Ciliary Currents of Non-Feeding Veligers in Putative Basal Clades of Gastropods
Ciliary Currents of Non-Feeding Veligers in Putative Basal Clades of Gastropods
复制标题
腹足类假定基底进化枝中非摄食维利格的纤毛电流
DOI：
10.2307/3226863
复制
发表时间：
1997
影响因子：
1.2
通讯作者：
R. R. Strathmann
中科院分区：
文献类型：
--
作者：
M. Hadfield;M. F. Strathmann;R. R. Strathmann
在所有幸存的物种中，腹足纲的最基础分支可能缺乏摄食幼虫阶段，尽管许多物种具有浮游的幼虫，其口前（原食）纤毛带用于运动。我们检查了膜下纤毛和电流，以与其他腹足类动物的摄食幼虫进行比较。这些幼虫代表了三个主要的始源胃足纲类：lottiid帽贝（Lottia pelta）和Tectura scutum)、裂壳帽贝（Diodora aspera）和齿形软足贝（Calliostoma ligatum）。紧靠原脊的羽下纤毛比较后方的纤毛长。膜下电流沿掌背区由后向前，沿掌腹区由前向后。这些观察到的颗粒路径和推断出的膜下纤毛的运动方向表明了一种清洁功能，电流从前方向背向和外侧流出地幔腔，并向后移动，沿足腹侧加入纤毛电流。只有在C. ligatum中，颗粒有时会在原鼻甲带下方的背侧到腹侧方向运输，然后只有在原鼻甲纤毛被阻滞时才会运输。颗粒不会在具有相对纤毛跳动的纤毛带之间被捕获，也不会在有纤毛的食物槽中被运送到口腔中，也不会被古腹足类寄生物摄入，而这些事件在其他腹足类寄生物中很容易观察到。暴露于浮游植物的古腹足动物肠道中没有藻类的荧光，但在其他腹足动物肠道中存在荧光。这些观察结果支持了Patellogastropoda和Vetigastropoda的纤毛不进食和绒毛下纤毛有其他功能的假设。如果丧失了进食的能力，则皮下调节已被修改为具有其他功能，也许是清洁功能。如果纤毛代表了祖先的状况，那么纤毛可能已经被修改为喂养。附加关键词：古腹足动物，食石动物，裂足动物科，小腹动物科，小腹动物科是腹足动物特有的幼虫形式。我们从不同的进化支中了解到食虫。它们在绒毛边缘相对的纤毛的原柄带和后柄带之间捕获颗粒食物；被捕获的颗粒在两个相对带之间的纤毛槽中沿着腭缘运输到口腔（Werner 1955; Strathmann & Leise 1979; Hansen 1991）。与此相反，一些腹足类动物有游动但不捕获食物的腹足体（Fretter 1967; Strathmann 1978a; Hadfield & Strathmann 1990; Hickman 1992）——这是腹足类动物中一些推断出的基底分支的情况。它们曾经被分类在单一的“始祖腹足目”下，现在被认为是属于几个单系动物。电子邮件：hadfield @ uhcc.夏威夷。edu groups。两个推测的早期分支是Patellogastropoda和Vetigastropoda（后者包括Pleurotomarioidea， Fissurelloidea和trochooidea） （Haszprunar 1988; Bieler 1992; Ponder & Lindberg 1996, 1997）。在这些群体中，幼虫明显没有悬浮摄食，这一现象支持了腹足类动物至少进化了两次摄食虫的假设（Ponder 1991; Haszprunar et al. 1995），也被认为是幼虫摄食丧失的一个可能例子（Strathmann 1978a,b; Nielsen 1987; Page 1994）。目前的证据不足以对这些关于摄食幼虫进化的替代假设进行强有力的检验（Strathmann 1978a, 1993），但可以而且应该获得更有力的证据，证明这些幼虫不会捕获和摄入颗粒食物。这些幼虫不进食的证据是它们在饲养过程中不需要颗粒食物。本文内容下载自http://about.jstor.org/terms Hadfield, Strathmann, & Strathmann，所有使用的都是，它们没有排列在腹状和食物槽带中的膜下纤毛（Fretter 1967; Strathmann 1978a; Moran 1997）。由于证据不足，这些群体中幼虫摄食的一些推论被忽视了。当然，很难证明是否定的。为了证明一个进化支缺乏进食动物，必须证明该进化支的所有成员都没有暂停进食的能力。虽然这样详尽的证据是不切实际的，但通过观察代表性物种的纤毛、颗粒运动和肠道内容物，可以获得支持或反对不摄食假设的证据。对非摄食动物和摄食动物的比较也表明了两种假说下进化过渡的终点。如果古胃足类动物的纤毛和水流代表了一种祖先的状态，那么我们就可以寻找一种合理的进化途径，使其成为一种由食物槽和与原始食物相对跳动的后掌带组成的蹼状进食装置。如果不喂养幼虫是一种衍生条件，那么人们应该能够解释独立失去幼虫喂养能力的进化枝之间的相似性。对祖先特征状态的推断需要的不仅仅是现存谱系的系统发育和特征分布；它们需要假定的转换概率（Swofford & Maddison 1992）。哪种假设最合理取决于特征和进化过程（Strathmann 1974, 1978a; Gosliner & Ghiselin 1984; Bull & Charnov 1985; Strathmann & Eernisse 1994）。为了观察纤毛和水流，我们从三组古腹足类动物中选择了幼虫：lottiid帽贝Lottia pelta （RATHKE）和Tectura scutum (RATHKE) (Patellogastropoda)，裂壳帽贝Diodora aspera (RATHKE) （Vetigastropoda）和trochid Calliostoma ligatum (GOULD) （Vetigastropoda）。这些物种代表了腹足纲的早期分支。Patellogastropoda被认为是最基础的腹足动物分支，有现存的后代（Haszprunar 1988; Bieler 1992; Ponder & Lindberg 1996）。根据这一系统发育假说，它的分化早于目前所有具有食性内脏的腹足类动物的进化枝。Haszprunar将具有食性腹足动物的Neritomorpha归入在Vetigastropoda之前的一个分支，但如果Neritomorpha起源于Vetigastropoda之后，正如其他人所建议的那样（Bieler 1992），那么Vetigastropoda也先于已知具有食性腹足动物的所有分支。
