Transcript reproductive strategies - The Federal University of Agriculture

COURSE CODE: FWM 312
COURSE TITLE: HERPETOLOGY:
AMPHIBIANS
NUMBER OF UNIT: 2 UNITS
COURSE DURATION: TWO HOURS PER WEEK
DEPARTMENT OF FORESTRY AND WILDLIFE MANAGEMENT
COLLEGE OF ENVIRONMENTAL RESOURCES MANAGEMENT
UNIVERSITY OF AGRICULTURE, ABEOKUTA
COURSE COODINATOR: DR O.A. AKINTUNDE
E-mail:
[email protected]
Office Location: E 211, COLERM
OTHER LECTURERS: DR I.O.O. OSUNSINA
DR M. O. O. OYATOGUN
TAXONOMIC ARANGEEMNT OF LIVING AMPHIBIANS
Class Amphibian
Subclass
Lissamphibia
Order
Urodela (tailed amphibians:
Salamanders)
Family
Crytobranchidae (hellbenders)
Ambystomatidae (mole salamanders)
Salamandridae (newts)
Proteidae (mudpuppies and oims)
Plethodoritidae (lungless salamanders)
COURSE CONTENT
Classification and characteristics of
important West African reptiles. Anatomy,
physiology and reproduction of African
reptiles.
Food and feeding habits.
Distribution and economic importance.
COURSE REQUIREMENT
This is a compulsory course for all
students in Department of Forestry and
Wildlife Management. In view of this,
students are expected to participate in all
the course activities and have minimum of
75% attendance to be able to write the
final examination.
TAXONOMIC ARANGEEMNT OF LIVING AMPHIBIANS
Order Anura
(tailess amphibians: frogs and toads)
Ranidae Family Ramidae (true frogs)
Pipidae (aquatic frogs in Africa)
Bufonidae (true toads)
Pelobatidae (spadefoo toads)
Hylidae (tree frogs)
Rhacophoidae (Asian tree frogs)
Leptodactylidae (terrestrial, aquatic or
arboreal frogs)
Order
Apoda (legless amphibians:
(Caecilians)
General features
There are 4000 or ore amphibian species.
The 4000 amphibians are divided very unequally into
three orders. These are the Anura (the Sahelian), the
tailless amphibians or frogs and toads are by far the
largest group with some 3500 species, the Urodela (or
Caudata), tailed amphibians or newts and salamanders
with 350 species and Gymnophiona (Apoda), worm-like
burrowing Caeciallan with over 150 known species.
Common amphibians’ characteristics include shell-less
eggs and a naked ore or less permeable skin richly
endowed with secretory glands but without scales, fur or
feathers.
General features
Most amphibians therefore require high levels of
humidity, or a fully aquatic environment, in which
to live. Some can be found which have adapted
to condition as dry as the desert e.g. South
American leaf frog Phyllomedusa bicolor
produces a waxy secretion which spreads
genera of spade foot toads spends much of their
lives in damp burrows below ground in arid
habitats and desert frogs retire underground to
produce temporary, impermeable cocoons that
tide them over until rains come again.
General features
Fertilization may be internal or external but with
the exception of caecilans the others have no
proper intromissive organs and other methods of
sperm transfer are employed.
Despite their name, amphibians are amphibious
only in fresh or mildly saline water, no species
can survive prolonged exposure to sea-water.
Amphibians do not drink, but absorb the water
they need directly through their skins during
immersion in ponds or streams.
FOOD AND FEEDING
Amphibians are almost without exception
carnivorous in the adult state. Vegetables matter
is rarely found amphibian guts. Anything that is
small enough to be swallowed is likely to be
taken as prey, those capable of delivering a
deterrent bite or sting. The major prey items of
amphibians are invertebrates, especially insects,
crustaceans, worms and molluscs, but larger,
vertebrate organisms are sometimes taken by
the bigger species.
DEFENCE
Amphibians are poorly endowed with tooth and claw. More usual
adaptations include
Heavy reliance through cryptic coloration, or not being detected in
the first place.
Rapid flight by leaping or powerful swimming or both sometimes
accompanied by alarm calls.
Feigning death
Adoption of characteristics defence postures including the so
called ‘unken and reflex’. This is stationary display adopted by
anurans and urodeles bearing aposematic coloration, in an
attempt to show their warning signals to the best advantage.
Simple defence postures involve hyperinflation with air and body
tilting to present a larger-than life image to would be predators
such as snakes that can be influenced by their perception prey
size.
SENSORY SYSTEMS AND
LEARNING ABILITIES
Eyes are will developed in anurans and most urodeles
but degenerates in some salamanders and burrowing
caecilians. Vision is critical in prey capture for most
anurans and many urodeles and is particularly keen for
detecting movement. Although each species has its
particular optimum light intensity for visual acuity may
are especially adopt at low light levels.
Tadpoles and some adult amphibians especially highly
aquatic ones also have lateral line detector organs along
the sides of the trunk and on the head, similar to those
widely occurring in fish. They are sensitive to water
currents and play a role in breeding behaviour during
displays in which males create such currents and direct
them towards females by tail action.
REPRODUCTIVE STRATEGIES
In urodeles, fertilization is usually internal but
there are exceptions with males of the entire
aquatic Asiatic salamanders (hynobiidae), giant
salamanders (cryptobranchidae) shedding
sperm over eggs after they are deposited. Some
urodeles with internal fertilization lay their eggs
in water and the larvae develop in the same
medium e.g. European newts. Others lay their
eggs on land and the hatch into aquatic larvae
after flooding of the nest site e.g. ambystoma
species or may developed completely in the
nest without ever entering water e.g.
plethodontois Desmognathus aeneus.
