“Speed-Accuracy Trade-Off in Plants”, 2020-06-15 (; similar):
Speed-accuracy trade-off (SAT) is the tendency for decision speed to covary with decision accuracy. SAT is an inescapable property of aimed movements being present in a wide range of species, from insects to primates. An aspect that remains unsolved is whether SAT extends to plants’ movement.
Here, we tested this possibility by examining the swaying in circles of the tips of shoots exhibited by climbing plants (Pisum sativum L.) as they approach to grasp a potential support. In particular, by means of 3-dimensional kinematical analysis, we investigated whether climbing plants scale movement velocity as a function of the difficulty to coil a support.
Results showed that plants are able to process the properties of the support before contact and, similarly to animal species, strategically modulate movement velocity according to task difficulty.
…To date, a great absent in the Fitts’s law literature is the “green kingdom”. At first glance, plants seem relatively immobile, stuck to the ground in rigid structures and, unlike animals, unable to escape stressful environments. But, although markedly different from those of animals, movement pervades all aspects of plant behavior (1880).
As observed by 1875, the tendrils of climbing plants undergo subtle movements around their axes of elongation. This elliptical movement, known as circumnutation, allows plants to explore their immediate surroundings in search, for instance, of a physical support to enhance light acquisition (2000). Also, 1875 (see also 2017) observed that the tendrils tend to assume the shape of whatever surface before they come into contact with. Implicitly this might signify that they “see” the support and plan the movement accordingly. In this view, climbing plants might be able to plan the course of an action ahead of time and program the tendrils’ choreography according to the “to-be-grasped” object.
Support for this contention comes from both theoretical and empirical studies suggesting that plant movement is not a simple product of cause-effect mechanisms but rather seems to be driven by processes that are anticipatory in nature (eg. 2017; et al 2019). For instance, a recent study shows that a climbing plant (Pisum sativum L.) not only is able to perceive a potential support, but it also scales the kinematics of tendrils’ aperture according to its size well ahead they touch the stimulus ( et al 2019). This has been taken as the demonstration that plants plan the movement purposefully and in ways that are flexible and anticipatory.
With this in mind, one of the empirical predictions stemming from Fitts’s law can be well-suited to model the 3-dimensional circumnutation of plants. Precisely, we refer to the evidence that movement time scales as a function of the target’s size: When the distance is constant, thinner targets are reached more slowly than thicker ones (see 2001). We test this prediction in Pisum sativum L. by assessing the change of velocity of the tendrils during their approach-to-grasp a thin or to a thicker support.
…Results: …The analysis of movement time confirms this evidence, showing that movement time was shorter for the thinner than for the thicker stimulus (β < 0) with a probability of 79.3%. This evidence suggests that plants are able to process the properties of the support and are endowed with a form of perception underwriting a goal-directed and anticipatory behavior ( et al 2019). However, in contrast with previous human and animal literature (eg. 1972; 1954; 2012), our results indicate an opposite pattern of what Fitts’s law predicts. Remember that according to Fitts’s law, the velocity of the movement is inversely proportional to ID (2D/W). In other words, our results seem to suggest that plants exhibit more difficulty grasping a thicker than a thinner support. These findings are line with previous reports showing a lower success rate of attachment for thick supports (1982), and a preference for plants to climb supports with a smaller diameter (1875; 1984; 1992 [The Biology of Vines]). Furthermore, by using the curvature of tendrils during the twining phase, 2006 demonstrate that for thinner supports, the contact angle (ie.t, the angle between the tip of the tendril and the tangent of the support) is a near-zero value. Instead, with thicker supports, the contact angle tends to increase as tendrils must curl into the support’s surface to maintain an efficient grip. When the support is too thick, the contact angle increases to an extent that the tendril curls back on itself, losing grip. Interestingly, field studies in rainforests showed that the presence of climbing plants tends to decrease in areas in which there is a prevalence of thicker supports (Carrasco-2009).
A possible explanation for this phenomenon may reside in the fact that, for plants, reaching to grasp thick supports is a more energy consuming process than grasping for thinner ones. Indeed, the grasping of a thick support implies that plants have to increase the tendril length in order to efficiently coil the support ( et al 2006), and to strengthen the tensional forces to resist gravity (2015)