Maintenance of Intraspecific Diversity in Response to Species Competition and Nutrient Fluctuations.

Jorin Hamer,Birte Matthiessen,Giannina S I Hattich,Silvia Pulina

doi:10.3390/microorganisms10010113

Abstract

Intraspecific diversity is a substantial part of biodiversity, yet little is known about its maintenance. Understanding mechanisms of intraspecific diversity shifts provides realistic detail about how phytoplankton communities evolve to new environmental conditions, a process especially important in times of climate change. Here, we aimed to identify factors that maintain genotype diversity and link the observed diversity change to measured phytoplankton morpho-functional traits Vmax and cell size of the species and genotypes. In an experimental setup, the two phytoplankton species Emiliania huxleyi and Chaetoceros affinis, each consisting of nine genotypes, were cultivated separately and together under different fluctuation and nutrient regimes. Their genotype composition was assessed after 49 and 91 days, and Shannon’s diversity index was calculated on the genotype level. We found that a higher intraspecific diversity can be maintained in the presence of a competitor, provided it has a substantial proportion to total biovolume. Both fluctuation and nutrient regime showed species-specific effects and especially structured genotype sorting of C. affinis. While we could relate species sorting with the measured traits, genotype diversity shifts could only be partly explained. The observed context dependency of genotype maintenance suggests that the evolutionary potential could be better understood, if studied in more natural settings including fluctuations and competition.

Highlights

Global biodiversity is threatened by five major drivers: habitat change, overexploitation, pollution, introduction of non-indigenous species, and climate change [1,2]
The coccolithophore Emiliania huxleyi and the diatom Chaetoceros affinis are different in their morpho-functional traits, such as cell shape and size, and nutrient uptake-related traits that are reflected in different nutrient uptake strategies; we assumed that the nine genotypes of each species used in this study show trait differences
While E. huxleyi showed a higher percentage of variability in Vmax, C. affinis exhibited higher variability in size

Summary

Introduction

Global biodiversity is threatened by five major drivers: habitat change, overexploitation, pollution, introduction of non-indigenous species, and climate change [1,2]. As a part of biodiversity, genetic or intraspecific diversity has received little attention for a long time [4], it has been shown to enhance ecosystem recovery [5] and was linked to physiological versatility and ecological resilience towards climatic stress [6]. Phytoplankton are diverse, globally distributed, and build the base for most marine food webs [8]. They account for approximately half of global primary productivity [9], and are substantial drivers for biogeochemical cycles [10,11]. Climate change-induced sea surface warming results in enhanced stratification, restricting nutrient availability, which is a major driver for phytoplankton composition and biomass [13–15]. Future predictions for phytoplankton communities in more stratified open oceans often suspect that smaller

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