RNA-SEQ APPLIED TO THE PEACOCK BLENNY SALARIA PAVO: UNVEILING THE GENE NETWORKS AND SIGNALLING PATHWAYS BEHIND PHENOTYPIC PLASTICITY IN A LITTORAL FISH

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RNA-SEQ applied to the peacock blenny Salaria pavo: unveiling the gene networks and signalling pathways behind phenotypic plasticity in a littoral fish

Publication . Cardoso, Sara de Jesus Dias; Canário, Adelino V. M.; Oliveira, Rui Filipe Nunes Pais de

Phenotypic plasticity is the ability of an individual genome to produce different phenotypes depending on environmental cues. These plastic responses rely on diverse genomic mechanisms and allow an organism to maximize its fitness in a variety of social and physical settings. The development of next-generation sequencing (NGS) technologies, especially RNA Sequencing (RNA-Seq), has made it possible to investigate the distinct patterns of gene expression known to be underlying plastic phenotypes in species with ecological interest. In teleost fishes, changes in phenotypes is often observed during the reproductive season, with shifts and adjustments in dominance status that can lead to the co-existence of multiple reproductive morphs within the same population. One such example is the peacock blenny Salaria pavo (Risso, 1810), a species where the intensity of mating competition varies among populations due to nest-site availability, such that two different levels of plasticity arise: 1) intraspecific variation in reproductive behaviour for males that can follow either of two developmental pathways, grow directly into nest-holder males, or behave first as female mimics to sneak fertilizations (sneaker males) and later transition into nest-holder males, and 2) inter-population variation in courting roles of females and nest-holder males. This system provides the ideal basis to apply RNA-Seq methods to study plasticity since differences in reproductive traits within and among populations can reveal which genetic and genomic mechanisms underpin the observed variation in behavioural response to changes in the social environment. However, the genomic information available for this species was scarce, and hence multiple sequencing techniques were used and the methodologies applied optimized throughout the work. In this thesis, we start by first obtaining a de novo transcriptome assembly to develop the first genetic markers for this species (Chapter 2). These microsatellites were used to elucidate the reproductive success (i.e. consisting of mating success and fertilization success) of male ARTs, which can be used as a proxy of Darwinian fitness (Chapter 3). In this study, we detected a fertilization success for nestholder males of 95%, and showed a stronger influence of the social environment rather than morphological variables in the proportion of lost fertilizations by nest-holder males of this species. Taking advantage of the developed transcriptome, we used highthroughput sequencing to obtain expression profiles for male morphs (i.e. intraspecific variation) and females in this species, and focus on the role of differential gene expression in the evolution of sequential alternative reproductive tactics (ARTs) that involve the expression of both male and female traits (Chapter 4). Additionally, we show how the distinct behavioural repertoires are facilitated by distinct neurogenomic states, which discriminate not only sex but also male morphs. Lastly, using two different target tissues, gonads and forebrain, we focus on the genomic regulation of sex roles in courtship behaviour between females and males from two populations under different selective regimes (inter-population variation), the Portuguese coastal population with reversed sex roles and the rocky Italian population with ‘conventional’ sex roles (Chapter 5). Here we demonstrate that variation in gene expression at the brain level segregates individuals by population rather than by sex, indicating that plasticity in behaviour across populations drives variation in neurogenomic expression. On the other hand, at the gonad level, variation in gene expression segregates individuals by sex and then by population, indicating that sexual selection is also acting at the intrasexual level, particularly in nestholder males by paralleling differences in gonadal investment. However, the genomic mechanisms underlying courtship behaviour were not fully elucidated, and more studies are necessary.

2019-05-06Doctoral thesis

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