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Burrowing behaviour in crayfish
GUO, Wei
This PhD thesis is devoted to exploring the unresolved ecological gaps in freshwater crayfish burrowing behaviour from three parts, which are: a) the extreme weather conditions like drought; b) aquatic contamination; c) interspecific interactions. The first chapter of the thesis deals with the introduction of the basic information and background related to the burrowing behaviour of freshwater crayfish. The unresolved ecological gaps related to freshwater crayfish burrowing behaviour are: a) the potential effects of drought on crayfish reproduction; b) effects of aquatic contamination on the freshwater crayfish burrowing behaviour; c) crayfish competition for shelter as a primary resource. The second chapter explores whether embryogenesis or postembryonic development of freshwater crayfish can occur without free standing water inside the burrow. To address this question, three experiments were conducted using artificial burrows with high air humidity and using marbled crayfish (Procambarus virginalis Lyko, 2017) as a model species. We found that the ability of marbled crayfish to undergo terminal phases of embryogenesis, including hatching, as well as early postembryonic development under high air humidity conditions only. Postembryonic development was suspended in the absence of free water, and successfully resumed when re-immersed. This similar ability to tolerate drought-like conditions during postembryonic development may also occur in other crayfish species, especially primary burrowers. The third and fourth chapters covers the effects of water contamination on crayfish (red swamp crayfish Procambarus clarkii as model species) burrowing behaviour. We tested the hypothesis that burrowing behaviour of the red swamp crayfish would be altered with exposure to PhACs and herbicides at concentrations frequently detected in aquatic environments. As representative PhACs, we chose methamphetamine (METH) and tramadol (TRA) (1 ?g/L) (Chapters 3), and, as herbicides, terbuthylazine (TERB) and metazachlor (META) (2 ?g/L) (Chapters 4). We reported for the first time that depth and volume of burrows constructed by methamphetamine-exposed females was significantly lower than of unexposed controls. Tramadol-exposed females consistently exhibited a tendency to excavate smaller burrows compared with controls, although this was not significant (Chapter 3). Impact of herbicides on burrowing behaviour was less clearly manifested, although male crayfish exposed to META constructed a significantly higher number of burrows than did other groups (Chapter 4). The fifth and sixth chapters describe aggression of marbled crayfish during interspecific interactions under laboratory conditions was quantified by characterizing their direct agonistic interactions and competition for shelter with calico crayfish Faxonius immunis and spiny-cheek crayfish Faxonius limosus. Differences in aggression may predict interactions and outcomes under natural conditions. We found marbled crayfish to dominate size-matched calico crayfish (Chapter 5) and spiny-cheek crayfish (Chapter 6) in agonistic encounters. The higher activity and aggressiveness of marbled crayfish could facilitate displacement of other non-indigenous crayfish species either by direct interaction or through competition for resources such as shelter and food. The seventh chapter of the thesis presents the general discussion and summary obtained by the five chapters mentioned above. These data represent basic scientific information valuable for practical application. The outcomes of interactions among crayfish under laboratory conditions can be critical to evaluating over-invaded communities and ecosystems harbouring invasive species that share similar life histories, niche preference, and adaptation strategies.
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