Body Size Responses Research Articles

Carcass additions increase juvenile salmonid growth, condition, and size in an interior Columbia River Basin tributary

Numbers of anadromous fish returning to freshwater ecosystems have declined precipitously across much of western North America, reducing a potentially important resource subsidy for juvenile salmonids. We added carcasses to three sections of a Snake River tributary and assessed juvenile Chinook salmon (Oncorhynchus tshawytcha) and steelhead trout (Oncorhynchus mykiss) growth, body condition, size, and diet responses in summer and early fall. Juvenile salmonids consumed an abundance of eggs and carcass tissue, which increased energy rations. Within 3 weeks of carcass additions, juvenile Chinook and steelhead growth rates were 1.1–5 and 6–23 times greater in treatment reaches relative to control reaches, respectively. We used long-term tagging and detection data from this system to assess the relationship between juvenile Chinook size and emigration survival for two different juvenile life histories. The increased growth rates and body size in response to carcass additions, coupled with a positive relationship between body size and survival, suggest that juvenile salmonid rearing productivity and emigration survival may be limited by depressed returns of anadromous fishes in this system and potentially other tributaries of the Columbia Basin.

Responses of zooplankton body size and community trophic structure to temperature change in a subtropical reservoir.

Understanding the effects of global warming on trait variation and trophic structure is a crucial challenge in the 21st century. However, there is a lack of general patterns that can be used to predict trait variation and community trophic structure under the ongoing environmental change. We investigated the responses of body size and community trophic structure of zooplankton to climate related factors (e.g., temperature). Isotopic niche breadth was applied to investigate the community trophic structure across a 1‐year study from a subtropical reservoir (Tingxi Reservoir) in southeastern China. Body size and community isotopic niche breadth of zooplankton were larger during water mixing than stratification periods and correlated significantly with water temperature change along the time series. The contributions of intra‐ and intertaxonomic components to body size and community trophic structure variation showed significant relationships with the temperature change going from the mixing to stratification periods. Water temperature imposed direct effect on body size, while direct and indirect effect on the community trophic structure of zooplankton occurred through trophic redundancy along time series. Water temperature and community properties (e.g., body size, trophic redundancy, or trophic interaction) showed complex interactions and integrated to influence community trophic structure of zooplankton. Our results can expand the knowledge of how elevated temperature will alter individual trait and community trophic structure under future climate change.

Do New World pitvipers "scale-down" at high elevations? Macroecological patterns of scale characters and body size.

Bergmann's rule describes the macroecological pattern of increasing body size in response to higher latitudes and elevations. This pattern is extensively documented in endothermic vertebrates, within and among species; however, studies involving ectotherms are less common and suggest no consistent pattern for amphibians and reptiles. Moreover, adaptive traits, such as epidermal features like scales, have not been widely examined in conjunction with Bergmann's rule, even though these traits affect physiological processes, such as thermoregulation, which are hypothesized as underlying mechanisms for the pattern. Here, we investigate how scale characters correlate with elevation among 122 New World pitviper species, representing 15 genera. We found a contra‐Bergmann's pattern, where body size is smaller at higher elevations. This pattern was mainly driven by the presence of small‐bodied clades at high elevations and large‐bodied clades at low elevations, emphasizing the importance of taxonomic scope in studying macroecological patterns. Within a subset of speciose clades, we found that only Crotalus demonstrated a significant negative relationship between body size and elevation, perhaps because of its wide elevational range. In addition, we found a positive correlation between scale counts and body size but no independent effect of elevation on scale numbers. Our study increases our knowledge of Bergmann's rule in reptiles by specifically examining characters of squamation and suggests a need to reexamine macroecological patterns for this group.

