[MARMAM] New Paper: Estimation of sexual maturity based on morphometrics of genital organs in male northern fur seals, Callorhinus ursinus

Yoko Mitani yo_mitani at fsc.hokudai.ac.jp
Sun Jan 3 18:57:40 PST 2021

Dear All,

We are pleased to announce publication of our latest paper on genital
morphometrics of northern fur seal males:
Yukino Hirakawa, Takanori Horimoto, Ippei Suzuki, and Yoko Mitani
"Estimation of Sexual Maturity Based on Morphometrics of Genital
Organs in Male Northern Fur Seals, Callorhinus ursinus," Mammal Study
46(1), 1-11, (21 December 2020). https://doi.org/10.3106/ms2020-0004


It's not always possible to obtain samples from dead male pinnipeds
that are fresh enough to determine the histological characteristics of
spermatogenesis and their stage of sexual maturity. We propose that
the morphometrics of genital organs of northern fur seals, Callorhinus
ursinus, can be used as a new indicator of sexual maturity. We
analyzed data from collected records of male fur seals around Hokkaido
during 2011–2017 to examine morphometrics of genital organs and their
stage in histological characteristics of spermatogenesis. First, we
investigated ontogenetic and seasonal variation in three genital
organs: testes, epididymides, and bacula. Second, we classified the
stages of histological characteristics of spermatogenesis into three
groups (Stage A–C) using non-linear discriminant analysis, based on
the stage in histological characteristics of spermatogenesis
determined by histological observation of seminiferous tubules.
Testicular size, testicular mass, and epididymal mass showed seasonal
variation associated with spermatogenesis. From our analysis, the
stage in histological characteristics of spermatogenesis could be
estimated using testicular mass with high accuracy of predicting
spermatogenesis. And measurement of baculum was suggested to be an
indicator of predicting sexual maturity. We conclude that this simple
estimation may be used to determine sexual maturity based on
individual growth patterns.

Kind regards,


三谷曜子 Yoko Mitani
海獣班 HokkaidOcean Mammal Team
〒040-0051 北海道函館市弁天町20番5号
Tel: 0138-85-6558; Fax: 0138-85-6625
Email: yo_mitani at fsc.hokudai.ac.jp

HokkaidOcean Mammal Team
Field Science Center for Northern Biosphere, Hokkaido University
Hakodate Research Center for Fisheries and Oceans
20-5 Benten-cho, Hakodate, Hokkaido 040-0051, JAPAN
TEL: +81-138-85-6558; FAX: +81-138-85-6625
E-mail: yo_mitani at fsc.hokudai.ac.jp

More information about the MARMAM mailing list