Shifts In Life-history Traits Research Articles

Effects of a transmissible cancer on life-history traits in Tasmanian devils.

Shifts in life history traits, such as timing of reproduction, can help mediate population declines following perturbations, and early reproduction should be favoured when adult survival is impacted more than juvenile survival. In Tasmanian devils, following the emergence of a fatal transmissible cancer, females started to breed precocially (i.e., at age one instead of typically age two) and the same time as populations started to decline following disease emergence. Here, we focus on a diseased site (Freycinet Peninsula, Tasmania, Australia) with 18 years of continuous mark-recapture data to test: (1) whether rates of precocial breeding in females continued to increase after the initial rise after the emergence of the disease, (2) whether there was a relationship between body size and breeding success for either one-year-olds or adult females (i.e., at least two-years-old), and (3) whether there was inbreeding depression in breeding success for either age category. We show that rates of precocial breeding did not continue to rise, and that the proportion of precocially breeding females has plateaued at around 50%. We also show that there was no effect of body size on the probability of breeding for either one-year-old or for adult females. Finally, we show that there was no evidence for inbreeding depression in breeding success for either age class. We discuss possible constraints that may have inhibited further rise in rates of precocial breeding in the context of limitations to growth in the offspring of precocially breeding (and therefore smaller) females.

The Chemosensory Repertoire of the Eastern Diamondback Rattlesnake (Crotalus adamanteus) Reveals Complementary Genetics of Olfactory and Vomeronasal-Type Receptors.

Pitviper sensory perception incorporates diverse stimuli through the integration of trichromatic color vision, bifocal heat-sensing, and dual-system chemoperception. Chemoperception, or olfaction, is mediated by chemoreceptors in the olfactory bulb and the vomeronasal organ, but the true genomic complexity of the gene families and their relative contributions is unknown. A full genomic accounting of pitviper chemoperception directly complements our current understanding of their venoms by generating a more complete polyphenic representation of their predatory arsenal. To characterize the genetic repertoire of pitviper chemoperception, we analyzed a full-genome assembly for Crotalus adamanteus, the eastern diamondback rattlesnake. We identified hundreds of genes encoding both olfactory receptors (ORs; 362 full-length genes) and type-2 vomeronasal receptors (V2Rs; 430 full-length genes). Many chemoreceptor genes are organized into large tandem repeat arrays. Comparative analysis of V2R orthologs across squamates demonstrates how gene array expansion and contraction underlies the evolution of the chemoreceptor repertoire, which likely reflects shifts in life history traits. Chromosomal assignments of chemosensory genes identified sex chromosome specific chemoreceptor genes, providing gene candidates underlying observed sex-specific chemosensory-based behaviors. We detected widespread episodic evolution in the extracellular, ligand-binding domains of both ORs and V2Rs, suggesting the diversification of chemoreceptors is driven by transient periods of positive selection. We provide a robust genetic framework for studying pitviper chemosensory ecology and evolution.

Feeding partridges with organic or conventional grain triggers cascading effects in life-history traits.

Farmland birds are declining across Europe and North America and the research of factors behind is the subject of extensive researches. Agricultural intensification is now recognized as a major factor governing the loss of biodiversity with strong evidence that pesticides induced direct bird mortality at a high dose. However, less attention has been given to the long-term effects of chronic exposure to low dose of pesticides. Here, we used an experimental procedure in which grey partridges were fed with untreated grains obtained from either organic (no pesticide) or conventional agriculture (with pesticide) for 26 weeks, thus strictly mimicking wild birds foraging on fields. We then examined a suite of life-history traits (ecophysiological and behavioural) that may ultimately, influence population dynamics. We show for the first time that ingesting low pesticide doses over a long period has long-term consequences on several major physiological pathways without inducing differential mortality. Compared to control partridges, birds exposed to chronic doses i) had less developed carotenoid-based ornaments due to lower concentrations of plasmatic carotenoids, ii) had higher activated immune system, iii) showed signs of physiological stress inducing a higher intestinal parasitic load, iv) had higher behavioural activity and body condition and v) showed lower breeding investment. Our results are consistent with a hormetic effect, in which exposure to a low dose of a chemical agent may induce a positive response, but our results also indicate that breeding adults may show impaired fitness traits bearing population consequences through reduced breeding investment or productivity. Given the current scale of use of pesticides in agrosystems, we suggest that such shifts in life-history traits may have a negative long-term impact on wild bird populations across agrosystems. We stress that long-term effects should no longer be ignored in pesticide risk assessment, where currently, only short-term effects are taken into account.

