The testis of greater white-toothed shrew Crocidura russula in Southern European populations: A case of adaptive lack of seasonal involution?

Authors

  • Diaa Massoud,

    1. Departamento de Genética e Instituto de Biotecnología, Universidad de Granada, Granada, Spain
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  • Francisco J. Barrionuevo,

    1. Departamento de Genética e Instituto de Biotecnología, Universidad de Granada, Granada, Spain
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  • Esperanza Ortega,

    1. Departamento de Bioquímica y Biología Molecular III e Inmunología, Universidad de Granada, Granada, Spain
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  • Miguel Burgos,

    1. Departamento de Genética e Instituto de Biotecnología, Universidad de Granada, Granada, Spain
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  • Rafael Jiménez

    Corresponding author
    1. Departamento de Genética e Instituto de Biotecnología, Universidad de Granada, Granada, Spain
    • Correspondence to: Rafael Jiménez, Departamento de Genética e Instituto de Biotecnología, Universidad de Granada, Laboratorio 127 CIBM, Centro de Investigación Biomédica, Avenida del Conocimiento, 18100 Armilla, Granada, Spain.

      E-mail: rjimenez@ugr.es

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  • Diaa Massoud and Francisco J. Barrionuevo contributed equally to this study.

ABSTRACT

Males of all seasonal breeding mammals undergo circannual periods of testis involution resulting in almost complete ablation of the germinative epithelium. We performed a morphometric, histological, hormonal, and gene-expression study of the testes from winter and summer males of the greater white-toothed shrew, Crocidura russula, in populations of the southeastern Iberian Peninsula. Unexpectedly, we found no significant differences between the two study groups. Surprisingly, female data confirmed a non-breeding period in the summer, evidencing that males retain full testis function even when most females are not receptive. This situation, which has not been described before, does not occur in northern populations of the same species where, in addition, the reproductive cycle is inverted with respect to those in the south, as the non-breeding period occurs in winter instead in summer. Considering that the non-reproductive period shortens at lower latitude locations, we hypothesize that in southern populations the non-breeding period is short enough to make testis regression inefficient in terms of energy savings, because: (1) testes of C. russula are very small, a condition derived from their monogamy that implies low investment in spermatogenesis; and (2) the spermatogenic cycle of this species is slow and long. The inverted seasonal breeding cycle and the lack of seasonal testis regression described here are new adaptive processes that deserve further research, and provide evidence that the genetic and hormonal mechanisms controlling reproduction timing in mammals are more plastic and versatile than initially suspected. J. Exp. Zool. (Mol. Dev. Evol.) 322B: 304–315, 2014. © 2014 Wiley Periodicals, Inc.

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