The aim of this study was to evaluate the effects of the last generation insecticide spirotetramat (STM) on embryos and larvae of the freshwater prawn Macrobrachium borellii. Both embryos and larvae were exposed to serial dilutions of STM to determine the LC50 values. After 96-h of exposure, live larvae were fixed for histological analysis. In addition, ovigerous females were exposed to a sublethal concentration of STM (1.7 mg/L) for 96 h to evaluate the activity of the enzymes catalase, glutathione-S-transferase, and superoxide dismutase as well as the lipoperoxidation (LPO) and protein oxidation levels in embryos. The larvae showed a high sensitivity to STM evidenced by the LC50-96 h value (0.011 mg/L). On the contrary, the embryos were highly resistant to STM exposure, and no lethal effect was observed in the treatments with high concentrations of this insecticide (LC50-96 h > 150 mg/L). Among all the biochemical parameters evaluated in the embryos exposed to STM, only LPO showed a significant increase compared to controls. This was probably due to a restricted entry of the insecticide through the embryonic coat. Thus, a preliminary study of the structure and permeability of the embryonic coat was carried out in control embryos. The analysis by electron microscopy revealed that its structure is formed by four embryonic envelopes composed of multiple layers while the assay with a fluorescent probe revealed that the embryonic coat increases its permeability during development. STM caused significant histopathological alterations in the hepatopancreas and gills of larvae. This study showed that although the embryos of M. borellii could be protected by the embryonic coat, the larvae are very vulnerable to the STM toxicity. So, it is necessary to continue evaluating the effects of these new pesticides on non-target organisms, such as aquacultured species, to help predict their ecotoxicological risks derived from the increasing agricultural activity developed worldwide.
The present study reports the first genome of Nitrosopumilus extracted from the marine sponge Thoosa mismalolli. The genomic study of Nitrosopumilus genus using seven genomes type strains (N. maritimus, N. piranensis, N. zosterae, N. ureiphilus, N. adriaticus, N. oxyclinae and N. cobalaminigenes), four genomes Candidatus species (Ca. N. koreensis, Ca. N. sp. AR2, Ca. N. salaria BD31, and SZUA-335), and six reference genomes (SI075, SI0036, SI0060, SI0034, SI0048, and bin36o) isolated from marine sponge, a tropical marine fish tank, dimly lit deep coastal waters, the lower euphotic zone of coastal waters, near-surface sediment, and MAG N. sp NMAG03 isolated from Thoosa mismalolli was performed. These genomes were characterized by means of a polyphasic approach comprising multilocus sequence analysis (MLSA) of 139 single-copy genes (SCG), core-pangenome, ANI, and in silico phenotypic characterization. We found that the genomes of the Nitrosopumilus genus formed three separate clusters (A, B, and C) based in 139 SCG sequence similarity. The genomes showed values between 75.2 and 99.5% for ANI, the core genome consisted of 168 gene families and the pangenome of 6,011 gene families. Based on the genomic analyses performed, the cluster A may contain a potential new species (NMAG03), and the cluster C could be represented by three new species of the genus. Finally, based on the results shown in this polyphasic approach, we support the use of the integrated approach for genomic analysis of poorly studied genera.
This study aimed to determine the impact of horticultural land use on the taxonomic composition and the composition of functional feeding groups of freshwater macroinvertebrate assemblages in lowland streams. Three streams running through intensively cultivated plots were compared to three less impacted streams, two of which run through a UNESCO Biosphere Reserve. Nutrient and pesticide measured concentrations, as well as the macroinvertebrate assemblages associated with aquatic vegetation, were analyzed in each stream. These concentrations were higher at the horticultural streams, negatively correlated to the richness, density, and diversity of the macroinvertebrate assemblages, leading to a dominance of tolerant families. The trophic structure of the macroinvertebrates assemblages was dominated by collector-gatherers in the horticultural streams, while all functional feeding groups were more equally distributed in less impacted streams. We concluded that horticulture reduces biodiversity and changes the trophic structure of the macroinvertebrate assemblage, eventually affecting stream functions. Mitigation measures are required to preserve the structure and function of these ecosystems.
