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Marine magafauna of coastal waters in southern Ireland
Svobodová, Hana ; Petrusek, Adam (advisor) ; Reif, Jiří (referee)
Land-based observations may contribute to an overall understanding of behaviour of large marine vertebrates and may help us understand how these animals react to climate change. I observed marine megafauna (cetaceans, Basking shark, and Sunfish) from Cape Clear Island situated in the south-west of Ireland. The study took place during the summer months (June - August 2008) because the majority of Leatherback turtles, Sunfish and other megafauna species are sighted in Irish waters in this period. Additionally to sightings, basic weather characteristics were recorded (sea state, visibility, glare and cloud cover) every day of observation. Unfortunately, no Leatherbacks, my target species, were recorded during the study period (51 days) at Cape Clear. The reason for the turtle absence could be relatively cold and wet weather during the study period. Although no data was obtained on turtles, over 124 sightings of other megafauna were made, mostly cetaceans (five species) but also one individual Basking shark and several Sunfish. The species richness increased with time during the study period, and significantly higher number of individuals as well taxa was observed in the second month of the study when the sea surface temperature was higher. However, I did not detect a significant relationship of number...
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Influence of experimental conditions on hatching of diapausing stages of the cladoceran Daphnia obtusa
Sailerová, Martina ; Petrusek, Adam (advisor) ; Vaníčková, Ivana (referee)
Diapause is often an adaptation for survival during periods of harsh environmental conditions. Some diapausing stages do not terminate the dormancy once the favourable conditions are restored. Such prolonged diapause may be enforced by environment if a diapausing stage cannot be reached by the cues inducing termination of dormancy. However, it may also be an advantageous bet-hedging strategy to allow only a fraction of dormant stages produced in any given season to hatch the next time conditions become favourable. I tested whether such strategy can be observed in hatching patterns of dormant eggs of Daphnia obtusa - a cladoceran occurring in small Central European temporary waters. I investigated the influence of intensity of illumination on hatching success, and effect of isolating the eggs encased in ephippia from the sediment. Fraction of eggs terminating diapause, fraction of embryos successfully leaving the egg membranes, and timing of the response were assessed at 15 ˚C under four intensities of illumination (100% = 35µmol.m2 .s-1 , 75%, 50%, 25%; photoperiod 12h light: 12h dark) and in complete darkness for 21 days. My results support previous suggestions that there is no genetically-fixed bet-hedging strategy in D. obtusa. I observed high proportion of eggs which terminated diapause in all...
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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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Seasonal dynamics of abundance and distribution of species and hybrids of the Daphnia longispina complex
Horová, Barbora ; Petrusek, Adam (advisor) ; Macháček, Jiří (referee)
I analysed seasonal changes in spatial heterogeneity of the taxonomic composition of the Daphnia longispina species complex in seven canyon-shaped reservoirs in the Czech Republic. The distribution patterns of species and interspecific hybrids along reservoir longitudinal axes differred between summer and autumn. In autumn, D. cucullata disappeared from upstream regions while D. longispina and D. galeata x longispina extended the shift from downstream regions to upstream. This temporal pattern may have been affected by decrease in fish predation pressure or deterioration of food conditions during the season. Powered by TCPDF (www.tcpdf.org)
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Vertical distribution of the freshwater jellyfish under natural and laboratory conditions
Hutňan, Martin ; Petrusek, Adam (advisor) ; Seďa, Jaromír (referee)
Vertical distribution of freshwater jellyfish Craspedacusta sowerbii was observed in an experimental set-up (two thermally stratified transparent perspex columns of 78 l volume) in two seasons. Light intensity and temperature gradients were established in order to uncover influence of these factors on vertical distribution of the medusae; unlike situation in the field, these were not accompanied with hypoxic conditions in the deeper layers. Medusae accumulated at depths that corresponded to the temperature of acclimation tank. Diel vertical migrations (DVM) of male medusae were observed in a thermally stratified water body. Crustaceoplankton (main food source of Craspedacusta) also showed differences in spatial distribution during day and night. Vertical distribution of medusae was limited by the bottom border of the epilimnion. The observations lead me to the following conclusions: 1) Behavior of Craspedacusta sowerbii under laboratory conditions supported the hypothesis that change in light intensity is the primary proximate cue controlling DVM. 2) A factor playing critical role in jellyfish vertical distribution is temperature. At both laboratory and field observations, medusae aligned with the bottom border of the epilimnion; this was consistent under different oxygen stratification patterns. 3) DVM...
