Abstract
Freshwater sulfide springs have extreme environmental conditions that only few vertebrate species can tolerate. These species often develop a series of morphological and molecular adaptations to cope with the challenges of life under the toxic and hypoxic conditions of sulfide springs. In this paper, we described a new fish species of the genus Jenynsia, Anablepidae, from a sulfide spring in Northwestern Argentina, the first in the family known from such extreme environment. Jenynsia sulfurica n. sp. is diagnosable by the lack of scales on the pre-pelvic area or the presence of a single row of scales, continuous or not, from the isthmus to the bases of the pelvic fins. Additionally, it presents a series of morphological and molecular characteristics that appear convergent with those seen in other fish species (e.g., Poeciliids) inhabiting sulfide springs. Most notably, J. sulfurica has an enlarged head and postorbital area compared to other fish of the genus and a prognathous lower jaw with a hypertrophied lip, thought to facilitate respiration at the air-water interface. Analyses of cox1 sequence showed that J. sulfurica has two unique mutations resulting in amino acid substitutions convergent to those seen in Poeciliids from sulfide springs and known to provide a physiological mechanism related to living in sulfide environments. A phylogenetic analysis, including molecular and morphological characters, placed J. sulfurica as sister taxa to J. alternimaculata, a species found in nearby, non-sulfide habitats directly connected to the sulfide springs. Thus, it can be inferred that the selection imposed by the presence of H2S has resulted in the divergence between these two species and has potentially served as a barrier to gene flow.
Highlights
Extremophile species inhabiting environments with abiotic conditions lethal for most organisms, are of great interest to physiologists, ecologists and evolutionary biologists [1, 2]
We first describe the newly discovered species of Jenynsia fish from a sulfide spring in Northern Argentina; we show that the mitochondrial cox1 gene of the new species has amino acid substitutions that are convergent to those seen in species of Poeciliidae adapted to sulfide springs [10, 15, 17, 18]; and we provide a new phylogenetic hypothesis based on the morphological data matrix of Ghedotti [25] and posteriorly modified by Aguilera et al [24], with the addition of available DNA data
We found that J. sulfurica’s cox1 gene differs from that of other Jenynsia species by having two non-synonymous substitutions that result in amino acid changes that are convergent with those observed in Poecilia sulphuraria and sulfide spring adapted populations of the P. mexicana species complex [21]
Summary
Extremophile species inhabiting environments with abiotic conditions lethal for most organisms, are of great interest to physiologists, ecologists and evolutionary biologists [1, 2]. These species offer valuable information on the limits of tolerance to abiotic conditions (e.g., [3]), on the process of adaptive divergence (e.g, [4]), and in the end, about the predictability of evolution (e.g., [5]). Associated to this, fish in sulfide springs often present modifications of the mouth (e.g., enlarged lower jaw, hypertrophic lips, mouth appendages) that are thought to facilitate respiration at the water-air interface, where oxygen concentrations are elevated compared to the rest of the water column [18,19,20]. Convergent amino acid substitutions in the cox protein across different sulfide-adapted Poecilia species have been proposed to reduce susceptibility to hydrogen sulfide
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