Evolution of freezing susceptibility and freezing tolerance in terrestrial arthropods.

Arthropods have evolved various adaptations to survive adverse seasons and it has long been discussed why some arthropods are freezing-susceptible and some are freezing-tolerant. However, which mode of frost resistance came first during the course of evolution? A commonly held opinion is that no choice of strategy has been offered in evolution, because each species of arthropod may have its own evolutionary and natural history, leading to cold-hardiness. Freezing tolerance is more frequent in holometabolous insect orders and partially used by certain vertebrates, like some terrestrially hibernating amphibians and reptiles. Supported by phylogenetic, ontogenetic and ecological arguments, we suggest here that freezing tolerance is more recent than freezing susceptibility in the course of arthropods evolution. In addition, we observe that three basic modes of freezing resistance in insect species exist in the field: (i) permanent or year-round freezing-susceptible species, (ii) alternative or seasonal freezing-susceptible/freezing-tolerant species, (iii) permanent or year-round freezing tolerant species.