Abstract
Sperm competition occurs when the sperm of two or more males compete to fertilize the egg/s of a particular female. Males of some species respond to a high risk of sperm competition by increasing the number of sperm in their ejaculates. Males may accomplish such a response by increasing the intensity or duration of contraction of the cauda epididymidis and vas deferens. During emission (first phase of the ejaculatory process), the vas deferens receives sperm from the cauda epididymidis and propels the sperm to the urethra. In this paper, we tested the hypothesis that males exposed to a high risk of sperm competition mobilize larger numbers of sperm from the cauda epididymidis to the vas deferens before initiation of copulatory behavior. This accumulation of sperm in the vas deferens would result in a larger number of sperm in the ejaculate. To test this hypothesis, we exposed male meadow voles, Microtus pennsylvanicus, to either low or high risks of sperm competition using soiled bedding of conspecific individuals. At three different times after this exposure (15, 30, or 60 min), we removed both vasa deferentia and counted the sperm within them. We found a significant increase in sperm numbers in the vas deferens of males after 30 min of being exposed to a high risk of sperm competition. The lower sperm numbers after 15 and 60 min of exposure suggest that the observed response is relatively slow and that sperm mobilized to the vasa deferentia may return to the cauda epididymides if ejaculation does not occur some time after the observed response. Our results indicate that the physiological response that may result in high sperm numbers in the ejaculate in relation to high risk of sperm competition can occur before initiation of copulatory behavior.
Similar content being viewed by others
References
Anderson M, Nyholt J, Dixson A (2004) Sperm competition affects the structure of the mammalian vas deferens. J Zool 264:97–103
Arletti R, Bazzani C, Castelli M, Bertolini A (1985) Oxytocin improves male copulatory performance in rats. Horm Behav 19:14–20
Batra SK (1974) Sperm transport through vas deferens: review of hypotheses and suggestions for a quantitative model. Fertil Steril 25:186–202
Baumgarten HG, Holstein AF, Rosengren E (1971) Arrangement, ultrastructure, and adrenergic innervation of smooth musculature of the ductuli efferentes, ductus epididymis and ductus deferens of man. Z Zellforsch Mikrosk Anat 120:37–39
Birkhead TR, Møller AP (1998) Sperm competition and sexual selection. Academic, San Diego
Boonstra R, Xia X, Pavone L (1993) Mating system of the meadow vole, Microtus pennsylvanicus. Behav Ecol 4:83–89
Brown RE (1985) The rodents I: effects of odours on reproductive physiology (primer effects). In: Brown RE, Macdonald DW (eds) Social odours in mammals, 1st edn, vol 1. Oxford Univ. Press, Oxford, pp 245–344
Cross BA, Glover TD (1958) The hypothalamus and seminal emission. J Endocrinol 16:385–395
delBarco-Trillo J, Ferkin MH (2004) Male mammals respond to a risk of sperm competition conveyed by odours of conspecific males. Nature 431:446–449
delBarco-Trillo J, Ferkin MH (2005) Two modes of input processing in relation to sperm competition in mammals. Acta Zool Sin 51:1122–1129
delBarco-Trillo J, Ferkin MH (2006) Male meadow voles respond differently to risk and intensity of sperm competition. Behav Ecol 17:581–585
delBarco-Trillo J, Ferkin MH (2007) Risk of sperm competition does not influence copulatory behavior in the promiscuous meadow vole (Microtus pennsylvanicus). J Ethol 25:139–145. DOI 10.1007/s10164-006-0008-x
Dewsbury DA (1982) Ejaculate cost and male choice. Am Nat 119:601–610
Dixson AF, Anderson MJ (2004) Sexual behavior, reproductive physiology and sperm competition in male mammals. Physiol Behav 83:361–371
Doty RL (1986) Odor-guided behavior in mammals. Experientia 42:257–271