Ground beetle (Coleoptera, Carabidae) life history traits as indicators of habitat recovering processes in postindustrial areas

The recovery of postindustrial ecosystems is difficult to predict and depends on numerous factors. Afforestation whereby trees are planted without improvement of soil properties is a popular means of landfill reclamation in Europe, to inhibit the effect of soil erosion. This slows down or completely prevents effective recolonization of many natural ecosystem components. The aim of the study was to test a method using the life-history traits of ground beetle assemblages as a predictor of the effectiveness of ecological restoration in afforested areas. The study was conducted on 45 sampling transects located in three ecosystem types: afforested landfills, landfills where spontaneous succession took place and reference forests. The following carabid life history traits were analysed: body size, dispersal power, food preferences, breeding type, and habitat preferences. In total, 2036 specimens belonging to 36 Carabidae species were collected. Non-metric multidimensional scaling was used to classify ground beetle assemblages according to ecosystem types (analysis of dissimilarity showed significant distance differences, p < .001). We noted shifts in life history traits towards early succession in assemblages of afforested areas. Generalized linear mixed models of afforested sites revealed significantly higher abundance of herbivorous, open-area species with medium body size, high dispersal power and a spring breeding cycle. In contrast, sites where spontaneous succession occured were dominated by carabids whose life history traits were similar to those of assemblages inhabiting the reference forests, i.e. medium body-sized predators with low dispersal power and an autumn breeding cycle. We conclude that an approach based on ground beetle life-history traits can be a useful tool indicating the direction and effectiveness of ecosystem recovery in post-industrial areas and can be used as a measurable criterion for assessment of restoration activities.

Local adaptation of phenology revealed in outcrosses between spawning segments of a salmonid population

Local adaptation has been demonstrated in spatially or temporally distant animal populations but seldom in proximate populations. To address the scale of local adaptation in Pacific salmon (Oncorhynchus spp.), two generations of hybrids between temporally separated spawning segments were made in a population of pink salmon (O.gorbuscha) and compared with controls to evaluate the genetic architecture underlying adult migration time and to test for declines in marine survival that resulted from outbreeding depression. Bayesian mixed-effects models revealed that adult migration times in hybrid lines were intermediate to those of controls and that additive sources of genetic variation were significant, thereby indicating that local adaptation has acted on additive genetic variation in shaping this trait. Similarly, a line cross analysis revealed that an additive model best described the genetic architecture of adult migration time. In contrast, marine survival was generally similar between control and hybrid lines, which suggested that the effect of outbreeding upon marine survival was minimal at such a fine scale of genetic divergence. The implications of these results are that (a) local adaptation can facilitate genetic divergence of life history traits between proximate subpopulations; (b) artificial relaxation of natural barriers to gene flow can cause maladaptive shifts in life history traits; and (c) wild populations may harbour fine-scale adaptive variation that supports productivity and sustainability.

The transition to modernity and chronic disease: mismatch and natural selection.

The Industrial Revolution and the accompanying nutritional, epidemiological and demographic transitions have profoundly changed human ecology and biology, leading to major shifts in life history traits, which include age and size at maturity, age-specific fertility and lifespan. Mismatch between past adaptations and the current environment means that gene variants linked to higher fitness in the past may now, through antagonistic pleiotropic effects, predispose post-transition populations to non-communicable diseases, such as Alzheimer disease, cancer and coronary artery disease. Increasing evidence suggests that the transition to modernity has also altered the direction and intensity of natural selection acting on many traits, with important implications for public and global health.

