Body Size Responses Research Articles

Rapid evolution meets invasive species control: the potential for pesticide resistance in sea lamprey

Rapid evolution of pest, pathogen, and wildlife populations can have undesirable effects, for example, when insects evolve resistance to pesticides or fishes evolve smaller body size in response to harvest. A destructive invasive species in the Laurentian Great Lakes, the sea lamprey (Petromyzon marinus) has been controlled with the pesticide 3-trifluoromethyl-4-nitrophenol (TFM) since the 1950s. We evaluated the likelihood of sea lamprey evolving resistance to TFM by (i) reviewing sea lamprey life history and control; (ii) identifying physiological and behavioural resistance strategies; (iii) estimating the strength of selection from TFM; (iv) assessing the timeline for evolution; and (v) analyzing historical toxicity data for evidence of resistance. The number of sea lamprey generations exposed to TFM was within the range observed for fish populations where rapid evolution has occurred. Mortality from TFM was estimated as 82%–90%, suggesting significant selective pressure. However, 57 years of toxicity data revealed no increase in lethal concentrations of TFM. Vigilance and the development of alternative controls are required to prevent this aquatic invasive species from evolving strategies to evade control.

Long-term and acute effects of temperature and oxygen on metabolism, food intake, growth and heat tolerance in a freshwater gastropod

Temperature affects the physiology and life-history of ectothermic animals, often increasing metabolic rate and decreasing body size. Oxygen limitation has been put forward as a mechanism to explain thermal responses of body size and the ability to survive stress. However the time-scales involved in growth performance and heat tolerance differ radically. In order to increase our understanding of oxygen and temperature effects on body size and heat tolerance and the time scale involved, we reared Lymnaea stagnalis under six combinations of temperature and oxygen tension from hatching up to an age of 300 days and recorded shell length during this whole period. At the end of this period, we determined scope for growth by measuring food intake rate, assimilation efficiency, respiration rate and ammonium excretion rate at two different temperatures. We also measured the snails’ ability to survive heat stress (CTmax), both at normoxia and hypoxia. We found that scope for growth and long term growth performance were much more affected by interactions of chronic oxygen and temperature conditions during rearing than by acute conditions during testing. Furthermore, our study shows that individual variation in growth performance can be traced back to individual differences in rates of food and oxygen consumption. Developmental acclimation also gave rise to differences in CTmax, but these were relatively small and were only expressed when CTmax was tested under hypoxia. The large effects of rearing oxygen conditions on growth and other physiological rates compared to modest effects of test oxygen conditions on CTmax suggest that small effects of hypoxia on the short term (e.g. heat tolerance) may nevertheless have large repercussions on the long term (e.g. growth and reproduction), even in a pulmonate snail that can compensate for hypoxia to some extent by aerial respiration.

Synergism and Antagonism of Proximate Mechanisms Enable and Constrain the Response to Simultaneous Selection on Body Size and Development Time: An Empirical Test Using Experimental Evolution.

Natural selection acts on multiple traits simultaneously. How mechanisms underlying such traits enable or constrain their response to simultaneous selection is poorly understood. We show how antagonism and synergism among three traits at the developmental level enable or constrain evolutionary change in response to simultaneous selection on two focal traits at the phenotypic level. After 10 generations of 25% simultaneous directional selection on all four combinations of body size and development time in Manduca sexta (Sphingidae), the changes in the three developmental traits predict 93% of the response of development time and 100% of the response of body size. When the two focal traits were under synergistic selection, the response to simultaneous selection was enabled by juvenile hormone and ecdysteroids and constrained by growth rate. When the two focal traits were under antagonistic selection, the response to selection was due primarily to change in growth rate and constrained by the two hormonal traits. The approach used here reduces the complexity of the developmental and endocrine mechanisms to three proxy traits. This generates explicit predictions for the evolutionary response to selection that are based on biologically informed mechanisms. This approach has broad applicability to a diverse range of taxa, including algae, plants, amphibians, mammals, and insects.

Limited spatial response to direct predation risk by African herbivores following predator reintroduction.

