Adaptive responses along a depth and a latitudinal gradient in the endemic seagrass Posidonia oceanica

Abstract

Seagrass meadows provide important ecosystem services and are critical for the survival of the associated invertebrate community. However, they are threatened worldwide by human-driven environmental change. Understanding the seagrasses' potential for adaptation is critical to assess not only their ability to persist under future global change scenarios, but also to assess the persistence of the associated communities. Here we screened a wild population of Posidonia oceanica, an endemic long-lived seagrass in the Mediterranean Sea, for genes that may be target of environmental selection, using an outlier and a genome-wide transcriptome analysis. We identified loci where polymorphism or differential expression was associated with either a latitudinal or a bathymetric gradient, as well as with both gradients in an effort to identify loci associated with temperature and light. We found the candidate genes underlying growth and immunity to be divergent between populations adapted to different latitudes and/or depths, providing evidence for local adaptation. Furthermore, we found evidence of reduced gene flow among populations including adjacent populations. Reduced gene flow, combined with low sexual recombination, small effective population size, and long generation time of P. oceanica raises concerns for the long-term persistence of this species, especially in the face of rapid environmental change driven by human activities.

Biogeographical scenarios modulate seagrass resistance to small‐scale perturbations

“…Our study suggests that resistance of a seagrass species, here C. nodosa , substantially varies across its distributional range and, therefore, that ecotypes, from a resistance functional perspective, may be a common characteristic for seagrasses at local and regional scales, as it was hypothesized long ago for other marine macrophytes (Gerard & Du Bois, ). This result expands the recent discovery of local seagrass ecotypes, according to physiological, genetic, and genomic criteria (Dattolo, Marín‐Guirao, Ruiz, & Procaccini, ; Jahnke et al, ; Procaccini et al, ), including C. nodosa (Marín‐Guirao et al, ). Functional differentiation particularly occurs for marginal populations of macrophytes (Wernberg et al, ), likely resulting from lack of connectivity and restricted gene flow, which has the potential to promote independent evolution of population units (Cánovas, Mota, Serra, & Pearson, ).…”

“…Understanding mechanisms behind this pattern requires integration of biogeography, in terms of varying ecological and evolutionary contexts, but also understanding that the sensitivity of seagrass performance responses may change according to the level of biological organization, for example. at molecular, shoot, plant, or meadow levels (Ceccherelli et al, ; Jahnke et al, ; Roca et al, ; York et al, ).…”

“…The biogeographical context considerably affects the phenology of certain seagrass species (Blok, Olesen, & Krause‐Jensen, ). However, variation across biogeographical scales has been largely overlooked as an element driving resistance to local‐scale impacts of seagrass species (Barry et al, ; Fraser et al, ; Jahnke et al, ). Not surprisingly, experimental approaches to tackle resistance of “ecological engineers,” for example seagrasses, to varying perturbations have followed the traditional reductionist perspective of setting up experiments at local scales, that is, at the patch scale in the case of seagrass meadows (Leoni et al, ).…”

Heat‐stress induced flowering can be a potential adaptive response to ocean warming for the iconic seagrass Posidonia oceanica

“…In fact, the contrasting ability of C‐plants and W‐plants to resist warming in this mesocosm experiment, together with the marked genetic differentiation existing between the two populations, can be interpreted as an adaptive feature that reflects the local adaptation of these plants (Marín‐Guirao et al, ). Further evidence for local adaptation of P. oceanica populations along the latitudinal gradient in the western Mediterranean basin was recently provided by Jahnke et al (), and is supported by the reduced gene flow and by the divergence among genes that regulate central metabolism and cell functions, with potential connection to temperature.…”

“…During the first three days of June 2016, fragments of rooted Posidonia oceanica rhizomes bearing apical growth meristems and a large number of connected shoots (>30 shoots per fragment) were collected by divers in shallow (5-7 m depth) and healthy meadows from two distant between the two populations, can be interpreted as an adaptive feature that reflects the local adaptation of these plants . Further evidence for local adaptation of P. oceanica populations along the latitudinal gradient in the western Mediterranean basin was recently provided by Jahnke et al (2018), and is supported by the reduced gene flow and by the divergence among genes that regulate central metabolism and cell functions, with potential connection to temperature.…”