Behavioural changes of native freshwater prawn in the presence of a predator fish

Predation pressure influences animal behaviour in relation to feeding, exposure to predators and habitat use. In the presence of a predator, prey usually decreases feeding and activity, avoiding predation-risk areas. This study evaluated the visual effects of a predator fish (red-bellied piranha Pygocentrus nattereri) on the behaviour and habitat use of Macrobrachium jelskii prawn. It was hypothesized that prawns would modify their behaviour in the presence of a predator, decreasing their general activity (foraging and locomotion) and seeking shelter more frequently. Twenty behavioural tests were carried out without and with the presence of a predator using five different M. jelskii individuals per trial. Behavioural data were collected using scan sampling with instantaneous recording of behaviours every 15 s during 5 min in each trial. The presence of the predator caused prawns to decrease their locomotion and feeding and increase environment exploration and predator inspection. Prawns used the shelter more frequently when the predator was present. Red-bellied piranha elicited anti-predator behaviour in M. jelskii. The patterns observed suggested that the most common anti-predatory behaviours exhibited by M. jelskii are beneficial as they reduce vigilance and active anti-predation strategies, such as escape.

Food density drives diet shift of the invasive mysid shrimp, Limnomysis benedeni

Understanding the diet preferences and food selection of invasive species is crucial to better predict their impact on community structure and ecosystem functioning. Limnomysis benedeni, a Ponto-Caspian invasive mysid shrimp, is one of the most successful invaders in numerous European river and lake ecosystems. While existing studies suggest potentially strong trophic impact due to high predation pressure on native plankton communities, little is known of its food selectivity between phyto- and zooplankton, under different food concentrations. Here, we therefore investigated the feeding selectivity of L. benedeni on two commonly occurring prey organisms in freshwaters, the small rotifer zooplankton Brachionus calyciflorus together with the microphytoplankton Cryptomonas sp. present in increasing densities. Our results demonstrated a clear shift in food selection, with L. benedeni switching from B. calyciflorus to Cryptomonas sp. already when the two prey species were provided in equal biomasses. Different functional responses were observed for the two food types, indicating somewhat different foraging mechanisms for each food type. These findings provide experimental evidence on the feeding flexibility of invasive mysid shrimps and potential implications for trophic interactions in invaded ecosystems.

Examination of the Trexler-DeAngelis Model of Maternal Provisioning Reveals That Matrotrophy Is Costly

The evolution of matrotrophy (post-fertilization maternal provisioning to developing embryos) has been explained through several hypotheses. Trexler and DeAngelis proposed in 2003 a theoretical model that defines the ecological conditions under which matrotrophy would be favored over lecithotrophy (pre-fertilization maternal provisioning). According to this model, matrotrophy offers a selective advantage in environments with abundant and constantly available food, whereas environments with limited and fluctuating food resources should instead promote a lecithotrophic mode of maternal provisioning. This model also proposes that matrotrophy entails the consequence of leaner reproductive females and in turn shorter lifespans. In this study, we examined the Trexler-DeAngelis model using data from 45 populations of five viviparous species from the fish genus Poeciliopsis (family Poeciliidae). We used the matrotrophy index (MI) as a measure of post-fertilization maternal provisioning, and the index of stomach fullness and individual body condition (BC) as proxies for food availability. We also estimated the magnitude of fluctuations in food availability by calculating the temporal variances of these two proxies. Neither abundant nor constantly available food were associated with greater degrees of matrotrophy, which fails to support the predictions of the Trexler-DeAngelis model with respect to the ecological drivers of increased post-fertilization provisioning to embryos. Nonetheless, in all five species we observed that females with greater degrees of matrotrophy had poorer BC compared to females that provided less nutrients to embryos after fertilization. This finding is consistent with one of the expected consequences of advanced matrotrophy according to the Trexler-DeAngelis model, namely, a detriment to the nutritional status of females. Our study provides compelling evidence that gestating females experience a trade-off between post-fertilization provisioning to embryos and self-maintenance, revealing in turn that matrotrophy is a costly reproductive strategy.