Abstract
Body and head shape in fish responds to environmental factors such as water flow rate, food sources, and niche availability. However, the way in which fish respond to these environmental factors varies. In Central Chile, multiple river and lake systems along the coast provide an ideal study site to investigate these types of shape changes. We use geometric morphometrics to characterize shape differences in Galaxias maculatus (Jenyns) between river and lake populations. Lake fish converge on a shape with a more fusiform body, narrower head, and larger eyes, while river fish have a more robust body, rounder head, and smaller eyes. These shape changes are consistent with a shift to zooplanktivorous foraging in lakes, as evidenced in other systems. Unlike some fish species that develop polymorphisms in body shape after colonization (e.g., benthic and limnetic forms), G. maculatus in lakes exhibit a monomorphic limnetic form.
Highlights
The ecomorphological hypothesis suggests that the morphological traits of organisms should reflect the conditions of the environments they inhabit, and this idea has been acknowledged for over 100 years [1–5]
The body and head shape of G. maculatus differed significantly depending on whether an individual was from a river or lake environment and on its size
River fish had smaller eyes and rounder heads, whereas lake fish had larger eyes and narrower heads which came to a sharper point
Summary
The ecomorphological hypothesis suggests that the morphological traits of organisms should reflect the conditions of the environments they inhabit, and this idea has been acknowledged for over 100 years [1–5]. Organisms in lotic environments (rivers) tend to exhibit consistent and predictable morphometric differences compared to those in lentic environments (lakes). These general morphometric responses to lake colonization are primarily influenced by differences in flow rate [6–11]. Plasticity occurs when an individual expresses a different phenotype in response to different environmental conditions. The changes resulting from plasticity occur within an individual’s lifetime and they are not heritable [23,27,28]. Both of these processes result in populations displaying traits that are suited to the conditions of their environments [3,4,10,21,23,26], and they are not mutually exclusive
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