Morphological divergence patterns among populations of Poecilia vivipara (Teleostei Poeciliidae): test of an ecomorphological paradigm

Abstract

The structure of body size and shape divergence among populations of Poecilia vivipara inhabiting quaternary lagoons in South-eastern Brazil was studied. This species is abundant throughout an environmental gradient formed by water salinity differences. The salinity gradient influences the habitat structure (presence of macrophytes) and the fish community (presence of large predators). Size and shape variation within and among populations was quantified by geometric morphometrics and analysed by indirect and direct gradient ordinations, using salinity and geography as a framework. Morphological divergence was associated with the salinity gradient. The evolutionary allometries observed were independent of within-group static allometries. Sexually dimorphic patterns were observed in size variation and within-population allometries. Specimens from freshwater (higher predation) sites presented smaller sizes, relatively longer caudal regions, lower anterior regions and a ventrally displaced eye. These features are consistent with an ecomorphological paradigm for aquatic organisms from populations subject to intense predation. A process of directional selection is postulated as the most likely force driving diversification among P. vivipara populations.

Growth pattern and survival in populations of Poecilia vivipara (Teleostei; Poeciliidae) inhabiting an environmental gradient: a common garden study

“…These authors found a direct association of mean body size with the salinity gradient, as well as other adult size correlates, such as fecundity and offspring size. Body shape also presented considerable variation and was convergent with patterns observed for other poeciliid species when contrasting high versus low predation populations (Gomes Jr. and Monteiro 2008).…”

“…Salinity can be a selective factor for some species (Purcell et al 2008;Purcell et al 2010) or generate phenotypic plasticity in others Deane and Woo 2009). The populations of P. vivipara examined in this study live in lagoons with extreme salinity differences within the same region (the Northern Rio de Janeiro plains), and they also present extreme variation of body size, shape (Gomes Jr. and Monteiro 2008), fecundity and reproductive allotment (Gomes Jr. and Monteiro 2007;unpubl. data).…”

“…The growth of the delta formed a large number of river arms that after closing formed inland lagoons, entrapping populations of P. vivipara that inhabited the paleoestuary in freshwater environments with a different fish community than the one found in the brackish water of the estuary and the brackish water lagoons closer to the ocean (Bizerril and Primo 2001). The phenotypic variation among P. vivipara populations and evolutionary processes in this gradient have been well described by (Neves and Monteiro 2003;Monteiro and Gomes Jr. 2005;Gomes Jr. and Monteiro 2007;Gomes Jr. and Monteiro 2008). These authors found a direct association of mean body size with the salinity gradient, as well as other adult size correlates, such as fecundity and offspring size.…”

“…See the map in Gomes Jr. and Monteiro (2008) for the exact position of collection sites. Females were brought back to the laboratory and kept until the birth of the offspring.…”

“…The livebearer Poecilia vivipara is widespread and abundant in the lagoons of Northeastern Rio de Janeiro State (Gomes Jr. and Monteiro 2008), although an environmental gradient caused by salinity (due to proximity with the ocean) results in considerable differences in biotic communities and physical environment, even among sites within the same lagoon (Primo et al 2002;Suzuki et al 2002;Chagas and Suzuki 2005). The lagoons started forming circa 5000 years ago, by sediment deposition from the Rio Paraíba do Sul (Southwestern region of the plains) and marine deposits from sea level fluctuations (Northeastern region) (Martin et al 1997).…”