Simultaneous character convergence and divergence in Western Australian land snails

Three distantly related genera of land snails, Amplirhagada Iredale, 1933, Quistrachia Iredale, 1939, and Westraltrachia Iredale, 1933, overlap in distributions only in the Napier and Oscar Ranges, east of Derby, Western Australia. The first two remain allopatric, Quistrachia having a more eastern range, while Westraltrachia overlaps both ranges. In the zone of sympatry, with changes proceeding from east to west, Westraltrachia diverges in feeding, and there is massive, gradual convergence in shell size, shape and colour between Amplirhagada and Westraltrachia. Shells of both genera depart markedly from their distinctive allopatric appearances to form a new morphotype in the north-west Napier Ranges. The species there are so similar in appearance that the two genera cannot be identified at a distance of 0.5 m. Thirteen species-level taxa are involved in these changes, four allopatric Amplirhagada , seven allopatric Westraltrachia, Quistrachia monogramma and Rhagada basedowana.
Westraltrachia species, the only large land snails in their main area of distribution (south-east Kimberlcy), are pre-adapted to graze on an occasionally present food resource, algal-fungal blooms on limestone seepage faces. They entered the Oscar and Napier Ranges, where this food resource is more abundant, and large land snails that are generalized feeders, Amplirhagada or Quistrachia , were already present and abundant. Hence feeding divergence occurred. Such specialization by Westraltrachia to minimize competition is readily understandable.
The selective pressures that led to the striking convergence in shell features in north-west Napier taxa are unknown.     

Three into two doesn't go: two-dimensional models of bird eggs, snail shells and plant roots

Three published two-dimensional analyses of three-dimensional structures are reinvestigated. (1) In their 1997 paper, Barta & Szekely sought shapes of bird eggs that maximized the size of eggs that packed under a circular brood patch. Inappropriately they measured egg size by cross-sectional area; maximizing volume implies different optima. Also their genetic algoridim mislocated their optima, probably because of too much mutation. (2) In this journal in 1985, Heath considered a section of an idealized snail shell; altering the overlap of adjacent whorls alters the ratio of shell material to volume enclosed. Heath located an overlap that minimized perimeter/area of the cross-section, which is different from minimizing surface-area/volume. I derive the surface area of a logarithmic helicospiral; some formulae used previously are slightly incorrect. Heath's alteration of overlap changed shell volume and aperture area; a more meaningful reanalysis keeps these characters constant. (3) In 1987, Fitter used a two-dimensional model of plant roots to show that topology, growth rate, and nutrient diffusion rate affect exploitation efficiency (area of nutrient depletion zone/volume of root). Recalculation and reanalysis show that only part of the effect of topology depends on overlap of depletion zones. I compare Fitter's model to coplanar root systems with three-dimensional depletion zones and then to fully three-dimensional branching. Finally I discuss further examples in which two-dimensional models could mislead.     

A morphologic and genetic analysis of Littorina saxatilis (Prosobranchia) from Venice, and on the problem of saxatilis—rudis nomenclature

Shell morphology and allozyme patterns of 17 enzymes are analysed within the isolated population of L. saxatilis Olivi (1792) from Venice, the type locality of the species. The shell morphology is compared to three different L. saxatilis phenotypes from Sweden, and showed to be similar to the brackish water 'tenebrosa' type. The Venice population is genetically more distant from British and Swedish populations than are the latter from each other. Less variability (heterozygosity) within the Venice compared to the Atlantic populations is probably a consequence of random genetic drift during a period of small population size.
The nomenclature of L. saxatilis in the Atlantic is discussed and it is suggested that until the exact taxonomic relationship between the Mediterranean and the Atlantic populations has been confirmed by, for example, cross-breeding experiments, the name 'saxatilis' should be kept for the non-Venetian populations (described by Maton (1797) under the name 'rudis').     