Predators affect ecosystems not only through direct mortality of prey, but also through risk effects on prey behavior, which can exert strong influences on ecosystem function and prey fitness. However, how functionally different prey species respond to predation risk and how prey strategies vary across ecosystems and in response to predator reintroduction are poorly understood. We investigated the spatial distributions of six African herbivores varying in foraging strategy and body size in response to environmental factors and direct predation risk by recently reintroduced lions in the thicket biome of the Addo Elephant National Park, South Africa, using camera trap surveys, GPS telemetry, kill site locations and Light Detection and Ranging. Spatial distributions of all species, apart from buffalo, were driven primarily by environmental factors, with limited responses to direct predation risk. Responses to predation risk were instead indirect, with species distributions driven by environmental factors, and diel patterns being particularly pronounced. Grazers were more responsive to the measured variables than browsers, with more observations in open areas. Terrain ruggedness was a stronger predictor of browser distributions than was vegetation density. Buffalo was the only species to respond to predator encounter risk, avoiding areas with higher lion utilization. Buffalo therefore behaved in similar ways to when lions were absent from the study area. Our results suggest that direct predation risk effects are relatively weak when predator densities are low and the time since reintroduction is short and emphasize the need for robust, long‐term monitoring of predator reintroductions to place such events in the broader context of predation risk effects.

Consequences of altered temperature regimes for emerging freshwater invertebrates

We used highly realistic temperature treatments based on down-scaled global circulation models for 1990–2000 (control) and 2100 (warming treatment) to experimentally assess the impacts of altered temperature regimes on the emerging adults of aquatic insect communities. Experiments were run for 6 weeks and emerging adults of insects were identified and measured for length. There were clear responses to the warming treatment, but responses were taxa- and gender-specific. Males of mayfly Ulmerophlebia pipinna Suter 1986 (Leptophlebiidae) emerged faster under 2100 temperatures. This resulted in a change in the sex ratio that could compromise populations. Mean body size of some insects decreased under warming conditions, which is in agreement with the general hypothesis of reduced body size in response to climate change. However, the degree to which organism size was affected by temperature varied within and between taxa. These changes show the potential for changed temperature regimes to impact ecological systems at individual, population, and community levels. Changes in body size and species composition of emerging insects are likely to impact different levels in both the aquatic and terrestrial communities, for example through disruption of interactions between emerging insects and riparian predators which rely on those resources.

Variable patterns of intraspecific sexual size dimorphism and allometry in three species of eusocial corbiculate bees

Sexual size dimorphism (SSD), in which one sex is larger than the other, has remained understudied in social insects, particularly bees. Using weight and linear structural measurements, we quantified the magnitude of SSD and its variation across nests in three species of corbiculate bees, two belonging to the highly eusocial Apini (Apis mellifera) and Meliponini (Melipona beecheii), and one to the primitively eusocial Euglossini (Euglossa viridissima). We asked if similar to most insects, including Hymenoptera, SSD is female-biased in these eusocial species. Contrary to expectations, we found that SSD was moderately male-biased in the two highly eusocial species and slightly male-biased for weight and not significant for linear size in E. viridissima. The possible roles of queen protogyny and reduced brood provisioning by queens in shaping these patterns of SSD are discussed. The allometry of SSD among nests differed among species as well, ranging from hypoallometry in A. mellifera, to isometry in M. beecheii, to hyperallometry in E. viridissima. This variation indicates that the phenotypic response of body size to differing conditions across nests differs both between sexes and among species. The variation detected among the three studied species in both SSD and allometry for SSD precludes any broad generalizations to other corbiculate bees. However, it does suggest that corbiculate bees can provide a new and diverse framework to analyze the effects of social environment on the evolution of animal sexual dimorphism.