Anuran 3D models reveal the relationship between surface area‐to‐volume ratio and climate

AbstractAimThe relationship size–environment has been continuously debated for ectotherms. Surface‐to‐volume ratios are recurrently suggested as the cause of body size responses to climate, but most inferences on organismal size clines stem from single linear measurements of body length. Here, we illustrate how new photogrammetric techniques can be applied to characterize amphibian morphologies with 3D models. Using the natterjack toad (Epidalea calamita) as model organism, we compared the performance of climatic models in accounting for body size (measured as snout‐to vent length, SVL) and body geometry (surface area‐to‐volume ratios) variation across macroclimatic gradients.LocationPalaearctic.TaxonEpidalea calamita (former genus Bufo).MethodsWe used photogrammetry techniques to reconstruct 104 museum specimens of Epidalea calamita into 3D models and to collect geometric data (volume and surface area) to calculate surface area‐to‐volume ratios (SA:V). We then apply spatial and non‐spatial regression to examine the relationships between SA:V, SVL and a set of bioclimatic variables.ResultsIn accordance with the water conservation hypothesis, SA:V decreased towards more arid environments, a pattern that remained consistent after accounting for spatial autocorrelation effects. Only mean annual temperature was significant correlated with SVL. The contrast between both sets of models indicates that more traditional body size metrics (SVL) and body geometry (SA:V) do not operate the same constraints.Main conclusionsWe show that the variation in SA:V can be explained by the geographical variation in aridity. Evaporative water loss in wet‐skinned ectotherms is highly dependent on the surface area of the skin exposed to the air. In contrast, SVL models detected that body length was more associated with mean annual temperature. This finding stresses the importance of selecting different metrics of body geometry and body size when examining variation across climatic gradients.

Trophic cascade strength is influenced by size frequency distribution of primary consumers and size-selective predation: examined with mesocosms and modeling

Understanding variation in trophic cascades is critical for developing management strategies for invasive and introduced species as well as in designing biomanipulation experiments. We evaluated, in fish driven trophic cascades, the responses of invertebrate biomass, body size, and production both experimentally and through a model. Experimental mesocosm treatments of small (Moina), large (Daphnia pulex), and mixed size zooplankton communities were characterized with and without size-selective fish (bluegill, Lepomis macrochirus). Experimental responses were typical of trophic cascades showing reduced biomass, body size and production of zooplankton and generally enhanced chlorophyll a. Although zooplankton biomass was similarly reduced in all fish treatments, production for the fish D. pulex treatment was lower than the other fish treatments because larger taxa have a lower ratio of production to biomass (P/B). As would be expected based on zooplankton production among fish treatments, response of chlorophyll a in treatments with D. pulex was faster and final concentration higher than in Moina or mixed size treatments. A model of changes in production under a range of reductions in body size and/or biomass, from no reduction to 99% reduction, supported experimental results indicating invertebrate production can be resilient to reduction of biomass when body size is reduced. Strength of trophic cascades may therefore, in part, be related to interactions among reduction in biomass, size-selective predation, and size frequency distribution and plasticity of prey community. Because size-selective predation is a common trait in trophic cascades, some level of compensation is likely in most trophic cascades.

Energy storage, body size and immune response of herbivore beetles at two different elevations in Costa Rica

The physiological condition and immune responses of organisms living at different elevations are expected to display local adaptations to the different climatic and biotic conditions. Small ectotherms with specialized diets are highly susceptible to environmental change, as their life cycle is largely affected by temperature and by the presence of specific resources. This study focuses on two species of rolled-leaf beetles (Chrysomelidae), both present at two different elevations in Costa Rica: Cephaloleia belti Baly, a diet-generalist, and Chelobasis bicolor Gray, a diet-specialist. Body size, energetic condition (lipid storage), muscle mass and immune condition (melanization response) were compared in beetle populations from a tropical rainforest (50 m elevation) and a tropical montane forest (2 000 m elevation). These measurements reflect current and past nutritional condition and hence are good estimators of individual fitness. We analyzed a total of 172 individuals from both species, sexes and elevations. We predicted that beetles at higher elevation would display larger body size, higher energetic condition and lower immune response associated with metabolic requirements and parasitic pressure in colder temperatures. In general, beetles at high altitude were larger, had more lipids and muscle and showed stronger melanization (i.e., immune response) than beetles at low altitudes. Such differences among populations at different elevations may reflect local adaptation to altitude or phenotypic plasticity. However, the effect of elevation was not equivalent amongst species or sex. Measuring physiological traits in organisms with broad elevational distributions could be useful in understanding possible species responses to climate change.

