**4.3 The inducible defense**

Another peculiar defensive mechanism, reported as inducible defense, has been described for some *Euplotes* species as the response to the presence of some predators, such as microturbellarians, ciliates, or amoebas. These predators can release active substances, called kairomones, which induce some behavioral and morphological changes (such as the formation of spines in *Euplotes*) as a defensive mechanism in response to the presence of the predator [85–88] for a review.

#### **Figure 21.**

*Reduction in the number of extrusomes (cortical granules) in* Spirostomum ambiguum *obtained by cold-shock treatment. (A) Extrusomes in an untreated cell. (B) Extrusome-deprived cell after cold shock. Magnification ×900. Pictures from [77].*

**33**

*Predator-Prey Interactions in Ciliated Protists DOI: http://dx.doi.org/10.5772/intechopen.78622*

mechanisms against unicellular predators.

**5. Conclusions**

**Figure 22.**

**Acknowledgements**

**Conflict of interest**

The authors have declared no conflict of interest.

It could be interesting to study the efficiency of the inducible defenses, if compared to mechanical and chemical defense by means of extrusomes. In this regard, a first study was performed to compare the efficiency of the defense mediated by trichocysts in *P. aurelia* with that mediated by cortical granules in *C. virens* and *S. ambiguum* [44]. The authors reported that the mechanical defense in *Paramecium* against metazoan predators appears to be equally effective as the chemical one, but can be successfully activated only during the very early interactions with the predator, whereas it is ineffective after the ingestion of the ciliate. In contrast, the chemical defense adopted by a toxic ciliate against metazoan predators can also be activated after the ingestion of the prey by the predator, but its effectiveness appears to be strictly linked to the cytotoxic potency of the compound stored in the protozoan cortical granules. It would also be interesting to compare these two

*Predator-prey interaction between* Climacostomum virens *and* Spirostomum ambiguum*. (A) 1: Cell of*  C. virens *contacts a cell of* S. ambiguum *with its buccal apparatus. 2:* S. ambiguum *shows rapid contraction while the predator swims backwards. 3: The same cells as in 2, a second later, showing a retreated* C. virens*, while* S. ambiguum *swims away. (B) Predator-prey interaction between* C. virens *and extrusome-deficient cells of* S. ambiguum *obtained by cold-shock treatment. 1:* C. virens *cell contacts a* S. ambiguum *cell which instantly shows contraction. 2:* C. virens *engulfs the contracted* S. ambiguum *cell and continues to eat the*  S. ambiguum *cell (3). Micrographs extracted from a film clip. Magnification ×50. Pictures from [77].*

In a general perspective, it is clear that the researches on predatory behavior and on the related defensive mechanisms in protists not only represent progress in knowledge about the ecological role played in nature by predator-prey interactions in aquatic microhabitats but will also provide new research opportunities for evolutionary biology and may also represent a relevant source of new natural products.

We are grateful to Dr. Gill Philip (University of Macerata) for the linguistic revision of the chapter. Financial support was provided by University of Macerata, Italy. *Predator-Prey Interactions in Ciliated Protists DOI: http://dx.doi.org/10.5772/intechopen.78622*

#### **Figure 22.**

*Extremophilic Microbes and Metabolites - Diversity, Bioprospecting and Biotechnological...*

