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Evolutionary Trends in Herpitology

Phoebe Hills zoology English

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Heterochrony
- A change in the relative timing of development stages in the course of phylogeny
- Arose early in the evolutionary history of amphibians
- Paedomorphosis
  - Neoteny
    - gonadal development normal, but without metamorphisis
  - Progenesis
    - Gonadal development accelerated, somatic development normal but arrested early
  - Origin of all modern Amphibs?
    - Temnospondyls
      - 340-110mya
      - Best known early tetrapod
      - Lissamphibia
      - Pedicellate teeth
        Juvenilles and adult forms of modern adults
        Not rigid
      - Evidence
        Small size of all modern amphibs
        Reduced skull bones
        Relatively large orbits of modern amphibs
        Tooth form
        Trends within Temnospondyls = similar in modern amphibs
- Direct development
  - Acceleration of developmental programme resulting in lack of larval stage
- Morphogical diversity
  - Differences in body shape arise from arresting development of specific body parts at different stages
- Salamanders
  - Common in salamanders
  - Neoteny
    - Obligate Neoteny
      - Axolotl
        Gills
        Lidless eyes
        Lab subject
        Gene expression
        Neurobiology
        Limb/organ regeneration
      - Proteidae
    - Faculatative neoteny
      - Hynobiidae
    - Associated with
      - Cave
      - Arid surface condition
      - Elevated speciation and extinction rates
      - Bonnet et al. 2014
  - Plethodontidae
    - Most diverse in size and body form
    - Biphasic
      - Spelerpini
      - Primitive
        Eggs in water, hatch into free-living aquatic larvae
    - Direct development
      - Courtship, mating and oviposition occur on land
        Terrestrial egg hatches into fully formed adult
      - Tropical species
        Bolitoglossa compacta
      - Correlated with
        Larger eggs
        Longer development time
        Altered pattern in organ formation
        Results in
        Loss of larval constraints
        Gain morphological diversity
    - Paedomorphisis
      - Bolitoglossa occidentalis
        Lungless
        Cirri (males)
        Associated with NASOLABIAL grooves
        Chemoreception
        Arrested digit development
        Aboreal feature
    - Well-developed tail
      - Fat storage
      - Prehensile
      - AUTOTOMY
      - Grows throughout life
        Post-sacral vertebrae
  - Difference in point at which SOMATIC development is arrested leads to different shapes among species
    - Also termed HETEROPLASY
      - Changes in the relative growths of organs or parts or parts of organs in ONTOGENY
- Issues with phylogeny
  - Distinguishing between Paedomorphic traits and shared traits
  - Salamanders lack many post-metamorphic S.D.C
Loss of
- Lungs
  - Species
    - Salamanders
      - 2spp ONCHYODACTYLUS
      - All Plethodontidae
        Ancestral habitats thought to be cold mountain streams
        Lungs produce unwanted buoyancy
        Questioned
        High O2 content allows cutaneous gas exchange
        Questioned
        Reduction in head width reduces effectiveness of buccal-pharyngeal pump
        Projecting the tongue for prey capture involves the HYOID
        Maybe linked with increasing terrestriallity
      - REDUCED in 1spp of;
        Ranadon
        Salamandrina
        Chioglossa
    - Frogs
      - 1spp Lungless
        Bornean flat-headed frog
      - Reduced
        Telmatobius
    - Caecilians
      - Typhlonectidae
        No pulmonary circulation
        Sealed nares
        Skull more mobile
        Increased gape
      - Wilkinson et al. 2014
      - Caecilita iwokramae
        Smallest
        Modifications to soft tissue only
        Lack of open external nares and covered internal nares
        No pulmonary circulation evident
        Tongue highly vascularized
        Not lungless (2014)
        Microcacecilia
- Limbs
  - Reduction in squamates