Spatiotemporal changes in flying insect abundance and their functional diversity as a function of distance to natural habitats in a mass flowering crop

To meet the dietary requirements of a burgeoning human population, the demand for animal-dependent crops continues to grow. To meet the demand, intensive farming practices are used. The gains in food production associated with agricultural intensification may be offset by its detrimental effects on pollinator populations through natural habitat fragmentation and pesticide use. Abundance and species richness of pollinators have been found to decrease with increasing distance to natural habitat in agroecosystems, reducing crop yields. A key aspect of crop pollination lies in the diversity of functional traits (functional diversity, FD) of flower-visitor communities within crop fields. Higher FD allows improved pollination success through complementarity between flower-visitors’ morphology, phenology and behaviour. Many studies reported negative effects of increasing distance to natural habitats on the abundance and richness of flower-visitor communities, but the link between FD and natural habitat isolation is less well understood. Also, a more complete understanding of the functional traits of flower-visitor communities within crops should consider potential variations through time. Differences in resources availability between seasons are important in tropical areas and could modify ecological responses of flower-visitor communities to isolation. In this study, we surveyed the Hymenoptera and Diptera communities within mango orchards of South Africa using pan traps at 100m, 200m and at the maximal distance possible from any natural habitat. We measured the response of insect abundance, wing span and body size as well as functional diversity to habitat isolation during mango flowering (dry season), and during the wet season (after mango fruit harvest). Flying insect abundance decreased with increasing distance to natural habitat during mango flowering, but no effect was detected during the wet season. FD of flying insects declined with increasing distance to natural habitat in both sampling periods. Insects captured during mango flowering were smaller but had higher wing length/body length ratios than those caught during the wet season. This study highlights that mango orchards are more inhospitable for flying insects during mango flowering. This effect might be due to low palatability of mango flowers, or pesticide use in mango fields. In order to maintain a high FD of flower-visiting species, and reduce the detrimental effects of habitat isolation to ultimately ensure better crop pollination, we propose establishment of patches of resource-rich habitats combined with judicious use of pesticides within orchards.

A global synthesis of seasonal temperature–size responses in copepods

AbstractAimBody size is a master trait with significant ecological importance. Seasonal changes in body size within diverse ectothermic species can result from different environmental conditions experienced during ontogeny in subsequent generations. Whilst intraspecific changes in adult size have been well studied under controlled experimental conditions and across geographical ranges, comprehensive analyses of temporal changes are lacking, and there remains considerable unexplained variation in body size responses within aquatic taxa. Using planktonic copepods as an exemplar taxon, we quantify variation in adult body mass within seasonally varying marine and freshwater environments. We describe how size variation relates to temperature, food concentration (chlorophyll‐a) and life‐history characteristics, including feeding strategy.LocationGlobal.MethodsUsing a meta‐analytic approach we extract quantitative data from published literature on seasonal size responses of copepods. We analyse competing models to determine the best predictors of these responses, and compare the relative importance of temperature and chlorophyll‐a concentration in explaining variation in body size.ResultsWe quantify 140 seasonal size responses from 33 different global locations, representing 48 planktonic copepod species from four taxonomic orders. We find that temperature (r2 = 0.50), rather than food (r2 = 0.22), is the dominant explanatory variable of changes in adult body size across seasons. A striking outcome is that calanoid copepods, which utilize feeding currents to capture prey, exhibit a four‐fold greater reduction in adult body mass per °C (−3.66%) compared with cyclopoid copepods (−0.91%), which are ambush feeders. By contrast, species body size or reproductive strategy did not explain variation in the seasonal temperature–size response.Main conclusionsOur findings lead us to suggest that feeding strategies may play a significant role in dictating the magnitude of seasonal temperature–size responses in copepods, with potential implications for other ectotherms with diverse feeding methods. Seasonal temperature–size responses were typically much more variable than responses in laboratory studies that provided excess food, suggesting that field conditions modify the temperature–size response.

Functional response and body size in consumer–resource interactions: Unimodality favors facilitation

Theoretical models suggest that competitive coexistence of consumers over shared resources can occur only under very restrictive conditions. Yet, in apparent defiance of the competitive exclusion principle, large numbers of species form natural communities while sharing a small number of limiting resources. Consumers not only coexist, but also show positive facilitative interactions among themselves. Since body size and functional responses may play important roles in these interactions, we investigate their joint effects on two consumers over a single resource. We find that two consumers with unimodal Type IV functional response can facilitate each other by increasing each other’s intake rates. But, this facilitation does not necessarily impact their co-existence. When the consumers differ in their body sizes, the larger consumer receives greater absolute benefits, and the smaller consumer gains more relative benefits. These results are consistent with empirical observations, and do not require any additional assumptions over the parameters governing dynamics of resources to explain net positive interactions between consumers.

