Munday Philip L, Wilson White J, Warner Robert R
ARC Centre of Excellence for Coral Reef Studies, School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia.
Proc Biol Sci. 2006 Nov 22;273(1603):2845-51. doi: 10.1098/rspb.2006.3666.
An example of alternative male strategies is seen in diandric protogynous (female first) hermaphrodites, where individuals either mature directly as male (primary males) or first reproduce as female and then change sex to male (secondary males). In some sex-changing fishes, the testes of primary males appear anatomically similar to those of non-sex-changing species, whereas the testes of secondary males have anatomical evidence of their former ovarian function. Here, we provide evidence that in the bluehead wrasse, Thalassoma bifasciatum, these strikingly different male phenotypes arise from differences in the ontogenetic timing of environmental sex determination, timing that can be experimentally altered through changes in the social circumstances. Juveniles differentiated almost exclusively as females when reared in isolation, regardless of whether they were collected from a reef with a high proportion of primary males or from a reef with a low proportion of primary males. In contrast, one individual usually differentiated as a primary male when reared in groups of three. Our results indicate that primary males of the bluehead wrasse are an environmentally sensitive developmental strategy that has probably evolved in response to variation in the reproductive success of primary males in populations of different sizes.
替代性雄性策略的一个例子见于具有双雄性先雌后雄（雌性先成熟）特征的雌雄同体鱼类，在这类鱼中，个体要么直接成熟为雄性（初级雄性），要么先作为雌性繁殖，然后转变为雄性（次级雄性）。在一些能改变性别的鱼类中，初级雄性的睾丸在解剖学上与不能改变性别的物种的睾丸相似，而次级雄性的睾丸则有其先前卵巢功能的解剖学证据。在此，我们提供证据表明，在蓝头濑鱼（Thalassoma bifasciatum）中，这些截然不同的雄性表型源自环境性别决定的个体发育时间差异，这种时间差异可通过社会环境的变化进行实验性改变。幼鱼在隔离饲养时几乎全部发育为雌性，无论它们是从初级雄性比例高的珊瑚礁还是从初级雄性比例低的珊瑚礁采集的。相比之下，当三条一组饲养时，通常有一条个体会发育为初级雄性。我们的结果表明，蓝头濑鱼的初级雄性是一种对环境敏感的发育策略，可能是为应对不同规模种群中初级雄性繁殖成功率的变化而进化而来的。