Predator-induced plasticity does not alter the pathway from evolution to ecology among locally adapted populations of Daphnia

In the growing field of eco-evolutionary dynamics, evidence for an influence of rapid shifts in phenotype on ecological processes is accumulating, yet, the contributions of phenotypic plasticity versus genetic change to these observed ecological changes are unclear. In one of the best studied ecosystems in terms of eco-evolutionary dynamics, landlocked versus anadromous alewife (Alosa pseudoharengus) have caused strong evolutionary divergence in their key zooplankton prey (Daphnia ambigua). We previously showed that such evolutionary differences have cascading ecological effects on consumer-resource dynamics and primary production. Yet, these locally adapted populations of Daphnia also differ in trait plasticity, which may, in turn, modify the pathway from evolution to ecology. Here we compared Daphnia from lakes with landlocked versus anadromous alewife for differences in rates of population growth in the presence and absence of predator cues over the course of a 39-day experiment. We predicted that predator-induced shifts in life history traits would facilitate faster rates of population growth. Contrary to our expectations, predator cue exposure did not alter rates of population growth. We instead found that Daphnia from lakes with landlocked alewife ultimately attained higher population densities (and exhibited faster population growth) when compared with Daphnia from lakes with anadromous alewife. Based on our previous work, these population level responses were unexpected, as Daphnia from lakes with landlocked alewife exhibit slower rates of somatic growth and delayed maturation. We discuss our results in lieu of the known differences in plasticity and how the population growth patterns may be influenced by resource limitation.

Life history trait divergence among populations of a non‐palatable species reveals strong non‐trophic indirect effects of an abundant herbivore

When large herbivores exert selection on their prey plant species, co‐occurring, non‐prey species may experience selection through non‐trophic indirect effects. Such selection is likely common where herbivores are overabundant. Yet, empirical studies of non‐trophic indirect effects as drivers of non‐prey trait evolution are lacking. Here we test for adaptive shifts in life history traits in an unpalatable species, Arisaema triphyllum, a common forest perennial that is unique because it exhibits size‐dependent sex switching. We collected A. triphyllum from six sites that experience a gradient in abiotic stress caused by deer browse pressure on prey plant species that generate indirect effects. We grew A. triphyllum from these sites in a common garden for five years to evaluate life history predictions linking strong indirect effects and abiotic stress to changes in life history traits: flowering onset size threshold, female flowering size threshold, relative growth rate (RGR), biomass allocation, and asexual reproduction. Despite observed differences among phenotypes in the field, expression of flowering onset size threshold, biomass allocation, and asexual reproduction did not differ among the six populations in the garden, indicating common plastic responses. In contrast, A. triphyllum collected from sites experiencing the two highest deer impacts exhibited smaller female flowering size thresholds and the highest RGR. Responses in these traits support the predictions of adaptive divergence in response to indirect effects. Our results reinforce the idea that non‐trophic indirect effects of large herbivores can elicit evolutionary responses in some traits of non‐prey species. In general, life history traits of unpalatable species may be cryptically adapting to stressful indirect effects where large herbivores are overabundant.

Fine scale spatio-temporal life history shifts in an invasive species at its expansion front

