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What are the different ways that genetic sex determination can occur? How do these ways differ in different groups of organisms compared to amphibians and reptiles?

  • Genetic sex determination is when the sex of the offspring are determined by a sex chromosome received by the heterogametic parent.
  • Mammals have heterogametic males (XY males/ XX females), and birds have the heterogametic female (ZW females/ZZ males).
  • Anurans, salamanders, most squamates, and some turtles exhibit GSD.
  • Female heterogamety is ancestral for batrachians, but there have been several independent derivations of male heterogamety (XY). And Lizards exhibit XY, XXY, or ZW, snakes exhibit ZW.


What is the difference between a homomorphic sex chromosome and a heteromorphic sex chromosome?

  • homomorphic=no morphological differences between the sex chromosomes and the other chromosomes in the body (autosomes); basically they look the same but have a gene on them that determine the sex
  • heteromorphic=sex chromosomes that look morphologically different than the other chromosomes (autosomes)


What is the ancestral condition for sex determination in tetrapods?

Genetic Sex Determination is the ancestral condition for tetrapods


What is the ancestral condition for sex determination for reptiles?

Genetic Sex Determination


What is the difference between Genetic Sex Determination and Temperature-Dependent Sex Determination?

  • Genetic sex determination is when the sex of the offspring are determined by a sex chromosome received by the heterogametic parent. Mammals, birds, anurans, salamanders, most squamates, and some turtles exhibit GSD.
  • Temperature-dependent sex determination (=environmental sex determination) is when the sex of the offspring is determined by a temperature during a critical period of development. All crocodilians, Sphenodon, most turtles, and some lizards have TSD.


Explain temperature-dependent sex determination. (just basics here, not physiological mechanism)

  • Temperature-dependent sex determination (=environmental sex determination) is when the sex of the offspring is determined by a temperature during a critical period of development.
  • The sex determination occurs during the 2nd trimester, and there is only a small temperature range (1-2 degrees) at which both sexes would be produced. At the threshold temperature range, the gonads can become either testes or ovaries.
  • All crocodilians, Sphenodon, most turtles, and some lizards have TSD.


Explain the physiological mechanism of Temperature-dependent sex determination.

  • Basically there are different enzymes that are expressed at different temperatures.
  • ~Aromatase produced in individuals that are to become females. This enzyme converts testosterone into estradiol, which initiates ovary differentiation.
  • ~5-reductase is produced in individuals that become males. This enzyme converts testosterone into dihydrotestosterone and initiates testosterone differentiation.
  • **Testosterone is present in all individuals, and temperature effects which enzymes are produced and these enzymes are what begin the process of sex determination or gonad development.


What are the different patterns of Temperature-dependent Sex Determination? For each, at what temperatures are males produced? and which groups show this type of pattern?

  • Pattern 1a; More males produced at lower temperatures, and females produced at higher temperatures. Most turtles have this.
  • Pattern 1b has just the opposite. Males are produced at higher temperatures and females at lower temperatures. Many TSD lizards have this pattern.
  • Pattern II looks like a bell curve. Males are produced at intermediate temperatures and females are produced at high and low temperatures. All crocodilians, some lizards, and a few turtles exhibit this pattern.


List some possible reasons for TSD in evolutionary terms.

1. Biased sex ratios- one sex may have better survival at certain temps.

2. Individual survival

3. Maternal effects-maternal contribution may effect.

4. Fecundity **These are not exclusive hypotheses and no single one is probably it.

**Different types of TSD suggests that there may be different selective advantages for different taxa.


Can Temperature dependent Sex Determination be facultative?

yes. Recent studies on Bassiana duperreyi (Scincidae) TSD: Pattern Ia (=males at lower temps) Behavioral changes associated with climate change; GSD known before this, TSD facultative.

Also exhibits GSD: XX-XY system
Radder et al. 2008. Genetic evidence of co-occurrence of chromosomal and thermal sex-determining systems in a lizard. 
Originally known to use GSD
Newer evidence for the TSD in “extreme” conditions

**TSD in extreme conditions bc females are produced more, but females also have better survivability
in extreme conditions. GSD may also be acting at same time? 


What do these graphs pertain to and what are they saying?

