Set Of Morphological Characters Research Articles

Organophosphatic brachiopods:Patterns of biodiversification and extinction in the Early Palaeozoic

From a database of 226 Cambrian - Ordovician genera of organophosphatic-shelled brachiopods comprisingthe Subphylum Linguliformea, 11 sets of morphological characters typify all orders and superfamilies. Seven sets of these large-scale evolutionary novelties were established already by the end of the mid Cambrian, 2 more by the end of the late Cambrian, and the remaining 2 before the end of the Arenig. The earliest linguliformeans are of Tommotian age and represent some of the oldest known benthic organisms with a mineralised skeleton. Major diversification at the generic level took place during the mid and late Cambrian, by which time members of the Order Lingulida spread from near-shore to deep-water environments and became dominant in low diversity benthic assemblages that inhabited mobile sandy bottoms. There was a significant decline in diversity of linguliformeans during the latest Cambrian. Following recovery in the late Tremadoc-early Arenig, they then became one of the most distinctive components of benthic assemblages inhabiting marginal environments, e.g. eutrophic basins, shallow mobile sands, and abyssal depths. During the Llanvirn, there was a significant, worldwide turnover in linguliformean brachiopod faunas, when the majority of epibenthic lingulides of the families Obolidae, Zhanatellidae and Elkaniidae became extinct and were replaced, in shallow marine biofacies, by assemblages dominated by bivalved molluscs and burrowing lingulides. There is no trace until the mid Ashgill of a significant decline of micromorphic taxa in linguliformean assemblages characteristic of outer shelf environments. However, all siphonotretides, paterinides and most acrotretide genera disappeared towards the end of the late Ordovician pre-Hirnantian Dicellograptus anceps Biozone.

Using fossil leaves as paleoprecipitation indicators: An Eocene example

Estimates of past precipitation are of broad interest for many areas of inquiry, including reconstructions of past environments and topography, climate modeling, and ocean circulation studies. The shapes and sizes of living leaves are highly sensitive to moisture conditions, and assemblages of fossil leaves of flowering plants have great potential as paleoprecipitation indicators. Most quantitative estimates of paleoprecipitation have been based on a multivariate data set of morphological leaf characters measured from samples of living vegetation tied to climate stations. However, when tested on extant forests, this method has consistently overestimated precipitation. We present a simpler approach that uses only the mean leaf area of a vegetation sample as a predictor variable but incorporates a broad range of annual precipitation and geographic coverage into the predictor set. The significant relationship that results, in addition to having value for paleoclimatic reconstruction, refines understanding of the long-observed positive relationship between leaf area and precipitation. Seven precipitation estimates for the Eocene of the Western United States are revised as lower than previously published but remain far wetter than the same areas today. Abundant moisture may have been an important factor in maintaining warm, frost-free conditions in the Eocene because of the major role of water vapor in retaining and transporting atmospheric heat.

Phylogenetics and character evolution in the grass family (Poaceae): Simultaneous analysis of morphological and Chloroplast DNA restriction site character sets

