Conner Jeffrey
Section of Neurobiology and Behavior, Cornell University, Ithaca, NY, 14853.
Evolution. 1989 Nov;43(7):1378-1386. doi: 10.1111/j.1558-5646.1989.tb02589.x.
The hypothesis that population density can affect sexual selection on male horn size was tested in a three-year study of a fungus beetle, Bolitotherus cornutus. Males of this species have horns that vary greatly in length. These horns are used in fights over females; longer-horned males win the majority of fights, regardless of population density. However, density does affect the relationship between horn length and access to females. In six populations of naturally and experimentally varying densities, longer-horned males gained a greater advantage in access to females in low-density populations than at high density. This increase in access to females causes an increase in the number of females inseminated by longer-horned males; thus, sexual selection for longer horns is stronger at lower densities.
在一项对角菌甲（Bolitotherus cornutus）进行的为期三年的研究中，对种群密度会影响雄性角大小的性选择这一假设进行了检验。该物种的雄性有长度差异很大的角。这些角用于争夺雌性；角较长的雄性在大多数争斗中获胜，无论种群密度如何。然而，密度确实会影响角的长度与接近雌性机会之间的关系。在六个自然密度和实验密度各不相同的种群中，角较长的雄性在低密度种群中比在高密度种群中获得了更大的接近雌性的优势。接近雌性机会的增加导致角较长的雄性使更多雌性受孕；因此，在较低密度下，对角较长的性选择更强。