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*evidence of climate change, temp increasing and nest temps are going up as well (temps at which
nests being incubated, should have fewer males bc temp) females seem to be responding to temp and
digging their nests deeper. Eventhough nests are being dug deeper, nest temps still increasing. On right certain times they
lay eggs. Nesting happens at earlier time to respond to temp change. Even with all adjustments, not able to
keep up bc curve is staying higher above threshold for most of time, so more of one sex than the other. 

*behavioral response not enough to keep up with climate change effects.


What are the different reasons why there are differences in brood size and size of young between taxa?

Generally, energy for reproductive effort in females is a limited resource
Production of few large offspring vs. production of many small offspring (K- vs. r-selection); 

**Differing levels of natural selection acting on eggs, larvae, and juveniles; One aspect of an individualʼs life history**

Usually offspring size relatively constant within a population; Optimized over time via natural selection
Great variation across amphibian and reptilian species


Compare and contrast the following pairs of terms:

Lecithotrophy vs Placentotrophy

Lecithotrophy: developing embryo receiving all nutrients from the egg yolk produced before development begins inside an egg; present in some viviparous and oviparous species.

Placentotrophy: developing embryo receiving nutrients exchanged via the placenta throughout development; present in viviparous species.

Both are forms of embryo nutrition in viviparous species.


Compare and contrast the following pairs of terms

Parthenogenesis vs Gynogenesis

Parthenogenesis: All female populations producing own unreduced eggs and resulting in clonal inheritance; no males present in this population. Present in several squamate groups.

Gynogenesis: All female population producing unreduced eggs that need to be stimulated by the reduced sperm of a male in the parental population for reproduction, although the sperm is shunted and not incorporated into the embryo. Present in some fish and salamanders.

Both have females that produce unreduced eggs, where no meiosis occurs, and both result in clonal inheritance by the mother; both are also unisexual species reproductive modes, and both unisexual species are thought to have arisen froma hybrid from two genetically distinct species.


What is the major challenge that must be overcome during the evolution of viviparity?
How has this been accomplished?

  • During evolution, viviparity accomplished by gradual increases in amount of time eggs are retained in oviducts
  • Oviparous squamates: Development of embryo before eggs laid, Incubation time may be very short
  • Main challenge for evolution of viviparity is gas exchange
  • Two main changes occur to facilitate and increase gas exchange: 1.) Reduction in the thickness of jelly or shell layers of egg 2.) Increase amount of vascularization in oviduct and respiratory structures of embryo
  • Route of nutrition may not change: Lecithotrophy
  • Embryonic respiratory structures in Amphibians: Greatly modified and vascularized gills or tails;  Reptiles: Increased vascularization and development of the chorioallantoic membrane (=placenta)
  • Embryo nutrition: Lecithotrophy (all nutrients from egg yolk), Matrotrophy  (in amphibians, larvae receive nutrition from oviductal (lipid-rich; histophagy) or ectodermal secretions (gymnophionans)), Also unfertilized eggs (oophagy) in some gynophionans and Salamandra, Adelophagy (feeding on siblings), Placentotrophy in some squamates (nutrients exchanged via placenta)


Describe the three general patterns of temperature-dependent sex determination. Which pattern do crocodilians exhibit?

Pattern 1a: males develop at lower temps; most turtles have this

Pattern 1b: males develop at higher temps: many lizards have this

Pattern 2: Males develop at intermediate temps, and females at high and low. Crocs have this pattern, also some lizards and turtles


Name the three embryonic membranes of the amniotic egg. Which membrane(s) is involved with the storage of waste products?

Amnion: inner most membrane surrounding embyro

Charion: Outermost membrane that forms a protective layer 

Allantois: Outgrowth from the rear of the gut, expansion to lie beneath the charion

The allantois stores all nitrogenous waste, much of it also fuses with the chorion (=chorioalloantioc membrane) to provide larger surface area for gas exchange. 


Give a major advantage and disadvantage of providing parental care to offspring.

advantage: increased offspring survivability

disadvantage: cost time and energy to parents, and may increase parents risk of predation


How have the triploid parthenogenetic lineages originated in the whiptail lizards of the genus Aspidoscelis?

Breeding between two separate species, such as A. inornata and A. tigris, produced hybrid parthenogenic females that produce unreduced gametes. These females mating with either another species or a male from the parental species could produce triploid gametes if the sperm is incorporated into the female unreduced gamete. 


