Ganmanee, Monthon

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Species range evolution of the rocky intertidal leaf oyster Isognomon nucleus (Lamarck, 1819) in the Indo-Pacific
(2026-08-01)
Mahyotsanun, Patteera
;
Shahdadi, Adnan
;
Ganmanee, Monthon
;
Chan, Benny K.K.
The small-sized leaf oyster, Isognomon nucleus, inhabits intertidal rock crevices across the tropical and subtropical Indo-Pacific (IP). This study examines the phylogeography of I. nucleus across the IP and the evolution of its distribution range using three mitochondrial markers, COX1, 12S, and 16S, and the nuclear ITS1 marker. Our phylogenetic analyses revealed a widely distributed Indo-Pacific lineage of I. nucleus from the Andaman Sea to Hawaii, and two further deeply diverged but morphologically cryptic lineages: Isognomon cf. nucleus 1, restricted to Taiwan, and Isognomon cf. nucleus 2, occurring in Taiwan and Hainan (China). Phylogeographic analyses revealed extensive gene flow within I. nucleus, spanning from the Andaman Sea in the Indian Ocean through the Philippines and Taiwan in the western Pacific to Hawaii in the Central Pacific. This high dispersal capacity is likely facilitated by west–east flowing equatorial currents and the species’ strong environmental tolerance. Higher pairwise Φst values between Hawaii and other localities indicate reduced gene flow between Hawaii and the Indo–West Pacific, consistent with Hawaii's geographic isolation. The Hawaiian endemic Isognomon californicus is closely related to I. cf. nucleus 1, suggesting that both evolved from a common ancestor and diverged as a result of limited dispersal between Taiwan and Hawaii. Demographic analyses detected clear signals of population expansion in I. nucleus coinciding with the sea level changes in the Last Glacial Maximum.
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Morphological and molecular evidence support the intertidal barnacle octomeris intermedia nilsson-cantell, 1921 (Thoracica, chthamalidae) as a valid species in indo-pacific waters
(2020-01-01)
Chan, Benny K.K.
;
Tsao, Yao Feng
;
Ganmanee, Monthon
Octomeris is a chthamalid intertidal barnacle with eight shell plates. There are currently two species of such barnacles: O. brunnea Darwin, 1854 (type locality in the Philippines), common in the Indo-Pacific region, and O. angulosa Sowerby, 1825, only recorded in South Africa. Octomeris intermedia Nilsson-Cantell, 1921, identified from the Mergui Archipelago in Myanmar, was considered to be conspecific with O. brunnea by Hiro (1939) based on samples collected in Taiwan. The morphological differences in shell and opercular plates between O. brunnea and O. intermedia are believed to be intra-specific variations due to different degrees of shell erosion. In the present study, the genetic and morphological differentiations of Octomeris in the Indo-Pacific region were examined. This study found two molecular clades (with inter-specific differences) based on the divergence in the COI genes, and the species also have distinct geographical distributions. The Octomeris brunnea clade covers samples collected from the Philippines and Taiwan waters and the other clade, which we argue is O. intermedia, is distributed in Phuket and Krabi, Thailand and Langkawi, Malaysia. Phuket and Krabi are located approximately 300 km south of the Mergui Archipelago, the type locality of O. intermedia. The morphology of samples collected from Thailand fits the type description of O. intermedia in Nilsson-Cantell (1921). Our study concludes that O. intermedia is a valid species based on morphological and molecular evidence.
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High thermal stress responses of Echinolittorina snails at their range edge predict population vulnerability to future warming
(2019-01-10)
Han, Guo dong
;
Cartwright, Stephen R.
;
Ganmanee, Monthon
;
Chan, Benny K.K.
;
Adzis, Kee A.A.
Populations at the edge of their species' distribution ranges are typically living at the physiological extreme of the environmental conditions they can tolerate. As a species' response to global change is likely to be largely determined by its physiological performance, subsequent changes in environmental conditions can profoundly influence populations at range edges, resulting in range extensions or retractions. To understand the differential physiological performance among populations at their distribution range edge and center, we measured levels of mRNA for heat shock protein 70 (hsp70) as an indicator of temperature sensitivity in two high-shore littorinid snails, Echinolittorina malaccana and E. radiata, between 1°N to 36°N along the NW Pacific coast. These Echinolittorina snails are extremely heat-tolerant and frequently experience environmental temperatures in excess of 55 °C when emersed. It was assumed that animals exhibiting high temperature sensitivity will synthesize higher levels of mRNA, which will thus lead to higher energetic costs for thermal defense. Populations showed significant geographic variation in temperature sensitivity along their range. Snails at the northern range edge of E. malaccana and southern range edge of E. radiata exhibited higher levels of hsp70 expression than individuals collected from populations at the center of their respective ranges. The high levels of hsp70 mRNA in populations at the edge of a species' distribution range may serve as an adaptive response to locally stressful thermal environments, suggesting populations at the edge of their distribution range are potentially more sensitive to future global warming.

Ganmanee, Monthon

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