Ontogenetic and sexual difference in pelvic bones between harbour porpoise (<i>Phocoena phocoena</i>) and Dall’s porpoise (<i>Phocoenoides dalli</i>)

DOI
  • Okabe Yuna
    Department of Aquabiology, Graduate School of Bioindustry, Tokyo University of Agriculture
  • Kobayashi Mari
    Tokyo University of Agriculture
  • Arai Yuichi
    Department of Bioindustry, Graduate School of Bioindustry, Tokyo University of Agriculture

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Other Title
  • ネズミイルカ（<i>Phocoena phocoena</i>）とイシイルカ（<i>Phocoenoides dalli</i>）の雌雄と成長段階における寛骨の形状比較

Abstract

<p>Pelvic bone is attached to the ischiocavernosus muscle, which is connected to the penis. The sizes of the penis and testes vary with breeding system, and they are larger in a multi-male system than in a single-male system. Harbour and Dall’s porpoises are members of Phocoenidae family. Although they have similar socialities, their breeding systems differ. Therefore, we predicted differences in the morphology of the pelvic bones in these species. Pelvic bones were collected from harbour porpoises (n = 54) and Dall’s porpoises (n = 76). The present study analyzed 29 semi-landmarks using linear regression and canonical variate analyses. Linear regression analysis showed that the length, height, and width of the pelvic bones were positively correlated with body length. There was a significant difference in the slope of the regression line between the males of both species. The shape of the pelvic bone was identified based on sex and sexual maturity; in mature males of both species, the pelvic bone at the center was wider than that in immature males and females. These differences in the size and shape of the pelvic bone are likely due to differences in the amount of the ischiocavernosus muscle attached to the pelvic bone.</p>

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