Ultrastructural examination of spermiogenesis within the testis of the ground skink, Scincella laterale (Squamata, Sauria, Scincidae)

Abstract

Although the events of spermiogenesis are commonly studied in amniotes, the amount of research available for lizards (Sauria) is lacking. Many studies have described the morphological characteristics of mature spermatozoa in lizards, but few detail the ultrastructural changes that occur during spermiogenesis. The purpose of this study was to gain a better understanding of the subcellular events of spermiogenesis within the temperate ground skink (Scincella laterale). The morphological data presented here represent the first complete ultrastructural study of spermiogenesis within the Scincidae clade. Samples of testes from 20 specimens were prepared using standard techniques for transmission electron microscopy. Many of the ultrastructural changes occurring during spermiogenesis within the ground skink are similar to that of other saurians. However, there were a few unique characteristics that to date have not been described during spermiogenesis in other lizards. For example, during early round spermatid development within the ground skink testis, proacrosomal granules begin to form within the acrosomal vesicle before making contact with the apex of the nucleus. Also, a prominent microtubular manchette develops during spermiogenesis; however, the circular component of the manchete is absent in this species of skink. This developmental difference in manchette formation may lead to the more robust and straight mature spermatozoa that are common within the Scincidae family. These anatomical character differences may be valuable nontraditional sources that along with more traditional sources (i.e., mitochondrial DNA) may help elucidate phylogenetic relationships, which are historically considered controversial at best, among species within Scincidae and Sauria.

Ultrastructure of spermatid development within the testis of the Yellow-Bellied Sea Snake,Pelamis platurus(Squamata: Elapidae)

“…18 Parallel microtubules far outnumber the circum-cylindrical fibers in P. platurus similar to that described in Agkistrodon species. 9 This absence of circum-cylindrical microtubules is also prominent in Scincella lateralis 23 and completely absent in Anolis lineatopus, 9 which have more robust-bodied spermatozoa than that of other squamate species. 23,41,42 The nuclear bodies of P. platurus do appear to have wider diameters than many other squamates, which have both types of microtubule during elongation.…”

“…9 This absence of circum-cylindrical microtubules is also prominent in Scincella lateralis 23 and completely absent in Anolis lineatopus, 9 which have more robust-bodied spermatozoa than that of other squamate species. 23,41,42 The nuclear bodies of P. platurus do appear to have wider diameters than many other squamates, which have both types of microtubule during elongation. During DNA condensation, the chromatin in P. platurus condenses in a spiral fashion, which was not documented in some squamates, 23 but was noted by Ferreira and Dolder 30 in the lizard Tropidurus itambre, in some Sceloporus species, 4 in the snake Cerastes cerastes, 14 and in Cottonmouths, 10 which resulted in large areas of open nucleoplasm.…”

“…This is comparable to what was reported in other squamates. 3,9,10,11 Also, the acrosomal granule is seen within this vesicle before nuclear contact, but in contrast to the basal positioned granule described in S. lateralis, 23 the granule is centrally located and then migrates to its basal position once the acrosome makes contact with the nucleus, much like that of and Agkistrodon piscivorus. 10 The granule's largest growth phase occurs in this basal position within the acrosome of P. platurus, A. piscivorus, and most other squamates.…”

“…23,41,42 The nuclear bodies of P. platurus do appear to have wider diameters than many other squamates, which have both types of microtubule during elongation. During DNA condensation, the chromatin in P. platurus condenses in a spiral fashion, which was not documented in some squamates, 23 but was noted by Ferreira and Dolder 30 in the lizard Tropidurus itambre, in some Sceloporus species, 4 in the snake Cerastes cerastes, 14 and in Cottonmouths, 10 which resulted in large areas of open nucleoplasm. These open areas of nucleoplasm continue as lacunae within the body of fully condensed nuclei in maturing spermatids in P. platurus, which is similar to Bothrops spermatozoa 21 and A. contortrix elongating spermatids, 9 but seem to have been lost in A. piscivorus spermatids, 10 Oxyuranus microlepidotus, and many other snake spermatozoa.…”

“…9 As flagellar differentiation progresses, large numbers of mitochondria become present in the posterior portion of the Pelamis platurus spermatid cytoplasm and are associated with the flagellum, which is consistent with other amniotes. 8,23,29,38,43 However, there are more than 40 concentric rings of mitochondria that run down the P. platurus midpiece to the annulus in sagittal section and they appear round to occasionally tubular in transverse section of the midpiece. These very long midpieces are considered a synapomorphy for snake speramtids and spermatozoa.…”