Abstract
Social behaviors are poorly known for the critically endangered Yangtze finless porpoise (YFP, Neophocaena asiaeorientalis asiaeorientalis). Here, group composition and dispersal patterns of the YFP population living in the Poyang Lake were studied by parentage-based pedigree analyses using 21 microsatellite loci and a 597 bp segment of the mitochondrial DNA control region. In this study, 21 potential mother-offspring pairs and six potential father-offspring pairs (including two potential parents-offspring pairs) were determined, among which 12 natural mother-offspring groups and a maternal group of three generations were found. No genetically-determined fathers were found associated with their offspring. This study also found that maternally related porpoises at the reproductive state tend to group together. This suggest maternal relationship and reproductive state may be factors for grouping in the YFP population. In natural mother-offspring groups, male offspring were all younger than two years old, which suggest male offspring may leave their mothers at approximately two years of age, or at least they were not in tight association with their mothers as they may have been under two years old. However, female offspring can stay longer with their mothers and can reproduce in the natal group.
Highlights
The social behavior of cetaceans is both complex and interesting
Various cetacean social behaviors have been reported, including fluid fission-fusion societies described in small delphinid species (e.g., bottlenose dolphins (Tursiops aduncus) [3]; spinner dolphins (Stenella longirostris) [4]), matrilineal groups in larger toothed whales (e.g., killer whales (Orcinus orca) [5]; sperm whales (Physeter macrocephalus) [6]), and associations among individuals of both sexes or just a single sex that vary in size, duration, and composition of Atlantic white-sided dolphins (Lagenorhynchus acutus) [7]
A total of 171 alleles were detected at 21 microsatellite loci among 122 individuals
Summary
The social behavior of cetaceans is both complex and interesting. Advances in molecular techniques have led to an increasing number of studies that combine molecular, observational, and photo-ID data to reveal a variety of grouping and dispersing patterns in cetacean species [1,2]. Various cetacean social behaviors have been reported, including fluid fission-fusion societies described in small delphinid species (e.g., bottlenose dolphins (Tursiops aduncus) [3]; spinner dolphins (Stenella longirostris) [4]), matrilineal groups in larger toothed whales (e.g., killer whales (Orcinus orca) [5]; sperm whales (Physeter macrocephalus) [6]), and associations among individuals of both sexes or just a single sex that vary in size (from few to hundreds of individuals), duration (temporary or permanent), and composition (single or multiple generations) of Atlantic white-sided dolphins (Lagenorhynchus acutus) [7]. The social behavior of freshwater dolphins was observed. Irrawaddy dolphins (Orcaella brevirostris) form fission-fusion group dynamics with frequent social interactions and cooperative feeding, and mother-young associations can be observed in the Ganges and Indus dolphins (Platanista spp.). Still, compared to marine cetaceans, knowledge about the social behavior of freshwater cetaceans remains very limited
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