Finding the frame shift: digit loss, developmental variability, and the origin of the avian hand

The origin of the tridactyl hand of crown birds from the pentadactyl hand of those early theropod dinosaurs lying along the avian stem has become a classic, but at times seemingly intractable, historical problem. The point in question is whether the fingers of crown birds represent digits 1-3 as predicted by generalized trends in the fossil record; or digits 2-4, as evidenced by the topology of the embryonic mesenchymal condensations from which the digits develop. The frame shift hypothesis attempted to resolve this paradox by making these signals congruent by means of a homeotic transformation in digital identity, but recently the paleontological support for this hypothesis was questioned. Here, we reassess the frame shift from a paleontological perspective by addressing what predictions a frame shift makes for skeletal morphology, whether the frame shift remains a viable explanation of the known fossil data, and where on the theropod tree the frame shift most likely occurred. Our results indicate that the frame shift remains viable, and based on the inferred pattern of digit loss, the frame shift likely occurred at a deeper position in theropod phylogeny than previously proposed. A new evolutionary model of the frame shift is described in which the early history of the frame-shifted hand is marked by an extended zone of developmental polymorphism. This model provides a new conceptual framework for the role of developmental variability in communicating broad evolutionary patterns on a taxonomically inclusive phylogenetic tree.     

The skull of Monolophosaurus jiangi (Dinosauria: Theropoda) and its implications for early theropod phylogeny and evolution

The Middle Jurassic was a critical time in the evolution of theropod dinosaurs, highlighted by the origination and initial radiation of the large‐bodied and morphologically diverse Tetanurae. Middle Jurassic tetanurans are rare, but have been described from Europe, South America and China. In particular, China has yielded a number of potential basal tetanurans, but these have received little detailed treatment in the literature. Chief among these is Monolophosaurus jiangi, known from a single skeleton that includes a nearly complete and well‐preserved skull characterized by a bizarre cranial crest. Here, we redescribe the skull of Monolophosaurus, which is one of the most complete basal tetanuran skulls known and the only quality source of cranial data for Middle Jurassic Chinese theropods. The cranial crest is atomized into a number of autapomorphic features and several characters confirm the tetanuran affinities of Monolophosaurus. However, several features suggest a basal position within Tetanurae, which contrasts with most published cladistic analyses, which place Monolophosaurus within the more derived Allosauroidea. Cranial characters previously used to diagnose Allosauroidea are reviewed and most are found to have a much wider distribution among Theropoda, eroding an allosauroid position for Monolophosaurus and questioning allosauroid monophyly. The use of phylogenetic characters relating to theropod cranial crests is discussed and a protocol for future use is given. The systematic position of Guanlong wucaii is reviewed, and a basal tyrannosauroid affinity is upheld contrary to one suggestion of a close relationship between this taxon and Monolophosaurus. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158 , 573–607.     

