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Is Blood Thicker Than Water? The Influence of Kin Within a Bull Shark Social Network
Natasha D Marosi1,2, Darren P Croft1, David M P Jacoby3
1Centre for Research in Animal Behaviour, College of Health and Life Sciences University of Exeter Exeter UK.
Ecology and Evolution
|August 7, 2026
Summary
Kinship influences social behavior in bull sharks, with genetic relatedness playing a small but significant role, especially in male interactions. This study offers rare evidence of kin selection in large marine predators.
Area of Science:
- Marine biology
- Behavioral ecology
- Population genetics
Background:
- Kinship's role in social structure (kinfluence) is well-studied in terrestrial animals but poorly understood in marine systems.
- While kin-based associations are known in some marine fish and mammals, research in elasmobranchs is limited, especially concerning fine-scale social behavior and genetic relatedness.
- Previous studies have not combined genomic relatedness with categorical kinship inference in elasmobranch social behavior.
Purpose of the Study:
- To investigate the influence of genetic relatedness and categorical kinship on the social behavior of bull sharks (Carcharhinus leucas).
- To examine how kin-based associations shape social interactions within a provisioning aggregation of bull sharks.
- To provide empirical support for kin selection in a large marine predator.
Main Methods:
- Utilized DArTseq SNP genotyping (3919 SNPs, 129 individuals) and behavioral data from 473 observation dives over 6 years at Shark Reef Marine Reserve, Fiji.
- Integrated genomic relatedness data with observations of active social preferences (join, lead, follow, parallel swim).
- Employed social network analyses and pedigree reconstruction to identify kin dyads and assess the influence of relatedness on social structure.
Main Results:
- Social network analysis revealed a structured network driven by active social preferences.
- Genomic relatedness had a small but significant influence on social behavior at both dyadic and community levels, particularly in male-male dyads.
- Pedigree reconstruction identified full and half-siblings; community-level analysis showed slightly stronger associations between sibling dyads than non-kin, but no significant dyadic-level relationship was detected.
Conclusions:
- This study provides rare empirical support for kin selection in a large marine predator, specifically bull sharks.
- The findings suggest that while genomic relatedness plays a role, its influence on social behavior in this context may be subtle.
- Further research is needed to fully understand the complex role of kinship in shaping social systems within elasmobranchs.
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