The interplay between resource supply and demand determines the influence of predation on prey body size

Predation has been shown to either increase or decrease the body mass of fish, as well as cause variable changes in growth rate. The mechanisms underlying these contrasting responses are not well understood. Here we compared intraspecific body size and growth responses to predation against a backdrop of 2006 estimates of asymptotic mass and growth constants (i.e., von Bertalanffy parameters) across species. We show that intraspecific responses can be quite large relative to interspecific variation and confirm that the magnitude and direction of body size responses is variable. We then employed the supply–demand (SD) model of body mass evolution to explore how predator-induced changes in resource demand or supply could alter body mass. The SD model predicts that any combination of increasing or decreasing body mass and increasing or decreasing growth rate is possible when predation risk is increased, which is consistent with the literature. Finally, we use three case studies to illustrate how the interplay of resource supply and resource demand determines the actual body mass and growth rate response to predation.

Do marine phytoplankton follow Bergmann's rule sensu lato?

Global warming has revitalized interest in the relationship between body size and temperature, proposed by Bergmann's rule 150 years ago, one of the oldest manifestations of a 'biogeography of traits'. We review biogeographic evidence, results from clonal cultures and recent micro- and mesocosm experiments with naturally mixed phytoplankton communities regarding the response of phytoplankton body size to temperature, either as a single factor or in combination with other factors such as grazing, nutrient limitation, and ocean acidification. Where possible, we also focus on the comparison between intraspecific size shifts and size shifts resulting from changes in species composition. Taken together, biogeographic evidence, community-level experiments and single-species experiments indicate that phytoplankton average cell sizes tend to become smaller in warmer waters, although temperature is not necessarily the proximate environmental factor driving size shifts. Indirect effects via nutrient supply and grazing are important and often dominate. In a substantial proportion of field studies, resource availability is seen as the only factor of relevance. Interspecific size effects are greater than intraspecific effects. Direct temperature effects tend to be exacerbated by indirect ones, if warming leads to intensified nutrient limitation or copepod grazing while ocean acidification tends to counteract the temperature effect on cell size in non-calcifying phytoplankton. We discuss the implications of the temperature-related size trends in a global-warming context, based on known functional traits associated with phytoplankton size. These are a higher affinity for nutrients of smaller cells, highest maximal growth rates of moderately small phytoplankton (ca. 102 µm3 ), size-related sensitivities for different types of grazers, and impacts on sinking rates. For a phytoplankton community increasingly dominated by smaller algae we predict that: (i) a higher proportion of primary production will be respired within the microbial food web; (ii) a smaller share of primary production will be channeled to the classic phytoplankton-crustacean zooplankton-fish food chain, thus leading to decreased ecological efficiency from a fish-production point of view; (iii) a smaller share of primary production will be exported through sedimentation, thus leading to decreased efficiency of the biological carbon pump.

Capture-induced stress in deep-water Arctic fish species

There are significant conservation benefits to studying the stress response of commercially important fish species. Particularly in the Arctic ecosystem, where reducing ice extent has resulted in heightened interest in developing commercial fisheries, there is a need to better understand how fish respond to capture stressors. To that end, blood lactate and glucose of Greenland halibut Reinhardtius hippoglossoides and Greenland shark Somniosus microcephalus were assessed after capture from fishing gear to evaluate factors that might influence physiological disturbance. Greenland halibut lactate values had a mean of 1.0 ± 0.7 mmol/L and showed a positive relationship with time since capture. Blood glucose concentrations for Greenland halibut had a mean of 1.8 ± 0.6 mmol/L and were positively related to both time since capture and fork length. Greenland shark lactate values varied depending on depth, with individuals captured at 300–600 m displaying significantly lower concentrations (1.6 ± 0.5 mmol/L) than those caught at depths between 600 and 700 m (6.4 ± 2.4 mmol/L) and 700–900 m (3.7 ± 1.2 mmol/L). Glucose values for the Greenland shark had a mean of 4.9 ± 1.5 mmol/L and were positively correlated with body length. Relative to temperate fish species, the metabolite concentrations are low but the inherent challenges with deep-water fish makes it difficult to obtain baseline (pre-stress) values to quantify the magnitude of stress response. This is the first study to document stress metabolites in these two Arctic species and suggests that there is a body size and depth-related physiological response to capture.

