UBC Theses and Dissertations

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UBC Theses and Dissertations

Ice-binding proteins and invertebrate freeze tolerance in the intertidal zone Box, Isaiah


The mechanisms behind freeze tolerance in intertidal invertebrates is poorly understood. Due to differences in habitat and physiology, many biochemical processes utilized by terrestrial freeze tolerant organisms are not possible for intertidal invertebrates. Here I investigate the potential role of ice-binding proteins (IBPs) in the freeze tolerance of intertidal invertebrates. I first used bioinformatics to determine if there is molecular evidence for IBPs in intertidal invertebrates. I found a significant overrepresentation of putative IBPs in intertidal invertebrates relative to invertebrates from other habitat types, with no taxonomic patterns. These putative IBPs had high sequential similarity to type II antifreeze proteins from fish and antifreeze glycoproteins from both fish and ticks. Using some basic gene mapping I was also able to investigate the potential evolutionary origin of one of these putative IBPs from a mussel species (Mytilus coruscus), finding that a duplication and neofunctionalization event likely occurred. Knowing this I investigated the role of IBPs in the freeze tolerance of the local mussel species M. trossulus, a species that is more freeze tolerant in individuals from high shore positions during the winter months. I predicted that IBP activity would be measured in the protein extract of the species and that said activity would be greatest in winter individuals from high shore heights. Using a series of freezing assays and chemical treatments, I was able to find ice nucleation activity in M. trossulus and show strong evidence the activity was mediated by a protein, which I interpreted as IBPs. IBP activity did not vary by season or by shore height. This means IBPs may play a role in the year-long freeze tolerance of the species, but other mechanisms must explain the seasonal and tidal patterns in their freeze tolerance. In all, this thesis expands on our knowledge of intertidal freeze tolerance and provides the groundwork for future research into IBPs in multiple intertidal species.

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