Abstract
Global environmental changes may have a profound impact on ecosystems. In this context, it is crucial to gather biological and ecological information of the main species in marine communities to predict and mitigate potential effects of shifts in their distribution, abundance, and interactions. Using genotyping by sequencing (GBS), we assessed the genetic structure of a keystone species in the Mediterranean shallow littoral ecosystems, the black sea urchin Arbacia lixula. This bioengineer species can shape their communities due to its grazing activity and it is experiencing an ongoing expansion with increasing temperatures. The population genomic analyses on 5,241 loci sequenced in 240 individuals from 11 Mediterranean sampled populations revealed that all populations were diverse and showed significant departure from equilibrium. Albeit genetic differentiation was in general shallow, a significant break separated the western and eastern Mediterranean populations, a break not detected in previous studies with less resolutive markers. Notably, no clear effect of the Almería-Oran front, an important break in the Atlanto-Mediterranean transition, could be detected among the western basin populations, where only a slight differentiation of the two northernmost populations was found. Despite the generally low levels of genetic differentiation found, we identified candidate regions for local adaptation by combining different genomic analysis with environmental data. Salinity, rather than temperature, seemed to be an important driver of genetic structure in A. lixula. Overall, from a population genomics standpoint, there is ample scope for A. lixula to continue thriving and adapting in the warming Mediterranean.
Highlights
The Mediterranean is a sea under siege (Coll et al, 2012)
Population Genomics of Arbacia lixula (Lejeusne et al, 2010), as illustrated by mass mortality events correlated with thermal anomalies (Rivetti et al, 2014; Garrabou et al, 2019), or multi-species collapses related to exceptional thermal conditions in the Levant basin (Rilov, 2016)
We have assessed the genetic structure of a keystone species in Mediterranean shallow littoral communities, the black sea urchin Arbacia lixula
Summary
The Mediterranean is a sea under siege (Coll et al, 2012) In this highly anthropized basin, the sum of direct human impacts, introduced species, and ongoing global change is altering the communities, ecosystem services, health and economic value of the marine environment (Linares et al, 2020). The ongoing warming trend of the surface seawater of the Mediterranean (Shaltout and Omstedt, 2014) can favor the expansion of non-indigenous species with tropical affinities (Raitsos et al, 2010; Bianchi et al, 2018), and the spreading of native warm-affinity biota toward northern waters of its basin, a process called “meridionalisation” of the Mediterranean Sea (Bianchi, 2007; Parravicini et al, 2015). Barren grounds are resilient states, and a decrease of sea urchin abundance below the tipping point is typically insufficient to revert to the macroalgal-dominated landscapes (hysteresis, Ling et al, 2015)
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