Amphibians: Reproduction & Parental Care

PART III

VERTEBRATE ZOOLOGY (VZ Lecture14 – Fall 2012 Althoff - reference PJH Chapter 10)

• Considerable variety/diversity among amphibians when it comes to modes of reproduction:

a) “behavioral lead-up”b) type of fertilization

• Several modes of parental care (or lack of it) a) within orders b) between orders

• Like some charactersitics/features already examined, this diversity/mix has likely served amphibians well the past 250 MY

In general….

• _____ species of amphibians lay eggs

• _____ that lay eggs deposit them in water…but some do on land

• As noted previously, some eggs hatch into _____ forms…others into miniatures of terrestrial adults

• _____ don’t offer any parental care

• Two major things impact monitoring/studying populations:

a) large annual fluctuations in productivity(lots of eggs laid but much variation in how many

survive to become adults)

b) local, annual variation in breeding habitat requires larger survey areas

In general….con’t

Caecilians

Global distribution of Caecilians

Caecilians

• Exhibit __________ fertilization

• Some lay eggs, coil up around the eggs until they hatch

• Some exhibit viviparity

• Some (~75%) exhibit ______________________

Phase I – growth of fetus initially achieved by yolk contained in the egg at time of fertilization….but yolk is exhausted before fetus fully develops (up to 9 fetus per female)

Phase II – balance of fetal growth achieved by ____________ feeding!

________________ Feeding

• Fetus develops specialized “__________________”

• Using embryonic teeth, individuals scrape the material lining the walls of the oviducts that by this time in is happening, the epithelium tissue has thickened, become highly vascularized, and starts to secrete a thick, white create substance referred to as _________________.

• “Biting” action probably stimulates further milk production

• Fetuses fairly evenly spaced out along oviduct evening out accessibility to growing fetuses

______ that is basically non-functional

Fetal caecilian – in utero

_____________

Salamanders – gamete exchange

• Some achieve fertilization externally

• Most, however, exhibit internal fertilizationby transfer of packet of sperm

__________________ = sperm on a gelatinous base

Red-spotted newtDusky salamander Two-lined

salamander

Fig. 10-14, p237 PJH

Species-specific spermatophores showing sperm caps

Salamanders – marking & pheromones

• Evident in terrestrial species

• Males may “mark” females….involves directphysical contact

• Male has specialized “courtship glands”….known as _________ glands…..applies secretion to a) her nostrils or

b) her body

• Some species, males have large gland under chin known as _________ gland….applies secretion to her nostrils with slapping motion

• Variations off of these two methods…

der

mis

epidermis

Fig. 10-15ab, p237 PJH

Rough skinned newt

Jordan’ssalamander

chin on snout

the “tail walk”

Fig. 10-15ab, p237 PJH

Two-lined salamander

Smooth newt

male usestooth to “scrape”

pheromone

male wafts pheromones toward female with tail

male deposits on female, then holding her with tail or jaws uses feet to insert spermatophore into her cloaca

female deposits egg sac on top of spermatophore

female picks off sperm cap with cloaca

Among salamanders…3 ways theyget eggs and sperm together

(only one way used per species)

Vernal Pools – Breeding Locations for Some Salamander & Frog Species

• Temporary wetlands

• Pools, because they dry out periodically, do ____ support breeding populations of fishes (thus, no predation/consumption of egg masses & larvae)

• Typically in woodland ecosystem types

• Some species are considered _______________ _____ species – a part of their life cycle must take place in such a pool

ex. mole salamanders wood frogs

• Lots of breeding takes place, lots of egg laying takes place in the vernal pools

Vernal pools - signs of breeding activity

blue spotted salamander egg masses

spottedsalamander egg mass

Vernal Pools – Breeding Evidence

• ___________________

• Spermatophores

• Egg masses

• Larvae

SOME USE _______ BASIN of A VERNAL POOLMarbled salamander with eggs. The marbledsalamander lays its eggs in the fall in the dried basinof the vernal pool. The female remains with the eggs which hatch when the pool fills in the fall.

SOME DO NOT USE A VERNAL POOL – Example would be red-backed salamander ( “ a non-vernalpool species)…it is not aquatic. Spends its entire life on the forest floor = ______________________

•Lays eggs in small nest•Nest under logs and forest litter

Finally…on salamander reproduction

• Some give birth to young (rare)

most that do thisyoung not fully developed, don’t look like adults

“really different”: alpine salamander give birth to “fully” developed young… apparently same ____________________ nourishment as described for some caecilians

Anurans

• Vocalizations, not pheromones, play large role in reproductive behavior…specifically attracting mates

• Two basic mating systems:1) ______________ – short-time period

(few days)vs.

2) _____________ –extend period (fewmonths)

_____________ Breeding Mating System

• Many toad species, few frog species do this• Often involves the vernal pool scenario—

response to temporary aquatic habitat availability• Males & females usually present in equal

numbers….and lots of them• Both sexes tend to arrival at breeding sites (i.e.,

vernal pools) at same time• Males have to out compete other males for

breeding opportunity by out-positioning, etc.

_____________ Breeding Mating System

• Most frog species• Males arrive first to the area and establish

territories…..some species, the males arrive at breeding calling site at night and return to a daytime retreat

• Few females come each day to breed• Few males do MOST of the breeding• Vocalizations seem to be critical to attracting

females, breeding females

Vocalizations

• Risk: can attract predators…but some evidence that, at least in vernal pools, likelihood of being “the” predated one is less than if in smaller groups or isolated…so large volume of calling attracts female

• Calling is energetically costly…a) call louder, takes more energyb) call more often, takes more energy

Fig. 10-18, p242 PJH - gray tree frogs

Calling rate, calls/hour

VO

2 w

hil

e ca

llin

g,

ml

O2/g

ram

/ho

ur ENERGETIC COST OF CALLING

Evidence for …_____________ hypothesis…

From gray tree frog studies….• Louder calling, longer calling by males

resulted in those males attracting more females

• Good gene hypothesis predicts that the characteristics of males that are favored by females identify ___________________ males

Anurans – gamete exchange

• Most exhibit _______________ fertilization

• For those that exhibit internal fertilization, male has his own extension of the cloaca that allows him to introduce sperm into the cloaca of the female

• Typical ‘coupling’….Male mounts female, uses his fore legs

to clasp either in her pectoral region or pelvic region. He hangs on for several hours, maybe days until she lays her eggs at which time he fertilizes them.

Anurans….reproduction continued

• Viviparity is rare…usually eggs left to develop on their own…but exceptions

• Adults may guard eggs, sometimes even males• Some sit beside eggs, some sit over eggs• Some guard post-hatching forms• Posion dart frogs deposit eggs on ground and

stay nearby until hatched—visually deterring predation of eggs

• Some carry their tadpoles• Lot more variations….

Fig. 10-21, p237 PJH

Wood frogs are an amphibian species of uplandforests. They venture to vernal pools in earlyspring, lay their eggs, and return to the moist woodland for the remainder of the year. The tadpoles develop in the pool and eventuallyfollow the adults to adjacent uplands. Thepresence of evidence of breeding by wood frogs (chorusing or mating adults, egg masses or tadpoles) indicates that a pool is a vernal pool

Example of “cycle”

Some Australian frog genera….

• Swallow eggs or newly hatched• Two “areas” develop in stomach….one portion

has reduction/cessation of HCl secretions, other retains normal “digestive” function—at least for one of species this has been discovered in, other species doesn’t do exactly same thing

• Young remain there through metamorphsis• Just another illustration of diversity in

approaches to reproduction—in this care post breeding strategies to ensuring perpetuation of the species