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Define or describe each term. If the term is characteristic of a particular group(s), be sure to
provide that information.

 Clonal inheritance

Hemiclonal inheritance

clonal: offspring produced that are identical to the mother, no incorporation of male sperm and produced from unreduced gametes. **occurs in parthenogenesis and gynogenesis**

hemiclonal: only half the genome passed, not both parents genomes are passed, reduction of eggs occurs, but not until after the paternal genome is deleted, and then there is a reconstitution of the hybrid by mating with pure species. **this is hybridogenesis**


Define or describe each term. If the term is characteristic of a particular group(s), be sure to
provide that information.



Heterogametic: heteromorphic sex chromosomes: ancestral for batrachians

Homogametic: no morphological differences between sex chromosomes, males carry gen in some species, females in others.


Define or describe each term. If the term is characteristic of a particular group(s), be sure to
provide that information. 


Allantois: Outgrowth from the rear of the gut, expansion to lie beneath the charion

The allantois stores all nitrogenous waste, much of it also fuses with the chorion (=chorioalloantioc membrane) to provide larger surface area for gas exchange. 


Why is it advantageous for some amphibians to deviate from the typical reproductive mode of laying aquatic eggs? Describe three forms of parental care exhibited by anurans and discuss the advantages and disadvantages of exhibiting parental care.

**All nonaquatic modes of reproduction in anurans are ways to remove eggs away from the water and the predators that are in the water. 

Egg attendance most common; Usually performed by male; (Eleutherodactylus, centrolenid frogs, Alytes, many hylids)

1.) Some species attend offspring:

(Most dendrobatid frogs)  parents guard terrestrial eggs; transport tadpoles from the nest to water

( Some Dendrobates, some hylids, and Chirixalus) females attend tadpoles; Periodically provide unfertilized eggs as source of nutrients for tadpoles

Some large aquatic and semi-aquatic frogs attend tadpoles (Pyxicephalus, some Leptodactylus)

2.) Many species carry the eggs on back

(Gastrotheca, Hemiphractus, Flectonotus, Fritziana) terrestrial with aquatic tadpoles or direct development
(Pipa pipa) aquatic; direct development

3.) Rhinoderma darwini: Males carry eggs in the vocal pouch Direct development (maybe patrotrophy)

4.) Rheobatrachus: Gastric brooding frogs; Females swallow fertilized eggs; undergo direct development in stomach



Generally, how does the brood size and size of young differ in amphibians and reptiles? 

Amphibians, such as many bufonids and hylids produce thousands of small eggs, the eggs hatch as relatively small size and under developed with a high mortality rate. 

Some other amphibians, such as Eleutherodactylus, dendrobatids, & viviparous bufonids, produce relatively a few large eggs or offspring, and these generally have a lower mortality rate. 

Reptiles have a maximum number of eggs that is usually smaller, and offspring produced are generally larger 


Generally, what type of tradeoffs exist between clutch number and size of offspring within a species?

Is clutch size variable within a species?


For some species, offspring size decreases as clutch size increases. 

The reproductive investment is also determined by resource availability; more resources usually means larger offspring. 

Clutch size is usually constant within a species, and most have clutch and offspring sizes that have been optimized through natural selection over time. (optimal offspring size theory)

There are a few deviations from this, such as the Deirochelys sp. of turtle that hasn't seemed to reach an optimal egg size, where if the females can produce larger eggs than they will when usually there is a physical constraint on most turtles; or some Anole lizards and some gekkos will produce only 1-2 eggs even if environmental conditions would allow them to be able to produce more; for these it is possible they have reached their optimal offspring size and in order to reach that, they can only have so many eggs at one time. 


What is life history evolution?


a set of coevolved traits affecting an individuals survival and reproductive potential

**the bigger picture that must be considered when looking at clutch size and offspring sizes within a species. 


What type of fertilization is ancestral for amphibians and what does it require?

What type of fertilization is ancestral for reptiles? What does it require?


External fertilization ancestral for amphibians (eggs fertilized outside females reproductive tract), likely for Osteolepida; This requres standing water for reproduction  **deviations from this involve the evolution of internal fertilization and direct development.

Internal fertilization is ancestral for amniota, evolved early in Anthracosauria; This requires a copulatory organ and an amniotic egg for reproduction. 


