Dr. Santiago C. González-Martínez

Research interests

I have broad interests in the field of ecological and population genetics and genomics. My main current research is directed towards understanding:

  1. Local adaptation in forest trees at both wide-range and local spatial scales, and in particular along environmental and geographical gradients.
  2. The genetic processes associated with range expansions in Mercurialis annua, in particular the role of sexually-antagonistic selection.
  3. The genetic basis of ecologically-relevant adaptive traits, using association genetics and related population approaches.
  4. The genetic responses of complex forest systems to climate change, with a focus on biotic interactions between forest trees and associated organisms (e.g. ectomycorrhizal fungi and symbiotic bacteria).

For more details, please visit my personal research webpage

Current projects

Sex-linked loci, sexual specialization and local adaptation in Mercurialis annua complex
The sexual and genetic systems of a plant species directly regulate how genes are transmitted across generations. Accordingly, their study is of central importance to understand plant evolution. Populations of widespread plants normally have higher fitness at their home site than in other parts of the range. However, the genetic and molecular mechanisms underlying local adaptation are not well understood yet. How do plant populations adapt to a rapidly changing world? Why and how separate sexes evolve and are maintained in plants? What are the consequences of broad variation in sexual systems for plant survival at different spatial scales (local, widerange)? In this project we conduct innovative and multidisciplinary research, using state-of-the-art sequencing technology, to investigate how natural selection brings about local adaptation in plant populations with contrasting sexual (separate vs. combined sexes) and genetic (diploidy vs. polyploidy) systems. To address these questions, we are studying the ecological genomics of local adaptation in the Mercurialis annua s.l. species complex. This species complex shows an unusually broad variation in its sexual and genetic systems, as well as large phenotypic geographical variation, thus providing an outstanding model to study, at the genomic level, the role of mating and genetic factors on local adaptation. More information in the project webpage.

Adaptive variation, environmental gradients and demography in Mediterranean conifers: from genes to phenotypes and niches
Environmental change across a wide range of temporal and spatial scales is the rule rather than the exception. Necessary conditions for species and their populations to survive under these circumstances are local adaptation and/or migration. Current and future species responses to predicted environmental changes are embedded in demographic and evolutionary processes that occurred in the past. Therefore, understanding range-wide patterns and interactions between environmental change, demography and evolution taking place in the past is essential for developing future management strategies. Species from the Mediterranean Basin, inhabiting highly heterogeneous environments, are particularly at risk because of the predicted increase in aridity and recent land-use change in this area. It is thus of great interest to assess the adaptive potential of Mediterranean species. In this project, we focus more specifically on forest trees as they are ecologically dominant in many ecosystems and, at the same time, many of them are also economically important. We propose to study three conifers presenting partially overlapping distribution but with distinct demographic histories: cluster or maritime pine (Pinus pinaster), Aleppo pine (Pinus halepensis) and English yew (Taxus baccata). Our main goal is to investigate the evolutionary response of these conifers to selection by looking at three distinct levels of variation, namely, patterns of molecular diversity at neutral (microsatellites) and adaptive (candidate genes and Single Nucleotide Polymorphisms or SNPs) loci, phenotypic traits known to respond to variation in bioclimatic conditions, as well as present and future species distribution. The combination of various disciplines –population genetics and genomics, biogeography and ecology– provides an integrated view and a powerful approach to understand the molecular mechanisms responsible for adaptation as well as the drivers of selection (both climatic and ecologic). It also provides a basis to identify adaptive population differences that might help a species to survive future environmental changes.

Fire and phylogenetic structure of soil bacterial and ectomycorrhizal fungal communities
Over 40.000 wildfires occur yearly in Mediterranean Europe causing a devastating environmental damage. Burning modifies the morphology, taxonomy and phylogenetic structure of plant communities. Fire also stamps a genetic fingerprint on primary producers as it acts as a demographic and selective force. Less known is how burning alters the decomposer system and its ecosystem services through changing the soil environment. In this project, we survey the fire-induced shifts in the soil microbial genomes, biogeochemical functions and community structure in Mediterranean forests that have been either submitted to experimental burning or recurrent wildfires. In particular we:

i) Investigate the physical and chemical parameters determining the phylogenetic structure of bacterial and ectomycorrhizal (EM) fungal communities. Due to the symbiotic nature of the ectomycorrhizal interaction, we also hypothesize that tree host genotypes harbor different associated EM fungal communities and this determines the bacteria in the mycorrhizosphere.

ii) Research fire as a community assembly process. We analyse the bacterial and EM community structure (by 454 GS FLX pyrosequencing of phylogenetic markers) in pre- and post-fire soil samples. We expect that closely related species showing a heat-resistant phenotype to be overrepresented in the post-fire community, resulting in phylogenetic clustering. This would imply the loss of phylogenetic diversity, which is linked to the ecosystem functioning.

iii) Seek for molecular signatures of demographic and selective effects of fire on soil microbial genomes. We investigate the fire’s fingerprint throughout the genomes (ie. in neutral markers) and in candidate genes (e.g. encoding ammonia monooxygenase, laccase etc.) to ascertain whether burning affects the effective population sizes or selects certain phenotypes.

Understanding community phylogenetic patterns and the molecular basis of adaptation to recurrent fire is essential for revealing evolutionary and ecological processes, and to predict how the ecosystem functioning can be altered through the increasing wildfire frequency caused by temperature rise.

Scenarios for forest biodiversity dynamics under global change in Europe: identifying micro-evolutionary scale tipping points
Forests are a major reservoir of biodiversity and trees, as keystone organisms, directly impact the diversity and functioning of forest communities. Predicting the response of trees to ongoing global change (GC) is thus a critical scientific and societal issue. Along with phenotypic plasticity and migration, genetic adaptation is a central component of this response, particularly in trees whose high levels of diversity and long distance gene flow facilitates the spread of favorable genes. However, the existence of abundant genetic variation does not guarantee adaptation: if the climate and environmental changes are too quick, or genetic modifications are too slow, the population would go extinct before it can adapt to the new environmental challenges. Our hypothesis is that there is a critical level of genetic diversity for stress responses, which, together with the demographic impact of stress, predicts the likelihood of adaptation or extinction. The main goal of this project is to identify tipping points in the demographic and micro-evolutionary dynamics of tree populations, and to assess how human actions interfere in the adjustment between the rate of evolution and the velocity of GC. It brings a new and critical dimension, that of time, by focusing on regeneration. In trees, regeneration (from fertilization to early plant recruitment) is a key period of the life cycle, when selection is expected to be very strong and has the potential to catalyze the rapid spread of evolutionary novelties in the next generation. The amount of genetic variation available in adults and how it is transmitted, selected and expressed in juveniles will condition the ecological properties of the whole ecosystem in the next decades to centuries, which remains a challenging short and non-equilibrium term of evolution for long-lived organisms.


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