the posterior end of the cell (**Figure 21A**) [77]. The cold-shock method was applied to *S. ambiguum* to obtain the cortical granule-deficient cells, which showed a markedly reduced number of extrusomes (**Figure 21B**). Both untreated and cortical granule-deficient cells were exposed to the attack of *C. virens*, and when the buccal apparatus of the predator makes contact with an untreated cell of *S. ambiguum,* it showed a rapid contraction while the predator swam backwards (**Figure 22A**). Similarly to untreated cells, cortical granule-deficient cells of *S. ambiguum* also showed rapid contraction after attack by *C. virens*, but they were successfully captured and sucked up by the predator into its buccal cavity (**Figure 22B**) [77]. The toxin involved in this interaction was purified by reversed phase high-performance liquid chromatography (RP-HPLC), and its structural characterization was carried out through nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) measurements and revealed as 2-(3-methylbut-2-enyl)benzene-1,4-diol(mono-prenyl hydroquinone) (**Figure 14**). Prenylated-hydroquinone derivatives are metabolites of abundant occurrence and have been isolated from fungi, algae, plants, animals, and bacteria [77]. In this case the involvement of this molecule in predator-prey interaction is clear. Interestingly, another freshwater species of the genus *Spirostomum, S. teres,* possesses a different colorless toxin used for defense, characterized as spiro[(2,5-dimethyl-5,6,7,8-tetrahydronaphthalene-1,4-dione)-8,6′-(pyrane2',5′-dione)] and named spirostomin (**Figure 14**) [84]. It is no novelty that closely related organisms can produce different or even biogenetically distant specific secondary metabolites [77], and it is very common for ciliates [56]. To date, the only reported exception to this phenomenon is related to the genus *Blepharisma* in which the three species *B. japonicum, B. stoltei* and *B. undulans* share the same mixture of blepharismins even if produced in different

Another peculiar defensive mechanism, reported as inducible defense, has been described for some *Euplotes* species as the response to the presence of some predators, such as microturbellarians, ciliates, or amoebas. These predators can release active substances, called kairomones, which induce some behavioral and morphological changes (such as the formation of spines in *Euplotes*) as a defensive mechanism in response to the presence of the predator [85–88] for a review.

*Reduction in the number of extrusomes (cortical granules) in* Spirostomum ambiguum *obtained by cold-shock treatment. (A) Extrusomes in an untreated cell. (B) Extrusome-deprived cell after cold shock. Magnification* 

**32**

**Figure 21.**

*×900. Pictures from [77].*

proportions [56].

**4.3 The inducible defense**

*Predator-prey interaction between* Climacostomum virens *and* Spirostomum ambiguum*. (A) 1: Cell of*  C. virens *contacts a cell of* S. ambiguum *with its buccal apparatus. 2:* S. ambiguum *shows rapid contraction while the predator swims backwards. 3: The same cells as in 2, a second later, showing a retreated* C. virens*, while* S. ambiguum *swims away. (B) Predator-prey interaction between* C. virens *and extrusome-deficient cells of* S. ambiguum *obtained by cold-shock treatment. 1:* C. virens *cell contacts a* S. ambiguum *cell which instantly shows contraction. 2:* C. virens *engulfs the contracted* S. ambiguum *cell and continues to eat the*  S. ambiguum *cell (3). Micrographs extracted from a film clip. Magnification ×50. Pictures from [77].*

It could be interesting to study the efficiency of the inducible defenses, if compared to mechanical and chemical defense by means of extrusomes. In this regard, a first study was performed to compare the efficiency of the defense mediated by trichocysts in *P. aurelia* with that mediated by cortical granules in *C. virens* and *S. ambiguum* [44]. The authors reported that the mechanical defense in *Paramecium* against metazoan predators appears to be equally effective as the chemical one, but can be successfully activated only during the very early interactions with the predator, whereas it is ineffective after the ingestion of the ciliate. In contrast, the chemical defense adopted by a toxic ciliate against metazoan predators can also be activated after the ingestion of the prey by the predator, but its effectiveness appears to be strictly linked to the cytotoxic potency of the compound stored in the protozoan cortical granules. It would also be interesting to compare these two mechanisms against unicellular predators.

#### **5. Conclusions**

In a general perspective, it is clear that the researches on predatory behavior and on the related defensive mechanisms in protists not only represent progress in knowledge about the ecological role played in nature by predator-prey interactions in aquatic microhabitats but will also provide new research opportunities for evolutionary biology and may also represent a relevant source of new natural products.

#### **Acknowledgements**

We are grateful to Dr. Gill Philip (University of Macerata) for the linguistic revision of the chapter. Financial support was provided by University of Macerata, Italy.

#### **Conflict of interest**

The authors have declared no conflict of interest.

*Extremophilic Microbes and Metabolites - Diversity, Bioprospecting and Biotechnological...*
