Diatoms Versus Copepods: Could Frustule Traits Have a Role in Avoiding Predation?

Alessandra Petrucciani,Alessandra Norici,Peter Chaerle

doi:10.3389/fmars.2021.804960

Alessandra Petrucciani, Alessandra Norici + Show 1 more

Open Access

https://doi.org/10.3389/fmars.2021.804960

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Abstract

Predation is one of the strongest selection pressures phytoplankton has evolved strategies to cope with. Concurrently, phytoplankton growth must deal with resource acquisition. Experiments on mono- and mixed cultures of morphologically different diatoms exposed to copepods were performed to assess if size and shape were primary drivers in avoiding predation. Additionally, frustule silicification was investigated as a potential factor affecting prey selection by copepods. Thalassiosira pseudonana, Conticribra weissflogii, Cylindrotheca closterium, and Phaeodactylum tricornutum were exposed to the presence of Temora longicornis, a calanoid copepod. The physiological response in terms of growth, elemental composition and morphology was determined. The power of Image Flow Cytometry allowed functional single-cell analyses of mixed cultures in the presence and absence of copepods. Results highlighted that T. pseudonana although the most eaten by copepods in monospecific cultures, was not the preferred prey when the bigger C. weissflogii was added to the culture. When pennates were co-cultured with centric diatoms, their growth was unaffected by predators. Our data suggested that the frustule morphology contributes to long-term prey-predator interaction since the elongated thinner frustule, which evolved more recently, benefited cells in escaping from predators also when facing competition for resources.

Highlights

Diatoms are important oceans’ primary producers, which strongly affect global food webs
Of the four monospecific cultured diatoms, T. pseudonana was the most affected by predation and showed a population decline when grown together with copepods compared to cultures maintained without these predators (Figure 1A)
Cells of T. pseudonana exposed to copepods changed in morphology and elemental composition (Figures 1A,C and Supplementary Tables 1, 2, 4), these alterations were insufficient to counter the decrease of the predated populations

Summary

Introduction

Diatoms are important oceans’ primary producers, which strongly affect global food webs. Evolution led to an explosion of morphological varieties of diatom cells, from a radial to an elongated geometry, with a significant change in the frustule silicification (Finkel and Kotrc, 2010; Kotrc and Knoll, 2015). This change in silicification is consistent with a decreasing availability of. Role of Morphology in Predation silicic acid in oceans through geologic eras (Maliva et al, 1989; Lazarus et al, 2009, 2014; Finkel et al, 2010; Finkel and Kotrc, 2010; Conley et al, 2017), so the more recently evolved pennate diatoms developed thinner, less silicified frustules. Beside the macroevolutionary morphological changes, increasing silicification of diatoms has been observed as a rapid response to a sudden exposure to predators (Pondaven et al, 2007; Pancicet al., 2019)

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