Ultrastructural characterization of the gonads of Triops
cancriformis (Crustacea, Notostraca) from populations containing both females and males: no evidence for hermaphroditic reproduction |
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Authors: | M Engelmann T Hahn Georg Hoheisel |
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Institution: | Max-Planck-Institut für Psychiatrie, Kraepelinstrasse 2, D-80804 Munich, Germany Tel.: (89) 30622 228; Fax: (89) 30622 569; e-mail: engelm@mpipsykl.mpg.de, DE Institut für Histologie und Embryologie, Universit?t Graz, Harrachgasse 21, A-8010 Graz, Austria, AT Institut für Zoologie, Universit?t Leipzig, Talstrasse 33, D-04103 Leipzig, Germany, DE
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Abstract: | The gonads of female and male Triops
cancriformis specimens from populations of the northern part of the species distribution area were examined by conventional transmission
electron microscopy in order to gain insight into the complicated reproductive mode of the species. Ovarian follicles consisted
of an oocyte and three nurse cells and were surrounded by a thin layer of follicular cells. Oocytes are initially smaller
than nurse cells and contained mitochondria of the cristae type as well as many free ribosomes. The prominent nucleus contained
a nucleolus. The cytoplasm of oocytes was filled with yolk globules that were surrounded by membranes of the endoplasmic reticulum.
Nurse cells also contained yolk globules. The follicle duct walls consisted of closely packed elongated cells covered by a
lamellar basal lamina. No distinct Golgi apparatus was found in the follicle duct cells. The passage of oocytes through the
duct was accompanied by a marked flattening of the follicle duct cells. Simultaneously, the oocytes were wrapped in eggshell
material before entering the longitudinal oviduct. Testicular lobes were not found in any of the investigated female specimens.
In male animals, the epithelial wall of the testicular tubules consisted of both germinal and vegetative cells. Maturing spermatids
formed multicellular nests located in clearly delimited cysts in the intercellular space of the testicular epithelium. The
lumen of the testicular tubules contained, exclusively, free mature spermatozoa. These characteristics point to the cystic
type of spermiogenesis. Mature spermatozoa were non-flagellate, had a regular ovoid shape of 4–5 μm diameter, and an acrosome
was not found. Only a negligible amount of spermatozoa (< 5%) showed signs of degeneration. In conclusion, the results provide
evidence for a parthenogenetic and/or bisexual reproduction mode rather than a hermaphroditic one in the populations examined.
Accepted: 4 August 1997 |
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