The developmental evolution of avian digit homology: An update

The identity of avian digits has been unresolved since the beginning of evolutionary morphology in the mid-19th century, i.e. as soon as questions of phylogenetic homology have been raised. The main source of concern is the persistent discrepancy between anatomical/paleontological and embryological evidence over the identity of avian digits. In this paper, recent evidence pertaining to the question of avian digit homology is reviewed and the various ideas of how to resolve the disagreement among developmental and phylogenetic evidence are evaluated. Paleontological evidence unequivocally supports the hypothesis that the fully formed digits of maniraptoran theropods are digits DI, DII, and DIII, because the phylogenetic position of Herrerasaurus is resolved, even when hand characters are excluded from the analysis. Regarding the developmental origin of the three digits of the avian hand the discovery of an anterior digit condensation in the limb bud of chickens and ostriches conclusively shows that these three digits are developing from condensations CII, CIII, and CIV. The existence of this additional anterior condensation has been confirmed in four different labs, using four different methods: Alcian blue staining, PNA affinity histochemistry, micro-capillary regression and Sox9 expression. Finally, recent evidence shows that the digit developing from condensation CII has a Hox gene expression pattern that is found in digit DI of mice forelimb and chick hind limbs. The sum of these data supports the idea that digit identity has shifted relative to the location of condensations, known as Frame Shift Hypothesis, such that condensation CII develops into digit DI and condensation CIII develops into digit DII, etc. A review of the literature on the digit identity of the Italian Three-toed Skink or Luscengola (Chalcides chalcides), shows that digit identity frame shifts may not be limited to the bird hand but may be characteristic of “adaptive” digit reduction in amniotes (sensu Steiner, H., Anders, G., 1946. Zur Frage der Entstehung von Rudimenten. Die Reduktion der Gliedmassen von Chalcides tridactylus Laur. Rev. Suisse Zool. 53, 537–546) in general. In this mode of evolution two digits are lost, in the course of the adaptation of the three anterior digits to a function that does not require the two posterior digits. This evidence suggests that the evolution of digits in tetrapods can proceed at least on two distinct levels of integration, the level of digit condensations and that of adult digits.     

NAD+ kinase in the development of a silkworm,Bombyx mori L.

The activity and molecular organization of NAD⁺ kinase have been studied throughout the life cycle of the silkworm, Bombyx mori. The apparent molecular weights of the enzyme forms revealed by 3–20% polyacrylamide gel electrophoresis were determined to be; I, 138,000; II, 152,000; III, 182,000 and IV, 205,000 daltons. The pattern and relative percentage composition of the molecular forms, as well as the specific activity of NAD⁺ kinase, were shown to undergo changes in the transition from one developmental phase to another. Form I of the NAD⁺ kinase is present only at the end of embryogenesis, form II is characteristic of actively growing larvae, form III is present at all developmental stages, except the end of embryogenesis, while form IV appears at the stages when development is provided by endogenic energy resources.     

Evolution of Hoxa-11 Expression in Amphibians: Is the Urodele Autopodium an Innovation?

In this paper we present preliminary results on the expressionof Hoxa-11 in the frog Xenopus laevis and the newt Notophthalmusviridescens. In amniote limbs, Hoxa-11 is expressed exclusivelyin the prospective zeugopodium and is involved in the developmentof zeugopodial character identity. While the Hoxa-11 expressionpattern in Xenopus is similar to those described in mice andchick, the newt Notophthalmus has a phase of autopodial Hoxa-11expression starting with the development of digit III. Expressionis particularly strong in the buds of the postaxial digits.This Hoxa-11 expression pattern is unique among tetrapods andadds to the list of developmental peculiarities of urodele limbdevelopment, which also include an anterior to posterior polarityof digit development. We propose a scenario to explain the evolutionaryorigin of urodele limb development. We assume that recent urodelesare derived from a lineage of amphibians which underwent partialdigit reduction, leaving only two digits intact, most likelydigits III and IV according to Morse's law. This implies thaturodele digits I and II are homologous to amniote digits IIIand IV, and that the postaxial digits of urodeles are an evolutionaryinnovation (re-invention). Supporting evidence for this homologyhypothesis is found in the developmental connections betweenthe basale commune and the postaxial zeugopodial element.     

Attack of the clones: Population genetics reveals clonality of Colletotrichum lupini,the causal agent of lupin anthracnose

