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Evolution of acoustic communication

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Laura May-Collado

on 15 January 2016

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Transcript of Evolution of acoustic communication

Evolution of acoustic communication in whales and their terrestrial relatives
Sound speed depends on water temperature, density, and depth
Because of the many advantages of using sound for communication many mammalian species have evolved acoustic signals that are:
Production mechanisms
Knowledge of acoustic structure poor
Duration Variable
Frequency range not fully known but probably most below 1kHz
Roars, snorts, grunts, bleats, squeals, chants, moaning, growls, hissing, wheeze-honk, screams, drumming, cries, clicks, bawls, mewing, chirps, mooing, wimps, bellow, sneeze, coughs, ‘ba’, ‘zer-zer’, barks, cheep calls, and tones among other even more specific descriptions.
A number of terrestrial species primarily rely on scent to communicate, but even these species emit acoustic signals for a variety of behaviors such as territoriality, courtship, warning, alarm, and long-distance communication.
Duration Variable
Variable contours
Air Sacs
Similar in acoustic structure but differ in sound production mechanisms
5 to up 75 kHz!
Simple contours
Social Context
< 5 kHz
Calls and Moans
A Phylogenetic Approach
Phylogenetic uncertainty: To test the dependence of our conclusions on the choice of phylogeny. Several proposed phylogenies.
Character correlations: To test the association between discrete characters of sociality and tonal sound complexity. SIMMAP 1.0 and MacClade
Character Optimization: To reconstruct the evolutionary history of tonal sounds and potential selective forces. Mesquite 1.12.
Independent Contrast: To test the relationship between tonal sound characteristics and selective forces e.i. body size, group size, etc. PDAP:PDTREE in Mesquite 1.12 (build h47).
Previous studies using standard statistical methods have found a strong negative relationship between body size (length) and tonal sound maximum/ minimum frequency.
Wang et al. 1995, n=9 spp, R2=0.93
Podos et al. 2002, n=17 spp, r=0.85
Body size is one of the most important morphological factors believed to influence animal signal frequency
Several social delphinids do not produce tonal sounds
Many toothed whales, whether social or ‘solitary’ produce tonal sounds
It was widely held that in communicative signals called whistles (high frequency modulated tonal sounds) evolved in association with ‘sociality’ because delphinids used them in a social context: ‘The dolphin hypothesis’ (Podos et al. 2002, Herman and Tavolga 1980)
To test ‘the dolphin hypothesis’ it was important to document if phylogenetic key ‘non-social’ toothed whales such as the boto dolphin (Inia geoffrensis) emitted or not whistles.
Their frequency range is greater than previously reported in other populations 5.30 to 48.10 kHz
The boto does whistle
The problem of broad concepts: ‘whistles’ and ‘sociality’ both represent a conglomerate of characters. The optimization of whistles and sociality will depend on the definitions chosen by any given author.
Relatively tonal sound high max and min frequencies appear derived in toothed whales. Particularly high mean max and min frequency evolved within ‘true dolphins’ (which are highly social)
(R-square = 9.7%, p- value = 0.03).
The evolutionary histories of sociality and tonal sounds are intertwined
Low frequency sounds travel longer distances: low frequency is associated with solitary species.
Group living species only need to communicate over short distances: high frequency is associated with social species.
There are a number of reasons that sound is such a popular way for animals to communicate.
SOFAR Channel
(Sound Fixing and Ranging)
Aquatic species rely more on sound for communication than their terrestrial relatives. The most studied communicative acoustic signals in these species are tonal sounds:
Cetartiodactyla (dolphins, whales, porpoises, deers, okapi, hippos, etc) shows great body size, habitat, and social structure diversity.
Species specific (in some species there are even family and individual specific signals).

Generally these signals are relatively less easily traced by predators.

Adaptable to various conditions (e.g., intensity, frequency, duration).
How did these acoustic signals evolve? What are the selective forces driving signal variation?



Combining molecules &
Passive Acoustics
Geographical Isolation
Morphological Constraints
Ecuador, Panama, Costa Rica, & databases from Atlantic Ocean
Body size and size of sound producing organs correlate.
Small bodies (small sound production organs) produce relatively high frequency sounds.
up to 97%
Matthews et al. 1999

(1) We expect low frequency signals in whales to be under selection because it enables long distance communication

(2) The degree to which whales have been able to respond to this selection through evolutionary history has been, at least in some cases, constrained by body size.

