7. Reptile communication Flashcards
What are the physical limits of reptile hearing?
Only one middle ear bone (columella)
Hear less well at higher frequencies than mammals
What did Reber et al (bearded dragon laser vibrometry study) show?
Columella is visible in tympanum and dampens it at higher frequencies (sweet spot at 1.44 kHz, mechanical limit at 14.33 kHz)
Tympanum can vibrate at actual frequencies, columella cannot
What makes crocodilian hearing different?
They have a partially cartilaginous columella which absorbs more vibrations (might hear a bit better)
What is known about tuataran communication?
(One living species)
No external ear and “hard to compare” middle ear
Highest sensitivity of ear (cochlear potential) to 200-400 Hz (corresponds to frequencies of their screeching “cries”)
How do squamata (lizards, snakes) communicate?
(Ca 11.000 living species)
Wide variety of communication systems
- Head bobbing, waving, postures
- Pheromones
- Colour changes
Vocal communication is rather an exception
What distinguishes chameleon vocalisation and hearing from other squamates?
They have a bony airborne sound receiver
Might use muscles in gular pouch to produce bio tremors (thereby sound)
What distinguishes gecko communication from other squamates?
geckos - oldest squamates - are very vocal
Specific call patterns and species vocal recognition (no cross-breeding)
Can flexibly adjust their signals in loud background noise:
- increase duration of brief call notes
- do NOT adjust amplitude of their call syllables
- Produce more high-amplitude syllable types from their repertoire
What makes the weeping lizard (Liolaemus chiliensis) unique?
Re-evolved vocal communication with harmonic distress calls (possibly due to closed vegetation habitats which could restrict vision)
What does head bobbing in lizards signify?
Head bobbing: fast “nodding” with specific pattern
- Territorial defence and courtship
- Sequence can indicate species and male quality
- Syntactic rules (more aggression towards robotic lizard that violated syntactic rules)
- no evidence for lizards “signal matching” a robot
How do serpents (within Squamata) communicate?
Compound bone instead of external ear - can still hear
No vocalisations except hissing —> unlikely to have intra-species vocal communication
Relies on pheromonal communication
Visual and tactile communication during competition and mating
Why do rattle-snakes rattle?
Inter-specific communication
During behavior: head and tail off the ground
Warning: don’t step on me
Voluntarily frequency control based on proximity
- habituate to external disturbance over time
- increase frequency when approached
- if human is fairly close, the 40Hz abruptly increase to 60-100Hz
- Experiments with human subjects -> the increase caused the sensation that the snake is closer than it is
How do turtles communicate?
Freshwater and sea turtles:
- females (in proximity to nest) and hatchlings (in nest) vocalise —> parental care suggested
No experimental evidence
- “11 call types”, yet no context specificity found
Tortoises:
- male mounting calls (amplitude and frequency modulation, might indicate male quality)
- # of mounting success of males correlates positively with number of mount calls, but negatively with their duration
- females prefer mounting calls with shorter duration, higher pitch and higher call rate
- Higher call rates in males correlates strongly with hematocrit values, ex) percentage of red blood cells in total blood volume
What are crocodylian brains like?
Avian-like, small compared to other reptiles and mammals
Relatively low neuron no.
Bigger neurons with larger body size, but not larger number
How are bird and mammal brains different in terms of executive function/behavioural control?
Mammals - prefrontal cortex
Birds - nidopallium caudolaterale (NCL) (tiny but present in crocodylians) (size varies in birds)
Structure is not homologous, function is
Why are crocodylians an intermediate model group?
Avian brain
Mammalian vocal tract (larynx, no syrinx)
How can crocodylians communicate through olfactory signals?
Mandibular glands (courtship?)
Paracloacal glands (territory?)
Dorsal integumentary glands (mother-offspring?)
How do crocodilians communicate through gestures?
In water:
- Dominant has back + neck out of water
- Subordinate only has head above
On land:
- Dominant has back high, snout low
- Subordinate is all low, horizontal head
Threat - open mouth
Submission - snout high, mouth closed
How do crocodilians communicate vocally?
Huge difference between groups, but highly conserved (particularly in early ontogeny)
- Alligators are most vocal, crocodiles and Tomistoma are least
- Pre-hatching calls (up to five days before)(synchronizes hatching?, alerts mothers that starts excavating nest)
- Contact calls (spontaneously produced chirps) (hatchlings and juveniles when approaching or being approached by conspecific, or during group foraging)
*Distress calls (louder, steeper frequency modulation)(hatchlings and juveniles when threatened/grabbed, scaling with size)(elicit protection by parents)
*Belloing (alligators) and roaring (crocodiles) (both sexes, mostly during breeding, contagious, with visual display
- bellowing advertising body size, larger individuals preferred as mates
Universality in crocodilian communication behavior - calls elicit same response in different species
What did Reber et al (2015, 2017) show about crocodilian vocalisation?
Recorded bellows and measured head length and total length
Formants in crocodilian bellows and alligators
- First evidence of formants in non-avian reptile
- Honest cues to size in crocodiles and birds = probably also in dinosaurs
- selection for low formants
What are the applications of crocodylian communication for conservation
Passive acoustic monitoring (with algorithm) - can count sexually reproductive animals
Better estimate of effective population size than previous estimation method (eye-shine survey)
What is unique about the indian gharial?
Harems, males essential for offspring survival (prestige as “good father”)
Selection pressure to evolve individuality cues?
POP signals (not possible without a ghana)
Identifying formants: Heliox approach
Heliox lighter that air, speed of sound increased —> source signal (F0) remains the same, formants change
Experiment:
- Chinese alligator quarantined, recording her own calls, playing them back —> bellow stimulation
Setup: box with water and air supply.
- did recordings in air and Heliox
Result: saw shift in high energy frequency bands, F0 remained same and formants changed
