Microstome–macrostome transformation in the polymorphic ciliateTetrahymena voraxleads to mechanosensitivity associated with prey-capture behaviour

Abstract

SUMMARYCiliates feed by phagocytosis. Some ciliate species, such as Tetrahymena vorax, are polymorphic, a strategy that provides more flexible food utilization. Cells of the microstomal morph of T. vorax feed on bacteria, organic particles and organic solutes in a non-selective manner, whereas macrostome cells are predators that consume specific prey ciliates. In the present study, we investigated a possible correlation between phagocytosis and mechanosensitivity in macrostome T. vorax. Microstome cells seem to be insensitive to mechanical stimulation whereas macrostome cells depolarise in response to mechanical stimulation of the anterior part of the cell. The amplitude of the receptor potential induced by either a prey ciliate or a 5m push by a glass needle was sufficient to elicit a regenerative Ca 2+ spike. The difference in mechanosensitivity of the two forms correlates with the swimming behaviour when hitting an obstacle; microstome cells swim alongside the obstacle whereas macrostome cells swim backwards, turn and resume forward swimming. Macrostome cells prevented from backward swimming and the subsequent turn failed to capture prey cells in their pouch. Macrostome cells consumed heterospecific prey ciliates preferentially over conspecific microstome cells. This selectivity is not due to electrical membrane responses elicited by physical contact. Both microstome and macrostome cells accumulated in an area containing putative substances released from heterospecific prey ciliates, but the substances did not elicit any electrophysiological membrane responses. We conclude that the mechanosensitivity of macrostome cells is associated with the prey-capture behaviour, whereas the selective phagocytosis is probably due to chemo-attraction to heterospecific prey ciliates.

Electrophysiological Properties of the Microstome and Macrostome Morph of the Polymorphic Ciliate Tetrahymena vorax

“…Transformation from microstome to macrostome T. vorax cells is associated with dramatic changes in cell size and shape, and gaining of novel mechanosensitivity that contributes to the different behaviour of the two morphs (Grønlien et al. ). Still, the present report shows that the general electrical membrane properties are strikingly similar in microstome and macrostome cells (Table ).…”

“…Recently, we have shown that microstome T. vorax cells seem to be insensitive to mechanical stimulation, whereas macrostome cells depolarize in response to mechanical stimulation of the anterior part of the cell (Grønlien et al. ). The difference in mechanosensitivity of the two morphs correlates with the swimming behaviour when hitting an obstacle, and the mechanosensitivity of macrostome cells may also be associated with their prey‐capture behaviour.…”

Genetic and Non-Genetic Mechanisms Underlying Cancer Evolution

“…Reaction norms allow organisms to quickly adapt to the changes in the environment and efficiently maximize their fitness under the given circumstances without changes in the genome. A well-known example of such phenotypic plasticity is described in the protist Tetrahymena vorax, which is able to switch between two distinct morphotypesmacrostome and microstome-in response to environmental changes, such as the relative abundance of bacteria versus other protists [142,143]. Interestingly, when a macrostome or microstome undergoes cell division it can either maintain its corresponding morphology or change to a distinct morphotype depending on resource abundance.…”

Feast or flee: bioelectrical regulation of feeding and predator evasion behaviors in the planktonic alveolateFavellasp. (Spirotrichia)

“…may be expected to utilize similar conserved sensory mechanisms, it is likely that they implement them in different ways due to their different morphological and ecological characteristics. Nevertheless, it is known that ionotropic mechanisms -those governed by voltage-, chemo-, or mechano-sensitive ion channels -are important in regulating the behaviors of ciliates (Preston and Van Houten, 1987;Shiono and Naitoh, 1997;Grønlien et al, 2011). For example, ionotropic mechanisms are known to be important in sensory processes that relate to prey capture in ciliates.…”

“…For example, ionotropic mechanisms are known to be important in sensory processes that relate to prey capture in ciliates. Contact of the freshwater ciliate Tetrahymena vorax with prey cells elicits ciliary reversal and backward swimming, which are regulated by transient depolarizations (Grønlien et al, 2011). Ionotropic mechanisms may also be important in regulating predator evasion behaviors.…”