Phylogeographic relationships and morphological evolution between cave and surface Astyanax mexicanus populations (De Filippi 1853) (Actinopterygii, Characidae).

The Astyanax mexicanus complex includes two different morphs, a surface- and a cave-adapted ecotype, found at three mountain ranges in Northeastern Mexico: Sierra de El Abra, Sierra de Guatemala and Sierra de la Colmena (Micos). Since their discovery, multiple studies have attempted to characterize the timing and the number of events that gave rise to the evolution of these cave-adapted ecotypes. Here, using RADseq and genome-wide sequencing, we assessed the phylogenetic relationships, genetic structure and gene flow events between the cave and surface Astyanax mexicanus populations, to estimate the tempo and mode of evolution of the cave-adapted ecotypes. We also evaluated the body shape evolution across different cave lineages using geometric morphometrics to examine the role of phylogenetic signal versus environmental pressures. We found strong evidence of parallel evolution of cave-adapted ecotypes derived from two separate lineages of surface fish and hypothesize that there may be up to four independent invasions of caves from surface fish. Moreover, a strong congruence between the genetic structure and geographic distribution was observed across the cave populations, with the Sierra de Guatemala the region exhibiting most genetic drift among the cave populations analysed. Interestingly, we found no evidence of phylogenetic signal in body shape evolution, but we found support for parallel evolution in body shape across independent cave lineages, with cavefish from the Sierra de El Abra reflecting the most divergent morphology relative to surface and other cavefish populations.

Mitochondrial phylogeography and molecular evolution of the rhodopsin visual pigment in troglobitic populations of Astyanax mexicanus (De Filippi, 1853).

Cave-adapted animals provide a unique opportunity to study the evolutionary mechanisms underlying phenotypic, metabolic, behavioral, and genetic evolution in response to cave environments. The Mexican tetra ( Astyanax mexicanus) is considered a unique model system as it shows both surface and cave-dwelling morphs. To date, at least 33 different cave populations have been identified, with phylogenetic studies suggesting an origin from at least two independent surface lineages, thereby providing a unique opportunity to study parallel evolution. In the present study, we carried out the most exhaustive phylogeographic study of A. mexicanus to date, including cave and surface localities, using two mitochondrial markers (cytochrome b (cyt b) and cytochrome c oxidase subunit I ( COI)) and nuclear rhodopsin visual pigment ( rho). Additionally, we inferred the molecular evolution of rho within the two contrasting environments (cave and surface) and across three geographic regions (Sierra de El Abra, Sierra de Guatemala, and Micos). In total, 267 individuals were sequenced for the two mitochondrial fragments and 268 individuals were sequenced for the rho visual pigment from 22 cave and 46 surface populations. Phylogeographic results based on the mitochondrial data supported the two-lineage hypothesis, except for the Pachón and Chica caves, whose introgression has been largely documented. The Sierra de El Abra region depicted the largest genetic diversity, followed by the Sierra de Guatemala region. Regarding the phylogeographic patterns of rho, we recovered exclusive haplogroups for the Sierra de El Abra (Haplogroup I) and Sierra de Guatemala regions (Haplogroup IV). Moreover, a 544 bp deletion in the rho gene was observed in the Escondido cave population from Sierra de Guatemala, reducing the protein from seven to three intramembrane domains. This change may produce a loss-of-function (LOF) but requires further investigation. Regarding nonsynonymous ( dN) and synonymous ( dS) substitution rates (omega values ω), our results revealed the prevailing influence of purifying selection upon the rho pigment for both cave and surface populations (ω<1), but relaxation at the El Abra region. Notably, in contrast to the other two regions, we observed an increase in the number of dN mutations for Sierra de El Abra. However, given that a LOF was exclusively identified in the Sierra de Guatemala region, we cannot dismiss the possibility of a pleiotropic effect on the Rho protein.

Host-parasite interactions in perpetual darkness: Macroparasite diversity in the cavefish Astyanax mexicanus.

Astyanax mexicanus has repeatedly colonized cave environments, displaying evolutionary parallelisms in many troglobitic traits. Despite being a model system for the study of adaptation to life in perpetual darkness, the parasites that infect cavefish are practically unknown. In this study, we investigated the macroparasite communities in 18 cavefish populations from independent lineages and compared them with the parasite diversity found in their sister surface fish populations, with the aim of better understanding the role that parasites play in the colonization of new environments. Within the cavefish populations, we identified 13 parasite taxa, including a subset of 10 of the 27 parasite taxa known for the surface populations. Parasites infecting the cavefish belong to five taxonomic groups, including trematodes, monogeneans, nematodes, copepods, and acari. Monogeneans are the most dominant group, found in 14 caves. The macroparasites include species with direct life cycles and trophic transmission, including invasive species. Surprisingly, paired comparisons indicate higher parasite richness in the cavefish than in the surface fish. Spatial variation in parasite composition across the caves suggests historical and geographical contingencies in the host-parasite colonization process and potential evolution of local adaptations. This base-line data on parasite diversity in cavefish populations of A. mexicanus provides a foundation to explore the role of divergent parasite infections under contrasting ecological pressures (cave vs. surface environments) in the evolution of cave adaptive traits.

