Mechanisms of enhancing genetic fitness in non-kinship-based groups: Insights from black-necked cranes

Understanding a species' mating strategies is essential for unraveling the intricacies of their group structure and formation, as well as for comprehending the delicate balance they trade-offs to optimize their overall fitness. Black-necked cranes (Grus nigricollis), a monogamous wetland species primarily found in the Qinghai-Tibetan Plateau and the largest alpine crane, is a captivating embodiment of fidelity and love, yet our study challenges this narrative. In this study, we successfully extracted DNA samples from black-necked cranes and reconstructed pedigrees of breeding groups at Flower Marsh. We discovered that these non-kinship-based groups exhibited high nest-site fidelity, with males showing higher nest-site fidelity than females. Despite their monogamous nature, none of the breeding pairs maintained strict monogamy throughout our four-year observation period, with a high rate of extra-pair fertilization detected. Indiscriminate offspring dispersal enabled black-necked crane groups to avoid inbreeding, while the high frequency of extra-pair fertilization increased genetic diversity. Our findings provide valuable insights into the mating strategies of black-necked cranes and the mechanisms that sustain low-sociality groups and offer important implications for the conservation of this unique species.

Methods
Observation and collection during four years.