Fast adaptation of tropical diatoms to increased warming with trade-offs

Peng Jin,Susana Agustí

doi:10.1038/s41598-018-36091-y

Peng Jin, Susana Agustí

Open Access

https://doi.org/10.1038/s41598-018-36091-y

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Abstract

Ocean warming with climate change is forcing marine organisms to shift their distributions polewards and phenology. In warm tropical seas, evolutionary adaptation by local species to warming will be crucial to avoid predicted desertification and reduction in diversity. However, little is known about the adaptation of phytoplankton in warm seas. Across the ocean, diatomic microalgae are the main primary producers in cold waters; they also contribute to tropical communities where they play a necessary role in the biological pump. Here we show that four species of diatoms isolated from the tropical Red Sea adapted to warming conditions (30 °C) after 200–600 generations by using various thermal strategies. Two of the warming adapted species increased their optimal growth temperature (Topt) and maximum growth rate. The other two diatoms did not increase Topt and growth, but shifted from specialist to generalist increasing their maximum critical thermal limit. Our data show that tropical diatoms can adapt to warming, although trade offs on photosynthetic efficiency, high irradiance stress, and lower growth rate could alter their competitive fitness. Our findings suggest that adaptive responses to warming among phytoplankton could help to arrest the sharp decline in diversity resulting from climate change that is predicted for tropical waters.

Highlights

Ocean warming with climate change is forcing marine organisms to shift their distributions polewards and phenology
Rising temperatures leading to poleward shifts in the thermal niches of phytoplankton has been predicted by the end of this century along with a sharp decline in tropical phytoplankton diversity in the absence of evolutionary responses to warming[14]
Increased temperature increased the growth of Chaetoceros sp. at the beginning of the selection period, while this positive effect was reversed toward the end of selection period (Fig. 1a)

Summary

Introduction

Ocean warming with climate change is forcing marine organisms to shift their distributions polewards and phenology. Diatoms have lower activation energies (i.e. less sensitive to increasing temperature) than other phytoplankton groups[17], but its adaptation to warming will be crucial to maintain an efficient biological pump in the tropical ocean[16]. Maximum at the optimum temperature) to “generalist” (maximum growth could be realized in a range of temperatures) and vice versa, with associated trade-offs in growth or other metabolic processes If such trade-offs exist, and there is selection for an increased temperature range, specialist-generalist trade-offs would result in lower maximum performance for growth in warm-adapted organisms[18]. Thermal adaptation could generate a higher and broader growth curve (i.e. reaction norm), increasing the temperature range[19] This adaptation is referred to as “hotter is broader and better” and will represent the win-win adaptation when organisms increased maximum growth and the breadth of reaction norm without trade-offs. Phytoplankton species can adapt their realized niches to track average increases in water temperature regardless of annual and seasonal fluctuations, so the mean SST should be a reliable experimental control value[24]

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