Fewell GD, Meredith M (2002) Experience facilitates vomeronasal and olfactory influence on Fos expression in medial preoptic area during pheromone exposure or mating in male hamsters. Brain Res 941:91–106
Fjellström D, Kihlström JE, Melin P (1968) The effect of synthetic oxytocin upon seminal characteristics and sexual behavior in male rabbits. J Reprod Fertil 17:207–209
Hamilton WJ (1941) Reproduction of the field mouse Microtus pennsylvanicus. Memoir/Cornell University Agricultural Experiment Station 237:1–23
Hib J (1974) The contractility of the cauda epididymis of the mouse, its spontaneous activity in vitro and the effect of oxytocin. J Reprod Fertil 36:191–193
Kihara K, De Groat WC (1997) Sympathetic efferent pathways projecting bilaterally to the vas deferens in the rat. Anat Rec 248:291–299
Kihara K, Sato K, Ando M, Azuma H, Oshima H (1995) Antegrade and retrograde fluid transport through the vas deferens. Am J Physiol 269:R1197–R1203
Knight TW (1974a) The effect of oxytocin and adrenalin on the semen output of rams. J Reprod Fertil 39:329–336
Knight TW (1974b) A quantitative study of factors affecting the contractions of the epididymis and ductus deferens in the ram. J Reprod Fertil 40:19–30
Kolbeck SC, Steers WD (1992) Neural regulation of the vas deferens in the rat: an electrophysiological analysis. Am J Physiol 263:R331–R338
Mappes T, Koskela E, Ylonen H (1998) Breeding suppression in voles under predation risk of small mustelids: laboratory or methodological artifact? Oikos 82:365–369
Newman SW (1999) The medial extended amygdala in male reproductive behavior: a node in the mammalian social behavior network. Ann N Y Acad Sci 877:242–257
Parker GA (1970) Sperm competition and its evolutionary consequences in insects. Biol Rev Camb Philos Soc 45:524–567
Pierce JD, Ferguson B, Salo AL, Sawrey DK, Shapiro LE, Taylor SA, Dewsbury DA (1990) Patterns of sperm allocation across successive ejaculates in four species of voles (Microtus). J Reprod Fertil 88:141–149
Pound N (1999) Effects of morphine on electrically evoked contractions of the vas deferens in two congeneric rodent species differing in sperm competition intensity. Proc R Soc Lond B 266:1755–1758
Pound N, Gage MJG (2004) Prudent sperm allocation in Norway rats, Rattus norvegicus: a mammalian model of adaptive ejaculate adjustment. Anim Behav 68:819–823
Prins GS, Zaneveld LJ (1979) Distribution of spermatozoa in the rabbit vas deferens. Biol Reprod 21:181–185
Prins GS, Zaneveld LJ (1980) Radiographic study of fluid transport in the rabbit vas deferens during sexual rest and after sexual activity. J Reprod Fertil 58:311–319
Ratnasooriya WD, Wadsworth RM (1987) Effect of mating on sperm distribution in the reproductive tract of the male rat. Gamete Res 17:261–266
Sharma OP, Hays RL (1976) A possible role for oxytocin in sperm transport in the male rabbit. J Endocrinol 68:43–47
Ventura WP, Freund M, Davis J (1973) Influence of norepinephrine on the motility of human vas deferens: a new hypothesis of sperm transport by the vas deferens. Fertil Steril 24:68–77
Acknowledgments
This work was supported by NSF Grant IOB 0444553 and NIH Grant HD 049525 to MHF. This research adhered to the Animal Behaviour Society Guidelines for the Use of Animals in Research. All animal procedures were approved by the IACUC of the University of Memphis and complied with the current laws of the USA.
Author information
Authors and Affiliations
Corresponding author
Additional information
Communicated by E. Korpimäki
Rights and permissions
About this article
Cite this article
delBarco-Trillo, J., Ferkin, M.H. Increased sperm numbers in the vas deferens of meadow voles, Microtus pennsylvanicus, in response to odors of conspecific males. Behav Ecol Sociobiol 61, 1759–1764 (2007). https://doi.org/10.1007/s00265-007-0408-0
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00265-007-0408-0