Hypoxia drives plastic divergence in cichlid body shape

Abstract

Organisms experience multiple selective agents that can influence phenotypes through heritable and/or plastic changes, often reflecting complex interactions between phenotype and environment. Environmental factors can directly influence phenotypes, but also indirectly affect phenotypic variation when genetic/plastic change in one trait results in correlated genetic/plastic change in another trait. In fishes, body shape is a trait that might be particularly prone to influence from environmental pressures that act on other morphological features. Variation in dissolved oxygen among aquatic environments has a large impact on the size of the gills and brains of fishes. It is likely that dissolved oxygen interacts with other environmental factors to both directly and indirectly influence patterns of body shape variation. We examined effects of dissolved oxygen on body shape variation among populations of an African cichlid fish (Pseudocrenilabrus multicolor) from multiple high-and low-oxygen sites within a single drainage in Uganda. A split-brood laboratory experiment was used to estimate plasticity of gill and brain size, and we used morphometric analyses to identify variation in body shape in F 1 offspring. Several analyses enabled us to identify genetic effects among populations, and effects of oxygen acting either directly on body shape or indirectly through its effects on gill and brain size. A large part of the variation in body shape was due to plastic variation in gill size associated with dissolved oxygen. Fish raised under low oxygen had deeper heads and shorter bodies, and this variation was driven by both direct effects of oxygen and indirect effects of gill size variation. Body shape variation in fishes should reflect interacting effects of multiple environmental factors that act directly or indirectly on morphology. Body shape might be particularly difficult to predict when phenotypes are plastic, because changes among populations would occur rapidly and be unrelated to genetic variation.

The occurrence of an Eastern African haplochromine cichlid in the Ituri River (Aruwimi, Congo basin): adaptive divergence in an introduced species?

“…Indeed, within the constricted space of the head, larger eyes are mostly correlated with shorter snouts and shorter premaxillary pedicels (Barel, 1983;Crispo & Chapman, 2010). The two populations examined differ from each other in a few measurements on the head, and head morphology in particular is known to display responses to a changing environment in 'Haplochromis' species, which has been demonstrated under experimental (e.g.…”

“…Crispo & Chapman, 2010;van Rijssel & Witte, 2013;Fig. 5 Principal component analysis plot of PC2 against PC1 for a PCA on 19 log-transformed measurements (n = 64).…”

“…Natural selection and phenotypic plasticity can also act simultaneously on morphological traits. In such cases, adaptive responses are a combination of plastic and genetic effects (Crispo & Chapman, 2010;van Rijssel et al, 2015). To what extent the morphological differences observed in the present study have a genetic basis are the results of phenotypic plasticity, or a combination of both, is not possible to assess at the moment, based on our data.…”

The effect of chronic volcanic pollution on the morphometric characteristics of juvenile Dolly Varden (Salvelinus malma W.) on the Kamchatka peninsula

“…Environmental factors can either directly influence body proportions or indirectly affect morphometric variation, when changes in one trait result in correlated changes in others (Crispo & Chapman, 2011). The correlation among morphological traits is timedependent and displays high developmental plasticity (Grunbaum et al, 2007).…”

“…The correlation among morphological traits is timedependent and displays high developmental plasticity (Grunbaum et al, 2007). It has been demonstrated that environmental factors such as current velocity, oxygen concentration, water temperature, and salinity may have a significant effect on fish morphotype (Mahon, 1984;Imre et al, 2002;Grunbaum et al, 2007;Paez et al, 2008;Crispo & Chapman, 2011;Franssen et al, 2012;Rajput et al, 2013).…”