Independent evolution of the sexes promotes amphibian diversification

Classic ecological theory predicts that the evolution of sexual dimorphism constrains diversification by limiting morphospace available for speciation. Alternatively, sexual selection may lead to the evolution of reproductive isolation and increased diversification. We test contrasting predictions of these hypotheses by examining the relationship between sexual dimorphism and diversification in amphibians. Our analysis shows that the evolution of sexual size dimorphism (SSD) is associated with increased diversification and speciation, contrary to the ecological theory. Further, this result is unlikely to be explained by traditional sexual selection models because variation in amphibian SSD is unlikely to be driven entirely by sexual selection. We suggest that relaxing a central assumption of classic ecological models—that the sexes share a common adaptive landscape—leads to the alternative hypothesis that independent evolution of the sexes may promote diversification. Once the constraints of sexual conflict are relaxed, the sexes can explore morphospace that would otherwise be inaccessible. Consistent with this novel hypothesis, the evolution of SSD in amphibians is associated with reduced current extinction threat status, and an historical reduction in extinction rate. Our work reconciles conflicting predictions from ecological and evolutionary theory and illustrates that the ability of the sexes to evolve independently is associated with a spectacular vertebrate radiation.     

'Flapping valves' in brachiopods

M. J. S. Rudwick and others postulate 'rhythmic-flow' feeding for the Permian richtho-feniacean bi-achiopods, whereas R. E. Grant claims that they fed by normal ciliary action. Suspension-feeding has two components, current generation and food capture; normal brachiopod lophophores do both, but this is neither universal nor compulsory among animals. Opening and closing the richthofeniid shell generated a 'tidal-flow' current precisely analogous to respiratory currents in mammals; this is neither inefficient nor 'self-defeating', as Grant claims. Grant's analysis fails because he chose the wrong mechanical analogy (a pump). Morphological features of richthofeniids are better explained on a tidal-flow hypothesis than on a ciliary-flow model, and all the data adduced by Grant in rejecting the former is compatible with it or favorable to it. It explains morphological features that are bizarre mysteries on the ciliaiy-current model, and is therefore superior even though it implies that these Permian brachiopods were radically innovative.     

Commissural asymmetry in brachiopods

Consistent asymmetric folding of the commissure is a characteristic feature of a small but significant number of brachiopod species. The feature may be obligate or facultative and is almost entirely confined to rhynchonellids, most of which are Mesozoic. The detailed nature of the asymmetry is very variable, but does not extend to internal hard parts such as crura. Taken as a whole, asymmetric brachiopod species show no preference for any particular environment or geographic region, and in no circumstances seem to have been markedly more or less successful than symmetric species. We are thus led to suggest that asymmetry was a genetically based condition which cropped up periodically in brachiopod evolution, and which possibly was selected neither particularly for nor against.     

Pollen morphological evolution in bat pollinated plants

This study assesses to what extent bat pollination has acted as a selective force on pollen morphology. Earlier pollen studies have suggested convergent evolution of verrucate exine ornamentation. Furthermore pollen of bat pollinated plants has been reported to be bigger than that of plants pollinated by other means. The generality of these ideas is tested using a sample of 130 species of both bat pollinated plants and relatives with another mode of pollination. An analysis of pollen size, shape, aperture number and type, and ornamentation type of 35 plant groups in which a transition towards bat pollination occurred was performed and showed a significant effect for pollen size only. Bat pollinated plants have bigger pollen than their relatives. Pollen size was shown to correlate with style length. Pollen shape, aperture system and exine ornamentation are in general not very different in bat pollinated plants in comparison with their relatives. There is no consistent trend for rougher exines to be associated with bat pollination.     

