Variability,function and phylogenetic significance of periostracal microprojections in unionoid bivalves (Mollusca)

Microprojections of unionoid shells are virtually unstudied but could be important characters for resolving questions on the phylogeny and ecology of these bivalves. By investigating 26 unionoid and three species of their closest living relatives, the Trigonioida, using scanning electron microscopy, we identified three types of periostracal microprojections. (1) Microridges were present only in one species from each of the two unionoid families Mycetopodidae (Anodontites trapesialis) and Iridinidae (Chambardia bourguignati) and may represent a synapomorphy for the mycetopodid‐iridinid clade. In A. trapesialis, microridges were additionally equipped with (2)ensp;flag‐like projections (microfringes), possibly a synapomorphic character for the Mycetopodidae. Examination of partially bleached specimens indicated that both microridges and microfringes are predominantly or purely organic. In contrast, previously undescribed (3) spicule‐like spikes represent calcifications within the periostracum. These were found in 20 of the 29 species and four of the six unionoid families. Spikes were particularly large and abundant in umbonal (juvenile) shell regions and species characteristic of fast‐flowing habitats. These structures may thus serve in protecting the periostracum and shell underneath, and/or stabilizing life position by increasing shell friction. Microfringes and microridges, on the other hand, possibly aid in the orientation of the mussel within the sediment.     

The phylogenetic significance of the carpophore in Apiaceae

Background and aims

Fruit structural characters have traditionally been important in the taxonomy of the family Apiaceae. Previous investigations using a limited number of taxa have shown that the carpophore may be especially useful in helping to circumscribe subfamily Azorelloideae. The present study examines, for the first time, carpophore structure in 92 species from 43 genera, representing all subfamilies of Apiaceae, and including all genera assigned to subfamily Azorelloideae. Phylogenetic interpretations are made for the first time, using all available information, and a standard terminology is proposed to describe the various character states found in carpophores.

Methods

Carpophore structure was studied in detail using light microscopy.

Key Results

Carpophores, when present, may be categorized into two main groups (B and C) based mainly on the arrangement of the vascular bundles in transverse section, and further divided into six sub-types according to the length of the carpophore (short in B1 and C1) and whether they are entire (B1–B3 and C1) or bifurcate (B4 and C2). Free carpophores are absent in subfamily Mackinlayoideae, and in tribes Lichtensteinieae and Phlyctidocarpeae, which have two opposite vascular bundles (Group A). Entire carpophores with one or two vascular bundles, or bifurcate carpophores with lateral vascular bundles (arranged side by side within the commissural plane), are the main types characterizing Azorelloideae. The short, hygroscopic carpophores found in Choritaenia are unique in Apiaceae and provide additional evidence for the exclusion of this genus from Azorelloideae. Carpophore type C2 is typical for most Apioideae sensu lato (exceptions are, for example, Arctopus and Alepidea, which have type B2).

Conclusions

A single carpophore and ventral vascular bundles not forming free carpophores are proposed to be the ancestral conditions in Apiaceae, while bifurcate carpophores with opposite vascular bundles are the derived state, present in most Apioideae. Secondary reductions seem to have occurred in several unrelated lineages in all major groups, e.g. many Azorelloideae, several protoapioids (including nearly all members of the tribe Saniculeae) and 29 euapioid genera (e.g. some Oenantheae).     

The functional and phylogenetic significance of dinoflagellate eyespots

The eyespots or stigmas from five species of dinoflagellates fall into three distinct categories: independent eyespot which is not membrane bound; independent eyespot which is surrounded by three membranes; eyespot situated at the periphery of a chloroplast. In all cases the eyespot is situated behind the longitudinal groove or sulcus and there is a strand of microtubules between the eyespot and the cell covering or theca. In two cases the strand has been clearly shown to originate near the base of the longitudinal flagellum, which is the one passing over the eyespot and is also responsible for directional movement of the cell. The microtubular strand is presumed to play a part in the transmission of directional stimulation from eyespot to flagellum and a hypothesis is advanced to explain how this may be brought about. Phylogenetically, the structure of the various types of eyespots would link these dinoflagellates with euglenids and chrysophytes , and the diversity found in the dinoflagellates is probably a reflection of the diverse origin of chloroplasts in this group.     