Equal temperature-size responses of the sexes are widespread within arthropod species.

Sexual size dimorphism (SSD) is often affected by environmental conditions, but the effect of temperature on SSD in ectotherms still requires rigorous investigation. We compared the plastic responses of size-at-maturity to temperature between males and females within 85 diverse arthropod species, in which individuals of both sexes were reared through ontogeny under identical conditions with excess food. We find that the sexes show similar relative (proportional) temperature-body size (T-S) responses on average. The high degree of similarity occurs despite an analysis that includes a wide range of animal body sizes, variation in degree of SSD and differences in the sign of the T-S response. We find no support for Rensch's rule, which predicts greater variation in male size, or indeed the reverse, greater female size variation. SSD shows no systematic temperature dependence in any of the 17 arthropod orders examined, five of which (Diptera, Orthoptera, Lepidoptera, Coleoptera and Calanoida) include more than six thermal responses. We suggest that the same proportional T-S response may generally have equivalent fitness costs and benefits in both sexes. This contrasts with effects of juvenile density, and food quantity/quality, which commonly result in greater size plasticity in females, suggesting these variables have different adaptive effects on SSD.

High-Arctic butterflies become smaller with rising temperatures.

The response of body size to increasing temperature constitutes a universal response to climate change that could strongly affect terrestrial ectotherms, but the magnitude and direction of such responses remain unknown in most species. The metabolic cost of increased temperature could reduce body size but long growing seasons could also increase body size as was recently shown in an Arctic spider species. Here, we present the longest known time series on body size variation in two High-Arctic butterfly species: Boloria chariclea and Colias hecla. We measured wing length of nearly 4500 individuals collected annually between 1996 and 2013 from Zackenberg, Greenland and found that wing length significantly decreased at a similar rate in both species in response to warmer summers. Body size is strongly related to dispersal capacity and fecundity and our results suggest that these Arctic species could face severe challenges in response to ongoing rapid climate change.

Nearshore–offshore–basin species diversity and body size variation patterns in Late Permian (Changhsingian) brachiopods

Body size is a fundamental and defining character of an organism, and its variation in space and time is generally considered to be a function of its biology and interactions with its living environment. A great deal of body size related ecological and evolutionary research has been undertaken, mostly in relation to extant animals. Among the many body size-related hypotheses proposed and tested, the size–bathymetry relationship is probably the least studied. In this study, we compiled a global body size dataset of Changhsingian (Late Permian, ca. 254Ma–252Ma) brachiopod species from low-latitude areas (30°S–30°N) and analyzed their species diversity and body size distribution patterns in relation to the nearshore–offshore–basin bathymetric gradient. The dataset contained 1768 brachiopod specimens in 435 species referred to 159 genera and 9 orders, from 135 occurrences (localities) of 18 different palaeogeographic regions. Treating the whole of the Changhsingian Stage as a single time slice, we divided the nearshore–offshore–basin bathymetric gradient into three broad depth-related environments: nearshore, offshore and basinal environments, and compared how the species diversity and body size varied along this large-scale bathymetric gradient.Here, we report an array of complex patterns. First, we found a clear overall inverse correlation between species diversity and water depth along the nearshore–offshore–basin gradient, with most species concentrating in the nearshore environment. Second, when the median sizes of all low-latitude brachiopod species from the three environments were compared, we found that there was no significant size difference between the nearshore and offshore environments, suggesting that neither the wave base nor the hydrostatic pressure exerts a critical influence on the body size of brachiopods. On the other hand, the median sizes of brachiopods from the nearshore environment and, to a lesser extent, the offshore environment were found to be significantly larger than that of basinal brachiopods. This trend of significant size reduction in basinal brachiopods mirrors the relative low species diversity in the basinal environment, and neither can be easily explained by the tendency of decreasing food availability towards deeper sea environments. Rather, both trends are consistent with the hypothesis of an expanding Oxygen Minimum Zone (OMZ) in the bathyal (slope to deepsea) environments, where hypoxic to anoxic conditions are considered to have severely restricted the diversification of benthos and favored the relative proliferation of small-sized brachiopods. Finally, a significant difference was also found between eurybathic and stenobathic species in their body size response to the nearshore–offshore–basin gradient, in that eurybathic species (species found in all three environments) did not tend to change their body size significantly according to depth, whereas stenobathic forms (species restricted to a single environment) exhibit a decline in body size towards the basinal environment. This pattern is interpreted to suggest that bathymetrically more tolerant species are less sensitive to depth control with respect to their body size change dynamics, in contrast to stenobathic species which tend to grow larger in shallower water depths.

