Chaoborus and Gasterosteus Anti-Predator Responses in Daphnia pulex Are Mediated by Independent Cholinergic and Gabaergic Neuronal Signals

Many prey species evolved inducible defense strategies that protect effectively against predation threats. Especially the crustacean Daphnia emerged as a model system for studying the ecology and evolution of inducible defenses. Daphnia pulex e.g. shows different phenotypic adaptations against vertebrate and invertebrate predators. In response to the invertebrate phantom midge larvae Chaoborus (Diptera) D. pulex develops defensive morphological defenses (neckteeth). Cues originating from predatory fish result in life history changes in which resources are allocated from somatic growth to reproduction. While there are hints that responses against Chaoborus cues are transmitted involving cholinergic neuronal pathways, nothing is known about the neurophysiology underlying the transmission of fish related cues. We investigated the neurophysiological basis underlying the activation of inducible defenses in D. pulex using induction assays with the invertebrate predator Chaoborus and the three-spined stickleback Gasterosteus aculeatus. Predator-specific cues were combined with neuro-effective substances that stimulated or inhibited the cholinergic and gabaergic nervous system. We show that cholinergic-dependent pathways are involved in the perception and transmission of Chaoborus cues, while GABA was not involved. Thus, the cholinergic nervous system independently mediates the development of morphological defenses in response to Chaoborus cues. In contrast, only the inhibitory effect of GABA significantly influence fish-induced life history changes, while the application of cholinergic stimulants had no effect in combination with fish related cues. Our results show that cholinergic stimulation mediates signal transmission of Chaoborus cues leading to morphological defenses. Fish cues, which are responsible for predator-specific life history adaptations involve gabaergic control. Our study shows that both pathways are independent and thus potentially allow for adjustment of responses to variable predation regimes

Indicator macroinvertebrate species in a temporary Mediterranean river: recognition of patterns in binary assemblage data with a Kohonen artificial neural network

Current classifications used in bioassessment programs, as defined by the Water Framework Directive (WFD), do not sufficiently capture the variability present in temporary Mediterranean streams. This may result in inaccurate evaluation of the water quality biological metrics and difficulties in setting reference conditions. The aim of the study was to examine if aquatic invertebrate data of increased taxonomical resolution but expressed on a binary abundance (frequent/rare) scale and referring to good bioindicator species only suffice to indicate clear gradients in water courses with high natural variability such as intermittent Mediterranean streams. Invertebrate samples were collected from 74 sites in the Quarteira River basin, located in southern Portugal. Their classification with the use of a Kohonen artificial neural network (i.e., self-organising map, SOM) resulted in five categories. The variables that drove this categorization were primarily altitude, temperature and conductivity, but also type of substrate, riparian cover and percentage of riffles present. According to the indicator species analysis (ISA), almost all the studied taxa were significantly associated with certain SOM categories except for the category that included sites with disrupted flow regime. The SOM and ISA allowed us to effectively recognize biotic and abiotic patterns. Combined application of both methods may thus greatly enhance the effectiveness and precision of biological surveillance and establish reference sites for specific channel units in streams with high natural variability such as intermittent Mediterranean streams. (C) 2016 Elsevier Ltd. All rights reserved.Foundation for Science and Technology (FCT) of Portugal [ERA-IWRM/0003/2009

A study of Daphnia-Leptodora-juvenile Percids interactions using a mathematical model in the biomanipulated Sulejow Reservoir

A model (DALIS 1.0) of pelagic zone trophic interactions was developed using long-term, comprehensive data sets of the Sulejow Reservoir. We calibrated the model using observations from the pelagic zone of the Sulejow Reservoir made between 1999 and 2001. The model performed well in the description of Daphnia sp. – L. kindtii interactions when hydrological conditions were stable. A discrepancy between observed and simulated results was found when water inflows were high, which washed out the biota. We suggested that the hydrological impacts should be coupled in the updated DALIS model. Using DALIS, we also tested two scenarios: the food web model (A) without Leptodora; and (B) without YOY fish, under both good and bad food conditions for Daphnia. Results indicated that Leptodora would have a more significant impact on the reduction of Daphnia biomass than juvenile fish during some periods. As the maintenance of high Daphnia densities is recognised as a key factor in top-down effects, the DALIS model may provide frameworks that support ongoing empirical work. It is therefore recommended that the model be incorporated into the programme of the Sulejow Reservoir restoration