Miura Toru, Koshikawa Shigeyuki, Matsumoto Tadao
Department of Biology, Graduate School of Arts and Sciences, University of Tokyo, Tokyo 153-8902, Japan.
J Morphol. 2003 Jul;257(1):22-32. doi: 10.1002/jmor.10100.
To elucidate the switching mechanism of caste differentiation in termites and to examine the possible induction of soldier-reproductive intercastes experimentally, we investigated the effects of juvenile hormone on the morphologies of soldier caste by applying a juvenile hormone analog (JHA) to nymphs of the damp-wood termite Zootermopsis nevadensis (Isoptera : Termopsidae). JHA treatment for about 2 weeks induced a variety of intermediate castes, showing both alate and soldier morphological features. The principal component analysis (PCA) of those morphological characters showed that those intercastes were a deviation from the developmental line into alates to soldier differentiation, which is known to be triggered by juvenile hormone. Detailed morphological examination of the compound eyes, wing joint, and mandibles showed that those intercastes expressed soldier features, although they had started to develop alate characteristics. The morphology of the resultant intercastes seemed to be determined by the nymphal stage, at which JHA treatment was applied. The induced intercastes with exaggerated soldier-specific characteristics (e.g., mandibles) repressed alate-specific characteristics (e.g., wings), namely, the alate and soldier morphological characteristics in induced intercastes show opposite responses against the application of JHA. On the other hand, ovarian development was not suppressed by the JHA application, even in the soldier-like individuals. Naturally differentiated presoldiers also possessed developed ovarioles, although ovaries of mature soldiers were degenerated. Our results suggest that the juvenile hormone plays complicated roles in the expression of caste morphologies and ovarian development in termites.
为了阐明白蚁种型分化的转换机制，并通过实验研究兵蚁-生殖型中间型的可能诱导情况，我们通过将保幼激素类似物（JHA）应用于湿木白蚁内华达古白蚁（等翅目：木白蚁科）的若虫，研究了保幼激素对兵蚁种型形态的影响。用JHA处理约2周诱导出了多种中间型，这些中间型表现出了有翅型和兵蚁的形态特征。对这些形态特征进行主成分分析（PCA）表明，这些中间型偏离了从若虫发育为有翅型再到兵蚁分化的发育路径，已知这一过程是由保幼激素触发的。对复眼、翅关节和上颚进行详细的形态学检查发现，尽管这些中间型已经开始发育有翅型特征，但它们仍表现出兵蚁的特征。所产生的中间型的形态似乎由施用JHA时若虫所处的阶段决定。诱导出的具有夸张兵蚁特异性特征（如上颚）的中间型抑制了有翅型特异性特征（如翅膀），也就是说，诱导出的中间型中的有翅型和兵蚁形态特征对JHA的施用表现出相反的反应。另一方面，即使在类似兵蚁样的个体中，JHA的施用也不会抑制卵巢发育。自然分化的前兵蚁也具有发育成熟的卵巢小管，尽管成熟兵蚁的卵巢已退化。我们的结果表明，保幼激素在白蚁种型形态的表达和卵巢发育中发挥着复杂的作用。
