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WALLACE RESOURCE LIBRARYLecture 07 – Mexican Herpetofauna and
Adaptation
This is an ‘example’ of a lecture that is given to A level students as part of their academic lecture series whilst on their expedition.It has been produced for the exclusive use of the lecturer conducting the series and is solely intended for educational purposes.Most of the material comes from Operation Wallacea sources and any other material that has been used has been credited (as far as is possible) to the appropriate author wherever possible.
This lecture is only to be used for EDUCATIONAL purposes.
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WALLACE RESOURCE LIBRARYLecture 07 – Mexican Herpetofauna and
Adaptation
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Lecture overview
• Herpetofauna• Amphibians• Reptiles• Survey methods for Herpetofauna• Adaptations• Adaptation activity
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Two types of herpetofauna
Reptiles– Lizards and snakes– Crocodiles– Turtles, tortoises and terrapins
• Amphibians– Salamanders (tailed)– Caecilians– Frogs and toads (without tail)
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Herpetofauna of the Yucatan• 188 species of amphibians and reptiles known or presumed to
occur in the Yucatán Peninsula
Group Families Genera Species
Caecillians 1 2 2
Salamanders 1 2 6
Frogs and Toads 7 15 36
Crocodiles 1 1 2
Turtles 6 13 16
Lizards 11 23 52
Snakes 6 48 74
Total 33 104 188
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Amphibians• Salamanders, caecilians, frogs and toads
– Wet, thin skin, some produce toxins.
– Developed legs (except caecilians)
– Some have webbed feet
– Adults are carnivorous
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Amphibians of Calakmul
Red-eyed treefrog
17 species of frogs and toads
Of which 8 are treefrogs
Mexican Salamander
2 species of Salamander
Mexican Caecillian
1 species of Caecillian known in Yucatan – not known if at Calakmul
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Reptiles
• Snakes, lizards, turtles, crocodiles– Tough, scaly skin
– Heart divided into more chambers than amphibians
– Oviparous reproduction
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Snakes• Snakes can sense other animals approaching through
detecting faint vibrations in the air and on the ground
• Prey are killed by constriction or venom
• Snake venom is modified saliva called Zootoxin
• Most snakes can be placed into one of four groups.
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Snakes
• Snakes can be classified into four main groups based on the structure of their teeth
– Aglyph– Opisthoglyph– Proteroglyph– Solenoglyph
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Snakes
Aglyphous snakes• These snakes do not have fangs with a
grooved channel which is necessary to transport venom
• They tend to have many teeth of relatively similar shape and size
• Some have lost theirvenom apparatusand fangs
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SnakesOpisthoglyphous snakes
• ‘Rear-fanged’ group• Fangs at the back of the mouth that
are grooved to channel venom into the puncture
• The snake must move the prey to the back of the mouth to envenomate
• Most venom is too weak to affect humans, the boomslang and the twig snake are two notable exceptions
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SnakesProteroglyphous snakes
• Known as ‘front-fanged’ snakes• Short jaw bones with few teeth
except for the front fangs which are still small
• The fangs point downwards and are completely folded around the venom channel to form a hollow needle
• Most toxic venom, neurotoxic• Classic example is the cobra
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SnakesSolenoglyphous snakes
• ‘Piped grooved’ long hollow fangs
• The snake can control the fangs, keeping them folded against the roof of the mouth
• The fangs swing into a biting position when the jaw is opened
• They can then stab their prey and inject large quantities of venom
• Seen in vipers and adders e.g.The Mexican jumping viper (Atropoides mumifer)
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Snakes
Different venoms attack different biological systems:
• Cytotoxic – attack cells e.g.– Myotoxin – damage muscle cells– Haemotoxin – damage red blood cells
• Neurotoxic– Attack the nervous system causing paralysis
leading to respiratory and heart failure
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Lizards
• Large and widespread group with close to 3800 species worldwide
• Ecologically successful due to efficient predation techniques
• Lizards typically have limbs and external ears, while snakes lack both these characteristics Dwarf Gecko
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Crocodiles• Two families:
– Crocodilidae – ‘true’ crocodiles and gharial
– Alligatoridae – alligators and caiman
• Large predatory carnivores
• Inhabit shores of lakes & rivers
• Remains found in Mayan ruin sites
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Tortoises and Turtles
• Turtles, tortoises and terrapins belong to the order – Testudines• Charatcterised by a special bony or cartilaginous shell developed
from their ribs• Some are terrestrial and some aquatic
Furrowed Wood Turtle Rhinoclemmys areolata)
Scorpion Mud Turtle Kinosternon scorpiodes
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Reptiles of CalakmulSnakes - 23 species
Lizards – 14 species
Crocodiles – 1 species
Turtles, Terrapins and Tortoises – 7 species
Slider Milk snakeMorelet’s Crocodile
Yucatan Banded Gecko
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Herpetofauna Survey Methods
Sampling can be active or passive
Transect surveys• Distance sampling• Fixed-width sampling
Trapping surveys• Active trapping (larger species)• Pitfall traps (smaller species)
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Fixed-width Searches
Pros• Good for both reptiles and amphibians• Can be used along transects or in specific areas (e.g. along
streams or around lakes) • Effort and time regulated searches of the undergrowth,
capturing any specimens found• Captures more cryptic species
Cons• Scares many away so capture rate
not necessarily high
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Pitfall traps
• Pros– Can be placed along transects or in
specific locations– Does not scare away animals like
active searching• Cons
– Labour intensive and not always successful
– Size of bucket influences species captured
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Concept of Adaptation
‘The adjustment or changes in behavior, physiology, and structure of an organism to become more suited to an
environment.’
• The word adaptation is normally reserved for inheritable genetic changes developed in a population over a long period of time.
• This is Evolution through Natural Selection
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Adaptations in Herps
Aposematism
• In latin apo = away and sematic = sign or meaning
• Some organisms are brightly coloured advertising that they are ‘nasty’ tasting or dangerous to be near as they can sting or bite.
.
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Types of MimicryBatesian mimicry• Mimic resembles a model that is
poisonous or unpleasant to eat• Mimic thus benefits because predators
have learned to avoid the model• Usually based on appearance, but also
calls, scents etc
Mullerian mimicry• Two or more equally poisonous or
distasteful species have a similar colour pattern
• Reinforces the warning each gives to predators
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Examples mimicry
Mimicry in coral snakes is complicated. There are a number of species of New World coral snakes belonging to two separate families, some poisonous (Elapidae) and some non-poisonous (Colubridae). Which is the poisonous one?
‘Red bordered by yellow – kills a fellow’!
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Herp QuizAdaptation Activity
Red –eyed Leaf FrogAgalychnis callidryas
Yucatan Banded GeckoColeonyx elegans
Milk snakeLampropeltis triangulum
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Lecture overview
• Herpetofauna• Amphibians• Reptiles• Survey methods for Herpetofauna• Adaptations• Adaptation activity