The phylogenetic significance of strepsirhinism in Paleogene primates

Two lines of evidence reviewed here argue against the recent proposal that strepsirhinism is an apomorphous feature in primates, shared only by adapiforms and lemuriforms. These are (1) the presence of strepsirhinism in several extant taxa of nonprimate mammals, including Tupaiidae, Tenrecidae, Erinaceus,and Didelphis,and (2) the inferred presence of strepsirhinism not only in adapiforms, but also in all plesiadapiforms and omomyids for which the relevant anatomical regions are known. Therefore, strepsirhinism cannot be invoked as an adaptive innovation underlying the initial strep-sirhine/haplorhine dichotomy. Likewise, the apparent retention of strepsirhinism in omomyids suggests either that the haplorhine oronasal configuration of extant tarsiids and anthropoids was acquired independently or that tarsiids and anthropoids form a clade to the exclusion of omomyids.     

Embryology of the Turbellaria and its phylogenetic significance

Developmental characters — including oocyte and yolk cell structure, patterns of cleavage, and modes of gastrulation — are presented and examined in relation to the phylogeny of the Turbellaria. Eggshell granules, which have been demonstrated to occur in the oocytes of entolecithal eggs and the yolk cells of ectolecithal eggs, are compared among species, and their potential value as a taxonomic character is discussed. The quartet 4d spiral cleavage of the entolecithal egg of polyclads is described as reminiscent of the primitive pattern of early development for the Turbellaria. This is compared to duet spiral cleavage of acoels, and possible phylogenetic schemes involving the two types of spiral cleavage are reviewed. The link between the precise spiral cleavage, which characterizes development of most archoophorans, and blastomere separation (Blastomeren-Anarchie), which occurs in several neoophoran orders, is established by the occurrence of quartet 4d spiral cleavage in one neoophoran order, and of both quartet spiral cleavage and Blastomeren-Anarchie in different species of a second neoophoran order. The epibolic gastrulation of polyclads is described as primitive for the Turbellaria because of its similarity to that of other members of the Spiralia. Although no identical process occurs in neoophoran development, the earlier event of formation of the hull membrane in some neoophorans, and the later event of formation of the definitive epidermis in all neoophorans studied are presented as processes of possible homology to the epibolic gastrulation of polyclads. The lack of correspondence between polyclads and neoophorans in the relationship of the definitive body axes to the egg axis is discussed, and an hypothesis is advanced to account for the differences. The phylogenetic relationships indicated by known developmental phenomena differ only slightly from the scheme presented by Karling in 1974.     

The gonangulum: A reassessment of its morphology,homology, and phylogenetic significance

The gonangulum is a sclerite in the female genitalic region of insects. Its presence or full development has long been considered an apomorphy supporting Zygentoma + Pterygota. Recent studies of female genitalia in several insect orders (K.-D. Klass and co-workers) revealed many new data on the gonangulum and homologous sclerotisations (laterocoxa LC9). Herein the gonangulum area is described (including articulations, muscle attachments, sulci) and compared among Archaeognatha, Zygentoma, Odonata, Dermaptera, Dictyoptera, and Notoptera. A wider perspective is provided to the topic by addressing some novel issues: identification of LC9 sclerotisations in non-insect taxa and in insects that secondarily lack an ovipositor; occurrence of homonomous sclerotisations in other abdominal segments of both sexes; morphological interpretation of LC9; and the role of paedomorphosis in LC9 evolution. As a result, there is currently no support for any insect lineage from this character system. For gonangulum-related characters both a significant intra-ordinal variation and frequent homoplasy are demonstrated using various Odonata, Dermaptera, and Dictyoptera as examples. Divergent fates of LC9 in simplified genitalia are shown using a dermapteran and an odonatan. We view all this as a showcase of how a renewed and more detailed examination of a character system can dramatically change the phylogenetic evidence drawn from it.     