A phylogenetic analysis of the grass family (Poaceae) was conducted using two character sets, one representing variation in 364 mapped and cladistically informative restriction sites from all regions of the chloroplast genome, the other representing variation in 42 informative “structural characters.” The structural character set includes morphological, anatomical, chromosomal, and biochemical features, plus structural features of the chloroplast genome. The taxon sample comprises 75 exemplar taxa, including 72 representatives of Poaceae and one representative of each of three related families (Flagellariaceae, Restionaceae, and Join-villeaceae);Flagellaria served as the outgroup for the purpose of cladogram rooting. Among the grasses, 24 tribes and all 16 subfamilies of grasses recognized by various modern authors were sampled. Transformations of structural characters are mapped onto the phylogenetic hypotheses generated by the analysis, and interpreted with respect to biogeography and the evolution of wind pollination in the grass family. A major goal of the study was to test the monophyly of several putatively natural groups, including Bambusoideae, Pooideae, Arundinoideae, and the “PACC clade” (the latter comprising subfamilies Panicoideae, Arundinoideae, Chloridoideae, and Centothecoideae), as well as to analyze the phylogenetic structure within these groups and others. Several genera of controversial placement (Amphipogon, Anisopogon, Anomochloa, Brachyelytrum, Diarrhena, Eremitis, Ehrharta, Lithachne, Lygeum, Nardus, Olyra, Pharus, andStreptochaeta) also were included, with the goal of determining their phylogenetic affinities. The two character sets were analyzed separately, and a simultaneous analysis of the combined matrices also was conducted. The combined data set also was analyzed using homoplasy-implied weights. Among major results of the combined unweighted analysis were resolution of a sister-group relationship betweenJoinvillea and Poaceae; resolution of a clade comprisingAnomochloa andStreptochaeta as the sister of all other grasses, withPharus the next group to diverge from the lineage that includes all remaining grasses; and resolution of other taxa often assigned to Bambusoideae s.l. (includingEhrharta and Oryzeae, and excluding a few other taxa as noted) as a paraphyletic assemblage, within which is nested a clade that consists ofBrachyelytrum, the PACC clade (includingAmphipogon), and Pooideae (including Brachypodieae, Stipeae,Anisopogon, Diarrhena, Lygeum, andNardus). Within the PACC clade,Aristida is identified as the sister of all other elements of the group; Chloridoideae, Centothecoideae, and Panicoideae are each resolved as monophyletic, the latter two being sister-groups; and the remaining Arundinoid elements constitute a paraphyletic group within which are nested these three subfamilies. Within the Pooideae, four “core tribes” (Bromeae, Hordeeae [i.e., Triticeae], Agrostideae [i.e., Aveneae], andPoeae, the latter includingSesleria) are resolved as a monophyletic group that is nested among the remaining elements of the subfamily (Brachypodieae, Meliceae, Stipeae,Anisopogon, Diarrhena, Lygeum, andNardus). A second principal goal of the analysis was to identify structural synapomorphies of clades. Among the synapomorphies identified for some of the major clades are the following: gain of a 6.4 kb inversion in the chloroplast genome inJoinvillea and the grasses; reduction to 1 ovule per pistil, gain of a lateral “grass-type” embryo, and gain of an inversion around the gene trnT in the chloroplast genome in the grasses; loss of arm cells in the clade that consists ofBrachyelytrum, Pooideae, and the PACC clade; loss of the epiblast and gain of an elongate mesocotyl internode in the PACC clade; gain of proximal female-sterile florets in female-fertile spikelets, gain of overlapping embryonic leaf margins, and gain ofPanicum- type endosperm starch grains in the clade that comprises Centothecoideae and Panicoideae; and loss of the scutellar tail of the embryo in Pooideae (in one of two alternative placements of Pooideae among other groups). These findings are consistent with an origin and early diversification of grasses as forest understory herbs, followed by one or more radiations into open habitats, concomitant with multiple origins of C4 photosynthesis and specialization for wind pollination.

Phylogeny of the neotropical moth tribe Josiini (Notodontidae: Dioptinae): comparing and combining evidence from DNA sequences and morphology

DNA sequences were gathered from mitochondrial COII and nuclear ribosomal 18S and 28S genes for 21 moth species in the tribe Josiini (Notodontidae: Dioptinae) and two outgroup genera. These data complement a previously published morphological character set for the same taxa. We examine whether relationships in the Josiini are best reflected by a single phylogenetic analysis of all the data, or by a consensus of separate trees generated from DNA and morphology. Even in cases where analyses of partitioned data produce incongruent cladograms, the underlying disagreement between partitions is relatively small. While both molecular and morphological data provide useful character information by themselves, we conclude that the best supported phylogenetic hypothesis is the one derived from combined analysis.

