Somatic Growth Rate Research Articles

Water Temperature, Prey Concentration and Salmonid Density Influence Daily Growth of Wild Juvenile Salmonids in Tributaries of the Upper Salmon River, Idaho (USA)

ABSTRACT Theory, experiments and field studies indicate that the somatic growth rate of freshwater consumers is shaped by the individual, additive and multiplicative effects of multiple factors, including consumer size and condition, temperature, prey resources and biotic interactions. While our understanding of how these factors affect wild populations of freshwater consumers is improving, the topic remains poorly studied, especially with respect to mobile species. Here, we report on an 8‐year, seven‐stream (n = 49 stream‐year combinations) observational study examining the individual and interactive effects of invertebrate prey concentration (F, mg/m3), mean daily water temperature (T, °C) and juvenile Chinook salmon (Oncorhynchus tshawytscha) density (D, fish/100 m2) on summer daily growth rates (%/d) of mobile, anadromous, juvenile Chinook salmon (age‐0+, n = 382) and sub‐yearling (age‐0+, n = 61) and yearling (age‐1+) steelhead trout (O. mykiss, n = 70) rearing in cold (mean daily summer: 12.1°C, range: 4.2°C–16.7°C) mountain tributaries of the Salmon River basin in central Idaho (USA). AICc model selection indicated that daily juvenile salmonid growth positively correlated with water temperature, prey biomass concentration, local juvenile Chinook density and the interaction between water temperature and food but with species and age‐specific differences. Water temperature was a covariate in all top‐ranked models, with daily growth (%/day) rate increasing (0.05%–0.23%/d) linearly with mean daily summer water temperature. In addition to a direct positive relationship with daily growth rate, there was evidence that prey concentration positively interacted with water temperature to accelerate daily growth (F × T). The positive relationship between juvenile salmonid daily growth rate and juvenile Chinook density is difficult to explain and could result from confounding factors. The individual success observed in these streams may contribute to population‐level benefits for the focal consumers, as prey‐rich, warm summers may result in larger individuals with higher energy reserves at the end of the summer/autumn growing season, contributing to improved overwinter survival. Our results, taken in combination with evidence from models, experiments and observational studies, have climate change implications. Current and predicted increases in water temperature will necessitate higher rates of prey consumption by aquatic ectothermic consumers to offset accelerated metabolic demands. Thus, to improve the resilience of mobile freshwater consumers in a warming climate, we suggest that natural resource managers not only consider physical and chemical habitat conditions but also biotic conditions, including the spatiotemporal quantity and quality of prey resources.

The Influence of Different Dietary Categories on Life-History of Daphnia pulex

The type and amount of food that Cladocera species eat is known to affect their growth, development, capacity for reproduction, and ultimately the size of their populations. This study examines the influence of different diet types and mixtures on the Daphnia pulex (Leydig, 1860) life-history characteristics such as development, growth, and reproduction in a lab setting. D. pulex was fed with a yeast diet (Saccharomyces cerevisiae), a fresh green algal diet (Scenedesmus acutus), an aquarium fish feed diet (Arthrospira platensis), and a mixture diet (yeast, algae and fish feed) in a controlled static experiment for 21 days in the study. When D. pulex was fed with only one type of food, body weight, body size, somatic, and population growth rates decreased compared to the mixed diet but continued to increase compared to the control group throughout the 21-day experimental duration (P≤0.05). In contrast, according to morphometric measurements, the effect of a diet containing only cyanobacteria caused a stagnation in growth rates, while growth rates increased in those fed with cyanobacteria-containing feeds added to the mixed diet (P≤0.05). Our results show that the type of food and its mixtures significantly affect the vital characteristics of the D. pulex population.

