Population structure of humpback whales in the western and central South Pacific Ocean as determined by vocal exchange among populations.

For cetaceans, population structure is traditionally determined by molecular genetics or photographically identified individuals. Acoustic data, however, has provided information on movement and population structure with less effort and cost than traditional methods in an array of taxa. Male humpback whales (Megaptera novaeangliae) produce a continually evolving vocal sexual display, or song, that is similar among all males in a population. The rapid cultural transmission (the transfer of information or behavior between conspecifics through social learning) of different versions of this display between distinct but interconnected populations in the western and central South Pacific region presents a unique way to investigate population structure based on the movement dynamics of a song (acoustic) display. Using 11 years of data, we investigated an acoustically based population structure for the region by comparing stereotyped song sequences among populations and years. We used the Levenshtein distance technique to group previously defined populations into (vocally based) clusters based on the overall similarity of their song display in space and time. We identified the following distinct vocal clusters: western cluster, 1 population off eastern Australia; central cluster, populations around New Caledonia, Tonga, and American Samoa; and eastern region, either a single cluster or 2 clusters, one around the Cook Islands and the other off French Polynesia. These results are consistent with the hypothesis that each breeding aggregation represents a distinct population (each occupied a single, terminal node) in a metapopulation, similar to the current understanding of population structure based on genetic and photo-identification studies. However, the central vocal cluster had higher levels of song-sharing among populations than the other clusters, indicating that levels of vocal connectivity varied within the region. Our results demonstrate the utility and value of using culturally transmitted vocal patterns as a way of defining connectivity to infer population structure. We suggest vocal patterns be incorporated by the International Whaling Commission in conjunction with traditional methods in the assessment of structure.

Estructura Poblacional de las Yubartas en el Centro y Occidente del Sur del Océano Pacífico, Determinada por el Intercambio Vocal entre las Poblaciones Resumen La estructura poblacional de los cetáceos se determina tradicionalmente por medio de genética molecular o individuos identificados fotográficamente. Sin embargo, los datos acústicos han proporcionado información sobre el movimiento y la estructura poblacional de una variedad de taxones con menos esfuerzo y menos costo que los métodos tradicionales. Las yubartas macho (Megaptera novaeangliae) producen una demostración vocal sexual, o canto, en continua evolución que es similar entre todos los machos en una población. La transmisión cultural rápida (la transferencia de información o comportamientos entre co-específicos por medio del aprendizaje social) de diferentes versiones de esta demostración entre poblaciones distintas pero interconectadas en el centro y occidente en la región del sur del Pacífico presenta una manera única para investigar la estructura poblacional con base en las dinámicas de movimiento de la demostración del canto (acústico). Al usar once años de datos, con base en la acústica investigamos a una estructura poblacional de la región al comparar secuencias estereotipadas de cantos entre las poblaciones y los años. Usamos la técnica de la distancia Levenshtein para agrupar poblaciones previamente definidas en grupos (con base vocal) basados en la similitud general de su canto en el espacio y el tiempo. Identificamos a los siguientes grupos vocales perceptibles: grupo occidental, una población al este de Australia; grupo central, poblaciones alrededor de Nueva Caledonia, Tonga y Samoa Americana; y región oriental, ya sea un grupo único o dos grupos, uno alrededor de las Islas Cook y el otro cerca de la Polinesia Francesa. Estos resultados son consistentes con la hipótesis de que cada conjunto reproductivo representa a una población distinta (cada una ocupó un nodo terminal único) en una meta-población, similar al entendimiento actual de la estructura poblacional con base en los estudios genéticos y de foto-identificación. Sin embargo, el grupo vocal central tuvo niveles más altos de cantos compartidos entre las poblaciones que en los otros grupos, lo que indica que los niveles de conectividad vocal variaron dentro de la región. Nuestros resultados demuestran la utilidad y el valor de usar patrones vocales transmitidos culturalmente como una forma de definir la conectividad para inferir la estructura poblacional. Sugerimos que los patrones vocales sean incorporados por la Comisión Internacional de Caza de Ballenas en conjunto con los métodos tradicionales de evaluación de la estructura.

