Progenetic dwarf males in the deep-sea wood-boring genus Xylophaga (Bivalvia: Pholadoidea)
Progenetic dwarf males in the deep-sea wood-boring genus Xylophaga (Bivalvia: Pholadoidea)
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DOI：
10.1093/mollus/eys037
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发表时间：
2013-02-01
影响因子：
1.2
通讯作者：
Kase, Tomoki
中科院分区：
文献类型：
--
作者：
Haga, Takuma;Kase, Tomoki
深海环境中沉没的植物残骸（以下称沉木）含有一种特殊的动物群，这种动物群直接或间接以木材分解为基础（Turner，1973年，1978年）。由于其短暂的性质，这种资源在生态上可与深海鲸鱼瀑布相媲美（Distel等人，2000年）。专性钻木和消耗木材（食木）的双壳类属Xylophaga、Xylopholas和Xyloredo都属于Xylophagaidae科（Turner，2002年;我们在此根据未发表的TH分子系统发育数据将其视为一个独立的科），主要分布在深海，从极地到热带地区一直延伸到深海带（Knudsen，1961年; Schiøtte，2005年）。它们被认为是最重要的生物体，可以将耐火沉木转化为社区其他成员的食物来源（Turner，1973; Distel & Roberts，1997; Distel，2003）。然而，对食木虫科的研究仍然很少，因为它们在很深的地方很难找到。因此，许多物种仅在模式产地被发现（参见Voight，2007）。迄今为止，对食木虫科的繁殖知之甚少。Purchon（1941）报道了小菜蛾的雌雄同体现象（Turton，1819），但泰勒，Young & Dove（2007）基于对Purchon（1941）数据的重新分析，将这一解释更正为雌雄异株。泰勒等人（2007）也显示了在X中具有快速生长速率和快速配子发生的雌雄异体现象（除了极少数同时雌雄同体的例子）。Depalmai Turner，2002. Purchon（1941）和Culliney & Turner（1976）建议X自我效能化。dorsalis和X. atlantica理查兹，1942年，因为这两个物种都有成对的精囊（即囊泡，其中精子从同一个人排出的存储）下足拉钩在上鳃腔。这种繁殖模式被认为是它们对深海短暂栖息地的资源适应（Purchon，1941年; Culliney和Turner，1976年;泰勒等人，2007年）。另一方面，基于具有pediveliger形态的微小个体的发生，经常建议以“幼年育雏”的形式进行延长的父母照顾，这些个体通过附着在大型木虱个体的壳或柔软部分上（Knudsen，1961，1967; Harvey，1996; Turner，2002; Voight，2007，2008，2009）。然而，这一拟议的发展模式仍然令人困惑，因为没有浮游幼虫发育意味着在深海扩散和寻找短暂资源的能力较低（Knudsen，1961年; Scheltema，1994年; Voight，2009年）。另一种假说认为，在许多木虱属物种中，小个体与较大的同种个体之间的关系是，它们代表的是侏儒雄性的交配伴侣，而不是外部育雏的后代。侏儒雄性通常是微小的个体（正常体型的50%或更小），在雌雄异株生物中附着在大个体上。它们被认为是在种群规模较小和/或雌性定居或难以找到的物种中进化而来的（例如Ghiselin，1974; Vollrath，1998）。本研究的目的是通过对附着在大个体X染色体上的微小同种进行详细的超微结构和组织学研究来验证这两个假设。supplicata（Taki & Habe，1950）.该物种分布于西太平洋从日本到菲律宾，水深200- 5050米（Higo，Callomon &后藤，1999; Haga，2011）。成虫达到最大壳长（SL）。15毫米。Xylophaga supplicata可以定殖广泛的…
Sunken plant debris (sunken wood, hereafter) in deep-sea environments harbours an idiosyncratic fauna that is based directly or indirectly on wood decomposition (Turner, 1973, 1978). This resource is ecologically comparable with deep-sea whale-falls, because of its ephemeral nature (Distel et al., 2000). The obligate wood-boring and wood-consuming (xylophagous) bivalve genera Xylophaga, Xylopholas and Xyloredo, all belonging to the family Xylophagaidae (Turner, 2002; we here regard it as an independent family based on unpublished molecular phylogenetic data of TH), occur primarily in the deep sea, extending down to the hadal zone, from polar to tropical regions (Knudsen, 1961; Schiøtte, 2005). They have been recognized as the most important organisms that convert refractory sunken wood into a food source available to other members of the community (Turner, 1973; Distel & Roberts, 1997; Distel, 2003). However, Xylophagaidae remain little studied, as they are difficult to find due to their patchy distribution at great depths. Therefore, many species are known only from the type localities (see Voight, 2007). The reproduction of Xylophagaidae is poorly known so far. Purchon (1941) reported protandric hermaphroditism in Xylophaga dorsalis (Turton, 1819), but this interpretation was recently corrected by Tyler, Young & Dove (2007) to gonochoristic based on a reanalysis of Purchon’s (1941) data. Tyler et al.(2007) also showed gonochorism with a fast growth rate and rapid gametogenesis (in addition to very few examples of simultaneous hermaphroditism) in X. depalmai Turner, 2002. Purchon (1941) and Culliney & Turner (1976) suggested selffertilization for X. dorsalis and X. atlantica Richards, 1942, because both species have paired seminal vesicles (ie vesicles in which spermatozoa discharged from the same individual are stored) beneath the pedal retractor in the suprabranchial cavity. Such reproductive patterns have been regarded as a resource adaptation to their deep-sea ephemeral habitats (Purchon, 1941; Culliney & Turner, 1976; Tyler et al., 2007). On the other hand, extended parental care in the form of ‘juvenile brooding’has often been suggested based on the occurrence of tiny individuals with pediveliger morphologies that are byssally attached to the shell or the soft parts of large Xylophaga individuals (Knudsen, 1961, 1967; Harvey, 1996; Turner, 2002; Voight, 2007, 2008, 2009). However, this proposed developmental mode remained puzzling, because the absence of pelagic larval development implies a low capacity for dispersal and for finding ephemeral resources in the deep sea (Knudsen, 1961; Scheltema, 1994; Voight, 2009). An alternative hypothesis concerning the association of tiny individuals with larger conspecifics in many Xylophaga species is that, instead of externally-brooded offspring, they represent mating partners in the form of dwarf males. Dwarf males are, in general, tiny individuals (50% or less of the normal body size) that attach to large individuals in gonochoristic organisms. They are believed to have evolved among species whose population size is small and/or in which the female is sedentary or hard to find (eg Ghiselin, 1974; Vollrath, 1998). The goal of our study was critically to test these two hypotheses by performing a detailed ultrastructural and histological study of tiny conspecifics attached to large individuals of X. supplicata (Taki & Habe, 1950). This species is found in the Western Pacific from Japan to the Philippines at depths of 200–5050m (Higo, Callomon & Goto, 1999; Haga, 2011). Adults attain a maximum shell length (SL). 15 mm. Xylophaga supplicata can colonize a wide range of …