Colletotrichum lupini, the causative agent of lupin anthracnose, affects lupin cultivation worldwide. Understanding its population structure and evolutionary potential is crucial to design successful disease management strategies. The objective of this study was to employ population genetics to investigate the diversity, evolutionary dynamics, and molecular basis of the interaction of this notorious lupin pathogen with its host. A collection of globally representative C. lupini isolates was genotyped through triple digest restriction site-associated DNA sequencing, resulting in a data set of unparalleled resolution. Phylogenetic and structural analysis could distinguish four independent lineages (I–IV). The strong population structure and high overall standardized index of association (r̅_d) indicates that C. lupini reproduces clonally. Different morphologies and virulence patterns on white lupin (Lupinus albus) and Andean lupin (Lupinus mutabilis) were observed between and within clonal lineages. Isolates belonging to lineage II were shown to have a minichromosome that was also partly present in lineage III and IV, but not in lineage I isolates. Variation in the presence of this minichromosome could imply a role in host–pathogen interaction. All four lineages were present in the South American Andes region, which is suggested to be the centre of origin of this species. Only members of lineage II have been found outside South America since the 1990s, indicating it as the current pandemic population. As a seedborne pathogen, C. lupini has mainly spread through infected but symptomless seeds, stressing the importance of phytosanitary measures to prevent future outbreaks of strains that are yet confined to South America.     

Pentadactyl pattern of the avian wing autopodium and pyramid reduction hypothesis

We report herein that a pentadactyl developmental pattern is evident in early wing morphogenesis of Gallus (chicken) and Struthio (ostrich). Five avascular zones (spatially predestined locations of contiguous metacarpal and phalangeal aggregation) and four interdigital vascular spaces are established by the regression patterns of autopodial vasculature. Transient vestiges of the first and fifth metacarpals are confirmed histologically and histochemically. They lie within the preaxial-most and postaxial-most avascular zones, respectively. These observations reveal conservative patterning of the avian hand and corroborate a II-III-IV metacarpal interpretation, argue for II-III-IV identity of ossified digits in birds, and favour a simple reduction rather than a homeotic shift in terms of the phenotype expressed by Hox genes in the phylogeny of the avian manus. We suggest that gradual, bilateral reduction of phalanges and metacarpals, via apoptosis mediated by BMP, occurred during the evolution of birds (Pyramid Reduction Hypothesis). This is congruent with the establishment of a central wing axis that became co-opted for coordinated movements. On the basis of evidence presented here, the direct avian ancestor is predicted to have been five-fingered with dominant digits (+ metacarpals) as follow: II, III, IV.     

A new genus and species of Renaudarctidae (Heterotardigrada: Arthrotardigrada) from Ryukyu Archipelago,Japan

A new armoured marine tardigrade, Nodarctus hallucis gen. et sp. nov., is described from specimens collected from sandy beaches of Haterumajima, Ishigakijima and Okinawajima Islands, Ryukyu Archipelago, Japan. It is a member of the rare family Renaudarctidae, which is characterized by a stocky body with dorsal and ventral plates and stumpy legs with digits, claws and accessory filaments. However, the collected animals have prominent characters that differ from the two known species of the family: subdivided dorsal segmental plates I–III lacking lateral processes, an acute caudal spike, indented sensory plates, short spikes and peculiar papillae on legs I–III, basal spikes of legs IV and only two digits on legs IV. These differences justify the erection of a new genus and species for the animal. Morphological affinities with other marine taxa, the function of the leg papillae and the distribution pattern of the new species are discussed.http://zoobank.org/urn:lsid:zoobank.org:pub:041878AA-B437-45BF-80E3-32591D21D965     

The hand structure of Carnotaurus sastrei (Theropoda,Abelisauridae): implications for hand diversity and evolution in abelisaurids

Abstract: Carnotaurus sastrei is an abelisaurid dinosaur from the Late Cretaceous of Argentina that has very reduced, but robust, forelimbs and derived hands with four digits, including a large, conical‐shaped metacarpal IV lacking an articulation for a phalanx. The analysis presented in this work highlights a series of additional autapomorphies of C. sastrei. For example, the proximal phalanges are longer than the metacarpals in digits II and III, and digit III includes only one phalanx besides the ungual. The hand of Carnotaurus shares several features with those of Aucasaurus and Majungasaurus, but the hands of the latter genera also display autapomorphies, indicating that the diversity in abelisaurid hand structure is similar to the diversity of cranial protuberances of these dinosaurs.     