What is most common among species when it comes to reproduction?


bisexual species, males and females necessary and both contribute to offspring genetically

Reproductive activities are syncronous

Reproductive timing usually triggered by environmental cues


Where do the major differences occur between the ova of amphibians and reptiles?

The eggs (ova) of amphibians and reptiles (amniotes) are structurally different. Major differences are in the extraembryonic membranes and external coverings; there are also major adaptations in amniotes for water conservation and embryonic protection. 



What is the structure of the amphibian ovum?


  • production of "jelly-covered eggs"
  • ovum enclosed in vitelline membrane (also called the chorion)
  • this is coated with layers or capsules or mucoproteins and mucopolysaccharides; these layers vary among taxa, many layers in salamanders, and fewer in anurans and gymnophonians. 
  • there is only one anamniotic or extra-embryonic membrane, then the yolk sac
  • generally laid in water or in moist locations on land

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What is the structure of a reptilian ovum?

How do the parts differ between taxa?

  • typical amniotic egg has an outer shell (leathery or calcareous) that protects against water loss and provided mechanical protection; the eggs of squamates and some turtles take up water during development, and the eggs of crocs and some turtles do not take up water during development. 
  • then 3 extra-embryonic membranes, plus the yolk sac
  • Amnion: inner most membrane surrounding embyro, provies fluid environment for embryo

    Charion: Outermost membrane that forms a protective layer

    Allantois: Outgrowth from the rear of the gut, expansion to lie beneath the charion

    The allantois stores all nitrogenous waste, much of it also fuses with the chorion (=chorioalloantioc membrane) to provide larger surface area for gas exchange. 

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What is the function of the yolk sac?

Where is the yolk synthesized?

What does it consist of?

the yolk sac stores nutrients for developing embryo.

It is synthesized in the liver and consists of lipoprotiens, phosphorylated protiens, and glycogen

**amount of yolk and relative proportions of main components vary across taxa**


What other types of fertilization exist within amphibians (Anurans, Salamanders, and Caecelians) other than the ancestral condition of external fertilization?

Explain each.

All Amphibians: Ancestral condition; external fertilization, females lay eggs in external environment and males release sperm over eggs

Anurans: Also have internal fertilization present in Leiolematid (intromittent organ), Bufonids, Altiphrynoides, and Brachycephalids all have cloacal apposition

Salamanders: only basal salamanders have external fertilization (Cryptobranchoidea) with eggs and sperm released into the water, but they also have internal fertilization in most salamanders, where the males produce a spermatophore (a proteinaceous base topped with a package of sperm) and the female generally picks this up with their cloaca; in some the males place the spermatophore within the females cloaca. 

Caecilians ALL have internal fertilization, and all males have a copulatory organ called a phyllodeum


Are there any deviations from the ancestral condition of internal fertilization in reptiles?

How is this form of fertilization accomplished within the different taxa?

Internal fertilization is present in all reptilian groups, the possession of a shelled egg requires internal fertilization, the fertilization must occur before the egg is laid down. 

Turtle and Croc males have a single penis;  this is likely the reptilian (maybe amniote) synapomorphy that was lost in Aves and Lepidosauria

Sphenodons have a cloacal apposition (no copulatory organ)

Squamate males have paired hemipenes which is an envagination of the cloacal wall, that becomes everted when engorged with blood. The surface of the hemipenis may be ornamented with folds, papillae, and/or spines. 


What are the selective advantages of internal fertilization?

  • increase efficiency 
  • protection of gametes
  • storage of sperm by female for later use; sperm production and egg production may be decoupled


Compare and contrast sexual vs asexual reproduction

Sexual reproduction: production of haploid gametes by both sexes, and a union of gametes produces a zygote. Both gametes are involved in meiosis, and there is production of a genetically variable offspring. 

Asexual reproduction is the production of reduced (haploid) or unreduced (diploid) eggs, with no incorporation of sperm, and clonal or hemiclonal inheritance. Asexual species usually the result of hybridization between 2 bisexual species, most populations are unisexual (all females).

Four general mechanisms involving sexual and asexual reproduction include: Sexual reproduction, Hybridogenesis, Parthenogenesis, and Gynogenesis



What groups have this type of reproduction?

