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.

WALLACE RESOURCE LIBRARYLecture 07 – Mexican Herpetofauna and

Adaptation

Lecture overview

• Herpetofauna• Amphibians• Reptiles• Survey methods for Herpetofauna• Adaptations• Adaptation activity

Two types of herpetofauna

Reptiles– Lizards and snakes– Crocodiles– Turtles, tortoises and terrapins

• Amphibians– Salamanders (tailed)– Caecilians– Frogs and toads (without tail)

Herpetofauna of the Yucatan• 188 species of amphibians and reptiles known or presumed to

occur in the Yucatán Peninsula

Group Families Genera SpeciesCaecillians 1 2 2Salamanders 1 2 6Frogs and Toads 7 15 36Crocodiles 1 1 2Turtles 6 13 16Lizards 11 23 52Snakes 6 48 74Total 33 104 188

Amphibians• Salamanders, caecilians, frogs and toads

– Wet, thin skin, some produce toxins.

– Developed legs (except caecilians)

– Some have webbed feet

– Adults are carnivorous

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

Reptiles

• Snakes, lizards, turtles, crocodiles– Tough, scaly skin

– Heart divided into more chambers than amphibians

– Oviparous reproduction

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.

Snakes

• Snakes can be classified into four main groups based on the structure of their teeth

– Aglyph– Opisthoglyph– Proteroglyph– Solenoglyph

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

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

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

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)

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

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

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

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

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

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)

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

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

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

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.

.

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

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’!

Herp QuizAdaptation Activity

Red –eyed Leaf FrogAgalychnis callidryas

Yucatan Banded GeckoColeonyx elegans

Milk snakeLampropeltis triangulum

Lecture overview

• Herpetofauna• Amphibians• Reptiles• Survey methods for Herpetofauna• Adaptations• Adaptation activity