Population dynamics of a desert riverine turtle, Pseudemys gorzugi, at the northern edge of its range

Estimating the key demographic parameters of animal populations can enhance our understanding of system dynamics and assist in developing and improving conservation decision–support models. The Rio Grande cooter Pseudemys gorzugi is a conservation reliant freshwater turtle native to lower Rio Grande River Basin (USA and Mexico), with limited knowledge regarding its natural history and population dynamics. In this study, we used seven years of capture–mark–recapture data from the northern edge of the species' range to estimate survival probabilities, changes in abundance, and the probability of transitioning between different size classes while explicitly accounting for the sampling process. We found relatively high survival probabilities across different strata, with large juveniles exhibiting the highest survival (0.98) and small juveniles the lowest (0.71). However, transition probabilities between strata were low, indicating slow somatic growth rates. Our pattern‐oriented modelling revealed a low overall mean estimate of egg survival (0.024), warranting further empirical confirmation. Our study provides the first comprehensive demographic analysis of P. gorzugi encompassing an array of size and sex classes. Overall, we consider the population of P. gorzugi in the Black River robust, highlighting the importance of this river system to the species' persistence in the northern extent of its range, where the population is isolated from its broader distribution. The demographic estimates and ecological insights provided by our study offer critical data for parameterizing decision‐support models to ensure that P. gorzugi conservation strategies are grounded in the best available science.

MicroRNA miR-210 Modulates the Water Flea Daphnia magna Response to Cyanobacterial Toxicity.

As a key form of post-transcriptional regulation, microRNAs (miRNAs) regulate gene expression by binding to target mRNAs, leading to mRNA decay or translational repression. Recently, the role of miRNAs in the response of aquatic organisms to environmental stressors has emerged. Daphnia, widely distributed cladocerans, play a crucial role in aquatic ecosystems. Cyanobacterial blooms often cause Daphnia populations to decrease, thereby disrupting ecosystem functionality and water quality. However, the post-transcriptional mechanisms behind Daphnia's response to toxic cyanobacteria are insufficiently understood. This study investigated the role of miR-210, a multifunctional miRNA involved in stress response and toxicity pathways, and its target genes (MLH3, CDHR5, and HYOU1) in two Daphnia magna clones exposed to toxic Microcystis aeruginosa. Results showed that M. aeruginosa inhibited somatic growth rates, led to microcystin accumulation, caused abnormal ultrastructural alterations in the digestive tract, and induced DNA damage in both clones. Notably, exposure significantly increased miR-210 expression and decreased the expression of its target genes compared with the controls. We identified miR-210s regulation on clonal-tolerance variations in D. magna to M. aeruginosa, emphasizing miRNAs' contribution to adaptive responses. Our work uncovered a novel post-transcriptional mechanism of cyanobacterial impact on zooplankton and provided essential insights for assessing cyanobacterial toxicity risks.

Impacts of estuarine habitat degradation on the modeled life history of marine estuarine-dependent and resident fish species.

Shallow coastal and estuarine habitats play an essential role in the life cycles of many fish species, providing spawning, nursery, feeding, and migration areas. However, these ecologically valuable habitats are increasingly threatened by anthropogenic activities, causing substantial changes in both habitat availability and quality. Fish species use these shallow coastal habitats and estuaries during various life stages, leading to their categorization into guilds based on how and when they rely on these areas. This differential functional use of estuaries means that changes to these habitats may affect each guild differently. To understand the impact of estuarine habitat degradation on fish populations, it is therefore necessary to consider the full life cycle of fish and when they rely on these coastal habitats. Here, we use conceptual size-structured population models to study how estuarine habitat degradation affects two functionally different guilds. We use these models to predict how reduced food productivity in the estuary affects the demographic rates and population dynamics of these groups. Specifically, we model estuarine residents, which complete their entire life cycle in estuaries, and marine estuarine-dependent species, which inhabit estuaries during early life before transitioning offshore. We find that total fish biomass for both guilds decreases with decreasing food productivity. However, the density of juveniles of the marine estuarine-dependent guild can, under certain conditions, increase in the estuary. This occurs due to a shift in the population biomass distribution over different life stages and a simultaneous shift in which life stage is most limited by food. At the individual level, somatic growth of juveniles belonging to the estuarine-dependent guild decreased with lower food supply in the estuary, due to increased competition for food. The somatic growth rates of fish belonging to the resident guild were largely unaffected by low food supply, as the total fish density decreased at the same time and therefore the per-capita food availability was similar. These outcomes challenge the assumption that responses to habitat degradation are similar between fish guilds. Our study highlights the need to assess not only fish biomass but also size distributions, survival, and somatic growth rates for a comprehensive understanding of the effects of habitat degradation on fish populations. This understanding is crucial not only for estuary fish communities but also for successful conservation and management of commercially harvested offshore population components.

