Mario Blanco-Sánchez: Natural selection consistently favours an acquisitive resource-use strategy in Mediterranean semiarid plants

In this new post, Mario Blanco-Sánchez, Ph.D student at University Rey Juan Carlos, Spain, presents his latest publication ‘Natural selection favours drought escape and an acquisitive resource-use strategy in semiarid Mediterranean shrubs’. He discusses how he dealt with a striking result and encourages young ecologists to pursue their own interests in the field!

A Spanish translation of this blogpost is available to read here!

About the paper

Mediterranean ecosystems show large spatiotemporal environmental heterogeneity, with high interannual climatic variation and contrasting resource availability. As a consequence of these fluctuating stresses, Mediterranean plants have evolved functional adaptations to cope with abiotic stress (especially drought), and are often assumed to be tolerant species that thrive in highly stressful ecosystems. However, how individuals of the same species differ in traits related to resource use and stress response and, importantly, how such among-individual variation is related to fitness is unknown for most Mediterranean plants. Furthermore, since environmental variation may affect both the phenotypic expression of individuals and the patterns of selection (i.e., the suite of traits related to individual fitness), accounting for the high spatiotemporal environmental variation of Mediterranean ecosystems is crucial to robustly assess how natural selection is acting in natural populations.

Differences in the biotic composition (reflecting differences in the environmental conditions) of a) south slopes; b) north slopes. (credit: Mario Blanco-Sánchez)

Using a phenotypic selection study in natural semiarid conditions, we evaluated patterns of selection of key ecophysiological traits in two Mediterranean gypsum endemic species—Centaurea hyssopifolia and Helianthemum squamatum—dwelling in environments with contrasting abiotic conditions (south- and north-facing slopes of gypsum hills) during two climatically contrasting years (dry and mesic). Our study provides a large picture of how selection acts in natural conditions, since it quantifies the magnitude and direction of natural selection through two different fitness components (reproduction and survival), and at different spatiotemporal scales. We found that while phenotypic variation was not linked to survival of individuals, natural selection via reproductive fitness consistently favoured an acquisitive resource-use strategy in Mediterranean semiarid plants, allowing the reproduction of individuals before the most limiting climatic conditions of mid-late summer. Overall, our study sheds light on the successful traits and strategies of Mediterranean gypsum plants in natural conditions, which may in turn provide insight on the evolutionary responses of these species to further environmental change.

The idea of our study came to us due to our expertise and previous experience working on gypsum ecosystems. We realized that south- and north-facing slopes of gypsum hills strongly differ in their abiotic and biotic conditions. In the northern hemisphere, south-facing slopes receive greater insolation, resulting in higher evapotranspiration and lower water availability, thereby leading to significant differences in the biotic structure of both slopes. We thought these environmental differences across slopes would impose different selection pressures on individuals living in gypsum habitats. As well, we thought that the remarkable interannual climatic variability of gypsum habitats could alter the patterns of selection. Therefore, evaluating the traits under selection in two different years was critical to fully understand how selection acts in natural populations of Mediterranean plants.

This paper enhances our understanding of the adaptive traits and strategies of plants growing in Mediterranean ecosystems, being particularly valuable for readers interested in evolutionary ecology, natural selection, and plants growing in special substrates.

About the research

Our study assessed patterns of selection in two dominant gypsum endemic species across contrasting environmental conditions and climatically contrasting years. As you can guess, collecting the data of such an extensive field study was not easy and required tons of teamwork. We spent many hours phenotyping our experimental individuals, characterizing the microenvironmental conditions experienced by each plant, processing the collected samples, and analyzing our data. However, the greatest challenge of our study was to understand the results obtained at first. We expected that, due to the high environmental stress of gypsum habitats, individuals with conservative phenotypic values (i.e., smaller and more sclerophyllous leaves, lower leaf nutrient concentrations, higher water use efficiency, etc.) would show higher reproductive fitness—especially under more restrictive conditions such as dry years and south slopes. This conservative phenotype would be adaptive since it would prevent water loss in environments where water is scarce. However, we were wrong. Surprisingly, plants with acquisitive phenotypic values at the intraspecific level (i.e., larger and less sclerophyllous leaves, lower water use efficiency, early reproductive phenology, etc.) showed higher reproductive fitness. Furthermore, the adaptive value of an acquisitive resource-use was strikingly consistent across species, slopes, and years. How could plants that spend more water have higher fitness in a semiarid ecosystem?

Laura Díaz-Guerra and Marina Ramos-Muñoz measuring leaf chlorophyll content in the field. (credit: Mario Blanco-Sánchez)

It was a fascinating result, but very complex to explain! One day, while I was reading some papers, I came up with a likely explanation. Selection favored individuals with a drought-escape strategy! Individuals with higher resource acquisition rates showed a drought-escape strategy that allowed their rapid development and reproduction before the most limiting climatic conditions of mid-late summer in gypsum habitats. Our study highlights the need to shift our focus to the intraspecific level to unveil unexplored and even surprising adaptive plant strategies. Future studies should aim at identifying the precise physiological mechanisms that maintain this acquisitive strategy in highly stressful Mediterranean environments such as gypsum ecosystems and the evolutionary potential of adaptive traits. This is key in order to make inferences related to the adaptation of Mediterranean semiarid species in the face of climate change.

About the author

Mario Blanco-Sánchez (credit: Marina Ramos-Muñoz)

I am a Ph.D. student at Universidad Rey Juan Carlos, Spain, and I am enrolled in the Conservation of Natural Resources graduate program. The published study is a key part of my Ph.D. thesis, which explores the evolutionary responses of gypsum endemic plants in a climate change context.

My passion for ecology and conservation started early during my bachelor’s degree when I received fantastic and inspiring lectures from many of my professors at Universidad Rey Juan Carlos. Then, during my Master´s degree, I started to collaborate with one of my supervisors and her expertise and passion for evolutionary ecology really hooked me. When she offered me the opportunity to carry out my own research in her group, it only took me a second to say yes! It was one of the best decisions of my entire life. Although everyone struggles during a Ph.D., all the team involved in my thesis have supported and helped me with everything I needed. I am very grateful to all my co-authors and collaborators for making this process easier due to their patience and kindness. After four years of intense work, I feel that I have significantly grown up, both in a personal and a professional sense, with my Ph.D. thesis being the most challenging but fulfilling project in which I have undertaken. My advice to young researchers is to follow their dreams and keep working as hard and well as they are doing right now. The world is full of opportunities that are waiting for you!

Enjoyed this blogpost? Read the research here!

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