Long‐term acclimation to reciprocal light conditions suggests depth‐related selection in the marine foundation speciesPosidonia oceanica

Abstract

Phenotypic differences among populations of the same species reflect selective responses to ecological gradients produced by variations in abiotic and biotic factors. Moreover, they can also originate from genetic differences among populations, due to a reduced gene flow. In this study, we examined the extent of differences in photo‐acclimative traits of Posidonia oceanica (L.) Delile clones collected above and below the summer thermocline (i.e., −5 and −25 m) in a continuous population extending along the water depth gradient. During a reciprocal light exposure and subsequent recovery in mesocosms, we assessed degree of phenotypic plasticity and local adaptation of plants collected at different depths, by measuring changes in several traits, such as gene expression of target genes, photo‐physiological features, and other fitness‐related traits (i.e., plant morphology, growth, and mortality rates). Samples were also genotyped, using microsatellite markers, in order to evaluate the genetic divergence among plants of the two depths. Measures collected during the study have shown a various degree of phenotypic changes among traits and experimental groups, the amount of phenotypic changes observed was also dependent on the type of light environments considered. Overall plants collected at different depths seem to be able to acclimate to reciprocal light conditions in the experimental time frame, through morphological changes and phenotypic buffering, supported by the plastic regulation of a reduced number of genes. Multivariate analyses indicated that plants cluster better on the base of their depth origin rather than the experimental light conditions applied. The two groups were genetically distinct, but the patterns of phenotypic divergence observed during the experiment support the hypothesis that ecological selection can play a role in the adaptive divergence of P. oceanica clones along the depth gradient.

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

“…The population genetic structure was not explained by geographic distance, as neither neutral nor non-neutral genetic variation were significantly correlated with geographic distance (no isolation by distance, IBD). These findings were in line with previous studies Dattolo et al 2017;Serra et al 2010). Conversely, neutral genetic variation was significantly correlated with temperature.…”

“…Irradiance measured at the Stareso site was markedly different between the two sampling times. Recent studies support the notion that P. oceanica living along the bathymetric gradient have differential resilience and are locally adapted to their local environment (Dattolo et al 2017;Marin-Guirao et al 2016). Shallow populations of P. oceanica show faster and higher induction of heat-response gene, a potential form of local adaptation to higher temperature regimes (Marin-Guirao et al 2016).…”

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, ).…”

Nutrient Loading Fosters Seagrass Productivity Under Ocean Acidification

“…Hence, at low pH, the increase in the cover of leaf epiphytes generated by nutrient enrichment, although moderate, may have indirectly contributed to enhance leaf growth of P. oceanica by reducing light stress 52 . Indeed, although shallow P. oceanica plants are adapted to live in high-light conditions, they activate specific mechanisms of defence from excessive light, that are modulated during the daily cycle 53 , 54 . However, further manipulative experiments are needed to assess the role of epiphytes as light screen on seagrass leaves.…”