Geographic Variation in Sperm Function: Swimming Performance and its Biochemical Correlates

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Most marine naimals reproduce by releasing gametes into open water, where fertilization takes place. External fertilization in the sea thus exposes gamelets to variation in environmental conditons, and fertilization success for free-spawning animals is highly variable. Temperature has a marked effect on fertilization success and varies with latitude and season. Therefore, natural selection should favor organisms with gametes that are tuned, phsyiologically and mechanically, to temperatures at which the animals normally reproduce. The strong correlation between latitude and temperature allows a test of this hypothesis by comparing gamete characteristics from animals collected along a latitude temperature gradient. This proposal examines such characteristics for closely-related species of marine animals, sea urchins, that live at different latitudes and together span a wide range of temperatures during their reproductive season. The proposed research uses motion analysis of the motility of sperm at different temperatures, as well as biochemical analysis of key enzymes involved in motility, to draw a connection between mechanisms and processes involved in fertilization success. Results of this work have implications for understanding the evolution of temperature adaptation as well as environmental factors that determine reproductive success in marine organisms.