Occurrence and phylogenetic significance of cytokinesis-related callose in green algae, bryophytes, ferns and seed plants

 In order to investigate the occurrence of callose in dividing cells, we cultivated a selection of 30 organisms (the prokaryotic cyanobacterium Anabaena and eukaryotic green algae, bryophytes, ferns and seed plants) under defined conditions in the laboratory. Samples from these photoautotrophs, which are members of the evolutionary 'green lineage' leading from freshwater algae to land plants, were analysed by fluorescence microscopy. The β-1,3-glucan callose was identified by its staining properties with aniline blue and sirofluor. With the exception of the prokaryotic cyanobacterium, all of the eukaryotic organisms studied were capable of producing wound-induced callose. No callose was detected during cytokinesis of dividing cells of unicellular green algae (and Anabaena). However, in all of the multicellular green algae and land plants (embryophytes) investigated, callose was identified in newly made septae by an intense yellow fluorescence. The formation of wound callose was never detected in cells with callose in the newly formed septae. Additional experiments verified that no fixation-induced artefacts occurred. Our results show that callose is a regular component of developing septae in juvenile cells during cytokinesis in multicellular green algae and embryophytes. The implications of our results with respect to the evolutionary relationships between extant charophytes and land plants are discussed. Received: 15 September 2000 / Revision received: 23 October 2000 / Accepted: 23 October 2000     

Crystals in calyces of Lamiaceae and their phylogenetic and adaptive significance

The diversity of crystal types is studied in fruiting calyces of 435 out of the c. 7,200 species, and 184 out of the c. 236 genera of Lamiaceae, mainly in the subfamilies Nepetoideae and Lamioideae. Calcium oxalate crystals are found in about half of the studied calyces, and belong to the following main types: prismatics in the inner epidermis, prismatics in fibres, prismatics in sclereids, prismatics in the mesophyll and druses in the mesophyll. Presence of epidermal prismatics may constitute a synapomorphy of the subfamily Nepetoideae or of a subclade within this subfamily consisting of the two largest tribes Mentheae and Ocimeae. The presence of narrow mesophyll prismatics seems to support a large clade of Lamioideae genera in a recent molecular phylogeny of the subfamily. Epidermal prismatics are found to be particularly frequent in closed calyces, calyces with a narrow mouth and internally hairy calyces. These findings and the position of the crystals in the calyces are regarded as supporting the hypothesis that calcium oxalate crystals protect the fruit against insect predators.     

Introduced galliforms as seed predators and dispersers in Hawaiian forests

In altered communities, novel species’ interactions may critically impact ecosystem functioning. One key ecosystem process, seed dispersal, often requires mutualistic interactions between frugivores and fruiting plants, and functional traits, such as seed width, may affect interaction outcomes. Forests of the Hawaiian Islands have experienced high species turnover, and introduced galliforms, the largest of the extant avian frugivores, consume fruit from both native and non-native plants. We investigated the roles of two galliform species as seed dispersers and seed predators in Hawaiian forests. Using captive Kalij Pheasants (Lophura leucomelanos) and Erckel’s Francolins (Pternistis erckelii), we measured the probability of seed survival during gut passage and seed germination following gut passage. We also examined which seeds are being dispersed in forests on the islands of O’ahu and Hawai’i. We found that galliforms are major seed predators for both native and non-native plants, with less than 5% of seeds surviving gut passage for all plants tested and in both bird species. Gut passage by Kalij Pheasants significantly reduced the probability of seeds germinating, especially for the native plants. Further, larger-seeded plants were both less likely to survive gut passage and to germinate. In the wild, galliforms dispersed native and non-native seeds at similar rates. Overall, our results suggest the introduced galliforms are a double-edged sword in conservation efforts; they may help reduce the spread of non-native plants, but they also destroy the seeds of some native plants. Broadly, we show mutualism breakdown may occur following high species turnover, and that functional traits can be useful for predicting outcomes from novel species’ interactions.

