A disjunct zonation pattern of Avicennia marina (Forsk.) Vierh. is frequently observed along the Kenyan coast. In Gazi Bay, there are five zones where samples were collected earlier and could be examined for genetic analysis, namely Seaward Cleared (A), Intermediate first Bridge (B), Intermediate Village (C), Landward Covered (D) and Landward desert (D). The objective of the present study was to investigate whether the disjunct zonation patterns of A. marina across the mangrove belt in the study site at Gazi Bay also shows a consistent genetic differentiation along disjunct landward zone and seaward zones, despite their short spatial distance. Genetic analysis was performed using two Inter-Simple Sequence Repeat (ISSR) and two Randomly Amplified Polymorphic DNA (RAPD) markers. A leaf sample of 19 individuals was taken from each zone; a total 95 individual are investigated. Four primers produced 47 bands ranging from 450bp- 3000bp, of which the ISSR primers revealed 20 polymorphic loci and RAPD primers 25 polymorphic loci. At the species level, the genetic diversity is high when using either RAPD marker (P= 96.24%, He=0.235, 7=0.338) or ISSR markers (P=95.24, He=0.316, 1=0.477). Considering both ISSR and RAPD loci, a PCA revealed that population A and B are genetically differentiated from population D and E while population C contained individual trees that were related either to the seaward (A&B) or the landward (D&E) populations. This pattern was due to the polymorphism in a few ISSR loci. It indicates that there is less contact and gene flow between the seaward and landward zones than within each zone. RAPD alone did not provide a suitable marker for distinguishing the two vegetation zones of A. marina. Among different hypotheses, the one that fits the best for the present study is: “the Avicennia zones show consistent genetic differentiation between landward and seaward trees. This implies that there is a clear and significant genetic structuring that separates both ecological zones and that pollinator movement and propagule dispersal between the two zones is expected to be reduced to a certain degree”. |
