The effect of ecological factors on eye morphology in the western rainbowfish, Melanotaenia australis

Abstract

Ecological factors such as spatial habitat complexity and diet can explain variation in visual morphology, but few studies have sought to determine whether visual specialisation can occur among populations of the same species. We used a small Australian freshwater fish (the western rainbowfish, Melanotaenia australis) to determine whether populations showed variation in eye size and eye position, and whether this variation could be explained by environmental (light availability, turbidity) and ecological (predation risk, habitat complexity, invertebrate abundance) variables. We investigated three aspects of eye morphology, (1) eye size relative to body size, (2) pupil size relative to eye size, and (3) eye position in the head, for fish collected from 14 sites in a major river catchment in northwest Western Australia. We found significant variation among populations in all three measures of eye morphology, but no effect of sex on eye size or eye position. Variation in eye diameter and eye position was best explained by the level of habitat complexity. Specifically, fish occurring in habitats with low complexity (i.e. open water) tended to have smaller, more dorsally-located eyes, than those occurring in more complex habitats (i.e. vegetation present). The size of the pupil relative to the size of the eye was most influenced by the presence of surrounding rock formations; fish living in gorge habitats had significantly smaller pupils (relative to eye size) than those occupying semi-gorge sites or open habitats. Our findings reveal that different ecological and environmental factors contribute to habitat-specific visual specialisations within a species.

Adaptive divergence in the eyes ofHeliconiusbutterflies likely contributes to pre- and post-mating isolation

“…Habitat-associated variation in eye morphology has been reported across taxa (e.g., insects: (Greiner, 2006); mammals: (Veilleux & Lewis, 2011); fish: (Lisney et al, 2020); snakes: (Liu et al, 2012); primates: (Kirk, 2004)), and this variation is generally interpreted as an adaptive response to the local sensory conditions. For example, visual perception in insects is affected by the total number of ommatidia and their size/density (Greiner, 2006; Land, 1997; Warrant, 2004), and nocturnal and crepuscular species often possess larger eyes and larger facets to enhance photon sensitivity in low-light environments (Freelance et al, 2021).…”

Environmental selection, rather than neutral processes, best explain patterns of diversity in a tropical rainforest fish

“…We therefore capitalise on growing knowledge of eco-evolutionary processes in Australian rainbowfishes ( Melanotaenia spp; family Melanotaeniidae) (e.g. McGuigan et al (2003), McGuigan et al (2005), Smith et al (2013), McCairns et al (2016), Gates et al (2017), Brauer et al (2018), Lisney et al (2020), Sandoval-Castillo et al (2020), Smith et al (2020)). In this genus, previous work has indicated not only the likely importance of hydroclimate as a driver of diversity, but the utility of integrative methods for assessing aquatic adaptation.…”

Predicting the functional morphology of lotic and lentic populations of the invasive Mozambique tilapia Oreochromis mossambicus (Peters, 1852)

“…Divergences become more intense when species living in extremely diverse ecological conditions lead to local adaptation and phenotypic modifications (Losos et al, 1998;Kocher, 2004). Selection pressures due to habitat modifications by both natural and anthropogenic influences are manifested in species in the form of phenotypic differences through either genetic variability, phenotypic plasticity, or a combination of both (Langerhans, 2003;Lisney et al, 2020). Phenotypic divergences also occur through evolutionary responses to selection pressures leading to significant changes in traits that are affected more, which can lead to speciation in many fishes (Langerhans et al, 2003;Burress and Wainwright, 2019).…”

“…A wide range of taxa showing this intra-species divergence related to environmental gradients, resource and habitat use is referred to as trophic polymorphism (Webster et al, 2011;Foster et al, 2015;Lisney et al, 2020). However, population mixing, mainly due to migration and gene flow, restricts the adaptive diversification in fishes (Collyer et al, 2015).…”

“…This allows us to predict the species responses to habitat alterations and to identify the species which are most susceptible and resilient to change (Ribeiro et al, 2016;Kelley et al, 2018). Hydrodynamics is the major physical factor that significantly influences the ecological characteristics of aquatic habitats (Bracciali et al, 2016;Lisney et al, 2020). Higher flow velocity was found to increase the prey encounter rate which makes the feeding conditions energy-intensive, making food searching and manipulation more difficult (Stoll and Fischer, 2011).…”