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Structural Relationships Between Spines and Lateral Plates in Threespine Stickleback (Gasterosteus aculeatus)
T. E. Reimchen
Vol. 37, No. 5 (Sep., 1983), pp. 931-946
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2408408
Page Count: 16
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Numerous freshwater populations of threespine stickleback (Gasterosteus aculeatus) have a series of three to eight bony lateral plates restricted to the anterior region of the body. There was a close relationship between total number of plates on individual fish and the positions which the plates occupied. Those positioned between the dorsal and pelvic spines are the least variable in occurrence of all lateral plates. Basal plates and ascending processes which support the dorsal and pelvic spines, respectively, overlap the central lateral plates and the amount of overlap is greatest in populations with long spines (>5 mm). A lateral force (50 g) exerted on the spine produced a significant increase in the angular spine deflection when lateral plates were artificially removed; a 200 g force resulted in penetration of the basal plate into the muscle tissue. Forces exerted by avian and salmonid predators, as deduced from the incidence of broken spines in one population and the force required to experimentally break the spines, range from 100 to 500 g. Lateral plates provide a structural base for the spine supports and a greater surface area over which the forces on the spines are distributed; it is proposed that the principal function of these plates is for stability of long erect spines during manipulation by predators. A rigorous analysis of strength of spines, force vectors on the body, and methods of manipulation for different species of predators should provide further information on functional aspects of these characters.
Evolution © 1983 Society for the Study of Evolution