Body size response to warming: time of the season matters in a tephritid fly

Whether shrinking body size is a universal response to climate change remains controversial. Moreover, the mechanisms underlying body size shifts are poorly understood. Here, assuming that life history traits evolve to maximize fitness according to life history plasticity theory, we hypothesized that under global warming temperate multivoltine insects should emerge earlier with a smaller body mass in the early growing season, but emerge later with a larger body mass in the late season. We tested this hypothesis by conducting two field artificial warming experiments in an alpine meadow: 1) with one pre‐dispersal seed predator species (tephritid flies, Tephritis femoralis) and its two host‐plant species flowering in early and late growing seasons, respectively, and 2) with the tephritid flies and one host species with a flowering season that occupies parts of both the early and late growing seasons. These experiments were complemented by a microcosm chamber warming experiment, in which increasing and decreasing temperature trends were set to simulate temperature variation pattern in early and late growing seasons, respectively, but photoperiod was held constant. Warming generally advanced the adult emergence and decreased the body size (adult body mass) in the early season but delayed the emergence and increased the size in the late season in both field experiments, indicating that the seasonally different effects of warming on the fly body size was constant regardless of host‐plant identity. The chamber warming resulted in consistent responses of emerging timing and body size to the simulated seasonal warming, demonstrating that the temperature increase per se and its interaction with direction of temperature change, but not other correlated effects, should be primarily responsible for the observed contrasting shifts of body size at different times of the season. Our results indicate that taking into account temperate seasonal patterns of temperature variation could be of general importance for predicting animal body size changes in the warmed future.

Response of body size and developmental time of Tribolium castaneum to constant versus fluctuating thermal conditions

Temperature has profound effects on biological functions at all levels of organization. In ectotherms, body size is usually negatively correlated with ambient temperature during development, a phenomenon known as The Temperature-Size Rule (TSR). However, a growing number of studies have indicated that temperature fluctuations have a large influence on life history traits and the implications of such fluctuations for the TSR are unknown. Our study investigated the effect of different constant and fluctuating temperatures on the body mass and development time of red flour beetles (Tribolium castaneum Herbst, 1797); we also examined whether the sexes differed in their responses to thermal conditions.We exposed the progeny of half-sib families of a T. castaneum laboratory strain to one of four temperature regimes: constant 30°C, constant 25°C, fluctuating with a daily mean of 30°C, or fluctuating with a daily mean of 25°C. Sex-specific development time and body mass at emergence were determined.Beetles developed the fastest and had the greatest body mass upon emergence when they were exposed to a constant temperature of 30°C. This pattern was reversed when beetles experienced a constant temperature of 25°C: slowest development and lowest body mass upon emergence were observed. Fluctuations changed those effects significantly – impact of temperature on development time was smaller, while differences in body mass disappeared completely. Our results do not fit TSR predictions. Furthermore, regardless of the temperature regime, females acquired more mass, while there were no differences between sexes in development time to eclosion. This finding fails to support one of the explanations for smaller male size: that selection favors the early emergence of males. We found no evidence of genotype × environment interactions for selected set of traits.

