Bass A, Andersen K
Section of Neurobiology and Behavior, Cornell University, Ithaca, N.Y.
Brain Behav Evol. 1991;37(4):204-14. doi: 10.1159/000114359.
In one species of vocalizing fish, the plainfin midshipman (Porichthys notatus), large, nest-guarding males ('type I') use striated muscles to produce acoustic communication signals that include short duration (less than 1 s) 'burps' important in agonistic encounters and long duration (in the order of minutes) 'hums' which function in attracting females to nest sites during the breeding season. Females, and a second group of smaller reproductively active males ('type II') that 'sneak' spawn, do not generate hums, although they produce burps. Differences in vocal behavior are paralled by a relative increase of 6-fold in the sonic muscle of type I males. Inter- and intrasexual dimorphisms in sonic muscle mass were matched by those in the cross-sectional area of sonic motor axons, but not by those in number of axons. Thus, axon size was 2- to 3-fold larger in type I males than in females, type II males, or juveniles, none of which differed significantly from each other. Axon number was similar between type I males and females of a similar body size, despite the extreme dimorphism in sonic muscle mass. Axon number, however, was slightly greater (0.1-fold) in type I males and females compared to the smaller-sized juveniles and type II males. Type II males, in comparison to the non-reproductive juvenile males, have gonads that are about 20-fold larger and produce mature sperm. Nevertheless, the two groups resemble each other in body and swimbladder size, as well as sonic motor axon size and number. This suggests that type II males represent a subset of juvenile males that undergo precocious gonadal hypertrophy and spermiogenesis, but retain juvenile-like nongonadal traits. The results are discussed within the context of the development of vertebrate motor systems as well as the evolution of alternative reproductive tactics among teleost fishes.
在一种能发声的鱼类——太平洋帆鳍鲈（Porichthys notatus）中，体型较大、守护巢穴的雄性（“I型”）利用横纹肌产生声学通讯信号，这些信号包括在争斗遭遇中很重要的持续时间较短（不到1秒）的“嗝声”，以及在繁殖季节吸引雌性到巢穴地点发挥作用的持续时间较长（几分钟左右）的“嗡嗡声”。雌性以及另一组较小的具有生殖活性的“偷巢”雄性（“II型”）虽然也会发出嗝声，但不会发出嗡嗡声。发声行为的差异与I型雄性的发声肌肉相对增加6倍并行。发声肌肉质量的两性间和两性内二态性与发声运动轴突的横截面积的二态性相匹配，但与轴突数量的二态性不匹配。因此，I型雄性的轴突大小比雌性、II型雄性或幼鱼大2至3倍，而雌性、II型雄性和幼鱼之间没有显著差异。尽管发声肌肉质量存在极端二态性，但体型相似的I型雄性和雌性之间的轴突数量相似。然而，与体型较小的幼鱼和II型雄性相比，I型雄性和雌性的轴突数量略多（0.1倍）。与非生殖性幼鱼雄性相比，II型雄性的性腺大约大20倍并产生成熟精子。然而，这两组在身体和鱼鳔大小以及发声运动轴突大小和数量方面彼此相似。这表明II型雄性代表了一部分幼鱼雄性，它们经历了性腺早熟肥大和精子发生，但保留了类似幼鱼的非性腺特征。本文在脊椎动物运动系统发育以及硬骨鱼类中替代生殖策略进化的背景下讨论了这些结果。