    - Whole lineages
      - Pygopodidae
      - Amphisbaenia
      - Dibamidae
    - Within linages
      - Scincidae
      - Anguidae
      - Occurs in all but 6 families
        42% do not show body elongation
        Extreme reduction occurs in elongated taxa
        Fossorial lifestyle
    - Evolution of limbless elongated body forms
      - Suite of other phenotypic changes
        Decrease body thickness
        Increase body length
        Presacral in snakes
        Tail length in lizards
      - Switch from AMBULATORY to UNDULATORY
        Implying elongation occurred first
      - Correlation between substantial elongation and limb reduction probably dictated by mechanical restraints
    - Ecomorphs
      - Snake-like
      - Lizard-like
      - Long-tailed surface dwellers
      - Short-tailed burrowers
  - Locomotion
    - Ambulatory
    - Undulatory
    - Concentina
    - Hydrostatic
      - Elaborate musculature
        Helix of connective tissue in skin
        form hydrostatic skeleton around viscera
      - Posture and forward force production
Sex determination
- Males and females are determined by diverse mechanisms
  - Evolve rapidly
- Sex differentiation
  - Gonads develop into testes or overies
  - Genes controlling this are highly conserved
- Sex DETERMINATION
  - Mechanisms that trigger the genes involved in sex determination
  - Reptiles have a large variable system
  - Heterogamy
    - Sex determined phenotype
      - E.g xy
    - Birds, snakes; Females
  - Heteromorphy
    - Chromosomes differ in size, centromere position ETC
    - Vipers, colubrids, chickens
    - Homomorphic
      - Primitive condition
      - Ratites & boas
- Evolutionary background: Fish
  - Not normally heteromorphic
  - sex genes over several chromosomes
    - Hermaphroditism
    - Sex reversal
      - Environmental cues
- Genetic sex determination; GSD
  - Implies sex of individual is fixed at fertilisation
  - Species
    - Amphibians
      - ZZ-ZW OR XX-XY
      - Variable Homogamy/heterogamy
    - Snek
      - ZZ-ZW & ZZ-ZZW, ZZ-ZWW
      - Female herogamy
      - Exception: boids
        Not heteromorphic
        But no ZW
        Patterns in faculatative PARTHENOGENIC offspring
        ZW spp produce only ZZ males
        XY spp produce only xx females
        But PARTHENOGENESIS in boids produces females
        Colour morphs not consistant with ZW system
        Likely XY
    - Few turtles
      - ZZ-ZW
      - Female heterogamy
      - Heteromorphy variable
    - Some lizards
      - ZZ-ZW OR XX-XY
        XX-XXY
    - Birds
      - ZZ-ZW
      - Female heterogamy, heteromorphic
    - Mammals
      - XX-XY
      - Male heterogamy, heteromorphic
- Environmental/temperature sex determination
  - Species
    - Crocs
    - Some chameleons
    - Most turtles
    - Tuatara
    - Dinosaurs
      - Climatic change in the wake of asteroid
        Only males produced
        Extinction
  - Types
    - Extremes (high/low)
    - Intermediate
      - Both sexes at all ranges
  - Temperature sensitive period (TSP)
    - temperature acts only at a specific stage in development
      - Embryonic stage 13-14 in Crocs
      - 29-31 in lizards
  - Pivotal Temperature
    - Temp at which 50% brood are male and 50% are female
      - as narrow as 1degrees celcius
  - Advantages
    - Fitness higher at extremes
    - Sex that develops at the higher temp = fitter
      - Larger size
      - Females in turtles
        Fecundity
      - Males in agonist spp
        Agamids
  - Molecular Mechanisms
    - Aromatase
      - Cytochrome P450
      - Oxidizes testosterone into oestrogen
      - During TSP levels are regulated by environment
        Methylation of promoter
        Demethylation at female temps
  - Ecological consequences
    - Timing and position of the nest is important
    - Sea turtles; depth is carefully chosen
      - Loggerhead = 94% females over 3 years
        Skewed sex ration
        Polygyny = 1 male to multiple females
    - Alligators; Levees warm = male. Swamps (cooler) = females.