Growth patterns in the stem of the palm Archontophoenix cunninghamiana

Studies on the growth of Archontophoenix cunninghamiana in two separate populations show that this species establishes only a narrow apical meristem complex before rising above ground This complex continues to expand in girth as it rises, until at a height of about 12 m its girth becomes fixed. The lower regions of the trunk expand, more than equalling the expansion at the apex, producing at least a 20-fold increase in volume. Anatomical observations show that this expansion, termed sustained primary growth , is due to cell enlargement and cell division in the ground tissue, and is relatively uniform along the radius of the stem. When the apex reaches a height of 12 m, sustained primary growth ceases abruptly, fixing the taper of the trunk. Subsequent growth produces a cylindrical top on this tapered base.
These results are considered in the light of a review of earlier work on palm growth. The determinate nature of this type of arborescence is discussed, and brief reference is made to its evolutionary status.     

Functional design and evolution of the pharyngeal jaw apparatus in euteleostean fishes

Functional and structural patterns in the pharyngeal jaw apparatus of euteleostean fishes are described and analysed as a case study of the transformation of a complex biological design. The sequential acquisition of structural novelties in the pharyngeal apparatus is considered in relation to both current hypotheses of euteleostean phylogeny and patterns of pharyngeal jaw function. Several euteleostean clades are corroborated as being monophyletic, and morphologically conservative features of the pharyngeal jaw apparatus are recognized. Functional analysis, using cinematography and electromyography, reveals four distinct patterns of muscle activity during feeding in primitive euteleosts (Esox) and in derived euteleostean fishes(Perca, Micropterus, Ambloplites, Pomoxis). The initial strike, buccal manipulation, pharyngeal manipulation, and the pharyngeal transport of prey into the oesophagus all involve unique muscle activity patterns that must be distinguished in analyses of pharyngeal jaw function. During pharyngeal transport, the upper and lower pharyngeal jaws are simultaneously protracted and retracted by the action of dorsal and ventral musculoskeletal gill arch couplings. The levator externus four and retractor dorsalis muscles, anatomical antagonists, overlap for 70–90°of their activity period. Levatores externi one and two are the main protractors of the upper pharyngeal jaws in the acanthopterygian fishes studied. The major features of pharyngeal jaw movement in primitive euteleosts are retained in many derived clades in spite of a dramatic structural reorganization of the pharyngeal region. Homologous muscles have radically changed their relative activity periods while pharyngeal jaw kinematics have been modified relatively little. Patterns of transformation of activity may thus bear little direct relationship to the sequence of structural modification in the evolution of complex designs. Overall function of a structural system may be maintained, however, through co-ordinated modifications of the timing of muscle activity and anatomical reorientation of the musculoskeletal system. Deeper understanding of the principles underlying the origin and transformation of functional design in vertebrates awaits further information on the acquisition of both structural and functional novelties at successive hierarchical levels within monophyietic clades. This is suggested as a key goal of future research in functional and evolutionary morphology.     

Shell shape variation in dog-whelks (Nucella lapillus (L.)) from the West Coast of Scotland

European populations of the common dog-whelk, Nucella lapillus (L.), usually show a neat and precise pattern of shell shape variation with the exposure of their habitat to wave action. Whilst this is the case along much of the west coast of Scotland, there are a number of instances where unusually elongated shells occur, somewhat reminiscent of the form described for the Severn Estuary. There are no obvious environmental or geographical correlates to explain the occurrence of these forms and a genetical interpretation is sought.     

Differential winter mortality and seasonal selection in the polymorphic ladybird Adalia bipunctata (L) in the Netherlands

