Accessory Glands Of Males

Accessory glands of the male reproductive tract have diverse functions related to sperm delivery and to the design of specific mating systems.

Sperm Delivery

Males of many insects use spermatophores to transfer sperm to females. A spermatophore is a bundle of sperm contained

FIGURE 1 Male reproductive system of T. molitor, showing testes (T), ejaculatory duct (EJD), tubular accessory gland (TAG), and bean-shaped accessory gland (BAG). [From Dailey, P. D., Gadzama J. M., and Happ, G. M. (1980). Cytodifferentiation in the accessory glands of Tenebrio molitor. VI. A congruent map of cells and their secretions in the layered elastic product of the male bean-shaped accessory gland. J. Morphol. 166, 289—322. Reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc.]

FIGURE 1 Male reproductive system of T. molitor, showing testes (T), ejaculatory duct (EJD), tubular accessory gland (TAG), and bean-shaped accessory gland (BAG). [From Dailey, P. D., Gadzama J. M., and Happ, G. M. (1980). Cytodifferentiation in the accessory glands of Tenebrio molitor. VI. A congruent map of cells and their secretions in the layered elastic product of the male bean-shaped accessory gland. J. Morphol. 166, 289—322. Reprinted by permission of Wiley-Liss, Inc., a subsidiary of John Wiley & Sons, Inc.]

in a protective packet. Accessory glands secrete the structural proteins necessary for the spermatophore's construction. Males of the yellow mealworm, Tenebrio molitor, have two distinct accessory glands, one bean-shaped and the other tubular (Fig. 1). Bean-shaped accessory glands contain cells of at least seven types and produce a semisolid material that forms the wall and core of the spermatophore. Tubular accessory glands contain only one type of cell, and it produces a mix of water-soluble proteins of unknown function. Spermatophores are not absolutely required for sperm transfer in all insects. In many insects, male secretions create a fluid medium for sperm transfer.

Effects on Sperm Management and on the Female

The effects of male accessory gland secretions in the female are best known for the fruit fly, Drosophila melanogaster, in which the function of several gene products has been explored at the molecular level. Since insects have a diversity of mating systems, the specific functions of accessory gland secretions are likely to reflect this variation.

In Drosophila, the accessory glands are simple sacs consisting of a single layer of secretory cells around a central lumen (Fig. 2). Genes for more than 80 accessory gland proteins have been identified so far. These genes code for hormonelike substances and enzymes, as well as many novel

Accessory

B glands

Accessory

B glands

Transgenic

FIGURE 2 Accessory gland of D. melanogaster. (A) The cells in this normal accessory gland express b-galactosidase driven by a promoter of a gene for an accessory gland protein. (B) A transgenic accessory gland, cells expressing the gene have been selectively killed after eclosion. These flies were used to explore the function of accessory gland secretions. In transgenic males, accessory glands are small and translationally inert. [From Kalb, J. M., DiBenedetto, A. J., and Wolfner, M. F. (1993). Probing the function of Drosophila melanogaster accessory glands by directed cell ablation. Proc. Natl. Acad. S ci. USA 90, 8093-8097. Copyright 1993, National Academy of Sciences, U.S.A.]

proteins. The gene products or their derivatives have diverse functions, including an increased egg-laying rate, a reduced inclination of females to mate again, increased effectiveness of sperm transfer to a female's spermatheca, and various toxic effects most likely involved in the competition of sperm from different males. A side effect of this toxicity is a shortened life span for females. Other portions of the reproductive tract contribute secretions with diverse roles. For example, the ejaculatory bulb secretes one protein that is a major constituent of the mating plug, and another that has antibacterial activity.

See Also the Following Articles

Egg Coverings • Spermatheca • Spermatophore

Further Reading

Chen, P. S. (1984). The functional morphology and biochemistry of insect male accessory glands and their secretions. Annu. Rev. Entomol. 29, 233-255.

Eberhard, W. G. (1996). "Female Control: Sexual Selection by Cryptic

Female Choice." Princeton University Press, Princeton, NJ. Gillott, C. (1988). Arthropoda—Insecta. In "Accessory Sex Glands," (Adiyodi and Adiyodi, eds.). Vol. 3 of "Reproductive Biology of Invertebrates," pp. 319-471. Wiley, New York. Happ, G. M. (1992). Maturation of the male reproductive system and its endocrine regulation. Annu. Rev. EntomoL 37, 303-320. Wolfner, M. F. (2001). The gifts that keep on giving: Physiological functions and evolutionary dynamics of male seminal proteins in Drosophila. Heredity 88, 85-93.

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