Morphology of the spermatozoa of the iguanian lizards ...

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]. SUBMICROSC. CYTOL. PATHOL., 32 (2), 261-271, 2000
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Morphology of the spermatozoa of the iguanian lizards
Uta stansburiana and Urosaurus ornatus (Squamata,
Phrynosomatidae)
D.M. SCHELTINGA, B.G.M. JAMIESON, S.E. TRAUTH' and C.T. MCALLISTER"
Department of Zoology and Entomology, University of Queensland, Brisbane, Qld, Australia; 'Department of Biological Sciences, Arkansas
State University, AR, USA; "Natural Sciences Department, Tarrant County College-South Campus, Fort Worth, TX, USA
SUMMARY - The spermatozoa of Uta stansburiana and Urosaurns ornatus show the following squamate autapomorphies:
a single perforatorium extending anteriorly from the apical tip of the paracrystalline subacrosomal cone;
the presence of an epinucleat electron lucent region; intermitochondrial dense bodies; and the fibrous sheath
extending into the midpiece. The acrosome vesicle is flattened and concentrically zoned apically; basally it overlies
a subacrosomal cone which invests the nuclear rostrum. A stopper-like perforatorial base plate, rounded nuclear
shoulders and a basal nuclear fossa are present. The proximal centriole contains a density within its centre for
approximately one half its length and lies at approximately 80 0 to the distal centriole. The two central singlets of
the axoneme extend into the short distal centriole. A peripheral dense fibre is associated with each of the nine
triplets of the distal centriole, and the fibre continues posteriorly with each of the nine doublets of the axoneme. A
central fibre is associated with the tWo central singlets. AJl fibres are absent or vestigial at the level of the annulus.
Mitochondria are short sinuous with a maximum of eight seen in transverse section. Uta and Urosaurus sperm differ
from each other in their arrangement of intermitochondrial dense bodies in two ways: 1) longitudinally, Uta
has five incomplete 'rings' of dense bodies, whereas Urosaurns has only four such rings; 2) in cross section, each
individual 'ring' of Uta may contain up to four irregularly spaced dense bodies, whereas Urosaurns contains a maximum
of only two dense bodies. The sperm of Uta and Urosaurus show strong similarities to those of the agamids
and polychrotids. No spermatozoal autapomorphies for the Phrynosomatidae were found.
KEy WORDS Uta - Urosaltrus - Phrynosomatidtu - iguanid - spermatozoa - phylogeny ­ but generally spermiogenesis occurs between late November
ultrastructure
and early August with mating occurring between April and
June (Nussbaum and Diller, 1976; Goldberg, 1977).
INTRODUCTION
Tree lizards, Urosaurus ornatus are small, insectivorous, saxicolous,
pardy arboreal lizards which occur throughout the
Side-blotched lizards, Uta stansburiana are small, insectivorous,
terrestrial lizards which occur throughout much of
western North America and its adjacent islands (Nussbaum
and Diller, 1976; Grismer, 1994). They inhabit a variety of
habitats including marine intertidal, arid and subtropical
zones, and range in altitude from sea level to approximately
2,750 m (Stebbins, 1966; Parker and Pianka, 1975; Grismer,
1994). Reproductive activity varies with location and altitude
southwestern North America and western Mexico (Martin,
1977; Dunham, 1982; Weins, 1993a,b). As noted for Uta,
geographical location affects several life history traits, such
as the period of reproductive activity with male Urosaurus
generally being reproductively active between April and
August (Michael, 1976; Martin, 1977; Dunham, 1982;
Ramirez-Bautista et aL., 1995).
Uta and Urosaurus are included with Sator and Sceloporus in
the Sceloporus-group of Etheridge and de Queiroz (1988). All
four genera possess the autapomorphic condition of clavicu­
Mailing address: Mr. David Scheltinga, Depattment of Zoology and lar hooks and for this reason have been regarded by many
authors as being closely related (Etheridge, 1964; Etheridge
Entomology, University of Queensland, Brisbane, Qld. 4072, AustraJia; e-mail:
dscheltinga@zoology.uq.cdu.au
Ultrastructure ofphrynosomatid spermatozoa 261

and de Queiroz, 1988; see Weins, 1993a). While the results
of Frost and Etheridge's (1989) phylogenetic analysis of mor­
phological characters placed these genera within the mono­
phyletic family Phrynosomatidae, their results questioned the
monophyly of the 'Sceloporus-group'. Monophyly of the latter
group was, however, supported in a more recent phylogenetic
analysis of morphological, karyotypic and behavioural characters
(Weins, 1993a). Results from Reeder's (I995) study of
mitochondrial ribosomal RNA showed the intergeneric relationships
were largely inconsistent with those based on mor­
phology and as with Frost and Etheridge's (1989) study,
found the placement of Uta to be ambiguous. Thus, data sets
based on morphological, behavioural and genetic data have
been unable to satisfactorily explain the relationships between
the phrynosomatid genera and in particular that of Uta.