    - GSD =1:1
    - Climate change
      - At risk
        Narrower and/or lower TSP
        Male bias at higher temps
        Tuatara
Senses and Communication
- Electromagnetic radiation
  - Radiation reception (Vision)
    - UV-Infrared
    - Effective over short/moderate distances
    - Mostly diurnal spp
      - Agamids and iguanids 320nm
      - Lacertids discriminate colours different only in UV light
    - Influenced by ambient conditions
    - Photoreceptors
      - Rods (Rhodopsin)
        Broad spectrum sensitivity
        Light levels
        Black and white vision
        Low spatial acuity
      - Cones
        Narrow range
        Several each with peak sensitivity at specific nm
        Colour vision via colour mixing
        PHOTOTRANSDUCTION
        Occurs in outer segment begining with the absorption of incident light by visual pigment molecules
        Ellipsoid packed with mitochondria
        Also helps focus light onto receptors
        May contain oil droplet with or without colour pigments
        Single, double or triple
    - Some amphibs and reptiles have colour vision
      - Tetrachromatic
        Dependent on visual signals
    - Anolis
      - diurnal high-acuity
      - Two-fovea
        Raptors
        1 for binocular vision
      - Retina is all cones; double large & small single
      - Visual displays are both static and dynamic
        Dewlap; Hyoid
        headbobs
        Sensitive to jerky movements
    - Nocturnal reptiles
      - Helmeted geckos; distinguish between blue and grey in very low light
      - Relatively larger eyes
      - Sacrifice spatial and temporal resolution for sensitivity
        Eye shine
        Tapetum lucidum
        Crocs and tree boas
      - Large cones adapated for sensitivity
      - Perceive colours in dim moonlight
      - Highly mobile pupil& multifocal eyes
        Snake eyes are unique
        No cillary muscles
        Achieves focus by moving lens directly
        Spectical protects eye
        Refractive contribution by spectical is almost equal to the lens
        Makes up for lack of cornea
    - Tuatara unique median eye
      - Pineal complex
        Circadium rythems
        Hormone production
        Can be light sensitive
  - Via pits
  - Infrared detecting pits
    - Pit vipers
      - Double chambered
    - Pythons
      - SIngle chambered
        FUNDUS
      - Associated with lips
- Sound
  - Tympanic middle ear
    - Developed in 5 major tetrapod groups
      - Anurans
      - Turtles
      - Lepidosaurs
      - Archosaurs
      - Mammals
    - Arose in the TRIASSIC
      - Coincides with sound-producing insects
    - Transforms sound energy in air to fluid motionin
      - Inner ear
      - Then to nerve cells via hair cells
    - Ear drums connected through mouth cavity
      - Direction hearing
    - Supported by the quadrate bone
      - Birds and reptiles
  - Hearing loss
    - Iguanas
    - Chameleons
      - lacks external tympanum
        Associated with jaw alterations for food capture
    - Snakes
      - Loss of tympanic membrane
        Almost complete loss of the cavity too
        Stapes embedded in mesenchyme
        Connected to jaw apperatus
        Quadrate
      - Groundborne vibrations
        Low sensitivity
        Low frequency
        Can pick up vibrations with skin on belly
        Somatic hearing
    - Sphenodon
      - Lacks tympanum
      - Middle ear cavity filled with loose tissue
        Adipose
      - Also in sea turtles
        Linked to need to reduce air-filled space
    - Caudates & caecilians
      - Retention of primitive/ancestral trait
        Or secondary loss
      - Anurans
        Lost and re-evolved middle ear many times
        Gardiner's tree frog
        Sechellophryne gardineri
        No middle ear with ear drum
        Can still croak
        Hear others
        Using mouth cavity to transmit sound to the inner ear
        Acts as resonator
        Inner ear
        Two organs
        Unique
        Amphibian papilla
        Low frequency
        More hair cells
        Basilar papilla
        High frequency
        Simpler structure
        One is tuned into mating call frequencies
        8th nerve transmits to brain
        Patches of epithelium covered with hair cells
        Separated by the rest of the inner ear by thin membranes
  - Production in
    - Anurans
      - Lungs compressed, mouth & nostrils closed
        Air flows over vocal cords into vocal sac
