Genetic individuality and levels of genetic connectivity between Roviana and Marovo lagoons were investigated using four coral reef fish species. The genetic attributes of each lagoon, and patterns between the lagoons were also considered in the context of several other Indo-Pacific populations of the same species. The four fish were selected based on their differing life histories and ecology to provide representation for a variety of coral reef fish species.
The Convict surgeonfish (Acanthurus triostegus) is a common, shallow water tropical water fish that is sometimes taken for food. This surgeonfish is herbivorous and has pelagic eggs, a highly dispersive larval stage (pelagic larval duration up to 70 days) and a benthic juvenile and adult stage. The Checkerboard wrasse (Halichoeres hortulanus) is also sometimes fished for food. This wrasse has pelagic eggs and its larvae can disperse for up to 32 days before settling in the coral reef environment. The Domino damselfish (Dascyllus trimaculatus) is a planktivorous fish common in the aquarium fish trade. It lays benthic eggs, from which larvae hatch and disperse for a period up to 26 days. This damselfish will only settle on anemones or branching coral following which it resumes a site-attached, benthic life. The Neon damselfish (Pomacentrus coelestis) is also common in the aquarium fish trade. This damselfish often occupies the rubble areas among coral reef patches feeding on plankton. It lays benthic eggs and has larvae that disperse for up to 24 days before resuming a benthic lifestyle.
Tissue collections were undertaken in Roviana and Marovo lagoons from December 8-21, 2010. Sampling elsewhere in the Indo-Pacific has been undertaken intermittently over the last 4 years. The mitochondrial control region was amplified and sequenced for P. coelestis (348 nucleotide base pairs, bp), D. trimaculatus (375 bp) and H. halichoeres (366 bp), and the mitochondrial ATPase region was amplified and sequenced for A. triostegus (830 bp). Intra- and inter-population genetic patterns were analysed using classical population genetic diversity measures (polymorphic sites, s; number of haplotypes, H; haplotype diversity, Hd; number of unique haplotypes; and nucleotide diversity, pi; using DNAsp version 5, (Librado and Rozas 2009)) and measures of genetic differentiation (pairwise ϕST, which takes into account differences in haplotype composition as well as the level of differentiation among haplotypes; and analyses of molecular variation were undertaken in Arlequin version 3.5, (Excoffier et al. 2005)). The haplotypic composition of the sampled locations was represented using PhyloGeoViz (version 2.4.4, (Tsai 2011)).
R
ESULTSC
ONVICTS
URGEONFISHThe Convict surgeonfish had relatively high levels of genetic diversity in both Marovo and Roviana lagoons (Hd, Table 36), but neither lagoon contained unique genetic variants (hereafter haplotypes; Figure 1a). Over the entire sampled range of the surgeonfish, 99.78% of the genetic variation reflected differences within sampling localities, rather than differences between locations. This indicates that there has been much historical gene flow among populations of the Convict surgeonfish in the Indo-Pacific and there is likely to be contemporary gene flow among these locations. However, there were differences in the genetic composition of Roviana and Marovo lagoons (proportion of haplotypes shared with other regions, Figure 1b), although these differences were not significant (pairwise ϕST, Table 36).
Chapter 6 Connectivity
Table 36 Convict surgeonfish-Sample sizes and genetic diversity measures for all sites included in the study (see Figures for sampling location key). Locations within the Solomon Islands are indicated in grey and genetic differentiation found between Roviana and Marovo lagoons is shown at the bottom right (significance was assessed following 10000 permutations).
Figure 116 Genetic (haplotype) composition of Convict surgeonfish at sites across the Indo-Pacific. Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site; proportions within pie charts represent the genetic composition of that location (see legend).
Figure 117 Genetic (haplotype) composition of Convict surgeonfish within the Solomon Islands (Roviana (ROV) and Marovo (MOR)). Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site;
proportions within pie charts represent the genetic composition of that location (see legend).
