The webpage text is licensed under a Creative Commons Attribution 4. Toggle navigation. WoRMS taxon details. Acropora hyacinthus Dana, Acropora Oken, Madrepora hyacinthus Dana,

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In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. A Nature Research Journal. As corals in tropical regions are threatened by increasing water temperatures, poleward range expansion of reef-building corals has been observed, and temperate regions are expected to serve as refugia in the face of climate change.

Among the three cryptic lineages found, only one was distributed in temperate regions, which could indicate the presence of Kuroshio-associated larval dispersal barriers between temperate and subtropical regions, as shown by oceanographic simulations as well as differences in environmental factors. The level of genetic diversity gradually decreased towards the edge of the species distribution.

This study provides an example of the reduced genetic diversity in recently expanded marginal populations, thus indicating the possible vulnerability of these populations to environmental changes.

This finding underpins the importance of assessing the genetic diversity of newly colonized populations associated with climate change for conservation purposes. In addition, this study highlights the importance of pre-existing temperate regions as coral refugia, which has been rather underappreciated in local coastal management. However, reef-building corals have a relatively narrow range of temperature tolerance and are considered especially vulnerable to climate change.

The most well-known impact of warming oceans on corals is the increase in mass coral bleaching 2. In addition, climate change exacerbates local stresses by reducing water quality, which further threatens coral reefs 2.

In contrast to tropical and subtropical regions where coral abundance is declining due to increasing water temperatures, rapid poleward expansions of the ranges of hermatypic corals have been reported in temperate Japanese regions 3 and the Mediterranean Sea 4. Given that all of the range-expanding coral species are classified as Near Threatened or Vulnerable on the IUCN Red List, temperate regions may serve as refugia for hermatypic coral species in the near future 3 if the coral species can overcome the seasonal fluctuations in temperature and reduced light intensities 5.

Among the multiple definitions of refugia, we use the term as defined by Keppel and Wardell-Johnson 6. Winter water temperature has risen by 1. While such temperate region can be potential coral refugia, temperate peripheral populations may suffer from reduced genetic diversity due to small population sizes and isolation 8. However, no studies have assessed the genetic diversity or structures of such coral populations, including the recently colonized temperate populations that expanded within the last 50 years as a result of climate change along the Kuroshio Current.

In addition, there is a lack of knowledge of the oceanographic larval dispersal processes that shape the genetic variations and population structures of corals in the high-latitude regions of Japan. This study aimed to assess the genetic structures of recently expanded populations and examine the potential role of temperate regions as coral refugia in Japan. We thus examined the genetic diversity and meta-population structures of the subtropical to northernmost temperate populations of the reef-building coral Acropora hyacinthus , and the results were further compared with contemporary larval dispersal simulations in an oceanographic model.

Our target species, Acropora hyacinthus Dana, , is widely distributed in the tropical, subtropical, and some part of temperate regions of the Indo-Pacific 9. Northward range expansion of A. Previous studies that included some temperate populations found cryptic lineages species of A.

The A. These ecological features of this species are suitable for comparing the genetic diversity and connectivity of populations among temperate and subtropical regions. We defined the region south of the Watase Line 16 as subtropical and the region north of the Watase Line as temperate Fig. The region was split along this line because the biogeography of this region is often split between Yakushima and the Amami Islands, and the Kuroshio Current passes through this region.

Sampling sites in this study. The thickest grey curve indicates the Kuroshio Current. The circles represent pre-existing populations, and the stars indicate recently expanded populations. Only m5 has possible null alleles, and we thus excluded this locus from the genetic analysis of the population. A previous study indicated that there are cryptic species lineages in Acropora hyacinthus that are morphologically indistinguishable Thus, we identified the cryptic lineages in our dataset using STRUCTURE analysis 17 to determine the lineage associated with the recently expanded populations in temperate regions.

The principal coordinate analysis PCoA results also supported different lineages Fig. Moreover, populations with two or three different genetic lineages belonged to different clades in the neighbour-joining NJ phylogenetic trees Suppl.

These results, as well as those of a previous study 11 , indicated that these populations are possibly different species Because we are interested in the genetic connectivity and diversity of the lineages that have recently expanded in temperate regions, we focused on one lineage green lineage in Fig. Initially, significant linkage disequilibrium was found in two pairs of loci m4 and Amil; m4 and Amil However, linkages disappeared in the final dataset, which included only one lineage and no clones.

The X-axis indicates individuals from different populations, and the Y-axis indicates the estimated proportions of different clusters shown in different colours. Left The first two coordinates explain High clonal rates After removing possible clones, the north peripheral populations had reduced genetic diversity, which was observed in particular in the recently expanded populations Fig. Notably, all temperate populations, except for one north Yakushima population KAHyn , had more than one fixed monomorphic locus.

All the recently expanded populations had 2 to 4 fixed loci out of 8 loci Suppl. In total, 24 individuals had private alleles.

Eight out of the 32 individuals Two out of 59 individuals 3. These results suggest that subtropical populations have more private alleles than temperate populations, and recently expanded populations possibly originated from a small number of individuals with low genetic diversity. Plots of genetic diversity along central-to-peripheral populations.

