PhD Code: MARES_14_19:
- Host institute 1: P3 - University of Bologna
- Host institute 2: P5 - University of Algarve
- Host institute 3: CCMAR (Algarve)
- T1 - Future Oceans: temperature changes - hypoxia - acidifation
- T2 - Understanding biodiversity effects on the functioning of marine ecosystems
- Laura Airoldi
- Ester Serrao
- (additional supervision will be provided by Dr. Jorge Assis – objective 1, Dr. João Neiva – objective 2, and Dr. Gareth Pearson – objective 3)
The evolutionary history of European biodiversity has been greatly shaped by the highly variable Pleistocene climatic variations, during which glacial/interglacial periods caused multiple range shifts. These have left their fingerprints on the current genetic diversity of species and their past influence can help to predict future consequences of further changes in climatic variables.
One of the consequences of such climatic variability was the separation of refugial populations that with time and isolation might have speciated. In the Adriatic Sea, the species Fucus virsoides was one such case (e.g., Canovas et al. 2011). Currently endemic to the Adriatic Sea, this species now has a very restricted distribution and several populations have been reported to have gone extinct. The causes of such regression are unknown but presumed to be related to climatic or habitat variables that have become unsuitable. It is also unknown whether the species retains differentiated populations and hotspots of unique genetic diversity along its range, presumed to occur along long-term persistence zones. Species distribution models, developed for other intertidal Fucus (Assis et al. 2014), suggest indeed, the occurrence of favourable persistence regions in the Adriatic, for such intertidal canopy species. This thesis plan aims to understand the past evolutionary history of this species, how has it influenced its present genetic background and fitness, also predicting its future under new climatic scenarios. In addition, comparing transcriptome and fitness responses to climatic stress between populations and with its sister species will allow to infer evolutionary selective processes involved in the adaptation of this species to the very distinct and unique habitat of the Adriatic sea.
The proposed MARES project will cover three objectives:
- 1) to develop a transferrable model for the distribution of Fucus virsoides, a species endemic to the Adriatic sea, and to use this to hindcast the species past range variations and forecast future changes.
- 2) to estimate the genetic diversity and differentiation within and between populations of Fucus virsoides along its distributional range. These will be compared with the results of objective 1 to understand past demographic causes of present genetic patterns.
- 3) to compare fitness responses and transcriptomes of Fucus virsoides with its Atlantic sister species Fucus spiralis and Fucus guiryi, to look for selective differences that F. virsoides might have developed during its evolutionary history.
- Distribution models will be produced by an ensemble of a set of transferable models, trained with distribution records in relation to current climate conditions, and projected onto multiple proxies of past climate extremes derived from ocean-atmosphere general circulation models (e.g., Neiva et al. 2014). Regions of long-term persistence will be inferred as those where suitable habitat occurred over the most extreme events of the recent past (Last Glacial Maximum, Mid-Holocene, present). The area of potential habitat will be determined for every region of persistence (Assis et al. 2014).
- Samples will be collected across the distributional ranges of F. virsoides to cover the potential expansion, contraction and persistence zones. Sampling will include sister taxa as reference points of comparison. These will be genotyped for multiple loci using high resolution nuclear markers already available, to recover the ancient biogeographic/demographic history of the species and to compare with sister species (Cánovas et al. 2011; Zardi et al. 2011).
- For comparison of fitness and gene expression (transcriptome) responses to climatic stress between populations and with its sister species, common garden experiments and comparative transcriptome analyses of gene expression will be conducted. Acclimated samples will be exposed to controlled thermal and heat shock (HS) treatments and physiological indicators of resilience relative to appropriate controls will be assayed after exposure . Physiological response (photosynthetic parameters, growth) will be determined during stress exposure and recovery in control conditions. For assessment of gene expression responses in RNA-seq experiments experimental tissues will be lyophilized and total RNA extracted. Generation and sequencing of cDNA libraries will be outsourced (Illumina). Gene expression from biological replicates will be analyzed by mapping reads onto de novo assembled reference transcriptomes (Velvet-Oases, Trinity; [Pearson et al., unpublished]); statistical analysis of differential expression between treatments will be performed with the aid of open-source software (e.g., RSEM). These results will be validated by real-time PCR (qPCR), following the methods of Pearson et al. (2009) and Martins et al. (2013). Functional annotation and statistical analysis will use public protein databases and expression and annotation data will be integrated in a relational database to facilitate analyses.
- Assis J, Serrão EA, Claro B, Perrin C, Pearson GA (submited) Climate-driven range shifts explain the distribution of extant gene pools and predict future loss of unique lineages in a marine brown alga.
- Cánovas FG, Mota CF, Serrão EA, Pearson GA. (2011). Driving south: a multi-gene phylogeny of the brown algal family Fucaceae reveals relationships and recent drivers of a marine radiation. BMC Evol. Biol. 11:371.
- Martins MJ, Mota CF, Pearson GA (2013). Sex-biased gene-expression in the broen alga Fucus vesiculosus. BMC Genomics 14:295 http://www.biomedcentral.com/1471-2164/14/294
- Neiva J, Assis J, Fernandes F, Pearson G a., Serrão EA (2014) Species distribution models and mitochondrial DNA phylogeography suggest an extensive biogeographical shift in the high-intertidal seaweed Pelvetia canaliculata. Journal of Biogeography, in press
- Pearson GA, Lago-Leston A, Mota C (2009) Frayed at the edges: selective pressure and adaptive response to abiotic stressors are mismatched in low diversity edge populations. Journal of Ecology 97: 450-462
- Zardi GI, Nicastro KR, Canovas F, Ferreira Costa J, Serrão EA, Pearson GA. (2011). Adaptive Traits Are Maintained on Steep Selective Gradients despite Gene Flow and Hybridization in the Intertidal Zone. PLoS One 6:e19402.
The candidate is expected to publish the results of the project together with the supervisors in at least three peer-reviewed scientific articles. He/she will present the outcomes at two international conferences. The topics of climate-induced evolutionary and selectiveresponses, range shifts, extinctions and genetic biodiversity are expected to raise much attention from the broad scientific community.