The genetic code of the ‘raor’ discovered

A group of investigators of the Instituto Mediterráneo de Estudios Avanzados, IMEDEA (CSIC-UIB), and of the Centro Nacional de Análisis Genómico (CNAG) of Barcelona have accomplished to decipher the pieces that make up the genetic code of the ‘raor’. A project with great impact on the biodiversity terrain and the conservation of the marine species.

The investigation that has allowed to obtain the first genome to a chromosome scale of this species, supposes an enormous step forwards to understand the role of the molecular biology in the conservation of the fishing resources.

The ‘raor’ species is very valued and known, but it is very unusual to talk about their behavior characteristics which make them a relevant scientific species. The Xyrichtys novacula, pearly razorfish or commonly known as cleaver wrasse, is a fish that has converted in to a media icon, especially for the balearic fishing tradition and its high culinary value. It is less known for its particular behavior and genetics. Same as the humans, the ‘raors’ incorporate chronotypes into their behavior, i.e. individual preferences for the times at which they perform their daily activities, with the result that some ‘raors’ are active at an earlier time than others.

They have been observed to have certain social behaviors, with the more aggressive males vigorously defending large patches of sandy bottom, which include the smaller territories of the females in their harem. These behavioral peculiarities are genetically encoded in both humans and other animals.

In a fisheries-exploited species such as the common ‘raor’, the fact that certain behaviors have a genetic basis may result in the elimination of certain genetic variants in natural populations that may compromise their future. Populations with little genetic diversity are less resilient, and this is where genetic studies come into play to guarantee the future of the common seabream. Josep Alós, one of the IMEDEA scientists leading this research, explains: "Knowing better what behavioral and genetic characteristics affect vulnerability to fishing can be very useful for designing conservation measures and ensuring the future of this species. Unfortunately, the genetic code of the common skate was not available to assess them.

IMEDEA and the National Centre for Genomic Analysis (CNAG) have worked together to decipher the genetic code of the common ‘raor’. Through this study, led by the CNAG's Genome Assembly and Annotation Team and the IMEDEA's Fish Ecology Laboratory, it has been possible to obtain all the genetic information contained in the 24 chromosomes of the common cleaver wrasse.

From this study it has been possible to conclude that ‘raors’ have one more chromosome than humans, despite the fact that the total size of their genome is smaller. Their genetic information is encoded in approximately 780 million units of genetic information, while in humans it has been estimated at 3.2 billion.

Another interesting peculiarity of this species is its lack of sex chromosomes. In humans, sex is attributed to us according to the combination of two types of chromosomes: XX for females and XY for males. In contrast, ‘raors’ do not have this chromosomal difference, as they are sequential hermaphrodites. This means that all ‘raors’ are born female and, after a few years, become male. This change is regulated by several genetic factors that change at a certain time in the life of the individual and are possibly related to internal growth and external factors, such as the absence of a dominant male in their social group.

The researcher in charge of this project, Margarida Barceló, explains that this information "will allow us to better understand how the different populations of ‘raors’ in the Balearic Islands are genetically connected. We will be able to determine whether they are isolated populations or if there are connections through marine currents. In addition, this knowledge will help us to assess the genetic conservation status of areas where fishing is more intense compared to protected areas, such as Marine Reserves. This, in turn, will give us the tools to provide advice to the administration to ensure sustainable management of the ‘raor’ fishery".