chapter 8

1. genotypic sex determination

2. temperature dependent sex determination

indifferent gonad that could be turned into either the testes or ovaries

genotypic sex determination

1. XX/XY

2. ZZ/ZW

when the sex chromosomes are different

ex: male mammals are XY

ancestral: female

evolved multiple times: male

1. seasonal reproduction

2. aseasonal reproduction

most species in temperate zones

1. only in later winter, early spring

2. only during summer

3. only during autumn

in tropics: wet season breeders (temperature and rainfall)

continuous reproductive cycles

some anurans in relatively aseasonal tropical habitats

males

like a capsule left behind:

1. made of cloacal glands

2. outer layer is a mass of sperm cells

internal fertilization: promotes female parental care

with the spermathecae

1. tubules in wall of cloaca

sperm is stored for later fertilization

mating behavior in which male frog grasps the female from behind to bring their cloacae into close proximity and aid fertiliztion

1. inguinal amplexus

2. axillary amplexus (majority of anurans)

3. cephalic amplexus

inguinal amplexus

cephalic amplexus

assists in amplexus for the male to grasp the female more firmly

caecilians

extension of male cloaca that assists in internal fertilization

genome of the female parent that passes unchanged from one generation to the next

paternal genome discarded and gametes produced by hybrid female contain only maternal genome

intermediate phenotype = hybrid female + parental species male

females that steal genomes from males of other species

has 3 outcomes:

1. sperm initiates development of embryo but sperm’s genetic material is not incorporated into embryo

2. sperm sometimes incorporates but resulting offspring has a higher ploidy (chromosomes) level

3. sperm genome replaces one of the original genomes in the hybrid offspring

ex: ambystoma species

1. aquatic larvae

2. direct development with female as parental care

yolk and maternal secretions

11-12 months

1. mode 1: pond breeding

2. mode 2: stream breeding

3. mode 3: nonaquatic eggs (has several subcategories)

pond breeding

more clustered together in a giant ball

stream breeding

more tube like sacs that are attached to substrate

terrestrial eggs

laid in shallow depressions or attached to leaves

direct development with no water required or a small amount of water

very limited

1. some populations where female fertilizes multiple eggs

2. some populations with few eggs and unfertilized ones get eaten by fertilized ones (offspring)

3. some populations with only 2 eggs fertilized

ex: european fire salamander

1. various arrangements of independent eggs

2. 3D arrangements

3. floating arrangements

4. foam nests

5. linear arrangements

ancestral form

cluster of eggs in water with arrangement dependent on O2 levels

1. cold: more O2, more clumped together

2. warm: less O2, film of eggs in single layer on top of water

mucus mixed with water and the frog paddles its feet to foam it

avantages:

1. less predators

disadvantages:

1. less food

offspring subsist on yolk in eggs instead

tree holes

ex: bromeliads where a single egg gets places in the direct center

mud nests, water sac on bottom of leaf

rain breaks mud nest open

in water sac, eggs are out of predators way and they simply drop out when ready

direct development where development occurs entirely in the egg

no metamorphosis (tadpole stage)

ex: australian turtle frog

1. egg attendance

2. transport of eggs

3. attendance of tadpoles and/or young

4. transport of tadpoles and/or young, and feeding of tadpoles

dendrobatids

transport tadpoles from terrestrial oviposition site to a body of water

1. lecithotrophy

2. matrotrophy

includes 9 species between the 2 types

yolk reserves

7 species

maternal secretions

2 species

1. large eggs, large yolk reserves

2. not dependent on standing water

1. reduction in total reproductive output

2. lower clutch size

3. increased vulnerability to predation

1. decrease in pathogens (cleaner eggs)

2. decrease in predation

3. increase in aeration

4. prevents desiccation (keeps moisture)

1. reduced reproductive output

2. decrease food intake

3. reduced survival of the parent

quality: larger egg size, smaller clutch size

• direct development, parental care

quantity: smaller egg size, larger clutch size

• species that lay eggs water, aquatic larval development

excess food:

• larvae hatch from large eggs, metamorphose sooner in larger in size

limited food:

• larvae hatch from small eggs, metamorphose earlier

favorable environment:

• small eggs might survive, female could increase fitness by producing many small eggs

unpredictable environment:

• produce a range of egg sizes that might increase the change that some offspring will survive

no aquatic larval stage

those with aquatic stage are relatively short and their external gills are lost quickly

pond dwelling larvae keep tail fin and lateral line

stream dwelling larvae lose tail fin and lateral line

a line of sensory receptors

1. egg fertilized

   • external gills develop

2. early stage: tadpoles subsist largely on yolk in

   • mouth development

3. late stage: tadpoles feed (are herbivores)

   • limb development

4. adult stage: primarily carnivorous

breeding in rain pool vs longer lasting temporary pond vs longer lasting pond has effects on duration of larval stage

rain pool: shortest (8 days)

longer lasting pond: longest (7 weeks)

not >: additional growth

yes >: decide if larval body size > max body size

not >: size specific growth rate

yes >: metamorphosis

not: metamorphosis

yes: additional growth

smaller density: grow larger

higher density: grow smaller (competition)

shorter duration (temporary pond): less paedomorphic

longer duration (longer lasting pond): more paedomorphic

more paedomorphic in cave dwelling (light absence) species