Download Reptile Reproduction

Reptile
Reproduction
Ch 9: Reproduction
and life histories
Ch 14: Mating systems
and sexual selection
1
ALL Reptiles have internal fertilization
2
Intromission organs
 hemipenes in squamates
(paired evaginations in
the wall of cloaca that are
everted to expose a
complex surface)
 penis in turtles and crocs
3
Whoosh Pond
at Cranberry
Lake Biological
Station, NY.
July 2011.
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Hemipenes
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Held inverted within the body
Everted for reproduction
Often with spines or hooks to
anchor within the female
Often forked hemipenes (each
hemipenis with two tips)
Only one is used at a time
5
6
Cloacal spurs in primitive snakes (e.g., Pythonidae,
Boidae, others): vestiges of hind limbs
Provide tactile
stimulation during
courtship
Video!
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Functional regions of a turtle oviduct
Sperm storage
Fertilization
Fibrous layer, mineral layer
Yolk
Ova
Liver
Ovaries
Sperm-storage tubules of a female
Anolis sagrei
Wrestling contest between two male
European adders (Vipera berus)
Sperm storage
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Known in all reptile groups
Especially common among turtles
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E.g. painted turtles
Pearse et al. (2001) Genetic markers substantiate long-term storage and
utilization of sperm by female painted turtles. Heredity 86(3): 378.
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Findings
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Microsatellite markers on free-ranging population over four
years
Genotyped 113 clutches: 80.5% re-mated each year
But some females used sperm stored for up to three years
to fertilize some or all eggs laid in consecutive nesting
seasons.
13.2% of all clutches examined showed evidence of
multiple paternity
Suggests 'last in, first out' operation of the females' sperm
storage tubules
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13
Reptiles have two reproductive modes
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Oviparity: egg laying
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Viviparity: live-bearing
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All turtles, crocodiles (and birds)
Some squamates
(snakes, lizards and amphisbaenids)
Only found in snakes, lizards and
amphisbaenids
Has evolved independently at least 114
times in reptiles and amphibians (~103 in
squamates)
Cold-Climate hypothesis (for reptiles)
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Oviparity: Reptile Eggs
…physical protection, water loss protection, respiration
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Reptile eggs
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Huge size variation among spcies
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Largest eggs ~ 300 g (pythons)
smallest eggs ~ 0.1 g (geckos)
Two layers:
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outer mineral layer
of calcium carbonate
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inner layer or shell membrane
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Aragonite in turtles
Calcite crocs and squamates
Proteinaceous fibers
Varying composition

Give reptiles eggs their variety
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Structure
of reptilian
eggshells
largely about
water retention
flexible –
harvest water
rigid – retain
water
Basic reptile egg structure
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Embryo
Amnion= cushion
membrane
Yolk sac= nutrition
Allantois= waste sac
Chorion= membrane
immediately inside shell
Albumin = egg white
Shell: hard or leathery
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Functional regions of a turtle oviduct
Sperm storage
Fertilization
Fibrous layer, mineral layer
Yolk
Ova
Liver
Ovaries
Functional regions of a turtle oviduct
Sperm storage
Fertilization
Fibrous layer, mineral layer
Yolk
Ova
Liver
Ovaries
Functional regions of a turtle oviduct
Sperm storage
Fertilization
Fibrous layer, mineral layer
Yolk
Ova
Liver
Ovaries
Functional regions of a turtle oviduct
Sperm storage
Fertilization
Fibrous layer, mineral layer
Yolk
Ova
Liver
Ovaries
What is the
optimal number
and size of eggs?
23
Egg teeth
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Assists in hatching by
splitting the inner
membrane and cracking
the outer membrane of
the egg.
It is not a true tooth,
and it is resorbed a few
weeks after hatching
Link
24
More egg teeth…
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Viviparity – Squamates only (among vertebrates, too)
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100 separate origins = 20% squamates
Only verts to begin embryonic development at fertilization
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Others hypoxia prevents until egg laying
Retention of embryos within the oviducts until development
is complete = live birth.
During evolution, accomplished by gradual increases in the
amount of time eggs are retained in oviducts. But why?
Increasingly common where environment is too cold or
growing season too short to allow normal development
 Female searches for microenviroments suitable for
embryo development
 Hastens development well beyond that possible in nest
chambers.
 No need for nesting!
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Northern water snake
 Nerodia sipedon occupies
cold waters.
 Females spend much of
their time optimizing the
thermal environment for
their young (that is, basking)
 Produce large broods of young (15-30)
 Males stay small and concentrate primarily on
survival (and mating)
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Sex Determination
Genetic in most species
 But in most turtles, all crocs, tuatara,
and some squamates it is environment
dependent (“TSD” or temperature
sex determination)
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Generally a pivotal temperature at which
50% of individuals are of each sex
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Phylogenetic
distribution of
sexdetermining
mechanisms
in extant
tetrapods
Incubation temperature and sex ratio in
the red-eared slider (Trachemys scripta)
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TSD patterns illustrate taxon-specific
pivotal temperatures
Type Ia TSD
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More females than males are produced at higher
temperatures– e.g., many species of turtles
(e.g. Loggerhead sea turtle Caretta caretta).
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Type Ib TSD
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More males than females are produced at higher
temperatures
Typical of tuatara, squamates
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Type II
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Females are produced at low and high incubation
temperatures with males at intermediate
temperatures
Crocodilians, and some turtles (Chelydra serpentina),
squamates.
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• Determination in 2nd Trimester
• Determined by “average”
temperature
• Start with undifferentiated gonads
• Override effect of sex chromosomes
• Female temps: enzyme aromatase
induced
• Converts testosterone >
estradiol, triggers more
estrogen production >
ovary development
• Male temps: enzyme 5-reductase
induced
• Testosterone >
dihydrotestosterone > testes
development
• Hormone cascades
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Mechanisms of TSD?
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Still poorly known
Related to males and females being more fit if
raised at different temperatures?
Permits female to “choose” the sex of her offspring
by nesting in cooler or warmer sites
?
?
37
Charnov–Bull model predicts that selection should favor TSD over chromosomebased systems when "the developmental environment differentially influences male
versus female fitness“…
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TSD, offspring sex choice, and turtles
Females can “choose” sex of offspring by
nesting in cool versus warm sites!
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Why choose?
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Adult females are almost always larger than
males
Turtles shell size correlates with how many eggs
the female can carry; larger turtles means
greater reproduction in females
Male size is unimportant for reproductive fitness
– small males quite adept at mating
So, what do you predict for nesting site selection
in a “bad” year or high-density conditions?
A “good” year?
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GSD:
(the exception)
?
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To here
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Extra credit? Good lecture anyways…