Biogeography of the recent brachiopods

The vertical, latitudinal, and circumcontinental zonality of the distribution of the species, genera, and families of recent brachiopods is considered. The distortions of the latitudinal and meridional symmetry of the biogeographic structure of the ocean are analyzed in view of the patterns of the global circulation of the surface and intermediate waters. Thus ancient faunas may be reconstructed based on data on the structural characteristics of the taxocene of recent brachiopods. The features of the paedomorphic evolution of brachiopods from the different families in extreme habitats (interstitial, underwater caverns, submarine rises, abyssal depths, hydrothermal areas, and margins of habitats) are discussed. The biogeographic structure of bottom dwellers is shown to simplify with depth as well as with simplification of the hydrological structure of the ocean. The important role of the bathyal oceanic zone (slopes of continents, islands, submarine mountains, ridges, and rises) in the preservation of faunal relicts is shown. The historical change from brachiopods to bivalves that occurred from the Paleozoic to the Mesozoic and Cenozoic is shown to have resulted not from competitive exclusion, but from complex and global changes in the plankton composition, which were unfavorable for articulate brachiopods, which had already developed specialized feeding habits, feeding on food that led to the production of almost no metabolic waste products; they had even partly lost their alimentary canal. The development of shelly plankton and, especially, of diatoms hampered the post-Paleozoic revival of large assemblages of articulate brachiopods in shallow-water habitats. The unfilled ecological niches were colonized by bivalves, which were widely adapted to feeding on live phyto-and zooplankton. Recent articulate brachiopods, which are adapted to feeding on the products of decay of dead plankton, form a belt of densely populated settlements of the organic biofilter outside the photic zone on the seaward edge of shelves and on the upper parts of the slopes of continents, islands, and submarine rises throughout the world.     

Gene orders in genomes of alpha-proteobacteria: similarity and evolution

The gene orders in the genomes of nine alpha-proteobacteria were compared using quantitative indices S (the relative number of common pairs of adjacent genes) and L (the mean difference between intergenic distances). A sample of 200 homologous genes, occurring in all 11 strains, was studied. In all of the genomes examined, 20 conserved, "uninterrupted" regions, including in total 63 out of 200 genes, were found. The rate of evolutionary change in the gene order widely varied in different evolutionary lineages. The highest rate (40 to 60 genome rearrangements per 100 Myr) was characteristic of the intercellular parasite Wolbachia (Rickettsiales). Computer simulation has showed that the S to L ratio observed in the sample testified that the probability of large genome rearrangements was somewhat lower than that of small ones.     

Veronica: Parallel morphological evolution and phylogeography in the Mediterranean

The genus Veronica s. lat. comprises about 450 species (including about 180 species from the southern hemisphere Hebe-complex), many of which grow in the Mediterranean area. Their extreme variability in morphology, life form and habitats has led to many suggestions regarding evolution and biogeography. Difficulties arise from parallel syndromes, widespread among alpine species and lowland perennials, and particularly among annual species of the genus. We have used sequences of the plastid trnL-F region and nuclear ribosomal ITS sequences to differentiate between different clades of Veronica and reveal cases of parallel evolution. Based on this data, cases of parallel evolution have been found in biogeographical patterns among the alpine species of Veroniceae, in which species from European mountains have affinities to those in the Central Asian/Himalayan region whereas alpine species from Turkey are probably more recently derived from lowland southwestern Asian taxa. Different subspecies of Veronica bombycina gained their characteristic morphology independently and parallel in adaptation to their alpine environment. Pinnatifid leaves have been gained parallel in perennial grassland species of Veronica. Finally, parallel evolutionary trends in many characters, not only morphological but also molecular characters, are common among annual species of Veronica.We wish to thank the Studienstiftung des deutschen Volkes for a doctoral scholarship to DCA and the Spanish Ministerio de Ciencia y Tecnologia for a postdoctoral grant (programa FPI) to MMO. This work was partially supported by the Junta de Castilla y Leon and the European Union (FSE) through the research project SA117/01. We also thank Prof. F. Ehrendorfer for critical comments and valuable discussions. Further, DCA thanks Daniela Hanfland and Yoshiki Nakamoto for help in the field. Manfred A. Fischer, Lena Struwe, Bernhard Dickore, Christoph Dobes, Eberhard Fischer, Niels Köster, Gerald Schneeweiss, Tod Stuessy, Tim Utteridge and Matsugo Yokota have provided plant material for this study.     

The genetics of plant morphological evolution.

Considerable progress has been made in identifying genes that are involved in the evolution of plant morphologies. Elements of the ABC model of flower development are conserved throughout angiosperms, and homologous MADS-box genes function in gymnosperm reproduction. Candidate gene and mapping analyses of floral symmetry, sex determination, inflorescence architecture, and compound leaves provide intriguing glimpses into the evolution of morphological adaptations.     