     

The phylogenetic significance of bone types in euteleost fishes

The paradentary is a small, sometimes dentigerous element in the lower jaw of some atherinomorph neoteleost fishes. Identification of the paradentary as a neomorphic, perichondrally ossified bone prompted re-examination of theories of the association of bone and teeth in teleost fishes. Teeth on a chondral lower jaw bone might be explained simply by epidermal-mesodermal interactions. Since the work of Kolliker in 1859, it has been known that there are two basic types of bone in teleost fishes: cellular bone, characterized by a matrix that has enclosed osteoblasts or osteocytes; and acellular bone, characterized by a relatively featureless matrix that lacks these bone-forming cells. Cellular bone is typical of lower teleosts, whereas acellular bone is typical of higher teleosts. Ontogenetic data indicate that acellular bone is derived relative to cellular bone. Even though identification of cellular and acellular bone can be made readily with histological preparations, acellular bone has been used infrequently as a character in analyses of teleost phylogeny. Acellular bone is considered here to be a derived character within teleost fishes. It is found in all Neoteleostei as well as some, but not all Salmoniformes. Independent of studies of bone, derived types of teeth in teleosts have been described in terms of their failure to become completely mineralized. Acellular bone and teeth of higher teleosts share several properties, including a large fraction of collagen. Teleosts lack a parathyroid gland; bone type is critical to the mechanism of calcium regulation. It is proposed that the character of acellular bone be incorporated into phylogenetic analyses of teleost fishes by correlating it with derived types of tooth structure.     

Egg teeth of squamate reptiles and their phylogenetic significance

Original and published data on the structure of egg teeth in squamate reptiles and the phylogenetic significance of corresponding characters are reviewed, elaborating A.M. Sergeev’s ideas on the subject. Problems are discussed concerning the use of this character in modern phylogenetic constructions and the necessity of new embryological investigations to resolve the issue concerning the formation of an unpaired egg tooth rudiment in all Squamata except the Dibamidae and Gekkota.     

The phylogenetic significance of sperm morphology in the Platyhelminthes

The phylogenetic significance of flatworm sperm morphology is discussed against the background of general spermatology. The modified type of spermatozoon of the Nemertodermatida, a group of primitive flatworms, indicates that the Platyhelminthes evolved from forms characterized by the primitive type of metazoan sperm and by the primitive mode of fertilization, implying the release of sperm freely into sea water.The occurrence of aberrant types of spermatozoa in most platyhelminths is obviously a consequence of early evolution of the internal mode of fertilization, which characterizes all true members of this group. It can be concluded, from the ultrastructure of these aberrant spermatozoa that higher metazoans cannot have evolved from seriated flatworms related to the recent Seriata (Proseriata and Tricladida). Even the seemingly primitive Acoela have such aberrant spermatozoa that evolution of higher metazoans from acoels related to the recent Acoela seems highly improbable.The ultrastructure of the spermatozoa of the parasitic groups of flatworms (Monogenea, Digenea, Cestoda) is very similar to that found in the Kalyptorhynchia, a further indication that the parasitic groups are related to the rhabdocoel turbellarians.     

