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Influence of predator odor on the rate of evacuation of the digestive tract of the invasive black-mouthed warbler (Neogobius melanostomus)
BRYLLOVÁ, Vendula
Over the past 30 years, the round goby (Neogobius melanostomus) has colonized a significant portion of the European river system and a similar trend can be observed in the Great Lakes of North America. In parallel, however, the round goby is coming under strong predation pressure from native predators at these sites, but this appears to be negligible in destabilising its populations. However, quantification of the indirect impact of these predators on the round goby is still lacking. The aim of the present thesis was to reveal the influence of chemical signals of the original, trophically higher predator (European eel - Anguilla anguilla) on the rate of gastric evacuation of the lower predator - round goby. In the experiment, round goby was tested in the following treatments: 1) without chemical signals (control group); 2) with chemical signals originating from the European eel fed by the round goby with enrichment of the water with the conspecific alarm cues from the skin of the round goby (conspecific treatment); 3) with chemical signals originating from the European eel fed by the earthworms (heterospecific treatment). The different treatments were tested on the evacuation rate of the larvae of Chironomus sp. in the digestive tract of the round goby. The rate of gastric evacuation of the round goby was not statistically significantly different among the treatments tested. Tested food was evacuated in all treatments within 9 hours from the start of the experiment. The results obtained show that the presence of chemical signals from a higher predator (European eel), with the simultaneous presence or absence of conspecific alarm cues originating from the food (of the lower predator), does not affect the rate of gastric evacuation of the round goby, which appears to be an additional advantage of this highly invasive aquatic species when colonizing new territories.
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Is the growth of brown frog's tadpoles influenced in different stages of its development by the presence of red-eared slide?
VODRÁŽKOVÁ, Magda
In the last few decades, the frequency and importance of invasive species has been increasing mainly due to the disproportionate growth of world trade in animals and plants. Predator-prey interactions drive the evolution of many behavioral and morphological traits in aquatic animals. In aquatic environments, chemical cues reliably enable prey to assess and avoid predation risk. The presence of a predator affects prey populations either by direct predation by reducing its abundance and changing its behavior, or by modifying various parts of its life history. The effect induced by the risk of predation can have a stronger impact on populations than the direct effect of mortality. Non-native red-eared sliders (Trachemys scripta elegans) have the potential to disrupt aquatic ecosystems in Central Europe because of their superior competitive abilities and omnivorous diets. I investigated whether continuous predator-borne cues are tied to changes in the hatching time, developmental stage, and body size at hatching of common frog tadpoles (Rana temporaria). Whether the developmental rates, growth rates and sizes at metamorphosis would alter in the presence of a predator and examined the dynamics of the ontogeny of tadpoles under different time patterns of an alien predator presence. The presence of a predator affected all factors examined. I found that in the absence of the slider, the embryos hatched in 12 days, while hatching was accelerated by two days in slider treatment. At the same time, the embryos hatched smaller and at a lower stage of development with the slider than without it. The presence of turtles shortened the time at metamorphosis of tadpoles from 110?11.7 days to 93?13.0 days (mean ? S.D.). The froglets were significantly smaller (12.8?0.99mm) in the presence of the predator than in the control treatment (15.2?1.27mm). The growth rate trajectories were similar between the predator treatment and the control. Thus, predator-induced tadpole defences were evident in higher developmental rates and smaller sizes at metamorphosis without significant changes in growth. I also found out that the tadpoles had a longer larval period and were smaller in size at metamorphosis and lower in body mass when the predator was present in early development than when the tadpoles developed without a predator. The early presence of a predator conspicuously reduced the growth increments of the tadpoles at early development. After the removal of the predator, growth accelerated above the level measured under the conditions of both the late predator and no predator. However, these growth rates did not exceed the growth rates of equally sized tadpoles in the other treatments and therefore were not sufficient to compensate for the growth slowdown in the first part of development. The presence of a predator in late tadpole development influenced neither the time to metamorphosis nor size/body mass at metamorphosis. Results show rather rarely documented types of amphibian prey responses to caged predators. This study extends the range of predators studied, including the effect on different phases of development of potential amphibian prey.
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Phenotypic plasticity of Daphnia cucullata in two lowland ponds
Volemanová, Eva ; Petrusek, Adam (advisor) ; Pichlová, Radka (referee)
4 ABSTRACT Characteristic high helmets in Daphnia cucullata, which increase resistance of Daphnia against various invertebrate predators, can be induced by chemical cues released by these invertebrates but also by small-scale turbulence. I evaluated the response of D. cucullata to both factors in several clones originating from two riverine pools differing in their predator regime. In a large pool, the dominant invertebrate predator is the cladoceran Leptodora kindtii, and the Daphnia population there shows a typical cyclomorphosis. In the second (small) pool, Daphnia do not produce helmets, despite the presence of the phantom midge larvae Chaoborus flavicans. I compared phenotypic changes of Daphnia cucullata clones from these pools to Chaoborus kairomones and to a small-scale turbulence in laboratory experiments. Kairomones induced significantly longer helmets in clones from both pools; however, only clones form the large pool reacted also to turbulence. As all daphnids in the experiments responded to chemical cues from Chaoborus, I assume that either the kairomone dose under natural conditions in the small pool is too low to induce helmets or the phenotypic response of the local population is mediated by other factors. On the other hand, the variation of response to small-scale turbulence suggests that...
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The influence of the presence of invasive map turtle on the activity of brown frog tadpoles.
KLAPKA, Vladimír
The thesis focuses on the factors that influence locomotor activity of tadpoles. An important factor is the risk of predation. The presence of a predator or its metabolites induced in many species of tadpoles reduced locomotor activity. Another factor that affects the locomotor activity of the tadpoles is the presence in the group of conspecific individuals. A laboratory experiment was created to evaluate the influence of these two factors on the locomotor activity of Rana temporaria tadpoles in the presence of metabolites of invasive turtle Trachemys scripta elegans. In the experiment, the rate of tadpole's locomotor activity was expressed by the length of tadpole's trajectory which was measured by camera and evaluated by EthoVision software. The measurement results show that tadpoles in the presence of metabolites of turtle showed antipredator behavior, reduce their locomotor activity. The presence of the tadpole in group with 5 other conspecific individuals did not affect the locomotor activity. The group could only communicate with chemical signals. Conversely interaction was found between the effect of the presence of metabolites of predator and influence group. Tadpoles in the group in the presence of a predator showed greater locomotor activity than single tadpoles in the presence of these metabolites.
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