(3) There is no evidence, however, that body size has constrained the evolution of maximum frequency.
River dolphins
Beaked whales
Belugas and Narwhals
Solitary boto
Tucuxi dolphins are delphinids that emit whistles. For the most part of their distribution they live in sympatry with botos. Thus, finding a place where their distributions did not overlap was fundamental.
Both solitary and grouped animals whistled
Whistles could propagate as far as 3.3 km
Production rate was higher during resting activities
Communication: but in a different context keeping distance between animals instead of promoting group cohesion

This cladistic test rejects the simple ‘dolphin hypothesis’ that whistles evolved as an adaptation for social communication in dolphins.
Group size explains some of the variation in tonal sound minimum frequency and frequency modulation (complexity).
The level of social structure and tonal sound complexity are correlated: Solitary species tend to produce simple tonal sounds where as social species tend to produced more complex ones.
New Hypotheses
Golfo de San Jose
Patos Lagoon
Western North Atlantic, USA
Turneffe, Belize

Costa Rica

Corpus Christy
South Padre Is
Western North Atlantic
Gulf of Mexico: Galveston, Corpus Christy and South Padre Is.
Central America
Turneffe (Belize)
Manzanillo (Costa Rica) and Bocas del Toro, Panama
South America
: Patos Lagoon (Brazil) and Gulf of San Jose (Argentina)
Guanabara Bay
Cananeia Bay
Sepetiba Bay
23.89 kHz
23.84 kHz
17.49 kHz
23.75 kHz
23.01 kHz
23.02 kHz
23.0 kHz
These results are reinforce by recent studies with the largest dolphin -killer whales- These dolphins are more than 9 m long and emit whistles with a fundamental frequency up to 75 kHz!
Whistles from North Atlantic populations
Bottlenose Dolphin
Caribbean Sea
Pacific Ocean
Costa Rica (Central America)
Wildlife Reserve
Area of sympatry
Bocas del Toro
Caribbean Sea
Pacific Ocean
Bocas del Toro
Ambient noise
High at low frequencies
Higher at high frequencies
Dolphin Whistles
Higher in frequency
Lower in frequency
Engine noise
Low boat traffic
High boat traffic
Engine noise
Ambient noise
Dolphin Whistles
Bottlenose Dolphin
Alarm &
Tonal sounds are emitted by in a few terrestrial and solitary species such as duikers, dik-diks, Kobus, and Reedbuck. Are emitted mainly as alarm and warning behaviors.
Present in most species-homologous? this is un specialized sound usually associated to alarm and warning.
While our understanding of what factors have played a major role on the evolution of acoustic communication in aquatic species is growing, there is a great need of data for terrestrial species to get the big picture.
Sound & Vibrations
That dolphin species overcome masking by ambient and engine noise in different manners is evidence of how plastic these dolphin signals are.

Intra-specific variation is likely influenced by a combination of: local noise levels, neighboring populations and species sympatry
Next step
New Projects
signal propagation characteristic in different environments
response to changes noise levels (i.e., engine noise)
competition for acoustic space
Acoustic structure: Maximum Frequency
Frequency range not fully known but probably most below 1kHz
Knowledge of acoustic structure poor
Roars, snorts, grunts, bleats, squeals, chants, moaning, growls, hissing, wheeze-honk, screams, drumming, cries, clicks, bawls, mewing, chirps, mooing, wimps, bellow, sneeze, coughs, ‘ba’, ‘zer-zer’ , cheep calls, and tones among other even more specific descriptions.
Terrestrial species use sound for a variety of behaviors such as territoriality, courtship, warning, alarm, and long-distance communication.
Nasal and Laringe
Most studied sounds: snorts and tonal sounds
Tonal sounds
Body Size
Minimum Frequency
Complex societies: complex signals
Dolphins: High frequency, shorter, and complext signals

Snort: ‘low-frequency barking sound resulting from a sharp expellation of air through the nostrils’ (Caro et al. 2004)
Tonal sounds are: narrowbanded and frequency
Standard statistical methods assume species as independent data points.

Similarity in size or whistles may be due to common ancestry, which may artificially inflate the number of observations (and degrees of freedom).
The problem
Laura J. May-Collado, Ph.D.
Co-founder of PANACETACEA
Postdoc at University of Vermont, Department of Biology
1. Sound can be used when it's dark or in day light.
2. A sound is broadcast in all directions.
3. Sound travels fast (350 m/s) than chemical signals particularly in seawater (1500m/s)