The European Starling (Sturnus vulgaris) is a cavity-nesting bird with great invasive potential. As a result of human intervention, this bird is now distributed across all continents (except Antarctica) and its distribution range is increasing at an alarming rate. The European Starling was introduced to Argentina in 1983 and is currently distributed across almost the entire country. It is considered one of the hundred most damaging invasive species in the world and constitutes a serious competitive threat to native cavity-nesting birds. Interactions between European Starlings and cavity-nesting birds generally have negative consequences on native bird populations, although there are still few reports in the literature that account for the degree of damage. In this study, we report for the first time details of the harassment strategy and subsequent cavity usurpation by European Starlings on a breeding pair of Green-barred Woodpeckers (Colaptes melanochloros) in an urban area of central-eastern Argentina. Over one breeding season, the woodpeckers excavated seven cavities, none of which were successful. In six of these reproductive attempts (86%) we recorded interactions with European Starlings and in five (71%) the cavity was usurped. On three occasions we recorded a cooperative harassment strategy by a group of European Starlings causing the woodpeckers to abandon the cavity. Our report is especially relevant if we consider the invasive potential of the European Starling worldwide and the frequently limited cavity supply in bird breeding habitats. Therefore, we encourage governmental authorities and environmental NGOs to take measures to control the populations of this aggressive invasive species.
High latitudes are experiencing intense ecosystem changes with climate warming. The underlying methane (CH4) cycling dynamics remain unresolved, despite its crucial climatic feedback. Atmospheric CH4 emissions are heterogeneous, resulting from local geochemical drivers, global climatic factors, and microbial production/consumption balance. Holistic studies are mandatory to capture CH4 cycling complexity. Here, we report a large set of integrated microbial and biogeochemical data from 387 samples, using a concerted sampling strategy and experimental protocols. The study followed international standards to ensure inter-comparisons of data amongst three high-latitude regions: Alaska, Siberia, and Patagonia. The dataset encompasses different representative environmental features (e.g. lake, wetland, tundra, forest soil) of these high-latitude sites and their respective heterogeneity (e.g. characteristic microtopographic patterns). The data included physicochemical parameters, greenhouse gas concentrations and emissions, organic matter characterization, trace elements and nutrients, isotopes, microbial quantification and composition. This dataset addresses the need for a robust physicochemical framework to conduct and contextualize future research on the interactions between climate change, biogeochemical cycles and microbial communities at high-latitudes.
In many insects, short photoperiods induce females to lay diapausing eggs, which are associated with a reduction in female fecundity, and/or with an increase in their growth rate, allowing for a larger size at adulthood. The effects of short photoperiods may also differ among populations, depending on the different selection pressures imposed by the winter conditions. Thus, this study aimed to experimentally assess the effects of short photoperiods on Aedes aegypti, an invasive mosquito species that also vectors several viral diseases. We compared life history parameters of the females reared from the first larval instar under contrasting photoperiods, in two populations from the temperate region of Argentina, one with a milder winter (BA) and the other with a harsher winter (SB). The results showed a significant increase in the time to oviposition, a trend to a larger size of females (significant only for SB) and higher inhibition of egg hatching (more pronounced in SB), in response to short photoperiods. No differences in fecundity were detected among treatments. The different reaction norms of the populations in female body size and egg hatching response suggest an adaptation to local conditions, which might favour a further expansion of A. aegypti towards colder climates.
