A Fiji Bull Shark?

Carcharhinus dakuwaqa? Quite possibly!
Click for detail - and I mean it!

I knew it!
Not only are our bulls huge and the most incredible collection of charismatic, intelligent sharks on the planet, they may well be a totally unique population - if not more than that!
This was revealed last week at the AES meeting.

From the poster.

Global Population Genetic Structure and Parentage Analysis of the
Bull Shark (Carcharhinus leucas)

C. Testerman1, J. Brunnschweiler2, M. Heithaus3, S. Gulak4, J. Werry5, R. Jabado6, C. Jones7, and M. Shivji1

1Save Our Seas Shark Center USA and Guy Harvey Research Institute, Nova Southeastern University, Dania Beach, FL, USA, 2ETH Zurich, Zurich, Switzerland, 3Florida International University, North Miami, FL, USA, 4National Marine Fisheries Service, Panama City, FL, 5Ocean and Coast Research, QLD, Australia, 6United Arab Emirates University, Al Ain, UAE, 7University of Aberdeen, UK

Project Synopsis

The bull shark (Carcharhinus leucas) is a globally distributed, large coastal shark that occurs in marine, estuarine and freshwater habitats.
It has been assessed as near threatened by the IUCN, is caught in recreational and commercial fisheries throughout its range, and shows evidence of recent declines in the Gulf of Mexico. Regional population studies have reported mitochondrial but not nuclear differentiation between the western North and South Atlantic (Karl et al., 2011) and among juvenile C. leucas sampled in river systems across northern Australia (Tillett et al., 2012).

We expanded on these studies by evaluating the global population genetic structure of C. leucas using 12, bi-parentally inherited, nuclear microsatellite loci and a globally distributed set of 470 samples. Our microsatellite data revealed strong genetic differentiation between samples from the western North Atlantic (WNA) and Indo-Pacific (I-P). No population structuring was detected within WNA and Indian Ocean sampling sites.

Fig. 1. Species global distribution indicated in gold shading. Sampling locations with fewer than 10 samples were not included in the population-based differentiation statistical analyses (Fig. 2) but were included in the individual-based analyses (Figs. 3 & 4).
Click for detail!

Notably, however, samples from Fiji demonstrated statistically significant genetic structuring from the remaining locations sampled.

Fig. 2. Charcharhinus leucas genetic differentiation based on population-level statistical analyses. Colored shapes (ovals and square) represent genetically distinct populations. FST values (p = 0.0000) between each population pair are indicated by arrows. Sampling locations (indicated by circles) within each population are not genetically differentiated.
Click for detail!

Assignment testing (GeneClass2) showed evidence of a low-level of first generation migrants from the WNA and western Pacific among the southwest Indian Ocean samples, a surprising finding considering the strongly coastal nature of C. leucas. Finally, parentage analysis of 2 litters suggests that the species may be genetically polyandrous, although this hypothesis will need further testing with more litters.

Conclusions:

Individual and population level analyses are concordant in showing at least 3 genetically distinct populations:

• Western North Atlantic
• Indo-Australia
• Fiji

Fig. 3. pie charts indicate the average proportional membership coefficient of individuals in the 3 distinct lineages inferred from nuclear microsatellite genotypes by the program STRUCTURE. Pie chart sizes are roughly proportional to sample sizes.
Click for detail!

Three 1st generation migrants were identified, indicating contemporary movement from both the Atlantic and Pacific oceans into the Indian Ocean. Complex patterns of migration and population structure require coordinated regional management efforts.
Parentage analyses of 2 litters revealed multiple paternity in both litters.

So there you have it!
This is the result of many years of DNA sampling on Shark Reef whereby so far, we've been able to send more than 70 samples to Mahmood - and counting as there are other, more local aspects we would like to explore.

So, do we have a Fiji endemic?
Probably not at all, because nearby locations like e.g. Tonga and Samoa are very likely to harbor the same Sharks. But from everything we know, Fiji with its robust population of Bull Sharks may well be considered to be the epicenter of this genetic strain, meaning that it would be perfectly acceptable to call this the Fiji Bull Shark - and depending on whether this is a subspecies/race or even an own species: how does Carcharhinus leucas dakuwaqa or Carcharhinus dakuwaqa sound to you!

Anyway, is this mega cool, or what!