Annual reversible plasticity of feeding structures: cyclical changes of jaw allometry in a sea urchin

Abstract

A wide variety of organisms show morphologically plastic responses to environmental stressors but in general these changes are not reversible. Though less common, reversible morphological structures are shown by a range of species in response to changes in predators, competitors or food. Theoretical analysis indicates that reversible plasticity increases fitness if organisms are long-lived relative to the frequency of changes in the stressor and morphological changes are rapid. Many sea urchin species show differences in the sizes of jaws (demi-pyramids) of the feeding apparatus, Aristotle's lantern, relative to overall body size, and these differences have been correlated with available food. The question addressed here is whether reversible changes of relative jaw size occur in the field as available food changes with season. Monthly samples of the North American Pacific coast sea urchin Strongylocentrotus purpuratus were collected from Gregory Point on the Oregon (USA) coast and showed an annual cycle of relative jaw size together with a linear trend from 2007 to 2009. Strongylocentrotus purpuratus is a long-lived species and under field conditions individuals experience multiple episodes of changes in food resources both seasonally and from year to year. Their rapid and reversible jaw plasticity fits well with theoretical expectations.

How reversible is development? Contrast between developmentally plastic gain and loss of segments in barnacle feeding legs

“…We identify here a new cost associated with developmentally plastic change: asymmetry in the ease, or time lag, of development in one direction versus development in the reverse direction. Although development may be more easily modified by environment earlier rather than later in life (Hoverman and Relyea 2007;Fischer et al 2014;Beaman et al 2016), developmentally plastic morphological changes can and do occur throughout life in many organisms (Relyea 2003;reviewed in Gabriel et al 2005;Neufeld 2012;Ebert et al 2014;Foster et al 2015;Beaman et al 2016). However, the ease with which plastic change is reversed (e.g., the time lag between change in environment and the appropriate phenotypic response) may not be symmetrical.…”

Predators indirectly induce stronger prey through a trophic cascade

“…Since the experiment ran for six months, we consider that uneaten food at the end of the experiment was a negligible proportion of the total amount provided, so it was reasonable to assume that individuals in the high-food replicates ate approximately four times more food than those in the low-food replicates (ignoring the unquantifiable amount of food the urchins may have obtained from algae growing on the small rocks that were provided for shelter in each container). Each E. radiata blade was ca 200 Â 40 mm and had a blotted mass of ca 4.3 g, so each of the eight individual urchins per replicate was provided with 0.08 g kelp d 21 in the 'þfood' treatment and 0.02 g kelp d 21 in the '2food' treatment. In a pilot feeding assay, run for 4 days during the previous summer when seawater temperatures were about 208C, 20-mm urchins ate an average of 0.07 g kelp d 21 and 30-mm urchins ate 0.15 g kelp d 21 when provided with surplus kelp.…”

“…Each E. radiata blade was ca 200 Â 40 mm and had a blotted mass of ca 4.3 g, so each of the eight individual urchins per replicate was provided with 0.08 g kelp d 21 in the 'þfood' treatment and 0.02 g kelp d 21 in the '2food' treatment. In a pilot feeding assay, run for 4 days during the previous summer when seawater temperatures were about 208C, 20-mm urchins ate an average of 0.07 g kelp d 21 and 30-mm urchins ate 0.15 g kelp d 21 when provided with surplus kelp. These feeding rates would likely have been lower over the course of our experiment because water temperatures were lower than they were in the feeding assay (down to 148C), so we consider that the urchins in the 'þfood' treatment received adequate food.…”

Re-examination of the effects of food abundance on jaw plasticity in purple sea urchins

“…These diferences are thought to reduce individual performance but ultimately increase population size in barrens by augmenting turnover of the population (Ling and Johnson 2009;Ling et al 2019). Conversely, the relatively longer jaws observed in urchins from barrens are thought to aid their success by increasing feeding eiciency on encrusting and calcareous algae, because longer jaws may facilitate scraping or grabbing algae from rocks (Ebert 1980b(Ebert , 2014Edwards and Ebert 1991;Fernandez and Boudouresque 1997).…”

“…Researchers have further observed that relative jaw length changes cyclically in the ield, following seasonal luctuations in food abundance, which suggests that this plastic response is reversible (Ebert 2014). Reversible morphological plasticity implies that there costs and beneits associated with the trait, further advocating a common assumption in the literature that having a greater jaw length to test diameter ratio is advantageous (Ebert 1996).…”