Ontogenic development of spermatids during spermiogenesis in the high altitude bunchgrass lizard (Sceloporus bicanthalis)

Abstract

The body of ultrastructural data on spermatid characters during spermiogenesis continues to grow in reptiles, but is still relatively limited within the squamates. This study focuses on the ontogenic events of spermiogenesis within a viviparous and continually spermatogenic lizard, from high altitude in Mexico. Between the months of June and August, testicular tissues were collected from eight spermatogenically active bunchgrass lizards (Sceloporus bicanthalis) from Nevado de Toluca, México. The testicular tissues were processed for transmission electron microscopy and analyzed to access the ultrastructural differences between spermatid generations during spermiogenesis. Interestingly, few differences exist between S. bicanthalis spermiogenesis when compared with what has been described for other saurian squamates. Degrading and coiling membrane structures similar to myelin figures were visible within the developing acrosome that are likely remnants from Golgi body vesicles. During spermiogenesis, an electron lucent area between the subacrosomal space and the acrosomal medulla was observed, which has been observed in other squamates but not accurately described. Thus, we elect to term this region the acrosomal lucent ridge. This study furthers the existing knowledge of spermatid development in squamates, which could be useful in future work on the reproductive systems in high altitude viviparous lizard species.

Spermiogenesis in the imbricate alligator lizard,Barisia imbricata(Reptilia, Squamata, Anguidae)

“…Rheubert et al (2011) proposed that structural components seen in epididymal spermatozoa (where a majority of the studies are focused) can be characterized in an ontogenic fashion during spermiogenesis and can be seen in the stages just prior to spermiation. Previous studies have shown that vertebrates follow the same general three‐step process of acrosome development, nuclear elongation/condensation, and flagellar development during spermiogenesis (see Russell et al,1990). A thorough investigation at these various stages reveals minute differences that developmentally may lead to more prominent differences in the mature spermatozoa.…”

The ultrastructure of spermatid development during spermiogenesis within the rosebelly lizard, Sceloporus variabilis (Reptilia, Squamata, Phrynosomatidae)

“…During nuclear elongation and condensation in S. variabilis , chromatin condenses into filaments almost immediately. This is similar to B. imbricata (Gribbins et al, ), but different from many other lizards, including S. bicanthalis (Rheubert et al, ) that typically have granular and then later filamentous condensation (Clark, ; Ferreira and Dolder, ; Vieira et al, ; Vieira et al, ; Gribbins, 2011; Rheubert et al, ). Also, S. variabilis differs from S. bicanthalis and many other lizards (see Gribbins, ) in that there is little spiraling of the chromatin during nuclear condensation.…”

“…In early studies of spermiogenesis within birds and lizards, the perforatorium was thought to arise from the subacrosomal granule (Humphreys, ; Del Conte, ) or the acrosomal granule (Adelina et al, ). More recently in Barisia imbricata (Gribbins et al, ) and in S. bicanthalis (Rheubert et al, ) the same granule appears to develop either during the late round or early elongation phases of spermiogenesis. However, these two studies call the granule within the subascrosomal space the developing basal plate of the perforatorium.…”

“…Though other species seem to have either mitochondria or ER near the Golgi (e.g., Ferreira and Dolder, ), none have described the ER surrounding a mitochondria and the specific, consistent location of these two organelles between the Golgi and the developing acrosomal vesicle. The location and arrangement of these two organelles is not observed in S. bicanthalis (Rheubert et al, ), and thus may be a synapomorphy for the variabilis group (Leaché, ) within the Sceloporus genus or more unlikely an autopomorphy for S. variabilis . The function of this complex is unknown; however, we propose that it simply expedites delivery of processed ER proteins and energy (Adenosine triphosphate) delivery to the Golgi during this highly active time of acrosome development.…”

“…Although there are many studies that outline incomplete ultrastructural descriptions (Clark, ; Butler and Gabri, ; Hondo et al, ; Al‐Dokhi, ; Mubarak, 2006) and comprehensive details (Courtens and Depieges, ; Carcupino et al, ; Vieira et al, 2001; Ferreira and Dolder, ; Gribbins et al, ; Rheubert et al, ,; Rheubert et al, ; Gribbins et al, ) regarding the developmental steps of spermiogenesis within squamates, no study to date offers a comparison between the spermiogenic events within two or more species within the same genus. Rheubert et al () provided the first ultrastructural account of spermiogenesis for Sceloporus bicanthalis (within the scalaris group; Leaché, ). The present study describes the spermiogenic events in the testis of Sceloporus variabilis (within the variabilis group; Leaché, ) and then compares spermatid development between these two species within Sceloporus and to other reptilian taxa.…”