Recently, the use ofsperm ultrastructure as another source of
phylogenetically important characters has gained increasing
use in the examination of reptilian relationships (see
Jamieson, 1995; Oliver et ai., 1996; Jamieson et ai., 1996).
Aspects ofsperm development and structure ofseveral iguanian
families have been previously examined. Spermiogenesis
has been examined in the following iguanian families:
Iguanidae (sensu strictu, Saita et af., 1988); Tropiduridae
(Sotelo and Trujillo-Cen6z, 1958; Cruz-Landim and Cruz­
Hofling, 1977; Cruz-Hofling and Cruz-Landim, 1978);
Polychrotidae (Clark, 1967); and Phrynosomatidae (Clark,
1967). However, as spermatids often show little resemblance
to those of mature sperm, characters described from spermatids
cannot be attributed to mature sperm with any certainty.
Furieri (1974) examined the mature sperm of the
Iguanidae (sensu fato) and based his analysis primarily on
three species; Pristitfactyius (as Cupriguanus) scapufatus (now
Polychrotidae) and Phymaturus paiiuma and Lioiaemus austromendocinus
(both now Tropiduridae, Liolaeminae). Unfortunately;
with the separation of the species ofiguanidae (sensu
iato) examined by Furieri into two different families the
importance of characters described by Furieri for use in phylogenetic
studies is reduced; although by describing the few
differences he did observe, some valuable information still
remains. The mature sperm of Tropidurus semitaeniatus and
T. torquatus (Tropiduridae, Tropidurinae) have recently been
described by Teixeira et af. (1999). Spermiogenesis and
mature sperm from families Agamidae and Chamaeleonidae,
two families closely related to the Iguanids, have also been
examined (Agamidae by AI-Hajj et aL, 1987; Charnier et af.,
1967; Dehlawi et af., 1990, 1992, 1993; Dehlawi and Ismail,
1990,1991; Ismail and Dehlawi, 1994; Ismail etaf., 1995;
Oliver et af., 1996; Chamaeleonidae by Jamieson, 1995;
Tuzet and Bourgat, 1973).
The present account is the first description of mature sperm
of the iguanian family Phrynosomatidae.
262 SCHELTINGA D.M. et at.
MATERIALS AND METHODS
Male Uta stansburiana were collected from Winkler Co.,
Texas, USA on April 20 rh 1991, while male Urosaurus ornatus
were taken from Llano Co., Texas, USA on May 28 rh 1993.
The lizards were euthanased by an injection of sodium pentobarbital
within 72 h of capture. Histotechnical procedures
as discussed by Newton and Trauth (1992) were employed to
prepare gonads and sperm ducts for transmission electron
microscopy (TEM). Testes and epididymides were separated
and placed into separate vials containing 2% glutaraldehyde
in 0.2 M sodium cacodylate buffer (pH 7.2). Following fIXation
for 2 h in the above solution, the material was rinsed in
four changes of 0.1 M cacodylate buffer, post-fixed in similarly
buffered 1% osmium tetroxide, rinsed in buffer, dehydrated
through an ascending series of ethanol/acetone mixtures,
infiltrated overnight in a diluted acetone/epoxy resin
mixture, and embedded in Mollenhauer's Epon-Araldite mixture
number 2. The embedded tissues were then transported
to Brisbane, Australia for sectioning and TEM.
The testis and ducts of an additional two Uta stansburiana
were collected from Washoe Co., Nevada on June 29 rh 1998.
The tissues were fixed for TEM in 3% glutaraldehyde in
0.1 M sodium phosphate buffer (pH 7.2) at 4°C for at least
two hours before being transported at ambient temperature
to Brisbane for processing and sectioning. On arrival in
Brisbane the material was rinsed in 0.1 M phosphate buffer,
post-fixed for 80 min in similarly buffered 1% osmium
tetroxide, rinsed in buffer, dehydrated through an ascending
ethanol series, and infiltrated and embedded in Spurr's
epoxy reSlll.
