Summary
The research aims to provide a detailed genetic, morphologic and biological characterization of three icefish species in the Weddell Sea, to evaluate the occurrence of interspecific hybridization events, and to detect intraspecific genetic differentiation by comparison with samples from other geographic areas. Notothenioids (Perciformes) play a key role in the Antarctic marine food web and, due to their ecophysiological constraints, including high stenothermy, they are expected to be particularly vulnerable to temperature increase. The three icefish species targeted by this project are the only representative of the genus Chionodraco and they show a different distribution on the Antarctic continental shelf. Two species are sympatric (C. hamatus and C. myersi, primarily with a circum-High-Antarctic distribution) and one is largely allopatric (C. rastrospinosus, Antarctic Peninsula and southern Scotia Arc).

Objectives
In this project, we will verify if the secondary contacts between the Chionodraco species, due to the expansion of C. rastrospinosus distribution or in general due to its newly documented sympatric condition, result in high levels of hybridization in Weddell Sea. We will characterize the species and their possible hybrids, using samples from the Weddell Sea, by genetics, morphology and biology. The genetic profiling will use a panel of 18 microsatellites that cross-amplify in the three species and allows precise species assignment and quantification of the hybridization rate. We will validate microsatellite results by sequencing 10 nuclear gene regions. We will also perform Intraspecific comparisons with available samples from other areas to detect genetic differentiation involving populations of Weddell Sea. The morphological approach will target meristic traits, as well as somatic and otolith morphology. Finally, we will characterize the three species and their hybrids from a biological point of view by analysing life history traits, such as age and growth, sexual maturity, reproductive investment and gametogenesis.

Project Partners
• University of Padova, Dept. Biology (Padova, Italy)
• University of Ferrara, Dept. Life Sciences & Biotechnology (Ferrara, Italy)

Main Publications
• La Mesa, M., Guicciardi, S., Donato, F., Riginella, E., Schiavon, L., Papetti, C. (2020). Comparative analysis of otolith morphology in icefishes (Channichthyidae) applying different statistical classification methods. Fisheries Research, 230 n. 105668. DOI: 10.1016/j.fishres.2020.105668
• Bargelloni, L., Babbucci, M., Ferraresso, S., Papetti, C., Vitulo, N., Carraro, R., Pauletto, M., Santovito, G., Lucassen, M., Mark, F.C., Zane, L., Patarnello, T. (2019) Draft genome assembly and transcriptome data of the icefish Chionodraco myersi reveal the key role of mitochondria for a life without hemoglobin at subzero temperatures. Communications Biology, 2 (1), n. 443. DOI: 10.1038/s42003-019-0685-y