First insight of the intergenerational effects of tri-n-butyl phosphate and polystyrene microplastics to Daphnia magna

As an emerging organic pollutant, tributyl phosphate (TnBP) can be easily adsorbed by microplastics, resulting in compound toxic effects. In the present work, the effects of polystyrene microplastics (PS-MPs) and TnBP on the survival, growth, reproduction and oxidative stress of Daphnia magna (D. magna) have been evaluated through multigenerational test. Compared with the alone exposure groups, the somatic growth rate and the expression values of growth related genes rpa1, mre11, rnha, and rfc3_5 in the F1 generation of the combined exposure groups were significantly lower (p < 0.05), indicating synergistic effect of PS-MPs and TnBP on the growth toxicity and transgenerational effects. In addition, compared with the PS-MPs groups, significantly lower average number of offspring and expression values of reproduction related genes ccnb, mcm2, sgrap, and ptch1 were observed in the combined exposure group and TnBP group (p < 0.05), indicating TnBP might be the major factor causing reproductive toxicity to D. magna. Although PS-MPs and TnBP alone or in combination also had toxic impacts on the growth, survival and reproduction of D. magna in generations F0 and F2, the effects were less than F1 generation. Regarding oxidative stress, the activity of SOD, CAT and GSH-Px and MDA content in the generations F0 and F1 of combined exposure groups were higher than the TnBP group but lower than the PS-MPs groups, suggesting that PS-MPs might be the dominant cause of the oxidative damage in D. magna and the presence of TnBP would alleviate oxidative stress by reducing the bioaccumulation of PS-MPs. The present work will provide a theoretical basis for further understanding of the toxic effects and ecological risks of combined TnBP and microplastic pollution on aquatic organisms.

Among‐river pattern in relative abundance of two salmonid fishes reflects temperature‐dependent competition

Abstract Temperature is a key driver in determining species distribution and abundance across climatic and geographical gradients. This occurs through direct physiological effects of temperature on performance, but may also result from temperature effects on species interactions. In the current study we experimentally test for temperature‐dependent competition between juvenile anadromous Atlantic salmon and brown trout and evaluate the role of temperature in shaping the relative abundance of these species across 88 Norwegian rivers. When the two species were reared in allopatry their somatic growth rates were similar across a range of temperatures (4–16°C). When reared in sympatry, the growth of salmon was greatly reduced at the coldest temperature relative to when reared in allopatry, whereas this was not the case for trout. The effect of interspecific competition on growth was more similar for the two species at warmer temperatures. Thus, interspecific competition effects were strongly asymmetric only at the lowest temperature, with trout outcompeting salmon. The results from the experiment were reflected in qualitative patterns of relative abundance of salmon and trout in natural populations, which shifted from being trout dominated in rivers with low summer temperatures to being salmon dominated in warmer rivers. These results provide an empirical example of how temperature effects on the relative abundance of species can only be understood in light of information about temperature‐dependent species interactions.

Developing isotopic proxies to reconstruct the metabolic rates and thermal histories of octopus

Understanding an animal's metabolic rate and thermal history is pivotal for ecological research. Recent studies have proposed the use of stable carbon and oxygen isotopes (δ13C and δ18O) in biogenic carbonates as proxies of metabolic rate and experienced temperature, respectively, to overcome the challenges of directly measuring these data in the field. Our study represents the first experimental investigation to develop δ13C and δ18O proxies in octopus. Octopus berrima hatchlings were raised in captivity, at varying water temperatures, for up to 110 days. O. berrima statoliths were then subsequently analysed for δ13C and δ18O values. The proportion of metabolically derived carbon, or respired carbon (Cresp), increased as the octopus grew (slope = 0.076, R2 = 0.72), suggesting an influence of somatic growth rate and body mass on δ13C values. Additionally, we identified an inverse correlation between δ18O values and environmental temperature (slope = −0.163, R2 = 0.91), which was subsequently used to develop a thermal reconstruction model. Our experiment aids in interpreting stable isotopic values in statoliths and their application as temperature and metabolic proxies in wild-caught octopus. Such proxies will increase our monitoring capabilities of these ecologically and commercially significant cephalopods and contribute to their conservation and effective management.