Experimental evidence of gradual size-dependent shifts in body size and growth of fish in response to warming.

A challenge facing ecologists trying to predict responses to climate change is the few recent analogous conditions to use for comparison. For example, negative relationships between ectotherm body size and temperature are common both across natural thermal gradients and in small‐scale experiments. However, it is unknown if short‐term body size responses are representative of long‐term responses. Moreover, to understand population responses to warming, we must recognize that individual responses to temperature may vary over ontogeny. To enable predictions of how climate warming may affect natural populations, we therefore ask how body size and growth may shift in response to increased temperature over life history, and whether short‐ and long‐term growth responses differ. We addressed these questions using a unique setup with multidecadal artificial heating of an enclosed coastal bay in the Baltic Sea and an adjacent reference area (both with unexploited populations), using before‐after control‐impact paired time‐series analyses. We assembled individual growth trajectories of ~13,000 unique individuals of Eurasian perch and found that body growth increased substantially after warming, but the extent depended on body size: Only among small‐bodied perch did growth increase with temperature. Moreover, the strength of this response gradually increased over the 24 year warming period. Our study offers a unique example of how warming can affect fish populations over multiple generations, resulting in gradual changes in body growth, varying as organisms develop. Although increased juvenile growth rates are in line with predictions of the temperature–size rule, the fact that a larger body size at age was maintained over life history contrasts to that same rule. Because the artificially heated area is a contemporary system mimicking a warmer sea, our findings can aid predictions of fish responses to further warming, taking into account that growth responses may vary both over an individual's life history and over time.

Absence of general rules governing molluscan body-size response to climatic fluctuation during the Cenozoic

ABSTRACT Body size is a key factor in predicting the outcome of organisms’ interaction with their environment. A negative temperature–size relationship (TSR) is claimed to be one of the universal responses to climatic warming. Studies on extant biota also predicted that groups with narrow latitudinal range, tropical affinity, and higher body size would show higher sensitivity to climatic fluctuation. To confirm the generality of these relationships among marine ectotherms, we compiled the data on body size and global temperature over the Cenozoic using a global database of marine molluscs of Class Gastropoda and Bivalvia. Molluscan species do not show any signature of TSR for any taxonomic, regional, or ecological category during the Cenozoic. We did not find any evidence supporting heightened response in groups with limited latitudinal spread or with large body size. The body-size response of tropical species is not different from those of temperate species. Response of infauna and epifauna does not show any difference either and hence, refutes the predicted variation due to difference in their thermal-specialisation. Our results highlight the limited validity of ‘universal rules’ in explaining the climate-induced morphological response of marine communities in deep time and underscore the complexity in generalising the biotic outcome of climatic fluctuation.