Seasonal selection acting on the melanic polymorphism in the two-spot ladybird Adalia bipunctata was investigated in The Netherlands. An increase in melanic frequency over the spring-summer reproductive period was quantified. The selective advantage gained by melanics averaged 9%, but significant heterogeneity occurred between populations. Adult hibernation behaviour is described. The beetles when outdoors show a highly clumped distribution both between and within trees. The distribution of the morph classes between aggregations is random. Survivorship in a hibernating cohort (initial n= 1898) on a grid of 70 lime trees near Utrecht was monitored by making three counts over the winter of 1981–1982. Intense selection favouring each melanic morph occurred during December and January. The relative fitness of non-melanics was 0.55 (melanics =1). The discovery of dead beetles in late January (about 5% of total losses) and the absence of spatially density-dependent mortality were consistent with a climatic stress rather than selective predation. The period of selection was associated with very cold temperatures averaging up to 4°C below normal and an overall mortality of nearly 75%. There was no change in morph frequency, near normal temperatures and a lower mortality from February to early April. Examination of groups of nearby trees in late January strongly suggested that similar differential mortality had occurred except on some willows. This difference was probably due to the more protected hibernation sites available on these trees. Samples of hibernating cohorts at three other sites showed no evidence of differential mortality. Laboratory experiments with hibernating beetles found no difference in survivorship or rate of weight loss between starved non-melanics and melanics in temperature regimes with and without periods of adult activity. It is concluded that the intense winter selection on the study limes is probably exceptional. Examination of changes in morph frequency through the annual cycle suggests that at some sites the selection favouring melanics during reproduction is counterbalanced by selection against melanics in late summer or early autumn. The results are discussed in relation to mathematical models of cyclical selection and to other field studies including that of Timoféeff-Ressovsky (1940), who found large decreases in melanic frequency during hibernation in Berlin.     

Sexual dimorphism in shells of Cochlostoma septemspirale (Caenogastropoda, Cyclophoroidea, Diplommatinidae, Cochlostomatinae)

Sexual dimorphisms in shell-bearing snails expressed by characteristic traits of their respective shells would offer the possibility for a lot of studies about gender distribution in populations, species, etc. In this study, the seven main shell characters of the snail Cochlostoma septemspirale were measured in both sexes: (1) height and (2) width of the shell, (3) height and (4) width of the aperture, (5) width of the last whorl, (6) rib density on the last whorl, and (7) intensity of the reddish or brown pigments forming three bands over the shell. The variation of size and shape was explored with statistical methods adapted to principal components analysis (PCA) and linear discriminant analysis (LDA). In particular, we applied some multivariate morphometric tools for the analysis of ratios that have been developed only recently, that is, the PCA ratio spectrum, allometry ratio spectrum, and LDA ratio extractor. The overall separation of the two sexes was tested with LDA cross validation.The results show that there is a sexual dimorphism in the size and shape of shells. Females are more slender than males and are characterised by larger size, a slightly reduced aperture height but larger shell height and whorl width. Therefore they have a considerable larger shell volume (about one fifth) in the part above the aperture. Furthermore, the last whorl of females is slightly less strongly pigmented and mean rib density slightly higher. All characters overlap quite considerably between sexes. However, by using cross validation based on the 5 continuous shell characters more than 90% of the shells can be correctly assigned to each sex.     

Stacking Increments: A New Model and Morphospace for the Analysis of Bivalve Shell Growth

A model employing stacking increments is introduced for the analysis of bivalve shell growth and form. The model is based on the components of shell growth that are potentially independent: the rate of mantle cell proliferation, the rate of precipitation of shell material, and the rate of translation of the pallial line, where the mantle is attached to the shell. This model is defined in terms of the following parameters: (1) the ratio of accretion of shell material at the shell margin to growth of the mantle by cell division, (2) the ratio of shell accretion at the pallial line to mantle growth, and (3) the ratio of the amount of pallial muscle translation, away from the umbo toward the shell margin, to mantle growth. In this model, the shape of a radial section through the shell is simulated by stacking of internal microgrowth increments. The mode of stacking of the increments is determined by the balance among the parameters defining growth. A theoretical morphospace defined on the basis of this model is largely consistent with the range of forms of naturally occurring bivalve shells. Analysis of the distribution of actual shell forms in relation to this morphospace suggests that the absolute rate of shell precipitation and the gradient in precipitation rate away from the shell margin along a radial cross-section are physiologically as well as geometrically constrained.     

