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Alternate Title

Effect of Temperature on Gamete Production and Biochemical Composition of Gonads in the Sea Urchin Lytechinus variegatus

Abstract

Temperature is one of the most important proximate factors affecting the biology of ectothermal organisms. In the sea urchin, Lytechimus variegatus, the reproductive cycle in wild populations is correlated with changing water temperature, suggesting that reproduction may be dependent, in part, on temperature. Adult L. variegatus (ca. 35.63 ± 1.24 g wet weight, 40-mm diameter) were collected in October 2001 from St. Joseph Bay, FL (30°N, 85.5°W) and transported to the University of Alabama at Birmingham. Sea urchins were placed into nine 80-liter aquaria (n = eight sea urchins per aquarium) maintained in enclosed incubators (n = three aquaria per incubator) at a specific constant temperature of 16, 22, or 28°C and 32 ppt salinity synthetic seawater (Instant Ocean). Within each aquarium, individuals were maintained in 1-liter containers with recirculation and were fed daily a formulated feed ad libitum for 8 wk. At the end of week 8, final measurements of each individual were recorded, individuals were dissected, gonads were measured, and gonad histology and biochemistry were analyzed. Gonad weights were highest for individuals held at the 22°C treatment, but did not vary between individuals held at 16 or 28°C. The acinus volume in the gonad was occupied primarily by nutritive phagocytes at all temperature treatments. In females, gamete volumes were highest for females held at 22°C, whereas gamete volumes were not different for females held at 16 or 28°C. In males, gamete volumes were significantly lower at 28°C, and gamete volumes were not different between males held at 16 or 22°C. Gamete volumes were small in all temperature treatments, suggesting that gamete production had not substantially advanced within the 8-wk study period. The cellular ultrastructure of the nutritive phagocytes varied with temperature. Vacuolated nutritive phagocytes were common in the acini of individuals held at 16°C, and globulated nutritive phagocytes were common in the acini of individuals held at 28°C, Females held at 22°C had the highest protein content in the gonad, and protein content was not different between females held at 16 or 28°C. The amount of lipid was highest for males held at 16°C and did not differ between males held at 22 or 28°C. These data lead us to suggest that L. variegatus utilize different nutrient allocation strategies in the gonad in response to temperature, which could affect the reproductive success of the species if subjected to long-term changes in seawater temperature.

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