Shallow water ray-finned marine fishes follow Bergmann’s rule

Understanding the interspecific variation in body size across macroclimatic gradients has been of paramount importance to naturalists and biogeographers. Bergmann’s rule, which describes a trend of increasing body size polewards, is arguably the best-known ecogeographical rule in terrestrial environments but remains largely unexplored in the marine realm. In this study we tested Bergmann's rule in marine ray-finned fishes (Pisces, Actinopterygii), analyzing the relationship between body size and latitude in 5662 species. To examine possible underlying mechanisms, we adopted a cross-species approach to evaluate the association of body size with four predictors: Sea Surface Temperature, Net Primary Productivity, Salinity, and Human impact. We analyzed the relationships between body size and environmental and anthropogenic variables building mixed linear models, which considered the taxonomic structure in the data. We conducted complementary analyses dividing the data into five latitudinal bands. Actinopterygii showed a clear Bergmannian pattern, with the largest species observed in temperate regions, being the first global analysis on ray-finned fishes showing a pattern consistent with Bergmann’s rule. Sea Surface Temperature and Net Primary Productivity were the best predictors, in accordance with the time to sexual maturity and resource availability hypotheses. Our analyses based on latitudinal bands showed a differential response of body size to the environment, with temperature, salinity and human impact more strongly associated with size variation at cold environments. These results agree with previous studies on Bergmann’s rule for terrestrial ectothermic, freshwater and marine fishes. Our findings suggest that temperature rise in the ocean and growing human impact may have effects on the distribution of body size, thus altering ecosystem functioning. Fundamental differences often assumed to exist between marine and terrestrial systems are not so evidently reflected in the emergence of large-scale body size gradients.

Information use during movement regulates how fragmentation and loss of habitat affect body size.

An individual's body size is central to its behaviour and physiology, and tightly linked to its movement ability. The spatial arrangement of resources and a consumer's capacity to locate them are therefore expected to exert strong selection on consumer body size. We investigated the evolutionary impact of both the fragmentation and loss of habitat on consumer body size and its feedback effects on resource distribution, under varying levels of information used during habitat choice. We developed a mechanistic, individual-based, spatially explicit model, including several allometric rules for key consumer traits. Our model reveals that as resources become more fragmented and scarce, informed habitat choice selects for larger body sizes while random habitat choice promotes small sizes. Information use may thus be an overlooked explanation for the observed variation in body size responses to habitat fragmentation. Moreover, we find that resources can accumulate and aggregate if information about resource abundance is incomplete. Informed movement results in stable resource-consumer dynamics and controlled resources across space. However, habitat loss and fragmentation destabilize local dynamics and disturb resource suppression by the consumer. Considering information use during movement is thus critical to understand the eco-evolutionary dynamics underlying the functioning and structuring of consumer communities.

Environmental determination of body size in mammals: Rethinking ‘island dwarfism’ in the golden bandicoot

AbstractThere are several cases of insular animal species exhibiting dramatic differences in body size when compared with mainland counterparts. Such pronounced morphological changes can arise from divergent selection via differing resource availability, competition or predation pressure. Past studies have not been able to demonstrate a reversal of these morphological changes when populations are removed from their island situation. This study examines the body size response of populations of the Barrow Island ‘dwarf’ subspecies of golden bandicoot (Isoodon auratus barrowensis: Ramsay, 1887) following translocation to an island and mainland site within their former range. Skeletal and mass measurements, body condition and fecundity of released animals and their offspring were compared to data from the source population. When comparing bandicoots born at translocation sites to source populations, males were significantly larger in skeletal size and mass, females were also significantly larger and exhibited higher reproductive output (number, frequency and average mass of pouch young). These effects occurred in a gradient according to environmental conditions, where animals were smallest and least productive at the densely populated source site, larger and more productive on a nearby island, and largest and most productive at a mainland site with some nutritional supplementation. These changes in skeletal size, mass and fecundity took place in the first 1–4 generations (18 months post‐release), suggesting that the response is not explained by natural selection. We posit that the small size of golden bandicoots on Barrow Island (315.8 ± 4.2 g, this study, cf 569.4 ± 19.3 g, mainland) is not a genotypic response to selective pressures, but rather a reversible phenotypic response to more favourable environmental conditions. A reduction in competitive pressures appeared to allow bandicoots to grow to a larger size and mass, and allow greater reproductive output. Ecological processes relating to resource limitation appear to drive ‘island dwarfism’ in I. auratus, and may apply to other insular species with morphological differentiation.

