Interpopulational comparative cytogenetics analysis among three Astyanax (Characiformes: Incertae Sedis) species of two streams of upper Paraná River basin, Brazil

Populations of Astyanax paranae, Astyanax fasciatus and Astyanax altiparanae collected from the Pindorama and Lopei streams (upper Paraná river basin, Brazil) were cytogenetically studied, checking for chromosomal differentiation and the evolutionary trend in the three species. Forty-eight chromosomes (8m + 20sm + 10st + 10a) were observed in both populations of Astyanax paranae. Astyanax fasciatus exhibited 50 chromosomes (8m + 18sm + 10st + 14a, Pindorama stream; 8m + 14sm + 12st + 16a, Lopei stream). The diploid number for A. altiparanae was 50 chromosomes in both populations (6m + 30sm + 4st + 10a). The three studied species exhibited multiple AgNORs with differences among the populations of A. paranae and A. fasciatus. Regarding the heterochromatin distribution, interpopulational differences were observed in the three species. The data of the present study demonstrate that both A. paranae and A. fasciatus exhibit karyotypical interpopulational differences more conspicuous than A. altiparanae populations, probably due to the characteristics that restricted both the A. paranae and the A. fasciatus to the upper portion of the streams, leading to the fixation of different chromosomal rearrangements in the populations. However, the absence of conspicuos interpopulational karyotypical differences in A. altiparanae suggests a gene flow between both populations. In the present study, the role of the streams as an environment which maintains the diversity of fish with different genetic pools became evident.

A contribution to ex-situ conservation of Mediterranean thymes: Germination trials

ABSTRACT. A contribution to ex-situ conservation of Mediterranean thymes: Germination trials. The germination process was studied of the seeds of seven endemic or threatened Mediterranean thymes collected from natural populations of the SW Iberian Peninsula. Four replicates of 50 seeds of each population were induced to germinate by alternating temperatures (6 hours at 20°C, 18 hours at 30°C; 40-60% humidity). The accumulated percentage germination curves, the germinability (percentages), and the germination rate (in terms of the vigour index, Iv) were determined. The results were as follows: Thymus caespititius, germinabilities null or low and germination rates slow (0%-11%; Iv = 0-1.26); Thymus mastichina, germinabilities moderate or high and germination rates fast or very fast (59%-92%; Iv = 12.84-35.67); Thymus praecox subsp. penyalarensis, germinabilities high and germination rates fast (79%; Iv = 19.53); Th. pulegioides, germinabilities low or moderate and germination rates slow or medium (2%-41%; Iv = 0.33-7.58); Thymus villosus subsp. lusitanicus, germinabilities moderate and germination rates medium (35%; Iv = 9.00); Thymus zygis subsp. sylvestris, germinabilities low, moderate, or high and germination rates slow, medium, or fast (2%-68%; Iv = 0.52-19.36); and Thymbra capitata, germinabilities high and germination rates fast (92%; Iv = 19.07). There were both interspecific and interpopulational differences in germinative capacity. Cooling the seeds for 7 days at 10-12°C prior to sowing produced no significant alterations in the results. A relationship was observed between seed weight and germination percentage.Key words. Germination, Iberian Peninsula, seed, Thymus, vigour.RESUMEN. Contribución a la conservación ex-situ de los tomillos mediterráneos: ensayos de germinación. Se estudiaron los procesos de germinación de las semillas de siete tomillos endémicos o amenazados de la Región Mediterránea, recolectados en poblaciones silvestres del SO de la Península Ibérica. Se indujeron a germinar 4 réplicas de 50 semillas de cada población con alternancia de temperaturas (6 horas a 20oC, 18 horas a 30oC; humedad del 40-60%). Se determinaron curvas de porcentajes acumulados de germinación, germinabilidad (en porcentaje) y la velocidad de germinación (mediante el índice de vigor, Iv). Para Thymus caespititius las germinabilidades fueron nulas o bajas y la velocidad de germinación fue lenta (0%-11%; Iv = 0-1.26); Thymus mastichina, germinabilidades moderadas o altas y velocidades de germinación rápidas o muy rápidas (59%-92%; Iv = 12.84-35.67); Thymus praecox subsp. penyalarensis, germinabilidades altas y velocidades rápidas (79%; Iv = 19.53); Th. pulegioides, germinabilidades bajas o moderadas y velocidades lentas o medias (2%-41%; Iv = 0.33-7.58); Thymus villosus subsp. lusitanicus, germinabilidades moderadas y velocidades medias (35%; Iv = 9.00); Thymus zygis subsp. sylvestris, germinabilidades lentas, moderadas o altas y40J. Blanco Salas et al.velocidades lentas, medianas o rápidas(2%-68%; Iv = 0.52-19.36); y Thymbra capitata, germinabilidades altas y velocidades rápidas (92%; Iv = 19.07). Se observaron diferencias interespecíficas e interpoblacionales en la capacidad germinativa. Un pretratamiento térmico (7 días a 10-12°C) no produjo alteración significativa en los resultados. También se observó relación entre el peso de las semillas y el porcentaje de germinación.Palabras clave. Germinación, Península Ibérica, semilla, Thymus, vigor.