<p>Ecological speciation through adaptation to different habitats can readily occur without strong geographic isolation when the same traits underlie both ecological divergence and reproductive isolation. In light-dependent corals with environment-mediated spawning, adaptation to varying light regimes across depths provides opportunities for such speciation. We show that depth-related distributions are common among sister lineages of corals within the photic zone. We then investigated molecular drivers of depth-associated adaptive divergence by analyzing sequence variation in proteins related to environmental sensing in depth-segregated and light-dependent lineages in the <i>Orbicella</i> species complex. Specifically, we analyzed 1) two genetically divergent ecotypes of <i>Orbicella faveolata</i> across a depth gradient, and 2) two depth-segregated sister species, <i>O. annularis</i> and <i>O. franksi</i>, with different spawning times following sunset. Genome-wide analyses indicate divergence across depths occurred through adaptation via positive selection on G-protein-coupled receptors (GPCRs). These molecules mediate chemo/photo/thermo-reception, enhancing physiological adaptation across environments, and are also involved in reproductive isolation via differences in spawning time. Our study proposes a molecular mechanism for the origin of depth-segregated coral species, common across anthozoans, in which ecological divergence operates at spatial scales smaller than their larval dispersal potential, and highlights avenues contributing to generating biodiversity in the sea.</p>

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Speciation across depth gradients in reef corals

  • Matías Gómez-Corrales,
  • Ana María González Angel,
  • Bishoy Kamel,
  • Mónica Medina,
  • Nancy Knowlton,
  • Don R. Levitan,
  • Carlos Prada

摘要

Ecological speciation through adaptation to different habitats can readily occur without strong geographic isolation when the same traits underlie both ecological divergence and reproductive isolation. In light-dependent corals with environment-mediated spawning, adaptation to varying light regimes across depths provides opportunities for such speciation. We show that depth-related distributions are common among sister lineages of corals within the photic zone. We then investigated molecular drivers of depth-associated adaptive divergence by analyzing sequence variation in proteins related to environmental sensing in depth-segregated and light-dependent lineages in the Orbicella species complex. Specifically, we analyzed 1) two genetically divergent ecotypes of Orbicella faveolata across a depth gradient, and 2) two depth-segregated sister species, O. annularis and O. franksi, with different spawning times following sunset. Genome-wide analyses indicate divergence across depths occurred through adaptation via positive selection on G-protein-coupled receptors (GPCRs). These molecules mediate chemo/photo/thermo-reception, enhancing physiological adaptation across environments, and are also involved in reproductive isolation via differences in spawning time. Our study proposes a molecular mechanism for the origin of depth-segregated coral species, common across anthozoans, in which ecological divergence operates at spatial scales smaller than their larval dispersal potential, and highlights avenues contributing to generating biodiversity in the sea.