Comparative osteology and relationships of the Umbridae (Pisces: Salmoniformes)

The phylogenetic relationships of the five living species of umbrids are examined through a comparative osteological study based on a series of cleared-and-stained specimens of each species. The Umbridae appear to be strictly monophyletic. In addition, for 45 characters, the outgroup Esox shares one character-state with at least one umbrid species, while two or more umbrid species share the other state. Assuming that the states shared with Esox are primitive for the Umbridae, the hypothesis that Dallia is more closely related to Umbra than to Novumbra is supported by compatibility and Wagner-tree analysis of the data. Thirteen derived characters are shared by Dallia and Umbra , 20 more are shared by the three species of Umbra , and four more by U. limi and U. pygmaea. Eight characters are considered likely to have undergone reversal or parallel evolution.     

A cytotaxonomic study of some Australian species of Drosera L. (Droseraceae)

KONDO, K. & LAVARACK, P. S., 1984. A cytotaxonomic study of some Australian species of Drosera L. (Droseraceae). Karyomorphological comparisons of 15 species of Australian Drosera are presented along with 11 new chromosome counts. In Australia the genus forms an extensive aneuploid series. The species which have chromosome numbers from n =10 to n = 19 show large chromosomes, while those which have chromosome numbers more than 20 show small chromosomes. Drosera paleacca shows the lowest chromosome number in the genus, 2 n = 10, with 10 large chromosomes, indicating a new basic number, x = 5. The non-staining gap between the chromatids of each chromosome is rather wide and their centromeric region is not seen throughout prophase, prometaphase, and metaphase. The C-banding and silver-staining analyses in Drosera petiolaris chromosomes suggest that Drosera chromosomes could have diffuse centromeres and simplified C-segments. Some taxonomic implications are considered, notably the possible removal of Drosera banksii from Drosera section Ergaleium to Drosera section Lasiocephala and the reduction to synonymy of Drosera section Prolifera .     

FOOD PREFERENCE AND THE EXTENT OF OVERLAP IN SOME INSECTIVOROUS BIRDS, WITH SPECIAL REFERENCE TO THE TYRANNIDAE

Analysis of published records of the food of flycatchers (Tyrannidae), swallows (Hirundinidae) and vireos (Vireonidae) of North America, and terns (Laridae) of the Pacific Ocean showed that size, rather than taxonomic, differences in food appear to be the most important ones for these birds. Although the distribution of insect sizes in nature approaches a two-parameter log-normal distribution, the distributions of the sizes of food items taken by birds show no significant differences from log-normal. Birds of a given feeding type (e.g. flycatchers) show a strong correlation of average prey size with bird body weight, and a significantly less strong correlation with bill characteristics, indicating that body size is a better predictor of prey size than any single bill character. The slopes and/or intercepts of regressions of food size against body weight are different for birds of different foraging type. Values of overlap in food preference are proportional to the similarity of the two species compared, expressed as the ratio of their weights. Because insect taxa differ in size and because the amount of overlap in taxonomic composition of foods is therefore very roughly proportional to the amount of overlap in size, taxonomic differences in food may merely reflect differences in size preferences. Values for overlap in food are greater than for most cases involving spatial niche parameters, indicating space is more easily divided than food, a conclusion supported by the relative rarity of large flycatchers.     

Mechanical constraints on aperture form in gastropods

Gastropod apertures reflect expanded states of their mantle edge under variable boundary conditions. The apertures are divided into two groups: apertures without distinct overlap zones (e.g., whorl overlap) and those with overlap zones. Each group follows a unique morphological rule. Apertures without overlap zones are generally circular in outline. Apertures with overlap zones are either elongated perpendicularly to the overlap zone or inflated abapically. Moreover, the latter abapically inflated apertures are generally accompanied by a straight section anterior to the overlap zone along the columellar axis (columellar part). Numerical analysis of an elastic double membrane tube whose main frame simulates the gastropod mantle indicates that these morphological rules are the products of mantle edge expansion under the condition that the head-foot mass presses against the mantle edge in both the overlap zone and the columellar part. The mantle edge in these two zones is thus in a completely or partly fixed boundary condition at the moment of shell growth. The rest of the mantle edge is free to expand either symmetrically or asymmetrically. It is hypothesized that the head-foot mass is a driving force for regulating the pattern of shell coiling and apertural shape.     

