Extreme marine nematodes towards the comprehension of origin and evolution of life in our changing Planet

Nematodes are the most abundant and diversified metazoans in terrestrial and marine ecosystems. They play an important role in benthic food webs and nutrient cycling and they are characterized by high sensitivity to environmental changes due to their short generation time and the lack of pelagic larvae dispersion. Terrestrial nematodes, such as Caenorhabditis elegans, have been used as model organisms for biology, immunology and physiology. Less investigated and less understood than their terrestrial counterparts, marine nematodes can tolerate or can even be favored by the occurrence of extreme environmental conditions, while most of macrofauna and meiofaunal species die or disappear. The discovery of abundant and well-adapted nematode communities in several extreme environments has opened new frontiers in the ecology and biology of the species thriving there. Here, we review the advances in the study of ecology, biology and physiology of marine nematodes from different types of extreme environments. Adaptations to temperature extremes, osmotic and ionic stress, deoxygenation and toxic chemicals are discussed, including the adaptation via symbiosis, and the potential of nematodes and their surviving mechanisms in the light of our changing Planet. This review highlights the importance to increase studies on biology and physiology of extreme marine nematodes in order to advance our understanding of how nematodes survive or even thrive in these harsh conditions. The behavior and physiology of different extreme nematode species can provide vital information on how organisms may respond to the stressful challenges generated by human activities, including deoxygenation, acidification and rises in temperature. From an evolutionary perspective, the discovery of nematode species from these environments sheds light on phylogenetic relationships, and help explain evolutionary pathways.