Production of reduced gametes by both sexes, but generally only maternal genome transmitted to next generation. 

Meiosis occurs, but not until parternal genome is deleted, the end result is the maternal genome duplicated, **Hemiclonal inheritance from hybrid**

Occurs in only a few groups of anurans; ex. Pelophylax ("Rana") esculenta complex of Europe, involves 2 species, lessonae and ridibunda, both have male and female hybrids that are formed in crosses of these 2 species and hybrids originally classified as P. esculenta. The sexual males are smaller and generally all females are produced. A "pure" species is not reconstituted. Some diploid and some triploid individuals in this population. 

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Explain the  Pelophylax ("Rana") esculenta complex of Europe. 

 involves 2 species, P. lessonae and P. ridibunda, both have male and female hybrids that are formed in crosses of these 2 species and hybrids originally classified as P. esculenta. The sexual males are smaller and generally all females are produced. A "pure" species is not reconstituted. **This was found to be a form of hybridogenesis


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What groups have this type of reproduction?


All female populations (unisexual); meiosis does not occur, individual will produce new unreduced eggs, clonal inheritance; great colonizers because only takes one individual instead of 2.  

Found in several squamate groups all over the phylogeny. Ex. Aspidoscelis & "Cnemidophorus" (out of 45 sp, 15 are parthenogenetic) either diploid or triploid unisexual species, have pseudocopulation where one individual plays the role of the male, but not male. Females that are involved in pseudocopulation produce more eggs, possibly because the behavior increases the gonadal activity

Other squamates also have this, including some iguanians, some lacertioids, some geckos, scincid Menetia and the snake Rhamphothyphlops braminus

**Also some non-hybrid facultative are Varanus, Python, Agkistrodon

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What groups have this?

Unisexual species, production of unreduced eggs, but development must be initiated by contact with sperm, meiosis does not occur, individual will produce new unreduced eggs, results in clonal inheritance. 

Some fish and salamanders of the "traditional" Ambystoma laterale-jeffersonianum complex 

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Define: kleptogenesis

incorporation of local male's nuclear genome in a normally unisexual species that have gynogenesis (sperm needed for initiation of developing egg, but sperm not incorporated), this trait does not seem to be passed down and occur again and again.

This is seen in Ambystoma complex and will increase the ploidy when it occurs. 


What is the generalized life cycle of Amphibians?

What are some deviations from this?

  • Amphibians generalized life cycle includes: Egg, larva, and adult; eggs and larva are aquatic, adult may or may not be terrestrial**probably ancestral life cycle for Amphibia; nutritional pattern is Lecithotrophy (all nutrients from egg); Anuran and Caudata exhibit aquatic eggs and larva; Gymnophonia have terrestrial eggs


  • Deviations include: larval or "adult" stages may be absent or extra stages may be present; 1.) larval development occurs in egg(direct development); this is seen in many anuran groups, and some salamanders, including Plethodon 2.) individuals mature in essentially a larval form (paedomorphosis); this occurs in some salamanders. 3.) An additional eft stage may occur, as in Notophthalmus (Egg, larva, eft, adult), eft is a non-reproductive terrestrial stage. 


What is the general life cycle for reptiles?

Reptile life cycles include either oviparity (hatched) or viviparity (born essentially as adults). No larval stages and embryonic development generally last much longer. 


How does metamorphosis differ between the different groups within Amphibia? (Anuran, Caudata, and Gymnophonia)

Anurans have very dramatic metamorphosis, from a tadpole to adult, and there is essentially a complete restructuring of most morphological systems like the skeletal, digestive, and respiratory systems. 

There is a less dramatic transition in salamanders and caecilians, larva are very similar to adults, some changes occur such as in the skin, teeth, cranial, and tongue, but not as drastic as in Anurans. 


What are the different reproductive modes seen in Reptiles?

Only 2 general modes: Oviparity (terrestrial egg laying) or viviparity (live birth)

**Type of reproductive mode is based on the site of egg deposition and type of larval development**


What are the different reproductive modes found in Salamanders?

Most salamanders are oviparous, but there are 4 general reproductive modes. 