Ecomorphological adaptation of Scorpaena porcus (Linnaeus, 1758): evidence from two different environments revealed by sagittae features and somatic growth rates

Improve the knowledge base on the ecomorphological adaptation of teleost species to different environments, trying to reconstruct how habitat can shape sagittae, is essential for conservational purposes, evolutionary evaluations, and population dynamics studies. Here is provided a comparative study between sagittae features, growth rates and age composition of two Scorpaena porcus populations inhabiting the Mediterranean waters, one from the Strait of Messina (Central Mediterranean Sea) and one from the Split area (Adriatic Sea). Additionally, the stomach contents of the Messina specimens have also been analysed to provide some preliminary information on the diet of S. porcus. A total of ninety individuals, half from each area, have been obtained from two extremely different environments. Results showed an overall different morphology, shape, and morphometry of sagittae among the size classes of the two investigated populations. Samples from Messina were characterized by a most elliptical and slender shape, with a more regular serration of margins than those from Split, which exhibited a wider sagitta, with a most enhanced anti-rostrum and longer rostrum. Concerning diet, specimens from Messina showed a preference for Crustacea (especially Brachyura and Amphipoda) and Teleost species, showing some differences with literature data from other geographical areas (Split one included). Results have confirmed the reliability of sagittae to detect the inter-population variability of S. porcus from different geographical areas, an essential tool for stock assessment, population studies and investigation on ecomorphological adaptation of teleost species to different habitats.

Seasonal variability in the otolith and somatic size relationship of Japanese anchovy larvae: Counter effects of somatic growth and temperature

Otolith microstructure analysis has played an essential role in understanding the recruitment mechanisms of fish. Despite the fundamental assumption of a close correlation between otolith size and somatic size in growth back-calculations, numerous studies have shown that somatic growth and temperature have negative and positive effects on otolith size at the same somatic size, respectively. However, few studies have investigated the effects of somatic growth and temperature on otolith and somatic size relationships at intra- and inter-cohort levels in the same study framework. The present study investigated the effects of somatic growth and temperature on the seasonal variability in the otolith and somatic size relationship in Japanese anchovy Engraulis japonicus larvae collected from multiple seasonal cohorts throughout the year in the Kii Channel, Japan. The otolith and somatic size relationships were strong within each seasonal cohort sample (R2 = 0.771–0.949), but the relationship became weaker when all the seasonal data were pooled (R2 = 0.571). Relative otolith size at a given somatic size (ROS) was negatively related to somatic growth rates within each seasonal cohort sample (i.e., at the intra-cohort level), but the relationship became weak when all the data were pooled. On the contrary, sea temperature had positive effects on ROS, which would explain the seasonal variability in the otolith and somatic size relationship. The multiple regression analysis showed that temperature influenced ROS almost six times more than somatic growth. Overall, the present study demonstrated that an uncoupling in the otolith size–somatic size relationship was generated by the counter effects of somatic growth and temperature. The observed counter effects should be taken into account in estimating past larval growth for larvae obtained from different environmental conditions.

Growth Dynamics of Flexor Muscle Fibers in Developing Male White Leghorn Chicks

The study examines the relationship between fiber orientation, functional activity, and growth dynamics in the flexor muscle of a male white Leghorn chick. It tests three hypotheses: similar histochemical fiber typing in muscle mass, distribution patterns influenced by species' functional activities, and fiber growth dynamics related to somatic growth rate. The study confirmed the hypothesis that all three basic fiber types (red, pink, and white) grow exclusively through hypertrophy. True hyperplasia was not evident in any age group, possibly in the late embryonic stage. Some cases of pink and white fibers showed splitting into smaller ones. All three basic fiber types grew by hypertrophy, regardless of location or functional activity. Muscle fiber growth in this muscle mass was directly related to the chick's somatic growth rate.

Food quality shapes gradual phenotypic plasticity in ectotherms facing temperature variability.

