The significance of partial migration for food web and ecosystem dynamics

Migration is ubiquitous and can strongly shape food webs and ecosystems. Less familiar, however, is that the majority of life cycle, seasonal and diel migrations in nature are partial migrations: only a fraction of the population migrates while the other individuals remain in their resident ecosystem. Here, we demonstrate different impacts of partial migration rendering it fundamental to our understanding of the significance of migration for food web and ecosystem dynamics. First, partial migration affects the spatiotemporal distribution of individuals and the food web and ecosystem-level processes they drive differently than expected under full migration. Second, whether an individual migrates or not is regularly correlated with morphological, physiological, and/or behavioural traits that shape its food-web and ecosystem-level impacts. Third, food web and ecosystem dynamics can drive the fraction of the population migrating, enabling the potential for feedbacks between the causes and consequences of migration within and across ecosystems. These impacts, individually and in combination, can yield unintuitive effects of migration and drive the dynamics, diversity and functions of ecosystems. By presenting the first full integration of partial migration and trophic (meta-)community and (meta-)ecosystem ecology, we provide a roadmap for studying how migration affects and is affected by ecosystem dynamics in a changing world.     

The distribution of coastal fish eDNA sequences in the Anthropocene

Aim

Coastal fishes have a fundamental role in marine ecosystem functioning and contributions to people, but face increasing threats due to climate change, habitat degradation and overexploitation. The extent to which human pressures are impacting coastal fish biodiversity in comparison with geographic and environmental factors at large spatial scale is still under scrutiny. Here, we took advantage of environmental DNA (eDNA) metabarcoding to investigate the relationship between fish biodiversity, including taxonomic and genetic components, and environmental but also socio-economic factors.

Location

Tropical, temperate and polar coastal areas.

Time period

Present day.

Major taxa studied

Marine fishes.

Methods

We analysed fish eDNA in 263 stations (samples) in 68 sites distributed across polar, temperate and tropical regions. We modelled the effect of environmental, geographic and socio-economic factors on α- and β-diversity. We then computed the partial effect of each factor on several fish biodiversity components using taxonomic molecular units (MOTU) and genetic sequences. We also investigated the relationship between fish genetic α- and β-diversity measured from our barcodes, and phylogenetic but also functional diversity.

Results

We show that fish eDNA MOTU and sequence α- and β-diversity have the strongest correlation with environmental factors on coastal ecosystems worldwide. However, our models also reveal a negative correlation between biodiversity and human dependence on marine ecosystems. In areas with high dependence, diversity of all fish, cryptobenthic fish and large fish MOTUs declined steeply. Finally, we show that a sequence diversity index, accounting for genetic distance between pairs of MOTUs, within and between communities, is a reliable proxy of phylogenetic and functional diversity.

Main conclusions

Together, our results demonstrate that short eDNA sequences can be used to assess climate and direct human impacts on marine biodiversity at large scale in the Anthropocene and can further be extended to investigate biodiversity in its phylogenetic and functional dimensions.     

The function of pulse song and sine song in the courtship of Drosophila melanogaster

Drosophila melanogaster females were subjected to pulse song before being allowed to mix with males. Sine song increases female receptivity, pulse song does not. Pulse song does however increase receptivity if the females are subjected to it while being courted by males which are deaf and which cannot produce any auditory stimulation themselves. It is suggested that sine song is summated and has a priming effect on female receptivity whereas pulse song functions as a species recognition signal in a trigger-like fashion.     