Chapter 6
Building social and ecological resilience to climate change in Roviana, Solomon Islands
D
OMINOD
AMSELFISHLevels of genetic diversity were similar across the sampled range of the Domino damselfish (pi, and Hd, Table 37), however the genetic composition of each locality varied, with each having a high proportion of unique haplotypes (Figure 118; including both Roviana and Marovo lagoons, Figure 119). Both lagoons shared only a small proportion of their haplotypes and were significantly differentiated from each other (pairwise ϕST = 0.2701, p = 0.0360, Table 37). The level of differentiation found between Domino damselfish populations in Roviana and Marovo lagoons was greater than the differences found between Tonga and Timor-Leste (pairwise ϕST = 0.0807, p = 0.0180), Tonga and Kavieng (pairwise ϕST = 0.12410, p = 0.0090) and Timor-Leste and Motupore Island (pairwise ϕST = 0.06911, p = 0.0451), despite these locations being more geographically distant from each other. The greatest population differentiation found across the sampled range of the Domino damselfish was found between Marovo lagoon and Kavieng (pairwise ϕST
= 0.3034, p = 0.0360). These results indicate that there is likely to be little contemporary gene flow among populations of the Domino damselfish across the sampled Indo-Pacific range, and between populations that are geographically near, such as Roviana and Marovo lagoons in the Solomon Islands.
Table 37 Domino damselfish- Sample sizes and genetic diversity measures for all sites included in the study (see Figures for sampling location key). Locations within the Solomon Islands are indicated in grey and genetic differentiation found between Roviana and Marovo lagoons is shown at the bottom right (significance was assessed following 10000 permutations).
Figure 118 Genetic (haplotype) composition of Domino damselfish at sites across the Indo-Pacific. Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site; proportions within pie charts represent the genetic composition of that location (see legend).
Chapter 6 Connectivity
Figure 119 Genetic (haplotype) composition of Domino damselfish within the Solomon Islands (Roviana (ROV) and Marovo (MOR)). Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site;
proportions within pie charts represent the genetic composition of that location (see legend).
C
HECKERBOARDW
RASSEThe sampled Solomon Island populations of Checkerboard wrasse had relatively low levels of nucleotide diversity (pi), but high levels of haplotype diversity (Hd; Table 38), sometimes indicative of population size expansion (for example after a bottleneck or a selective sweep). The Marovo lagoon population did not share any haplotypes with locations outside of the Solomon Islands and was significantly differentiated from the Ashmore Reef population (pairwise ϕST = 0.3152, p = 0.0090). The Roviana lagoon population was also significantly different from the Ashmore Reef population (pairwise ϕST = 0.2647, p = 0.0090) as well as the Timor-Leste population of Checkerboard wrasse (pairwise ϕST = 0.1747, p = 0.0360). While there was no significant difference between the populations of Roviana and Marovo lagoons (pairwise ϕST = 0.0090, p = 0.5676, Table 38), Roviana lagoon’s population of Checkerboard wrasse was more similar to the populations of Tonga (pairwise ϕST = 0.0000, p = 0.5045), Fiji (pairwise ϕST = 0.0000, p = 0.7658), Kavieng (pairwise ϕST = 0.0000, p = 0.8198) and Lihou Reef (pairwise ϕST = 0.0000, p = 0.5135), than to Marovo lagoon’s checkerboard wrasse population. Similarly, Marovo lagoon’s population was more similar to the populations of Kavieng (pairwise ϕST = 0.0063, p = 0.3333), Lizard Island (pairwise ϕST = 0.0000, p = 0.5405) and Timor-Leste (pairwise ϕST = 0.0000, p = 0.3694), than to the population in Roviana lagoon. Although most of the genetic variation found across the sampled range of the Checkerboard wrasse could be contributed to intra–population differences (93.23%), there was still a significant amount that could be attributed to among population differences (6.77%). These genetic patterns indicate that there may be little contemporary gene flow among the sampled Checkerboard wrasse populations across the Indo-Pacific, however there is likely to be contemporary gene flow between the populations of Marovo and Roviana lagoons.
Chapter 6
Building social and ecological resilience to climate change in Roviana, Solomon Islands
Table 38 Checkerboard wrasse-Sample sizes and genetic diversity measures for all sites included in the study (see Figures for sampling location key). Locations within the Solomon Islands are indicated in grey and genetic differentiation found between Roviana and Marovo lagoons is shown at the bottom right (significance was assessed following 10000 permutations).
