Crypsis in the mud crab Panopeus americanus Saussure, 1857 (Decapoda, Panopeidae): relationship to sexual maturity

Abstract

The present study analyses the cryptic colouration patterns in mud crabs, Panopeus americanus that live in an impacted intertidal mangrove area. The main objectives were to identify the cryptic/non-cryptic transition sizes (males and females) and their relationships to morphological and functional sexual maturity. Individuals were collected from the remnant mangrove of Araçá, on the coast of São Sebastião, São Paulo, Brazil. They were sexed, measured and classified into three colouration categories: white homogeneous, cryptic heterogeneous or dark homogeneous (non-cryptic). A logistic regression was performed to detect the size at which 50% of the population reached the dark homogeneous colouration and functional sexual maturity in females. Morphological sexual maturity for both sexes was estimated through relative growth. A progressive change from heterogeneous to dark homogeneous colouration following growth was observed. Using both analyses of maturity, we detected (1) that individuals of the white homogeneous colouration can be classified as non-reproductive and (2) that there is an overlap between the size at which 50% of females reached the dark homogeneous colouration and their functional sexual maturity (approximately 14.00 mm CW). These findings are primarily explained by ontogenetic changes in habitat use during the species’ life cycle.

Relative growth, morphological sexual maturity, heterochely, and handedness in Panopeus occidentalis (Brachyura, Panopeidae)

“…As a result, injury to or structure. This was observed in the present study, and in other studies on Trichodactylus fluviatilis Latreille, 1828 (Lima et al 2013), A. schmitti (Frigotto et al 2013), and P. americanus (Carvalho-Batista et al 2015).…”

“…The positive allometric growth observed between carapace width (CW) and abdomen width (AW) in both juvenile and adult phases in females indicates a high investment in abdominal growth during development. The abdomen in brachyuran females is related to reproduction, since it is used for egg incubation (Hartnoll 1974;Castiglioni and Negreiros-Fransozo 2004;Pescinelli et al 2014;Carvalho-Batista et al 2015). A larger abdomen increases reproductive efficiency (Castiglioni and Negreiros-Fransozo 2004;Cobo and Alves 2009;Pescinelli et al 2014;Carvalho-Batista et al 2015), because it provides a wider area for egg protection, improving incubation conditions (Mantelatto and Fransozo 1994).…”

Improved camouflage through ontogenetic colour change confers reduced detection risk in shore crabs

“…This suggests that selection for camouflage may be more intense in simple visual scenes. We also predicted that crabs would be hardest to find when placed against their original habitat type, because this would support a substrate-specific (or specialist) background matching hypothesis (Carvalho-Batista et al, 2015;Detto, Hemmi, & Backwell, 2008;Krause-Nehring et al, 2010;Stevens et al, 2013). In contrast, the mudflat crabs characterized by the dark green phenotype were hardest to find against all background types.…”

“…Many marine crustaceans are extremely variable in appearance among individuals in early life, with intraspecific diversity in colour and patterning declining with age (Anderson, Spadaro, Baeza, & Behringer, ; Booth, ; Carvalho‐Batista et al, ; Duarte et al, ; Krause‐Nehring, Matthias Starck, & Richard Palmer, ; Palma & Steneck, ; Todd et al, ). However, the reasons for such ontogenetic changes have seldom been experimentally explored and remain somewhat mysterious, but may reflect a reduction in predator risk as individuals grow larger and become more defended (thus have a reduced need for camouflage), or a switch to different habitat types with age (Hultgren & Stachowicz, ; Todd, ; Wilson et al, ).…”

Color Change, Phenotypic Plasticity, and Camouflage

“…A further largely unresolved question is why many crabs are highly variable in appearance among individuals as juveniles, but undergo ontogenetic changes as they grow (Figure 3). In many species, adults become less patterned and often darker, and apparently less cryptic (Palma and Steneck, 2001;Todd et al, 2006Todd et al, , 2009Stevens et al, 2014b;Carvalho-Batista et al, 2015;Jensen and Egnotovich, 2015;Russell and Dierssen, 2015). Two possible explanations are that older/larger crabs move to different habitat types, requiring a different type of camouflage, or that as they grow bigger they become less susceptible to predation (Todd et al, 2009).…”