Cultural evolution of killer whale calls: background, mechanisms and consequences

Abstract

Cultural evolution is a powerful process shaping behavioural phenotypes of many species including our own. Killer whales are one of the species with relatively well-studied vocal culture. Pods have distinct dialects comprising a mix of unique and shared call types; calves adopt the call repertoire of their matriline through social learning. We review different aspects of killer whale acoustic communication to provide insights into the cultural transmission and gene-culture co-evolution processes that produce the extreme diversity of group and population repertoires. We argue that the cultural evolution of killer whale calls is not a random process driven by steady error accumulation alone: temporal change occurs at different speeds in different components of killer whale repertoires, and constraints in call structure and horizontal transmission often degrade the phylogenetic signal. We discuss the implications from bird song and human linguistic studies, and propose several hypotheses of killer whale dialect evolution.

Independent acoustic variation of the higher- and lower-frequency components of biphonic calls can facilitate call recognition and social affiliation in killer whales

“…Complex repertoires of stereotyped calls-vocal dialects-represent a form of animal culture [3]. Killer whale dialects slowly change in time through learning errors and innovations [2,25,[49][50][51]; this process of cultural change is called cultural evolution [52,53]. Since the variability of sound contours is limited due to the natural physical constrains, call contours of unrelated killer whale social units can sometimes become more similar due to the random convergence [42].…”

Simple foraging rules in competitive environments can generate socially structured populations

“…From foraging benefits motivating related individuals to stay in groups, further differentiation—behavioral, cultural, genetic—could be promoted through time. Stable groupings, which here we propose could be driven by competition for limited resources alone, then provide favorable contexts for individuals to copy behavior from one another (e.g., Estebán et al., ; Klopfer, ; Whitehead & Rendell, ), promoting between‐group behavioral divergence that can be reinforced by cultural or genetic drift and selection (e.g., Cantor & Whitehead, ; Filatova et al., ).…”

“…Social communities composed by groups of related individuals, even in sympatry, differ in a variety of behavioral and morphological traits, which seems to be rooted on dietary specialization. By specializing on distinct prey—most famously mammals versus fish (Ford et al., )—killer whale social communities display distinct movement and hunting techniques more adjusted to their particular feeding habits and surrounding environment, along with distinct social systems and communication repertoires (e.g., Filatova et al., ; Yurk, Barrett‐Lennard, Ford, & Matkin, ). Finally, from their matrifocal social structures, foraging specializations seem to have triggered not only behavioral, but also genetic divergence (Foote et al., ; Hoelzel, Dahlheim, & Stern, ).…”

Song variation of the South Eastern Indian Ocean pygmy blue whale population in the Perth Canyon, Western Australia

“…Increased complexity within songs is thought to be a reflective of cognitive fitness, which may be a favourable trait for sexual selection [6, 55, 70, 71]. Innovation is a cultural process whereby an individual makes a change to the song structure and this change is then copied by other whales and can spread through the population [11, 15, 20, 30, 41]. Vocal learning is the primary mechanism by which changes to song are proliferated throughout the population as well as the means by which juveniles learn the characteristic vocalisations of the population [19, 23, 26, 58].…”

“…A better understanding of the driving factors behind changes to vocal repertoires may provide clues as to the purpose of particular vocal signals, such as whether they have a reproductive or social context [7, 26–29]. It is thought that vocalisations within a familial group with a social context are least susceptible to change whilst those songs with a reproductive context are most likely to change [6, 27, 28, 30].…”