Natural
variation of carotenoids in the eggs and gonads of the echinoid genus, Strongylocentrotus:
implications for their role in ultraviolet radiation photoprotection
M.D.
Lamare, J. Hoffman-2004
Journal of Experimental Marine Biology and Ecology, 312(2): 215-233
Abstract:
We
examined variability in carotenoid concentration in the gonads and eggs of
four sea urchin species (Strongylocentrotus purpuratus, Strongylocentrotus
franciscanus, Strongylocentrotus pallidus and Strongylocentrotus
droebachiensis) to explore the possible role of carotenes as
photoprotectants. Carotene concentrations were measured in gonads and
gametes of each species, while in eggs the ultraviolet radiation (UV-R)
sensitivity and self-shading capacity by carotenes were calculated. Mean
concentrations of carotenes in gonads ranged from 0.13±0.017 mg g−1
dw (S. purpuratus), 0.14±0.019 mg g−1 dw (S.
franciscanus), 0.29±0.079 mg g−1 dw (S. pallidus)
to 0.36±0.06 mg g−1 dw (S. droebachiensis). In
eggs, concentrations ranged from 0.026±0.003 to 0.09±0.034 mg g−1
dw. UV-R sensitivity in eggs was quantified by measuring UV-R induced
first-cleavage delay. Intra-specifically, cleavage delay varied
significantly between individuals, and could be correlated with carotene
concentration. Interspecific differences in cleavage delay and carotene
concentrations were not correlated. Using the observed concentration of
β, β-echinenone (which makes up between 82.4% and 94.9% of the
total carotene concentration in the eggs) and a molar extinction coefficient
of
=13.7×103
mol−1 cm−1 at 334 nm, we calculated
self-shading efficiency in the eggs. Self-shading capacity (J334)
indicated that the eggs could only screen from 4.6% (J334=0.046)
down to 1.5% (J334=0.015) of UV-R at 334 nm. While not
sunscreens, we suggest that carotenes can photoprotective in echinoid eggs,
probably by mitigating the effects of reactive oxygen species.
(Friday
Harbor Laboratories, University of Washington, Friday Harbor, WA 99250, USA,
e-mail: miles.lamare@stonebow.otago.ac.nz)