Figure 4.1 Sexual behavior and ultimately reproduction are mediated by interactions between environmental factors, the nervous system (brain), and the hormonal system. Gonadotropin-releasing hormone (GnRH) stimulates the pituitary to produce

1
Figure 4.1 Sexual behavior and ultimately
reproduction are mediated by interactions between
environmental factors, the nervous system
(brain), and the hormonal system.
Gonadotropin-releasing hormone (GnRH) stimulates
the pituitary to produce gonadotropins
(lutenizing hormone and follicle-stimulating
hormone), which, in turn, stimulate testes or
ovaries to produce mature gametes and androgens.
Androgens not only effect development of
secondary sexual structures but also feed back on
sexual behavior and the brain.
2
Figure 4.2 Spermatogenesis. Diagrammatic
representation of a cross section through a
seminiferous tubule in a reptile testis.
3
Figure 4.3 Structure of spermatozoan of a hylid
frog. Only the base of the tail is shown, and the
head of the sperm has been shortened. Redrawn
from Costa et al., 2004.
4
Figure 4.4 Development of eggs in amphibians and
reptiles. Fertilization occurs internally in all
reptiles after eggs are ovulated into the
oviducts. Fertilization occurs externally in most
amphibians. Corpora lutea are often prominent in
reptiles but rare in amphibians. Following
production of the clutch, the process is repeated
as unused ovarian follicles mobilize lipids for
production of the subsequent clutch. Subsequent
clutches may be produced within the same season
or in the following season, depending upon
species and the environment.
5
Figure 4.5 Oogenesis. Cross section through the
ovary of the skink Carlia bicarinata, showing a
corpus luteum (left) and a maturing follicle
(right) with its ovum. Abbreviations CL, corpus
luteum F, follicular cells Tf, theca folliculi
Y, yolk Zp, zona pellucida. (D. Schmidt)
6
Figure 4.6 Comparison of anatomy of the
anamniotic amphibian egg and the amniotic reptile
egg.
7
Figure 4.7 Wall of the oviduct of the lizard
Sceloporus woodi during shell production. Two
proteinaceous fibers are emerging from the
endometrial glands of the oviduct. Scale bar 5
µm. Adapted from Palmer et al., 1993.
8
Figure 4.8 Positions used by frogs during
amplexus. Adapted from Duellman and Trueb, 1986.
9
Figure 4.9 Diagrammatic representations of a
spermatophore and a single spermatozoan of the
salamander Ambystoma texanum. Sperm are located
on the periphery of the cap of the spermatophore
the sperm heads point outward and tails are
directed inward. Adapted from Kardong, 1992.
10
Figure 4.10 Nest of the Gladiator frog, Hypsiboas
boans, from western Brazil. (J. P. Caldwell)
11
Figure 4.11 Nest of the saltwater crocodile
(Crocodylus porosus). (R. Whitaker)
12
Figure 4.12 Indian python (Python molurus)
brooding clutch of eggs. (M. T. O'Shea)
13
Figure 4.13 Effects of temperature on incubation
period and developmental rate in eggs of the
Australian skink Bassiana duperreryi.
Developmental rate is the inverse of the observed
incubation period divided by the shortest
incubation period in the laboratory. Adapted from
Shine and Harlow, 1996.
14
Figure 4.14 Spatial arrangement of hatchlings of
Chrysemys picta in the nest during winter. From
Breitenbach et al., 1984.
15
Figure 4.15 Sex ratios for four tortoise species
(Gopherus polyphemus, G. agassizii, Testudo
graeca, T. hermanni) raised at different
incubation temperatures showing that males are
produced at low developmental temperatures and
females are produced at high developmental
temperatures. Adapted from Burke et al., 1996.
16
Figure 4.16 Genetic and environmental factors
affect embryo and hatchling phenotypes and can
affect the sex of offspring in species that have
temperature-dependent sex determination (TSD).
Maternal effects cut across genetic and
environmental effects, whereas paternal effects
are only genetic.Adapted from Valenzuela, 2004.
17
Figure 4.17 Evolutionary hypotheses to explain
TSD center on sex ratios, maternal effects,
fecundity, and survival, none of which is
mutually exclusive. Most hypotheses can be
categorized by the fitness component that they
address. Adapted from Valenzuela, 2004.
18
Figure 4.18 Offspring sex ratios differ in
offspring produced in the first clutch of the
season for Jacky Dragons in Australia in response
to differing operational sex ratios (OSR) in
experimental arenas of the mother. The response
is exactly the opposite from what theory
predicts. In successive clutches (23) sex ratios
did not differ as a result of varying OSR, but
the sex ratio of hatchlings was biased toward
females. Adapted from Warner and Shine, 2007.
19
Figure 4.19 Annual variation in the trade-off
between number of eggs and size of eggs in
Lacerta agilis. The influence of body size on
clutch size has been removed by expressing clutch
size as residuals from the common regression.
Adapted from Olsson and Shine, 1997.
20
Figure 4.20 Species and populations of Sceloporus
lizards with variable clutch size have relatively
massive clutches of eggs at any given body size
when compared with Anolis lizards that have fixed
clutch sizes of a single egg. In addition, clutch
mass increases linearly with body size in Anolis
but exponentially in Sceloporus. Adapted from
Andrews and Rand, 1974. Refer to the original
paper for species identifications.