Quality control of Cotesia flavipes (Cameron) (Hymenoptera: Braconidae) from different Brazilian bio-factories

The goal of this study was to evaluate the quality of Cotesia flavipes from different bio-factories as biological control agents. We evaluated biological characteristics of the parasitoids throughout their lifespan, and measured the body length and width, abdomen width, thorax width and width and length of the right forewing of female and male parasitoids. Our results showed that the number of males and pupal viability were similar among the bio-factories; the number of emerged females was greater in bio-factories I and II; the egg-pupa period and the pupal period were shorter in bio-factory IV; and a greater longevity was found in bio-factories II and III. Sex ratio (at approximately 60% females) was satisfactory (in terms of suitability for release) across all bio-factories. For morphometric measurements, the body, abdomen and wing widths were similar in males; however, thorax width was greater in the males from bio-factory I; bio-factory III produced females with the highest body length; bio-factory I produced females with the greatest abdomen width; bio-factories III and IV produced females with the greatest wing length. Among the bio-factories studied, bio-factory IV produced the best quality C. flavipes, with respect to the greatest number of parasitoids per pupal mass (a mean of 57% more parasitoids) in a satisfactory sex ratio, and with the shortest developmental time, which facilitates faster rearing in the laboratory. Studies such as this, which assess the quality of a mass-produced C. flavipes, are crucial for the continued use of this parasitoid in controlling Diatraea saccharalis in the field.     

The taxonomy and morphological and anatomical differentiation of populations ofLeiothrix crassifolia (Eriocaulaceae)

The morphological and anatomical leaf and scape differentiation ofLeiothrix crassifolia is analysed and classified into seven types (I, II, III, IV, V, VI, VII). The species has a relatively wide distribution in the campo rupestre of Minas Gerais in Brazil. Variation in the isolated populations on different mountain ranges is complex, does not follow a clear geographical pattern, and defies taxonomic classification.L. nubigena andL. obtusifolia are included inL. crassifolia.     

Cloning and analysis of a bifunctional methyltransferase/restriction endonuclease TspGWI, the prototype of a Thermus sp. enzyme family

Background  

Restriction-modification systems are a diverse class of enzymes. They are classified into four major types: I, II, III and IV. We have previously proposed the existence of a Thermus sp. enzyme family, which belongs to type II restriction endonucleases (REases), however, it features also some characteristics of types I and III. Members include related thermophilic endonucleases: TspGWI, TaqII, TspDTI, and Tth111II.     

Trackways of the American Crocodile (Crocodylus acutus) in Northwestern Costa Rica: Implications for Crocodylian Ichnology

We documented trackways of free-living Crocodylus acutus on beaches at the mouths of Tamarindo and Ventanas estuaries, Costa Rica. Our crocodiles had estimated total lengths of 1–3 meters or more. Manus prints have five digits, with digits I–III bearing claw marks. Pes prints have four digits, with claw marks on digits I–III. The pes is plantigrade. Claws generally dig into the substrate. Apart from claw marks, digit I and the heel of the pes are usually the most deeply impressed parts of footprints. Trackways are wide-gauge. Pes prints are usually positioned just behind ipsilateral manus prints of the same set and may overlap them. Manus and pes prints angle slightly outward with respect to the crocodile's direction of movement. Claw-bearing digits of both the manus and pes may create curved, concave-toward-the-midline drag marks as the autopodium is protracted. The tail mark varies in depth and clarity, and in shape from nearly linear to markedly sinuous. Sometimes the tail mark hugs the trackway midline, but sometimes it is closer to, or even cuts across, prints of one side. American crocodile footprints and trackways are similar to those observed in other extant crocodylian species, indicating substantial trackway conservatism across the group.     

