Seasonal variation in the response to a toxin-producing cyanobacteria in Daphnia

Many populations of water fleas (Daphnia) are exposed to algal blooms dominated by microcystin-producing cyanobacteria. However, the severity of these effects on Daphnia fitness remain poorly understood in natural populations. We investigated seasonal changes in body size, reproduction and survival of D. longispina individuals from five eutrophic lakes in southern Sweden. We tested whether individuals collected before, during or following algal blooms differed in their reproduction and survival when experimentally exposed to microcystin-producing cyanobacteria. The concentration of microcystin in the lakes was significantly higher during summer and autumn compared to spring, but there were substantial differences between lakes. The reproductive output of individuals declined consistently over the season, and this decline was stronger for Daphnia collected during periods of, or from lakes with, high microcystin concentration. There was little evidence that individuals adapted to the toxin over the season. The strong seasonal changes in body size, reproduction and survival in these D. longispina appear to be caused partly by variation in the abundance of toxin-producing cyanobacteria. Populations were unable to adapt sufficiently quickly during summer and autumn to recover from the negative effects of microcystin. We therefore suggest that seasonal increases in tolerance to microcystin-producing cyanobacteria have limited effects on the eco-evolutionary dynamics between Daphnia and phytoplankton

A field experiment reveals seasonal variation in the Daphnia gut microbiome

The gut microbiome is increasingly recognized for its impact on host fitness, but it remains poorly understood how naturally variable environments influence gut microbiome diversity and composition. We studied changes in the gut microbiome of ten genotypes of water fleas Daphnia magna in submerged mesocosm enclosures in a eutrophic lake over a period of 16 weeks, from early summer to autumn. The microbial diversity increased when Daphnia were reintroduced from the laboratory to the lake, and the composition of gut microbes drastically changed. Both gut microbiome diversity and composition continued to change over the 16-week period, with alpha diversity peaking in late summer. The gut microbiome community was clearly distinct from that of the surrounding water, and temporal changes in the two communities were independent of each other. There were no consistent differences in the gut microbiomes among Daphnia genotypes in the lake environment. The change in gut microbiome over the season was accompanied by a decline in reproductive output and survival. There were weak, but statistically supported, effects of microbiota composition on Daphnia fitness, but there was no evidence that natural variation in microbiome diversity or composition was associated with tolerance to the cyanotoxin microcystin. We conclude that the gut microbiome of Daphnia is highly dynamic in a natural lake environment, but that host genetic effects on microbiome diversity and composition between genotypes within a population can be vanishingly small. These results emphasize that establishing the ecological effects of gut microbiota will require large-scale experiments under natural conditions

Predation risk and the evolution of a vertebrate stress response: Parallel evolution of stress reactivity and sexual dimorphism

Predation risk is often invoked to explain variation in stress responses. Yet, the answers to several key questions remain elusive, including the following: (1) how predation risk influences the evolution of stress phenotypes, (2) the relative importance of environmental versus genetic factors in stress reactivity and (3) sexual dimorphism in stress physiology. To address these questions, we explored variation in stress reactivity (ventilation frequency) in a post-Pleistocene radiation of live-bearing fish, where Bahamas mosquitofish (Gambusia hubbsi) inhabit isolated blue holes that differ in predation risk. Individuals of populations coexisting with predators exhibited similar, relatively low stress reactivity as compared to low-predation populations. We suggest that this dampened stress reactivity has evolved to reduce energy expenditure in environments with frequent and intense stressors, such as piscivorous fish. Importantly, the magnitude of stress responses exhibited by fish from high-predation sites in the wild changed very little after two generations of laboratory rearing in the absence of predators. By comparison, low-predation populations exhibited greater among-population variation and larger changes subsequent to laboratory rearing. These low-predation populations appear to have evolved more dampened stress responses in blue holes with lower food availability. Moreover, females showed a lower ventilation frequency, and this sexual dimorphism was stronger in high-predation populations. This may reflect a greater premium placed on energy efficiency in live-bearing females, especially under high-predation risk where females show higher fecundities. Altogether, by demonstrating parallel adaptive divergence in stress reactivity, we highlight how energetic trade-offs may mould the evolution of the vertebrate stress response under varying predation risk and resource availability