The dynamic shifts in life history traits by non-native populations at an invasion front may be driven by a combination of phenotypic plasticity and micro-evolutionary processes, allowing for appropriate responses to changes in biotic and abiotic factors associated with range expansion. The temporal and spatial scale at which these shifts occur, however, is largely unexplored. We examined the age-specific life-history responses of female round goby (Neogobius melanostomus) across a fine spatial scale by comparing traits of individuals at the expanding front of an invasive pathway with those of individuals living at the previous year’s front. Females in the new front were younger, exhibited higher body condition index and fecundity, and greater reproductive allocation than those living at the previous year’s front. No difference in back-calculated length at age or in seasonal growth increment was found between occupants of the old and new fronts. Age-specific differences in reproductive investment were observed; age-1 females from the new front exhibited greater reproductive effort but similar reproductive allocation, whereas age-2 females showed greater reproductive allocation in the new front, but similar reproductive effort. These age-specific differences may be related to differences in population density and other biotic factors encountered during ontogeny, or to micro-evolutionary processes. Our results demonstrate that fine scale changes in energy allocation towards reproduction through increases in reproductive allocation and fecundity occur at the invasion front, highlight how quickly those shifts can occur at the expansion front, and suggest that such changes in newly colonised areas facilitate range expansion.

Patterns and drivers of intraspecific variation in avian life history along elevational gradients: a meta-analysis.

Elevational gradients provide powerful natural systems for testing hypotheses regarding the role of environmental variation in the evolution of life-history strategies. Case studies have revealed shifts towards slower life histories in organisms living at high elevations yet no synthetic analyses exist of elevational variation in life-history traits for major vertebrate clades. We examined (i) how life-history traits change with elevation in paired populations of bird species worldwide, and (ii) which biotic and abiotic factors drive elevational shifts in life history. Using three analytical methods, we found that fecundity declined at higher elevations due to smaller clutches and fewer reproductive attempts per year. By contrast, elevational differences in traits associated with parental investment or survival varied among studies. High-elevation populations had shorter and later breeding seasons, but longer developmental periods implying that temporal constraints contribute to reduced fecundity. Analyses of clutch size data, the trait for which we had the largest number of population comparisons, indicated no evidence that phylogenetic history constrained species-level plasticity in trait variation associated with elevational gradients. The magnitude of elevational shifts in life-history traits were largely unrelated to geographic (altitude, latitude), intrinsic (body mass, migratory status), or habitat covariates. Meta-population structure, methodological issues associated with estimating survival, or processes shaping range boundaries could potentially explain the nature of elevational shifts in life-history traits evident in this data set. We identify a new risk factor for montane populations in changing climates: low fecundity will result in lower reproductive potential to recover from perturbations, especially as fewer than half of the species experienced higher survival at higher elevations.

Trans‐generational priming of resistance in wild flour beetles reflects the primed phenotypes of laboratory populations and is inhibited by co‐infection with a common parasite

Summary Trans‐generational priming renders offspring of immune‐challenged parents less susceptible to disease‐induced mortality, and has been demonstrated in a variety of arthropod taxa under controlled laboratory conditions. However, relatively little is known about the applicability of these laboratory results to priming in wild populations, especially in the context of environmental variables like maternal co‐infection and potential trade‐offs with other life history traits. We performed nearly parallel trans‐generational priming experiments on laboratory and wild strains of Tribolium beetles against the bacterial pathogen Bacillus thuringiensis (Bt). We investigated the impact of maternal immune challenge on offspring survival and development time, as well as the correlation between development and survival by priming status. Furthermore, we manipulated wild beetle parental co‐infection with a gregarine parasite that was prevalent in the wild population in order to determine the impact of co‐infection on the efficacy of trans‐generational priming. Trans‐generational priming resulted in a large but birth order‐dependent acceleration of offspring development time, and enhanced offspring survival against infection, in both laboratory and wild populations. However, adult parental co‐infection with gut protozoa severely curtailed primed offspring survival against Bt infection. These results suggest that shifts in life history traits associated with trans‐generational priming in laboratory model systems extend to wild populations. These traits, including survival, development, and interference from co‐infection, are important parameters for predicting the impact of priming on disease dynamics in the wild.

