Abstract
Life in extreme environments is typically studied as a physiological problem, although the existence of extremophilic animals suggests that developmental and behavioral traits might also be adaptive in such environments. Here, we describe a new species of nematode, Tokorhabditistufae, n. gen., n. sp., which was discovered from the alkaline, hypersaline, and arsenic-rich locale of Mono Lake, California. The new species, which offers a tractable model for studying animal-specific adaptations to extremophilic life, shows a combination of unusual reproductive and developmental traits. Like the recently described sister group Auanema, the species has a trioecious mating system comprising males, females, and self-fertilizing hermaphrodites. Our description of the new genus thus reveals that the origin of this uncommon reproductive mode is even more ancient than previously assumed, and it presents a new comparator for the study of mating-system transitions. However, unlike Auanema and almost all other known rhabditid nematodes, the new species is obligately live-bearing, with embryos that grow in utero, suggesting maternal provisioning during development. Finally, our isolation of two additional, molecularly distinct strains of the new genus—specifically from non-extreme locales—establishes a comparative system for the study of extremophilic traits in this model.
Highlights
Extremophilic animals offer a window into how development, sex, and behavior together enable resilience to inhospitable environments
We show that PS8402 shows obligate vivipary with embryonic growth in utero and that vivipary evolutionarily predated the colonization of Mono Lake
Our description of Tokorhabditis n. gen. presents a model for extreme physiological resilience, one in a group of nematodes (“Rhabditidae”) that are manipulated and well used as laboratory organisms
Summary
Extremophilic animals offer a window into how development, sex, and behavior together enable resilience to inhospitable environments. A recent survey of an alkaline, hypersaline, and arsenic-rich site (Mono Lake, California, USA) identified an ecological community of nematodes that have independently colonized the lake with various success[8] Among these nematodes was an undescribed species (represented by strain PS8402) belonging to the paraphyletic group “Rhabditidae,” which includes the celebrated model Caenorhabditis elegans, in addition to many other species cultured in the laboratory[9]. Beyond a full description of PS8402, a phylogenetic infrastructure that includes closely related species is needed to establish PS8402 as a model for the evolution of extreme lifestyles To this end, we have identified two other nematode isolates that, together with PS8402, form a clade that is exclusive of Auanema. We present morphological, life-history, and phylogenetic data that support the new species as a potential model for extremophilic physiology in nematodes
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