Yusa Yoichi, Yoshikawa Mai, Kitaura Jun, Kawane Masako, Ozaki Yuki, Yamato Shigeyuki, Høeg Jens T
Faculty of Science, Nara Women's University, Nara 630-8506, Japan.
Proc Biol Sci. 2012 Mar 7;279(1730):959-66. doi: 10.1098/rspb.2011.1554. Epub 2011 Aug 31.
How and why diverse sexual systems evolve are fascinating evolutionary questions, but few empirical studies have dealt with these questions in animals. Pedunculate (gooseneck) barnacles show such diversity, including simultaneous hermaphroditism, coexistence of dwarf males and hermaphrodites (androdioecy), and coexistence of dwarf males and females (dioecy). Here, we report the first phylogenetically controlled test of the hypothesis that the ultimate cause of the diverse sexual systems and presence of dwarf males in this group is limited mating opportunities for non-dwarf individuals, owing to mating in small groups. Within the pedunculate barnacle phylogeny, dwarf males and females have evolved repeatedly. Females are more likely to evolve in androdioecious than hermaphroditic populations, suggesting that evolution of dwarf males has preceded that of females in pedunculates. Both dwarf males and females are associated with a higher proportion of solitary individuals in the population, corroborating the hypothesis that limited mating opportunities have favoured evolution of these diverse sexual systems, which have puzzled biologists since Darwin.
不同的性系统如何以及为何进化是引人入胜的进化问题，但很少有实证研究探讨动物中的这些问题。有柄（鹅颈）藤壶表现出如此多样的性系统，包括同时雌雄同体、矮雄与雌雄同体共存（雄花两性异体）以及矮雄与雌性共存（雌雄异体）。在此，我们报告了首个系统发育控制测试，以验证这一假说：该类群中多样的性系统及矮雄存在的最终原因是由于小群体交配，非矮个体的交配机会有限。在有柄藤壶的系统发育中，矮雄和雌性多次进化。与雌雄同体种群相比，雌性在雄花两性异体种群中更易进化，这表明在有柄藤壶中矮雄的进化先于雌性。矮雄和雌性都与种群中更高比例的独居个体相关，这证实了以下假说：有限的交配机会有利于这些多样的性系统的进化，自达尔文时代以来，这些性系统一直困扰着生物学家。
