Unknown Ancestor Research Articles

Conservation of gene structure and activity in the regulation of reproductive organ development of conifers and angiosperms.

The Norway spruce (Picea abies) gene DAL2 shows distinct structural similarities to angiosperm MADS-box genes which act in the control of the development of the sexual organs of the flower. Transcription of DAL2 is restricted to the reproductive organs, the unisexual cones, of Norway spruce. In this paper we show that DAL2 in the compound female cone is exclusively expressed in the developing ovule-bearing organ, the ovuliferous scale. When expressed constitutively in transgenic Arabidopsis the gene causes developmental alterations very similar to those observed in plants ectopically expressing the Arabidopsis gene AGAMOUS and the closely related Brassica napus gene BAG1. These alterations include homeotic transformations of floral organs. On the basis of these data and analysis of the phylogeny of the plant MADS-box gene family, we propose that DAL2 acts to control reproductive organ development in spruce. We also propose that DAL2 shares a common origin with AGAMOUS and related genes from other angiosperms, in an ancestral MADS-box gene that was active in the control of ontogeny of ovule-bearing organs in the unknown last common ancestor of conifers and angiosperms.

Relationships of the Chimaeriformes and the basal radiation of the Chondrichthyes

The origin and early evolution of the cartilaginous fishes (Chondrichthyes) has been the subject of considerably more debate than of data. The two modern groups, Chimaeriformes and Elasmobranchii, differ so radically in morphology that in the past they have often been considered unrelated -- descended from some remote and unknown common ancestor. The current consensus promotes the Chimaeriformes and Elasmobranchii as sister taxa of the Class Chondrichthyes which are linked by an assemblage of Palaeozoic fossil taxa, but no taxonomic or phylogenetic scheme has been accepted for the Class. Of the two groups, the Chimaeriformes is the less understood. The few species of Chimaeriformes existing today are enigmatic, principally deeper-water fish that are not readily accessible for study. In the past the fossil record of both groups has been relatively scanty, primarily due to the poor potential for skeletal fossilization, and so has provided little useful input into fundamental discussions of vertebrate diversification. However, these situations are changing. Chimaerids are increasingly becoming the subject of renewed biological and limited fisheries interests. Regarding extinct chondrichthyans, the last 30 or so years have entailed discoveries of new fossils that illuminate our view of Palaeozoic life and are eliciting dramatic changes in our understanding of these early fishes, their relations, and the origins of jawed conditions. Morphological examination of fossil chondrichthyans indicates that the plesiomorphous state of the gnathostome suspensorium is autodiastylic and that complex labial cartilages are primitive and likely to have been critical to the mechanical architecture of the first jaws. Analysis of cranial morphology, cranial proportions, the phyletic and developmental history of calcified tissues, and postcranial data including the evolution of the prepelvic tenaculum are now feasible. Cumulatively, when the results of these analyses are subject to cladistical evaluation, the result is one predominant cladogram supporting two monophyletic subclasses: the Elasmobranchii and the Euchondrocephali. The latter subclass contains a monophyletic group of holocephalans including the Cochliodontomorpha, and within this taxon, the restricted Chimaeriformes. Alternative cladograms of the non-holocephalan Euchondrocephali are dependent upon whether whole-body or cranial characters alone are employed in the analysis, or the additive or non-additive treatment of characters. Otherwise, only the discovery and description of additional members of this diverse assemblage are expected to alter these patterns of associations

Genome polymorphism of human adenoviruses of subgenus C.

The genome of adenovirus (AV) types 1, 2, and 5 is known to be very variable as evidenced by the great number of genome types described (36, 61, and 35 for AV1, 2, and 5 respectively). Physical maps were constructed for nearly all of the restriction or R-variants by biochemical methods and by adapting restriction fragments of defined molecular weight. The alterations found with seven DNA restriction endonucleases were mapped on the genome. Altered restriction sites, found for the genome types of each of the three serotypes, appeared to be randomly distributed over the genome, although mutations seemed to occur preferentially on distinct sites of the genome. Many strains, especially those of AV5, were genomically much more related with one another than with the prototype. This finding is compatible with the interpretation that the related strains were derived from an unknown common ancestor.

