Animal Reproduction Science 114 (2009) 269–278 Contents lists available at ScienceDirect Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci Testis size, sperm characteristics and testosterone concentrations in four species of shrews (Mammalia, Soricidae) R.N. Parapanov a,∗ , S. Nusslé a , M. Crausaz b , A. Senn b , J. Hausser a , P. Vogel a a Department of Ecology and Evolution, University of Lausanne, CH-1015 Lausanne, Switzerland b Foundation F.A.B.E.R., rue de la Vigie 5, 1003 Lausanne, Switzerland article info Article history: Received 19 February 2008 Received in revised form 8 September 2008 Accepted 23 September 2008 Available online 1 October 2008 Keywords: Sperm competition Testis size Sperm number Sperm motility Sperm length Testosterone concentration abstract The aim of this study was to establish and compare the sperm characteristics in four shrew species in the context of the sperm competition hypothesis. As expected, the large relative testis size in promiscuous species was associated with a high number of cauda epididymal spermatozoa and a high concentration of circulating testosterone. In addition, in Sorex and Neomys, species with high intensity of sperm competition, the spermatozoa stored in cauda epididymis were characterized by high percentage of progressive motility whereas in Crocidura and Suncus, the cauda epididymal spermatozoa were motile but with very low percentage of pro- gressive motility. This capability is achieved only following the passage through the vas gland, a specialized region for sperm stor- age located along the vas deferens in these shrew species. The hypothesis that sperm competition is positively correlated with spermatozoa length could not be confirmed. In Crocidura and Sun- cus, the total sperm length is increased by the large sperm head due to a big acrosome. This trait, specific to the subfamily Crocidurinae, may results from a selective pressure independent of the context of sperm competition, related to a specific, but as yet unclear role, for the acrosome during the fertilization. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The efficiency of spermatogenesis is a key to reproductive success in the male. Male fertility is characterized by many important contributing factors. One of the most important is the number of ∗ Corresponding author. E-mail address: roumen.parapanov@unil.ch (R.N. Parapanov). 0378-4320/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2008.09.013