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A comparison of genetic connectivity in two deep sea corals to examine whether seamounts are isolated islands or stepping stones for dispersal

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ABSTRACT

Ecological processes in the deep sea are poorly understood due to the logistical constraints of sampling thousands of metres below the ocean’s surface and remote from most land masses. Under such circumstances, genetic data provides unparalleled insight into biological and ecological relationships. We use microsatellite DNA to compare the population structure, reproductive mode and dispersal capacity in two deep sea corals from seamounts in the Southern Ocean. The solitary coral Desmophyllum dianthus has widespread dispersal consistent with its global distribution and resilience to disturbance. In contrast, for the matrix-forming colonial coral Solenosmilia variabilis asexual reproduction is important and the dispersal of sexually produced larvae is negligible, resulting in isolated populations. Interestingly, despite the recognised impacts of fishing on seamount communities, genetic diversity on fished and unfished seamounts was similar for both species, suggesting that evolutionary resilience remains despite reductions in biomass. Our results provide empirical evidence that a group of seamounts can function either as isolated islands or stepping stones for dispersal for different taxa. Furthermore different strategies will be required to protect the two sympatric corals and consequently the recently declared marine reserves in this region may function as a network for D. dianthus, but not for S. variabilis.

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Predicted dispersal of passive particles from the Tasmanian seamounts.The dispersal probabilities were generated using “Connie2.0” CSIRO Connectivity Interface http://www.csiro.au/Connie2/ and are based on the sum across years 1993–2007. Dispersal was modelled at 995 m depth (the black cross marks release point), with a dispersal period of 25 days, and across the likely reproductive period for D. dianthus and S. variabilis in the Southern Ocean (January to May44). The figure was created in R version 3.1.289 using the packages raster90, rasterVis91 and sp92.
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f6: Predicted dispersal of passive particles from the Tasmanian seamounts.The dispersal probabilities were generated using “Connie2.0” CSIRO Connectivity Interface http://www.csiro.au/Connie2/ and are based on the sum across years 1993–2007. Dispersal was modelled at 995 m depth (the black cross marks release point), with a dispersal period of 25 days, and across the likely reproductive period for D. dianthus and S. variabilis in the Southern Ocean (January to May44). The figure was created in R version 3.1.289 using the packages raster90, rasterVis91 and sp92.

Mentions: There was no evidence of isolation by distance in either species across the Tasmanian Seamounts (D. dianthus: Mantel’s R2 = 0.025, p = 0.321; S. variabilis Mantel’s R2 = 0.014, p = 0.106). For D. dianthus, values of Nem based on coalescent estimates of migration were generally large and ranged from 0.09 to 156. Of the 50 estimates of migration between all pairs of sites, 38 resulted in Nem > 1, and 20 of these with Nem > 10 indicating sufficient gene flow for ecological connectivity among most seamounts49. Seventy three percent of pairwise estimates of Nem among seamounts were significantly greater than 1 (and only 3% significantly <1; Table S6) emphasising the considerable gene flow among populations of D. dianthus. Furthermore, in 15 of the 25 seamount pair comparisons there was significant bi-directionality in migration (Fig. 5, Table S6) and overall ≈70% of migration in D. dianthus occurred in a westerly direction. This is consistent with estimates of particle dispersal at ~1000 m in the Tasmanian Seamount region which predicts a westward flow in the months when D. dianthus is most likely to be spawning (Fig. 6). However, tests of four different models of gene flow showed strong support only for a full model of dispersal (p > 0.9) above a westward, eastward or panmictic pattern of dispersal, suggesting either that reproduction and dispersal occurs outside of the period of predominately westward flow or other mechanisms are influencing gene flow in this species.


A comparison of genetic connectivity in two deep sea corals to examine whether seamounts are isolated islands or stepping stones for dispersal
Predicted dispersal of passive particles from the Tasmanian seamounts.The dispersal probabilities were generated using “Connie2.0” CSIRO Connectivity Interface http://www.csiro.au/Connie2/ and are based on the sum across years 1993–2007. Dispersal was modelled at 995 m depth (the black cross marks release point), with a dispersal period of 25 days, and across the likely reproductive period for D. dianthus and S. variabilis in the Southern Ocean (January to May44). The figure was created in R version 3.1.289 using the packages raster90, rasterVis91 and sp92.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5385499&req=5

f6: Predicted dispersal of passive particles from the Tasmanian seamounts.The dispersal probabilities were generated using “Connie2.0” CSIRO Connectivity Interface http://www.csiro.au/Connie2/ and are based on the sum across years 1993–2007. Dispersal was modelled at 995 m depth (the black cross marks release point), with a dispersal period of 25 days, and across the likely reproductive period for D. dianthus and S. variabilis in the Southern Ocean (January to May44). The figure was created in R version 3.1.289 using the packages raster90, rasterVis91 and sp92.
Mentions: There was no evidence of isolation by distance in either species across the Tasmanian Seamounts (D. dianthus: Mantel’s R2 = 0.025, p = 0.321; S. variabilis Mantel’s R2 = 0.014, p = 0.106). For D. dianthus, values of Nem based on coalescent estimates of migration were generally large and ranged from 0.09 to 156. Of the 50 estimates of migration between all pairs of sites, 38 resulted in Nem > 1, and 20 of these with Nem > 10 indicating sufficient gene flow for ecological connectivity among most seamounts49. Seventy three percent of pairwise estimates of Nem among seamounts were significantly greater than 1 (and only 3% significantly <1; Table S6) emphasising the considerable gene flow among populations of D. dianthus. Furthermore, in 15 of the 25 seamount pair comparisons there was significant bi-directionality in migration (Fig. 5, Table S6) and overall ≈70% of migration in D. dianthus occurred in a westerly direction. This is consistent with estimates of particle dispersal at ~1000 m in the Tasmanian Seamount region which predicts a westward flow in the months when D. dianthus is most likely to be spawning (Fig. 6). However, tests of four different models of gene flow showed strong support only for a full model of dispersal (p > 0.9) above a westward, eastward or panmictic pattern of dispersal, suggesting either that reproduction and dispersal occurs outside of the period of predominately westward flow or other mechanisms are influencing gene flow in this species.

View Article: PubMed Central - PubMed

ABSTRACT

Ecological processes in the deep sea are poorly understood due to the logistical constraints of sampling thousands of metres below the ocean&rsquo;s surface and remote from most land masses. Under such circumstances, genetic data provides unparalleled insight into biological and ecological relationships. We use microsatellite DNA to compare the population structure, reproductive mode and dispersal capacity in two deep sea corals from seamounts in the Southern Ocean. The solitary coral Desmophyllum dianthus has widespread dispersal consistent with its global distribution and resilience to disturbance. In contrast, for the matrix-forming colonial coral Solenosmilia variabilis asexual reproduction is important and the dispersal of sexually produced larvae is negligible, resulting in isolated populations. Interestingly, despite the recognised impacts of fishing on seamount communities, genetic diversity on fished and unfished seamounts was similar for both species, suggesting that evolutionary resilience remains despite reductions in biomass. Our results provide empirical evidence that a group of seamounts can function either as isolated islands or stepping stones for dispersal for different taxa. Furthermore different strategies will be required to protect the two sympatric corals and consequently the recently declared marine reserves in this region may function as a network for D. dianthus, but not for S. variabilis.

No MeSH data available.


Related in: MedlinePlus