Limited by blue blood? Genetic, structural and functional traits driving haemocyanin evolution and thermal adaptation in octopods.

The octopods worldwide colonisation of diverse thermal habitats from -1.8°C to more than 30°C relied on the capacity of their circulatory and ventilatory system to supply sufficie nt oxyg en f or aerob ic metaboli sm at a giv en environmental temperature. The blood pigment haemocyanin transports oxygen in octopods, which however, suffices oxygen supply only within a defined thermal range and thus may limit octopod radiation and distribution. This study aims to determine and link genetic, structural and functional properties of haemocyanin to understand mechanisms of protein evolution relevant to thermal adaptation in octopods. A combinatio n o f oxyge n bindin g experiments , nati ve g el electrophores is a nd gene sequencing was used to compare properties of haemocyanin between cold and warm adapted octopods. orphological and COI barcode identification of octopods collected during cruise ANT XXVII/3 of RV “Polarstern” confirmed high species diversity in sub and high Antarctic waters. Physiological and structural analysis of haemocyanin revealed differential oxygen binding properties and a heterogeneous abundance of two distinct isoforms of the functional unit G (FU-G) among polar species. The haemocyanin of Antarctic Pareledone charcoti displayed fewer acidic amino acids than of the temperate Enteroctopus dofleini. However, comparisons across multiple species from warm and cold habitats showed highly variable isoelectric properties of haemocyanin FU-G. We conclude that differenti al haemocyan in isofo rm patte rns am ong polar species likely explain differences in oxygen binding. The lack of a universal “cool” haemocyanin among Antarctic octopods may reflect independent colonisation and adaptation events to sub-zero temperatures. Further analysis will focus on warm adapted octopods and the search for amino acid residues that account for adaptive changes of haemocyanin