Linking the evolution of habitat choice to ecosystem functioning: direct and indirect effects of pond-reproducing fire salamanders on aquatic-terrestrial subsidies

Shifts in life history traits and in the behaviour of species can potentially alter ecosystem functioning. The reproduction of the central European fire salamander (Salamandra salamandra), which usually deposits its larvae in first-order streams, in small pool and pond-like habitats, is an example of a recent local adaptation in this species. Here we aimed to quantify the direct and indirect effects of the predatory larvae on the aquatic food webs in the ponds and on the flux of matter between the ponds and adjacent terrestrial habitats. Our estimates are based on biomass data of the present pond fauna as well as on the analysis of stomach content data, growth rates and population dynamics of the salamander larvae in pond habitats. By their deposition of larvae in early spring, female fire salamanders import between 0.07 and 2.86 g dry mass m(-2) larval biomass into the ponds. Due to high mortality rates in the larval phase and the relatively small size at metamorphosis of the pond-adapted salamanders compared to stream-adapted ones, the biomass export of the metamorphosed salamanders clearly falls below the initial biomass import. Catastrophic events such as high water temperatures and low oxygen levels may even occasionally result in mass mortalities of salamander larvae and thus in a net 100 % import of the salamander biomass into the pond food webs. Indirect effects further accelerate this net import of matter into the aquatic habitat, e.g. the feeding of salamanders on aquatic insect larvae with the emergence of terrestrial adults-thus preventing export-and on terrestrial organisms that fall on the water surface (supporting import). This study demonstrates that the adaptation of salamanders to pond reproduction can alter food web linkages across ecosystem boundaries by enhancing the flux of materials and energy from terrestrial (i.e. forest) to the aquatic (i.e. pond) habitat.

Life-history trait and functional diversity patterns of ground beetles and spiders along a coastal heathland successional gradient

We investigated patterns in species richness and diversity, life-history traits and functional diversity of carabid beetles and spiders along a coastal heathland successional gradient. We sampled in five successional stages on the island of Hiddensee, Germany. Species richness of carabids and spiders and Simpson diversity for spiders did not differ among stages. Functional dispersion (FDis), a measure of functional richness, was lowest in the youngest stage for both carabids and spiders. Older successional stages represent more heterogeneous habitats and offer a broader range of niches, which might enhance functional dispersion. Functional evenness (FEve) differed among successional stages for spiders, indicating an uneven distribution of species abundances in the functional trait space. Functional divergence (FDiv) did not differ among stages for either taxon. Shifts in life-history traits were noted in both arthropod groups, but not always in the same direction: Body size of carabid beetles increased towards older successional stages, but decreased for spiders. The number of flightless carabid species increased towards older habitats. Each successional stage seemingly favors species with distinct life-history traits (species sorting). We conclude that a trait-based approach including the use of functional diversity measurements (FDis) could contribute valuable information for biodiversity conservation.

Life history change in response to fishing and an introduced predator in the East African cyprinid Rastrineobola argentea

Fishing and introduced species are among the most important stressors affecting freshwaters and can also be strong selective agents. We examined the combined effects of commercial fishing and an introduced predator (Nile perch, Lates niloticus) on life history traits in an African cyprinid fish (Rastrineobola argentea) native to the Lake Victoria basin in East Africa. To understand whether these two stressors have driven shifts in life history traits of R. argentea, we tested for associations between life history phenotypes and the presence/absence of stressors both spatially (across 10 Ugandan lakes) and temporally (over four decades in Lake Victoria). Overall, introduced Nile perch and fishing tended to be associated with a suite of life history responses in R. argentea, including: decreased body size, maturation at smaller sizes, and increased reproductive effort (larger eggs; and higher relative fecundity, clutch volume, and ovary weight). This is one of the first well-documented examples of fisheries-induced phenotypic change in a tropical, freshwater stock; the magnitude of which raises some concerns for the long-term sustainability of this fishery, now the most important (by mass) in Lake Victoria.