How did these acoustic signals evolve?
What are the selective forces driving signal variation?
May-Collado and Agnarsson 2006, 2007a-b
We also found that changes in sound complexity were significantly concentrated within social lineages when both traits were treated as two state characters. Complex tonal sounds are associated with social species while simple tonal sounds are associated with solitary species.
Despite the possible differences in the context in which tonal sounds are produced by riverine dolphins and other delphinoids, there is no a priori reason to assume that whistles produced by these toothed whales are not homologous (contra Podos et al. 2002)
Killer whale
# Inflection points
(R2 = 12.4%, df = 23, p-1tailed = 0.04)
Species emitting longer tonal sounds tend to show a greater number of inflection points (cetaceans 12% and toothed whales 45%).
Tonal sound complexity
Apart from directly adjacent populations, distance was a poor predictor of similarity in whistles between populations.
Relative increase in frequency with latitude
Coastal Guyana Dolphin
Interestingly, absolute distance do seem to predict whistle similarity in species with more restricted distribution like the Guyana dolphin an endemic dolphin species to Latin America.
This suggests that apart from adjacent populations, populations within the same region are for the most part isolated, and similarities to distant populations could reflect similar acoustic conditions that prompt animals to respond in a similar manner.
A recent study of spinner dolphins (Stenella longirostris) where some distantly separated populations from the Atlantic and Pacific oceans were more similar to each other than to neighboring popu- lations (Camargo et al. 2007).
While species whistles are clearly distinct when found in intraspecific groups, this is not the case when the species are interacting in interspecific groups
In general, animals are believed to produce signals that are adapted to their particular environment. Cetaceans respond acoustically to environmental noise in a variety of ways, including whistle production rate, shifts in signal frequency, and an increase or decrease in signal duration.
The hypothesis that maximum frequency is negatively correlated with body size is rejected. (Wang et al. 1995-93% and Podos et al. 2002- 85%)
Minimum frequency is negatively correlated with body size but a much smaller percent of frequency variation is explained by body size after accounting for phylogenetic relationships.
Group size also significantly explained variation in the mean minimum tonal sound frequency within toothed whales.
Dolphin Hypothesis rejected
whistle complexity: # inflection points, modulation
35 km
Steiner 1981 suggested that zoogeographical relationships also may play an important role in dolphin whistle variation. He observed that differences in dolphin whistle structure were greater between sympatric species than between allopatric species.
Samarra et al. 2010
Work in collaboration with Susan Parks, Syracuse University
Bottlenose dolphins
High frequencies and more 'complex' tonal sounds are derived of social delphinids.
Alarm &
The Latin American Student Field Research Award by American Society of Mammalogists.
Cetacean Behavior and Conservation Award by Animal Behavior Society
Lener-Gray Research Grant by The American Natural History Museum
Pre-doctoral Travel Fellowship by Smithsonian Research Institute
Dissertation Year Fellowship by Florida International University
Tinker Research Opportunities Award by LAAC-FIU
Russell E. Train Scholarship through WWF and IIE
Whale and Dolphin Conservation Society
Oceanic Society, Belize
Cetacean International Society
Judith Parker Travel Grant
Project Aware
Dr. Douglas Wartzok (FIU)
Dr. Ingi Agnarsson (UBC)
Dr. Mike Heithaus (FIU)
Dr. Maureen Donnelly (FIU)
Dr. Wayne Maddison (UBC)
Dr. Volker Deecke (UBC)
Dr. Tim Collins (FIU)
Dr. Zhenim Chen (FIU)
Dr. Rachel Collin (STRI)
Julie Oswald and Shannon Rankin (NOAA)
Project in collaboration with Mike Heithaus, Florida International University
Tonal Sounds
Leaf muntjac
Blue whale
Desert Camel
Frequency variables
Duration and Modulation
Variations in dolphin whistle acoustic structure have been generally referred to as geographic variations, and not dialects. Some studies suggest a general geographical pattern relating to distance-the further apart the populations the more different their whistle structure is.
Maximum Frequency
Research Boat
Engine off
Research Boat
Engine off
Hypothesis: Minimum and maximum tonal sound frequency in cetaceans is negatively correlated with body size
Dolphin Hypothesis: Whistles evolved in social true dolphins
0 m
50 m
May-Collado 2010. Ethology. 116:1-10
May-Collado & Wartzok. 2008. J. Mammal. 89: 1229-1240
May-Collado & Wartzok. 2008. J. Mammal. 89: 1229-1240
May-Collado & Wartzok. 2009. J. Acoust. Soc. Am. 125:1202-1213
May-Collado & Wartzok. 2007. J. Acoust. Soc. Am. 121:1203-1212
May-Collado, Agnarsson, Wartzok 2007. BMC 7:136
May-Collado, Agnarsson, Wartzok 2007. BMC 7:136
May-Collado, Agnarsson, Wartzok 2007. BMC 7:136
May-Collado, Agnarsson, Wartzok 2007. BMC 7:136
May-Collado, Agnarsson, Wartzok 2007. Mar. Mamm. Sci. 23:524-552
40 KHz!
May-Collado and Warzok 2015. IWC Reports.
Agnarsson, May-Collado 2011.Molecular Phylogenetics and Evolution
Frisk 2012. doi:10.1038/srep00437
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