Abstract
It has been well documented that nutritional state can influence the foraging behavior of animals. However, photosynthetic animals, those capable of both heterotrophy and symbiotic photosynthesis, may have a delayed behavioral response due to their ability to photosynthesize. To test this hypothesis we subjected groups of the kleptoplastic sea slug, Elysia clarki, to a gradient of starvation treatments of 4, 8, and 12 weeks plus a satiated control. Compared to the control group, slugs starved 8 and 12 weeks displayed a significant increase in the proportion of slugs feeding and a significant decrease in photosynthetic capability, as measured in maximum quantum yield and [chl a]. The 4 week group, however, showed no significant difference in feeding behavior or in the metrics of photosynthesis compared to the control. This suggests that photosynthesis in E. clarki, thought to be linked to horizontally-transferred algal genes, delays a behavioral response to starvation. This is the first demonstration of a link between photosynthetic capability in an animal and a modification of foraging behavior under conditions of starvation.
Highlights
Foraging behavior of animals, defined here as actively searching for and consuming food, encompasses diverse processes such as dispersal, predator-prey interactions, predation risk, and resource optimization [1,2,3,4]
Unlike the case for many Elysia species, which are tiny, observations of feeding behavior and measurements of photosynthesis are possible with E. clarki
An increased length of starvation increased the likelihood of foraging behavior in E. clarki, asusual with starvation [2,3,11]
Summary
Foraging behavior of animals, defined here as actively searching for and consuming food, encompasses diverse processes such as dispersal, predator-prey interactions, predation risk, and resource optimization [1,2,3,4]. Animals deprived of food are more likely to travel further and invest more time in search of food than satiated conspecifics [5], thereby utilizing energy that might otherwise have been allocated to purposes such as growth or reproduction. Starved animals may exhibit reduced anti-predatory behavior to gain increased access to a food source [3]. Some models based upon risk-sensitive foraging theory suggest that animals will choose a more variable array of energy-yielding food items during periods of starvation [4,6]. Starvation generally modifies the actions related to food acquisition [3,8,10,11] which in turn may have consequences for an organism’s survival and interspecific interactions [3]
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