Habitat constraints on carotenoid‐based coloration in a small euryhaline teleost

Abstract

Display of bright and striking color patterns is a widespread way of communication in many animal species. Carotenoid‐based coloration accounts for most of the bright yellow, orange, and red displays in invertebrates, fish, amphibians, reptiles, and birds, being widely considered a signal of individual health. This type of coloration is under the influence of several factors, such as sexual selection, predator pressure, pigment availability, and light transmission. Fish offer numerous examples of visual communication by means of color patterns. We used a small cyprinodontid fish, Aphanius fasciatus (Valenciennes, 1821), as a model species to assess habitat constraints on the color display in male caudal fin. Populations from natural and open/closed artificial habitats were tested for differences in the pigmentation of caudal fins. The most important factors explaining the intensity of coloration were the habitat type and the chlorophyll concentration in the sediment, followed by water turbidity; yellow fins were observed in natural habitats with low chlorophyll concentration and high water turbidity, while orange fins occurred in artificial habitats with high chlorophyll concentration and low turbidity. Furthermore, A. fasciatus in artificial habitats showed a higher somatic and a lower reproductive allotment with respect to natural habitats, according to the existing literature on the species. Furthermore, in closed artificial habitats, where the most intense reddish coloration of caudal fins was observed, a trade‐off between somatic growth and the coloration intensity of a carotenoid‐based sexual ornament has been observed; in these populations, intensity of caudal fin coloration was negatively related to the somatic allotment. Results of this study suggested how both the pigmentation of male's caudal fin and the life history strategies of the species are constrained by habitat characteristics.

A comparative analysis of habitat quality between artificial and natural creeks in the Mediterranean killifish Aphanius fasciatus: Implications for conservation

“…Three were natural salt marsh creeks and four were artificial creeks. Natural habitats are intertidal creeks, characterized by daily water renewal due to tidal excursion that increases the turbidity and exports nutrients and, thus, reduces local primary productivity (Cavraro et al, 2018). Artificial habitats were man‐made artificial creeks made for different purposes: traditional fish farming, small marinas, and even military defence lines.…”

“…These samples were transferred to the laboratory, photographed on a white background using a reference colour chart and a millimetre reference scale that allowed subsequent image analysis, and then released. Each photograph was processed as described in Cavraro et al (2018) and used to calculate two indices: a redness index (Ir) for the caudal fin and a contrast index (Ic) for the lateral bars. The photographs were analysed in ImageJ (Schneider, Rasband & Eliceiri, 2012), as per the Levin, Ben‐Dor & Singer (2005) methodology.…”

“…Following this, the RGB values were linearly transformed using the coefficients of a linear regression calculated between the RGB values of the five reference colour patches and those taken from a photo of the colour chart used as reference. Since the caudal fin of male A. fasciatus shows a yellow–orange carotenoid‐based pigmentation, the Ir index can give information about the intensity of the coloration (Levin, Ben‐Dor & Singer, 2005; Cavraro et al, 2018). This was calculated using the formula: …”

“…The aim of this study was, thus, to compare habitat quality between artificial and natural creeks, using coloured secondary sexual traits as indicators. Fish in artificial habitats were expected to express more conspicuous traits with respect to fish living in natural habitats (as found in Cavraro et al, 2018) due to the higher availability of resources (i.e. carotenoids from micro/macroalgae and benthic prey) (Grether, Hudon & Millie, 1999) and a higher level of algal coverage (Kjernsmo & Merilaita, 2012) that, in addition, offers protection from predators and a substrate for egg deposition.…”

“…fecundity, longevity, growth), due to different morphological and trophic properties of habitats. Furthermore, males in artificial habitats have shown more intense caudal fin pigmentation (Cavraro et al, 2018). Since many animal pigments (e.g.…”