Zooplankton play a key role in aquatic ecosystems constituting an essential intermediate component in aquatic food webs. Cladocerans in particular are widely studied as model of generalist filter feeders. At the regional level, the cladoceran Daphnia spinulata is found in numerous habitats with wide conductivity range (160 μS cm−1 to 14.000 μS cm−1), but information about the species's tolerance range or life history is scarce. Our objective was to generate essential information about D. spinulata's life history and the main parameters related to two contrasting salinity levels representative of water bodies of the pampean plain. Results obtained in laboratory bioassays showed that individuals at low conductivity (700 μS cm−1) had more moults, a lower mortality and a higher life expectancy at birth, a higher generation time, and an earlier peak density than those at high‐conductivity treatments (5000 μS cm−1). The maximum density reached was similar for both conductivities indicating a similar growth capability attained by different strategies. Moreover, the results indicated that D. spinulata at different conductivities was able to reproduce, with the offspring thus contributing to population growth. This study provided a knowledge of the life history strategies of this endemic cladoceran at two different conductivities, thus generating crucial information on the population dynamics and for evaluating the species's role as a possible salinity indicator in pampean water bodies. Nevertheless, future investigations will be necessary in order to identify the absolute limits of tolerance and the optimum conductivity for this species and determinate which stressors will act as a mictic stimuli. El zooplancton cumple un papel esencial en los ecosistemas acuáticos, constituyendo un eslabón intermedio en las tramas tróficas acuáticas. Los cladóceros, en particular, son ampliamente estudiados como modelos de filtradores generalistas. A nivel regional, el cladócero Daphnia spinulata es encontrado en numerosos ambientes con un amplio rango de conductividad (desde 160 μS cm−1 hasta 14.000 μS cm−1), pero la información en relación a sus rangos de tolerancia o historia de vida, es muy escasa. Nuestro objetivo fue generar información acerca de la historia de vida del cladócero Daphnia spinulata y evaluar cómo los principales parámetros están influenciados por dos niveles de salinidad contrastantes representativos de cuerpos de agua de la región pampeana. Los resultados obtenidos a través de ensayos de laboratorio mostraron que los organismos a baja conductividad (700 μS cm−1) tienen más mudas, una menor mortalidad, una mayor esperanza de vida al nacer, un tiempo generacional más largo y un pico de densidad más temprano que aquellos organismos en tratamientos con conductividad elevada (5000 μS cm−1). La máxima densidad alcanzada por la población fue similar en ambas conductividades, indicando una capacidad de crecimiento parecida pero alcanzada a través de diferentes estrategias. Además, los resultados indicaron que D. spinulata fue capaz de reproducirse a diferentes conductividades, y que su descendencia contribuyó efectivamente al crecimiento poblacional. Así, este estudio provee información acerca de las estrategias en relación a la historia de vida de un cladócero endémico expuesto a dos conductividades diferentes, generando información valiosa sobre la dinámica de la población y para posibles evaluaciones sobre el rol de esta especie como indicador de salinidad en ecosistemas acuáticos pampeanos. Sin embargo, investigaciones futuras son necesarias para identificar los límites absolutos de tolerancia y los óptimos de conductividad de esta especie, así como también cuáles son los forzantes que actúan como estímulo míctico. Our objective was to generate essential information about D. spinulata's life history and the main parameters related to two contrasting salinity levels representative of water bodies of the pampean plain. This study provided a knowledge of the life history strategies of this endemic cladoceran at two different conductivities, thus generating crucial information on the population dynamics and for evaluating the species's role as a possible salinity indicator in pampean water bodies.
Understanding factors affecting nest survival of woodpeckers in threatened landscapes is a key tool for land managers, particularly when conservation depends on public policies. However, information of Neotropical woodpeckers breeding in southern temperate forests is noticeably sparse despite the worrying conservation status of these ecosystems and woodpeckers’ key role as cavity providers. Our objective was to assess the relationship between tree cavity features, vegetation structure, and landscape configuration on the nest survival of the Green-barred Woodpecker (Colaptes melanochloros) and the Campo Flicker (C. campestris). We monitored nests of these woodpeckers during 3 breeding seasons from 2015 to 2018 in a woodland of east-central Argentina threatened by selective tree logging and soil material extraction. We recorded features that presumably influence nest survival at a micro-scale (cavity, cavity-tree features, and foliage cover around the cavity) and a macro-scale (forest cover and shape index within a 500-m circle around the nest). We did not find support for a relationship between daily nest survival rates (DSR) and cavity features, vegetation structure, or landscape configuration. However, new cavities were more successful than reused ones for the Green-barred Woodpecker. We also found a surprisingly high rate (~33% of nest failures) of nest abandonment for both species. Abandonment may be a factor regulating this population and causes of abandonment warrants further investigation. Given the importance of new cavities to the success of Green-barred Woodpeckers, our results indicate the preservation of medium-size trees (20 cm < diameter at breast height [DBH] < 50 cm) with wood softened by degradation processes (preferred by the species to excavate cavities) would facilitate persistence both of this woodpecker and the cavity nesting community. Effective audit of soil material extraction and controlled selective timber logging practices (including preservation of mature trees) in compliance with existing regulations could contribute to this type of habitat maintenance.