Sections were cut with diamond knives, on a LKB 2128 UM
IV microtome. Thin sections, 50-80 nm thick, were collected
on carbon stabilized, colloidin-coated, 200 fJm mesh copper
grids, stained for 30 sec in Reynolds' lead citrate, rinsed in
distilled water, then placed in 6% aqueous uranyl acetate for
4 min, rinsed in distilled water, and stained for a further 2
min in lead citrate before final rinsing. Electron micrographs
were taken on an Hitachi 300 electron microscope at 75 kV
and a JEOL 100-s electron microscope at 60 kYo Light
microscopic observations and photographs of spermatozoa,
from glutaraldehyde-fIXed tissue squashes, were made using
an Olympus BH2 microscope with Nomarski interference
contrast and an attached OM-2 camera.
RESULTS
Spermatozoal morphology
The sperm of Uta stansburiana and Urosaurus ornatus are sufficiently
similar to be described together (Fig. 1), while noting
the few observed differences. The spermatozoa are filiform
(Fig. 4k), with the average dimensions (respectively) for

B
E
me
. ---­
H
1.0 ... m
FIGURE lA-I Transmission e1ecrron micrographs of mature spermatozoa of Urosaurus ornatus. (A) Longitudinal section (LS) through the nuclear
rostrum and acrosome. Note the Stopper-like perforatorial base plate and the rransversely striated perforarorium. (B-F) A series of rransverse sections
(TS) through the acrosome and nucleus. Note that anteriorly, in (B-D), the acrosome is laterally compressed in rransverse sections, while
further posteriorly, in (E), it is unilaterally ridged, and at irs posrerior limir, in (F), it is circular. (C) TS rhrough rhe nucleus. (H) LS through
the apical end of rhe aUOSOlTle vesicle showing its concentric zonation. (1) LS through the subacrosomal cone showing the epinuclear electron
lucent region. All to same scale as indicated. avo acrosome vesicle; co: cortex of acrosome vesicle; etc epinuclear electl'on lucenr region; me:
medulla of acrosome vesicle; n: nucleus; nr: nuclear rostrum; ns: nuclear shoulders; p: perforarorium; pb: perforatorial base plate; pm: plasma
membrane; .Ie: subacrosomal cone; sf: flange of subacrosomal material.
264 SCHELTINGA D.M. et al.

mi2
mi3,
pf
'.­o
l.O ... m
FIGURE 3A-H Transmission elecrron micrographs of mature spermatozoa of Urosaurus OI-natus. (A) Longitudinal section (LS) through the entire
midpiece showing rhe four alternating rings of dense bodies (incomplete rings) and mitochondria, and the annulus. Arrows indicate the position
of'ring' srructures which are present but not observed in this section, (B-G) A series of transverse sections (TS) through the nuclear fossa (B), distal
centriole (C), axoneme region of the midpiece (D), annulus (E), principal piece (F) and endpiece (G), (H) LS through the endpiece. All to
same scale as indicated, an: annulus; ax: axoneme; cf: cenrral fibre; db: dense body (mitochondrial transformarion); de: distal centriole; fs: fibrous
shearh; m: mitochondrion; mi: mitochondrial ring; n: nucleus; nf: nuclear fossa; pe: proximal centriole; pcm: pericentriolar material; pf: peripheral
dense fibre; pm: plasma membrane; rs: 'ring srructtlre',
Ultrastructure ofphrynosomatid spermatozoa 265

4a). The nucleus is elongate and circular in transverse section
(Figs. 2g and 4h) with a diameter of 0.46 /lm (n = 1)
and 0.53 /lm (n = 1) immediately posterior to the shoulders
and 0.65 /lm (n = 3, SD = 0.04) and 0.60 /lm (n =4,
SD =0.02) at the posterior end for Uta stansburiana and
Urosaurus ornatus respectively. Basally the nucleus ends with
a shallow nuclear fossa which appears asymmetrical in one
plane (seen to a lesser extent in U. stansburiana) (Figs. 3a,b,
4j and 5a,e,f). At the level of the nuclear fossa the nucleus
slightly flares out laterally.
Neck region
The neck region includes the proximal and distal centrioles
and associated densities, including the first of the dense
bodies of the midpiece. The nuclear fossa contains the anterior
halfofthe proximal centriole and invests dense material
which extends bilaterally as an insignificant laminar structure
(Figs. 3a, 4j and 5a,j). The proximal centriole is composed
of nine short triplets of microtubules and is tilted at
approximately 80 0
relative to the distal centriole (Figs. 3a,
4j and 5a,ej). The distal centriole does not project into the
fibrous sheath (Figs. 3a and 5aj). Within the core and only
the 'lateral' half of the proximal centriole a short solid cylinder
of electron dense material is observed (Figs. 4j and 5e).