CARDIOVASCULAR ADAPTATION TO PHYSICAL ACTIVITY IN ETHNICALLY DIFFERENT YOUNG ATHLETES

Objective: Cardiovascular adaptation to intense physical training is determined by many factors including age, gender, body size, load training, ethnicity and blood pressure response to exercise. Our retrospective study aimed to assess secondary left ventricular (LV) remodelling to exercise, in terms of interventricular septum (IVS) and posterior wall (PW) thickness, in young male black soccer players (BP) compared to male white soccer players (WP). Design and method: 77 BP and 53 WP (17.8 years old), trained with the same load and having the same lifestyle, were evaluated with maximal ergometric test, echocardiography and speckle-tracking global longitudinal strain (GLS). 30 younger BP and 27 WP (13.2 years old) were selected and followed up for 4 years. Results: In the older group of athletes blood pressure response to exercise and GLS were comparable in BP and WP, whereas IVS and PW thickness were significantly higher in BP (IVS: 10.04 ± 0.14 and 9.35 ± 0.10 mm, p < 0.001; PW: 9.70 ± 0.20 and 9.19 ± 0.10 mm, p < 0.05; in BP and WP respectively). Considering the younger group of athletes no significant difference was found in blood pressure while a higher LV remodelling was detected (IVS = 9.29 ± 0.3 and 8.53 ± 0.12 mm, p < 0.002; PW = 9.01 ± 0.2 and 8.40 ± 0.20, p = 0.1; in BP and WP respectively). The degree of LV remodelling was proportional with body-size and LV mass during the four years of follow-up (IVS = 10.52 ± 0.17 and 9.03 ± 0.22 mm, p < 0.001; PW: 10.06 ± 0.17 and 8.26 ± 0.19 mm, p < 0.001; in BP and WP respectively). Conclusions: Since no significant difference in blood pressure response to exercise was detected and since all principal determinants of cardiovascular response to exercise were overcome by specific selection of all athletes enrolled, ethnicity seems to remain the principal factor involved in cardiovascular adaptation to physical training.

Fish predation and macroinvertebrate abundance on snags in low-gradient blackwater streams

AbstractInvestigations into how fish affect macroinvertebrates in lotic ecosystems have produced equivocal results, and few researchers have examined fish effects on invertebrates in sandy-bottomed blackwater streams. We measured the responses of macroinvertebrate density, biomass, and body size to varying levels of fish predation on snags in 2 southeastern USA blackwater streams. We manipulated fish densities in 3 large enclosures (46–64 m2) in each of 2 streams and included treatments without fish (0X = control), with fish at ambient density (1X), and with fish at 2× ambient density (2X). Macroinvertebrates in enclosures were sampled using 20 tag alder (Alnus serrulatus) snags, ½ of which were allowed to colonize for 2 wk (colonizing community) and ½ for 2 mo (established community). Increasing invertivorous fish biomass resulted in a significant decrease in total macroinvertebrate density, but not macroinvertebrate biomass, in both types of communities (colonizing and established). We found that the bi...

Defensive behaviors of the Oriental armyworm Mythimna separata in response to different parasitoid species (Hymenoptera: Braconidae).

This study examined defensive behaviors of Mythimna separata (Lepidoptera: Noctuidae) larvae varying in body size in response to two parasitoids varying in oviposition behavior; Microplitis mediator females sting the host with the ovipositor after climbing onto it while Meteorus pulchricornis females make the sting by standing at a close distance from the host. Mythimna separata larvae exhibited evasive (escaping and dropping) and aggressive (thrashing) behaviors to defend themselves against parasitoids M. mediator and M. pulchricornis. Escaping and dropping did not change in probability with host body size or parasitoid species. Thrashing did not vary in frequency with host body size, yet performed more frequently in response to M. mediator than to M. pulchricornis. Parasitoid handling time and stinging likelihood varied depending not only on host body size but also on parasitoid species. Parasitoid handling time increased with host thrashing frequency, similar in slope for both parasitoids yet on a higher intercept for M. mediator than for M. pulchricornis. Handling time decreased with host size for M. pulchricornis but not for M. mediator. The likelihood of realizing an ovipositor sting decreased with thrashing frequency of both small and large hosts for M. pulchricornis, while this was true only for large hosts for M. mediator. Our results suggest that the thrashing behavior of M. separata larvae has a defensive effect on parasitism, depending on host body size and parasitoid species with different oviposition behaviors.