Thoosa mismalolli is one of the most abundant and common excavating sponges along Mexican and Central America shallow reefs. This sponge harbors a microbiome unknown so far. In the present study, the metagenome of T. mismalolli was sequenced, and total reads obtained were classified, and contigs were assembled to analyze the microbiota. The results showed that the highest number of contigs was assigned to the phylum 'Candidatus Poribacteria' (8848), followed by the phylum Proteobacteria (6415), and Chloroflexi (3972). 22 MAGs with <8.5% redundancy using MaxBin 2 were detected: 'Candidatus Poribacteria' (5), Proteobacteria (5), Chloroflexi (6), Gemmatimonadetes (2), Actinobacteria (2), and Thaumarchaeota (2). The phylogenetic tree based on the 139 single-copy gene (SCG) suggested a subdivision into two clades of the phylum Proteobacteria. The presence Thaumarchaeota is also interesting to highlight because contains ammonia-oxidizing archaea considered key members of the global nitrogen and carbon biogeochemical cycles. In addition, shotgun metagenomic analysis revealed that protein sequences associated for amino acids (13.0%) and carbohydrate metabolism (12.4%) predominated. In this study, the first microbiome and functional potential of T. mismalolli is reported, which also represents the first investigation of a microbiota sponge in the Mexican Pacific reefs.
This study examined the changes in sex ratios and sex reversal rates in pejerrey Odontesthes bonariensis, that occur with the progression of the spawning season in a seminatural setting. Four groups of hatchery-produced pejerrey larvae were stocked in floating cages in La Salada de Monasterio lake (Pampas region), a natural habitat of this species, and reared from hatching beyond gonadal sex determination with minimum human interference. Cage 1 was stocked at the beginning of the spring spawning season and the other cages with monthly delays until cage 4 in early summer. The genotypic (amhy+: XY/YY, amhy-: XX) and phenotypic (testis: male, ovary: female) sex ratios and proportions of genotype/phenotype mismatched individuals were estimated and their relation to water temperature and daylength during the experiment was analyzed by generalized linear modelling (GLM). Water temperature varied between 11°C and 30.5°C and daylength duration between 11 h 22 min and 14 hours 35 min. Sex genotyping revealed nearly balanced sex ratios of XY/YY (46-49.1%) and XX (50.9-54%) fish in cages 2-4 whereas the genotypic sex ratio in cage 1 was clearly biased towards XY/YY fish (60.6%). Phenotypic males ranged from 42 to 54.4% in cages 1-3. Cage 4, in turn, had significantly more phenotypic males (66%). The percentage of XX-males (phenotypic male/genotypic female) was 23.1% in cage 1, decreased to a minimum of 5.4% in cage 2, and gradually increased in cages 3 and 4 to a maximum of 40.7% in the latter. The percentages of XY/YY-females (phenotypic female/genotypic male) were highest in cage 1 (30%) and decreased progressively in the other cages to a significantly lower value (4.3%) in cage 4. These results generally support the findings of laboratory studies on the effect of temperature on sex determination of this species and also provide novel evidence of a XX genotype-specific masculinizing effect of short daylength. This article is protected by copyright. All rights reserved.
Studies of the relationships between the temporal variation of biological phenomena and environmental factors are essential to understanding the dynamics of communities. Phenology is a structuring element and, together with voltinism, is related to timing of reproductive activities. The aim of this study is to ascertain the structure and composition of the Chironomid assemblage and its emergence patterns in relation to the environmental variables through the use of the Chironomid pupal exuviae technique using the Neotropical streams as a model. The streams presented similar species compositions. The highest density of pupal exuviae was recorded during spring and the greatest richness in late summer and early autumn. Chironominae presented greater prevalence throughout the year with oscillations for Orthocladiinae and Tanypodinae. Chironominae and Tanypodinae presented emergence peaks in spring-summer and Orthocladiinae in autumn-winter. Rainfall, photoperiod and water and air temperatures structured the Chironomid assemblage, influencing emergence. Univoltine, bivoltine and multivoltine species were recorded. The species presented interspecific synchronization in emergence peaks at different times of the year.