The most basal clades of gastropods may lack feeding larval stages in all surviving species, although many species have planktonic veliger larvae with a preoral (prototrochal) band of cilia for locomotion. We examined subvelar cilia and currents for comparison with feeding larvae of other gastropods. The larvae represented three major groups of archaeogastropod grade: the lottiid limpets Lottia pelta and Tectura scutum, the fissurellid limpet Diodora aspera, and the trochid Calliostoma ligatum. Subvelar cilia immediately adjacent to the prototroch were longer than those farther posterior. Subvelar currents were from posterior to anterior along dorsal areas of the velum and from anterior to posterior along ventral areas of the velum. These observed particle paths and inferred directions of beat of subvelar cilia suggest a cleansing function, with currents exiting the mantle cavity in an anterior direction dorsally and laterally and moving posteriorly to join ciliary currents along the foot ventrally. Only in C. ligatum were particles sometimes transported in the dorsal to ventral direction just below the prototrochal band and then only when the prototrochal cilia were arrested. Particles were not captured between bands of cilia with opposed ciliary beat, transported toward the mouth in a ciliated food groove, or ingested by the archaeogastropod veligers, whereas these events were observed easily in other gastropod veligers. Fluorescence of algae was absent in guts of the archaeogastropod veligers exposed to phytoplankton but present in guts of other gastropod veligers. These observations support the hypothesis that veligers of the Patellogastropoda and Vetigastropoda do not feed and that the subvelar cilia serve other functions. If capacity to feed has been lost, subvelar ciliation has been modified for other functions, perhaps cleansing. If the ciliation represents the ancestral condition, then ciliation for cleansing may have been modified for feeding. Additional key words: archaeogastropod, lecithotrophy, Fissurellidae, Lottiidae, Trochidae Veligers are the characteristic larval form of gastropods. Feeding veligers are known from diverse clades. They capture particulate food between opposed prototrochal and metatrochal bands of cilia on the edge of the velum; the captured particles are transported around the velar margin to the mouth in a ciliated groove between the two opposed bands (Werner 1955; Strathmann & Leise 1979; Hansen 1991) In contrast, some gastropods have veligers that swim but are not known to capture food (Fretter 1967; Strathmann 1978a; Hadfield & Strathmann 1990; Hickman 1992)-the condition in some of the inferred basal clades within the gastropods. These were once classified under the single order Archaeogastropoda and are now thought to belong to several monophyletic a Author for correspondence. E-mail: hadfield @uhcc.hawaii.edu groups. Two inferred early branches are the Patellogastropoda and the Vetigastropoda (the latter including the Pleurotomarioidea, Fissurelloidea, and Trochoidea) (Haszprunar 1988; Bieler 1992; Ponder & Lindberg 1996, 1997). The apparent absence of larval suspension feeding in these groups has been taken as support for the hypothesis that feeding veligers evolved at least twice in the gastropods (Ponder 1991; Haszprunar et al. 1995) and also has been offered as a possible example of loss of larval feeding (Strathmann 1978a,b; Nielsen 