Figure 120 Genetic (haplotype) composition of Checkerboard wrasse at sites across the Indo-Pacific. Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site; proportions within pie charts represent the genetic composition of that location (see legend).
Figure 121 Genetic (haplotype) composition of Checkerboard wrasse within the Solomon Islands (Roviana (ROV) and Marovo (MOR)). Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site; proportions within pie charts represent the genetic composition of that location (see legend).
Chapter 6 Connectivity
N
EON DAMSELFISHThe Neon damselfish had relatively low levels of genetic diversity within the Solomon Islands relative to other sampled locations (Hd and pi, Table 39), although both lagoons still had a very high proportion of unique haplotypes (Figure 123). Roviana lagoon shared no haplotypes outside of the Solomon Islands, and the majority of haplotypes found within the Solomon Islands were shared with locations of eastern Australia and Papua New Guinea (Figure 122). Accordingly the Marovo lagoon population was significantly different from those of Ningaloo Reef (pairwise ϕST = 0.1137, p = 0), Ashmore Reef (pairwise ϕST = 0.2983, p
= 0), Timor-Leste (pairwise ϕST = 0.1854, p = 0) and the Wessels Islands (pairwise ϕST = 0.4629, p = 0); and the Roviana lagoon population was significantly differentiated from the same locations (NIN pairwise ϕST = 0.1839, ASH pairwise ϕST = 0.2983, TIM pairwise ϕST = 0.2561, ENG pairwise ϕST = 0.5685, for all comparisons p = 0) aswell as Lihou Reef (pairwise ϕST = 0.1257, p = 0.0270) and Motupore Island (pairwise ϕST = 0.0725, p = 0.0451) although to a lesser extent. These genetic patterns indicate that there is little contemporary gene flow among the sampled Neon damselfish populations across the Indo-Pacific (16.82%
of the genetic variation is found among populations); however there is likely to be contemporary gene flow between the populations of Marovo and Roviana lagoons as there is no significant difference in their genetic composition (pairwise ϕST, Table 39).
Table 39 Neo damselfish-Sample sizes and genetic diversity measures for all sites included in the study (see Figures for sampling location key). Locations within the Solomon Islands are indicated in grey and genetic differentiation found between Roviana and Marovo lagoons is shown at the bottom right (significance was assessed following 10000 permutations).
Figure 122 Genetic (haplotype) composition of Neon damselfish at sites across the Indo-Pacific. Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site; proportions within pie charts represent the genetic composition of that location (see legend).
Chapter 6
Building social and ecological resilience to climate change in Roviana, Solomon Islands
Figure 123 Genetic (haplotype) composition of Neon damselfish within the Solomon Islands (Roviana (ROV) and Marovo (MOR)). Size of the pie charts relate to the total number of genetic variants (haplotypes) found at that site;
proportions within pie charts represent the genetic composition of that location (see legend).
S
UMMARYIn summary, although the genetic patterns found across Roviana and Marovo lagoons in the Solomon Islands and their relationship with other sampled sites in the Indo-Pacific varied across the four studied fish species, they do lend some consensus. Generally, levels of genetic diversity within the Solomon Islands and within each lagoon were similar to other sampled sites across the Indo-Pacific (except in the case of the Neon damselfish where levels were lower). There was a high incidence of unique haplotypes in the Solomon Islands (excepting the Convict surgeonfish) indicating there is little contemporary gene flow, and therefore little connectivity, among these sites and the wider Indo-Pacific. The presence of unique haplotypes (except in the Convict surgeonfish) in both Roviana and Marovo lagoons highlights the genetic individuality of each lagoon. Marovo and Roviana lagoons often differed in their genetic composition, indicating that there may be little genetic connectivity between the lagoons (i.e. a low proportion of shared haplotypes) and each lagoon may have different levels of connectivity with regions outside of the Solomon Islands (i.e. proportion of haplotypes shared with other regions and not the other lagoon).
Chapter 7 Horticulture & agroforestry vulnerability assessment