Stability and evolution in sperm whale cultural dialects

• Main Authors: Cultural Evolution Society 2021 2021, Hersh, Taylor
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Sperm whale
• Online Access: https://dx.doi.org/10.48448/j9qk-5m93; https://underline.io/lecture/21923-stability-and-evolution-in-sperm-whale-cultural-dialects

For species with culturally distinct vocalizations, like sperm whales, cultural evolution can manifest as changes in vocal repertoires over time. In social situations, sperm whales communicate using stereotyped click patterns, called codas. Different socially segregated, cultural clans of whales have different coda dialects, but it is unknown whether and how these dialects evolve. To address this, we looked for changes in sperm whale codas over time off the Galápagos Islands. First, codas were classified into types using contaminated mixture models. Then, repertoires of codas were hierarchically clustered based on similarities in coda type usage to determine which clan made each repertoire. Generalized linear models weighted by coda sample size and with year as a predictor were used to determine if within-type coda durations varied across years for two well-sampled clans: the Plus-One clan (1,865 codas, 1985–1989) and the Regular clan (3,813 codas, 1985–1995). While there is no evidence that the Plus-One clan dialect changed over a 5-year timespan, several different Regular clan coda types were about 16% longer in 1995 than in preceding years. In showing that coda duration changes are unlikely due to sampling bias, environmental variation, or individual variation, we posit that cultural drift, or a cultural fad, occurred between 1991 and 1995. Additional Regular clan codas, recorded after 1995, will allow further testing of this hypothesis. These results suggest that sperm whale dialects can change over time, but that different codas and clans may exhibit different patterns of stability and evolution.