Solid phase extraction and metabolic profiling of exudates from living copepods

Copepods are ubiquitous in aquatic habitats. They exude bioactive compounds that mediate mate finding or induce defensive traits in prey organisms. However, little is known about the chemical nature of the copepod exometabolome that contributes to the chemical landscape in pelagic habitats. Here we describe the development of a closed loop solid phase extraction setup that allows for extraction of exuded metabolites from live copepods. We captured exudates from male and female Temora longicornis and analyzed the content with high resolution LC-MS. Chemometric methods revealed 87 compounds that constitute a specific chemical pattern either qualitatively or quantitatively indicating copepod presence. The majority of the compounds were present in both female and male exudates, but nine compounds were mainly or exclusively present in female exudates and hence potential pheromone candidates. Copepodamide G, known to induce defensive responses in phytoplankton, was among the ten compounds of highest relative abundance in both male and female extracts. The presence of copepodamide G shows that the method can be used to capture and analyze chemical signals from living source organisms. We conclude that solid phase extraction in combination with metabolic profiling of exudates is a useful tool to develop our understanding of the chemical interplay between pelagic organisms

Divergent foraging behaviour and shape in lateral plate morphs of threespined stickleback (Gasterosteus aculeatus).

Adaptation to different foraging resources is believed to be an important driving force of divergence between populations. Following colonization of freshwater, threespined sticklebacks (Gasterosteus aculeatus) have occupied and adapted to different types of aquatic niches. Adaptation to freshwater often involves, among other things, loss of lateral plates, shift to benthic resource exploitation, and change in body shape. Here, divergence in foraging behaviour and body shape is investigated among different lateral plate morphs coexisting in brackish water, and in a monomorphic population from a river habitat. Foraging behaviour was tested experimentally in the lab by observing fish that were offered benthic and pelagic prey simultaneously, while tracking the movements of the fish automatically. Shape differences were characterized using geometric morphometric Thin plate spline analysis. Significant and corresponding differences in foraging behaviour and shape were found between the plate morphs, and between sticklebacks from river and the lake. The results indicate ecological divergence towards benthic and pelagic habitat use between the plate morphs, resembling that of coexisting benthic-pelagic species pairs. This further suggests a possibility for evolution of ecologically based reproductive barriers between the coexisting morphs, although this remains to be investigated in more detail

Effects of predation risk on life history strategies in marine plankton

This thesis explores how different aspects of life history strategies in common marine planktonic organisms change when they perceive a chemical cue of predation risk. Predators can have dramatic effects on prey organisms by inducing responses only by their presence. Such induced defenses can actually have stronger effect on a community than the consumption itself, as the defenses influence a larger proportion of the prey and may create cascading effects in the food web. Despite their huge ecological importance much is still unknown about how marine plankton adjust life history traits according to prevailing predation pressure. Here, I have looked into some life history traits in marine plankton when experimentally exposed to predator chemical cues. Three studies focus on copepods, the dominating group of zooplankton. Importantly, my findings suggest that marine copepods do respond to predator chemical cues by altering several key life history traits. Paper I shows an effect of perceived predation risk on growth and development on naupliar stages of a common coastal species. In paper II non-consumptive effects on egg-carrying were demonstrated. Paper III documents significant costs in male copepod spermatophore production. Perceived risk generally altered swimming behavior and also feeding rates under food limited conditions. All in all, papers 1-III demonstrate that vital life history traits in copepods, like growth, development and reproductive investments by both females and males are to some extent regulated by predation risk. Paper IV considers chain length plasticity in a diatom, one of the most ecologically important phytoplankton groups. Based on experiments and an empirical model, we show that chain length plasticity in a common diatom species is consistent with a grazer avoidance strategy. Altogether, the results presented in my thesis suggest that predation risk is one of the mechanisms that regulate fundamental life history traits in marine plankton

Predator chemical cues increase growth and alter development in nauplii of a marine copepod

Copepods are a fundamental trophic link in the marine food web. While much attention has been devoted to the role of temperature and food for copepod development and growth, little is known about how marine copepods adjust their life history according to the prevailing predation risk. This is striking, considering the potential advantage of risk-sensitive life history, and the many reports of freshwater zooplankton showing strong effects of risk cues on growth and development. Here, we measured growth and development in nauplii of the marine copepod Temora longicornis. We incubated newly hatched nauplii individually with or without a predator chemical cue. Individuals were followed and measured repeatedly over time, generating high-resolution data. We estimated treatment-specific stage transition probabilities from daily molting frequencies. The nauplii showed an increased growth rate when exposed to fish kairomones. However, the corresponding response in development differed between stages, with the later naupliar stages generally displaying a higher molting probability and higher body mass (ash-free dry weight) per stage. These results suggest that development and growth in marine copepods is flexible and sensitive to predation risk. Our findings also indicate that investment in growth might be beneficial in copepods despite higher visibility

Is chain length in phytoplankton regulated to evade predation?

Formation of cell chains in phytoplankton is ecologically important, but no single factor driving the evolution of chain formation has been identified. Chain length in the diatom Skeletonema marinoi declines in response to grazer cues, which reduces grazing losses in simple laboratory incubations. Here we explore a more ecologically relevant scenario with fluctuating populations of different sized grazers, and test whether chain-length plasticity provides a selective advantage by lower grazing mortality. We used a model with empirical grazer densities, the effect of grazer cues on chain length, and size selective grazing rates. Finally we compared the model outcome with Skeletonema chain length and copepod biomass in the field. Low copepod densities induced chain-length reduction in Skeletonema, showing that the signaling system is sensitive enough to operate in nature. The model shows that reducing chain length in response to copepod cues reduces annual grazing losses by 31 and 36% compared with fixed traits with either single cells or long chains, respectively. The field measurements agree well with chain length being regulated by grazer abundances. We conclude that chain-length plasticity is a selective trait, and suggest that grazer regime could be an evolutionary driver of chain formation in phytoplankton

Arctic complexity: A case study on diel vertical migration of zooplankton

- © The Author 2014. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited

Non‑consumptive effects of predator presence on copepod reproduction: insights from a mesocosm experiment

14 pages, 8 figures, 2 tablesReproduction in planktonic animals depends on numerous biotic and abiotic factors. One of them is predation pressure, which can have both direct consumptive effects on population density and sex ratio, and non-consumptive effects, for example on mating and migration behaviour. In copepods, predator vulnerability depends on their sex, motility pattern and mating behaviour. Therefore, copepods can be affected at multiple stages during the mating process. We investigated the reproductive dynamics of the estuarine copepod Eurytemora affinis in the presence and absence of its predator the mysid Neomysis integer in a mesocosm experiment. We found that the proportion of ovigerous females decreased in the presence of predators. This shift was not caused by differential predation as the absolute number of females was unaffected by mysid presence. Presence of predators reduced the ratio of males to non-ovigerous females, but not by predation of males. Our combined results suggest that the shift from ovigerous to non-ovigerous females under the presence of predators was caused by either actively delayed egg production or by shedding of egg sacs. Nauplii production was initially suppressed in the predation treatment, but increased towards the end of the experiment. The proportion of fertilized females was similar in both treatments, but constantly fell behind model predictions using a random mating model. Our results highlight the importance of non-consumptive effects of predators on copepod reproduction and hence on population dynamics. © 2014 Springer-Verlag Berlin HeidelbergThe research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 228224, MESOAQUA (Grant Number: MESOAQUA 16. COPEPODSEX.HEUSCHELE). J. H. was funded by a Deutsche Forschungsgemeinschaft Research Fellowship (grant number HE 6050/1-1)Peer Reviewe