WIS 2-1A: an ancient retrotransposon in the Triticeae tribe

WIS 2-1A, the first retrotransposon found in wheat, has been recently studied and characterized. Southern hybridization experiments utilizing several species from the Triticeae revealed the presence of homologous sequences in all the taxa tested, showing high levels of interspecific variability and almost no intraspecific differentiation. Further experiments using in situ hybridization in several species showed that the retroposon was almost completely dispersed throughout the genomes tested. These results suggested that WIS 2-1A is an ancient element that probably was present in the unknown common ancestor of the Triticeae and that only under rare circumstances does it become active. DNA fragments homologous to the WIS 2-1A reverse transcriptase gene were isolated from most of the Triticeae species using PCR. The fragments obtained were sequenced and analyzed. Even though the sequence alignment was consistent with the phylogenetic studies made in the past, the genus Thinopyrum showed new evidence for a possible horizontal propagation of the retroelement.Mention of a trade name or proprietary product does not constitute a guarantee, warranty or recommendation of the product by the U.S. Department of Agriculture or the University of Missouri and does not imply its approval to the exclusion of other products that may be suitableAll programs and services of the U.S. Department of Agriculture are offered on a non-discriminatory basis without regard to race, colour, national origin, religion, sex, age, marital status, or handicap.

Interrelationships of Mesozoic mammals

Polyphyletic or monophyletic origins of mammals have been subjects of considerable controversy for a century. Late Triassic—Early Jurassic mammals are more diverse than previously thought. The stumbling block in establishing mono‐ or polyphyletic origins of mammals is the uncertain position of the Haramiyidae (the oldest Multituberculata, and possibly the oldest mammals), known only from isolated teeth. Triconodonta and Theria probably shared an unknown common ancestor, while Monotremata possibly branched from early Eupantotheria at the end of the Early Jurassic, before the Dryolestoidea did, from the forms in which the cochlea started to coil and small cerebellar hemispheres developed. Aegialodontia gave rise to Metatheria but not to Eutheria. Deltatheroida belongs to Metatheria. A group of Cretaceous therian mammals with tribosphenic molars informally classified as “Tribotheres”; cannot be assigned either to Metatheria or Eutheria.

Polystichum kwakiutlii sp. nov., the Elusive Bipinnate Ancestor of P. andersonii

In preparing treatment of Polystichum for Flora of North America, it becomes desirable to name an undescribed species collected only once, in 1934, from northern British Columbia coast at Alice Arm. The importance of describing this poorly known species lies in its probable involvement in hybrid origins of P. andersonii Hopkins. The story begins with discovery that P. andersonii is a tetraploid (Taylor and Lang, 1963). At first it was thought it might be an autotetraploid (W. Wagner in Hitchcock, et al., 1969, p. 85), but a cytological analysis of a triploid hybrid between P. andersonii and P. munitum yielded 41 II's and 41 I's at meiosis (W. Wagner, 1973). Despite this evidence, W. Wagner doubted that P. munitum contributed a genome to P. andersonii because the characters of P. andersonii seem so distinct from those of P. munitum that ancestral affinity seems unlikely (W. Wagner, 1973). However, further study of these plants and comparison with other, well-documented cases of allopolyploidy in Polystichum indicated that, indeed, P. andersonii is an allotetraploid with P. munitum as one of its diploid ancestors (D. Wagner, 1979). The problem was that no species was known that could be considered second diploid parent of P. andersonii. It was not hard to predict what this second ancestor of P. andersonii would look like; exercise was similar to that used by W. Wagner (1971) in describing unknown diploid ancestor of Dryopteris cristata and D. carthusiana, known informally as D. semicristata. Dryopteris semicristata has not yet been found, but a herbarium specimen that matched predictions for second parent of P. andersonii, one collected at Alice Arm, was reported in my monograph (D. Wagner, 1979). The most important characters are completely divided pinnae coupled with presence of a vegetative bulbil. The Alice Arm plant was left undescribed at that time in hope that living material could be found to confirm prediction that it was indeed diploid. The material serving as type of this species remains only known collection. It is fragmentary, comprised of upper one-half of three fertile fronds, so that rediscovery is necessary to provide information about stem and lower part of leaves. I traveled to Alice Arm in 1975 to search for this intriguing plant. Unfortunately, although I did find P. braunii and P. setigerum, I did not find hoped-for diploid. It is not clear whether Alice Arm referred to on label is town (a ghost mining town in 1975) or inlet of same name, at whose head town is located. Nobody has yet reported finding this plant. In order to emphasize reality of this entity, and hopefully encourage search for it, it is formally named here, in honor of one of peoples in whose territory it

Phytogeny and behavioural evolution in ants, with a discussion of the role of behaviour in evolutionary processes