21
Figure 4.21 Variation in the size of the pelvic
opening of turtles and width of eggs associated
with increasing body size in three species of
emydid turtles.Adapted from Congdon and Gibbons,
1987.
22
Figure 4.22 Schematic diagrams of sex steroid
production in relation to gametogenic cycle of a
spring-breeding temperate-zone reptile. Steroid
levels match the peaks of gametogenesis androgen
production begins simultaneously with
spermiogenesis and continues until the testes
regress estrogen production occurs during final
maturation of ovarian follicles, stopping at
their maturation and ovulation. Corpora lutea
produce progesterone, which continues while ova
remain in the oviducts production declines and
corpora lutea degenerate with egg-laying, but in
viviparous taxa, progesterone is produced
throughout pregnancy. Adapted from Whittier and
Crews, 1987.
23
Figure 4.23 Hybridogenesis in the frog Pelophylax
Rana esculenta. Two general breeding systems
(LE and RE) exist involving sexual and unisexual
species, with considerable variation within each.
At three localities in Denmark, southern Sweden,
and northern Germany, all-hybrid populations of
P. esculenta occur in the absence of sexual
species. Because the male-determining "y" factor
is on the L genome, hybridization can and does
produce male hybrids. In the RE system, male
hybrids (LyRx) are more successful than female
hybrids (LxRx) in reproducing with P. ridibunda,
resulting in female hybrids being less common.
Hybrid triploids are produced in some populations
when a P. lessonae male (LL) fertilizes a P.
esculenta (LR) egg.
24
Figure 4.24 The cost (hybrid load) to
hybridogenesis in Pelophylax Rana esculenta is
high, with about 63 of offspring produced in
all-hybrid populations dying before or during
metamorphosis (Christiansen et al., 2005).
Aneuploidy occurs when the ploidy level is not a
multiple of the haploid number of chromosomes for
the species.
25
Figure 4.25 Four sexual species of Ambystoma from
which unisexual Ambystoma"steal" genomes. From
left to right, A. jeffersonianum, A. tigrinum, A.
texanum, and A. laterale. (J. P. Bogart).
26
Figure 4.26 Kleptogenesis occurs in salamanders
of the Ambystoma lateralejeffersonianum complex.
mtDNA has persisted unchanged since the hybrid
origin of unisexual populations in the Pliocene,
but unisexuals pick up and use genomes of sexual
species each time they breed yet do not pass
those genomes on from generation to generation.
In effect, they are "stealing" genes adapted to
local conditions from sexual males.
27
Figure 4.27 Skin-graft test for genetic
similarity in the unisexual Aspidoscelis
uniparens (left) and the bisexual A. tigris
(right). Because of the clonal nature of A.
uniparens, all 9 grafts were accepted in
contrast, all 10 grafts were rejected in A.
tigris. Adapted from Cuellar, 1976.
28
Figure 4.28 Genealogy of the parthenogenetic
teiid and gymnophthalmid lizards. The lines
originating on species names denote the parents
that hybridized to create the parthenoforms/parthe
nogens (black circles). In many cases, a single
hybridization event produced diploid
parthenoforms, in others, a single hybridization
produced triploid parthenoforms, and in yet
others, backcrosses between a parthenoforms and a
sexual species produced triploid parthenoforms.
Parthenogenesis has arisen independently in the
Teioidea multiple times. Adapted from Reeder et
al., 2002.
29
Figure 4.29 Relationship between hormone
production, follicle development, and behavior in
parthenogenetic whiptail lizards (Aspidoscelis)
during pseudocopulation. Adapted from Crews and
Moore, 1993.
30
Figure 4.30 Hypothetical growth rates for
populations of parthenogenetic and sexually
reproducing Aspidoscelis based on laboratory data
on A. exsanguis and assuming no mortality. The
starting point on the graph represents hatching
of one egg. Because 50 (males) of the sexually
reproducing species do not produce eggs,
population size of the parthenogenetic population
is more than double that of the sexual species
after only 3 years. Adapted from Cole, 1984.
31
Figure 4.31 Age distribution patterns of a snake,
lizard, and tortoise population. Point-in-time
patterns differ between a moderate-lived snake,
Agkistrodon contortrix a short-lived lizard,
Basiliscus basiliscus and a long-lived tortoise,
Geochelone gigantea. The bars denote the percent
(of total population) of males or females present
in each age class open bars, unsexed
individuals shaded bars, females solid bars,
males. Adapted from Vial et al., 1977 Van
Devender, 1982 and Bourn and Coe, 1978,
respectively.
32
Figure 4.32 Top Hypothetical survivorship curves
for animal populations (see text). Bottom
Representative survivorship curves for amphibians
and reptiles with short life spans (left) and
long life spans (right). Although the lower
graphs are superficially similar, note the great
difference in age scale.Data from the following
AmphibiansPj, Hairston, 1983 Rc, Briggs and
Storm, 1970 ReptilesCc, Brown and Parker, 1984
Ts, Frazer et al., 1990 Us, Tinkle, 1967.
33
Figure 4.33 Prim diagram showing axes of
variation in life history traits of lizards.
Adapted from Dunham et al., 1988, with taxonomy
for the Iguania updated.
34
Figure 4.34 Prim diagram showing axes of
variation in life history traits of snakes. Only
three snake families are included, so the
analysis must be considered preliminary.
Nevertheless, coadapted sets of life history
traits appear evident. Adapted from Dunham et
al., 1988, with errors corrected.