REPRODUCTIVE STRATEGIES
Tiger salamander can produce more than 5, 000 eggs in
one season while others species lay just a few hundreds
eggs each year. At the other extreme, live bearing
terrestrial species e.g. salamandra atra produce one or
two young. Parental care also occurs among urodeles,
either sex of some fully aquatic salamanders attends to
the eggs and appears both to defend and oxygenate
them, and females of some species that ovipost in
terrestrial nests remain there until hatch time.
Commonest mode of anuran reproduction follows the
classic pattern of egg deposition and larval development
in lotic or lentic fresh waters, although there are
variations.
REPRODUCTIVE STRATEGIES
The deposition of eggs in the small water
volumes of tropical plants (bromelids)
Another is the production of eggs with
sufficient yolk to see the larvae through
the metamorphosis without any need to
feed.
Some lay egg on land which hatch into
larvae that fall or crawl into nearly
freshwater
REPRODUCTIVE STRATEGIES
Numerous tropical species make foam nests in which tadpoles
hatch either in trees overhanging water or on a bank next to it and
form which they gain access to the water for normal larval
development.
About 10% of known anurans species exhibit some form of care and
this can be performed by males or females such as the driving off of
potential avian predators some carry eggs or tadpoles around with
them.
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Pipa species, the eggs develop into tadpoles which implanted in the
mother’s back and then escape into the water.
Male European midwife toads carry eggs entwined around their legs
and release tadpoles into ponds when the eggs hatch
Some frogs carry tadpoles eggs in a dorsal pouch until hatch time.
Gastric brooding frogs (Rheobatrachus species) of Australia, the
eggs are swallowed by the female, tadpoles develop in her stomach
during an enforced fast and are finally regurgitated after
metamorphosis as fully formed frog lets
AMPHIBIANS AS HARBINGERS OF DOOM
Oven the past few years, amphibians have
attracted attention as subjects of study. The
prospect of a Global Amphibian Decline (GAD)
proposed at the First World Congress of
Herpetology held in Britain in 1989. Following a
crisis meeting in the United State in 1990, a
Declining Amphibian Task Force (DAPTF) was
set up in 1991 under the auspices of the
International Union for the conservation of
Nature and Natural Resources (IUCN) to
investigate the matter and recommended any
necessary action.
AMPHIBIANS AS HARBINGERS OF DOOM
The central hypothesis of GAD is that
amphibians are especially susceptible to
environmental change and should therefore
receive particular attention with respect to both
study and conservation. Two features of
amphibians biology have been widely cited as
underpinning this hypothesis; firstly, their
typically naked and permeable skins may make
them highly vulnerable to chemical pollutants
and radiation and secondly, the lifestyle of many
species requiring both aquatic and terrestrial
habitats to be maintained in suitable conditions.
Cause of global amphibian declines
AMPHIBIANS AS HARBINGERS OF DOOM
Simple causes – The tadpoles of frog are highly
susceptible to fish predation.
Disease – There can be little doubt that the
proximal cause of large-scale amphibian deaths
in several situations has been infection with
fungal, bacterial or viral pathogens. Diseases
are dramatic and their results are easily seen
when amphibian populations are large and
usually occur on this scale only under stressrelated circumstances that compromise immune
systems.
AMPHIBIANS AS HARBINGERS OF DOOM
Environmental deterioration – There are several ways in
which changes in the quality of their environment could
affect amphibians.
Pesticides constitute perhaps the best known e.g. DDT
and its breakdown product DDE are highly persistent.
Acidification of groundwater by atmospheric pollutants
especially sulfurs dioxide dissolving in rain.
Another problem receiving increasing attention is the
damage to catalytic chemical especially
chlorofluorocarbon (CFCs), released from industrial
processes resulting in ozone holes permitting greater
amounts of solar radiation especially highly energy
ultraviolet (UV) range to reach the earth’s surface.
SEXUAL SELECTION IN ANURANS
There are two important general mating system of
anurans
Male frogs and toads invariably grasp females in
an amplexus embrace which may last from
seconds to many weeks prior to oviposition.
Male anurans usually employ vocalization during
their breeding seasons
And there are three types of breeding behaviours
found among the anura.
SEXUAL SELECTION IN ANURANS
Explosive breeding with all reproduction
being completed in a fairly short time
period (often less than two weeks).
Species using this system often do so in
response to environmental cues such as
heavy rains in the tropics.
Protracted breeding, with activity spread
over several months.
SEXUAL SELECTION IN ANURANS
Protracted breed accompanied by male parent care.
Hundreds or thousands of adult toad descend upon their chosen
breeding ponds and engage in frantic bouts of mating and spawning
that continue day and might but which are often all over within a
couple of weeks. In typically explosive breeding pattern there is
furious scramble competition between males for females. Largest
females are the most fecund and only a small proportion (20%) of
males will obtain a female at all. Unpaired males toads constantly
search the area around the spawning site, both in the water and on
land, looking either for single females or perhaps for females
bearing small males that could be displayed. A high proportion (often
80-90%) of common toad females are amplexed before they reach
the water’s edge and substantial numbers are drowned by the
combined assaults of multiple males.