title: Shape, colour plasticity, and habitat use indicate morph-specific camouflage strategies in a marine shrimp.
abstract: Colour and shape polymorphisms are important features of many species and may allow individuals to exploit a wider array of habitats, including through behavioural differences among morphs. In addition, differences among individuals in behaviour and morphology may reflect different strategies, for example utilising different approaches to camouflage. Hippolyte obliquimanus is a small shrimp species inhabiting different shallow-water vegetated habitats. Populations comprise two main morphs: homogeneous shrimp of variable colour (H) and transparent individuals with coloured stripes (ST). These morphs follow different distribution patterns between their main algal habitats; the brown weed Sargassum furcatum and the pink-red weed Galaxaura marginata. In this study, we first investigated morph-specific colour change and habitat selection, as mechanisms underlying camouflage and spatial distribution patterns in nature. Then, we examined habitat fidelity, mobility, and morphological traits, further indicating patterns of habitat use.
  
  
  
  H shrimp are capable of changing colour in just a few days towards their algal background, achieving better concealment in the more marginal, and less preferred, red weed habitat. Furthermore, laboratory trials showed that habitat fidelity is higher for H shrimp, whereas swimming activity is higher for the ST morph, aligned to morphological evidence indicating these two morphs comprise a more benthic (H) and a more pelagic (ST) life-style, respectively.
  
  
  
  Results suggest that H shrimp utilise a camouflage strategy specialised to a limited number of backgrounds at any one time, whereas ST individuals comprise a phenotype with more generalist camouflage (transparency) linked to a more generalist background utilisation. The coexistence within a population of distinct morphotypes with apparently alternative strategies of habitat use and camouflage may reflect differential responses to substantial seasonal changes in macroalgal cover. Our findings also demonstrate how colour change, behaviour, morphology, and background use all interact in achieving camouflage.
authors.affiliation: Centro de Biologia Marinha, Universidade de São Paulo, São Sebastião, Brazil. rafaduarte87@usp.br.|Programa de Pós-Graduação em Biologia Comparada, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil. rafaduarte87@usp.br.
authors.forename: Rafael C
authors.initials: RC
authors.lastname: Duarte
authors.affiliation: Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall, TR10 9FE, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Stevens
authors.affiliation: Centro de Biologia Marinha, Universidade de São Paulo, São Sebastião, Brazil.
authors.forename: Augusto A V
authors.initials: AA
authors.lastname: Flores
mesh_terms: D000818:Animals; D000067558:Biological Mimicry; D003116:Color; D033364:Decapoda / Q000502:physiology*; D017753:Ecosystem; D010641:Phenotype; D010858:Pigmentation
keywords: Camouflage strategy; Caridean shrimp; Colour change; Geometric morphometrics; Habitat use; Life-styles; Polymorphism