Dental characters of the Quaternary tapirs in China, their significance in classification and phylogenetic assessment

Most of the Quaternary tapir fossils from China are isolated teeth. The purpose of this paper is to identify them and to extract systematic and evolutionary information from them. Based on morphology and W/L ratio, isolated teeth can be identified successfully. On the whole, the identification of P¹, M³ and P₂ is believed to be reliable, while it is difficult to distinguish P₃ from P₄, M₁ from M₂ etc. Concerning the variations of the teeth, P¹ is the most variable one in dimension. In the Quaternary tapirs in China, some dental characters can be used as reliable indicators to evaluate their evolutionary levels. The degree of the atrophy of the upper canine relative to the caniniform I³ is reflected in the C/I³ diameter ratio, which is decreasing during evolution. P¹ changes considerably in outline and strength of the hypocone. Some forms are without hypocone, such as Tapirus sanyuanensis, some have a very faint hypocone, such as Tapirus indicus; although most of them show a developed hypocone. For other cheek teeth, the W/L ratio is decreasing through geologic time. Two lineages can be tentatively proposed: one is the Tapirus peii-Tapirus sinensis-Megatapirus augustus progression; the other is the T. sanyuanensis-T. indicus lineage. T. sanyuanensis and T. peii stand on the base, and it is very probable that the latter is more primitive.     

The origin of the coelom in Brachiopoda and its phylogenetic significance

The origin of the mesoderm and the subsequent formation of the coelom in the larvae of the brachiopod species Notosaria nigricans and Calloria inconspicua is documented in detail at the ultrastructural level. During gastrulation, the blastocoel is completely displaced by the invaginating archenteron. Initial mesoderm formation was observed in late wedge-shaped to early three-lobed stages in both species. Proliferation of mesodermal cells from the archenteral epithelium mainly occurs in the dorsolateral (C. inconspicua) and caudolateral (N. nigricans) parts of the archenteral wall. Thus, a compact mesodermal cell mass pushes its way towards the subepidermal basal lamina. During further development of the larva, the mesoderm is separated from the archenteral epithelium by an extracellular matrix secreted frontad from behind. As a result, a single coelomic anlage is formed. The initial mesoderm in both species is of archenteral/endodermal origin. Considering endodermal origin as the crucial character for enterocoely, coelom formation through proliferation of a compact, endodermally derived mesodermal cell mass in Brachiopoda is clearly identified as enterocoely. Endodermal origin of mesoderm and, therefore, of the coelomic epithelium is hypothesised as a synapomorphy of Brachiopoda and Deuterostomia. As a consequence: (1) Brachiopoda and Deuterostomia are considered sister groups, (2) Brachiopoda group within Radialia and (3) lophophorates (”Tentaculata”) remain as a paraphyletic grouping. Accepted: 26 November 1999     

The sound-transmitting apparatus in primitive snakes and its phylogenetic significance

Summary The structure of the sound-transmitting apparatus in primitive snakes (Scolecophidia, Henophidia) is reviewed and compared with that of advanced snakes (Caenophidia) and of some fossorial lizards. Assuming a constant course of the chorda tympani, the ophidian stylohyal can be homologized with the intercalary cartilage of lizards while the cartilaginous distal portion of the ophidian stapes represents the internal process. The cladistic significance of the stapes-quadrate-articulation in the Henophidia and Caenophidia is discussed. The Booidea and the Caenophidia show a shift of the stapes-quadrate-articulation which is correlated with changes in the suspensorium as an adaptation to relatively larger prey. However, convergence cannot be ruled out. Dibamus is shown to be the only lizard known so far which approaches the ophidian middle ear structure. Convergence has to be assumed since there is no sign of a stylohyal in Dibamus and since the course of the ramus communicans externus n. facialis cum glossopharyngeo supports the hypothesis that snakes are to be derived from a pre-lacertilian stage of lepidosaurian evolution.