Phylogeny of the neotropical moth tribe Josiini (Notodontidae: Dioptinae): comparing and combining evidence from DNA sequences and morphology

DNA sequences were gathered from mitochondrial COII and nuclear ribosomal 18S and 28S genes for 21 moth species in the tribe Josiini (Notodontidae: Dioptinae) and two outgroup genera. These data complement a previously published morphological character set for the same taxa. We examine whether relationships in the Josiini are best reflected by a single phylogenetic analysis of all the data, or by a consensus of separate trees generated from DNA and morphology. Even in cases where analyses of partitioned data produce incongruent cladograms, the underlying disagreement between partitions is relatively small. While both molecular and morphological data provide useful character information by themselves, we conclude that the best supported phylogenetic hypothesis is the one derived from combined analysis.

There is no support for Jensen's hypothesis of nemerteans as ancestors to the vertebrates

Nemerteans (phylum Nemertea) have been viewed by mostzoologists as descended from, or closely related to,the flatworms. This view is based mainly on theirsupposedly acoelomate body. Their ancestry, however,is a point of controversy and there is evidence for acoelomate, protostomous origin. Notwithstanding thesedifferent views, most zoologists consider nemerteansto be phylogenetically distant from the chordates.Four authors (Hubrecht, Macfarlane, Jensen, Willmer),however, have postulated that nemerteans instead areclosely related to the chordates and that they sharea most recent common ancestor with the vertebrates. We argue that this view is based on a flawed view ofhomology and of seeing evolution as a series ofprogressions, which has no support in modernevolutionary thinking. Since there are nomorphological synapomorphies supporting aChordata-Nemertea clade, these authors instead guesswhat characteristics in extant nemerteans gave rise tocharacters observed in recent chordates. For example,they propose that the nemertean proboscis sheath hasevolved into the notochord. This is mere speculation,lacking testable propositions and is hence void ofinformation, and thus becomes futile in our view. However, the idea of a nemertean-vertebrate sisterrelationship as such is a testable hypotheses, and wetest it by applying the parsimony criterion to a setof morphological characters, and a set of molecular(the 18S rRNA gene) characters. Both tests reject thehypothesis.

Mixed Mating System in Agalinis neoscotica (Scrophulariaceae) with Bud Pollination and Delayed Pollen Germination

Many species of angiosperms have mixed mating systems in which a portion of progeny result from self-fertilization and some from outcrossing. We show that Agalinis neoscotica has evolved a novel set of developmental and morphological characters in the flower that assure self-pollination without sacrificing the opportunity for outcrossing. Pollinator exclusion, emasculation tests, and controlled self- and cross-pollinations conducted at three field sites indicate that A. neoscotica is self-compatible. An overall mean pollen-ovule ratio of 128.5 for four populations indicates facultative selfing and indicates that self-fertilization occurred. An estimation of the mating system, using two enzyme loci in each of two natural populations, verifies that selfing occurs in each population, but neither population is completely selfing. Seeds of A. neoscotica are produced by a mix of self-fertilization and cross-fertilization. Observations of buds and flowers of A. neoscotica show that this species differs from its close relatives by precocious self-pollination in bud, thus assuring reproduction in the absence of pollinators, and in three characteristics that provide an opportunity for outcrossing: delayed germination of self pollen, presentation of additional stigmatic area, and lengthened period of anthesis. These results indicate that examination of preanthesis buds and flowers throughout anthesis is necessary for understanding the modes of selfing involved in mixed mating systems.

A Dryopithecus skeleton and the origins of great-ape locomotion.

The evolution of skeletal adaptations to orthograde postures, characteristic of extant hominoids, is of great interest as it provides the key to understanding the origins of apes and humans. We report here the recent discovery of an extraordinary partial skeleton of Dryopithecus laietanus from Can Llobateres (Spain). It provides evidence that orthograde postures and locomotion appeared at least 9.5 million years ago. Our results indicate that the body structure of this Miocene ape closely resembles that of extant hominoids and differs from the pronograde pattern of Miocene proconsulids in a set of important morphological characters. Dryopithecus also shows more traits reflecting structural adaptations for suspension than occurs in African apes. A similar positional behaviour is inferred for Sivapithecus indicus, thus strengthening previous hypotheses linking both Miocene forms with Pongo.