Identifying the morphological signatures of hybridization in primate and human evolution

Recent studies point to contact and possible admixture among contemporaneous hominin species during the Plio-Pleistocene. However, detection of hybridization in fossils-and especially fossil hominins-is contentious, and it is hindered in large part by our lack of understanding about how morphological hybridity is manifested in the primate skeleton. Here, we report on a study of known-pedigree, purebred yellow and olive baboons (n = 112) and their hybrids (n = 57), derived from the baboon colony of the Southwest Foundation for Biomedical Research. The hybrids were analyzed in two different groups: (1) F1 = olive x yellow first-generation hybrids; (2) B1 = olive x F1 backcross hybrids. Thirty-nine metric variables were tested for heterosis and dysgenesis. Nonmetric data were also collected from the crania. Results show that these primate hybrids are somewhat heterotic relative to their parental populations, are highly variable, and display novel phenotypes. These effects are most evident in the dentition and probably indicate the mixing of two separately coadapted genomes and the breakdown in the coordination of early development, despite the fact that these populations diverged fairly recently. Similar variation is also observed in museum samples drawn from natural hybrid zones. The results offer a strategy for detecting hybrid zones in the fossil record; implications for interpreting the hominin fossil record are discussed.     

Nonheterochronic developmental changes underlie morphological heterochrony in the evolution of the Ardeidae

Evolutionary changes in developmental timing and rates (heterochrony) are a source of morphological variation. Here we explore a central issue in heterochronic analysis: are the alterations in developmental timing and rates the only factor underlying morphological heterochrony? Tarsometatarsal growth through endochondral ossification in Ardeidae evolution has been taken as a case study. Evolutionary changes in bone growth rate (morphological heterochrony) might be either (a) the result of alterations in the mitotic frequency of epiphyseal chondrocytes (process‐heterochrony hypothesis), or (b) the outcome of alterations in the number of proliferating cells or in the size of hypertrophic chondrocytes (structural hypothesis). No correlation was found between tarsometatarsal growth rates and the frequency of cell division. However, bone growth rates were significantly correlated with the number of proliferating cells. These results support the structural hypothesis: morphological acceleration and deceleration are the outcome of evolutionary changes in one structural variable, the number of proliferating cells.     

Gzhelian brachiopods of the family Linoproductidae Stehli and regularities in their evolution in the Middle and Late Carboniferous of the Moscow Region

This paper completes the revision of the Middle and Late Carboniferous brachiopods of the family Linoproductidae from the Moscow Region. The species cannot be completely described according to the methods previously elaborated by the author because of the poor state of preservation of the material from Gzhelian deposits. Problems of the generic diagnostics of the Gzhelian linoproductids are discussed; a new species, Linispinus parvus, is described from the uppermost Kasimovian deposits that have been referred to the Gzhelian Stage. Regularities in the group evolution in the Moscovian, Kasimovian, and Gzhelian ages are analyzed.     

The origin of the spiriferidine brachiopods

Wright, Anthony D. 197901 15: The origin of the spiriferidine brachiopods. Lethaia . Vol. 12. pp. 29–33. Oslo. ISSN 0024–1164.
In recent years doubts have been expressed as to whether the strophic spiriferidines should continue to be grouped with the non-strophic spiriferids in the order Spiriferida or not. The solution to this problem will only be found by establishing the origin of the spiriferidines. A characteristic feature of the spiriferidines is their well developed micro-ornament; this is shared also by the orthid Platystrophiinae, and together with the striking similarity in overall morphology (well recognized in the early nineteenth century) it suggests that here, in the Platystrophia plexus, is the ancestral stock of the strophic spirebearers.
The Platystrophünae share with the non-strophic Rhynchonellida the potential to develop a spire. It is here considered that the former gave rise to the spiriferidines and the latter to the non-strophic spire-bearers. These quite separate developments justify the separation of the spire-bearers into the two orders Spiriferida and Atrypida.     

Climatic control of brachiopods in the lower Namurian

The fauna and lithology of a marine band in the lower Edale Shales (Namurian E₂b) at Edale, Derbyshire, England, are described quantitatively. Two brachiopods, Rugosochonetes sp. and Productus hibernicus were the dominant elements of the fauna. The average age at death was about 3 years, although the maximum age of Rugosochonetes (ca. 7 years) was probably a little greater than that of Productus (ca. 5 years). Both sediment deposition and fauna were climatically controlled. The climate was seasonal from wet to dry. Quartz was deposited and Rugosochonetes sp. flourished during the wet periods. Carbonate deposition and Productus hibernicus were dominant during the dry periods.