Gotelli Nicholas J, Spivey Henry R
Department of Zoology, University of Vermont, 05405, Burlington, VT, USA.
Acacia Corporation, Box 2425, 36547, Gulf Shores, AL, USA.
Oecologia. 1992 Oct;91(4):474-480. doi: 10.1007/BF00650319.
In sexually dimorphic animals, large male body size is often associated with direct interference competition among males for access to females or resources used in reproduction. In constrast, small male body size may be associated with indirect scramble competition among males for temporal or spatial access to females. Minute, "parasitic" males of the acrothoracican barnacleTrypetesa lampas (Hancock) appear to compete with one another for permanent attachment sites on the external body of the female. Several spatial patterns suggest indirect male-male competition: 1) males were consistently aggregated on the anterior surface of the female ovarian disc; 2) the average distance from attached males to the site of insemination correlated positively with local male density; 3) average male body size on a female decreased as a function of male density; 4) the distribution of males on the left and right hand sides of the female ovarian disc was more even than expected, suggesting that males avoided crowded settlement sites. The number of males attached to a female increased with female body size and matched a null model in which males colonized female "targets" of differing areas. These results suggest that competition between males primarily affected settlement sites and male body sizes within, rather than among, females. Male parasitism may have evolved through both sexual selection for efficient access to females (Ghiselin 1974) and natural selection for reduced burrow density in a space-limited habitat (Turner and Yakovlev 1983).
在两性异形的动物中，雄性体型较大通常与雄性之间为接近雌性或获取用于繁殖的资源而进行的直接干扰竞争有关。相比之下，雄性体型较小可能与雄性之间为在时间或空间上接近雌性而进行的间接争夺竞争有关。微小的“寄生性”雄性顶胸藤壶Trypetesa lampas（汉考克）似乎在雌性体外相互竞争永久附着位点。几种空间模式表明存在雄性间的间接竞争：1）雄性始终聚集在雌性卵巢盘的前表面；2）附着的雄性到受精部位的平均距离与局部雄性密度呈正相关；3）雌性身上雄性的平均体型随雄性密度的增加而减小；4）雌性卵巢盘左右两侧雄性的分布比预期更均匀，这表明雄性会避开拥挤的定居点。附着在雌性身上的雄性数量随雌性体型的增大而增加，并且符合一个空模型，即雄性在不同面积的雌性“目标”上定殖。这些结果表明，雄性之间的竞争主要影响雌性个体内部而非不同雌性之间的定居位点和雄性体型。雄性寄生现象的进化可能是通过性选择以有效接近雌性（吉塞林，1974年）以及自然选择以在空间有限的栖息地降低洞穴密度（特纳和亚科夫列夫，1983年）。