Temporal genetic stability and high effective population size despite fisheries-induced life-history trait evolution in the North Sea sole

Heavy fishing and other anthropogenic influences can have profound impact on a species' resilience to harvesting. Besides the decrease in the census and effective population size, strong declines in mature adults and recruiting individuals may lead to almost irreversible genetic changes in life-history traits. Here, we investigated the evolution of genetic diversity and effective population size in the heavily exploited sole (Solea solea), through the analysis of historical DNA from a collection of 1379 sole otoliths dating back from 1957. Despite documented shifts in life-history traits, neutral genetic diversity inferred from 11 microsatellite markers showed a remarkable stability over a period of 50 years of heavy fishing. Using simulations and corrections for fisheries induced demographic variation, both single-sample estimates and temporal estimates of effective population size (N(e) ) were always higher than 1000, suggesting that despite the severe census size decrease over a 50-year period of harvesting, genetic drift is probably not strong enough to significantly decrease the neutral diversity of this species in the North Sea. However, the inferred ratio of effective population size to the census size (N(e) /N(c) ) appears very small (10(-5) ), suggesting that overall only a low proportion of adults contribute to the next generation. The high N(e) level together with the low N(e) /N(c) ratio is probably caused by a combination of an equalized reproductive output of younger cohorts, a decrease in generation time and a large variance in reproductive success typical for marine species. Because strong evolutionary changes in age and size at first maturation have been observed for sole, changes in adaptive genetic variation should be further monitored to detect the evolutionary consequences of human-induced selection.

Human predators outpace other agents of trait change in the wild

The observable traits of wild populations are continually shaped and reshaped by the environment and numerous agents of natural selection, including predators. In stark contrast with most predators, humans now typically exploit high proportions of prey populations and target large, reproductive-aged adults. Consequently, organisms subject to consistent and strong 'harvest selection' by fishers, hunters, and plant harvesters may be expected to show particularly rapid and dramatic changes in phenotype. However, a comparison of the rate at which phenotypic changes in exploited taxa occurs relative to other systems has never been undertaken. Here, we show that average phenotypic changes in 40 human-harvested systems are much more rapid than changes reported in studies examining not only natural (n = 20 systems) but also other human-driven (n = 25 systems) perturbations in the wild, outpacing them by >300% and 50%, respectively. Accordingly, harvested organisms show some of the most abrupt trait changes ever observed in wild populations, providing a new appreciation for how fast phenotypes are capable of changing. These changes, which include average declines of almost 20% in size-related traits and shifts in life history traits of nearly 25%, are most rapid in commercially exploited systems and, thus, have profound conservation and economic implications. Specifically, the widespread potential for transitively rapid and large effects on size- or life history-mediated ecological dynamics might imperil populations, industries, and ecosystems.

Hybridization and invasiveness in the freshwater snail Melanoides tuberculata: hybrid vigour is more important than increase in genetic variance

Many invasive taxa are hybrids, but how hybridization boosts the invasive process remains poorly known. We address this question in the clonal freshwater snail Melanoides tuberculata from Martinique, using three parental and two hybrid lines. We combine an extensive field survey (1990-2003) and a quantitative genetic experiment to show that hybrid lines have outcompeted their parents in natural habitats, and that this increased invasiveness co-occurred with pronounced shifts in life-history traits, such as growth, fecundity and juvenile size. Given the little time between hybrid creation and sampling, and the moderate standing genetic variance for life-history traits in hybrids, we show that some of the observed trait changes between parents and hybrids were unlikely to arise only by continuous selection. We therefore suggest that a large part of hybrid advantage stems from immediate heterosis upon hybridization.

