Temperature effects on life history traits of two sympatric branchiopods from an ephemeral wetland

Consolidation of temperature-dependent toxicity and thermoregulatory behavior into risk assessments of insecticides under thermal scenarios: A prospective study on Eremias argus

In this study, the temperature-dependent chemical toxicity of three insecticides and the resulting thermoregulatory (TR) behavior of the lizard Eremias argus have been consolidated into the current risk assessment framework. According to acute dermal toxicity assays, an increase of ambient temperature from 15 °C to 35 °C decreased the acute dermal toxicity of beta-cyfluthrin (BC) but increased the toxicity of chlorpyrifos (CPF). The toxicity of avermectin (AVM) did not show significant temperature-dependent responses. Based on thermal preference trials, lizards changed their body temperature via TR behavior to adaptively reduce toxicity under sub-lethal doses, which can be understood as a "self-rescue" behavior attenuating lethal effects. However, the risk quotient indicated that the effectiveness of this "self-rescue" behavior is limited. Metabolomics analysis showed that six different metabolites (i.e., creatine, glutamate, succinate, N-acetylaspartate, acetylcholine, and lactate) contributed to TR behavior changes. Biochemical assays and insecticide residue results demonstrated that the temperature-dependent toxicity of BC, CPF, and AVM affected lizards in the three aspects of biotransformation, oxidative stress, and neurometabolic interference. This work clarifies the ecotoxicological impacts of representative insecticides on reptiles from toxicological understanding to risk relevance. This knowledge may improve ecological predictions of agrochemical applications in the context of global climate change.

Trans- and Within-Generational Developmental Plasticity May Benefit the Prey but Not Its Predator during Heat Waves

Simple Summary

Heat waves can have fatal effects on arthropods such as insects and mites since their heat tolerance is often lower than the diurnal maximum temperatures during heat waves. Plastic modifications by the parents, however, can rapidly result in favorable adaptations in offspring traits. This question was investigated by using a prominent natural enemy/pest couple in biological control, the predatory mite Phytoseiulus persimilis and its prey, the spider mite Tetranychus urticae. We exposed both species separately to extreme or mild heat waves during their juvenile development, a vital phase of arthropod life, for two generations and assessed various fitness-relevant parameters of the offspring generation. Under extreme heat waves, adult body sizes of predator and prey males and prey females were insensitive, when they derived from parents also reared under extreme heat waves. Irrespective of their origin, offspring reached earlier adulthood under extreme heat waves. In general, prey benefitted more from parental modifications compared to the predator. However, further investigations are needed to verify whether these changes affect the interactions between the predators and their prey to an extent that it may jeopardize biological control during extreme heat waves.

Abstract

Theoretically, parents can adjust vital offspring traits to the irregular and rapid occurrence of heat waves via developmental plasticity. However, the direction and strength of such trait modifications are often species-specific. Here, we investigated within-generational plasticity (WGP) and trans-generational plasticity (TGP) effects induced by heat waves during the offspring development of the predator Phytoseiulus persimilis and its herbivorous prey, the spider mite Tetranychus urticae, to assess plastic developmental modifications. Single offspring individuals with different parental thermal origin (reared under mild or extreme heat waves) of both species were exposed to mild or extreme heat waves until adulthood, and food consumption, age and size at maturity were recorded. The offspring traits were influenced by within-generational plasticity (WGP), trans-generational plasticity (TGP), non-plastic trans-generational effects (TGE) and/or their interactions. When exposed to extreme heat waves, both species speeded up development (exclusively WGP), consumed more (due to the fact of WGP but also to TGP in prey females and to non-plastic TGE in predator males), and predator females got smaller (non-plastic TGE and WGP), whereas prey males and females were equally sized irrespective of their origin, because TGE, WGP and TGP acted in opposite directions. The body sizes of predator males were insensitive to parental and offspring heat wave conditions. Species comparisons indicated stronger reductions in the developmental time and reduced female predator-prey body size ratios in favor of the prey under extreme heat waves. Further investigations are needed to evaluate, whether trait modifications result in lowered suppression success of the predator on its prey under heat waves or not.

Preliminary Study of Temperature Effects on Size and Shape in the Modern Spinicaudatan Eulimnadia texana (Crustacea: Branchiopoda)

Studies of temperature effects on morphology in Spinicaudata have focused on length, with no data on shape. To fill this gap, size and shape variability in response to temperature fluctuations was investigated by rearing the modern spinicaudatan Eulimnadia texana. Two days after hydration, juvenile individuals were separated into four different temperature treatments: 20°C, 23°C, 26°C, and 29°C. Hermaphrodite size and shape were analysed by looking at linear combinations of size variables and using Fourier shape analysis; methods that are also used to describe fossil size and shape for better comparison. Size differences were considerable, with reduced growth at low and high temperatures and accelerated growth at the optimum temperature of 26°C, revealing that the reaction of size to increasing temperature is non-linear. The height of the dorsal margin, which is associated with space for egg production in Eulimnadia texana, accounts for a high amount of size variability in this species and, presumably, in most of the Limnadiidae. Hermaphrodite shapes reared under temperatures of 20°C and 29°C are statistically distinct, while intermediate temperatures yield intermediate shapes. The rate of shape change along temperature is comparatively low between 23°C and 26°C and accelerated at lower and higher temperatures. With increasing temperature, the highest point of the dorsal margin is shifted towards the anterior of the carapace, while it assumes a median position at 20°C. Our result that temperature has strong effects on carapace size and shape implies considerable ecophenotypic variability in Spinicaudata.

Population Density Effects on Carapace Growth in Clam Shrimp: Implications for Palaeontological Studies

Fossil morphological data are time-averaged and generally reflect an overlap of different sources of carapace variability. To examine whether a proposed relationship between size and population density in fossil spinicaudatans is biologically meaningful, we set up rearing experiments involving two extant species: Eulimnadia texana and Eocyzicus argillaquus. Three and five days after hydration, clam shrimp were transferred into cups of various population densities that ranged between 1 and 15 inds/400 ml. Size and shape were measured 14 and 16 days after hydration, respectively. Every second day, we recorded length and sex of E. texana, which matured faster in lower-density cups. According to our growth model, population density and maximal carapace length follow a logarithmic relationship. At maturity, hermaphrodites yielded similar lengths across all population densities (~4.7 mm at 24°C), independent of age. Hence, clam shrimp can put off reproductive maturity as a response to decreased growth under higher density conditions. Growth rate generally decreases at maturity, but that effect is more pronounced in clam shrimp of high population densities, while low-density adults keep growing. For both species, multivariate analyses reveal that carapace size of low-density individuals is significantly larger than carapace size of higher-density individuals, while size values of intermediate densities cannot be distinguished. Shape distinction is strong in hermaphrodites of E. texana: 39.8% of the density-dependent shape variation is associated with relative umbo height, which is generally higher in individuals of smaller population densities. The H/L ratio, which is often used as a simple shape indicator, does not contribute to the main variation in shape, but it forms one of several ratios significant for 18.3% of the shape variability. In turn, the H/L ratio drives 30% of the shape variation in E. argillaquus. In addition, higher densities triggered shifts in ontogenetic growth trajectories in one third of the individuals, which led to aberrant morphologies. The present rearing experiment shows that some of the morphological variability on fossil bedding planes can be explained by population density. Also, it implies a considerable amount of ecophenotypic variability in Spinicaudata that affects our understanding of fossil taxonomy and palaeoecology.