Organisms exhibit reversible physiological adjustments as a response to rapidly changing environments. Yet such plasticity of the phenotype is gradual and may lag behind environmental fluctuations, thereby affecting long-term average performance of the organisms. By supplying energy and essential compounds for optimal tissue building, food determines the range of possible phenotypic changes and potentially the rate at which they occur. Here, we assess how differences in the dietary supply of essential lipids modulate the phenotypic plasticity of an ectotherm facing thermal fluctuations. We use three phytoplankton strains to create a gradient of polyunsaturated fatty acid and sterol supply for Daphnia magna under constant and fluctuating temperatures. We used three different fluctuation periodicities to unravel the temporal dynamics of gradual plasticity and its long-term consequences for D. magna performance measured as juvenile somatic growth rate. In agreement with gradual plasticity theory, we show that in D. magna, fluctuation periodicity determines the differential between observed growth rates and those expected from constant conditions. Most importantly, we show that diet modulates both the size and the direction of the growth rate differential. Overall, we demonstrate that the nutritional context is essential for predicting ectotherm consumers' performance in fluctuating thermal environments.

Growth of Pacific staghorn sculpin (Leptocottus armatus) is reduced at contaminated sites in the Lower Duwamish River, Washington

The Lower Duwamish River is a highly industrialized waterway flowing into the densely urbanized Puget Sound waterfront of Seattle, Washington, USA. The river has been profoundly altered from its natural state following more than a century of channelization, recurrent dredging, shoreline armoring, and pollution discharges. As part of a Natural Resource Damage Assessment addressing historical pollution at three designated Superfund sites (i.e., the assessment area), juvenile Pacific staghorn sculpin (Leptocottus armatus) were sampled throughout the lower river in order to evaluate injury from exposure to polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), and butyltins (BTs). Sculpin live in close association with the river sediments within and upriver of the assessment area. Fish were collected for analysis of contaminant concentrations in composited whole bodies and stomach contents, as well as individual fish health metrics including daily somatic growth rates measured from otoliths. Sediment contaminant concentrations were also measured at sites near to fishing locations. Fish growth rates varied from 0.65 to 1.05 mm/day, and were significantly lower at unremediated downriver sites compared to upriver and remediated locations. Sculpin growth rates were negatively correlated with concentrations of PCBs in fish bodies, PAHs in stomach contents, as well as PCBs, DDTs and PAHs in sediment. Mixed effects models for whole-body and stomach content contaminants showed positive correlations between growth rate and water temperature. Temperature was not a significant confounding variable for the relationship between growth rate and sediment contaminants. Overall, these results show that juvenile sculpin are harmed by contaminant exposure in the Lower Duwamish River. Furthermore, this study demonstrates the utility of using paired biological and chemical indicators of pollutant-induced injury in a resident fish to inform a complex Natural Resource Damage Assessment and associated restoration efforts.

Aquatic insects balance growth with future supply of algal food resources

Many consumers depend on the contemporaneous growth of their food resources. For example, Tanytarsus gracilentus midges feed on algae, and because midge generation time is much longer than that of algae, individual midges benefit not just from the standing stock but also from the growth of algae during their lifespans. This implies that an intermediate consumption rate maximizes midge somatic growth: low consumption rates constrain midge growth because they do not fully utilize the available food, whereas high consumption rates suppress algal biomass growth and consequently limit future food availability. An experiment manipulating midge presence and initial algal abundance showed that midges can suppress algal growth, as measured by changes in algal gross primary production (GPP). We also found a positive relationship between GPP and midge growth. A consumer–resource model fit to the experimental data showed a hump‐shaped relationship between midge consumption rates and their somatic growth. In the model, predicted midge somatic growth rates were only positively associated with GPP when their consumption rate was below the value that optimized midge growth. Therefore, midges did not overexploit algae in the experiment. This work highlights the balance that consumers which depend on contemporaneous resource growth might have to strike between short‐term growth and future food availability, and the benefits for consumers when they ‘manage' their resources well.

Effects of release method on the survival, somatic growth, and body condition of headstarted turtles

AbstractHeadstarting involves ex situ rearing of vulnerable life stages, then releasing individuals into the wild once they are larger and less vulnerable to predation. Sometimes, headstarted animals display underdeveloped behaviors that may lead to an acclimation period of reduced survival and growth after release. Using data from a 6‐year headstarting program, we tested whether the early release condition affected survival, body condition, and somatic growth rate in 2 groups of headstarted Blanding's turtles (Emydoidea blandingii) released into Rouge National Urban Park (RNUP) in Toronto, Ontario, Canada. The first group included turtles released directly into the wild (i.e., hard release). The second group included turtles released into an in situ enclosure in which individuals remained for a week without food supplementation before being fully released into the wild (i.e., delayed release). Release condition did not affect survival or growth rate. In the delayed‐release group, body condition initially declined rapidly and remained low for up to 1 year after release. Given the lack of wild juveniles in RNUP, we compared body condition of headstarted turtles at various time points since release to similar‐sized wild juveniles from 2 other Ontario populations, one from Algonquin Provincial Park (APP) and one near Lake Erie (LE). Body condition of headstarted turtles was similar to those of wild APP turtles regardless of release method, and higher than those of wild LE turtles. Our results indicate that delayed release did not improve post‐release outcomes for headstarted turtles in an urban landscape and headstarted turtles sustain similar health metrics as wild turtles.

