Jenynsia luxata, a new species from Northwestern Argentina, with additional observations of J. maculataRegan and phylogeny of the genus (Cyprinodontiformes: Anablepidae)

Genetic assimilation and the evolution of direction of genital asymmetry in anablepid fishes

Phylogenetic comparative studies suggest that the direction of deviation from bilateral symmetry (sidedness) might evolve through genetic assimilation; however, the changes in sidedness inheritance remain largely unknown. We investigated the evolution of genital asymmetry in fish of the family Anablepidae, in which males' intromittent organ (the gonopodium, a modified anal fin) bends asymmetrically to the left or the right. In most species, males show a 1 : 1 ratio of left-to-right-sided gonopodia. However, we found that in three species left-sided males are significantly more abundant than right-sided ones. We mapped sidedness onto a new molecular phylogeny, finding that this left-sided bias likely evolved independently three times. Our breeding experiment in a species with an excess of left-sided males showed that sires produced more left-sided offspring independently of their own sidedness. We propose that sidedness might be inherited as a threshold trait, with different thresholds across species. This resolves the apparent paradox that, while there is evidence for the evolution of sidedness, commonly there is a lack of support for its heritability and no response to artificial selection. Focusing on the heritability of the left : right ratio of offspring, rather than on individual sidedness, is key for understanding how the direction of asymmetry becomes genetically assimilated.

Processes that drive the population structuring of Jenynsia lineata (Cyprinidontiformes, Anablepidae) in the La Plata Basin

The distribution of genetic diversity across a species distribution range is rarely homogeneous, as the genetic structure among populations is related to the degree of isolation among them, such as isolation by distance, isolation by barrier, and isolation by environment. Jenynsia lineata is a small viviparous fish that inhabits a wide range of habitats in South America. To decipher the isolation processes that drive population structuring in J. lineata, we analyzed 221 sequences of the mitochondrial cytochrome c oxidase I gene (COI), from 19 localities. Then, we examined the influence of the three most common types of isolation in order to explain the genetic variation found in this species.Our results revealed a marked structuration, with three groups: (a) La Plata/Desaguadero Rivers (sampling sites across Argentina, Uruguay, and Southern Brazil), (b) Central Argentina, and (c) Northern Argentina. A distance-based redundancy analysis, including the explanatory variables geographical distances, altitude, latitude, and basin, was able to explain up to 65% of the genetic structure. A variance partitioning analysis showed that the two most important variables underlying the structuration in J. lineata were altitude (isolation by environment) and type of basin (isolation by barrier).Our results show that in this species, the processes of population diversification are complex and are not limited to a single mechanism. The processes that play a prominent role in this study could explain the high rate of diversity that characterizes freshwater fish species. And these processes in turn are the basis for possible speciation events.

First record sheds light on the distribution of the cyprinodontiform genus Jenynsia (Günther, 1866) in the High Andean Plateau

This is the first record of the genus Jenynsia in the High Andean Plateau (HAP). It has been found at elevations between 3400 and 3900 m in three endorreheic systems: Salar Antofalla, Antofagasta de la Sierra and El Peñón, northwestern Argentina, South America. This finding increases the number of known HAP fish genera to five. Furthermore, in contrast to the old Andean species-rich genus Orestias, the presence of Jenynsia obscura populations in young high-altitude, non-marine saline wetlands reported here supports a recent dispersal into the HAP.

Molecular and morphological convergence to sulfide-tolerant fishes in a new species of Jenynsia (Cyprinodontiformes: Anablepidae), the first extremophile member of the family

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.

Multigene phylogeny supports diversification of four-eyed fishes and one-sided livebearers (Cyprinodontiformes: Anablepidae) related to major South American geological events

The high diversity of Neotropical fishes has been attributed to major South American palaeogeographic events, such as Andean uplift, rise of the Isthmus of Panama and marine transgressions. However, the unavailability of temporal information about evolution and diversification of some fish groups prevents the establishment of robust hypotheses about correlations between species diversification and proposed palaeogeographical events. One example is the Anablepidae, a family of teleost fishes found mostly in coastal habitats of Central and South America, but also in some inner river basins of South America. Historical aspects of the distribution patterns of the Anablepidae were never analysed and no accurate estimation of time of its origin and diversification is presently available. A multi-gene analysis was performed to estimate Anablepidae phylogenetic position, age and biogeography, comprising seven nuclear genes. The suborder Cyprinodontoidei was recovered in three major clades, one comprising all the Old World Cyprinodontoidei and two comprising New World lineages. Anablepidae was recovered as the sister group of the New World Poeciliidae, with the Amazonian genus Fluviphylax as their sister group. The ages found for the origin and diversification of Cyprinodontiformes were congruent with the pattern recorded for other vertebrate groups, with an origin anterior to the Cretaceous-Paleogene (K-Pg) transition and diversification during the Paleogene. The age estimated for the split between the Atlantic and Pacific lineages of Anableps was congruent with the rise of Panamanian Isthmus. The results suggest Miocene marine transgressions as determinant to the current distribution of Jenynsia.

First record of the genus Jenynsia from marine water on the coast of Punta del Este, Maldonado, Uruguay (Cyprinodontiformes: Anablepidae)

The first report of the genus Jenynsia occurring in marine waters is presented here. The evolution of high salinity tolerance within Anablepidae is discussed and a hypothesis is proposed that this characteristic is a plesiomorphic trait in Jenynsia which was probably present in the common ancestor of the Anablepidae.