Population ecology, genetics and phylogeography of Tetraclita species (Crustacea: Cirripedia) from the West Pacific Ocean to East Indian Ocean
Date Issued
2016
Date
2016
Author(s)
Chen, Hsi-Nien
Abstract
The genus Tetraclita is a common intertidal barnacle in the Indo-West Pacific and a good model for studying population ecology, diversity and biogeography of intertidal species. There are four Tetraclita species in the West Pacific including Tetraclita japonica, Tetraclita kuroshioensis, Tetraclita squamosa and Tetraclita singaporensis and these species have almost allopatric distribution. The aim of the present study was to understand the population ecology, biogeography and phylogeography of Tetraclita barnacles from the West Pacific to East Indian Ocean. Variations on population ecology and life history pattern of T. japonica and T. kuroshioensis were studied among geographic regions in the West Pacific (Japan, Taiwan and Hong Kong) and correlated with environmental factor. Results showed that T. japonica populations in Hong Kong had the lowest number of cohorts (3) than Japan and Taiwan (> 5). Settlement density and settler growth rate of T. japonica was also higher in Hong Kong compared to Taiwan. These differences probably resulted from higher sea surface temperature and chlorophyll a concentration. Besides, results suggested that larval release, settlement and recruitment of Tetraclita barnacles happen in summer months. It is therefore, the biogeography and phylogeography of Tetraclita species are highly affected by oceanographic processes during the summer months in the West Pacific and East Indian Ocean regions. T. kuroshioensis was selected as a model to study historical and ecological biogeography because this species had the widest distribution from the West Pacific to East Indian Ocean. A total of 19 populations across the West Pacific, three populations from NE Indian Ocean and one population from SE Indian Ocean were collected. The genetic diversity was examined using mitochondrial COI (cytochrome oxidase subunit I) and nuclear microsatellite markers. Mitochondrial DNA analysis on T. kuroshioensis revealed four distinct genetic lineages. One of the lineages was identified as T. kuroshioensis. Among the other three lineages, one lineage exhibited strong genetic differentiation but had similar morphology to T. kuroshioensis. This lineage was regarded as T. cf. kuroshioensis (OTU 1). In contrast, the other two lineages exhibited genetic variations to the known Tetraclita references and also had distinct morphological features on scutum and tergum. These two lineages were regarded as undescribed Tetraclita species (T. sp. nov. 1 = OTU 3; T. sp. nov. 2 = OTU 2). AMOVA analysis based on mtDNA COI gene showed significant genetic difference between NE Indian Ocean and Pacific Ocean T. kuroshioensis populations. To further elucidate the phylogeographic pattern of T. kuroshioensis, eight microsatellite markers were developed from T. kuroshioensis through transcriptome sequencing. STRUCTURE analysis through microsatellite markers showed that T. kuroshioensis was composed of four genetically distinct groups. One genetically distinct group contained most Pacific Ocean populations and one SE Indian Ocean population (KBA) whereas the OI population formed a genetically distinct group alone. The other genetically distinct groups were composed of two Philippine populations (PGP and BCP) and NE Indian Ocean populations (AII, PKT and PCI), respectively. Alternatively, the PCoA plot showed similar result to STRUCTURE analysis. AMOVA analysis based on microsatellite dataset also revealed significant differentiation between NE Indian and Pacific Ocean populations. The contemporary gene flow among these genetic groups was rare and only found from Pacific Ocean populations to the Philippines populations. The distribution of the OI population and the Philippines populations appears to be related to the presences of glacial refugia during the Pleistocene. The present results revealed the population ecology and life history pattern of Tetraclita barnacles can be influenced by environmental factors such as sea surface temperature and food availability which might affect geographical distribution as well. The present study also highlighted the hidden genetic diversity of T. kuroshioensis. The strong genetic subdivisions of T. kuroshioensis could be resulted from Pleistocene glaciation or other past geological events. Limited contemporary gene flow from the present day ocean currents also sustained genetic differentiation and prevented mixture among distinct genetic lineages/groups.
Subjects
Tetraclita
population ecology
life history
phylogeography
population genetics
Type
thesis
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