Evidence of social learning across symbolic cultural barriers in sperm whales

Reviewer #1 (Public Review):

Summary:

This manuscript presents evidence of 'vocal style' in sperm whale vocal clans. Vocal style was defined as specific patterns in the way that rhythmic codas were produced, providing a fine-scale means of comparing coda variations. Vocal style effectively distinguished clans similar to the way in which vocal repertoires are typically employed. For non-identity codas, vocal style was found to be more similar among clans with more geographic overlap. This suggests the presence of social transmission across sympatric clans while maintaining clan vocal identity.

Strengths:

This is a well-executed study that contributes exciting new insights into cultural vocal learning in sperm whales. The methodology is sound and appropriate for the research question, building on previous work and ground-truthing much of their theories. The use of the Dominica dataset to validate their method lends strength to the concept of vocal style and its application more broadly to the Pacific dataset. The results are framed well in the context of previous works and clearly explain what novel insights the results provide to the current understanding of sperm whale vocal clans. The discussion does an overall great job of outlining why horizontal social learning is the best explanation for the results found.

Weaknesses:

The primary issues with the manuscript are in the technical nature of the writing and a lack of clarity at times with certain terminology. For example, several tree figures are presented and 'distance' between trees is key to the results, yet 'distance' is not clearly defined in a way for someone unfamiliar with Markov chains to understand. However, these are issues that can easily be dealt with through minor revisions with a view towards making the manuscript more accessible to a general audience.

I also feel that the discussion could focus a bit more on the broader implications - specifically what the developed methods and results might imply about cultural transmission in other species. This is specifically mentioned in the abstract but not really delved into in detail during the discussion.

Reviewer #2 (Public Review):

Summary:

The current article presents a new type of analytical approach to the sequential organisation of whale coda units.

Strengths:

The detailed description of the internal temporal structure of whale codas is something that has been thus far lacking.

Weaknesses:

It is unclear how the insight gained from these analyses differs or adds to the voluminous available literature on how codas varies between whale groups and populations. It provides new details, but what new aspects have been learned, or what features of variation seem to be only revealed by this new approach?
The theoretical basis and concepts of the paper are problematical and indeed, hamper potentially the insights into whale communication that the methods could offer. Some aspects of the results are also overstated.

Reviewer #3 (Public Review):

Summary:

The study presented by Leitao et al., represents an important advancement in comprehending the social learning processes of sperm whales across various communicative and socio-cultural contexts. The authors introduce the concept of "vocal style" as an addition to the previously established notion of "vocal repertoire," thereby enhancing our understanding of sperm whale vocal identity.

Strengths:

A key finding of this research is the correlation between the similarity of clan vocal styles for non-ID codas and spatial overlap (while no change occurs for ID codas), suggesting that social learning plays a crucial role in shaping symbolic cultural boundaries among sperm whale populations. This work holds great appeal for researchers interested in animal cultures and communication. It is poised to attract a broad audience, including scholars studying animal communication and social learning processes across diverse species, particularly cetaceans.

Weaknesses:

In terms of terminology, while the authors use the term "saying" to describe whale vocalizations, it may be more conservative to employ terms like "vocalize" or "whale speech" throughout the manuscript. This approach aligns with the distinction between human speech and other forms of animal communication, as outlined in prior research (Hockett, 1960; Cheney & Seyfarth, 1998; Hauser et al., 2002; Pinker & Jackendoff, 2005; Tomasello, 2010).

Author response:

We thank the reviewers for their positive assessments and constructive feedback.

In light of their comments, we will aim to improve the explanation of the methods and interpretation of results, as well as their relation to well-established literature in this research area.

The major contributions of our work are threefold:

• First, we introduce a novel way of analyzing codas that specifically targets subcoda structures by considering inter-click intervals within codas in terms of transition probabilities. By describing codas’ click patterns via Variable Length Markov Chains, we do not need to consider codas in their entirety, but we can detect coda subunits.This enables a new dimension for quantitatively comparing differences among various individuals, social units, and clans; which we term ‘vocal style’.

• Using this approach, we reinforce findings from past research, including the idea that identity codas function as symbolic markers of vocal clan identity (Hersh et al., 2022; Sharma et al., 2024). More importantly, we offer new insights into the function of non-identity codas, which comprise the majority of coda types produced by sperm whales but have been largely uncharacterized.

• Our work reveals that non-identity coda vocal styles are more similar for spatially overlapped clans, and suggests that this similarity in style may be maintained by social learning across clan boundaries. This opens up a paradigm shift in our understanding of between-clan acoustic interactions.

From a broader perspective, our work builds on two well-established research areas: the form and function of sperm whale codas, and statistical generative models, specifically Variable Length Markov Chains on finite data spaces. Our methods, results, and interpretations are grounded in theories and concepts from these fields.

For clarity, we will ensure that our terminology aligns with field standards and existing research. We will clearly introduce each key theory or concept at first mention and justify its relevance. In particular, we will clarify the definition and meaning of the distance between subcoda trees for a general audience. We agree with the reviewers’ comments on the broader implications and will refine our work accordingly.