The effect of growth rate and ageing on colour variation of European pond turtles

Abstract

Many chelonians have colourful dots, patches and stripes throughout their body that are made up, at least in part, of carotenoids. Therefore, turtles are very suitable models to study the evolution and functionality of carotenoid-based colouration. Recent studies suggested a close link between colouration and immune system in these taxa. However, more research is needed to understand the role of these colourful stripes and patches in turtle visual signalling. The purpose of this study was to explore the relationship between growth rate and colouration in European pond turtles. In particular, we wanted to answer the question of whether there is a trade-off between growth and colour expression. We also aimed to explore the effect of body size and age on colour variation. Turtles from a reintroduction-breeding program were recaptured, weighed and measured over an 8-year period to estimate their growth rates and age. We also measured with a spectrometer the reflectance of colour patches in two different body parts: shell and forelimb. We found that turtles with a faster growth rate had brighter limb stripes independently of their age. On the other hand, shell colouration was related to body size with larger turtles having brighter shell stripes and higher values of carotenoid chroma. Our results suggest that fast-growers may afford to express intense colourful limb stripes likely due to their higher intake of carotenoids that would modulate both growth and colour expression. However, shell colouration was related to body size probably due to ontogenetic differences in the diet, as juveniles are strictly carnivorous while adults are omnivorous. Alternatively, shell colouration might be involved in crypsis as the shell is visually exposed to predators.

Body coloration and mechanisms of colour production in Archelosauria: the case of deirocheline turtles

“…Sexual dichromatism has been hypothesized to result from females becoming duller as they grow and age [37]. Growth is known to affect the reflectance spectra of colourful regions in some turtles [99]. Moreover, males of some species of deirocheline turtles undergo ontogenetic colour change as they get larger and older [49,100].…”

First report of rapid eye color change in a non‐avian tetrapod

“…with variation in immune function (Ibáñez, Marzal, López, & Martín, 2013;Ibáñez, Polo-Cavia, Polo-Cavia, López, & Martín, 2014;Polo-Cavia, López, & Martín, 2013), behavior Mafli, Wakamatsu, & Roulin, 2011;Thomas, 2002), sex (Blake, 1921;Bulté, Germain, O'Connor, & Blouin-Demers, 2013;Ibáñez et al, 2013;Wang, Yang, Liang, & Shi, 2013), and age/ size (Ennen, Lindeman, & Lovich, 2015;Ibáñez, Martín, Marzal, & Bertolero, 2017;Ibáñez et al, 2013). Eye color is poorly studied in turtles but is well described in Eastern box turtles (Terrapene carolina carolina).…”

The value of long-term studies in behavioural ecology

“…En España la tradición de estudios longitudinales es aún escasa, y su uso en ecología de comportamiento se circunscribe de manera casi exclusiva al seguimiento de individuos marcados en poblaciones de aves (p. ej., Blas et al 2009;Kim et al 2013;Potti et al 2013;Senar et al 2014;Rodríguez et al 2016;Ibáñez et al 2017).…”

“…ej., Sergio et al 2007Sergio et al , 2009, 2011) y/o con poblaciones bajo cierto grado de amenaza (p. ej., Sanz-Aguilar et al 2009;Oro et al 2014;Hernández et al 2015;Ibáñez et al 2017). Esta transferencia de conocimiento aplicado sería la única manera de justificar ante los gestores el cierto grado de alteración que inevitablemente va a conllevar nuestra presencia y manipulación de los individuos en áreas protegidas.…”

“…adversas (pocos recursos alimentarios) los rasgos reproductivos de las gaviotas siguieron una relación cuadrática débil con la edad, y que el carácter cuadrático de dicha relación se acentuaba en años de bonanza ambiental (muchos recursos alimentarios), cuando los individuos de edades intermedias aumentaban mucho su éxito reproductor(Oro et al 2014).Un buen ejemplo del potencial de aunar conservación con el estudio de cuestiones de ecología evolutiva nos lo ofrece un estudio recientemente publicado con galápagos europeos Emys orbicularis(Ibáñez et al 2017). Aprovechando las reintroducciones de la especie que se llevan haciendo desde 2006 en el Delta del Ebro, se planteó la posibilidad de estudiar los compromisos entre desarrollo somático y la expresión de señales fenotípicas, como es la coloración, gracias a que los ejemplares liberados en el medio eran de edad conocida y estaban marcados individualmente.…”