Kobayashi Yukimasa, Niikura Kazuhiro, Oosawa Yuuki, Takami Yasuoki
Laboratory of Systematic Zoology, Department of Biological Sciences, Graduate School of Sciences and Engineering, Tokyo Metropolitan University, Minami-Ohsawa 1-1, Hachioji, Tokyo, 192-0397, Japan.
J Morphol. 2013 Dec;274(12):1323-52. doi: 10.1002/jmor.20181. Epub 2013 Aug 2.
The egg morphology and successive changes in the developing embryos of the carabid ground beetle Carabus insulicola (Carabidae) are described based on light and scanning electron microscopy observations. Newly laid eggs of this species are ellipsoid and measure approximately 6.1 × 2.9 mm, before increasing to 6.6 × 3.4 mm at hatching. The egg period is about 11 days at 23°C. The egg shell is characterized by a thin fragile chorion covering a hard serosal cuticle. The embryo forms on the ventral egg surface, where it develops for the duration of the egg period. During the process of thoracic leg formation, two subcoxal rings, subcoxae-1 and 2, are clearly discernible at the basalmost region of the leg rudiments, and these subcoxae participate in the formation of the larval pleura and sterna. The result thus provides tangible evidence for the subcoxal theory, that is, that thoracic pleura and sterna are derived from subcoxal regions. Despite the complete absence of abdominal appendages in the larvae of this species, two pairs of appendage-like swellings, the medial and lateral ones, temporarily arise in the first eight abdominal segments during the middle of embryonic development. The medial swellings are assumed to be serially homologous with the coxal part of the thoracic leg, and they later flatten out and participate in the formation of the larval pleura (hypopleurites). In the light of the serially homologous relationships among gnathal appendages, thoracic legs, and abdominal appendage-like swellings, we identified the subcoxal regions in both the gnathal and abdominal segments. Although, the lateral swellings soon degenerate and disappear, it is considered that the swellings originate in the abdominal subcoxae-2 and may be homologous to the tracheal gills of larvae of Gyrinidae. Based on the embryological results, new interpretations for the constituent of gnathal appendages are proposed.
基于光学显微镜和扫描电子显微镜观察结果，描述了岛屿步甲（Carabus insulicola，步甲科）的卵形态及发育胚胎的连续变化。该物种新产下的卵呈椭圆形，长约6.1×2.9毫米，孵化前增大到6.6×3.4毫米。在23℃下，卵期约为11天。卵壳的特征是有一层薄而脆弱的卵膜覆盖着坚硬的浆膜表皮。胚胎在卵的腹面形成，并在卵期内发育。在胸足形成过程中，在腿芽最基部区域可清楚地看到两个亚基节环，即亚基节-1和亚基节-2，这些亚基节参与幼虫侧板和腹板的形成。因此，这一结果为亚基节理论提供了确凿证据，即胸侧板和腹板源自亚基节区域。尽管该物种幼虫完全没有腹部附肢，但在胚胎发育中期，前八个腹节会暂时出现两对附肢样肿胀，即内侧和外侧肿胀。内侧肿胀被认为与胸足的基节部分具有系列同源性，它们后来变平并参与幼虫侧板（下侧板）的形成。根据颚附肢、胸足和腹部附肢样肿胀之间的系列同源关系，我们确定了颚节和腹节中的亚基节区域。虽然外侧肿胀很快退化并消失，但认为这些肿胀起源于腹部亚基节-2，可能与豉甲科幼虫的气管鳃同源。基于胚胎学结果，对颚附肢的组成提出了新的解释。
