Signatures of the evolution of parthenogenesis and cryptobiosis in panagrolaimid nematodes

Most animal species reproduce sexually, but parthenogenesis, asexual reproduction of various forms, has arisen repeatedly. Parthenogenetic lineages are usually short lived, though in some environments parthenogenesis may be advantageous. Panagrolaimus nematodes have colonised environments ranging from arid deserts to arctic and antarctic biomes. Many are parthenogens, and most have cryptobiotic (anhydrobiotic and/or cryobiotic) abilities. We compared the genomes and transcriptomes of parthenogenetic and sexual Panagrolaimus species to identify systems that contribute to these striking abilities. The parthenogens are triploids of hybrid origin. All Panagrolaimus have acquired genes through horizontal gene transfer, some of which are likely to contribute to cryptobiosis.