Systematics of the genus Cidaria Treitschke (Lepidoptera, Geometridae, Larentiinae)

The genus Cidaria Treitschke is revised. Eight species of the genus which occur widely in the Palaearctic and northern India, are recognized, of which one, Cidaria luteata sp. nov. , is described as new while two subspecies of C. fulvata (Forster) are elevated to species, C. nugata Felder stat. rev., and C. distinctata Staudinger stat. nov. C. ochripennis Prout is proposed as a junior synonym of C. ochreata Staudinger. C. deletaria Hampson is excluded from the genus. All species of Cidaria and their genitalia are described and illustrated. The cladistic analysis of these eight species of Cidaria is carried out using two data matrices, the first comprising morphological characters alone and the second morphological and distributional characters. The most parsimonious cladogram of Cidaria is selected, and its monophyly defined. The character analysis shows that some distribution characters contribute to resolving the in group node. The choice of multiple trees is discussed.     

Structure of clathrin-coated vesicles from small-angle scattering experiments

Previously published small-angle neutron and X-ray scattering data from coated vesicles, reassembled coats, and stripped vesicles have been analyzed in terms of one common model. The neutron data sets include contrast variation measurements at three different D20 solvent concentrations. The model used for interpreting the data has spherical symmetry and explicitly takes into account polydispersity, which is described by a Gaussian distribution. Å constant thickness of the clathrin coats is assumed. The fitting of the model shows that the coated vesicles consist of a low-density outer protein shell (clathrin) and a central protein shell (accessory polypeptides and receptors) of approximately six times higher density. For the X-ray scattering and neutron contrast variation data, the polydispersity of the samples is of the order of 90 Å (full-width-at-half-maximum value) and the average outer radius is approximately 400 Å. The inner high-density shell has inner and outer radii of 115 and 190 Å, respectively. Å simultaneous fit to the three neutron contrast variation data sets identifies the lipid membrane with a thickness of 40 Å and an outer radius of 196 Å. Thus, the membrane and the high-density protein shell overlap in space, which shows that the lipid membrane contains protein. The molecular mass of the average particle is 27 × 106 Da. The coated vesicles consist, on average, of approximately 85 % protein and 15 lipids. About 40% of the protein mass is situated in the central high-density shell, which gives a large amount of protein in the lipid membrane. The densities of the central shell and the lipid membrane show that the hydration is small in the central region. Å comparison of the total mass, the mass distribution, and the structure of the average-size particles with the barrel structure shows that the accessory polypeptides are incorporated in the lipid membrane. The results from the neutron data for the reassembled coats show that the structure of these particles is very similar to the structure of the native coats. The main difference is a higher density of the central protein shell, which shows that the membrane is replaced by protein in the reassembled coats.     

Mobile organisms in a geologically complex area: Lepidoptera in the Indo-Australian tropics

The Indo-Australian tropical archipelagos have increased in extent and proximity through the Tertiary whilst also changing their configuration. The development of new land areas between old cratonic ones involves extensive dispersals of plants and animals from the latter to the former. The vicariance approach, though suited to the study of the fragmentation of old, cratonic land areas, is of uncertain value in this situation; the representation of emergence or convergence and fusion of land areas in cladogram form presents immense problems and to attempt it may be pointless.
Distribution of Lepidoptera species largely reflects the present day geography of the area for both lowland and montane habitats. Significant discordances at a higher taxonomic level can be examined in the light of hypotheses of past geography such as those concerning the evolution of the Melanesian Arcs.
There are many advantages and some disadvantages in using Lepidoptera for such studies, involving their taxonomy, completeness of geographical coverage, range of dispersal ability and specificity to environmental conditions. Both cladistic and phenetic methods can provide basic data for biogeographic studies. The importance of an understanding of habitat preferences is stressed.
Patterns of probable recent development involving well-defined groups of very similar species are examined in the hope they will provide a yardstick whereby potentially older patterns can be assessed, and lead in time to methodology that will satisfy the stringent requirements of current thinking in the philosophy of science.     