A Molecular Phylogenetic Perspective on the Evolutionary Radiation of the Salamander Family Salamandridae

?Phylogenetic relationships were examined within the salamander family Salamandridae using 18 species representing 14 salamandrid genera and six outgroup taxa from the families Ambystomatidae, Dicamptodontidae, Plethodontidae, and Proteidae. Mitochondrial DNA sequences encoding the 12S and 16S ribosomal RNA and the intervening valine transfer RNA provided 431 phylogenetically informative nucleotide sequence positions from a multiple align? ment of approximately 1,000 bases per species. This variation was analyzed in conjunction with 44 previously reported morphological characters representing primarily hyobranchial myology and osteology, cranial osteology, and reproductive biology The molecular and morphological character sets were highly congruent, with only 2.8% of the total character incongruence attrib? utable to conflict between them. Parsimony analysis of the combined molecular and morphological data produced a single most-parsimonious tree whose topology was identical to that of the mostparsimonious tree derived from the molecular data alone. This tree suggests that the true sal? amanders (Chioglossa, Mertensiella, and Salamandra) form a monophyletic sister group to the newts (all remaining salamandrid genera). Within the newts, the first phylogenetic split separates Salamandrina from the remaining genera, within which Pleurodeles and Tylototriton form a monophy? letic sister group to the remaining taxa. The genus Triturus appears not to be monophyletic. Using a phylogenetic reconstruction of character changes, we tested hypotheses of adaptation in the evolution of aquatic suction feeding and terrestrial feeding featuring tongue protrusion. Phylo? genetic trends in the evolution of salamandrid courtship behavior were also examined. [Salamandridae; molecular phylogenetics; mitochondrial DNA; congruence; feeding morphology; court? ship.] Reconstruction of phylogeny is funda? mental to an understanding of the evolu? tion of biological diversity because phylo? genetic trees provide the historical maps along which character evolution is traced. Historical analysis is important for testing hypotheses of adaptive evolution (Baum and Larson, 1991) and for revealing pat? terns of homoplasy that indicate the action of natural selection and developmental constraints (Alberch, 1988; Wake, 1991). Salamanders are a particularly good group for phylogenetic studies of the interactions of design limitations, heterochrony, and se? lection (Wake and Larson, 1987; Wake, 1991). The family Salamandridae exhibits con? siderable morphological and behavioral di? versity. It contains 15 genera and 53 rec? ognized species and is distributed 1 Present address: Department of Biology, Univer? sity of Oregon, Eugene, Oregon 97403, USA. E-mail: titus@darkwing.uoregon.edu. throughout the Holarctic, with the greatest diversity in Europe (seven genera) and Asia (four genera) (Frost, 1985). Salaman? drid evolution has been studied from a va? riety of aspects, including courtship be? havior (Salthe, 1967; Halliday, 1977; Arntzen and Sparreboom, 1989), antipredator behavior (reviewed by Brodie, 1983), tox? icity (Brodie et al., 1974), morphology (Ozeti and Wake, 1969; Wake and zeti, 1969; Zhao and Hu, 1988; Sever, 1992), karyology (reviewed by Macgregor et al., 1990), pro? tein variation (Hedgecock and Ayala, 1974; Rafinski and Arntzen, 1987; Hayashi and Matsui, 1989; Reilly, 1990), and mitochon? drial DNA (Wallis, 1987; Wallis and Arntz? en, 1989, Caccone et al., 1994). Phylogenetic relationships within the Salamandridae have been a source of much conflict. Monophyly of the Salamandridae, although generally accepted, relies largely on interpretation of a single character, the frontosquamosal arch. This character is not present in all salamandrids, and its ab-

The danube delta: geographical characteristics and ecological recovery: P. Gastescu, GeoJournal, 29(1), 1993, pp 57–67

