First insight of genetic diversity, phylogeographic relationships and
population structure of marine sponge Chondrosia reniformis from the
eastern and western Mediterranean coasts of Tunisia
The cytochrome oxidase subunit I (COI) gene was amplified and analyzed
for 70 Mediterranean Chondrosia reniformis, collected from eight
localities in Tunisia. Polymorphism results revealed high values of
haplotype diversity (Hd) and very low nucleotide diversity (π). Thus,
these results suggest that our sponge populations of C. reniformis may
have undergone a bottleneck followed by rapid demographic expansion.
This suggestion is strongly confirmed by the results of neutrality tests
and “mismatch distribution”. The important number of haplotypes
between localities and the high genetic differentiation (Fst ranged from
0.590 to 0.788) of the current C. reniformis populations could be
maintained by the limited gene flow Nm (0.10 - 0.18). Both haplotype
Network and the biogeographic analysis showed a structured distribution
according to the geographic origin. C. reniformis populations are
subdivided into two major clades: Western and Eastern Mediterranean.
This pattern seems to be associated with the well-known discontinuous
biogeographic area: the Siculo-Tunisian Strait, which separates two
water bodies circulating with different hydrological, physical, and
chemical characteristics. The short dispersal of pelagic larvae of C.
reniformis and the marine bio-geographic barrier created high
differentiation among populations. Additionally, it is noteworthy to
mention that the “Mahres / Kerkennah” group diverged from Eastern
groups in a single sub-clade. This result was expected, the region
Mahres / Kerkennah, presented a particular marine environment.