Circles indicate H E , expected heterozygosity, diamonds indicate H O , observed heterozygosity, and triangles indicate allelic richness. IBD patterns based on oceanographic distances using different sample sets a all populations; b excluding recently colonized populations.

This result suggests that populations in temperate regions were generally genetically close to each other. The Tsukijima population in Miyazaki TUK was one of the most isolated populations in the temperate region, most likely because the artificial structure surrounding this population N.

Yasuda pers. The estimation of recent gene flow based on the assignment method using GeneClass2 showed that 95 out of individuals were successfully assigned to one of the populations. Most of the successfully assigned individuals 15 out of 16 in the recently expanded populations suggested self-seeding. Only one out of 76 1. Larval dispersal generally occurred northward along the Kuroshio Current Fig. Larval dispersal from temperate to subtropical areas seemed uncommon within a single generation because larval dispersal is physically limited to the path of the Kuroshio Current here called the Kuroshio-associated barrier , although dispersal could be achieved through multiple generations or occasional long dispersals Fig.

The Kuroshio-associated barrier corresponds to the biogeographic boundary called the Watase Line Fig. Unidirectional dispersal was observed from the western Kyushu region E in Fig. The colour contours on the right indicate the probability of a larva arriving at a sink site from a source site. Cryptic lineages were found in A. The Kuroshio-associated barrier also matched the Watase Line, which is the biogeographic barrier that separates terrestrial fauna and was caused by land bridges and sea barriers in past climates Larval dispersal simulations using particle tracking averaged over 24 years indicated discontinuous patterns of connectivity between Yakushima and the Amami Islands Fig.

This discontinuity is possibly due to the Kuroshio path crossing between Yakushima and the Amami Islands, which prevents direct dispersal of single generations from the subtropics to areas further north referred to as the Kuroshio-associated dispersal barrier. This study demonstrates that the Watase Line can be found in marine species due to the existence of the Kuroshio-associated dispersal barrier. The limited larval transport from subtropical to temperate regions within a single generation Fig.

Further regular monitoring of the distributions of all cryptic lineages using genetic markers is necessary to assess the poleward migration of the species. Alternatively, IBD patterns produced by a simple linear stepping-stone model explains the reduced genetic diversity near the edge. If a population structure is assumed to exhibit linearly uniform distribution over a large distance with limited migration in a simple linear stepping-stone model, then IBD genetic structure can theoretically be observed Under such a situation, Tajima 19 demonstrated that the level of DNA polymorphism is highest in the central populations and gradually decreases towards peripheral populations.

Our data relatively fit this linear stepping-stone model because significant IBD patterns were observed when oceanographic distance was used.

Although more data are needed, a linear stepping-stone model can at least partially explain the observed patterns. Environmental factors, such as low sea water temperature 22 , high concentration of chlorophyll a, particulate organic carbon POC 23 , reduced aragonite saturation 24 , light intensity 25 , and high turbidity 26 around northern populations Suppl.

On the other hand, the larger genetic diversity in the subtropical populations can be partly explained by possible hybridization between closely related lineages as found in Fig.

Some previous studies have also provided evidence for reduced genetic diversity in peripheral coral populations. For example, both brooder and broadcaster coral species in the southernmost reef in the Pacific showed lowered genetic diversity In the Atlantic, another coral species, Montastraea cavernosa , showed lower genetic diversity in peripheral populations These studies suggested that a small founding population, small effective population size of genetic drift, or inbreeding depression caused reduced genetic diversity in peripheral coral populations.

However, expanding coral populations do not always follow this trend of reduced genetic diversity, as was demonstrated in the Mediterranean coral Oculina patagonica The clonal rates were higher in temperate regions than in subtropical regions. Although the mechanism is unclear, different habitat characteristics i. In Acropora palmata , different rates of asexual reproduction are known to be related to different habitat characteristics While the historical gene flow analysis e.

This result concords with the fact that peripheral temperate coral populations are mostly self-sustained by local spawning Recently expanded populations were therefore possibly seeded from other temperate populations by occasional long dispersal and then sustained themselves by self-seeding. One possible explanation is that harsh environments around GAH Suppl. Alternatively, the Goto population was colonized by other genetically diverged populations, such as those from Taiwan through the Taiwan-Tsushima warm current system 32 , that were not analysed in this study.

Previous study has claimed that peripheral populations with low genetic diversity are some of the most active regions of speciation because of such genetically distinct features Further genetic analysis of Goto will be interesting to examine potential speciation in such a peripheral region. Significant IBD patterns were detected only when oceanographic distance was used Fig. This result indicates that overall, the effect of genetic drift is stronger than the effect of gene flow between distant populations.

We expected that the larval dispersal model rather than oceanographic distance would have significant IBD patterns because genetic structure is considered to be most associated with larval dispersal.

However, the IBD patterns that were derived using the number of larvae between sites based on numerical simulations did not improve in comparison to those using Euclidean distances and oceanographic distances Fig.


Acropora hyacinthus

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Crown-of-thorns starfish preferentially prey upon Acropora corals. It was described by Nemenzo in Acropora hyacinthus occurs in plate- or table-shaped wide colonies that consist of a number of thin branches in a lattice structure. It has strongly inclined branchlets.


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