Publié par : Sibylline | septembre 10, 2015

Les cachalots aussi ont leurs patois

cachalots assoupis observés en 2008 par Luke Rendel et son équipel, University of St Andrews

cachalots assoupis observés en 2008 par Luke Rendel et son équipel, University of St Andrews

10 Septembre 2015. Les groupes de cachalots parlent des dialectes différents composés de sons qu’ils se transmettent entre eux. 

Les cachalots utilisent des dialectes différents selon le groupe auquel ils appartiennent, selon une étude publiée mardi dans la revue Nature Communications. Le résultat est épatant puisqu’il est un signe de l’existence d’une forme de culture chez ces cétacés. 

Les baleines s’apprennent les dialectes entre elles. Pour cette étude, les chercheurs ont comparé les sons qu’émettent les cachalots et leur comportements sociaux en combinant des données recueillies sur plus de 18 ans et des simulations informatiques. Pour Mauricio Cantor, les modélisations indiquent que les différents dialectes ne peuvent évoluer comme ils le font que lorsque les baleines apprennent de leurs pairs les sons qu’ils émettent. Ni le hasard, ni la seule génétique ne peuvent conduire à des groupes employant différents langages. « Nos résultats renforcent l’hypothèse que les principales caractéristiques de la culture humaine (comme l’apprentissage social) peuvent se retrouver dans les populations animales », conclut le chercheur.

La culture, chez l’humain seulement ? La notion de culture animale est très controversée. Pour certains scientifiques, la culture, définie grossièrement comme une forme d’apprentissage social qui établit une distinction entre des groupes, n’existe que chez l’homme et c’est même ce qui le différencie de l’animal. Pour Mauricio Cantor de l’université Dalhousie au Canada et coauteur de l’étude, tout dépend de ce que l’on entend par « culture ». « Dans notre étude, nous employons le terme culture au sens large comme définissant un comportement qui est socialement appris et partagé avec un sous-ensemble de la population.

Culture animale. Selon Mauricio Cantor, « les animaux peuvent, comme nous, découvrir de nouvelles choses, apprendre et copier les compétences de l’autre, passer cette information de génération en génération ». « L’idée de l’existence de la culture animale a gagné du terrain au cours des 10-20 dernières années », précise le chercheur.

(a) Coda transmission mechanisms are represented as changes in the coda repertoires vector (squares: coda types; colours: frequency of usage: absent=0, always=100%). Calf agents change repertoires three times (between 0 and 2 year old) under one of following mechanisms. (i) Individual learning: newborn agenta starts with an empty coda vector; half of the elements are randomly selected to receive absolute frequencies of usage from a uniform distribution ∈[0,100]. (ii) Genetic inheritance: newborn agent b starts with an empty coda vector, which is filled with the same coda types and frequencies of its mother B. (iii) Oblique social learning: newborn agent c starts with an empty coda vector; at the age 0 year it randomly samples 62 elements (including zeroed elements) from the coda vector of other adult agents, kin-related or not; at ages 1 and 2 years, the calf repeats the process, replacing a portion of sampled elements. For iv–vi, calves gain an initial repertoire via oblique social learning, then at ages 1 and 2 years, the following effects were included. (iv) Homophily: calf d copies from adult agents of the social unit A, which has the highest coda repertoire similarity with its own social unit. (v) Conformism: calf e preferentially copies the coda types with higher frequencies of usage, here the three codas commonly performed by the adults. (vi) Symbolic marking: calves f and g were born in different social units, which have a specific subset of codas (‘symbol’) that all members always perform to mark the identity of the unit (the sequences of red codas). Both calves copy codas from other adults, but also deliberately copy their units’ ‘symbols’. (b) Oblique social learning (iii) and the additional effects (iv–iv) occurred at the three social levels. (vii) Social unit: calf agents copy only from agents of their own social unit. (viii) Predefined clans: simulation started with predefined clan labels and calves copy from any agent inside of its predefined clan. (ix) Population: calves copy from any agent in the population. In all scenarios, calves had a low individual learning probability (replacing 1 random coda type by a random frequency) per year.

(a) Coda transmission mechanisms are represented as changes in the coda repertoires vector (squares: coda types; colours: frequency of usage: absent=0, always=100%). Calf agents change repertoires three times (between 0 and 2 year old) under one of following mechanisms. (i) Individual learning: newborn agenta starts with an empty coda vector; half of the elements are randomly selected to receive absolute frequencies of usage from a uniform distribution ∈[0,100]. (ii) Genetic inheritance: newborn agent b starts with an empty coda vector, which is filled with the same coda types and frequencies of its mother B. (iii) Oblique social learning: newborn agent c starts with an empty coda vector; at the age 0 year it randomly samples 62 elements (including zeroed elements) from the coda vector of other adult agents, kin-related or not; at ages 1 and 2 years, the calf repeats the process, replacing a portion of sampled elements. For iv–vi, calves gain an initial repertoire via oblique social learning, then at ages 1 and 2 years, the following effects were included. (iv) Homophily: calf d copies from adult agents of the social unit A, which has the highest coda repertoire similarity with its own social unit. (v) Conformism: calf e preferentially copies the coda types with higher frequencies of usage, here the three codas commonly performed by the adults. (vi) Symbolic marking: calves f and g were born in different social units, which have a specific subset of codas (‘symbol’) that all members always perform to mark the identity of the unit (the sequences of red codas). Both calves copy codas from other adults, but also deliberately copy their units’ ‘symbols’. (b) Oblique social learning (iii) and the additional effects (iv–iv) occurred at the three social levels. (vii) Social unit: calf agents copy only from agents of their own social unit. (viii) Predefined clans: simulation started with predefined clan labels and calves copy from any agent inside of its predefined clan. (ix) Population: calves copy from any agent in the population. In all scenarios, calves had a low individual learning probability (replacing 1 random coda type by a random frequency) per year.

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