Blacktip reef sharks, Carcharhinus melanopterus, have high genetic structure and varying demographic histories in their Indo‐Pacific range

Abstract

For free-swimming marine species like sharks, only population genetics and demographic history analyses can be used to assess population health/status as baseline population numbers are usually unknown. We investigated the population genetics of blacktip reef sharks, Carcharhinus melanopterus; one of the most abundant reef-associated sharks and the apex predator of many shallow water reefs of the Indian and Pacific Oceans. Our sampling includes 4 widely separated locations in the Indo-Pacific and 11 islands in French Polynesia with different levels of coastal development. Four-teen microsatellite loci were analysed for samples from all locations and two mitochondrial DNA fragments, the control region and cytochrome b, were examined for 10 locations. For microsatellites, genetic diversity is higher for the locations in the large open systems of the Red Sea and Australia than for the fragmented habitat of the smaller islands of French Polynesia. Strong significant structure was found for distant locations with FST values as high as ~0.3, and a smaller but still significant structure is found within French Polynesia. Both mitochondrial genes show only a few mutations across the sequences with a dominant shared haplotype in French Polynesia and New Caledonia suggesting a common lineage different to that of East Australia. Demographic history analyses indicate population expansions in the Red Sea and Australia that may coincide with sea level changes after climatic events. Expansions and flat signals are indicated for French Polynesia as well as a significant recent bottleneck for Moorea, the most human-impacted lagoon of the locations in French Polynesia.

DoesGSTunderestimate genetic differentiation from marker data?

“…To understand the genetic structure of blacktip reef sharks ( Carcharhinus melanopterus ), Vignaud et al . () sampled 758 individuals from 15 sites (4 widely separated locations in the Indo‐Pacific and 11 islands in French Polynesia) widely distributed in the Indian and Pacific Oceans. Each sampled individual was genotyped at 17 microsatellite loci.…”

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

“…Population structuring and connectivity in large sharks vary in relation to environmental features, movement ecology, and habitat preferences (Dudgeon et al, 2012;Heist, 2005). Oceanic species generally exhibit high levels of genetic connectivity, including across ocean basins (e.g., basking shark Cetorhinus maximus ;Hoelzel, Shivji, Magnussen, & Francis, 2006), while coastal species tend to exhibit more structure (e.g., blacktip reef shark Carcharhinus melanopterus [Mourier & Planes, 2013;Vignaud et al, 2014] and scalloped hammerhead shark Sphyrna lewini [Duncan, Martin, Bowen, & De Couet, 2006]). Despite the bull shark being able to undergo long-distance migrations (Brunnschweiler, Queiroz, & Sims, 2010;Daly, Smale, Cowley, & Froneman, 2014;Heupel et al, 2015;Kohler & Turner, 2001;Lea, Humphries, Clarke, & Sims, 2015), its dispersal may be restricted, as is suggested by high genetic differentiation observed between Fiji, the Atlantic, and Indo-West Pacific Oceans (Testerman, 2014).…”

Population genetics of four heavily exploited shark species around the Arabian Peninsula

“…) and population structuring on relatively small geographic scales (e.g., blacktip reef shark: Vignaud et al. ; bull shark: Karl et al. ; dusky shark: Benavides et al.…”

“…Moreover, global and range‐wide studies on several species that included samples from ocean basins in the Arabian region demonstrated substantial genetic differentiation between this region and widely separated Indo‐Pacific locations, as well as a strong separation between Indo‐Pacific and Atlantic clades for blacktip reef (Vignaud et al. ), silky (Clarke et al. ), spot‐tail (Giles et al.…”

“…Patterns of genetic population structure in sharks are not uniform across species, but range from localized genetic subdivision (e.g., leopard shark: Lewallen et al 2007; nurse shark: Karl et al 2012;zebra shark: Dudgeon et al 2009) and population structuring on relatively small geographic scales (e.g., blacktip reef shark: Vignaud et al 2014a; bull shark: Karl et al 2011;dusky Ahonen et al 2009;lemon shark: Schultz et al 2008;sandbar shark: Portnoy et al 2010), to population differentiation detectable only across ocean basins (e.g., shortfin mako shark: Schrey and Heist 2003;whale shark: Castro et al 2007;Schmidt et al 2009;Vignaud et al 2014b) and nearly global panmixia (basking shark: Hoelzel et al 2006). Genetic subdivision in sharks is commonly facilitated by geographic dispersal barriers, such as large oceanic expanses (lemon shark: Schultz et al 2008;spot-tail shark: Giles et al 2014) or environmental gradients along continuous landmasses extending across different geographic regions (blacktip shark: Keeney and Heist 2006).…”