Boosting photovoltaic performance for Sb2S3solar cells by ionic liquid-assisted hydrothermal synthesis.

Bulk and surface trap-states in the Sb2S3films are considered one of the crucial energy loss mechanisms for achieving high photovoltaic performance in planar Sb2S3solar cells. Because ionic liquid additives offer interesting physicochemical properties to control the synthesis of inorganic material, in this work we propose the addition of 1-Butyl-3-methylimidazolium hydrogen sulfate (BMIMHS) into a Sb2S3hydrothermal precursor solution as a facile way to fabricate low-defect Sb2S3solar cells. Lower presence of small particles on the surface, as well as higher crystallinity are demonstrated in the BMIMHS-assisted Sb2S3films. Moreover, analyses of dark current density-voltageJ-Vcurves, surface photovoltage transient and intensity-modulated photocurrent spectroscopy have suggested that adding BMIMHS results in high-quality Sb2S3films and a successful defect passivation. Consequently, the best-performing BMIMHS-assisted device exhibits a 15.4% power conversion efficiency enhancement compared to that of control device. These findings show that ionic liquid BMIMHS can effectively be used to obtain high-quality Sb2S3films with low-defects and improved optoelectronic properties.

Sb2O3 nanoparticles anchored on N-doped graphene nanoribbons as improved anode for sodium-ion batteries.

Sodium-ion batteries (SIBs) are emerging as a promising alternative to conventional lithium-ion technology, due to the abundance of sodium resources. Still, major drawbacks for the commercial application of SIBs lie in the slow kinetic processes and poor cycling performance of the devices. In this work, a hybrid nanocomposite of Sb2O3 nanoparticles anchored on N-doped graphene nanoribbons (GNR) is implemented as anode material in SIBs. The obtained Sb2O3/N-GNR anode delivers a reversible specific capacity of 642 mA h g-1 after 100 cycles at 0.1 A g-1 and exhibits a good rate capability. Even after 500 cycles at 5 A g-1, the specific capacity is maintained at about 405 mA h g-1. Such good Na storage performance is mainly ascribed to the beneficial effect of N doping for charge transfer and to the improved microstructure that facilitates the Na+ diffusion through the overall electrode.

A novel nanocomposite based on NiOx-incorporated P3HT as hole transport material for Sb2S3 solar cells with enhanced device performance.

To achieve superior photovoltaic performance on Sb2S3 solid state solar cells (ssSCs), the concomitant development of efficient hole transport materials (HTMs) is required. Herein, a novel solution processed HTM obtained by mixing NiOx nanoparticles (NiOx-NP) and poly(3-hexylthiophene) (P3HT) is reported. These P3HT:NiOx-NP nanocomposite HTMs were obtained with different controlled concentrations of NiOx-NP using a common solvent. Incorporation of NiOx-NP significantly impacts on the structural and hole-transport layer properties of the nanocomposite films, which in turn contributes to improve the photovoltaic performance of the corresponding devices. Thus, Sb2S3 ssSCs based on HTM with an optimum concentration of NiOx-NP in P3HT, i.e. P3HT:2% NiOx-NP, yield a 50% improvement in the power conversion efficiency relative to control devices fabricated with pristine P3HT. The improved hole separation and injection at the Sb2S3/HTM interface, determined by steady-state photoluminescence quenching and electrochemical impedance spectroscopy studies, correlate well with the higher hole mobility of the nanocomposite and the current density and fill factor enhancements.

Microbiome differences between river-dwelling and cave-adapted populations of the fish Astyanax mexicanus (De Filippi, 1853).

Symbiotic relationships between host and microbiome can play a major role in local adaptation. Previous studies with freshwater organisms have shown that microbiome performs numerous important biochemical functions for the host, playing a key role in metabolism, physiology or health. Experimental studies in fish groups have found an effect of enzymatic activity of gut microbiota on a variety of metabolic processes. The goal of this study was to compare stomach microbiome from cave and surface Astyanax mexicanus, in order to evaluate the potential response of microbiota to contrasting environmental conditions and physiological adaptations of the host. Stomach microbiota was obtained from three different populations: Pachón cave, and two surface rivers (Rascón and Micos rivers). The stomach microbiome was analyzed using the Ion 16S Metagenomic kit considering seven variable regions: V2, V3, V4, V6-7, V8 and V9. A high diversity was observed across samples, including 16 phyla, 120 families and 178 genera. Gammaproteobacteria, Firmicutes, Bacteroidetes and Betaproteobacteria were the most abundant phyla across the samples. Although the relative abundance of the core OTUs at genus level were highly contrasting among populations, we did not recover differences in stomach microbiome between contrasting habitats (cave vs. surface rivers). Rather, we observed a consistent association between ß-diversity and dissolved oxygen concentration in water. Therefore, and unexpectedly, the microbiota of A. mexicanus is not linked with the contrasting conditions of the habitat considered here but is related to water parameters.