Body size and allometric shape variation in the molly Poecilia viviparaalong a gradient of salinity and predation

Abstract

BackgroundPhenotypic diversity among populations may result from divergent natural selection acting directly on traits or via correlated responses to changes in other traits. One of the most frequent patterns of correlated response is the proportional change in the dimensions of anatomical traits associated with changes in growth or absolute size, known as allometry. Livebearing fishes subject to predation gradients have been shown to repeatedly evolve larger caudal peduncles and smaller cranial regions under high predation regimes. Poecilia vivipara is a livebearing fish commonly found in coastal lagoons in the north of the state of Rio de Janeiro, Brazil. Similar to what is observed in other predation gradients, lagoons inhabited by P. vivipara vary in the presence of piscivorous fishes; contrary to other poeciliid systems, populations of P. vivipara vary greatly in body size, which opens the possibility of strong allometric effects on shape variation. Here we investigated body shape diversification among six populations of P. vivipara along a predation gradient and its relationship with allometric trajectories within and among populations.ResultsWe found substantial body size variation and correlated shape changes among populations. Multivariate regression analysis showed that size variation among populations accounted for 66% of shape variation in females and 38% in males, suggesting that size is the most important dimension underlying shape variation among populations of P. vivipara in this system. Changes in the relative sizes of the caudal peduncle and cranial regions were only partly in line with predictions from divergent natural selection associated with predation regime.ConclusionsOur results suggest the possibility that adaptive shape variation among populations has been partly constrained by allometry in P. vivipara. Processes governing body size changes are therefore important in the diversification of this species. We conclude that in species characterized by substantial among-population differences in body size, ignoring allometric effects when investigating divergent natural selection’s role in phenotypic diversification might not be warranted.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0251-7) contains supplementary material, which is available to authorized users.

Demographic Expansion and Contraction in a Neotropical Fish during the Late Pleistocene-Holocene

“…Poecilia vivipara successfully colonizes rivers and inland habitats varying in salinity from 0 to 36 parts per thousand [22]; the latter figure actually being equal to the salinity of sea water. Populations of P. vivipara at either extreme of the salinity gradient differ significantly in traits such as body size and shape, fecundity, and reproductive allotment, which are likely determined genetically [38] [39]. Poecilia vivipara also varies markedly in personality traits including boldness, activity, and sociability/shoaling behaviour, which are modulated by environmental factors such as water transparency/visibility, salinity, and dissolved oxygen [40].…”

Predation risk and abiotic habitat parameters affect personality traits in extremophile populations of a neotropical fish (Poecilia vivipara)

“…The degree of predation risk was based on the records of piscivorous fishes in the studied lagoons during the past 20 years (Araújo, Perez, Magazoni, & Petry, ; Di Dario et al., ; Felice, ). While lagoons differed in the number of piscivorous species (Table ), no reliable information on the relative abundances of these species was available.…”

“…The degree of predation risk was based on the records of piscivorous fishes in the studied lagoons during the past 20 years (Araújo, Perez, Magazoni, & Petry, 2014;Di Dario et al, 2013;Felice, 2014).…”

Morphological variation among populations of Hemigrammus coeruleus (Characiformes: Characidae) in a Negro River tributary, Brazilian Amazon

“…Predation has received much attention in morphometric studies of freshwater fishes both in nature and in the laboratory, where it has been shown to act as an important selective pressure on body shape Gomes-Jr., Monteiro, 2008;Burns et al, 2009;Webster et al, 2011;van Rijssel, Witte, 2013, Araújo et al, 2014. Elongate bodies, such as those from UN2, UN3 and UN5, are often associated with steady-swimming and relatively good swimming performance (Langerhans, Reznick, 2010).…”

“…Although a large number of fish studies have documented morphological variation due to ecological causes, only a few studies have done so using neotropical species, e.g., Cichlasoma minckleyi (Kornfield, Taylor 1983) (Trapani, 2003), Bryconops caudomaculatus (Günther 1864) and Biotodoma wawrini (Gosse 1963) (Langerhans et al, 2003), Poecilia vivipara Bloch, Schneider 1801 (Neves, Monteiro, 2003;Monteiro, Gomes-Jr., 2005; Gomes-Jr., Monteiro, 2008;Araújo et al, 2014), Poecilia reticulata Peters 1859 Hendry et al, 2006, Burns et al, 2009, Bryconops sp. cf.…”