Variation in body size in the giant rhinoceros beetle Trypoxylus dichotomus is mediated by maternal effects on egg size

1. The egg size of insects can vary depending on maternal body size or resource status, and it may influence offspring body size by determining initial resource level.2. The giant rhinoceros beetle Trypoxylus dichotomus exhibits considerable variation in body size, some of which is attributed to the variation in larval food (humus) quality, although a substantial amount of variation in body size remains unexplained. In the present study, changes in the egg size and offspring body size in response to several maternal variables were examined (i.e. body size, age, and, nutritional status).3. Nutritional intake of the females during the adult stage did not affect the egg size. Larvae hatched from small eggs partially recovered from the initial disadvantage during their ontogenetic processes by increasing growth rate (i.e. compensatory growth); however, there was still a positive relationship between egg size and pupal body size.4. Older females produced small eggs, but because of compensatory growth, the pupae were no longer small. By contrast, due to a lack of compensatory growth, small females produced small eggs as well as small pupae.5. These results suggest that maternal body size affects offspring body size through effects on egg size. This transgenerational effect may account for some of the variation in adult body size of T. dichotomus.

Effects of humic stress on the zooplankton from clear and DOC‐rich lakes

Summary Humic stress is associated with the widespread and ongoing browning of lakes. Natural landscape gradients in dissolved organic carbon (DOC) potentially result in aquatic communities with different tolerances to humic substances and thus expected contrasting responses to further lake browning. If zooplanktonic species are adapted to different background concentrations of DOC, then we expected that the zooplankton from naturally DOC‐rich lakes would maintain higher diversity, biomass and overall density in the face of experimental browning than the zooplankton from DOC‐poor lakes. We tested this hypothesis in a common‐garden experiment by exposing, in enclosures, zooplankton from replicate DOC‐rich and DOC‐poor source lakes to simulated browning and to clear water. We conducted a 2 × 2 × 3 factorial‐design field transplant experiment with zooplankton from replicate DOC‐rich (>8.5 mg L−1) and DOC‐poor (<3.5 mg L−1) lakes (Québec, Canada) over eight weeks. There were two fixed effects: water treatment (brown or clear water) and zooplankton source (from DOC‐rich or DOC‐poor lakes). Lake source was included as a random variable in the model for the response of copepod body size in the enclosures. A substance derived from peat, ‘SuperHume’, was used as a source of DOC. The diversity, biomass and total density of zooplankton from DOC‐rich and DOC‐poor lakes did not differ upon experimental addition of further DOC. This was despite the presence of different copepod body size phenotypes between source lakes that could have potentially caused different community responses: several dominant species of copepods (Cyclops scutifer, Leptodiaptomus minutus and Tropocyclops prasinus mexicanus) had a larger mean population body size in DOC‐rich source lakes than in DOC‐poor source lakes. Our findings suggest that the zooplankton from DOC‐rich lakes does neither better nor worse than zooplankton from DOC‐poor lakes when faced with browning from a humic stressor.

Level of UV-B radiation influences the effects of glyphosate-based herbicide on the spotted salamander.

Glyphosate-based herbicides are the number one pesticide in the United States and are used commonly around the world. Understanding the affects of glyphosate-based herbicides on non-target wildlife, for example amphibians, is critical for evaluation of regulations pertaining to the use of such herbicides. Additionally, it is important to understand how variation in biotic and abiotic environmental conditions, such as UV-B light regime, could potentially affect how glyphosate-based herbicides interact with non-target species. This study used artificial pond mesocosms to identify the effects of generic glyphosate-based herbicide (GLY-4 Plus) on mortality, cellular immune response, body size, and morphological plasticity of larvae of the spotted salamander (Ambystoma maculatum) under conditions that reflect moderate (UV(M)) and low (UV(L)) UV-B light regimes. Survival within a given UV-B level was unaffected by herbicide presence or absence. However, when herbicide was present, survival varied between UV-B levels with higher survival in UV(M) conditions. Herbicide presence in the UV(M) treatments also decreased body size and reduced cellular immune response. In the UV(L) treatments, the presence of herbicide increased body size and affected tail morphology. Finally, in the absence of herbicide, body size and cellular immune response were higher in UV(M) treatments compared to UV(L) treatments. Thus, the effects of herbicide on salamander fitness were dependent on UV-B level. As anthropogenic habitat modifications continue to alter landscapes that contain amphibian breeding ponds, salamanders may increasingly find themselves in locations with reduced canopy cover and increased levels of UV light. Our findings suggest that the probability of surviving exposure to the glyphosate-based herbicide used in this study may be elevated in more open canopy ponds, but the effects on other components of fitness may be varied and unexpected.