Predator–prey interactions in a changing world: humic stress disrupts predator threat evasion in copepods

Water Colour Shapes Diving Beetle (Coleoptera: Dytiscidae) Assemblages in Urban Ponds

Dramatic land-use changes in urban landscapes can drive water colour darkening by washing compounds, such as organic matter and iron, from terrestrial ecosystems into urban blue space, consequentially affecting aquatic communities. Here, I studied how pond water colour changes along an urban gradient and how diving beetles (Dytiscidae) respond to the water colour gradient in 11 ponds with fish and 15 ponds without fish in the Helsinki Metropolitan Area, Finland. I found that the pond water colour exhibited a non-significant decreasing pattern along the urban gradient, indicating that urbanisation may not necessarily drive brownification in urban ponds. Dytiscid species richness and abundance exhibited significant positive correlations with increasing water colour in ponds with fish but no significant correlation in ponds without fish. Some species, such as Agabus spp. and Dytiscus spp., appeared tolerant to highly coloured water, whereas some species, such as Hyphydrus ovatus and Hygrotus spp., tended to occur in clear water, indicating that brown water may provide dytiscids with prey refuges, but some species are intolerant to brown water. The study highlights the importance of urban pondscape heterogeneity to meet the needs of aquatic invertebrates that prefer different water colours and for the multifunctioning of urban ponds.

Hatching under brownification: DOC-mediated changes in physical, but not chemical properties of water affect hatching patterns of Cladocera resting eggs

Dissolved organic carbon (DOC) is often related to the brownification of water in continental aquatic systems and to changes in the physiology of zooplankton organisms. Zooplankton resting eggs are particularly sensitive to changes in light and chemical characteristics of water, but the physical and chemical effects associated to DOC on dormant stages have never been tested before. Herein, we tested how DOC affects hatching rates and time to hatching of Cladocera (Diaphanosoma birgei) resting eggs. In order to analyze the chemical (i.e., toxic) and physical (i.e., light attenuation) effects of DOC on hatching patterns, resting eggs were exposed to different concentrations of DOC (0, 50, and 100 mg L^-1) in an experimental design which isolated chemical from physical effects. When evaluating the physical effects of DOC, hatching was more than 150% less in 100 than 50 mg L^-1 DOC and time to hatching was 66% lesser in 50 mg L^-1 DOC than control. Hatchling numbers and time to hatching were not affected by DOC chemical effects. We conclude DOC effects on hatching mainly relied on light attenuation, while chemical effects were likely of minor importance. DOC may change Cladocera emergence patterns mainly through light attenuation in the water column.

Effects of Added Humic Substances and Nutrients on Photochemical Degradation of Dissolved Organic Matter in A Mesocosm Amendment Experiment in the Gulf of Finland, Baltic Sea

Humic substances, a component of terrestrial dissolved organic matter (tDOM), contribute to dissolved organic matter (DOM) and chromophoric DOM (CDOM) in coastal waters, and have significant impacts on biogeochemistry. There are concerns in recent years over browning effects in surface waters, due to increasing tDOM inputs, and their negative impacts on aquatic ecosystems, but relatively little work has been published on estuaries and coastal waters. Photodegradation could be a significant sink for tDOM in coastal environments, but the rates and efficiencies are poorly constrained. We conducted large-scale DOM photodegradation experiments in mesocosms amended with humic substances and nutrients in the Gulf of Finland to investigate the potential of photochemistry to remove added tDOM and the interactions of DOM photochemistry with eutrophication. The added tDOM was photodegraded rapidly, as CDOM absorption decreased and spectral slopes increased with increasing photons absorbed in laboratory experiments. The in situ DOM optical properties became similar amongst the control, humic-, and humic+nutrients-amended mesocosm samples towards the end of the amendment experiment, indicating degradation of the excess CDOM/DOM through processes including photodegradation. Nutrient additions didn't significantly influence the effects of added humic substances on CDOM optical property changes, but induced changes in DOM removal.

Does humic acid alter visually and chemically guided foraging in stickleback fish?