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Zusammenfassung Die Struktur des schalleitenden Apparates im Mittelohr primitiver Schlangen (Scolecophidia, Henophidia) wird beschrieben und mit höheren Schlangen (Caenophidia) sowie mit einigen grabenden Lacertiliern verglichen. Unter der Annahme eines konstanten Verlaufes der Chorda tympani lässt sich das Stylohyale der Schlangen mit dem Processus dorsalis homologisieren, während das knorpelige distale Ende des Stapes der Schlangen dem Processus internus entspricht. Die kladistischen Implikationen der Struktur des Mittelohres werden diskutiert. Die Booidea und die Caenophidia zeigen eine Verschiebung das Stapes-Quadratum-Gelenkes, welche möglicherweise mit Änderungen der Proportionen des Suspensoriums als Anpassung an relativ grössere Beute zusammenhängt. Konvergenz kann hierbei nicht ausgeschlossen werden. Dibamus ist die einzige bislang bekannte Echse welche im Bau des Mittelohres den Schlangen nahe kommt. Allerdings ist Konvergenz anzunehmen, da Dibamus keinerlei Hinweis auf das Vorhandensein eines Stylohyale liefert, und da der Verlauf des Ramus communicans externus n. facialis cum glossopharyngeo die Hypothese stützt, dass Schlangen nicht von rezenten Unterordnungen der Lacertilier abgeleitet werden können.

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Abbreviations (used in the figures) chr chorda tympani - ci carotis interior - crst cartilaginous distal extension of the stapedial shaft - dper ductus perilymphaticus - fc carotis facialis - par articulatory process of quadrate - pt pterygoid - q quadrate - rce ramus communicans externus - rci ramus communicans internus - st supratemporal - stp stapes - sty stylohyal - vcl vena capitis lateralis - lX n. glossopharyngeus - Vll_hy ramus hyomandibularis of facial nerve     

Base composition, selection, and phylogenetic significance of indels in the recombination activating gene-1 in vertebrates

Background

Echinoderms and chordates belong to the same monophyletic taxon, the Deuterostomia. In spite of significant differences in body plan organization, the two phyla may share more common traits than was thought previously. Of particular interest are the common features in the organization of the central nervous system. The present study employs two polyclonal antisera raised against bovine Reissner's substance (RS), a secretory product produced by glial cells of the subcomissural organ, to study RS-like immunoreactivity in the central nervous system of sea cucumbers.

Results

In the ectoneural division of the nervous system, both antisera recognize the content of secretory vacuoles in the apical cytoplasm of the radial glia-like cells of the neuroepithelium and in the flattened glial cells of the non-neural epineural roof epithelium. The secreted immunopositive material seems to form a thin layer covering the cell apices. There is no accumulation of the immunoreactive material on the apical surface of the hyponeural neuroepithelium or the hyponeural roof epithelium. Besides labelling the supporting cells and flattened glial cells of the epineural roof epithelium, both anti-RS antisera reveal a previously unknown putative glial cell type within the neural parenchyma of the holothurian nervous system.

Conclusion

Our results show that: a) the glial cells of the holothurian tubular nervous system produce a material similar to Reissner's substance known to be synthesized by secretory glial cells in all chordates studied so far; b) the nervous system of sea cucumbers shows a previously unrealized complexity of glial organization. Our findings also provide significant clues for interpretation of the evolution of the nervous system in the Deuterostomia. It is suggested that echinoderms and chordates might have inherited the RS-producing radial glial cell type from the central nervous system of their common ancestor, i.e., the last common ancestor of all the Deuterostomia.     

Apigenin and amentoflavone glycosides in the psilotaceae and their phylogenetic significance

Documentation of amentoflavone O-glucosides as the predominant flavonoid glycosides in both genera of the Psilotaceae clearly distinguishes this family from all other families of vascular plants. Psilotum and Tmesipteris also possess apigenin C- and O-glycosides as common flavonoid types. Apigenin 7-O-rhamnoglucoside occurs in both genera and the previously undocumented apigenin 7-O-rhamnoglucoside-4′-O-glucoside, although identified only in Tmesipteris, may also be present in Psilotum. The existence of flavone C-glycosides in both genera may provide a phytochemical relationship between the Psilotaceae and some ferns. The phylogenetic significance of these results is discussed.