This blog post is provided by Alicia Dalongeville, Emilie Boulanger and Stéphanie Manel and tells the #StoryBehindThePaper for the paper “Climate differently influences the genomic patterns of two sympatric marine fish species”, which was recently published in the Journal of Animal Ecology. Boulanger and colleagues show how the genetic variation of two marine fish species is linked to climatic conditions across the Mediterranean Sea, suggesting their ability to adapt to climate change. Featured image of the white seabream (Diplodus sargus) and the striped red mullet (Mullus surmuletus) by @reservebenfit.

CLIMATE SHAPES GENETIC DIVERSITY

Genetic diversity within a species is an important component of biodiversity, as it offers the species the ability to adapt to its environment. Decrypting how genetic variation is shaped by climatic conditions is essential to accurately predict the impact of climate change on living organisms. But fishes are highly mobile and can exchange genes over long-distances, which makes it difficult to detect the influence of climate on their genetic variation. 

TWO EXPLOITED MARINE FISH

The white seabream Diplodus sargus (picture, left) and the striped red mullet Mullus surmuletus (right) are fishes targeted by small-scale fisheries. They both inhabit rocky and sandy coastal shores across the Mediterranean Sea and Eastern Atlantic Ocean, and spend their first month of life as planktonic larvae that can disperse with oceanic currents. They offer a promising model for studying the genetic response of marine fishes to climate variations.

PAPER IN FOCUS

Our study was conducted across the entire Mediterranean Sea, a recognized hotspot of biodiversity, which harbours heterogeneous conditions of water temperature, salinity, and primary productivity (the production of organic substances by plants and algae, which can be used as food by other organisms). Previous research in the area has shown a spatially homogeneous genetic distribution for both species. However, there has not been any study covering the entire Mediterranean Sea with a high number of fish samples and a high number of genetic markers. This finer resolution has the potential to uncover hidden patterns of genetic variation and reveal species adaptation to their local climatic conditions.

We collected 297 individuals of white seabreams in 59 different locations, and 526 individuals of striped red mullet in 64 different locations, and we used next generation sequencing methods to develop 8206 (white seabream) and 2794 (striped red mullet) Single Nucleotide Polymorphism (SNP) genetic markers to characterize each individual. Then we applied a landscape genomics approach to test whether the variation of genetic markers between individuals was related to temperature, salinity, or primary productivity of the area where they lived.

We detected a common barrier to genetic exchanges for both species at the entrance of the Mediterranean Sea (called the Alboran Sea). This barrier has been previously documented for other fish species, and is created by circular oceanic currents coming from the Atlantic Ocean that prevent the movement of larvae and adult fish between the Alboran Sea and the rest of the Mediterranean Sea.

We also found that water temperature and primary productivity influence the genetic variation of the two species, by revealing specific genetic markers associated with these two climatic variables. By matching these markers on the genome of each species, we identified a total of 14 genes potentially involved in the adaptation of the white seabream and the striped red mullet to temperature and productivity.

Our study thus indicates that despite genetic exchanges over long distances, both species are adapted to the local climatic conditions prevailing in their living area. Such information is important for the sustainable management of fisheries and the design of protected area in face of climate change. Indeed, fish populations adapted to cold waters are at risk of extinction due to warming, and human pressures should be relieved to offer them the chance to adapt. Conversely, warm-adapted populations can be sources of well-adapted genes brought to other populations by exchanges of larvae and adult fishes. Protecting these populations can boost the adaptation of the species to climate change.