A evolução paralela de duas espécies do gênero Phalloceros

Abstract

Parallel evolution occurs when closely related, but independent, lineages colonize similar environments, and during the evolutionary process, they develop similar traits. A way to demonstrate parallel evolution is studying multiple populations that independently colonized environments under different selection pressures. The intensity of predation pressure generally varies along rivers and streams with sudden changes after waterfalls, which prevent predatory fishes to colonize upstream. Thus, headwaters are usually low-predation environments, while downstream sites are high-predation environments. The adaptive divergence between high and low-predation environments occurs independently in several streams and, therefore, can be classified as parallel evolution. In the fish family Poeciliidae, the genus Phalloceros is composed of 22 species, among which six species inhabit rivers and coastal streams of the Atlantic Forest in Rio de Janeiro State. In this context, this study evaluated the parallel evolution of two Phalloceros species (P. harpagos and P. anisophallos) measuring the extension and nature of the ecological (trophic ecology) and phenotypic (life-history traits and morphology) divergence of populations under high and low-predation environments. Phalloceros harpagos and P. anisophallos were collected in streams of Guapi-Macacu River and Ilha Grande Bay Basins, respectively. In high-predation environments, higher biomass of macroinvertebrates per capita may have led to a more carnivorous diet that was reflected in the shorter intestine of females and males of both species. There was also a correlation between high-predation environments and reduced length at maturity of females and males, increased reproductive allotment and fecundity. Although they show substantial matrotrophy (substantial supply of maternal nutrients to embryos after fertilization), P. harpagos and P. anisophallos do not show superfetation (the ability of females to carry simultaneously more than one brood at different developmental stages). This result corroborates the lack of superfetation in P. anisophallos, but suggests a possible intraspecific variation of this trait in P. harpagos. In high-predation environments, shorter intestines along with higher degree of matrotrophy may have circumvented the effect of increased reproductive allotment, maintaining a more streamlined phenotype of pregnant females. In addition, males of both species showed higher gonopodia in high-predation environments, possibly due to the advantage of coercive mating in these environments and pre or post-copulatory female choices. These results suggest that there is parallelism in trophic morphology, life-history and morphological traits of these Phalloceros species related to the predation regime either by direct or indirect selective pressure of predation