The Lesser White-fronted Goose [Anser erythropus (Linnaeus, 1758)] is one of the most threatened Palearctic goose species, with the Fennoscandinavian subpopulation in particular having seen a drastic decline over the last century. In the 1990s, captive-bred Lesser White-fronted Geese were used successfully for reintroduction and restocking in Sweden and Finland. The discovery of Greater White-fronted Goose [Anser albifrons (Scopoli, 1769)] mtDNA haplotypes in some of these captive-bred birds (Ruokonen et al. 2000) suggested that hybridisation had occurred during captive propagation and led to the discontinuation of the release of captive goslings. Here we report two hybrids of Lesser×Greater White-fronted Geese that were collected on their wintering grounds in England in 1936 and Holland in 1966. Birds from western Russia normally do not migrate south to Western Europe. Hence, these birds most likely originated from the Fennoscandinavian subpopulation and were collected prior to the commencement of the captive-breeding programmes. Both specimens show a heterogeneous set of morphological characters, some of which shared with the putative parent species and others being intermediate between the two White-fronted Goose species. A Canonical Discriminant Function analysis positions both specimens between the two putative parent species, making their hybrid status likely. We show, thus, that hybridisation between Greater and Lesser White-fronted Geese does occur naturally, albeit perhaps infrequently, and argue that the presence of Greater White-fronted Goose mtDNA haplotypes in Lesser White-fronted Goose may be the result of this naturally occurring hybridisation. Our data provide additional information on the debate whether the restocking programmes were halted for the right reasons and whether it is desirable to re-commence with the reintroduction programme.

A combination of molecular and morphological characters for delimitation of taxa in EuropeanParella

The merits of morphological characters, isozyme patterns and random amplified polymorphic DNA (R.A.P.D.) markers for bryophyte species delimitation were investigated using European species of Porella. Isozymes and R.A.P.D. markers allow rapid detection of genetic differences in morphologically highly-variable groups of organisms. Twenty-two clones of the European Porella species (eight species are currently recognised: P. arborisvitae, P. baueri, P. canariensis, P. cordaeana, P. obtusata, P. pinnata, P. platyphylla, P. platyphylloidea) were investigated together with three populations of Canadian P. platyphylloidea. Isozyme patterns of esterase, glutamate-oxaloacetate transaminase, peroxidase and malate enzyme were studied by electrophoresis. R.A.P.D. fingerprints were made using the polymerase chain reaction and six primers. Data were also obtained for 39 morphological characters scored for ten or more individuals of each population. Eight distinct isoenzyme patterns were obtained corresponding to the seven species and aberrant population 267. These results were supported by the R.A.P.D. analysis which showed population 267 to be close to P. platyphylla but also to possess affinities with P. platyphylloidea. The analysis allowed a reassessment of relationships between the European Porella species and the definition of improved morphological character sets for discriminating the taxa.

Molecular evidence that the spiny mouse (Acomys) is more closely related to gerbils (Gerbillinae) than to true mice (Murinae).

Spiny mice of the genus Acomys traditionally have been classified as members of the Murinae, a subfamily of rodents that also includes rats and mice with which spiny mice share a complex set of morphological characters, including a unique molar pattern. The origin and evolution of this molar pattern, documented by many fossils from Southern Asia, support the hypothesis of the monophyly of Acomys and all other Murinae. This view has been challenged by immunological studies that have suggested that Acomys is as distantly related to mice (Mus) as are other subfamilies (e.g., hamsters: Cricetinae) of the muroid rodents. We present molecular evidence derived from DNA.DNA hybridization data that indicate that the spiny mouse Acomys and two African genera of Murinae, Uranomys and Lophuromys, constitute a monophyletic clade, a view that was recently suggested on the basis of dental characters. However, our DNA.DNA hybridization data also indicate that the spiny mice (Acomys) are more closely related to gerbils (Gerbillinae) than to the true mice and rats (Murinae) with which they have been classified. Because Acomys and the brush-furred mice Uranomys and Lophuromys share no derived morphological characters with the Gerbillinae, their murine morphology must have evolved by convergence, including the molar pattern previously considered to support the monophyly of the Murinae.