Quantifying humpback whale song sequences to understand the dynamics of song exchange at the ocean basin scale.

Humpback whales have a continually evolving vocal sexual display, or "song," that appears to undergo both evolutionary and "revolutionary" change. All males within a population adhere to the current content and arrangement of the song. Populations within an ocean basin share similarities in their songs; this sharing is complex as multiple variations of the song (song types) may be present within a region at any one time. To quantitatively investigate the similarity of song types, songs were compared at both the individual singer and population level using the Levenshtein distance technique and cluster analysis. The highly stereotyped sequences of themes from the songs of 211 individuals from populations within the western and central South Pacific region from 1998 through 2008 were grouped together based on the percentage of song similarity, and compared to qualitatively assigned song types. The analysis produced clusters of highly similar songs that agreed with previous qualitative assignments. Each cluster contained songs from multiple populations and years, confirming the eastward spread of song types and their progressive evolution through the study region. Quantifying song similarity and exchange will assist in understanding broader song dynamics and contribute to the use of vocal displays as population identifiers.

Straight as an arrow: humpback whales swim constant course tracks during long-distance migration.

Humpback whale seasonal migrations, spanning greater than 6500 km of open ocean, demonstrate remarkable navigational precision despite following spatially and temporally distinct migration routes. Satellite-monitored radio tag-derived humpback whale migration tracks in both the South Atlantic and South Pacific include constant course segments of greater than 200 km, each spanning several days of continuous movement. The whales studied here maintain these directed movements, often with better than 1° precision, despite the effects of variable sea-surface currents. Such remarkable directional precision is difficult to explain by established models of directional orientation, suggesting that alternative compass mechanisms should be explored.

Migratory convergence facilitates cultural transmission of humpback whale song.

Cultural transmission of behaviour is important in a wide variety of vertebrate taxa from birds to humans. Vocal traditions and vocal learning provide a strong foundation for studying culture and its transmission in both humans and cetaceans. Male humpback whales (Megaptera novaeangliae) perform complex, culturally transmitted song displays that can change both evolutionarily (through accumulations of small changes) or revolutionarily (where a population rapidly adopts a novel song). The degree of coordination and conformity underlying song revolutions makes their study of particular interest. Acoustic contact on migratory routes may provide a mechanism for cultural revolutions of song, yet these areas of contact remain uncertain. Here, we compared songs recorded from the Kermadec Islands, a recently discovered migratory stopover, to multiple South Pacific wintering grounds. Similarities in song themes from the Kermadec Islands and multiple wintering locations (from New Caledonia across to the Cook Islands) suggest a location allowing cultural transmission of song eastward across the South Pacific, active song learning (hybrid songs) and the potential for cultural convergence after acoustic isolation at the wintering grounds. As with the correlations in humans between genes, communication and migration, the migration patterns of humpback whales are written into their songs.

Dynamic horizontal cultural transmission of humpback whale song at the ocean basin scale.

Cultural transmission, the social learning of information or behaviors from conspecifics, is believed to occur in a number of groups of animals, including primates, cetaceans, and birds. Cultural traits can be passed vertically (from parents to offspring), obliquely (from the previous generation via a nonparent model to younger individuals), or horizontally (between unrelated individuals from similar age classes or within generations). Male humpback whales (Megaptera novaeangliae) have a highly stereotyped, repetitive, and progressively evolving vocal sexual display or "song" that functions in sexual selection (through mate attraction and/or male social sorting). All males within a population conform to the current version of the display (song type), and similarities may exist among the songs of populations within an ocean basin. Here we present a striking pattern of horizontal transmission: multiple song types spread rapidly and repeatedly in a unidirectional manner, like cultural ripples, eastward through the populations in the western and central South Pacific over an 11-year period. This is the first documentation of a repeated, dynamic cultural change occurring across multiple populations at such a large geographic scale.