The growth rates and size at maturity of decapod crustaceans usually vary throughout latitudes. Here, we evaluated whether these life history traits can be stable within the same latitude range, where some environmental factors are constant, especially temperature. To this end, we estimated and compared the growth rates and size at sexual maturity of three populations of the fiddler crab Minuca vocator, located at latitude 23° S, in mangroves of the subtropical Brazilian coast. Variations in the growth rate of the abdominal width of females and of the propodus of the major cheliped of males were assessed by the allometric technique. The abdomen growth rates of females and the cheliped growth rates of males varied among the three populations, resulting in different sizes at maturity. These results do not support our prediction that growth rates and size at sexual maturity would remain stable in populations of the same latitude range. The differences in these life history traits could be a consequence of contrasting local conditions among mangroves. Therefore, we suggest that these crabs show plasticity and responsiveness to local-scale environmental variations, to optimize the energy allocation for maintenance, reproduction, and somatic growth.
The Patagonian steppe is a vast territory with a diverse array of aquatic environments with low fish richness, including several exotic species which are mostly salmonids. Unlike the Andean region, knowledge of the ichthyofauna and fisheries of the Patagonian plateau is comparatively scarce. The characteristics of the ichthyofauna and their assemblages and fisheries vary greatly in the large basins that cross the steppe. Fish assemblages of north Patagonia include elements of the Patagonian, Andean Cuyean, and Pampean ichthyological provinces, where Austral and Brazilic subregion species overlap. Salmonid richness increases from northern to southern latitudes, as do anadromous species. The steppe also presents some endorheic basins inhabited by species of high conservation value and restricted distribution. Threats and impacts that have been identified include land and water use, damming, pollution, climate change, and exotic species introduction. Historical and current management policies have permitted uncontrolled stocking of exotic species due to their high fishing value, thus favoring a reduction in the distribution and abundance of native fishes, including endangered species with an extreme degree of endemism.KeywordsPatagonian steppeNon-native speciesNative speciesManagement policiesSalmonid introductionsSalmonid impactFish assemblageRecreational and artisanal fisheries
Human disturbance might be perceived as a threat by animals and interfere in their vital activities. Urbanisation generates changes in habitat structure that allows only a low number of species to adapt, which results in a decrease of species richness and an increase of the abundance of a few dominant species. To survive in urbanised areas, animals need to be highly tolerant to human approximation. One key characteristic of successful invasive species is their high behavioural plasticity. This plasticity could translate to higher chances of surviving in urbanised areas and becoming tough competitors for native species. The Eurasian collared-dove is a successful invader in Europe, it arrived to México during the nineties and has been spreading in the country since. We compared its tolerance to human approximation to that of the already well-established feral pigeon and other native species in agricultural and urban sites. We found the Eurasian collared-dove is less tolerant to humans than the feral pigeon, but more tolerant than native species. Also, we observed that birds showed higher tolerance to humans in urban areas than in agricultural sites, regardless of the species. Interestingly, feral pigeons restrained their distribution to human settlements, and acting as a counterpart, common ground doves were only found in rural sites. However, the Eurasian collared-dove was present also in agricultural areas, which could suggest the Eurasian collared-dove represents a higher threat than the feral pigeon for native species in our study area. We highlight the importance to further understand the behavioural traits that could promote the Eurasian collared-dove invasion to better design management plans for dove diversity in urban areas.