Molecular phylogeny of the genus Dahlia Cav. (Asteraceae, Heliantheae-Coreopsidinae) using sequences derived from the internal transcribed spacers of nuclear ribosomal DNA

Sequences of the internal transcribed spacers (ITS) of the 18S-26S nuclear ribosomal DNA were used to resolve phylogenetic relationships among 13 species of the genus Dahlia . Phylogenetic reconstruction from both parsimony analysis and pairwise distance data produced a single tree in which four clades could be distinguished, these broadly separating the species into the different chromosome numbers found in Dahlia ( x = 16, x = 17 and x = 18). Although species based on x = 16 were divided into two clades, there is the suggestion that this separation may be artificial and that these should be combined as a single clade. The phylogeny produced here has been discussed with reference to the existing taxonomic treatment of the genus. It currently appears that the genus Dohlia is monophyletic and it is evident that the different basic chromosome numbers withim the dysploid series in Dahlia have evolved only once. This proposed monophyly of the genus coupled with the successful production of hybrids withim the dysploid series (2 n = 32, 2 n = 34 and 2 n = 36) suggests that the species of Dahlia have evolved from a common ancestor.     

The systematics of the Phelsuma madagascariensis species group of day geckos (Reptilia: Gekkonidae) in the Seychelles

Conventional taxonomy of the Seychelles populations of the Phelsuma madagascariensis species group has failed to illustrate the principal patterns of phenetic variation between island populations. The taxonomic history of the populations is discussed critically, and a revised nomenclature is suggested from the results of a recent comprehensive study of the forms using multivariate morphometrics. Three phenetic groups from the granitic islands are referred to as Phelsuma sundbergi sundbergi from the north western islands; P. s. ladiguensis from the north eastern islands; and P. s. longinsulae from the southern islands. Phelsuma abbotti populations from Aldabra and Assumption are considered subspecifically distinct, and not conspecific with the granitic island forms. The other coralline island populations are closely allied to the races from the granitic islands and probably represent recent colonization or introductions by man.     

CAUSE OF BIMODAL DISTRIBUTION IN THE SHAPE OF A TERRESTRIAL GASTROPOD

The distribution of a phenotypic state is often discontinuous and dispersed. An example of such a distribution can be found in the shell shapes of terrestrial gastropods, which exhibit a bimodal distribution whereby species possess either a tall shell or a flat shell. Here we propose a simple model to test the hypothesis that the bimodal distribution relates to the optimum shape for shell balance on the substrates. This model calculates the theoretical shell balance by moment and obtains empirical distribution of shell shape by compiling published data and performing a new analysis. The solution of the model supports one part of the hypothesis, showing that a low-spired shell is the best balanced and is better suited for locomotion on horizontal surface. Additionally, the model shows that both high- and low-spired shells are well balanced and suited on vertical surfaces. The shell with a spire index (shell height divided by diameter) of 1.4 is the least well balanced as a whole. Thus, spire index is expected to show a bimodal distribution with a valley at 1.4. This expectation was supported by empirical distribution of a spire index, suggesting that the bimodality of shell shape in terrestrial gastropods is related to shell balance.     

A revision of the brassoline genus Selenophanes (Lepidoptera: Rhopalocera)

The Brassoline genus Selenophanes is revised: three new subspecies are described and three lectotypes designated. The nine known holotypes and two of the three lectotypes are figured. Along the Andes there is a fairly close agreement in the distribution of some of the species and subspecies of Selenophanes with the recently recognized endemic centres. East of the Andes there is no close correspondence between subspecies and endemic centres; each subspecies has, in general, a distribution across several centres. A similar distribution has been noted previously in the Brassoline genus Catoblepia.