1987; Page 1994). Present evidence is insufficient for a strong test of these alternative hypotheses on the evolution of feeding veligers (Strathmann 1978a, 1993), but stronger evidence can and should be obtained for the premise that these larvae do not capture and ingest particulate food. The evidence that these larvae do not feed is that they do not require particulate food during rearing and This content downloaded from 157.55.39.127 on Wed, 29 Jun 2016 04:32:51 UTC All use subject to http://about.jstor.org/terms Hadfield, Strathmann, & Strathmann that they lack subvelar cilia arranged in metatrochal and food groove bands (Fretter 1967; Strathmann 1978a; Moran 1997). Some inferences of larval feeding in these groups have been disregarded because of insufficient evidence. It is, of course, difficult to prove a negative. To prove that a clade lacks feeding veligers, it would be necessary to demonstrate an incapacity for suspension feeding in all members of the clade. Although such exhaustive proof is impractical, evidence for or against the hypothesis of non-feeding can be obtained by observations of cilia, particle movements, and gut contents in veligers of representative species. Comparisons between non-feeding and feeding veligers also indicate the end points of evolutionary transitions under either hypothesis. If the cilia and currents of archaeogastropod veligers represent an ancestral condition, then one can look for a plausible evolutionary route to a velar feeding apparatus that consists of a food groove and metatrochal band beating in opposition to the prototroch. If a non-feeding veliger is a derived condition, then one should be able to account for similarities between clades that independently lost the capacity for larval feeding. Inferences on ancestral character states require more than a phylogeny and the distribution of traits in surviving lineages; they require assumed probabilities of transitions (Swofford & Maddison 1992). Which assumptions are most plausible depends on the traits and evolutionary processes (Strathmann 1974, 1978a; Gosliner & Ghiselin 1984; Bull & Charnov 1985; Strathmann & Eernisse 1994). For observations of velar cilia and currents, we selected larvae from three groups of archaeogastropod grade: the lottiid limpets Lottia pelta (RATHKE) and Tectura scutum (RATHKE) (Patellogastropoda), the fissurellid limpet Diodora aspera (RATHKE) (Vetigastropoda), and the trochid Calliostoma ligatum (GOULD) (Vetigastropoda). These species represent inferred early branches of the Gastropoda. The Patellogastropoda is inferred to be the most basal gastropod offshoot with extant descendants (Haszprunar 1988; Bieler 1992; Ponder & Lindberg 1996). Under this phylogenetic hypothesis, its divergence precedes all clades of gastropods presently possessing feeding veligers. Haszprunar assigns the Neritomorpha, which has feeding veligers, to a branch preceding that of the Vetigastropoda, but if the Neritomorpha originated after the Vetigastropoda, as suggested by others (Bieler 1992), then the Vetigastropoda also preceded all clades of gastropods known to have feeding veligers.