Dale L. Travis Lecture Series
Spring 2017 Lecture
Top Dog? The
Ecological Role of the
Coyote in Northeastern
Forests

March 28, 2017
7:30 pm, Gateway Center at
ESF
Dr. Jacqueline Frair
Looking ahead…

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Exam II: April 10 Mon
Extra time etc.: arrange with ODS!

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those taking exam at ODS please get ESF grading
sheet from instructor first!
Topics
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Water relations
Energetics and performance
Amphibian reproduction
Reptile reproduction
Body support and locomotion
Feeding
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TSD continued…
Conservation Implications of TSD
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Hatchling loggerhead turtles in Florida shifted from 87 to
99.9% ♀
a 2° C warming of the sand would put temperatures solidly
in the female-producing range for the entire population
Mrosvovsky and Provancha (1992) Sex ratio
of hatchling loggerhead sea turtles: data
and estimates from a 5-year study.
Canadian Journal of Zoology, 70:530.
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Turtles and Global Warming
• Projected temperature changes ~ 2-3 degrees C by 2100
• Slow generation times
• Remote possibility that turtles can evolve quickly enough to track such
environmental change and maintain balanced sex ratios in the wild.
Janzen (1994) Climate change and temperature-dependent sex determination in
reptiles. Proceedings of the National Academy of Sciences USA 91:7487.
Turtles and Global Warming
Fraction males
Surprise! Historic trends in sex ratios
of freshwater turtles …
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
Year
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Conservation biology (2005) 19:552
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Conservation
intervention
opportunities
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Parental Care
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Nearly all crocodilians care for their young
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About 100 species of squamates (not many) exhibit
some type of parental care
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Likely necessary to defend against predators
E.g. egg brooding in pythons
Egg attendance
Turtles rarely if ever exhibit parental care
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Likely has costs without major benefits
Time, energy, and increased predation
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Parental care by the mugger
crocodile (Crocodylus palustris)
Arizona black rattlesnake (Crotalus
cerberus) attending offspring
Clutch defense by the skink Eutropis longicaudata
Parthenogenesis –
reproduction without sex
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Some reptiles reproduce asexually
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~ 40 squamate species (mostly lizards, a few snakes)
In most cases these species:
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Result from hybridization of two species
Consist only of females
Reproduce by clonal inheritance
Do not require interactions with other species to reproduce
Do not require sperm
Often require bi-sexual “type” mating to trigger hormone
cascade
Lineages do not last long – ~100k years
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Aspidoscelis uniparens –
desert grassland whiptail lizard
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Parthenogenetic
One of ~15 unisexual all female lizard species
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Pseudocopulation by captive
Aspidoscelis uniparens
• One female plays the
role of the male
• Display courtship
behavior that
increases gonadal
activity (as in many
unisexual species)
The ‘flower pot’ snake
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Ramphotyphlops braminus
Successful invasive species
Fossorial – often introduced
via soil of imported plants
Introduced throughout the
tropics and even in
greenhouses from Florida to Ohio
A single female can be the founder of an entire new
population because of parthenogenesis
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“Evidence for viable, non-clonal but fatherless Boa
constrictors”
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male snakes = ZZ
female snakes= ZW
One female produced
offspring with WW
chromosomes (?)
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Two broods - 12 and 10 babies.
Males present
Had produced sexually before
Perhaps facultative when no
good males around
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Mating systems
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Australian sleepy lizards (Tiliqua rugosa):
male following a female
tends to be monogamous (even outside breeding season ) with pairs reforming every
year for up to 20 years.
An explosive
mating
aggregation of
red-sided garter
snakes
(Thamnophis
sirtalis parietalis)
• Communal hibernation
males exit first, wait
females produce male-attract
pheromone
upon mating male transfers
pheromone to female that
makes female unattractive
adds cloacal plug
female-like males that steal
heat, confuse other males,
open-up mating opportunities
Scramble
competition
by green sea
turtles
(Chelonia
mydas)
Lekking behavior of the Galápagos
marine iguana (Amblyrhynchus cristatus)
End: Reptile reproduction
70
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We do not cover:
9.6 Embryonic development
 9.6 Reproductive cycles
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Do read

9.8 Life histories of reptiles
71