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Distribution and genetic variation of invasive crayfish of the genus Orconectes
Filipová, Lenka ; Petrusek, Adam (advisor) ; Kozák, Pavel (referee)
Crayfish are an important part of European fauna, but since the 19th century native crayfish species have been largely influenced by biological invasions, when large number of their populations was dramatically reduced due to the introduction of the pathogen of the crayfish plague (oomycete Aphanomyces astaci) to Europe. Several North American crayfish species were then brought to the European continent to substitute lost populations of native crayfish, the most widespread being the spiny-cheek crayfish (Orconectes limosus), the signal crayfish (Pacifastacus leniusculus) and the red swamp crayfish (Procambarus clarkii). However, these crayfish can carry pathogen of the crayfish plague and therefore represent a serious threat to the native species. My work focused mostly on the spiny-cheek crayfish (O. limosus). Available literature data suggest that the species was brought to Europe only once, and all European individuals may be descendants of the founder population. However, other cases of introduction may not have been documented, and cannot be ruled out. The first aim of my thesis was to evaluate the haplotype variation of the spiny-cheek crayfish populations from Europe and North America. Mitochondrial gene for cytochrome c oxidase subunit 1 (COI) of selected O. limosus individuals from several...
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Evolution, ecology and systematics of symbiotic shrimps (Crustacea: Decapoda: Caridea)
Horká, Ivona ; Petrusek, Adam (advisor) ; Fikáček, Martin (referee) ; Chan, Tin-Yam (referee)
This thesis is focused on symbiotic associations of caridean shrimps with a variety of marine animals of different phyla. Currently, five caridean families comprise symbiotic species. Palaemonidae (including the traditionally recognised subfamily Pontoniinae of predominantly symbiotic species) is the most species-rich and ecologically important of them. Its representatives live from temperate to tropical marine or brackish waters, with the highest diversity in the Indo-West Pacific biogeographic area and the western Atlantic. The thesis is composed of two parts, one focusing on ecology and evolutionary biology, the other on systematics. The first part consists of three studies providing new knowledge on the evolution of symbioses in palaemonid shrimps. We confirmed that inter-phylum host-switching events and colonization of new hosts likely played a major role in the evolution of palaemonid symbiotic shrimps and these evolved multiple times (Chapter 1). Similarly, the switching from ecto- to endosymbiotic mode, associated with new body forms and ecological adaptations, occurred several times in palaemonid evolution. Reversal back to a free-living mode is rare, occasionally observed among ectosymbiotic lineages. Our results also confirm the necessity of systematic revision of this group,...
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Hosts and transmission of the crayfish plague pathogen Aphanomyces astaci
Svoboda, Jiří ; Petrusek, Adam (advisor) ; Maguire, Ivana (referee) ; Jussila, Japo (referee)
The crayfish plague pathogen, the oomycete Aphanomyces astaci, has been decimating populations of European crayfish species for more than 150 years, and is therefore considered one of the 100 worst world's invasive species. A. astaci is highly specialised for a parasitic life, but it can be isolated from moribund crayfish and grown on synthetic media, as it is the case also for several other oomycetes (chapter 7). The life of A. astaci includes three basic forms: mycelium in host's tissues, and the infective units occurring in water, zoospores and cysts. All North American crayfish species tested so far have shown some resistance to A. astaci, i.e., they could carry the infection for long, serving as vectors of the pathogen. Massive sporulation from infected North American crayfish starts when the host is moulting, stressed, or dying (chapter 4). However, I could show in my experiments that some sporulation occurs even from apparently healthy and non-moulting American crayfish hosting A. astaci, so infected North American crayfish must be considered a permanent source of the infection (chapter 4). Five genotype groups of A. astaci have already been distinguished. Strains from a particular genotype group probably share the same original host crayfish species of North American origin. Nevertheless, they can...
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