The family Formicidae is redefined on the basis of all common characters shared by its members, which allows a hypothetical sketch of its unknown presumed ancestor. The first cladistic analysis is presented of internal ant phylogeny at the subfamily level, based on the 10 extant subfamilies commonly recognized in the literature. Although some weaknesses remain, this phylogenetic reconstruction shows several concrete improvements. None of the fossil subfamilies allow comparison with the recent subfamilies by neontological criteria. Among recent subfamilies no autapomorphic characters have been found for the Aneuretinae which clearly show only primitive character states easy to identify by comparison with the Dolichoderinae. The former subfamily has been regarded as a straightforward synonym of the latter. The Ponerinae have been still characterized tentatively on the basis of two weak synapomorphies but the real monophyly of its members appears to be questionable. The subfamilial phylogeny, as a whole, appears relatively weakly documented on several branchings with exception of the Nothomyrmeciinae, Dolichoderinae, and Formicinae on one side which can be easily opposed to all remainder recent subfamilies on the other side, by having a constriction after abdominal segments I and II only instead of after segments I, II, and III. Another important conclusion reached in this paper concerns the Formicinae, which can no longer be considered as the most advanced extant ants. A variety of complex and simple behaviours, chosen as examples of general evolutionary trends within the ants, all show a mosaic picture of parallelisms and convergences. Two reasons are offered to explain these findings. The first, particular to ants, is that eusociality represents an evolutionary constraining influence allowing further selection only for a few behaviours like nesting behaviour, communication modes, social parasitism, etc. It is not surprising, therefore, that the few rewarding options appear convergently in different stems within the ants, and among other, unrelated, social insects as well. The second, more general, reason is the understandable tendency of taxonomists to produce phylogenies based on purely morphological characters. An analysis of the major morphological trends among ants shows that all correspond to behavioural evolutionary sequences. Such sequences are, of course, much more difficult to describe and to quantify than is morphology. Only one systematically «pure» (i.e. without morphological correlates and virtually free from important selection pressures) ethological character has been found to be widely consistent with the subfamily classification proposed here and increasing its information contents. This is the manner in which ants transport other adult ants. This is probably the highest rank phylogenetically relevant character detected so far which is based on behaviour only.

The polyplacophoran“Chiton” carbonariusStevens, 1858, in North America and new related species

“Chiton” carbonariusStevens, 1858, is reassigned as the type species toGlaphurochitonRaymond, 1910. This species evolved from an unknown Mississippian ancestor, and spread rapidly into the Midcontinent region, Eastern Interior, and Appalachian basins during the Morrowan.Glaphurochiton carbonariusserved as the root stock for development of several species:G. concinnus(Richardson) during the Desmoinesian andG. subcircularisn. sp. during the Virgilian in the Eastern Interior basin andG. elimatusn. sp. in the Appalachian basin and possiblyG.?riddlei(Frederickson) in the Midcontinent region during the Missourian.Glaphurochitonis believed to have been essentially restricted to a mud bottom based upon its occurrence and relative abundance. Commonly the only taxon present, often abundantly, in black and gray shales,Glaphurochitonis rare to absent in limestones, algal limestones, reefs, and shales with an abundance of crustose calcareous algae. The latter lithologies commonly support a diverse polyplacophoran fauna essentially lackingGlaphurochiton.

Early Neolithic Horsebean from Yiftah'el, Israel

Charred seeds of horsebean (Vicia faba L.) from the seventh millennium B.C. that were found at Yiftah'el, Israel, push back the known use of this vetch by about 2000 years. Horsebean should be included in the ensemble of legumes grown by some early Neolithic people. The site, situated near the southwest outlet of Biq'at Bet Netofa, lies in a valley with heavy soil suitable for growing contemporary cultivars of horsebean. The still unknown wild ancestor of the horsebean may have originated in similar habitats in the Levant.

