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<p>Cymothoid isopods are obligate ectoparasites of fishes, with body shapes reflecting their site of attachment and reproductive strategies. Buccal cavity species tend to be elongated, branchial parasites are twisted, and surface dwellers are dorsoventrally flattened. These adaptations, along with marked ontogenetic changes during sex transformation from male to female, contribute to sexual dimorphism and ontogenetic allometry. In this study, Geometric Morphometric Analysis (GMA) was used to examine intra- and interspecific shape variation in five species, viz. <i>Agarna malayi</i>, <i>Joryma sawayah</i>, <i>Cymothoa frontalis</i>, <i>Cymothoa indica</i>, and <i>Nerocila orbignyi</i>, collected from host fishes along the Odisha coast, India. A total of 143 adults were analysed based on 20 dorsal landmarks. Procrustes superimposition, Principal Component Analysis (PCA), and Discriminant Function Analysis (DFA) revealed marked sexual differences, with females showing greater variation linked to marsupium development and host adaptation. Significant interspecific variation (<i>p</i> &lt; 0.05) enabled reliable species discrimination, especially among females.</p>

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A comparative analysis of intrasexual and interspecific shape variation in cymothoid isopods based on geometric morphometrics

  • 期刊论文

  • 发表日期：

    2026年2月15日

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  • Sandeep Kumar Mohapatra,
  • Sanmitra Roy,
  • Jaya Kishor Seth,
  • Basudev Tripathy,
  • Anil Mohapatra

摘要

Cymothoid isopods are obligate ectoparasites of fishes, with body shapes reflecting their site of attachment and reproductive strategies. Buccal cavity species tend to be elongated, branchial parasites are twisted, and surface dwellers are dorsoventrally flattened. These adaptations, along with marked ontogenetic changes during sex transformation from male to female, contribute to sexual dimorphism and ontogenetic allometry. In this study, Geometric Morphometric Analysis (GMA) was used to examine intra- and interspecific shape variation in five species, viz. Agarna malayi, Joryma sawayah, Cymothoa frontalis, Cymothoa indica, and Nerocila orbignyi, collected from host fishes along the Odisha coast, India. A total of 143 adults were analysed based on 20 dorsal landmarks. Procrustes superimposition, Principal Component Analysis (PCA), and Discriminant Function Analysis (DFA) revealed marked sexual differences, with females showing greater variation linked to marsupium development and host adaptation. Significant interspecific variation (p < 0.05) enabled reliable species discrimination, especially among females.