Fitness benefits of size-dependent diet switching in a marine herbivore

Abstract

Although diet is one of the most important parameters affecting the fitness of terrestrial and marine herbivores, host plant choice and subsequent fitness on that host are not always correlated. This study investigated the effect of diet on fitness of the sea urchin Holopneustes purpurascens, which show an ontogenetic change in host plant use subsequent to recruitment. To test whether fitness on host plant mirrored host plant choice, small and large individuals were collected from both hosts and fed either host plant (Ecklonia radiata or Delisea pulchra). Small urchins survived better than large individuals. Those fed E. radiata produced fewer test lesions, grew faster and were more fecund than those fed D. pulchra, irrespective of size. This pattern was enhanced when the host plant the urchin previously inhabited was assessed. Our results show that diet is driving the previously recorded ontogenetic change in host plant use associated with increasing size in H. purpurascens, where medium-sized individuals switch from D. pulchra to E. radiata.

Effects of five southern California macroalgal diets on consumption, growth, and gonad weight, in the purple sea urchinStrongylocentrotus purpuratus

“…We acknowledge that the sea urchins used in our experiment were collected from a single site, and the barren conditions present there suggest that the urchins had low food availability for some time prior to the experiment. Consumer history has been shown to influence urchin somatic and gonad growth ( Livore & Connell , 2012 ; Williamson & Steinberg , 2012 ), and the proportion of time food is available has been shown to affect their grazing, growth and resource allocation ( Spirlet, Grosjean & Jangoux , 1998 ). Thus, our results could have been affected by the prior history of the individual urchins used in our experiment.…”

Positive Indirect Interactions in Marine Herbivores and Algae

“…It also preferentially consumes the kelp [95]. The focal organism, the gastropod P. eximius, resides with H. purpurascens in the temporary shelter the urchin builds within the fronds of the kelp [65].…”

Using external morphology as a proxy for stomach size in Hemigrapsus sanguineus

“…Diet quality is not static and can differ considerably between populations (Rand et al., 2010 ), across individuals (Bolnick et al., 2002 ; Jack & Wing, 2011 ), and within individuals through time (Williamson & Steinberg, 2012 ). For instance, populations of Atka mackerel ( Pleurogrammus monopterygius ) exhibit differential consumption and thus growth rates based on the energetic quality of available prey in the area (Rand et al., 2010 ), and individual sea urchins ( Holopneustes purpurascens ) switch to more nutritious host plants as they grow bigger (Williamson & Steinberg, 2012 ). Intraspecific variation in diet quality is especially important to recognize in omnivorous species, in which a single individual may consume prey at multiple trophic levels (e.g., Jack & Wing, 2011 ).…”

“…General estimates of diet quality therefore provide insight into basic biological processes, such as reproduction and behavior. Diet quality is not static and can differ considerably between populations (Rand et al, 2010), across individuals (Bolnick et al, 2002;Jack & Wing, 2011), and within individuals through time (Williamson & Steinberg, 2012). For instance, populations of Atka mackerel (Pleurogrammus monopterygius) exhibit differential consumption and thus growth rates based on the energetic quality of available prey in the area (Rand et al, 2010), and individual sea urchins (Holopneustes purpurascens) switch to more nutritious host plants as they grow bigger (Williamson & Steinberg, 2012).…”