1.) Pond breeding with small eggs; low oxygen and small prey (Sirenidae & Amphiuma & others)

2.) Stream breeding with large eggs; high oxygen and larger prey (Cryptobranchus, Necturus, Dicamptodon, & others)

3.) Non-aquatic eggs with large eggs; high oxygen, aquatic larva or direct development, more yolk because advanced or direct development (some Ambystomids & Plethodontids)

4.) Viviparity; produce larvae or miniatures of adult, only found in ~12 Old World Salamanders, may have lecithotrophy or one of the three forms of matrotrophy. 


What is lecithotrophy? What is matrotrophy? What are 3 different forms of matrotrophy seen in Salamanders?

lecithotrophy- receiving all nutrients from yolk

matrotrophy- additional resources by female

oophagy-fetuses feed on sibling ova

adelphophagy- fetuses feed on developing siblings

histophagy-fetuses absorb maternal secretions 


What are the different reproductive modes found in Anurans?

Most are oviparous, but many different specific places of egg deposition in non-aquatic situations

1.) Aquatic eggs; may be in still or flowing water, or depressoins. This is ancestral anuran mode, egg laying in still water (common in ranids, bufonids, and hylids); egg mass structure and jelly layer dependent on oxygen availability. 

2.) Aquatic eggs in specialized environments; may be in Bromeliads, leaf axils or tree holes (some hylids and rhacophorids),  foam nest on water (leptodactylids and myobatrachids), or on dorsum of female (Pipa)

3.) Nonaquatic eggs: Leaves over water; walls of tree holes; arboreal; Foam in burrows or above water; Terrestrial nest with direct development;  Carried by parent on maleʼs legs, dorsum, dorsal pouch, in vocal sacs, in stomach; Retained in oviducts (viviparity), Lecithotrophy or histophagy; Possible histotrophy (fetus absorbs nutrients)

**All nonaquatic eggs are adaptations to get young out of water and in environment with fewer predators so they will have a higher reproductive success and survivability of young. 


What are the different reproductive modes found in Caecelians?

Caecilians have some oviparous forms: aquatic larvae or direct development

Also, viviparous, after depletion of yolk, young feed off oviductal secretions (histophagy); Young feed off external skin of mother (dermatophagy)


What is parental care? Why give parental care? What are the disadvantages of parental care to the parent?

Parental care is providing care to the eggs and/or offspring. 

Parental care/protection provided may increase the chances of offspring survival.

The cost to the parent may be investment of time and energy as well as increased predation risks to parent. 


What form of parental care is provided by all 3 groups of amphibians?

Egg attendance; this is the most common form of parental care. 

One or both parents attends clutch of eggs during development.

Only form of parental care in salamanders (~20% of salamanders)  and caecilians (all oviparous ceacilians)


What type of parental care is seen in reptiles?

Less common in reptiles

 Essentially non-existent in turtles

 Exhibited by all crocodilians; Females guard nests;  At hatching, females open nest; May assist young to escape from nest; Some species carry young to the water (e.g., American Alligator); Parents and young often remain together for several months to few years

~100 squamate species exhibit parental care; Egg brooding in some pythons; Egg attendance (E.g., Plestiodon (=Eumeces) Some “advanced” snakes (i.e., some colubrids, viperids, and elapids)) 


What is viviparity? In what groups is this common? uncommon?

Retention of embryos within the oviducts until development is complete; live birth

Common in some groups such as caecilians and squamates

Uncommon in others such as batrachians

Absent in others such as turtles & crocs


List 3 advantages and 2 disadvantages for viviparity.


1.) egg protection

2.) increased rate of embryonic development

3.) advanced development=increased offspring survival


1.) reproductive output is reduced (number of clutches and eggs)

2.) reduced agility of female (increased risk of predation)


What Amphibian taxa have viviparous species present?

~50% of caecilians

 ~12 species of salamander (Mertensiella and a few Salamandra)

6 species of frogs (Eleutherodactylus jasperi and some African bufonids)


Which reptile species have viviparous species present?

Viviparity evolved only in squamates, but independently numerous times (>100X)
Entirely viviparous: Xenosauridae, Xantusiidae, Aniliidae, Uropeltidae, Acrochordidae, Tropidophiidae
At least 34 derivations in Scincidae; at least 14 derivations in Colubridae

Rare in many other ʻfamiliesʼ

Evolution of viviparity thought to be associated with cool environments
 More rapid development => thermoregulating female