Sensory systems function under the influence of multiple, interacting environmental properties. When environments change, so may perception through one or more sensory systems, as alterations in transmission properties may change how organisms obtain and use information. Humic acids, a natural and anthropogenically produced class of chemicals, have attributes that may change chemical and visual environments of aquatic animals, potentially with detrimental consequences on their ability to locate necessary resources. Here, we explore how environmental disturbance affects the way threespine sticklebacks (Gasterosteus aculeatus) use visual and olfactory information during foraging. We compared foraging behavior using visual, olfactory, and bimodal (visual and olfactory) information in the presence and absence of humic acids. We found evidence that humic acids reduced olfactory-based food detection. While visual perception was not substantially impaired by humic acids, the visual sense alone did not compensate for the loss of olfactory perception. These findings suggest that a suite of senses still may not be capable of compensating for the loss of information from individual modalities. Thus, senses may react disparately to rapid environmental change, and thereby push species into altered evolutionary trajectories.

Visual detection thresholds in two trophically distinct fishes are compromised in algal compared to sedimentary turbidity

Increasing anthropogenic turbidity is among the most prevalent disturbances in freshwater ecosystems, through increases in sedimentary deposition as well as the rise of nutrient-induced algal blooms. Changes to the amount and color of light underwater as a result of elevated turbidity are likely to disrupt the visual ecology of fishes that rely on vision to survive and reproduce; however, our knowledge of the mechanisms underlying visual responses to turbidity is lacking. First, we aimed to determine the visual detection threshold, a measure of visual sensitivity, of two ecologically and economically important Lake Erie fishes, the planktivorous forage fish, emerald shiner (Notropis atherinoides), and a primary predator, the piscivorous walleye (Sander vitreus), under sedimentary and algal turbidity. Secondly, we aimed to determine if these trophically distinct species are differentially impacted by increased turbidity. We used the innate optomotor response to determine the turbidity levels at which individual fish could no longer detect a difference between a stimulus and the background (i.e. visual detection threshold). Detection thresholds were significantly higher in sedimentary compared to algal turbidity for both emerald shiner (meansediment ± SE = 79.66 ± 5.51 NTU, meanalgal ± SE = 34.41 ± 3.19 NTU) and walleye (meansediment ± SE = 99.98 ± 5.31 NTU, meanalgal ± SE = 40.35 ± 2.44 NTU). Our results suggest that across trophic levels, the visual response of fishes will be compromised under algal compared to sedimentary turbidity. The influence of altered visual environments on the ability of fish to find food and detect predators could potentially be large, leading to population- and community-level changes within the Lake Erie ecosystem.

CrusTF: a comprehensive resource of transcriptomes for evolutionary and functional studies of crustacean transcription factors

Background

Crustacea, the second largest subphylum of Arthropoda, includes species of major ecological and economic importance, such as crabs, lobsters, crayfishes, shrimps, and barnacles. With the rapid development of crustacean aquaculture and biodiversity loss, understanding the gene regulatory mechanisms of growth, reproduction, and development of crustaceans is crucial to both aquaculture development and biodiversity conservation of this group of organisms. In these biological processes, transcription factors (TFs) play a vital role in regulating gene expression. However, crustacean transcription factors are still largely unknown, because the lack of complete genome sequences of most crustacean species hampers the studies on their transcriptional regulation on a system-wide scale. Thus, the current TF databases derived from genome sequences contain TF information for only a few crustacean species and are insufficient to elucidate the transcriptional diversity of such a large animal group.

Results

Our database CrusTF (http://qinlab.sls.cuhk.edu.hk/CrusTF) provides comprehensive information for evolutionary and functional studies on the crustacean transcriptional regulatory system. CrusTF fills the knowledge gap of transcriptional regulation in crustaceans by exploring publicly available and newly sequenced transcriptomes of 170 crustacean species and identifying 131,941 TFs within 63 TF families. CrusTF features three categories of information: sequence, function, and evolution of crustacean TFs. The database enables searching, browsing and downloading of crustacean TF sequences. CrusTF infers DNA binding motifs of crustacean TFs, thus facilitating the users to predict potential downstream TF targets. The database also presents evolutionary analyses of crustacean TFs, which improve our understanding of the evolution of transcriptional regulatory systems in crustaceans.

Conclusions

Given the importance of TF information in evolutionary and functional studies on transcriptional regulatory systems of crustaceans, this database will constitute a key resource for the research community of crustacean biology and evolutionary biology. Moreover, CrusTF serves as a model for the construction of TF database derived from transcriptome data. A similar approach could be applied to other groups of organisms, for which transcriptomes are more readily available than genomes.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4305-2) contains supplementary material, which is available to authorized users.