The impact of zebra mussel (Dreissena polymorpha) periostracum and biofilm cues on habitat selection by a Ponto-Caspian amphipod Dikerogammarus haemobaphes

Dikerogammarus haemobaphes is one of several Ponto-Caspian gammarids invading Europe in recent decades. Previously, it exhibited active preferences for habitats associated with another Ponto-Caspian alien, zebra mussel. Now we tested gammarid preferences for living mussels and their empty shells with biofilm and/or periostracum present or absent, to find the exact cues driving gammarid responses. We observed a strong preference of gammarids for biofilmed shells, even if the biofilm was relatively young (2-day old). However, the biofilm quality, related to the substratum on which it had developed (shells with or without the periostracum, or coated with nail varnish) did not affect their behaviour. In the absence of biofilm, gammarids positively responded to the shell periostracum. Furthermore, they clearly preferred living zebra mussels over old empty shells, independent of the presence or absence of biofilm, confirming the importance of a periostracum-associated cue in their substratum recognition. On the other hand, shells obtained shortly after mussels’ death were preferred over living bivalves. Thus, the attractant is associated with fresh mussel shells, rather than with living mussels themselves. The ability of alien gammarids to locate sites inhabited by zebra mussels may contribute to their invasion success in novel areas inhabited by this habitat-forming bivalve

The Braveheart amphipod: a review of responses of invasive Dikerogammarus villosus to predation signals

Predator pressure is a fundamental force driving changes at all levels of the community structure. It may protect native ecosystems from alien species. Therefore, resistance to diverse predators resulting from a universal anti-predator strategy seems crucial for invasion success. We present a comprehensive review of the responses of an invasive amphipod Dikerogammarus villosus to sympatric and allopatric predator signals. We summarize diverse aspects of the gammarid anti-predator strategy, including predator identification, morphological and behavioural adaptations, effectiveness of shelter use and resistance to indirect predator effects. The response of D. villosus is independent of predator species (including totally allopatric taxa), which assures the high flexibility of its predator recognition system. It has a harder exoskeleton and better capability of utilizing shelters compared to other gammarids, resulting in relatively high resistance to predators. Therefore, it can use predator kairomones as indirect food signals (sharing the diet with the predator) and follow the predator scent. This resistance may allow D. villosus to reduce the costs of its physiological responses to predators and sustain growth in their presence. This might facilitate invasion success by increasing its competitive advantage

Keep calm and don't stop growing: Non-consumptive effects of a sympatric predator on two invasive Ponto-Caspian gammarids Dikerogammarus villosus and Pontogammarus robustoides.

Predators shape prey populations by elimination of individuals (consumptive effects) and by inducing modifications in prey behaviour, physiology or morphology (NCE-non-consumptive effects). Due to the resource allocation to defence, decreased feeding and higher stress, the costs of predator NCEs can be considerable. Therefore, the resistance to NCEs may be crucial for population growth and interspecific competition. We tested the resistance of Ponto-Caspian gammarids Dikerogammarus villosus and Pontogammarus robustoides to NCEs imposed by their predator, the racer goby Babka gymnotrachelus. As D. villosus is often avoided by predators in the presence of alternative food, we hypothesised that it would bear lower behavioural and physiological costs of anti-predator responses. We tested gammarid feeding in short-time experiments (2-4 h) with food (chironomid larvae) located at various distances from the stony shelter (to enforce food searching, Experiment I) or in the direct gammarid proximity (no searching needed, Experiment II). Moreover, we checked the predator effect on gammarid growth in a 2-week Experiment III. Both gammarids exposed to predators reduced feeding efficiency outside the shelter (Experiment I). Contrary to our expectations, the response of D. villosus was stronger. When food was provided in their direct proximity (Experiment II), the feeding of both species was unaffected by predators, indicating that a shelter supplied with food can reduce predator NCEs. The growth of P. robustoides was reduced in the presence of predators (Experiment III), whereas that of D. villosus was unaffected. Although D. villosus has a more effective defence strategy than P. robustoides, it bears similar or even higher behavioural costs of NCEs. However, it exhibits the higher resistance to the long-term predator presence, sustaining its growth rate under such conditions. This may be one of the factors contributing to the great invasion success of D. villosus, currently taking place in European fresh waters

The 3-way Generalized Linear Model analysis to test the effect of the gammarid species, presence of predators, and food proximity on the percentage of chironomids consumed (Experiment I).

