An integrative approach to species delimitation of Antarctic benthic amphipods

The Antarctic Peninsula, particularly its northern part, is one of the regions that has experienced significant warming over the past 50 years, at a rate higher than the global average (Kim et al. 2014; Carrasco et al. 2021). The rise in atmospheric temperature and sea surface temperature affects cryospheric processes and the ecosystems in this region (Convey and Peck 2019). Amphipod crustaceans are one of the most speciose and dominant groups in the sublittoral zone of the Southern Ocean, with a high diversity in life styles, trophic types and habitats (Broyer et al. 2008). They constitute a significant trophic resource for a number of Southern Ocean fishes, invertebrates, seabirds and mammals and play a key role in coastal Antarctic ecosystems in terms of carbon flow, nutrient storage, and nutrient cycling (Jażdżewska 2011; Jażdżewska and Siciński 2017; Revanales et al. 2024). The integrative approach to studying benthic Antarctic amphipods is a multi-component strategy that combines morphological analysis, molecular and genetic methods, ecological and biogeographical data, and behavioral and functional traits to obtain a more complete and reliable picture of their taxonomy, ecology, and evolution. The taxonomic composition of benthic amphipods from Maritime Antarctica was studied during the austral summers of 2019/20 and 2022/23, within the frameworks of the XXVIII and XXXI Bulgarian Antarctic Expeditions and the IV Turkish Antarctic Expedition. A total of 27 localities were surveyed: 15 along the coastline of the South Bay (Livingston Island) and 12 along the coastline of the Marguerite Bay (Horseshoe and Dismal Islands). For the purpose of this research, two mitochondrial ( cox 1 and 16S rDNA) and two nuclear (Histone 3 and 28S rDNA) regions were sequenced for representative specimens. Within the integrative taxonomy we applied, a total of 38 amphipod species, belonging to 23 families were revealed (Fig. 1). Species relationships were assessed on individual gene-based phylogenetic hypotheses. Biogeographic and phylogenetic relationships were explored based on the multilocus phylogeny ( cox 1+16S+28S+H3). Our analyses revealed higher than previously thought diversity with evidence of several species-complexes. Despite the increasing research efforts in recent years, only 10% of known Antarctic amphipod species are represented by barcodes (Grant and Linse 2009; Jażdżewska et al. 2021). This study highlights the importance of integrating multiple lines of evidence to address the significant knowledge gap in Antarctic amphipod diversity. Expanding morphological and genetic datasets across different regions is crucial for advancing our understanding of the evolutionary history and ecological roles of benthic amphipods in Southern Ocean ecosystems.