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Amphibians are the fastest known declining taxonomic group in the world with 48% of populations in decline (Stuart et. al. 2004). These declines in amphibian populations are partially due to the lack of basic life history data (Semlitsch 2003). For example, amphibians are known for their bright coloration and ability to rapidly change color. Coloration is key to amphibian survival in terms of defense (as camouflage or a warning sign to predators), thermoregulation (darker skin warms faster), and communication (primarily mating displays) (Rudh and Qvanstrom 2013). One aspect of amphibian coloration that is poorly understood is how much the environment influences amphibian pigmentation.
Amphibian coloration is dictated by three main types of chromatophores underneath the skin. Chromatophores are cells that contain pigments which reflect light. Iridophores contain pigments that reflect light that contribute to bluish coloration. Melanophores are the cells that control expression of melanin that can be expanded and contracted to darken or lighten the skin. Xanthophores are the cells responsible for the red and yellow coloration (Bagnara et. al. 1968) and contain pteridine organelles and dietary carotenoid pigments (Bagnara et. al. 1968 and Kraemer et. al. 2012). There are 600 different derivatives of carotenoids that have two major uses. They can be metabolized into Vitamin A and other antioxidants or used to physiologically change pigmentation. In particular, they are well known for being in orange and yellow vegetables like carrots and causing the bright pink coloration of the skin of some gulls. This coloration of gulls is due to their highcarotenoid diet of shrimp and algae (McGraw and Hardy 2006). Allocating carotenoids toward pigmentation rather than toward Vitamin A is a potential sign of health since that organism is able to use these nutrients for coloration instead of as antioxidants (Hill and Johnson 2012). This suggests that increasing access to carotenoids through diet can affect pigmentation which can reflect health in some organisms. We want to know whether carotenoids consumed through diet will affect pigmentation of amphibians as well.
Professor Heather Waye conducted research studying whether spot patterns in Eastern Tiger Salamanders (Ambystoma tigrinum) changed during maturation (Waye 2013). She made the observation that some of the salamanders’ yellow coloration faded during their time in captivity. This may have been caused due to differences in abiotic factors (e.g. lighting, temperature) or diet. Captive salamanders have been fed a diet limited to domestic crickets, fish, and earthworms. Adult salamanders in the wild have been found to eat earthworms, crickets, grasshoppers, small mice, other amphibians (including their own larvae), mollusks, and other small insects (Reese 1969 and Moriarity and Hall 2014). Mollusks have been found to contain carotenoids (Vershinin 1996). I hypothesized that adding carotenoidrich food to their diet will result in an increase in intensity of the yellow in their skin.
Tiger salamander, Animal pigments, Carotenoids
Novak, Katherine, "Can Diet Affect Coloration in Tiger Salamanders?" (2018). Undergraduate Research Symposium 2018. 10.