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ON THE DEVELOPMENT OF CERTAIN SPECIES OF VERY LARGE BODY SIZE BY LINEAR-DOMINANCE MATING HIERARCHY LEONARD HERSHER* Linear-dominance mating hierarchy (LDMH) is a reproductive social structure characterized by the mating dominance of the alpha male over all other males, the dominance of the beta male over all males except the alpha, and so on, progressing in orderly fashion down to the omega male, which dominates no other male. It is a relatively rare social system of mating behavior, much less common than monogyny, harem formation , mating within male-controlled territory, or other forms of reproductive behavior. Recent studies [1,2] suggest that LDMH social organization fosters the development of some species of very large body size. The system of LDMH strongly influences the content of the gene pool, restricting to very few large males the opportunity to pass genes for body size to succeeding generations. A detailed and thorough study of elephant seals (Mirounga), the only Phocinae known to mate exclusively by LDMH social structure, revealed that only three dominant males accounted for 87 percent of matings (97 cows) during one full breeding season, with the alpha male a partner in 40 percent [I]. By comparison, 80 percent of matings by the harem-forming gray seal (Halichoerus grypus ) were found to be distributed among about 20 males [3]. Elephant seals, male and female, are generally scattered over a large area (such as an entire beach) when the females are in estrus. When a low-ranking male attempts to mate, he is displaced by a higher-ranking male, wherever on the beach the mating pair may be and however distant they are from the alpha male. The higher-ranking male is in turn displaced by a still-higher-ranking male. This displacement behavior is The author is grateful to Professors William M. Shields and Lytt I. Gardner, State University of New York, for their advice and encouragement. *Department of Pediatrics, University Hospital, State University of New York, 750 East Adams Street, Syracuse, New York 13210.© 1985 by The University of Chicago. All rights reserved. 003 1-5982/86/290 1-0463$01 .00 88 \ Leonard Hersher ¦ Linear-Dominance Mating Hierarchy unique, among pinnipeds, to Mirounga. Eventually the only male left that cannot be displaced is the alpha, who completes mating with the female that is in estrus. Only when more than one female is in estrus at the same time can the beta or some other high-ranking male mate successfully , taking advantage of the fact that the alpha is too occupied and perhaps too far away to see the second-ranked male in the act of mating. In harem mating, on the other hand, although the harem master mates with almost all the females in his tightly packed harem, he ignores mating in the adjacent harem. Monogynous male seals mate, of course, with only one female. A fully grown LDMH male elephant seal weighs about 8,000 pounds. All other seals (17 species) are probably harem forming or monogynous and range in weight from 300 pounds {Phoca vitulina) to 1,000 pounds (Erignathus). Few reliable data on mating behavior are available for most earless seals. Exactly the same relationship between large body size and LDMH exists among African antelope (Bovidae). Of the 74 species extant, only two are reliably known to establish LDMH—namely, Taurotragus derbianus (giant eland) and Syncerus coffer (African plains buffalo [2]. Mature adult male weight of both these species is 1,800-2,000 pounds. All other species of African antelope whose mating behavior is known are much lighter, the next heaviest males weighing 600 pounds. The lightest African antelope, the royal (Neotragus pygmaeus L.), weighs about 9 pounds. Some African male antelope establish dominance ranks but remain most of the breeding season alone in temporary territories (usually including a "stamping ground"). Each male mates with the females that are in estrus whenever a female herd passes through that male's territory but does not mate in the territories of other males. These territorial antelope males (eight species) range in size from 350 to 600 pounds. Monogamous antelope males (24 species) weigh from 9 to 140 pounds. Both Phocidae and African Bovidae acquire dominance...


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