Most studies exploring land use impacts have focused on taxonomic metrics, but interest in the functional approach has increased because it helps to understand the relationships between community structure and functioning of aquatic ecosystems. We evaluated how functional and taxonomic approaches contribute to assessing the effects of land use on macroinvertebrate assemblages of lowland streams. We also studied the relationships between both approaches. We sampled benthic macroinvertebrates in 17 sites with different land uses (agricultural, peri-urban, and extensive livestock). We computed the taxonomic metrics and biotic indexes as well as functional richness (FRic), divergence (FDiv), dispersion (FDis), and Rao diversity indexes for each site. We performed general linear mixed models to compare land-uses and also performed correlation analysis between taxonomic and functional indexes. Taxonomic richness was significantly higher in extensive livestock than in the other two land uses, while Shannon diversity was significantly different between land uses (extensive livestock>peri-urban>agriculture). FRic and FDiv were significantly lower in peri-urban land use than in agricultural and extensive livestock sites. Only taxonomic richness showed a significant and positive relationship with FRic, FDis, and Rao, but they fit better to a logarithmic function. Therefore, an increase in taxonomic richness and Shannon diversity did not necessarily imply an increase in the functional aspects of the macroinvertebrate assemblage. Using only one of these approaches could lead to partial evaluations and loss of information. Combining them could improve bioindication and predictive potential and help assess the effects of multiple stressors on freshwater ecosystems to improve biomonitoring.
Nursery areas are essential habitats for sharks, offering protection and increasing the survival of newborns. We conducted interviews with local fishers and collected data from artisanal fishery landings between January 2013 and December 2019 to investigate Chetumal Bay as a nursery area for the bull shark (Carcharhinus leucas) in the Mesoamerican Reef region. The bull shark is a coastal euryhaline shark that inhabits temperate and tropical waters worldwide. In the Mexican Caribbean, bull sharks are caught mainly as bycatch in a multi-specific artisanal fishery using nylon bottomset gillnets, longlines, and hand lines. We record 63 bull sharks in the catches ranging from 67 to 125 cm TL corresponding to immature individuals, 23 neonates with either open or healing umbilical scars (67 and 78 cm TL), and 40 YOY with present but healed umbilical scars (79 to 125 cm TL), with a notable absence of large size juveniles and adults in the catches. Bull sharks were present in landings between May and November; the highest abundance was during July. Our data provide evidence to recognize Chetumal Bay as a nursery area for bull sharks, meeting all the criteria proposed to identify nursery areas. These findings constitute the first documented evidence of a bull shark nursery area in an estuary within the Mexican Caribbean as well as within the entire region of the Mesoamerican Reef System. Moreover, we discuss the importance of this nursery in light of a newly described distinct lineage of bull sharks in Chetumal Bay.
The aim of this study was to evaluate the toxic effects of the pesticide cypermethrin (CYP) in the digestive gland of the apple snail, Pomacea canaliculata, analysing histological and histochemical alterations. Adult snails were exposed to sublethal CYP concentrations (10, 25, and 100 µg/L) under acute (1 day) and sub-chronic (14 days) conditions. Histological analyses of the morphology of the digestive gland were performed and a histopathological condition index (HI) was calculated. Also, both intracellular accumulation of lipofuscins (LF) and neutral lipids (NL) were evaluated. CYP exposure induced tissue damage to this organ, such as disorganisation of the connective tissue, fibrosis, haemocytic infiltration, atrophy, and necrosis under acute and sub-chronic conditions. These alterations, integrated into a single HI value, revealed notable CYP effects during both acute and sub-chronic exposures. Cell type replacement, measured as VvBAS, was only observed in the sub-chronic treatment. Under acute conditions, the pyrethroid affected NL accumulation at the highest concentration, while in sub-chronic conditions NL accumulation was only observed at the lowest concentrations. P. canaliculata also showed a dose-dependent response of LF under acute CYP exposure conditions. However, under sub-chronic conditions, this parameter was not sensitive to pesticide exposure. All these relevant structural lesions may affect the normal function of the digestive gland, even though the species presented additional mechanisms, as infiltration of hemocyte and basophilic cell hyperplasia, that help it to tolerate the exposure to pollutants. This study showed that some histological and histochemical parameters are sensitive in P. canaliculata at CYP concentrations to which the snail could be exposed in the environments it inhabits.
