An Electron Microscope Study of Spermatid Differentiation in the Toad, Bufo Arenarum Hensel

Abstract

The differentiation of the male germ cells into spermatozoa has long been a subject of particular interest to cytologists. In the period from 1890 through the first decade of the present century, Meves (28), McGregor (27), Ballowitz (2), and a number of other skilled observers made notable contributions to our understanding of the metamorphosis Of the germ cells in several vertebrate species. Little has been added in the ensuing years to their remarkably detailed and accurate descriptions of spermatid differentiation in the tailed amphibia. This phase of spermatogenesis has not, however, been as thoroughly investigated in the tailless amphibia.The reproductive physiology of the toad, Bufo arenarum Hensel, has received more attention in recent years than has that of other members of this group. Houssay (21) has studied the hypophyseal control of testicular function. Burgos and Mancini (10) described the normal histology of the testis and the sequence of events in the spermatogenic wave. The meiotic process has been investigated by Saez, Rojas, and De Robertis (32). The present paper records the results of an electron microscope study of the late stages of spermatogenesis in this species. The observations provide new information on the development of the acrosome and head cap; the formation of the perforatorium; the changes in the physical state of the chromatin during spermatid maturation; and the relation of the centrioles to the axial filament and undulating membrane of the tail. Materials and MethodsAdult male toads of the South American spedes, Bufo arenarum Hensel, were shipped from Argentina 1 before and during the breeding season. The testes studies were carefully dissected

The ultrastructure of the spermatozoa of Epipedobates flavopictus (Amphibia, Anura, Dendrobatidae), with comments on its evolutionary significance

“…4) is similar to that of most neobatrachians ( Ford, 1993) described to date, such as Bufo arenarum ( Burgos & Fawcett, 1956), B. marinus ( Swan et al, 1980;, Melanophryniscus cambaraensis ( Báo et al, 2001), Odontophrynus cultripes ( Báo et al, 1991), Lepidobatrachus laevis ( Waggener & Carroll, 1998), and Pachymedusa dacnicolor ( Rastogi et al, 1988).…”

“…The numerous and randomly distributed mitochondria distinguish E. flavopictus from several other Neobatrachia so far examined, which usually have a mitochondrial collar, as in Bufonidae ( Burgos & Fawcett, 1956;Swan et al, 1980; and Leptodactylidae ( Pugin-Rios, 1980 andBao et al, 1991). The presence of mitochondria creates a large separation between the axial sheath and the plasma membrane in the anterior tail region of E. flavopictus.…”

“…Similarity of function, however, is not a requirement for homology ( Lauder, 1994). Lee and Jamieson, 1992 were probably influenced by the earlier work of Burgos and Fawcett (1956), the first to suggest that the coarse strands of dense material, observed around the tapering end of the nucleus in the spermatozoon of B. arenarum, form a perforatorium.…”

“…Had Burgos and Fawcett (1956) chosen a different name (without implying a function) for the a e r re, a ' a ro o al one', ar en (1) a ove wo ld vani . Fig.…”

“…(C) Preferred hypothesis for the evolution of the subacrosomal cone, when considering the conical perforatorium homologous to the subacrosomal cone in anurans, number of steps=4. Data for families used in the analysis was obtain from the present work (Dendrobatidae) and from the following literature: Caudata ( Selmi et al, 1997), Pipidae ( Reed & Stanley, 1972;Bernardini et al, 1986), Bombina ( Furieri, 1975and Pugin-Rios, 1980), Discoglossidae ( Pugin-Rios, 1980Lee & Kwon, 1996), Ascaphus ( James, 1970 andJamieson et al, 1993), Leiopelmatidae ( Scheltinga et al, 2001), Pelobatidae ( James, 1970;Asa & Phillips, 1988), Pelodytidae ( Pugin-Rios, 1980), Ranidae ( Poirier & Spink, 1971;Pugin-Rios, 1980), Microhylidae (Chiasmocleis albopunctata, personal observation), Myobatrachidae ( Lee & Jamieson, 1992), Leptodactylidae ( Pugin-Rios, 1980 andBao et al, 1991;Waggener & Carroll, 1998;Amaral et al, 1999), Rhinodermatidae ( Pugin-Rios, 1980), Bufonidae ( Burgos & Fawcett, 1956;Báo et al, 2001), and Hylidae ( Rastogi et al, 1988;Lee & Kwon, 1992;.…”