The PLEKHA7–PDZD11 complex regulates the localization of the calcium pump PMCA and calcium handling in cultured cells

The plasma membrane calcium ATPase (PMCA) extrudes calcium from the cytosol to the extracellular space to terminate calcium-dependent signaling. Although the distribution of PMCA is crucial for its function, the molecular mechanisms that regulate the localization of PMCA isoforms are not well understood. PLEKHA7 is implicated by genetic studies in hypertension and the regulation of calcium handling. PLEKHA7 recruits the small adapter protein PDZD11 to adherens junctions, and together they control the trafficking and localization of plasma membrane associated proteins, including the Menkes copper ATPase. Since PDZD11 binds to the C-terminal domain of b-isoforms of PMCA, PDZD11 and its interactor PLEKHA7 could control the localization and activity of PMCA. Here, we test this hypothesis using cultured cell model systems. We show using immunofluorescence microscopy and a surface biotinylation assay that KO of either PLEKHA7 or PDZD11 in mouse kidney collecting duct epithelial cells results in increased accumulation of endogenous PMCA at lateral cell–cell contacts and PDZ-dependent ectopic apical localization of exogenous PMCA4x/b isoform. In HeLa cells, coexpression of PDZD11 reduces membrane accumulation of overexpressed PMCA4x/b, and analysis of cytosolic calcium transients shows that PDZD11 counteracts calcium extrusion activity of overexpressed PMCA4x/b, but not PMCA4x/a, which lacks the PDZ-binding motif. Moreover, KO of PDZD11 in either endothelial (bEnd.3) or epithelial (mouse kidney collecting duct) cells increases the rate of calcium extrusion. Collectively, these results suggest that the PLEKHA7–PDZD11 complex modulates calcium homeostasis by regulating the localization of PMCA.     

The Thermosensitive Potassium Channel TREK-1 Contributes to Coolness-Evoked Responses of Grueneberg Ganglion Neurons

Neurons of the Grueneberg ganglion (GG) residing in the vestibule of the murine nose are activated by cool ambient temperatures. Activation of thermosensory neurons is usually mediated by thermosensitive ion channels of the transient receptor potential (TRP) family. However, there is no evidence for the expression of thermo-TRPs in the GG, suggesting that GG neurons utilize distinct mechanisms for their responsiveness to cool temperatures. In search for proteins that render GG neurons responsive to coolness, we have investigated whether TREK/TRAAK channels may play a role; in heterologous expression systems, these potassium channels have been previously found to close upon exposure to coolness, leading to a membrane depolarization. The results of the present study indicate that the thermosensitive potassium channel TREK-1 is expressed in those GG neurons that are responsive to cool temperatures. Studies analyzing TREK-deficient mice revealed that coolness-evoked responses of GG neurons were clearly attenuated in these animals compared with wild-type conspecifics. These data suggest that TREK-1 channels significantly contribute to the responsiveness of GG neurons to cool temperatures, further supporting the concept that TREK channels serve as thermoreceptors in sensory cells. Moreover, the present findings provide the first evidence of how thermosensory GG neurons are activated by given temperature stimuli in the absence of thermo-TRPs.     

Lipid and Phenolic Constituents from Seeds of Hypericum perforatum L. and Hypericum tetrapterum Fr. and their Antioxidant Activity

Seeds of Hypericum perforatum and H. tetrapterum were extracted with dichloromethane and methanol and investigated by chromatographic and mass spectrometric methods. Both species yielded a fatty oil fraction amounting to 30.5% and 18.0% of the seed weight, respectively. Linoleic acid (C18:2n‐6) was shown to be the predominant fatty acid constituent. Moreover, xanthone derivatives, i.e. tetrahydroxyxanthones (THX), xanthone‐glycosides and xanthone‐sulfonates, were assigned in methanolic extracts. For structure elucidation, one representative xanthone, namely 1,3,6,7‐THX, was synthesized and analyzed via HPLC‐DAD/MSⁿ and GC/MS. Total THX contents were quantitated applying a validated HPLC‐DAD method, resulting in 1.25 g/kg (H. perforatum) and 0.27 g/kg (H. tetrapterum), respectively. Moreover, the free radical scavenging capacity of the methanol extracts was tested using the DPPH antioxidant assay. Both, H. perforatum (IC₅₀ = 8.7 mg/l) and 1,3,6,7‐THX (IC₅₀ = 3.0 mg/l), exhibited good DPPH free radical scavenging activity compared to Trolox (IC₅₀ = 6.6 mg/l).