Contribution of the nursery areas to the major fishing grounds of the Brazilian sardine (Sardinella brasiliensis) in Southeastern Brazilian Bight inferred from otolith fingerprints

In the late seventies, studies on the population structure of Sardinella brasiliensis suggested the existence of two stocks (23–25°S and 26°S−28°S) based on distinct regional somatic growth rates and spawning areas. This scenario was recently confirmed by using geochemical signatures of whole otoliths combined with basic biological data from two-year-old individuals collected in southeast-south Brazil. However, information about sardine movements and connectivity between their main juvenile recruitment areas and the adult fishing grounds is currently limited. In this work, otolith natal elemental fingerprints (core section) of recruits (age 0+) and adults (age 2+), collected respectively in the main spawning areas (2019) and fishing grounds (2021) were evaluate. Otolith geochemical signatures (element/Ca) of recruits were compared with those of adult fish from the same cohort to estimate connectivity between juvenile recruitment areas (Rio de Janeiro RJ: 22°S, São Paulo SP: 23°S and Santa Catarina SC: 26°S) and regional adult populations captured in the major fishing grounds (22–23°S, 24–25°S and 26–27°S). Uni and multi-elemental signatures showed significant differences for recruits and adult’s individuals. This variability was mainly driven by Ba/Ca, Cu/Ca and Mg/Ca ratios. Pairwise comparisons associated recruits and adults from the northern distribution area (RJ+SP), but differentiated them from those individual from south (SC). The leave-one-out matrix combining otolith fingerprints reassigned the individuals to their original areas with moderate to high accuracy, for both recruits (RJ: 79%, SP: 73% and SC: 67%) and adults (RJ: 75%, SP: 60% and SC: 69%). A multinomial logistic regression suggested that for the 2019 cohort the replenishment of adult populations of S. brasiliensis along the Southeastern Brazilian Bight was mostly derived from the northern recruitment area (RJ+SP=89%). Nonetheless, minor contribution from the southern counterparts to the northern stock was detected (11%), supporting the hypothesis of meta-population structure for this species.

Somatic Growth and Maturity for Four Species of River Cooter Including Pseudemys concinna suwanniensis, P. nelsoni, P. peninsularis, and P. texana.

Pseudemys is a genus of commonly occurring freshwater turtles with limited growth information across their long lifespans. We used 11,361 mark-recapture events to estimate the somatic growth rates of P. nelsoni, P. peninsularis, P. concinna suwanniensis, and P. texana from freshwater springs and developed a Bayesian growth model to estimate the species-specific, site-specific, and individual effects on growth. We corroborated evidence for fast juvenile growth and slower adult growth in Pseudemys but found uncommonly fast growth rates, with turtles doubling or tripling in size in the first year. P. texana males had the smallest average maximum size (L∞, 243 mm), while P. c. suwanniensis females had the largest (423 mm). Environmental conditions at springs had significant effects on k, the growth coefficient, but not L∞. We derived, using a ratio of length at maturity to L∞ (71.7% and 87%, males and females), that females matured 1.15-1.57 times older than males except for P. c. suwanniensis, which matured three times older. Given the local abundance declines in many Pseudemys from anthropogenic impacts, this study provides important baseline life history information for Pseudemys species for use in ongoing conservation efforts and presents a novel hierarchical modeling approach using a long-term mark-recapture dataset.

