Post-mating morphological changes in the spermatozoon and spermatophore wall of the crayfish Astacus leptodactylus: Insight into a non-motile spermatozoon

Abstract

Morphology of the crayfish spermatozoon and of the spermatophore wall during three stages of final maturation including freshly ejaculated, post-mating, and after spermatozoa release was studied and compared. The crayfish spermatophore consists of a sperm mass enveloped by a three layered spermatophore wall. After mating, the thickness of the outer layer of the spermatophore is increased. The matrix in the middle layer of the spermatophore becomes reticulated, and granules inside this layer release their contents. Fibers in the inner layer degrade to small particles. The spermatozoon capsule swells and the space between the capsule and the spermatozoon appears. The area of the plasma membrane is increased by wrinkling of the surface and alteration from a single to a multilayered structure at the anterior part of the acrosome. The density of the subacrosome zone increases in the vicinity of the main body of the acrosome. With the onset of fertilization, the layers of the spermatophore are dissolved by female glair gland secretions. The spermatozoon extracellular capsule, plasma membrane, and membranous lamellae are eliminated, and bundles of filaments are released from anterior part of the acrosome. The subacrosome zone loses electron density and retracts. The electron-dense material of the innermost layer of the acrosome is discharged and, together with acrosome filaments, forms a filament/droplet structure at the anterior part of the spermatozoon. The most important change is observed in the subacrosome zone, which may play a key role in the fertilization. Also, morphological changes of the spermatozoon that occur after release from the capsule, especially formation of the filament/droplet structure, may contribute to the mechanism of egg-spermatozoon binding in the crayfish, representative of animals with non-motile spermatozoa.

Different aspects of reproduction strategies in crayfish: A review

“…These spermatozoa subsequently fertilize eggs which are released through the gonopores. The eggs a attach to the pleopods of female for brooding (Hamr, 2002;Niksirat et al, 2014bNiksirat et al, , 2015a.…”

“…A sticky layer covers the surface of freshly ejaculated spermatophore and helps attachment of the spermatophore to the body of a female until fertilization (Dudenhausen and Talbot, 1983;Niksirat et al, 2014b). The freshly ejaculated spermatophore is soft in decapods, but after mating it becomes hardened to protect the sperm mass (Malek and Bawab, 1971;Uma and Subramoniam, 1979).…”

“…The freshly ejaculated spermatophore is soft in decapods, but after mating it becomes hardened to protect the sperm mass (Malek and Bawab, 1971;Uma and Subramoniam, 1979). Post-mating spermatophore storage in crayfish and other decapods is accompanied by morphological and molecular changes that are necessary for the spermatozoon to develop fertilizing ability (Alfaro et al, 2003;Vanichviriyakit et al, 2004;Alfaro et al, 2007;López Greco and Lo Nostro, 2008;Aungsuchawan et al, 2011;Braga et al, 2014;Niksirat et al, 2014bNiksirat et al, , 2015b.…”

“…Extensive morphological changes associated with postmating storage have been observed in the spermatophore of the crayfish, including changes in the morphology of spermatophore wall components and spermatozoon organelles such as plasma membrane and subacrosome zone (Dudenhausen and Talbot, 1983;Niksirat et al, 2014b). These changes occur after release of the spermatozoon from the capsule, especially the formation of the filament/droplet structure, may contribute to the mechanism of egg-spermatozoon binding in the narrow-clawed crayfish A. leptodactylus (Niksirat et al, 2014b).…”

“…These changes occur after release of the spermatozoon from the capsule, especially the formation of the filament/droplet structure, may contribute to the mechanism of egg-spermatozoon binding in the narrow-clawed crayfish A. leptodactylus (Niksirat et al, 2014b). Subcellular localization of calcium in the noble crayfish spermatophore using oxalate-pyroantimonate techniques showed that calcium plays important roles in the postmating spermatophore hardening and spermatozoon capacitation.…”