Variación fenotípica de la concha en Neritinidae (Gastropoda: Neritimorpha) en ríos de Puerto Rico

Abstract

RESUMEN: Los gasterópodos Neritinidae de Puerto Rico presentan un ciclo de vida anfídromo y exhiben polimorfismo en los patrones de coloración de la concha. Se identificó que la oviposición aumenta río arriba conforme los individuos alcanzan mayores tamaños, a pesar de que la densidad poblacional disminuye. La frecuencia de siete fenotipos previamente establecidos se analizó en diez ríos de la isla durante dos años (n=8 751 individuos). Debido a que el río Mameyes es el más conservado, se tomó como modelo para estudiar la variación a lo largo del río y entre hábitats durante tres años. El fenotipo de líneas axiales y puntos (N. virginea) fue el predominante en toda la isla y el fenotipo pateloide (N. punctulata) fue el menos frecuente. Se observaron diferencias significativas de las frecuencias de los fenotipos (principalmente en los secundarios) entre ríos, a lo largo de ellos y entre hábitats. Esta variabilidad espacial puede responder a gradientes de salinidad y depredación. Se observó plasticidad fenotípica en algunos individuos.

ABSTRACT: Gastropods of the Neritinidae family exhibit an amphidromous life cycle and an impressive variability in shell coloration in Puerto Rican streams and rivers. Various nominal species have been described, but Neritina virginea [Linné 1758], N. punctulata [Lamarck 1816] and N. reclivata [Say 1822] are the only broadly reported. However, recent studies have shown that these three species are sympatric at the river scale and that species determination might be difficult due to the presence of intermediate color morphs. Individuals (8 751) were collected from ten rivers across Puerto Rico, and from various segments and habitats in Mameyes River (the most pristine island-wide) during three years (2000-2003), and they were assigned to one of seven phenotypes corresponding to nominal species and morphs (non-nominal species). The “axial lines and dots” morph corresponding to N. reclivata was the most frequent island-wide, while the patelliform N. punctulata was scant, but the only found in headwater reaches. The “yellowish large tongues” phenotype, typical of N. virginea s.s. was the most frequent in the river mouth. The frequency of secondary phenotypes varied broadly among rivers, along the rivers, and among habitats, seemly influenced by salinity and predation gradients. The occurrence of individuals with coloration shifts after predation injuries, suggests phenotypic plasticity in the three nominal species, and urges for the use of molecular markers to unravel the possible occurrence of a species complex, and to understand the genetic basis of polymorphism. The longitudinal distribution of individual sizes, population density and egg capsules suggested the adaptive value of upstream migration, possibly to avoid marine predators.