Deep connections: divergence histories with gene flow in mesophotic Agaricia corals

Abstract

Vastly understudied, mesophotic coral ecosystems lie below shallow reefs (> 30 m depth) and comprise ecologically distinct communities. Brooding reproductive modes appear to predominate among mesophotic-specialist species and may limit genetic connectivity among populations. Using reduced representation genomic sequencing, we assessed spatial population genetic structure (at 50 m depth) in an ecologically important mesophotic-specialist species, Agaricia grahamae among locations in the Southern Caribbean. We also tested for hybridisation with the closely related (but depth-generalist) species Agaricia lamarcki, within their sympatric depth zone (50 m). In contrast to our predictions, no spatial genetic structure was detected between the reefs of Curaçao and Bonaire (~ 40 km apart) within A. grahamae. However, cryptic taxa were discovered within both nominal species, with those in A. lamarcki (incompletely) partitioned by depth and those in A. grahamae occurring sympatrically (at the same depth). Hybrid analyses and demographic modelling identified contemporary and historical gene flow among cryptic taxa, both within and between A. grahamae and A. lamarcki. These results (1) indicate that spatial genetic connectivity in these ecologically important mesophotic species may be maintained over large geographic distances and (2) highlight that gene flow links taxa within this relativity diverse Caribbean genus.

Cryptic diversity and spatial genetic variation in the coral Acropora tenuis and its endosymbionts across the Great Barrier Reef

“…Hybridization and interspecific gene flow may be integral aspects of coral evolution (Hobbs et al, 2021 ; Willis et al, 2006 ). Yet, few studies have formally tested for gene flow between recent discrete taxa using demographic inference until recently (exceptions include: Cooke et al, 2020 ; Fifer et al, 2021 ; Hellberg et al, 2016 ; Ladner & Palumbi, 2012 ; Prada & Hellberg, 2020 ; Prata et al, 2022 ; Rippe et al, 2021 ). These historical analyses provide information on the speciation process and timing, including whether divergence occurred in the absence of gene flow (i.e.…”

“…Recent genetic studies have revealed surprising divisions and gene exchange among coral taxa, provoking re‐evaluations of both deep evolutionary relationships (Fukami et al, 2008 ; Kitahara et al, 2014 ; Ying et al, 2018 ) and relationships among closely related taxa. For example, population genomic surveys have uncovered distinct genetic clusters within Acropora (Cooke et al, 2020 ; Fifer et al, 2021 ; Rose et al, 2018 ; Underwood et al, 2020 ), Agaricia (Bongaerts et al, 2017 ; Prata et al, 2022 ), Montastraea (Rippe et al, 2021 ; Sturm et al, 2020 ), Pachyseris (Bongaerts et al, 2021 ), Pocillopora (Smith et al, 2017 ; van Oppen et al, 2018 ) and Siderastrea (Rippe et al, 2021 ), where some earlier microsatellite‐based studies had failed to detect these clusters. (For full taxonomic authorities for all species mentioned throughout this paper, see the World Register of Marine Species: www.marinespecies.org ).…”