        Air can be pumped back and forth
        Vocal sac can be single/paired, internal or external
      - Highly repititous
      - Larger frogs (Bullfrogs) have deeper calls than smaller arboreal species
      - ADEVERTISEMENT CALLS
        Males
        Mating
        Territorial
        Low groan
      - DISTRESS CALLS
        Males and females
        Made when being attacked
        V. dramatic
        High-pitched scream
        Startle behaviour
      - WARNING CALLS
        Males and females
        Startled or disturbed
      - RELEASE CALLS
        Males and unreceptive females
        Grabbed by another searching for a mate
      - RESPONSE CALLS
        Females (some spp)
      - SPECIES RECOGNITION
        Males
      - Males and females have vocal cords
        Males better developed larynx
      - ULTRASOUND
        Hole-in the head frog
        up to 38KHz
        Both ultrasonic and within human hearing
        Habitat; streams and foaming rapids
        Concave-eared torrent frog
        Open and close "Eustachian tubes"
        Higher frequency when closed
  - Crocodilians
    - Rely heavily on hearing
      - Hunting
      - Communication
        Distress
        Aggressive behaviour
        Reception of underwater sounds = social communication
    - Unique
      - Tympanic membranes are concealed by flat flaps
        Raised or lowered by muscles
      - Complex bony air-filled passages
      - Branching EUSTACHIAN tube
    - Whole ear is less developed in aquatic spp
    - Auditory canal continuous from one side of the head to the other
      - Pinpoint orientation of prey
    - High development of middle and inner ears
      - Indicates effectiveness over wide range of frequencies
    - APICAL PITS
      - Scales, face & body
      - Sensitive to vibrations in water
- Chemoreception
  - Olfactory and taste
    - Taste receptors in tongue
      - Exc. snakes and aranids; kerintanised
  - Gustation
  - Vomeronasal system
    - Snakes
    - Accessory olfactory organ in squamates
      - Receive particles from tongue
    - Distance unreliable
      - Works at night
    - Types of flicks
      - Simple downwards extention
        Rapid pick up of nonvolitile chemical stimuli
      - Multiple oscillations
        Collection of odorants
    - Chemicals dissolved in liquid
      - Harderian gland
  - Nasal olfactory system
  - Caecilians
    - Subfossorial
      - Chemical communication important
    - Tenticle
      - Moved by eye muscles and lubricated by eye gunk
      - Paired sensory structure
      - Emerge from cavity between eye and nostril
      - Derived from tear duct
      - Connected to VNO
  - Scent glands
    - Lizards
      - Femoral pores
        Secrete waxy substance
        Lipids and proteins
      - Information on sex, identitiy & kinship
      - Larger in males
    - Snakes
      - Skin and anal
      - Female sex attractants present in dorsal skin
      - Anal glands at base in tail (both)
        Female larger
        Muscular sphincter for Q. release
        Defensive
        Also may play a role in intraspecific alarm pheromones
    - Turtles
      - Musk
        Rathke's gland
      - 4 glands in limb axis
        Axillary
        Inguinal
      - Small amounts, foul smelling liquid
      - Courtship, alarm, predator deterrence, anti-microbial?
- Mechanoreception
  - Lateral line systems
    - Amphibians
      - All larvae
      - Some fully aquatic adults
    - Hair cells produce receptor potential
      - In proportion to amount of stimulus
      - Unique to vertebrates
      - Two types of cilia
      - Bending causes bending of cell membrane
        Leads to opening and closing ion channels
        Appear gated
    - Direction can be detected
  - Tentacled Snake
    - Erpeton tentaculatum
    - No lateral line
    - Habitat
      - Murky lakes
      - Slow moving rivers
      - Fully aquatic
    - Mechanosensory & visual info integrated in OPTIC TECTUM
      - Adopt J shape and startle fish into mouth
  - Saharan sand vipers also rely on vibration and some sand-dwelling skinks

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Description: Zoology with animal behaviour degree--- herpitology module; evolutionary trends
Created by: Phoebe Hills · May 2018
Updated: May 12, 2018
Views: 2
Tags: herpitology evolution trends degreelevel
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Evolutionary Trends in Herpitology

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