On the Head of the Liopelmid Frog, Ascaphus Truei

This paper gives the first account of the larval cranial anatomy of either of the genera of Liopelmid frogs. A single, partly grown larva of Ascaphus truei, Stejneger, has been studied in transverse sections and in two-dimensional reconstructions. Its chondrocranium, jaws, gill arches, and head muscles are described and figured. Comparisons are made throughout with similar structures of Urodeles and certain other frogs, particularly Discoglossus pictus and Kana temporaria. A summary of the characters which Ascaphus shares with the Urodeles is given on pp. 175-7 and with Discoglossus on pp. 177-8. The reader is referred to these lists as an important part of this summary. Noble (1931, &c.) considers Ascaphus (with Liopelma) to be one of the two most primitive living frogs. The findings of this paper are in full agreement with this view. Thus larval Ascaphus is shown to be a persistently primitive ‘link-animal’ whose cranial structures, in almost every case, differ from those of other frogs--often radically--and throw much light on the evolution of the modern-type frog tadpole from the unknown (larval) ancestor. Ascaphus is shown to have more characters in common with the Urodeles than any other frog larva yet described. Most of these are probably a simple retention of an ancestral Amphibian plan which led on to the frogs and Urodeles (contrast the writings of Holmgren and Säve-Söderbergh). Others seem to link these two orders even more closely together. Such are: (1) The presence of ‘urobranchial’ prongs on the basibranchial copula and the attachment to them of Subarcuales obliqui and Eecti cervicis muscles; (2) the presence of a pair of Branchio-hyoideus externus muscles and other similarities of the musculature. The relationship of Ascaphus to the Gymnophiona is far less marked. Ascaphus, however, has remained more primitive than the present-day Urodeles by retaining: (1) a? Vth gill bar, with its Subarcualis rectus and S. obliquus muscles, and (2) four pairs of S. obliqui muscles instead of two. In these points it is, in fact, the most primitive living tetrapod. Ascaphus is, however, somewhat specialized in relation to a sucker mechanism and to a peculiar method of larval progression which it employs. These have led to an exaggerated autostyly of the palatoquadrate which has developed an additional fusion to the anterior tip of the auditory capsule; to a rigid fusion of the central part of the supra-rostral system to the skull; to the general heavy build of the head cartilages and to the great size of several of the mandibular and hyoid muscles; to a general consolidation and widening of parts of the hyobranchial apparatus; to a widening of the posterior jaw cartilages and the development from them of unique posterior spurs. A pre-oral mouth cavity and a long ‘posterior narial tube’ to the inner nostril are also parts of this specialization. Among the frogs Ascaphus is shown to be most nearly related to the Discoglossidae, which appear to have been derived from an ancestor with many Ascaphus-like characters. This is in further agreement with Noble's classification and is particularly true of Discoglossus pictus. Ascaphus is unique among frogs in the posterior position of its splanchnic head structures; see the list on p. 147. A forecast is made of the probable evolution of the moderntype tadpole's jaw system from that of the unknown ancestor and this is diagrammatically summed up in Text-fig. 7, pp. 158-9. Evidence is collected to show that the ‘anterior basal process’ (= commissura quadrato-cranialis anterior) is not an ethmoidal structure by origin, as has been held up to now, and consequently Säve-Söderbergh's use of it to explain an ethmoidal structure in a Stegocephalian Amphibian is criticized. An account of the muscles has been given in summary form on pp. 126 to 146 and cannot be further condensed here. But it may be noted that Edgeworth's theories (1935) of the primitive muscular content of a single branchial segment break down when applied to Ascaphus. It is now probable that a single segment could simultaneously contain a Subarcualis rectus, a S. obliquus, and a Transversus ventralis muscle. Further, Edgeworth's term ‘Transversus ventralis II’ must be changed to ‘S. obliquus II’ in the frogs and his ‘S. rectus IV’ must probably be changed to ‘S. recti IV, III, and II’ in the Urodeles.

THE SYSTEMATIC POSITION OF THE FUCALES

T HE Fucales are probably the most widely distributed and the most abundant of all the brown algae. They have certainly reached the highest level of morphological and anatomical differentiation, yet their systematic position remains one of apparent isolation, and it has recently been claimed that they have been derived independently of all the other brown algae (Dekker, ig29). The discovery of the microgametophyte of Laminaria by Sauvageau (I9I5) and Kylin (I9I6 b) focused attention upon the origin of this group and also lead to speculation as to some similar course of evolution for the Fucales. A primitive (probably heterosporous) type had zoospores germinating in situ, the enclosed gametophytes became suppressed leaving only the gametes, which are thus in a sense homologous with the zoospores. An approach to this condition was seen by Sauvageau (I9I5) in Saccorhiza bulbosa, where a few zoospores which had failed to escape germinated within the sporangium. Some such interpretation has been widely held (cp. Kylin, i9i6a, I9I8; Lloyd Williams, ig2i; Svedelius, I927, I929), but whilst the discovery of the life cycles of such types as Asperococcus or Desmarestia have strengthened the idea of relationship between Laminariales and Ectocarpales, no such links have been found between the Fucales and the lower Phaeosporae. It is well known that meiosis occurs in the young unilocular sporangium1 and also in the early stages of the oogonium and antheridium; but in their later development striking differences are found. In the latter, when nuclear multiplication is completed, delicate protoplasmic partitions form giving a number of antherozoid mother cells within each of which an antherozoid is developed (Fig. i d). In the oogonium of Fucus vesiculosus also evanescent wall formation has been described (Farmer & Williams, I898). This septation recalls the plurilocular rather than the unilocular sporangium and according to Kylin (I933, I937) entirely invalidates the comparison with the unilocular sporangium of the Phaeosporae. A further difficulty on which Kylin now lays much stress is the different ciliation of the zoospore and antherozoid. On both these grounds, Kylin now regards the Fucales as an isolated family originating from an unknown ancestor, and has recently expressed this view in the following emphatic words: die Oogonien und die Antheridien der Fucaceen