Ziegenhorn MA (2016), Best Dressed Test: A Study of the Covering Beha...

ECB-ART-44625

PLoS One 2016 Jan 01;114:e0153581. doi: 10.1371/journal.pone.0153581.

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Best Dressed Test: A Study of the Covering Behavior of the Collector Urchin Tripneustes gratilla.

Ziegenhorn MA .

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Many sea urchin genera exhibit cryptic covering behaviors. One such behavior has been documented in the sea urchin Tripneustes gratilla, and previous studies have theorized that this behavior serves as protection from UV radiation. However, other hypotheses have been presented such as protection from predators or added weight to help T. gratilla resist strong currents. A field study was conducted in October-November 2015 in Moorea, French Polynesia to assess urchin covering behavior in natural habitats. The study found that urchins partially underneath rocks covered more, and with more algae, than urchins totally underneath rocks. To test if this behavior was driven by light intensity, a series of 30-minute experimental trials were run on 10 individuals in bright and dim conditions. Individuals were given red and clear plastic, and percent cover of each was recorded. These tests were repeated once fifty percent of spines had been removed from the urchin, in order to determine whether spine loss affects T. gratilla covering behavior. The study found that urchins had a distinct preference for cover that best protects them from UV radiation. Spine loss did not significantly affect urchin ability to cover, and urchins with removed spines still preferred opaque cover. Additionally, covering behavior was mapped onto a phylogeny of echinoderms to determine how it might have evolved. Understanding urchin covering behavior more fully is a step towards an understanding of the evolution of cryptic behavior across species.

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Genes referenced: LOC100887844 LOC100893907 LOC582915 LOC583082

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	Fig 1. Maps of Moorea.(a) Map of the South Pacific, with the location (red box), latitude, and longitude of Moorea, French Polynesia noted. (b) Map of Moorea showing the field site between the motus Tiahura and Fareone (blue dot) and collection spot at Haapiti (red dot).
	Fig 2. Experimental study set up.Diagram of urchin test setup, depicting the tub divided in two, the two urchins (in black) and the two cover types. Red plastic cover is represented by red rectangles, and clear cover is represented by clear rectangles with purple borders.
	Fig 3. Urchin cover in the field.Percent cover of algae and coral rubble on urchins in found partially underneath or totally underneath rocks in the motu Tiahura reef.
	Fig 4. Average cover pre and post spine loss.Average percent cover of both cover types comparing pre and post spine loss data. Both light conditions and all individuals were averaged into one column for each cover type in order to better visualize the differences in covering pre and post spine loss. Cover percentages were taken at the end of the thirty -minute test period.
	Fig 5. Average percent cover versus time.Average values of percent cover versus time in the bright light condition pre-spine loss (5a), in the dim light condition pre-spine loss (5b), in the bright light condition post-spine loss (5c), and in the dim light condition post-spine loss (5d). ‘Red’ refers to opaque plastic cover, and ‘clear’ refers to clear plastic cover. Lines of best fit, calculated from the geom_smooth function in R as conditional means, are included in blue, and error margins are represented by shaded areas.

References [+] :

Dubois, Regeneration of spines and pedicellariae in echinoderms: a review. 2001, Pubmed, Echinobase