<p>The 3-way Generalized Linear Model analysis to test the effect of the gammarid species, presence of predators, and food proximity on the percentage of chironomids consumed (Experiment I).</p

The effect of the predator presence on the mean percentages of consumed chironomids (A) and consumption rates (B) by <i>Dikerogammarus villosus</i> (D.v.) and <i>Pontogammarus robustoides</i> (P.r.) in Experiment II.

<p>Treatments labelled with the same letter do not differ significantly (P > 0.05) from one another. Error bars indicate standard errors of the mean.</p

The effect of the predator presence and food proximity (Experiment I) on the mean numbers of chironomids consumed by <i>Dikerogammarus villosus</i> (D.v.) and <i>Pontogammarus robustoides</i> (P.r.) (A) and mean times (log transformed) spent by the gammarids in the open field (B, C).

<p>Treatments labelled with the same letter do not differ significantly (P > 0.05) from one another. Error bars indicate standard errors of the mean.</p

Three-way nested ANOVA to test the effect of the tanks (random factor), gammarid species and presence of predators on the gammarid growth rate (Experiment III).

<p>Three-way nested ANOVA to test the effect of the tanks (random factor), gammarid species and presence of predators on the gammarid growth rate (Experiment III).</p

Experimental setup for Experiment I to test the effect of the predator presence and food proximity on the consumption of chironomids by gammarids.

<p>Experimental setup for Experiment I to test the effect of the predator presence and food proximity on the consumption of chironomids by gammarids.</p

Keep calm and don’t stop growing: Non-consumptive effects of a sympatric predator on two invasive Ponto-Caspian gammarids <i>Dikerogammarus villosus</i> and <i>Pontogammarus robustoides</i>

<div><p>Predators shape prey populations by elimination of individuals (consumptive effects) and by inducing modifications in prey behaviour, physiology or morphology (NCE—non-consumptive effects). Due to the resource allocation to defence, decreased feeding and higher stress, the costs of predator NCEs can be considerable. Therefore, the resistance to NCEs may be crucial for population growth and interspecific competition. We tested the resistance of Ponto-Caspian gammarids <i>Dikerogammarus villosus</i> and <i>Pontogammarus robustoides</i> to NCEs imposed by their predator, the racer goby <i>Babka gymnotrachelus</i>. As <i>D</i>. <i>villosus</i> is often avoided by predators in the presence of alternative food, we hypothesised that it would bear lower behavioural and physiological costs of anti-predator responses. We tested gammarid feeding in short-time experiments (2–4 h) with food (chironomid larvae) located at various distances from the stony shelter (to enforce food searching, Experiment I) or in the direct gammarid proximity (no searching needed, Experiment II). Moreover, we checked the predator effect on gammarid growth in a 2-week Experiment III. Both gammarids exposed to predators reduced feeding efficiency outside the shelter (Experiment I). Contrary to our expectations, the response of <i>D</i>. <i>villosus</i> was stronger. When food was provided in their direct proximity (Experiment II), the feeding of both species was unaffected by predators, indicating that a shelter supplied with food can reduce predator NCEs. The growth of <i>P</i>. <i>robustoides</i> was reduced in the presence of predators (Experiment III), whereas that of <i>D</i>. <i>villosus</i> was unaffected. Although <i>D</i>. <i>villosus</i> has a more effective defence strategy than <i>P</i>. <i>robustoides</i>, it bears similar or even higher behavioural costs of NCEs. However, it exhibits the higher resistance to the long-term predator presence, sustaining its growth rate under such conditions. This may be one of the factors contributing to the great invasion success of <i>D</i>. <i>villosus</i>, currently taking place in European fresh waters.</p></div