Kin relationships in cultural species of the marine realm: case study of a matrilineal social group of sperm whales off Mauritius island, Indian Ocean

International audienceUnderstanding the organization and dynamics of social groups of marine mammals through the study of kin relationships is particularly challenging. Here, we studied a stable social group of sperm whales off Mauritius, using underwater observations, individual-specific identification, non-invasive sampling and genetic analyses based on mitochondrial sequencing and microsatellite profiling. Twenty-four sperm whales were sampled between 2017 and 2019. All individuals except one adult female shared the same mitochondrial DNA (mtDNA) haplotype—one that is rare in the western Indian Ocean—thus confirming with near certainty the matrilineality of the group. All probable first- and second-degree kin relationships were depicted in the sperm whale social group: 13 first-degree and 27 second-degree relationships were identified. Notably, we highlight the likely case of an unrelated female having been integrated into a social unit, in that she presented a distinct mtDNA haplotype and no close relationships with any members of the group. Investigating the possible matrilineality of sperm whale cultural units (i.e. vocal clans) is the next step in our research programme to elucidate and better apprehend the complex organization of sperm whale social groups

Nursing Behavior in Sperm Whales (Physeter macrocephalus)

In mammals, lactation is the universal behavior of feeding offspring and has a fundamental nutritional and social value with offspring staying near their mothers. In order to obtain milk, terrestrial mammal offspring squeeze the breast of lactating females and suckle the nipples with their tongues. In the specific case of cetacean species, it was reported that lactating females intentionally eject milk from their mammary slit into the calves’ mouths. Nursing behavior in sperm whales has already been broadly described, but the results of our current study, based on 127 underwater videos, recording over 7 years and displaying explicit nursing behavior, bring a higher level of understanding. We first showed that sperm whale calves are proactive in getting milk. We were then able to illustrate and describe with a high level of precision their suckling behavior: firstly, the calf bumps its head onto the female’s genital area to signal the mother its willingness to suckle; secondly, the calf introduces its lower jawbone into the genital slit, this action makes the nipple pop up from its slit; thirdly, the calf squeezes the nipple with its tongue against the hard palate and suckles; fourthly, the calf removes its jawbone from the female and swims off. Moreover, our underwater visual observations provided the first direct evidence for allosuckling in sperm whales, a situation during which a calf obtains milk from an adult female who is not its mother

Study of behaviours and emitted codas during sperm whales social interactions

International audienceSperm whales live in the matrilineal population structure based on complex social interactions. Groups of 10-20 adult females stay together and raise their offspring. During social activities, they emit specific patterned time sequences of clicks, called codas. These codas are also the social unit acoustic signature. However, no associations were already done between these emitted sounds and behaviours. To answer this question, we used a dataset including simultaneous video and acoustic recordings during sperm whale activities close to the sea surface. In 2017 and 2018, 114 days of observations for 25h33min was done. A total of 1,810 behaviours and of 1,324 codas were extracted. We analyzed their internal structures, based of number of clicks and also the variation of inter-click intervals. Results showed firstly that the 8-clicks codas were the most frequent sequences for this social unit, and secondly that codas seems to be call and contact signals for this haptic species