Abstract:
The venomous box jellyfish Chiropsoides buitendijki can be observed throughout Thailand's coastal areas, including the Gulf of Thailand and the Andaman Sea. It is among the species that can cause severe skin injuries. The occurrence of C. buitendijki blooms has varied across locations and can be seasonal. Therefore, an interesting question is whether the box jellyfish aggregates found in these different places are genetically different. I analyzed genetic variation of C. buitendjiki populations from the Thai waters using partial nucleotide sequences of mitochondrial Cytochrome Oxidase subunit I gene (COI) (790 base pairs). During 2017-2018, the C. buitendijki samples were collected from Northern Andaman (Phang Nga, N = 30), Southern Andaman (Trang, N= 40), and Gulf of Thailand (Songkla, N= 5). All specimens were identified to species level based on diagnostic morphologies and genetic variation inferring from 16S and 18S rDNA sequences. I detect morphological differences between the Andaman and Gulf of Thailand samples (umbrella size and Rhopaliar niche ostia). However, only COI and 16S rRNA revealed genetic differences (8.6-9.2 for COI and 4.8-5.4 for 16S rRNA), which still fell within the intra-specific variation for Cubozoans. Population genetics analyses revealed a total of 32 haplotypes with 91 variable sites (11.51%). Haplotype diversity within each sample ranged from 0-0.933, and nucleotide diversity ranged from 0-0.005. The Andaman samples (H=0.816-0.933, π = 0.002-0.005) have much higher haplotype diversity and nucleotide diversity higher than the Gulf of Thailand sample (H and π = 0). Furthermore, analysis of molecular variance (AMOVA), pairwise FST, and the minimum spanning network showed a significant difference between the Gulf of Thailand and the Andaman samples (FST = 0.963 - 0.977, P<0.007). However, the genetic differences between the Andaman samples were inconclusive. The pairwise FST value suggested significant genetic difference (FST = 0.3381, P<0.007), but the minimum spanning network and gene flow analysis did not support such difference. The bush-like haplotype network showed no geographic structuring. In addition, the gene flow analysis suggested the panmixia model for these populations. These inconsistent results may be due to the hyper diverse nature of COI in invertebrates that led to a high number of private haplotypes in each sample (πsyn = 7.4%). The results also suggest antagonistic effects of box jellyfish lifehistory traits (limited dispersal, asexual reproduction) and the population mixing due to oceanic currents in the Andaman Sea during the southwest monsoon. The results suggested different dispersal patterns of box jellyfish in the Gulf of Thailand and the Andaman Sea, a consideration for management actions