Temperature-dependent oxygen isotope fractionation in otoliths of juvenile Chinook salmon (Oncorhynchus tshawytscha)

Oxygen thermometry has become a widely used technique for reconstructing thermal history in calcifying organisms but interpretation can be subject to predictive error from vital effects. To better understand these processes in Chinook salmon (Oncorhynchus tshawytscha) we experimentally constructed a temperature-dependent, otolith–water fractionation relationship for oxygen isotopes (δ18O) by rearing post-yolk absorptive juvenile fish at nominal temperatures from 6 to 21 °C. Temperature and otolith precipitation rate had significant effects on the otolith–water δ18O fractionation, but somatic growth rate did not. The slope of the δ18O fractionation equation also differed significantly from that of synthetic aragonite. Our results suggest the expression of kinetic effects on δ18O fractionation in otoliths of Chinook salmon that are increasingly constrained at higher temperatures by other physical and physiological processes involved in mineral formation. Species-specific δ18O fractionation equations have considerable utility to reconstruct temperature history in Pacific salmon, but applications should recognize the potential for inferential uncertainty arising from interacting vital effects.

Effects of Glyphosate on Female Reproductive Output in the Marine Polychaete Worm Ophryotrocha diadema.

Glyphosate is a broad-spectrum herbicide widely employed in agriculture. Exposure to this genotoxic and endocrine-disrupting compound has adverse effects on terrestrial and aquatic organisms and on humans as well. Here, we explored the effects of glyphosate on female reproductive output and somatic growth rate in the marine polychaete worm, Ophryotrocha diadema. Adult focal individuals were exposed to different concentrations of pure glyphosate (0.0, 0.125 0.250, 0.500, 1.000 µg/mL) administered once a week for 3 weeks. Toxic effects and mortalities were observed at the three higher concentrations, whereas only a decrease in growth rate was noted after exposure to 0.125 µg/mL, which did not affect female allocation. An area of focus in future studies should be the effects of contaminants, their metabolites, and ecologically relevant human-driven stressors in the context of global warming.

Transcriptome analysis reveals the molecular basis of anti‐predation defence in Daphnia pulex simultaneously responding to Microcystis aeruginosa

Abstract1. The influence of cyanobacteria on interspecies interactions has received growing attention as a predictor of aquatic ecosystem function. It is well‐known that cyanobacteria greatly affect predator‐induced phenotypic plasticity in planktonic animals. However, the underlying molecular mechanism remains unclear.2. Here, we used Daphnia pulex as a model organism for inducible defence, examining its morphological and life‐history responses to fish kairomone while feeding on 100% Chlorella pyrenoides, or while feeding on 70% Chlorella and either microcystin‐producing or ‐free Microcystis aeruginosa, separately. Transcriptome profiles of kairomone‐exposed D. pulex fed different types of food were detected using RNA‐seq. How the differentially expressed genes and pathways identified are responsible for the altered adaptive traits under Microcystis stress was discussed.3. Daphnia pulex fed 100% Chlorella matured at a smaller body size, elongated tail spine length, and produced smaller offspring as adaptive morphological and reproductive responses to fish kairomone. These anti‐predation defences entailed a cost in decreased somatic growth rate. Microcystis stress caused defence trade‐offs in both morphology and reproduction: reduction of body size at maturity was stronger whereas tail spine elongation was unchanged or inhibited. Given that reproductive investment was reduced overall in Daphnia exposed to fish kairomones, there was a trade‐off for unchanged offspring size by reducing offspring number in Daphnia fed Microcystis. Defence‐induced costs to growth were increased by Microcystis exposure.4. Transcriptome analysis revealed that neuronal signals including acetylcholine and glutamate signalling implicated in kairomone reception and/or transmission exhibited stronger responses under Microcystis stress. Cuticle development associated with the biosynthesis of wax esters and chitin, modification of lipo‐chitin saccharides, and the stability of collagen triple helix apparently participated in the morphological changes. The arachidonic acid pathway and biosynthesis of cholesterol and steroid hormones mediated altered reproductive performance. In addition, metabolic processes such as detoxification, food assimilation, lysosome dysfunction and apoptosis activation were involved in the survival and growth of Daphnia, which may contribute to the increased defence‐induced cost in growth when fed Microcystis.5. Taken together, these findings advance our understanding of the molecular mechanisms underlying anti‐predation defensive responses by Daphnia to cyanobacterial stress. This work also provides a reference for further exploring the functional genes that mediate zooplankton–fish coevolution dynamics under eutrophic conditions.