Lecture Exam 2 Flashcards
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.
- Biased sex ratios- one sex may have better survival at certain temps.
- Individual survival
- Maternal effects-maternal contribution may effect.
- 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?
*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.
# 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
Homogametic
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
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.
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
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.
Hybridogenesis
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.
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
Parthenogenesis
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
Gynogenesis
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
