John Visser

The Ultrastructure of the Spermatozoon of Typhlonectes natans (Gymnophiona: Typhlonectidae)

The spermatozoon of Typhlonectes natans consists of a long slender head approximately 18 ~im long and a distinct acrosome attached to the anterior margin of the head. A well-demarcated midpiece contains 35-40 spherical mitochondria that consist of many delicate cristae mitochondriales. The tail has a wavy 9 + 2 axoneme that runs helically along the axial rod. An undulating membrane connects the axoneme and axial rod. On the basis of acrosome structure the Gymnophiona appear to be more closely related to the Urodela than to the Anura. al of Herpetology, Vol. 25, No. 4, pp. 4 1-447, 1991 right 1 91 Society for the Study of Amphibi s and R ptiles ltrastructure of the Spermatozoon of Typhlonectes atans ophiona: Typhlonectidae) RD VAN DER HORST,1 JOHN VISSER,2 AND LIZ VAN DER M RWE3 art ent of Physi logical Sciences, University of th Western Cape, B llville 7535, South Africa, art ent of Z logy, University of Natal, Piete maritzburg, South Africa, and , edical Research Council, P.O. Box 70, Tygerberg, South Africa CT. The spermat zoon of Typhlon ctes natans consists of a long slender head approximately 18 long and a distinct acr some attached o the anterior margin of the head. A well-demarcated midpiece ains 35-40 spherical mitochondria that consist of many deli ate cristae mitochondriales. T e tail has 9 + 2 axoneme that runs helically along the axial rod. An undulating membra conn cts the e e and axial rod. On the basis of acrosome structur the Gymnophiona appear to be more closely The limbless Gymnophiona comprise a small, primitive order of predominantly burrowing amphibians. They occur only in Central and South America, tropical Africa, the Seychelles, and Southeast Asia. Apparently all male caecilians have an intromittent organ for internal fertilization and the aquatic Typhlonectidae, as well as members of other families, are viviparous (Parker, 1956; Wake, 1968; De Sa and Berois, 1986). Wake (1977) reviewed the reproductive biology of caecilians; despite detailed descriptions of their reproductive systems and demonstration of active spermatogenesis in some 50 species very little information is available on their sperm. Light microscopic data are available on sperm of only five species of caecilians (Seshachar, 1940, 1943, 1945; De Sa and Berois, 1986). In contrast, sperm ultrastructure of the other two orders of Amphibia is well documented. Salamander (Fawcett and Hilfer, 1961; Baker and Biesele, 1967; Martan and Wortham, 1972; Wortham et al., 1982) and anuran (Burgos and Fawcett, 1956; Fouquette and Delahoussaye, 1977; van der Horst, 1979; Duellman and Trueb, 1986) sperm show considerable variation. This variation can be useful in sperm ultrastructural studies, as sperm morphology relates to mode of fertilization (Franzen, 1970), is of importance n phylogenetic reconstruction (Fouquette and Delahoussaye, 1977), and has become a useful taxonomic tool to distinguish between closely related species in anurans and other animal groups (Van der Horst et al., 1986; Hodgson and Bernard, 1986; Visser and van der Horst, 1987; Hodgson et al., 1990). This is the first detailed description at the ult astructural level of the spermatozoon of a orders of Amphibia is well documented. ander (Fawcett and Hilfer, 1961; Baker and ele, 1967; Martan and Wortham, 1972; Woret al., 1982) and anuran (Burgos and Faw, 1956; Fouquette and Delahoussaye, 1977; er Horst, 1979; Duellman and Trueb, 1986) show considerable variation. This varican be useful in sperm ultrastructural ies, as sperm morphol gy relates to mode ertilization (Franzen, 1970), is of importance logenetic reconstruction (Fouq ett and oussaye, 197 ), and has become a useful o ic to l to distinguish between closely ed species in anurans and other animal s (Van der Horst et al., 1986; Hodgson a d 441 This content downloaded from 207.46.13.172 on Tue, 23 Aug 2016 06:15:27 UTC All use subject to http://about.jstor.org/terms G. VAN DER HORST ET AL. member of the Gymnophiona. The limited data on caecilian sperm are also used to draw comparisons with the sperm of the other two amphibian orders. MATERIALS AND METHODS Five specimens of Typhlonectes natans were collected by Louis Porras in the drainage system of the Magdalena River, Colombia, during the breeding season (November). Testes and vasa deferentia were removed and fixed in 2.5% Millonig phosphate buffered glutaraldehyde. After washing in 0.1 M phosphate buffer the material was osmicated in 1% osmium tetroxide and again washed in 0.1 M phosphate buffer. Half of the material was processed for transmission electron microscopy as follows: small testis and vas deferens blocks (1 mm3) were stained in a solution containing 1.5% ferrocyanide and 2% osmium tetroxide and rinsed in buffer. The material was then routinely dehydrated in ethanol, cleared in propylene oxide and embedded in EPON 812. The EPON blocks were sectioned using a Reichert OMU3 ultramicrotome. Gold sections were finally contrasted with uranyl acetate and Reynolds lead citrate. The sections were studied and photographed using a Philips 420 electron microscope operating at 80 kv. The other half of the osmicated material was prepared for scanning electron microscopy. After a final phosphate buffer rinse the material was routinely dehydrated in ethanol and dried by the critical point method using CO2 as transitional fluid. Small tissue blocks were mounted on aluminum stubs, sputter coated with gold and examined with a Hitachi X60 scanning electron microscope operating at 10-20 kv.