The spectre of past spectral conditions: colour plasticity, crypsis and predation risk in freshwater sculpin from newly deglaciated streams

Abstract

Coastrange sculpin (Cottus aleuticus) have colonised recently deglaciated streams of Glacier Bay National Park, Alaska, USA, within the last 200 years. Highly cryptic colouration across a marked gradient of stream substrate colours within Glacier Bay could result from physiological (rapid) or morphological (slower) colour change. Laboratory experiments revealed that physiological colour plasticity occurred on the order of minutes, with significant variation in the degree of colour change among individuals and between populations. In contrast, morphological colour plasticity occurred on the order of weeks to months. Experimentally manipulated spectral conditions influenced the magnitude and variance of subsequent physiological colour plasticity. In-stream predation trials revealed significantly more predation attempts on higher background contrast sculpin models, providing evidence that background colour matching has strong fitness consequences. Colour plasticity with apparent fitness consequences occurs at multiple interacting time scales in coastrange sculpin and may play an important role in the colonisation of recently deglaciated streams.

The heritable basis and cost of colour plasticity in coastrange sculpins

“…All surviving individuals used to measure costs for the fast‐change treatment also had their colour change plasticity quantified at the end the 6‐month period to allow us to indirectly measure the cost of plasticity capacity in this subgroup (substrate colour changed every 2 days). All individuals were placed in a one‐gallon tank in complete darkness for 10 min (see Whiteley et al ., for detailed protocol). They were then immediately placed on a white background surrounded by a white box and photographed every minute for 30 min.…”

Environmental and hormonal factors controlling reversible colour change in crab spiders

“…Other animals that can undergo reversible changes in colour (such as fish, reptiles, amphibians, crustaceans and cephalopods) are also known to exhibit background matching (Hanlon et al, 1999;Norris and Lowe, 1964;Thurman, 1988;Whiteley et al, 2011). Background colour alone was not sufficient to trigger colour change in T. onustus under laboratory conditions: control spiders from the injection experiment that were also submitted to yellow background did not change colour over time under laboratory conditions.…”

“…Most colouration studies have been conducted on animals that establish a fixed colour pattern that is retained through their lifespan (Reed et al, 2008;Steiner et al, 2008; but see Whiteley et al, 2011). Temporal and spatial habitat heterogeneity that occurs within an individual's lifetime may favour the evolution of reversible plasticity by enabling phenotypic changes in response to environmental variation.…”

“…Many fish, reptiles and invertebrates exhibit reversible colour plasticity during their lifetime (e.g. Hanlon et al, 1999;StuartFox et al, 2006;Whiteley et al, 2011). Colour reversibility has many different functions in animals, including an involvement in thermoregulation (Brown and Sandeen, 1948), crypsis through background matching to avoid predator detection , and social interactions .…”

Costs of colour change in fish: food intake and behavioural decisions

“…Classic examples include the rapid and dynamic background matching of octopuses (Hanlon et al, 1999;Hanlon, 2007;Hanlon et al, 2009) and chameleons (StuartFox and Moussalli, 2009). Many fish darken their body colouration in response to dark visual backgrounds (Sugimoto, 2002;Mills and Patterson, 2009;Leclercq et al, 2010), which functions to facilitate predator avoidance and reduce predation risk (Sumner, 1935a;Sumner, 1935b;Whiteley et al, 2011), and is a plastic and reversible change (Sugimoto, 2002;Leclercq et al, 2010).…”