Genomic regions and genes related to inter-population differences in body size in the ground beetle Carabus japonicus

Body size is a key trait in diversification among animal species, and revealing the gene regions responsible for body size diversification among populations or related species is important in evolutionary biology. We explored the genomic regions associated with body size differences in Carabus japonicus ground beetle populations by quantitative trait locus (QTL) mapping of F2 hybrids from differently sized parents from two populations using restriction site-associated DNA sequencing and de novo assembly of the beetle whole genome. The assembled genome had a total length of 191 Mb with a scaffold N50 of 0.73 Mb; 14,929 protein-coding genes were predicted. Three QTLs on different linkage groups had major effects on the overall size, which is composed chiefly of elytral length. In addition, we found QTLs on autosomal and X chromosomal linkage groups that affected head length and width, thoracic width, and elytral width. We determined the gene loci potentially related to control of body size in scaffolds of the genome sequence, which contained the QTL regions. The genetic basis of body size variation based on a small number of major loci would promote differentiation in body size in response to selection pressures related to variations in environmental conditions and inter-specific interactions.

Larval stress alters dengue virus susceptibility in Aedes aegypti (L.) adult females

In addition to genetic history, environmental conditions during larval stages are critical to the development, success and phenotypic fate of the Aedes aegypti mosquito. In particular, previous studies have shown a strong genotype-by-environment component to adult mosquito body size in response to optimal vs stressed larval conditions. Here, we expand upon those results by investigating the effects of larval-stage crowding and nutritional limitation on the susceptibility of a recent field isolate of Aedes aegypti to dengue virus serotype-2. Interestingly, female mosquitoes from larvae subjected to a stressed regime exhibited significantly reduced susceptibility to disseminated dengue infection 14days post infection compared to those subjected to optimal regimes. Short term survivorship post-infected blood feeding was not significantly different. As with body size, dengue virus susceptibility of a mosquito population is determined by a combination of genetic and environmental factors and is likely maintained by balancing selection. Here, we provide evidence that under different environmental conditions, the innate immune response of field-reared mosquitoes exhibits a large range of phenotypic variability with regard to dengue virus susceptibility. Further, as with body size, our results suggest that mosquitoes reared under optimal laboratory conditions, as employed in all mosquito-pathogen studies to date, may not always be realistic proxies for natural populations.

Urban habitats can affect body size and body condition but not immune response in amphibians

Does urbanization affect key life-history traits in native organisms? Some studies show that urban areas reduce diversity in certain taxa, but there is little insight into how these environments affect physiological and ecological traits. Urban areas have distinct physical structure and ecological processes compared to original habitats. The environmental changes associated with urban areas can influence the costs and benefits of different traits and behaviors of local organisms. Some of these effects have been explored in groups such as birds, but we might expect stronger effects in animals with reduced mobility, such as amphibians. Importantly, the effects of urban habitats on amphibians have not been explored, in spite that these are the most threatened vertebrate group in the world. Here, we compared three main traits related to the fitness of amphibians in urban and natural habitats: body size, body condition and immune response. To test the generality of our results, we assessed adult males of four amphibian species. We found that the body size was larger in urban environment populations in three of four studied species, while the body condition was better in the urban populations of two aquatic newt species. Finally, we found no effect of urbanization on the immune response of individuals of any species. In conclusion, we show that different species of amphibians may be affected differently by anthropogenic habitat alteration depending on their specific ecology.

Uptake Kinetics and Subcellular Compartmentalization Explain Lethal but Not Sublethal Effects of Cadmium in Two Closely Related Amphipod Species.

