Of Clams and Clades: Genetic Diversity and Connectivity of Small Giant Clams (Tridacna maxima) in the Southern Pacific Ocean

• Published in: Ecology and evolution Vol. 14; no. 10; pp. e70474 - n/a
• Main Authors: Nevatte, Ryan J., Gillings, Michael R., Morejohn, Kirby, Ainley, Lara, Liggins, Libby, Pratchett, Morgan S., Hoey, Andrew S., Doll, Peter C., Pasisi, Brendon, Williamson, Jane E.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01.10.2024; John Wiley and Sons Inc; Wiley
• Subjects: Archipelagoes; Atolls; Australia; Biogeography; Cook Islands; Coral reefs; Coral Sea; cytochrome oxidase 1; Endangered & extinct species; Environmental changes; Genetic analysis; Genetic diversity; Genetics; Geographical distribution; Haplotypes; Islands; Marine parks; Mitochondrial DNA; Mollusks; Morphology; phylogeography; Population Genetics; Population structure; Populations; Reefs; Shellfish; Tridacna maxima; Tridacninae; Wildlife conservation; Coral Sea; Pacific Ocean; Indian Ocean; Australia; Cook Islands; Great Barrier Reef; Cook Islands; mitochondrial DNA; Coral Sea; Australia; Tridacninae; cytochrome oxidase 1; phylogeography
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.70474

ABSTRACT Giant clams (Tridacna and Hippopus) are large marine bivalves occupying tropical and subtropical reefs in the Indo‐Pacific. Giant clam populations have declined in many areas of the Indo‐Pacific and continue to be threatened by harvesting and environmental change. The small giant clam (Tridacna maxima) occurs throughout the Indo‐Pacific and has been subject to several phylogeographic studies across its range. However, given its broad range, there are several areas where the genetic diversity and connectivity of T. maxima populations has not been characterised. Here, we analyse the mitochondrial marker cytochrome oxidase 1 (CO1) to examine the genetic diversity and connectivity of T. maxima in two regions: Australia's Coral Sea Marine Park and the Cook Islands. Samples were collected from 13 reefs within the Coral Sea Marine Park and ten islands within the Cook Islands archipelago. Tridacna maxima across the sampled region of the Coral Sea did not display any population structure, whereas significant population structure was detected for T. maxima within the Cook Islands. For the Cook Islands, most pairwise comparisons involving an island in the northern group (Manihiki) were significant, as were comparisons for Palmerston (a more centrally located island) and the southern islands, Rarotonga and Mangaia. Both regions displayed high haplotype diversities (> 0.90), indicating that they are important repositories of genetic diversity. Additional CO1 data from throughout T. maxima's distribution showed that the Coral Sea clams belonged to the clade occurring in the South‐Western Pacific Ocean, whilst those from the Cook Islands belonged to a unique clade found in the Central Pacific Ocean. This clade extended from Fiji in the west to French Polynesia in the east and the atolls of Palmyra and Tarawa (Kiribati) in the north. Our assessment of genetic diversity and population structure in these regions will assist with management decisions for the species. We sequenced the cytochrome oxidase 1 (CO1) gene in small giant clams (Tridacna maxima) in Australia's Coral Sea Marine Park and Cook Islands to assess the genetic diversity and connectivity of these populations. Both regions had very high haplotype diversities but differed in their population structures, with no structure detected within the Coral Sea and significant structure in the Cook Islands archipelago. When these regions were placed into a global context with additional CO1 data from across T. maxima's distribution, we found that clams from the Coral Sea belonged to a mitochondrial clade present in the South‐Western Pacific Ocean, whilst those from the Cook Islands were part of a clade unique to the Central Pacific Ocean.