Gap junctions in olfactory neurons modulate olfactory sensitivity

<p>Abstract</p> <p>Background</p> <p>One of the fundamental questions in olfaction is whether olfactory receptor neurons (ORNs) behave as independent entities within the olfactory epithelium. On the basis that mature ORNs express multiple connexins, I postulated that gap junctional communication modulates olfactory responses in the periphery and that disruption of gap junctions in ORNs reduces olfactory sensitivity. The data collected from characterizing connexin 43 (Cx43) dominant negative transgenic mice OlfDNCX, and from calcium imaging of wild type mice (WT) support my hypothesis.</p> <p>Results</p> <p>I generated OlfDNCX mice that express a dominant negative Cx43 protein, Cx43/β-gal, in mature ORNs to inactivate gap junctions and hemichannels composed of Cx43 or other structurally related connexins. Characterization of OlfDNCX revealed that Cx43/β-gal was exclusively expressed in areas where mature ORNs resided. Real time quantitative PCR indicated that cellular machineries of OlfDNCX were normal in comparison to WT. Electroolfactogram recordings showed decreased olfactory responses to octaldehyde, heptaldehyde and acetyl acetate in OlfDNCX compared to WT. Octaldehyde-elicited glomerular activity in the olfactory bulb, measured according to odor-elicited <it>c-fos </it>mRNA upregulation in juxtaglomerular cells, was confined to smaller areas of the glomerular layer in OlfDNCX compared to WT. In WT mice, octaldehyde sensitive neurons exhibited reduced response magnitudes after application of gap junction uncoupling reagents and the effects were specific to subsets of neurons.</p> <p>Conclusions</p> <p>My study has demonstrated that altered assembly of Cx43 or structurally related connexins in ORNs modulates olfactory responses and changes olfactory activation maps in the olfactory bulb. Furthermore, pharmacologically uncoupling of gap junctions reduces olfactory activity in subsets of ORNs. These data suggest that gap junctional communication or hemichannel activity plays a critical role in maintaining olfactory sensitivity and odor perception.</p

Adaptive and non-adaptive responses to toxin-producing cyanobacteria in water fleas

Organisms regularly encounter stressful conditions that negatively affects their fitness. One way to minimize these negative effects is to use cues from the environment in order to develop an appropriate phenotype. Many populations of water fleas (Daphnia spp.) are exposed to algal blooms dominated by toxin- producing cyanobacteria during parts of the summer season, which can reduce growth, reproductive output and survival. Theory suggests that seasonal exposure to toxic cyanobacteria will favour maternal and transgenerational effects that promote tolerance. However, it is poorly understood if, and to what extent, Daphnia can develop tolerance when exposed to toxins over one or several generations.Here, I first investigate the scope and efficacy of maternal (Paper I) and transgenerational (Paper II) effects in this system. Secondly, I examined how the overall fitness, and tolerance to the cyanotoxin microcystin in particular, changes across the season in a natural lake environment (Paper III and IV). Finally, I attempted to link variation in growth, reproductive output and survival to changes in the diversity and composition of the gut microbiome (Paper II and IV), one possible mechanism that enable cumulative transgenerational adaptive change in response to a toxic diet.In agreement with previous studies, I find that exposure to toxin-producing cyanobacteria consistently reduces fitness in Daphnia, both in terms of reproductive output and survival. The ability of mothers to transfer tolerance to their offspring was limited (Paper I), and there was little evidence that these positive effects accumulate across several generations (Paper II). These results fit well with studies of natural seasonal variation in how microcystin-producing cyanobacteria affected fitness, which provided no robust evidence for an increase in tolerance following blooms (Paper III and IV). Instead, the fitness of Daphnia declined steadily over the season in both experiments, an effect that could partly be attributed to natural exposure to microcystin-producing cyanobacteria (Paper III).The gut microbiome was strongly influenced by seasonal changes in a lake environment (Paper IV). The microbiome was also affected by different cyanobacteria environments in the laboratory (Paper II), but these effects were only weakly correlated with the ability to tolerate microcystin-producing cyanobacteria.In summary, this work shows that there are both adaptive and non-adaptive responses to toxin-producing cyanobacteria in Daphnia. The adaptive value of transgenerational effects in this system was consistently small, and does not support the existence of a dedicated machinery to transfer information between generations. This probably also means that induced changes in tolerance within a season have a limited influence on the dynamics of Daphnia populations, even in populations that are recurrently exposed to toxic algal blooms