Eulimnogammarus cyaneus and Eulimnogammarus verrucosus, closely related amphipod species endemic to Lake Baikal, differ with respect to body size (10- to 50-fold lower fresh weights of E. cyaneus) and cellular stress response (CSR) capacity, potentially causing species-related differences in uptake, internal sequestration, and toxic sensitivity to waterborne cadmium (Cd). We found that, compared to E. verrucosus, Cd uptake rates, related to a given exposure concentration, were higher, and lethal concentrations (50%; LC50) were 2.3-fold lower in E. cyaneus (4 weeks exposure; 6 °C). Upon exposures to species-specific subacutely toxic Cd concentrations (nominal LC1; E. cyaneus: 18 nM (2.0 μg L-1); E. verrucosus: 115 nM (12.9 μg L-1); 4 weeks exposure; 6 °C), Cd amounts in metal sensitive tissue fractions (MSF), in relation to fresh weight, were similar in both species (E. cyaneus: 0.25 ± 0.06 μg g-1; E. verrucosus: 0.26 ± 0.07 μg g-1), whereas relative Cd amounts in the biologically detoxified heat stable protein fraction were 35% higher in E. cyaneus. Despite different potencies in detoxifying Cd, body size appears to mainly explain species-related differences in Cd uptake and sensitivities. When exposed to Cd at LC1 over 4 weeks, only E. verrucosus continuously showed 15-36% reduced oxygen consumption rates indicating metabolic depression and pointing to particular sensitivity of E. verrucosus to persisting low-level toxicant pressure.

Impact of agrochemicals on non-target species: Calathus fuscipes Goeze 1777 (Coleoptera: Carabidae) as model

Carabid beetles are important in the biological control of arable crop pests. Agricultural practices can produce over time a delayed toxic effect at the organismal and population levels and can compromise the survival on these species. In this research, we quantified the cumulative sublethal effect on body size, Malpighian tubules and immune responses in Calathus fuscipes adults living in the potato field and exposed to lambda-cyhalothrin and cymoxanil-based commercial formulates. Reductions of morphological parameters such as body, pronotum and elytron in both males and females from the potato field indicated that the pre-imaginal stages (larvae and pupae) suffer the sublethal effects of exposure to the larvicide control action of lambda-cyhalothrin. Ultrastructural alterations recorded in Malpighian tubules at the level of plasma membrane, mitochondria and nucleus indicated the reduction of the detoxification capability. The basal phenoloxidase and lysozyme-like enzyme activities have measured as markers of immune competence. Spectrophometric analyses showed that the chronic exposure in field causes an increase of basal phenoloxidase enzyme activity, while the lytic activity of haemolymph was not affected. As a result, the use of larvicides and fungicides have a harmful effect on beneficial species such C. fuscipes living in the soil of potato fields. These morphological and physiological results recorded at the organismal level can provide useful information of effects at the population and community levels to preserve the biodiversity of agroecosystem.

Empirical evidence for fast temperature-dependent body size evolution in rotifers

Organisms tend to decrease in size with increasing temperature by phenotypic plasticity (the temperature-size rule; ectotherms) and/or genetically (Bergmann’s rule; all organisms). In this study, the evolutionary response of body size to temperature was examined in the cyclically parthenogenetic rotifer Brachionus plicatilis. Our aim was to investigate whether this species, already known to decrease in size with increasing temperature by phenotypic plasticity, presents a similar pattern at the genetic level. We exposed a multiclonal mixture of B. plicatilis to experimental evolution at low and high temperature and monitored body size weekly. Within a month, we observed a smaller size at higher temperature, as compared to body size at lower temperature. The pattern was consistent for the size of both mature females and eggs; rotifers kept at high temperature evolved to be on average 14% (after 2 weeks) and 3% (after 3 weeks) smaller than the ones kept at low temperature (10 and 5% in the case of eggs, respectively). We therefore found that B. plicatilis is genetically programmed to adjust its body size-to-environmental temperature.