Phylogenetic review of tonal sound production in whales in relation to sociality.
BACKGROUND
It is widely held that in toothed whales, high frequency tonal sounds called 'whistles' evolved in association with 'sociality' because in delphinids they are used in a social context. Recently, whistles were hypothesized to be an evolutionary innovation of social dolphins (the 'dolphin hypothesis'). However, both 'whistles' and 'sociality' are broad concepts each representing a conglomerate of characters. Many non-delphinids, whether solitary or social, produce tonal sounds that share most of the acoustic characteristics of delphinid whistles. Furthermore, hypotheses of character correlation are best tested in a phylogenetic context, which has hitherto not been done. Here we summarize data from over 300 studies on cetacean tonal sounds and social structure and phylogenetically test existing hypotheses on their co-evolution.


RESULTS
Whistles are 'complex' tonal sounds of toothed whales that demark a more inclusive clade than the social dolphins. Whistles are also used by some riverine species that live in simple societies, and have been lost twice within the social delphinoids, all observations that are inconsistent with the dolphin hypothesis as stated. However, cetacean tonal sounds and sociality are intertwined: (1) increased tonal sound modulation significantly correlates with group size and social structure; (2) changes in tonal sound complexity are significantly concentrated on social branches. Also, duration and minimum frequency correlate as do group size and mean minimum frequency.


CONCLUSIONS
Studying the evolutionary correlation of broad concepts, rather than that of their component characters, is fraught with difficulty, while limits of available data restrict the detail in which component character correlations can be analyzed in this case. Our results support the hypothesis that sociality influences the evolution of tonal sound complexity. The level of social and whistle complexity are correlated, suggesting that complex tonal sounds play an important role in social communication. Minimum frequency is higher in species with large groups, and correlates negatively with duration, which may reflect the increased distances over which non-social species communicate. Our findings are generally stable across a range of alternative phylogenies. Our study points to key species where future studies would be particularly valuable for enriching our understanding of the interplay of acoustic communication and sociality.
May-Collado
Laura J
LJ
Florida International University, Department of Biological Sciences, 11200 SW 8th Street, Miami, FL 33199, USA. lmayc002@fiu.edu
Agnarsson
Ingi
I
Wartzok
Douglas
D
D000818:Animals; D005075:Biological Evolution; D004289:Dolphins / Q000502:physiology*; D010802:Phylogeny; D012919:Social Behavior; D013016:Sound; D014828:Vocalization, Animal / Q000502:physiology*; D014907:Whales / Q000502:physiology*
J Acoust Soc Am. 2002 Feb;111(2):1122-5
11865816
Gene. 2004 May 26;333:27-34
15177677
Anim Behav. 1998 Oct;56(4):829-838
9790693
J Acoust Soc Am. 2007 Feb;121(2):1203-12
17348541
J Acoust Soc Am. 2001 Jan;109(1):407-11
11206170
J Acoust Soc Am. 2002 Jul;112(1):34-7
12141361
Proc Natl Acad Sci U S A. 2001 Jun 19;98(13):7384-9
11416211
J Acoust Soc Am. 2004 Nov;116(5):3178-85
15603163
J Acoust Soc Am. 2006 Jul;120(1):510-7
16875247
J Acoust Soc Am. 2005 Mar;117(3 Pt 1):1456-64
15807033
Sci Sin. 1981 Mar;24(3):407-15
7256251
J Acoust Soc Am. 2002 Dec;112(6):3064-72
12509029
Anim Cogn. 2005 Jan;8(1):17-26
15221637
Cladistics. 1988 Mar;4(1):3-22
34933495
Evolution. 1990 May;44(3):539-557
28567979
Science. 2000 Aug 25;289(5483):1355-7
10958783
J Acoust Soc Am. 2005 Apr;117(4 Pt 1):2318-29
15898672
Syst Biol. 1998 Mar;47(1):90-124
12064244
J Acoust Soc Am. 2004 Dec;116(6):3757-69
15658726
Trends Ecol Evol. 1986 Dec;1(6):144-50
21227802
J Acoust Soc Am. 2006 Sep;120(3):1361-5
17004459
J Acoust Soc Am. 2005 Jun;117(6):3919-27
16018493
J Morphol. 1996 Jun;228(3):223-85
8622183
J Evol Biol. 2007 Jul;20(4):1439-58
17584238
Anat Rec (Hoboken). 2007 Jun;290(6):745-59
17516447
Evolution. 2006 Jul;60(7):1509-15
16929667
BMC Bioinformatics. 2006 Feb 23;7:88
16504105
J Acoust Soc Am. 2005 Dec;118(6):3941-5
16419837
J Acoust Soc Am. 2006 Sep;120(3):1695-705
17004490
Trends Ecol Evol. 1998 Jun 1;13(6):228-32
21238276
Mol Phylogenet Evol. 2006 Feb;38(2):344-54
16325433
J Acoust Soc Am. 2005 May;117(5):3297-306
15957796
J Acoust Soc Am. 2001 Jun;109(6):3038-47
11425146
Am Nat. 2019 Jun;193(6):755-772
31094602
J Acoust Soc Am. 2001 Mar;109(3):1240-6
11303937