Plastics, especially microplastics (<5 mm in length), are anthropogenic polymer particles that have been detected in almost all environments. Microplastics are extremely persistent pollutants and act as long-lasting reactive surfaces for additives, organic matter, and toxic substances. Biofilms are microbial assemblages that act as a sink for particulate matter, including microplastics. They are ubiquitous in freshwater ecosystems and provide key services that promote biodiversity and help sustain ecosystem function. Here, we provide a conceptual framework to describe the transient storage of microplastics in fluvial biofilm and develop hypotheses to help explain how microplastics and biofilms interact in fluvial ecosystems. We identify lines of future research that need to be addressed to better manage microplastics and biofilms, including how the sorption and desorption of environmental contaminants in micro-plastics affect biofilms and how microbial exchange between microplastics and the biofilm matrix affects biofilm characteristics like antibiotic resistance, speciation, biodiversity, species composition, and function. We also address the uptake mechanisms of microplastics by consumers and their propagation through the food web.
At the south of its geographical distribution, the fiddler crab Leptuca uruguayensis shows two population spawning events, with more than 65% of the females being ovigerous. The aim of this study was to assess the energy dynamics in L. uruguayensis females to estimate how they mix the capital and the income breeding strategies in the first and second spawns of the short reproductive season. The relationship between the hepatosomatic (HIS) and gonadosomatic (GSI) indices was used to assess the contribution of the hepatopancreas to ovary maturation, as indicative of the capital breeding strategy, whereas the feeding rate and the energy available in the food resource (sediment) were estimated to assess the importance of energy intake in ovary maturation, as indicative of the income breeding strategy. Before the first spawn, a significant negative relationship between the HSI and GSI (p< 0.001) and an increase of 28.2% in the feeding rate were recorded. This suggests that the first spawn was mainly supported by energy reserves in the hepatopancreas, indicating that females used mostly the capital breeding strategy. After the first spawn, total lipid content in the hepatopancreas decreased by 33%. On the days before the second spawn, the relationship between the HSI and GSI showed a negative but not significant (p= 0.125) trend, whereas the feeding rate increased even more. This suggests that the intense feeding activity provided the most important energetic source for ovary re-maturation, indicating that females used mostly the income breeding strategy. Also, in the second spawn, the GSI was 24.1% smaller, a fact that affected female fecundity and weight of the egg clutches, which were respectively 12% and 11% lower than in the first spawn. However, the energy supply allocated to each embryo was equivalent in both spawns. This study shows how L. uruguayensis females mixed the capital and income breeding strategies to take advantage of all available resources to produce two spawns in a short reproductive season.
Cadmium (Cd2+) and copper (Cu2+) are considered immunotoxic metals and their presence in combination in the aquatic environment may cause effects on shrimp species as Litopenaeus vannamei. Thus, this research evaluates the combined effects of Cd2+ and Cu2+ on shrimp inoculated with Vibrio harveyi bacteria. The experiments were performed at 96-hours of exposure to sublethal concentrations of both metals. No mortality was observed in organisms exposed to the sum of Criterion of Continuous Concentration (ΣCCC) in Cd + Cu mixture and those inoculated with V. harveyi. Higher clotting times were recorded in Cd + Cu + V. harveyi treatment at higher metal concentrations. No significant differences (P > 0.05) were recorded in hemocyanin content between shrimp exposed to metals and those experimentally infected. Significantly higher (P < 0.05) total hemocyte count (THC) was recorded at 96 h exposure in the ΣCCC and 10% treatments of Cd + Cu + V. harveyi experiment. Regarding Cd + Cu + V. harveyi bioassay, the highest phenoloxidase (PO) activity was recorded in shrimp inoculated with V. harveyi (0.326 ± 0.031 PO units/mg protein) at 96-h exposure. The lowest PO activity was observed in organisms exposed to Cd + Cu + V. harveyi. Regarding superoxide dismutase (SOD) activity, shrimp exposed to higher metal concentrations at 96 h showed the lowest hemolymph activity (6.03 ± 0.62 SOD units/mL). Protein decrease was observed in organisms exposed to metal mixture. The results showed that L. vannamei could be more susceptible to V. harveyi when exposed to Cd + Cu.
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