Biological associations of color variation in the Indo-Pacific swimming crab Charybdis hellerii

Abstract

A marine biological invasion is a natural process accelerated by human activities, and the crab Charybdis hellerii is an example of a globally widespread invasive species. This study evaluated color variation in C. hellerii and its relationship to the sex, size and sexual maturity of these crabs, and compared the efficiency of a freeware digital image-editing program with a commercially available program. The color of the individuals was analyzed using standardized digital images. The color pattern varied significantly with size; smaller and immature individuals were darker than larger and mature ones. The female abdomen changed in morphology and color with sexual maturity, becoming wider and orange-colored. There was no statistical difference in the color values between males and females and immature males did not show morphological or color differences in their abdomen. This study highlights the possible relationships of the color and physiological state of the reproductive system, which could help in future studies of behavior, avoiding the need to dissect and/or remove individuals from nature for assessment of sexual maturity. The freeware program showed the same efficiency in digital image analysis as a widely known commercial program.

Color variation of the freshwater crab Dilocarcinus pagei Stimpson, 1861 captured in the Amazon region at Itacoatiara, Amazonas, Brazil

“…The positive and negative relationships of color intensity recorded in D. pagei may further indicate the existence of a hierarchy in this species and could be an important character during territorial disputes or choice of partners; as noted in the blue crab Callinectes sapidus Rathbun, 1896 (Baldwin and Johnsen, 2012). Watanabe et al (2015) suggests that the color variation related to the size of C. hellerii may indicate a dominance hierarchy among individuals for resources such as food and females available for mating (males only).…”

“…The recorded values of the images were collected from a histogram provided by free software GIMP (GNU Image Manipulation Program, EUA) obtained from the selected area of each morphological structure (cephalothorax surface, external surface of chelipeds, abdomen and pereiopods). This software has the same accuracy as other software described by Watanabe et al (2015) who investigated the coloring pattern of the crab C. hellerii.…”

“…The abdomen experiences positive allometric growth because it has the function of incubation chamber during reproduction (Davanso et al, 2016). This positive allometric growth may alter the concentration of chromophores in the abdomen as observed in C. hellerii and A. cribrarius by Watanabe et al (2015) and Pinheiro and Taddei (2000), respectively. The color variation of the chelipeds and pereiopods of D. pagei shows the same pattern as the cephalothorax.…”

Histórico de introdução do siri invasor <i>Charybdis hellerii</i> (A. Milne-Edwards, 1867) (Decapoda, Portunidae) na costa americana: ferramentas moleculares e morfologia comparativa

“…Embora diversos caracteres diagnósticos tenham sido apontados para a identificação de cada uma delas por Spiridonov & Türkay (2001) (Watanabe et al, 2015). Indivíduos pequenos e imaturos foram mais escuros que os maiores e maduros.…”

“…Indivíduos pequenos e imaturos foram mais escuros que os maiores e maduros. O abdômen das fêmeas também mudou de cor com a maturidade sexual (Watanabe et al, 2015).…”