The molecular basis of convergent phenotypes is often unknown. However, convergence at a genomic level is predicted when there are large population sizes, gene flow among diverging lineages or strong genetic constraints. We used whole-genome resequencing to investigate genomic convergence in fishes ( Poecilia spp.) that have repeatedly colonized hydrogen sulfide (H 2 S)-rich environments in Mexico. We identified genomic similarities in both single nucleotide polymorphisms (SNPs) and structural variants (SVs) among independently derived sulfide spring populations, with approximately 1.2% of the genome being shared among sulfidic ecotypes. We compared these convergent genomic regions to candidate genes for H 2 S adaptation identified from transcriptomic analyses and found that a significant proportion of these candidate genes (8%) were also in regions where sulfidic individuals had similar SNPs, while only 1.7% were in regions where sulfidic individuals had similar SVs. Those candidate genes included genes involved in sulfide detoxification, the electron transport chain (the main toxicity target of H 2 S) and other processes putatively important for adaptation to sulfidic environments. Regional genomic similarity across independent populations exposed to the same source of selection is consistent with selection on standing variation or introgression of adaptive alleles across divergent lineages. However, combined with previous analyses, our data also support that adaptive changes in mitochondrially encoded subunits arose independently via selection on de novo mutations. Pressing questions remain on what conditions ultimately facilitate the independent rise of adaptive alleles at the same loci in separate populations, and thus, the degree to which evolution is repeatable or predictable. This article is part of the theme issue ‘Convergent evolution in the genomics era: new insights and directions'.

Bird predation poses a strong selection pressure on fish. Since birds must enter the water to catch fish, a combination of visual and mechano-acoustic cues (multimodal) characterize an immediate attack, while single cues (unimodal) may represent less dangerous disturbances. We investigated whether fish could use this information to distinguish between non-threatening and dangerous events and adjust their antipredator response to the perceived level of risk. To do so, we investigated the antipredator behavior of the sulphur molly (Poecilia sulphuraria), a small freshwater fish which is almost exclusively preyed on by piscivorous birds in its endemic sulfide spring habitat. In a field survey, we confirmed that these fish frequently have to distinguish between disturbances stemming from attacking birds (multimodal) and those which pose no (immediate) threat such as bird overflights (unimodal). In a laboratory experiment, we then exposed fish to artificial visual and/or acoustic stimuli presented separately or combined. Sensitivity was high regardless of stimulus type and number (more than 96% of fish initiated diving), but fish dove deeper, faster, and for longer when both stimuli were available simultaneously. Based on the system’s high rates of bird activity, we argue that such an unselective dive initiation with subsequent fine-tuning of diving parameters in accordance to cue modality represents an optimal strategy for these fish to save energy necessary to respond to future attacks. Ultimately, our study shows that fish anticipate the imminent risk posed by disturbances linked to bird predation through integrating information from both visual and acoustic cues.

Natural selection drives the evolution of traits to optimize organismal performance, but optimization of one aspect of performance can influence other aspects of performance. Here, we asked how phenotypic variation between locally adapted fish populations affects locomotion and ventilation, testing for functional trade‐offs and trait–performance correlations. Specifically, we investigated two populations of livebearing fish (Poecilia mexicana) that inhabit distinct habitat types (hydrogen‐sulphide‐rich springs and adjacent nonsulphidic streams). For each individual, we quantified different metrics of burst swimming during simulated predator attacks, steady swimming and gill ventilation. Coinciding with predictions, we documented significant population differences in all aspects of performance, with fish from sulphidic habitats exhibiting higher steady swimming performance and higher ventilation capacity, but slower burst swimming. There was a significant functional trade‐off between steady and burst swimming, but not between different aspects of locomotion and ventilation. Although our findings about population differences in locomotion performance largely parallel the results from previous studies, we provide novel insights about how morphological variation might impact ventilation and ultimately oxygen acquisition. Overall, our analyses provided insights into the functional consequences of previously documented phenotypic variation, which will help to disentangle the effects of different sources of selection that may coincide along complex environmental gradients.

Se describe la diversidad, y por primera vez, la distribución vertical de insectos barrenadores (Scolytinae, Platypodinae y Bostrichidae) asociados al borde e interior de un manglar. Para determinar la diversidad en estos espacios, se capturaron insectos con trampas de intercepción cebadas con alcohol etílico al 70 % y mediante una luz ultravioleta como atrayente. Con la finalidad de analizar la distribución vertical, se colocaron trampas cebadas con alcohol etílico a 1,5 m, 6 m y 12 m de altura. De acuerdo con el índice de diversidad (1D) el borde fue 1,36 más diverso que el interior con 15,82 y 11,67 respectivamente. Las trampas utilizadas a 6 m capturaron la mayor diversidad tanto en el borde como en el interior, a pesar de que las trampas a 1,5 m capturaron la mayor abundancia. En el borde, diez de los doce meses presentaron diferencias significativas en su abundancia y para el interior estas diferencias se presentaron en ocho de los doce meses. En cuanto a la diversidad (1D), en el borde estas diferencias estadísticas se presentaron en abril, mayo, julio y agosto, mientras que en el interior en junio, noviembre y diciembre. Tales diferencias pueden estar relacionadas con la variabilidad en las condiciones ambientales del manglar, lo que produce cambios en la estructura y composición de las comunidades de insectos.

La inactivación genética (ADN) del esperma de peces se realiza mediante luz ultravioleta que, en irradiaciones crecientes, genera efectos paradójicos (efecto Hertwig) en los porcentajes de supervivencia. En este trabajo se diluyeron muestras de semen provenientes de diez machos de botete diana (Sphoeroides annulatus) en solución extendedora Cortland modificada en dilución 1:50, y se utilizaron para probar el efecto de nueve dosis de radiación ultravioleta (0.2-1.0 J cm-2) sobre la duración de la motilidad en segundos, el índice de motilidad del esperma, y los porcentajes de supervivencia de embriones obtenidos de la fertilización de huevos provenientes de cinco hembras de la misma especie. Los tiempos de motilidad del esperma en las muestras irradiadas con 0.2-0.9 J cm-2 resultaron estadísticamente no diferentes de los controles, mientras que las muestras irradiadas con 1.0 J cm-2 fueron significativamente menores. El índice de motilidad (IM), por otra parte, permitió la diferenciación estadística de cuatro grupos en cuanto a su respuesta a diferentes dosis de radiación. El primer grupo se caracterizó por valores altos del IM, e incluyó a los controles y a las muestras irradiadas con 0.2-0.3 J cm-2 ; el segundo agrupó a las irradiaciones de 0.4 a 0.7 J cm-2 , en las cuales se observó un descenso del IM; en el tercer grupo (0.8-0.9 J cm-2) el IM aumentó nuevamente; y en el último (1.0 J cm-2) se observó el menor IM. En cuanto a los porcentajes de supervivencia, se observó una curva descendente con valores altos de supervivencia en los controles y en las muestras irradiadas con 0.2 J cm-2 , con un descenso en los tratamientos de 0.3 a 0.4 J cm-2 , y una recuperación significativa a partir del tratamiento de 0.5 y hasta 0.8 J cm-2 , observándose nuevamente un decremento en la supervivencia de los tratamientos de 0.9 a 1.0 J cm-2. Ambos resultados, IM y supervivencia, indican que la dosis óptima para la producción de organismos haploides se encuentra cercana a 0.7 J cm-2. En el tratamiento de 0.7 J cm-2 se observaron larvas con las características típicas del síndrome haploide, indicando nuevamente que ésta puede ser la dosis más adecuada para producir organismos ginogenéticos.