This material is of a similar electron density and composition
to that of the dense bodies of the midpiece. Dense
pericentriolar material surrounds the proximal centriole and
extends posteriorly around the distal centriole and possibly
continues as the peripheral dense fibres (Figs. 3a and 5aj).
Midpiece
The midpiece includes the neck region at its anterior end.
The entire short mid piece of Urosaurus ornatus and Uta
stansburiana are shown in longitudinal section in Figs. 3a
and 5a (respectively). Each begins with the first 'ring' of
dense bodies and ends posteriorly at a small annulus. The
dense bodies are separated longitudinally by one or more
tiers of short sinuous mitochondria with distinct lamellate
cristae; in transverse section a maximum of eight mitochondria
are usually seen (Figs. 3a,c,d and 5a-f). There are five
incomplete 'rings' of irregularly ovoid dense bodies in Uta
stansburiana (Fig. 5a-f), while only four incomplete 'rings'
are seen in Urosaurus ornatus (Fig. 3a). In both species the
first ring abuts onto the base of the nucleus, and the last is
separated from the annulus by mitochondria (Figs. 3a and
5a). These arrangements superficially resemble the arrangement
of ring structures (rs), mitochondria (mi) and the
annulus (an), seen in Cnemidophorus sexlineatus and,
Sphenomorphus-group and Egeria-group skinks, and represented
by the expressionrsl/mi 1, rs2/mi2, rs3/mi3, rs4/mi4,
rs5/mi5, an; for Uta stansburiana, and rsl/mil, rs2/mi2,
268 SCHELTINGA D.M. eta!'
rs3/mi3, rs4/mi4, an; for Urosaurus ornatus (Newton and
Trauth, 1992; Jamieson and Scheltinga, 1993, 1994). In
U. stansburiana and U. ornatus the dense bodies do not form
continuous rings, being interrupted by mitochondria
(Fig. 5b-d). In transverse section 'ring' of U. stansburiana is
composed of up to four distinct, irregularly spaced dense
bodies, whereas those of U. ornatus contain only two distinct,
irregularly spaced dense bodies. The distance between
each 'ring' of dense bodies remains relatively constant at
approximately 0.73 /lm in U. stansburiana and 0.93 /lm in
U. ornatus.
The distal centriole is composed of nine short triplets of
microtubules and forms the basal body of the axoneme.
The two central singlets of the axoneme extend anteriorly
into the centriole (Fig. 3c). Associated with the two singlets
is a fibre which is initially located closer to doublet 9, posteriorly
it decreases in size and occurs centrally, between the
singlets (Figs. 3c,d and 5b,c). The central fibre is vestigial at
the level of the annulus.
Nine peripheral dense fibres are associated with the distal
centriole (Figs. 3c and 5b) and continue posteriorly, though
much narrower, along the axoneme into the midpiece. One
is attached externally to each triplet or doublet. Initially the
peripheral fibres at doublets 3 and 8 are not distinctly
enlarged compared to the other fibres, however, more posteriorly,
at an undetermined level, all but the peripheral fibres
associated with doublets 3 and 8 become greatly reduced in
size (Figs. 3d and 5d). Posteriorly, the peripheral fibres at 3
and 8 form double fibre structures, separate from their associated
doublets and become closely associated with the
fibrous sheath. At the level of the annulus, all nine dense
fibres are already vestigial or absent (Fig. 3e).
The fibrous sheath extends anteriorly into the midpiece to
the level of rs3 in Uta stansburiana and mid mi2 in
Urosaurus ornatus (Figs. 3a and 5a,f). It has an annulated
structure and encloses the axoneme and associated peripheral
fibres (Figs. 3a,d-jand 5a,d,fh). The distance that the
fibrous sheath extends anteriorly into the midpiece is constant
within each species but differs between the species.
The fibrous sheath extends 2.04 /lm (n = 5, SD = 0.07) and
2.46 /lm (n = 2, SD = 0.04) into the midpiece for U. stansburiana
and U. ornatus respectively, which equates to
53.8% and 63.5% of the total midpiece length respectively.
The midpiece terminates at a well developed annulus which
appears triangular when seen in longitudinal section of the
sperm (Figs. 3a,e and 5a).
Principalpiece
The fibrous sheath continues to surround the axoneme into
the principal piece. Posterior to the annulus (for some distance)
the plasma membrane is widely separated from the
fibrous sheath by granular cytoplasm (Figs. 3a and 5a). All

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