Seasonal variation in the response to a toxin-producing cyanobacteria in Daphnia

Many populations of water fleas (Daphnia) are exposed to algal blooms dominated by microcystin-producing cyanobacteria. However, the severity of these effects on Daphnia fitness remain poorly understood in natural populations. We investigated seasonal changes in body size, reproduction and survival of D. longispina individuals from five eutrophic lakes in southern Sweden. We tested whether individuals collected before, during or following algal blooms differed in their reproduction and survival when experimentally exposed to microcystin-producing cyanobacteria. The concentration of microcystin in the lakes was significantly higher during summer and autumn compared to spring, but there were substantial differences between lakes. The reproductive output of individuals declined consistently over the season, and this decline was stronger for Daphnia collected during periods of, or from lakes with, high microcystin concentration. There was little evidence that individuals adapted to the toxin over the season. The strong seasonal changes in body size, reproduction and survival in these D. longispina appear to be caused partly by variation in the abundance of toxin-producing cyanobacteria. Populations were unable to adapt sufficiently quickly during summer and autumn to recover from the negative effects of microcystin. We therefore suggest that seasonal increases in tolerance to microcystin-producing cyanobacteria have limited effects on the eco-evolutionary dynamics between Daphnia and phytoplankton

Sex and the Syndrome: Individual and Population Consistency in Behaviour in Rock Pool Prawn Palaemon elegans

Animal personality has been widely documented across a range of species. The concept of personality is composed of individual behavioural consistency across time and between situations, and also behavioural trait correlations known as behavioural syndromes. Whilst many studies have now investigated the stability of individual personality traits, few have analysed the stability over time of entire behavioural syndromes. Here we present data from a behavioural study of rock pool prawns. We show that prawns are temporally consistent in a range of behaviours, including activity, exploration and boldness, and also that a behavioural syndrome is evident in this population. We find correlations between many behavioural traits (activity, boldness, shoaling and exploration). In addition, behavioural syndrome structure was consistent over time. Finally, few studies have explicitly studied the role of sex differences in personality traits, behavioural consistency and syndrome structure. We report behavioural differences between male and female prawns but no differences in patterns of consistency. Our study adds to the growing literature on animal personality, and provides evidence showing that syndromes themselves can exhibit temporal consistency

Egg sizes - data for mothers

Data of the mothers for which egg sizes were measured. iid = individual identity of the mother, tox = treatment of the mother (0 = non-toxic, 1 = toxic), gid = genotype identity, avt = z-score for the average time interval between the first and second, and second and third brood, abs = z-score for the average size of the second and third brood

Maternal effects experiments

Data from all 5 maternal effects experiments. eid = experiment number (1-5), iid = individual identity, gid = genotype identity, trt = treatment (C = control, CC = control/control, CM = control/full, E = early, EC = early/control, EM = early/full, F = full, FC = full/control, FM = full/full, L=late, LC = late/control, LM = late/full, M = full, MC = full/control, MM = full/full) mid = mother identity, ar1 = age at first brood, ar2 = age at second brood, ar3 = age at third brood, bs1 = size first brood, bs2 = size second brood, bs3 = size third brood, txp = toxicity as the proportion of cyanobacteria in the food (measured as the fraction of total organic carbon weight per liter medium), txc = toxicity as the concentration of cyanobacteria (measured as mg of organic carbon per liter of medium), txm = toxicity as the concentration of microcystin (ug/L), gr2 = fitness estimate after 2 broods, gr3 = fitness estimate after 3 broods