Data from: Genetic kinship analyses reveal that Gray's beaked whales strand in unrelated groups

Some marine mammals are so rarely seen that their life history and social structure remain a mystery. Around New Zealand, Gray’s beaked whales (Mesoplodon grayi) are almost never seen alive, yet they are a commonly stranded species. Gray’s are unique among the beaked whales in that they frequently strand in groups, providing an opportunity to investigate their social organization. We examined group composition and genetic kinship in 113 Gray’s beaked whales with samples collected over a 20-year period. Fifty-six individuals stranded in 19 groups (2 or more individuals), and 57 whales stranded individually. Mitochondrial control region haplotypes and microsatellite genotypes (16 loci) were obtained for 103 whales. We estimated pairwise relatedness between all pairs of individuals and average relatedness within, and between, groups. We identified 6 mother–calf pairs and 2 half-siblings, including 2 whales in different strandings 17 years and 1500 km apart. Surprisingly, none of the adults stranding together were related suggesting that groups are not formed through the retention of kin. These data suggest that both sexes may disperse from their mothers, and groups consisting of unrelated subadults are common. We also found no instances of paternity within the groups. Our results provide the first insights into dispersal, social organization, and the mating system in this rarely sighted species. Why whales strand is still unknown but, in Gray’s beaked whales, the dead can tell us much about the living.部分海洋哺乳动物因极难被活体观测，其生活史与社会结构至今仍是未解之谜。在新西兰周边海域，格雷氏喙鲸（Gray’s beaked whales，学名*Mesoplodon grayi*）几乎从未被观测到活体，却是搁浅事件高发的物种。该物种在喙鲸类中独树一帜，常以群体形式搁浅，这为研究其社会组织结构提供了难得契机。本研究依托20年间收集的样本，对113头格雷氏喙鲸的群体组成与遗传亲缘关系展开分析：其中56头个体隶属于19个群体（每群体至少包含2头个体），剩余57头为单独搁浅个体。研究人员为其中103头个体获取了线粒体控制区单倍型（mitochondrial control region haplotypes）与16个基因座的微卫星基因型（microsatellite genotypes）数据。我们计算了所有个体间的两两亲缘关系，并估算了群体内部及群体间的平均亲缘系数。共鉴定出6对母子（母女）以及2对半同胞个体，其中2头个体分别在间隔17年、相距1500公里的两次搁浅事件中被发现。令人意外的是，共同搁浅的成年个体间均无亲缘关系，这表明群体并非通过亲缘保留形成。上述数据提示，雌雄个体均可能离开其出生群体，且由无亲缘关系的亚成体组成的群体较为常见。同时，研究未发现群体内部存在父系亲缘关联的案例。本研究结果首次为这种极难观测的物种的扩散模式、社会组织结构与交配系统提供了认知依据。鲸类搁浅的原因至今尚未明确，但就格雷氏喙鲸而言，搁浅的个体仍能为我们揭示活体种群的诸多奥秘。