Pollen Morphology of the Family Cistaceae in Relation to its Taxonomy

Abstract Results of the examination of pollen grains of 65 species of eight genera (Cistus, Crocanthemum, Fumana, Halimium, Helianthemum, Hudsonia, Lechea, and Tuberaria) of the family Cistaceae Juss, are presented. A set of morphological characters including the type of aperture structure, the shape and size of the pollen grains and the exine structure and sculpturing, allowed the recognition of six pollen types (Cistus type, Crocanthemum type, Fumana type, Helianthemum type, Hudsonia type and Lechea type). These six types of pollen grain form three groups, which correspond well with the three main evolutionary trends of the tribes within the family. The palynological data presented here agrees well with the systems suggested by Janchen (1925) and Takhtajan (1987) in which the family Cistaceae is divided into three tribes, namely Cisteae, Hudsonieae and Lechidieae.

IBPGR morphological descriptors — their relevance in determining patterns within a diverse spring barley germplasm collection

The International Board for Plant Genetic Resources (IBPGR) promotes a minimum set of morphological characters thought satisfactory for the custodial management of crop germplasm collections. The purpose of such conserved germplasm is as a genetic resource for future plant breeding programmes. Because future plant breeding requirements are not always known, the curator's strategy in maintaining an adequate germplasm resource is to conserve as wide a range of genetic diversity as possible. How is diversity measured to ensure a wide range of conserved germplasm? The IBPGR minimum descriptors detail genetic diversity at particular points in a genome corresponding to the observed characters. The purpose of the present study was to investigate whether diversity as identified by the IBPGR minimum set of descriptors could yield satisfactory measures of diversity in a contrasting set of genomic markers. A diverse spring-sown barley collection of 1379 cultivars was evaluated for the 12 IBPGR minimum taxonomic characters. An additional nine phenotypic characters and six biochemical markers were evaluated to enable diversity comparisons. Cluster analysis of the various sets of data revealed groups of accessions for each of the three data sets. A poor level of agreement (congruence) between data sets was observed in all comparisons indicating that, for cultivated barley at least, diverse collections according to the IBPGR minimum descriptors is not necessarily related to equivalent levels of diversity in other genetic characters. Implications of the relevance of the IBPGR descriptor list and appropriate collection strategies are discussed.

Estimates of hierarchical variation in flower morphology in natural populations ofScleranthus annuus (Caryophyllaceae), an inbreeding annual

The variation in two sets of morphological characters of the flowers of the highly inbreedingScleranthus annuus (Caryophyllaceae) was assessed using 15–20 plants from each of 20 natural populations from the southernmost region of Sweden. The stamen fertility data set consisted of 10 characters describing the degree of fertility of the ten stamens/staminoids, while the sepal/gynoecium data set comprised 10 sepal characters, together with style and stigma length. Substantial variation was found in both the degree of development and the fertility of the stamens, the degree of variability in stamen fertility being related to stamen position within the flower. Considerable variation was found in the characters of the sepal and the gynoecium. Hierarchical analyses of variance indicated that 29% of the variation in total male reproductive effort was distributed among populations, 28% among plants within populations and 43% represented within-plant variation. The corresponding averages for the characters from the sepal/gynoecium data set are 26, 38, and 35%: a greater proportion of the total variance in female reproductive characters is accounted for by among individual variation than is the case with the male reproductive characters. Significance tests of Mahalanobis’ distances derived by canonical variate analyses indicated that all populations were significantly separated using the sepal/gynoecium data set, while only 50% of the pairwise comparisons on the basis of the stamen fertility data set were significant. Cluster analysis did not reveal any aggregation of the populations. The incongruence of the two data sets and their ability to discriminate between the populations is discussed.

A proposed revision of the IBPGR barley descriptor list

The International Board for Plant Genetic Resources (IBPGR) promote a set of morphological characters considered to be the minimum number for the description of crop germ plasm collections. The format and style of these IBPGR minimum descriptors are typical across numerous crop and species genera. However, no research publications have reviewed the relative usefulness of individual descriptors, nor indeed if additional descriptors should be included into the "minimum descriptor list".A diverse collection of 1,379 spring sown barleys were evaluated for the 12 IBPGR "minimum" descriptors, an "additional" 9 morphological descriptors of similar type of the minimum descriptors, and a contrasting group of 3 hordein and 3 leaf esterase biochemical markers. Multivariate analyses were performed on combinations of the "minimum", "additional" and biochemical markers to reveal detailed associations amongst these various descriptors. The IBPGR minimum descriptor list for barley was shown to be inadequate in descriminating between accessions, and a revised list is proposed.

