Population structure, connectivity, and demographic history of an apex marine predator, the bull shark Carcharhinus leucas

Abstract

Knowledge of population structure, connectivity, and effective population size remains limited for many marine apex predators, including the bull shark Carcharhinus leucas. This large‐bodied coastal shark is distributed worldwide in warm temperate and tropical waters, and uses estuaries and rivers as nurseries. As an apex predator, the bull shark likely plays a vital ecological role within marine food webs, but is at risk due to inshore habitat degradation and various fishing pressures. We investigated the bull shark's global population structure and demographic history by analyzing the genetic diversity of 370 individuals from 11 different locations using 25 microsatellite loci and three mitochondrial genes (CR, nd4, and cytb). Both types of markers revealed clustering between sharks from the Western Atlantic and those from the Western Pacific and the Western Indian Ocean, with no contemporary gene flow. Microsatellite data suggested low differentiation between the Western Indian Ocean and the Western Pacific, but substantial differentiation was found using mitochondrial DNA. Integrating information from both types of markers and using Bayesian computation with a random forest procedure (ABC‐RF), this discordance was found to be due to a complete lack of contemporary gene flow. High genetic connectivity was found both within the Western Indian Ocean and within the Western Pacific. In conclusion, these results suggest important structuring of bull shark populations globally with important gene flow occurring along coastlines, highlighting the need for management and conservation plans on regional scales rather than oceanic basin scale.

Genetic population structure and demography of an apex predator, the tiger shark Galeocerdo cuvier

“…The tiger shark displays moderate genetic diversity with a very low number of mitochondrial haplotypes and haplotype diversity for the sequences studied compared to other shark species, such as the bull shark Carcharhinus leucas (Pirog, Jaquemet, et al, ), the great white shark Carcharodon carcharias (Pardini et al., ), the blue shark Prionace glauca (Veríssimo et al., ), the blacktip reef shark Carcharhinus melanopterus (Vignaud et al., ), or the tope shark Galeorhinus galeus (Chabot, ; Chabot & Allen, ). Furthermore, using the same protocol on the same date from extraction to marker testing for polymorphism, we characterized 20 microsatellite loci for the bull shark (Pirog et al., ), and only eight for the tiger shark (Pirog et al., ), which supports a lower genetic diversity in the latter species.…”

High connectivity within restricted distribution range in Pocillopora corals

“…Indeed, in the bullshark Carcharhinus leucas , the mitochondrial genes used supported an Indo‐Pacific barrier to gene flow between both ocean basins while microsatellites do not. Integrating information from both types of markers and using Bayesian computation with a random forest procedure (ABC‐RF), this discordance was found to be due to a complete lack of contemporary gene flow (Pirog et al, 2019). Consequently, it appears necessary to achieve multi‐specific connectivity models with many markers distributed over the whole genome to accurately estimate gene flow, and genomics seems promising for this.…”

Intra-specific variation in movement and habitat connectivity of a mobile predator revealed by acoustic telemetry and network analyses

“…In northern Australia, for example, female C. leucas are known to return to their natal estuaries to give birth (Tillett et al 2012). However, further genetic studies along the east coast of Australia are needed to determine if C. leucas exhibits some type of reproductive philopatric behaviour, and if individuals from tropical and temperate waters form a single population (Pirog et al 2019b). Moreover, sex ratios from the reef-based population were biased towards females, which could have limited our ability to detect male movement.…”