Explaining variation in life-history traits: growth rate, size, and fecundity in a marine snail across an environmental gradient lacking predators

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 296:229-239 (2005) - doi:10.3354/meps296229 Explaining variation in life-history traits: growth rate, size, and fecundity in a marine snail across an environmental gradient lacking predators L. Miguel Pardo1,2,*, Ladd E. Johnson1 1Département de biologie & Québec-Ocean, Université Laval, Québec, Québec G1K 7P4, Canada2Universidad Austral de Chile, Facultad de Ciencias, Instituto de Biologia Marina ‘Jurgen Winter’, Independencia 641, Valdivia, Chile *Email: luispardo@uach.cl ABSTRACT: Intertidal invertebrates are model organisms for examining the environmental control of life-history traits because of the sharp gradients in biological and physical factors found in their habitat, including wave action, temperature, food availability, and predation. However, the effect of a particular factor on ecological and evolutionary processes is difficult to separate when multiple factors vary simultaneously. We examined shifts in life-history traits in the intertidal gastropod Littorina saxatilis Olivi across an intertidal shoreline where predation appears to have little influence. We determined the density, size, fecundity, and size at maturity of snails in 4 distinct zones across the shoreline and estimated growth rates in each zone. Size, fecundity, median size at maturity, and growth rate all exhibited pronounced clines across the shoreline with higher values in the lower zones, where food abundance was highest. Snail density, however, peaked in the mid-zones. The clines in life-history traits corresponded with food availability and environmental stress (wave forces and desiccation stress), and these factors were the likely determinants of the patterns observed. We also conducted a reciprocal transplant experiment between the extreme zones to assess if any differences in growth rate might have a genetic basis. Snails transplanted from the high zone to the low zone grew 7 times faster than snails that remained in the high zone and, more unexpectedly, 1.6 times greater than local snails from the low zone. Snails transplanted from the low zone to the high zone did not grow at all while local snails from the high zone had slow, although measurable, growth. These divergent responses of transplanted snails (i.e. counter-gradient variation) suggest that there may be differential size-dependent selection between the extreme zones with the greater wave forces of the low shore selecting against fast growth which would otherwise be supported by the abundance of food found there. KEY WORDS: Cline · Counter-gradient variance · Littorina saxatilis · Resource gradient · Rocky intertidal shore Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 296. Online publication date: July 12, 2005 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2005 Inter-Research.

Adaptation to environmental stress in Daphnia magna simultaneously exposed to a xenobiotic

In standardized ecotoxicological testing chemicals are investigated under optimal conditions for the test organisms despite the fact that environmental factors such as predation pressure and food availability are important parameters regulating natural populations. Food limitation and predator presence can induce shifts in life-history traits in various Daphnia species, especially trade-offs in reproductive biomass allocation. These adaptive responses are thought to ensure survival of the population in a highly variable environment. A xenobiotic dispersant (used in textile dyeing processes) also shifted the biomass allocation of Daphnia magna. To assess whether the dispersant could hinder D. magna adaptation to varying environmental conditions, we conducted experiments with food level and presence of Chaoborus larvae as environmental factors and simultaneous exposure to the dispersant. At low food level and in presence of the predator, D. magna produced fewer but larger sized neonates, regardless of dispersant exposure. The dispersant shifted biomass allocation towards more but smaller sized offspring in all experiments. However, the adaptive response to the environmental factors and the dispersant effect cancelled each other out in that they induced independently from each other opposite shifts in biomass allocation. In summary, the dispersant exposure resulted not in an inhibition of the adaptive response but in a reduction of the value of the response. Our study with this model substance demonstrates that xenobiotics can affect the adaptation of organisms to environmental stress which can result in effects likely to be overlooked in standardized testing.

Shifts in Life-History Traits as a Response to Cannibalism in Larval Long-Toed Salamanders ( Ambystoma macrodactylum )

We examined the potential influence of cannibalism on life-history characteristics of larval long-toed salamanders (Ambystoma macrodactylum). Using a 2 × 2 factorial design, crossing morphology with diet, we exposed typical morph larvae to one of four types of stimulus animals: cannibal morphs fed a conspecific diet, cannibal morphs fed a heterospecific diet (i.e., Tubifex), typical morphs fed a conspecific diet, and typical morphs fed a heterospecific diet. Test larvae exposed to stimulus animals fed a conspecific diet exhibited a slower growth rate and an increase in the time taken to reach metamorphosis. These changes in life history likely represent a cost of antipredator behavior.