Caloplaca marina and C. rosei, Two Difficult Species in North America

Caloplaca marina and C. rosei, Two Difficult Species in North America

SYSTEMATICS AND POPULATION GENETICS OF FIRE ANTS (SOLENOPSIS SAEVISSIMA COMPLEX) FROM ARGENTINA

Specimens of seven fire ant species collected from their native ranges in Argentina were studied by protein electrophoresis and morphological analysis. Concordance between the genetic and morphological character sets is strong (96% agreement on identifications), suggesting that recognition of reproductively isolated populations and partitioning of intra- and interspecific variation can in most cases be achieved using appropriate characters of either type in this taxonomically difficult group. Genetic differentiation between native (Argentina) and introduced (USA) conspecific populations of two species, Solenopsis invicta and S. richteri, is rather typical of the differentiation existing between conspecific populations found within either country. Furthermore, there appears to have been little reduction of variability (heterozygosity) at enzyme loci following colonization by either species of the United States, although some rare alleles have been lost in the introduced populations. Hybridization is rare between S. invicta and S. richteri where their native ranges overlap in central Argentina, in contrast to the extensive hybridization of these species in the United States, suggesting that prezygotic barriers to gene flow have been compromised in introduced populations. Phylogenetic analysis of the seven species indicates that S. invicta and S. richteri are relatively distantly related within the S. saevissima complex. Given that hybrids between these species in the United States suffer little apparent loss of fitness, genomic incompatibilities generally may be insufficient to create effective postzygotic barriers to interspecific gene flow in this group of ants.

Morphogenesis, evolution and organic stability

Homology is a key concept in analysing the logical relations between ontogeny and phylogeny. Following Darwin, it is usually defined in historical terms as the property common to a set of morphological characters with similar structures due to descent from a common ancrestral form. Bateson argued that this cannot in any way illuminate the generative origins of such structural similarities, and that homology should be understood in term of the properties of common generative mechanisms operating during ontogeny, whose nature is to be understood dynamically, not historically. The task is then to identify the real nature of these ontogenetic processes and the variations which they can undergo to generate a variety of homological equivalent forms. Bateson's position is adopted and applied to the analysis of insect segmentation as revealed in recent mutant and gene transcript studies in Drosophila. An interpretation of the dynamics of segmentation and its perturbation by both genetic mutants and physiological disturbances (“phenocopies”) is then considered in term of a class of morphogenetic transformations defined as “homeological”. This dynamic ontogenetic concept can then be used as a basis for understanding ontogenetic transformations in the manner proposed by Bateson, avoiding the logical inconsistencies of the Darwinian concept of homology.

ORIGIN AND EVOLUTION OF CONTINENTAL BIOTAS: SPECIATION AND HISTORICAL CONGRUENCE WITHIN THE AUSTRALIAN AVIFAUNA.

Factors governing the origin and evolution of continental biotas were investigated using an analysis of speciation patterns within the Australian avifauna. Phylogenetic relationships within seven lineages of birds were analyzed by numerical cladistic techniques applied to data sets of morphological characters. These relationships revealed extensive congruence among the spatial and temporal histories of lineages whose species are endemic to common areas of endemism. A general hypothesis is constructed to explain this congruence in which widespread biotas are postulated to have been partitioned into areas of endemism by the origin of geomorphological and/or ecological-climatic barriers. Congruence in these phylogenetic patterns of differentiation suggests the following historical pattern of interrelationships for areas of endemism along the northern and eastern coasts of Australia: (Kimberley Plateau + Arnhem Land) + ([New Guinea + Cape York Peninsula] + [Atherton Plateau + Eastern Coastal Rainforest]). Likewise, this study indicates that the arid interior avifauna was segregated into two closely related biotas (Eastern and Western Desert biotas) by the Eyrean Barrier. These biotas are, in turn, related to a more mesic avifauna that was itself subdivided into areas of endemism located in the Southwest and Southeast corners of the continent.