Zool 406 -Salamander Reproduction

How many salamander species have internal fertilization? which don’t?

~90% of species

But not Cryptobranchis or Hynobiids

What is a spermatophore?

A protinaceous pedestal capped by sperm packet

How does internal fertilization work in salamanders as they don’t have an intromittent organ?

Deposition and collection of spermatophore

→ the male drops the spermatophore; must induce female to pick it up = elaborate courtship

T/F Fertilization is always immediate in salamanders?

False

It can be delayed by hours to years

How is sperm stored in Salamanders?

Spermatheca in roof of cloaca; open independently or by common duct into main cloacal chamber

Sperm is held here

—> muscular contractions will expel sperm as eggs enter the cloaca from the oviducts

In what two locations are phermones produced in salamaders?

1. Mental gland = terrestrial

2. Cloaca = aquatic

What is the function of pheromones?

• Increase likelihood of female participation 

• Increase male insemination success

Which groups have no courtship behaviour vs the most elaborate courship behaviour?

No courtship = Cryptobranchids + Hynobiid

Most elaborate = Ambystomatids + Plethodontids

What are two examples of pheromone delivery in salamanders?

1. Slapping: Male submandibular mental gland contacts female nasal region directly → pheromones to females vomeronasal organ via nasolabial grooves

2. Injection: male with enlarged premaxillary teeth; during courtship males drags teeth across females neck, lacerates skin, releases secretions from mental gland → direct deliver to female circulatory system

What are the two main components of plethodon pheromones?

1. PRF = plethodon receptivity factor = shortens mating time

2. PMF = plethodon modulatory factor = lengthens courtship time

Together they shorten mating time

How does Plethodon shermani deliver pheromones?

Male pheromone from mental gland to female snout during courtship; increases female receptivity

• From snout, pheromones go directly to vomeronasal organ

• Vomeronasal organ transduces and transmits information to brain

What do reproducing male and female Desmognathus welteri look like?

1. Orientation

• Repeated episodes of slow approach by male, and following if female moves away

• During approach and follow; male undulates tail and does butterfly movements with forelimbs

2. Persuasion

• Begins when female ceases to move away

• Male begins stimulating female with nudging, head rubbing, tail undulation, butterfly, pulling

• Culminates in male attempting to slide his body under her head while undulating tail laterally and snapping

3. Sperm transfer - tail straddling walk

• Male slides beneath females head

• Female straddles male undulating tale with her forelimbs

• Pair move together in tail-straddling walk

How is mating energetically expensive?

• Males and females must fatten up

• Multiple weeks at breeding site, no feeding, mortality up to 50%

How is multiple mating beneficial to males and females?

Males

• Increases likelihood of siring offspring

Female

• Individual success can be ensured

Both:

• Fertilization assurance

• Long-term benefit of genetic diversity of progeny

How is multiple mating not beneficial?

• Courtship with multiple partners is costly in terms of fitness and energy

How does multiple paternity possibly arise?

May be a result of anatomy:

• Sperm storage

• Unknown duration of storage, if long term could result in multiple paternity

What are the problems vs. benefits of the rare phenomena of parthenogenesis in salamanders?

Problems:

• Inability to purge deleterious mutations

• inability to generate genetic variability than via mutation

Benefits:

• Lose cost of meiosis

• Lose cost of producing males

What is gynogenesis? why would the male engage help produce unisexual females?

• Sperm is required but there is no genetic contribution from the male

• Offspring are clones of the mother

• Lineage coexists with sperm donors

• Balance is required – can’t out compete sexual females
  
  

Why do males waste sperm on unisexual female lineages

• Male discrimination

• “Leakage” of genes

What is parental investment?

 Energy above what is required for the embryo to grow and develop sufficiently to hatch and begin to obtain food

What is the most common form of parental investment in plethodontids?

Egg brooding

What is the difference in parental care in pond-feeders vs stream breeders?

• Pond-feeders

 = generally small eggs without parental care

• Stream breeders

= generally large eggs with parental care

Why may parental investment differ across salamander species?

• May be food availability

• Small numerous hatchings are better where food is small and dense

• Large hatchlings better if food is large and less dense

What are some selections for larger hatchings in streams?

• Longer embryonic periods

• Greater total embryo mortality

• Embryo hiding and guarding

T/F Biparental guarding is common in salamanders?

False

It is usually the female who guards eggs

What are 4 proposed hypotheses for plethodontid lung loss?

1. Adaptations to fast-flowing stream habitat in Appalacchia

2. Decreased head size of ancestors

3. Terrestrial mating

4. Hypobranchial apparatus function

Why is aquatic mating metabolically expensive?

Migration and interruption in mating to breathe.

What is the function of the hypobranchial apparatus?

Buccal pump for lung ventilation, buccal suction for gape and suck prey capture, protrusion of tongue for prey capture.

Loss of lungs negates lung ventilation = evolution of a more efficient feeding apparatus.