Pigmentation plasticity enhances crypsis in larval newts: associated metabolic cost and background choice behaviour

Abstract

In heterogeneous environments, the capacity for colour change can be a valuable adaptation enhancing crypsis against predators. Alternatively, organisms might achieve concealment by evolving preferences for backgrounds that match their visual traits, thus avoiding the costs of plasticity. Here we examined the degree of plasticity in pigmentation of newt larvae (Lissotriton boscai) in relation to predation risk. Furthermore, we tested for associated metabolic costs and pigmentation-dependent background choice behaviour. Newt larvae expressed substantial changes in pigmentation so that light, high-reflecting environment induced depigmentation whereas dark, low-reflecting environment induced pigmentation in just three days of exposure. Induced pigmentation was completely reversible upon switching microhabitats. Predator cues, however, did not enhance cryptic phenotypes, suggesting that environmental albedo induces changes in pigmentation improving concealment regardless of the perceived predation risk. Metabolic rate was higher in heavily pigmented individuals from dark environments, indicating a high energetic requirement of pigmentation that could impose a constraint to larval camouflage in dim habitats. Finally, we found partial evidence for larvae selecting backgrounds matching their induced phenotypes. However, in the presence of predator cues, larvae increased the time spent in light environments, which may reflect a escape response towards shallow waters rather than an attempt at increasing crypsis.

The key role of behaviour in animal camouflage

“…In the filefish Monacanthus chinensis , which can switch from a brown to green variant, substrate choice also occurs only in brown individuals (Gilby et al, ). Similar findings were reported for larval newts ( Lissotriton boscai ), where lighter larvae that had been on light backgrounds spent more time on light than on dark backgrounds, but darker larvae showed no clear preference (Polo‐Cavia & Gomez‐Mestre, ). In crab spiders, substrate (flower colour) preference exists, but only by yellow and not by white individuals, potentially due to different prey‐capture strategies (Heiling et al, ).…”

“…In the Polo‐Cavia & Gomez‐Mestre () study of larval newts, preferences for backgrounds that matched their body lightness better could either be explained by imprinting over a period of days on the preferred background, or by a comparison between body and background coloration by the newt. Without experiments preventing newts from seeing their own appearance the two cannot be disentangled.…”

You cannot have it all: Heritability and constraints of predator‐induced developmental plasticity in a Neotropical treefrog

“…Given that the efficacy of tadpole phenotypes may depend on pond characteristics such as background vegetation or water turbidity (Eterovick et al. ; Polo‐Cavia and Gomez‐Mestre ), each distinct habitat may be more or less advantageous to certain tadpole morphologies (Kopp et al. ).…”

Extreme colour variation in the larvae of the executioner clownfrog, Dendropsophus carnifex (Anura: Hylidae), living in nearby ponds of different light exposure and duration

“…This colour plasticity could potentially be due to distinct camouflage strategies to face predation (see Rudh & Qvarnström, ). For example, some tadpoles show paler or darker phenotypes in order to avoid predators through background matching (Kats & Van Dragt, ; King et al, ; Polo‐Cavia & Gomez‐Mestre, ) while some may even bury themselves in the muddy bottom to improve crypsis (Touchon & Warkentin, ). On the other hand, disruptive coloration works by breaking up the outlines of the tadpole with a strongly contrasting pattern.…”

“…For instance, tadpoles inhabiting turbid water often look pale, while conspecifics living in tannin‐stained water are frequently brightly coloured (Thibaudeau & Altig, ). In response to predator presence, coloration may change to either enhance background matching, improve camouflage through disruptive coloration (Polo‐Cavia & Gomez‐Mestre, ), or promote bright colours on expendable body parts in order to lure predators away from vital areas (Touchon & Warkentin, ). Nonetheless, reports or detailed studies on the variation of tadpole coloration are still scarce.…”