive herds. Rarity of larval morphological expertise leads many researchers to study larval ecology by quantifying emergence, either with field emergence traps or removing substrate from the field for observation under laboratory conditions. We investigated the comparability of these methods in Florida seepages where two recently implicated EHDV vectors, Culicoides stellifer Coquillett and Culicoides venustus Hoffman, are common. We compared the abundance and composition of emerging Culicoides collected from emergence traps with removed substrate samples (soil plugs) at three seepages. Soil plugs were sampled adjacent to the emergence trap and from underneath the trap footprint, and then monitored under laboratory conditions for 11-13 wk to compare the methods and to assess the role of incubation period for removed substrate samples. Emergence traps and removed substrate sampling largely agreed on community compositions and trends within different seepages. However, comparatively large numbers of C. stellifer emerged later than expected and well into the incubation period with emergence still occurring after 13 wk (90 d). Removed substrate samples were more similar to emergence traps at shorter incubation times. The importance of time for the capture of Culicoides in removed substrate sampling was more pronounced than we anticipated and is important from both a methodological and biological perspective.

Larval Ecology of Gobiid Fishes in a Subtropical Embayment: Environmental Preferences and Spatiotemporal Habitat Partitioning

Larval ecology of gobiid fishes in Xiangshan Bay of the east coast of China was examined from ichthyoplanktonic data collected during 10 weekly cruises in spring–early summer of 2015. Particular attention was given to their environmental preferences and spatiotemporal habitat partitioning. A total of 87, 007 gobiid larval individuals, distributed in 9 species, were collected. The thermal and salinity preferences of 6 of the 9 gobiid larvae have been determined using a quotient-rule analysis. This work filled some gaps in larval ecology of these poorly studied gobiids. Temporal succession in gobiid larvae composition was strongly evident. The bay ecosystem was mainly occupied by Asian freshwater goby Acanthogobius ommaturus, branded goby Chaeturichthys stigmatias and tank goby Glossogobius giuris, with preferences for temperature bellow 19°C during April to early May, while striped sand goby Amoya pflaumi and burrowing goby Trypauchen vagina, which preferred water temperature above 22°C, predominated the larval assemblage in early June. With respect to spatial distribution, relatively little variation was detected among species. Most of gobiid larvae exhibited little obvious habitat preference except pinkgray goby Amblychaeturichthys hexanema and A. ommaturus, which distributed preferably in the inner zone and mouth of the bay ecosystem, respectively. Water temperature was the major structuring factor of gobiid larvae assemblage structure in the bay. The gobiid larvae exhibited to be particularly susceptible to the rapid rising temperature shocks. Sharp decline in the total abundance of gobiid larvae was detected with each rapid heating process. In addition, significant shift in larval fish composition occurred following the process. The results suggest that pattern of temperature increase in spring and early summer plays a vital role in recruitment success of the gobiid larvae.

Mosquito (Diptera: Culicidae) Larval Ecology in Rubber Plantations and Rural Villages in Dabou (Côte d'Ivoire).

In Côte d'Ivoire, rubber cultivation has more than doubled since 2010. These mass agricultural areas require a large workforce with little information on how this environment might impact risk of mosquito-borne diseases. The objective of this study was to assess the larval ecology of mosquitoes in rubber areas of Dabou, Côte d'Ivoire. From January to June 2017, an entomological survey was conducted of mature (MP) and immature (IP) rubber plantations, as well as in villages surrounded by rubber plantations (SV) and remote from rubber plantations (RV). The number and type of potential and positive breeding sites were recorded, and mosquito larval densities and diversity were estimated. Seven genera divided into 31 species including major vector such as Anopheles gambiae s.l. and Aedes aegypti were identified. A total of 1,660 waterbodies were identified with a larvae positivity rate of 63.1%. A majority of waterbodies were identified in SV (N = 875, 53.4% positivity rate), followed by MP (N = 422, 81.8% positivity rate), IP (N = 194, 72.2% positivity rate) and least in RV (N = 169, 57.4% positivity rate). The most important breeding sites for disease vectors were leaf axils in IP (N = 108, 77.1%), latex collection cups in MP (N = 332, 96.2%) and the containers abandoned in the SV (N = 242, 51.8%) as well as in the RV (N = 59, 60.8%). All these results allow us to affirm that the cultivation of rubber trees has an impact on the larval ecology by increasing the number of available sites and favoring a high larval density and diversity.

Histogenesis and cell differentiation in the retina of Thunnus thynnus: A morphological and immunohistochemical study

This study examines the anatomical development of the visual system of Atlantic bluefin tuna, Thunnus thynnus, during the first 15 days of life at histological level, with emphasis in the immunohistochemical characterization of different cell types. As an altricial fish species, the retina was not developed at hatching. The appearance of eye pigmentation and the transformation of the retina from an undifferentiated neuroblastic layer into a laminated structure occurred during the first two days of life. At 16 days after hatching (DAH), the ganglion cells were arranged in a single row in the central region of the retina and the outer segments of the photoreceptors were morphologically developed. Furthermore, at this age, all the retinal cell types were immunohistochemically characterized. The presence of ganglion cell axons was confirmed with the TUJ1 antibody and the existence of functional synapses in the plexiform layers with antibodies against SV2. Cone opsins were immunostained with antibodies against visinin and CERN-922 immunoreactive rods were also identified. Different subpopulations of amacrine cells were immunostained with antibodies against αTH and PV. Highly GS-immunoreactive Müller cells were also detected at this age. These observations suggested that the T. thynnus retina was fully functional at the end of the second week of life. Basic studies on early morphology of the visual system and larval behavior are necessary to support applied research on larval rearing. Furthermore, they may have implications for understanding larval ecology in the wild.

Internal ultrastructure of the planktonic larva of the coral Porites panamensis (Anthozoa: Scleractinia)

Introduction: The scleractinian coral life cycle includes planktonic larvae that settle on the benthos, allowing the primary polyp to clone and build a sexually reproducing adult colony. The larval physiology and ecology of Eastern Tropical Pacific scleractinians needs the exploration of basic aspects such as the internal morphology of planulae. Objective: To describe histological and cytological characteristics of Porites panamensis larvae. Methods: During August-July 2019, at Islas Marias Biosphere Reserve, Central Mexican Pacific, we made 14 collections of coral larvae and identified the species with C cytochrome oxidase subunit 1 gene. We used a scanning electron microscope and other techniques. Results: The ectoderm was composed by heterogeneous, mono-ciliated, columnar epithelial cells. Nematocysts were clustered at the oral pole of the ectoderm, and cells were evident in the aboral pole of the ectoderm gland. The endoderm had secretory cells, lipids and symbionts. Conclusions: The abundance of secretory cells and nematocysts in the aboral pole suggests their importance in substrate exploration and larval settlement. Our results support previous descriptions of larval ultrastructure in other coral species.