Absence asymmetry: The evolution of monorchid beetles (Insecta: Coleoptera: Carabidae)
Absence asymmetry: The evolution of monorchid beetles (Insecta: Coleoptera: Carabidae)
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不对称性的缺失：独科甲虫的进化（昆虫纲：鞘翅目：步甲科）
DOI：
10.1002/jmor.10319
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发表时间：
2005
影响因子：
1.5
通讯作者：
J. Galián
中科院分区：
文献类型：
--
作者：
K. Will;J. Liebherr;D. Maddison;J. Galián
本文报道了步甲族Abacetini、Harpalini和Platynini(昆虫纲：鞘翅目：步甲科)中174种甲虫的不对称单性，即完全没有一个睾丸，并有双侧对应的睾丸。在任何其他步甲类甲虫部落或其他甲虫家族的受检个体中没有发现这种情况。Platynini内的一个单兰分类群在化蛹初期显示对称的输精管，这表明发育不发达的输精管在化蛹时发生了发育停滞。睾丸发育中断的时间点尚不清楚。在任何动物支系中都很少发现完全缺乏双边器官对中的一个器官--缺失不对称--另外，在昆虫中，人们只知道Ptilidae科微小甲虫的睾丸、金龟亚科金龟子的卵巢和一些蚜虫的卵巢。根据目前对步甲科的系统发育假说，睾丸丢失至少独立发生过三次，考虑到Abacetini内部的变异，最多可能有五种来源。明确的多个独立起源的系统发育证据表明，这种不对称是适应性的或功能性的原因。先前提出的分类群特有假说，即哈帕里尼部落中的食草动物导致睾丸丧失的假说被驳回。甲虫腹部的最佳内脏填塞是一种普遍的解释。具体地说，基于各器官系统的功能，我们假设内部器官和压力的相互作用，以优化每个系统中器官的大小和空间使用，导致了单兰状态的多重起源和维持。睾丸是唯一的冗余的对称配对结构，不被认为与腹部的其他对称结构在发育上是相关的。在所有可能的器官中，它们最有可能绕过维持两侧对称的限制，导致缺失不对称--尽管观察到的频率非常小。然而，仅仅基于我们对内部器官大体形态的观察，没有任何功能可以最终解释这些类群中一个睾丸的个体发育丧失。与其他动物群体中器官的类似缺失不对称不同，没有戏剧性的身体形态限制--例如蛇和肺的丧失，金龟子的体型较小和相对巨大的精子--或改善运动性能的适应性情景--例如，鸟类和卵巢因飞行限制而丧失--适用于这些步甲甲虫。我们初步认为，睾丸的丧失完全是由这些甲虫内部器官之间的相互作用驱动的，可能是由于选择压力，以最大化在这些分类群中发现的相对较大的附腺。然而，由于这些睾丸丢失和附腺大小增加的进化事件的顺序尚不清楚，较大的附腺可能是二次进化来补偿睾丸输出的减少。J.Morphol。©2005 Wiley-Liss Inc.
Asymmetrical monorchy, or the complete absence of one testis coupled with the presence of its bilateral counterpart, is reported for 174 species of the carabid beetle tribes Abacetini, Harpalini, and Platynini (Insecta: Coleoptera: Carabidae) based on a survey of over 820 species from throughout the family. This condition was not found in examined individuals of any other carabid beetle tribes, or of other adephagan beetle families. One monorchid taxon within Platynini exhibits symmetrical vasa deferentia at the beginning of the pupal stadium, suggesting that developmental arrest of the underdeveloped vas deferens takes place in pupation. The point at which development of the testis is interrupted is unknown. Complete absence of one organ of a bilateral pair—absence asymmetry—is rarely found in any animal clade and among insects is otherwise only known for testes in the minute‐sized beetles of the family Ptiliidae, ovaries in Scarabaeinae dung beetles, and ovaries of some aphids. Based on current phylogenetic hypotheses for Carabidae, testis loss has occurred independently at least three times, and up to five origins are possible, given the variation within Abacetini. Clear phylogenetic evidence for multiple independent origins suggests an adaptive or functional cause for this asymmetry. A previously posited taxon‐specific hypothesis wherein herbivory in the tribe Harpalini led to testis loss is rejected. Optimal visceral packing of the beetle abdomen is suggested as a general explanation. Specifically, based on the function of various organ systems, we hypothesize that interaction of internal organs and pressure to optimize organ size and space usage in each system led to the multiple origins and maintenance of the monorchid condition. Testes are the only redundant and symmetrically paired structures not thought to be developmentally linked to other symmetrical structures in the abdomen. Among all possible organs, they are the most likely—although the observed frequency is very small—to bypass constraints that maintain bilateral symmetry, resulting in absence asymmetry. However, based solely on our observations of gross morphology of internal organs, no function conclusively explains the ontogenetic loss of one testis in these taxa. Unlike the analogous absence asymmetry of organs in other animal groups, no dramatic body‐form constraint—e.g., snakes and lung loss, ptiliid beetles' small body‐size and relatively giant sperm—or adaptive scenario of improved locomotory performance—e.g., birds and ovary loss due to flight constraints—applies to these carabid beetles. We tentatively suggest that testis loss is driven wholly by an interaction among the internal organs of these beetles, possibly due to selective pressure to maximize the comparatively large accessory glands found in these taxa. However, as the ordering of these evolutionary events of testis loss and accessory gland size increase is not known, large accessory glands might have secondarily evolved to compensate for a decreased testicular output. J. Morphol. © 2005 Wiley‐Liss, Inc.