Presentation on theme: "Amphibians: Reproduction & Parental Care PART III VERTEBRATE ZOOLOGY (VZ Lecture14 – Fall 2012 Althoff - reference PJH Chapter 10)"— Presentation transcript:
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
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 fertilization by transfer of packet of sperm __________________ = sperm on a gelatinous base
Salamanders – marking & pheromones Evident in terrestrial species Males may “mark” females….involves direct physical 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…
Fig ab, p237 PJH Rough skinned newt Jordan’s salamander chin on snout the “tail walk”
Fig ab, p237 PJH Two-lined salamander Smooth newt male uses tooth 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 they get 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 spotted salamander egg mass
SOME USE _______ BASIN of A VERNAL POOL Marbled salamander with eggs. The marbled salamander lays its eggs in the fall in the dried basin of 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-vernal pool 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 this young 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 (few months)
_____________ 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 energy b) call more often, takes more energy
Fig , p242 PJH - gray tree frogs Calling rate, calls/hour V O 2 while calling, ml O 2 /gram/hour 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 , p237 PJH
Wood frogs are an amphibian species of upland forests. They venture to vernal pools in early spring, lay their eggs, and return to the moist woodland for the remainder of the year. The tadpoles develop in the pool and eventually follow the adults to adjacent uplands. The presence 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