The external morphology and distribution of cuticular hair organs on the claws of the American lobster, Homarus Americanus (Milne-Edwards)

Four classes of microscopic cuticular hair organs were found on the chelae of Homarus americanus (Milne-Edwards). Type I and Type II organs possess long single sensillae, 30–60 μm and 70–130 μm, respectively. Type III organs are toroid bumps 20–30 μm in diameter, with a small tuft of fibers projecting from the center. Type IV organs are small conical hairs ≈ 1 μm in length.Type IV organs were uniformly distributed over the claws. The distributions of Types I, II, and III organs were analysed through multivariate analysis of variance (MANOVA) with respect to claw, side, and area. Type I organs showed significance of the three-way interaction only. Type II organs showed significance of side, area, and the claw by area interaction. Type III organs showed significance of area, and all interactions. Changes in number and density of Types I, II and III organs, and in number of Type IV organs, were found with growth.     

Morphology and distribution of ovipositor sensilla of female cotton leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae), and evidence for gustatory function

The ovipositor of Spodoptera littoralis has many sensilla, which implies a distinct sensory function of this organ in the assessment of the egg laying substrates and placement of eggs. The ovipositor is composed of two papillae densely packed with sensilla. Scanning electron microscopy showed that there are four categories of sensilla chaetica (s. chaetica), characterized based on differences in distribution, length and morphology, distributed on each papilla: Type I with 69 ± 2.9 sensilla on each papilla (length: 29–163 μm) distributed at the base; Type II with 19 ± 1.8 sensilla (length: 287–446 μm) distributed medially; Type III with 120 ± 7.8 sensilla (length: 62–156 μm) distributed distally; and Type IV 8 ± 0.9 sensilla (length: 72–91 μm) scattered between Type III sensilla. The structure of s. chaetica Types I–III suggests a mechanosensory function, whereas electrophysiological analysis of s. chaetica Type IV showed responses from four gustatory neurons and one mechanosensory neuron. Of the chemoreceptive neurons, one responded to salt, one to the secondary compound caffeine, one to sugars, mainly sucrose and fructose, and lastly one potentially to water. Behavioral studies are needed to verify the role of these sensilla during choice of oviposition site.     

Developmental basis of mammalian digit reduction: a case study in pigs

Digit reduction has occurred in parallel in many mammalian lineages. However, despite this pattern's prevalence, the developmental mechanisms underlying mammalian digit reduction remain controversial. We therefore undertook a study of digit development in the pig (Sus scrofa), a mammal with reduced first, second, and fifth digits. Our results indicate that from its earliest formation, the pig limb bud is significantly narrower than that of the model pentadactyl mammal, mouse. Furthermore, the cartilage condensations of the pig's reduced digits are noticeably smaller than those of their nonreduced counterparts from the time of their formation. In addition, growth rates of pig digits are comparable, as are the patterns of cell death in developing pig and mouse limbs. Taken together, results suggest that pig's first, second, and fifth digits are primarily reduced through evolutionary modifications in the early developmental patterning of their limbs. Results of this study, coupled with those from study of limb development in other mammals, suggest that although major developmental reorganizations (e.g., complete digit or limb loss) during early limb development may be selected against, it may be common for more subtle evolutionary modifications in limb development (e.g., changes in relative digit size) to occur at this time.     

The phenoloxidases of the ascomycete Podospora anserina: The three forms of the major laccase activity

In Podospora anserina three laccase activities (I, II and III) were identified. Present results show the existence of an additional lacaase (an anodic protein; MW 80,000; R_f 0.07). Laccase IV derived from the dissociation at acid pH (4.5) of a protein which showed identical molecular weight (390,000) and R_f (0.1) to the oligomeric laccase I. The recovery of laccase I activity when starting from laccase IV (purified by means of isoelectric focusing) suggests that laccase I itself was the source of laccase IV. In turn, laccase IV gave rise to the laccase III after electrophoresis or dialysis at basic pH (8.5).     

Tbx Genes Specify Posterior Digit Identity through Shh and BMP Signaling

Despite extensive studies on the anterior-posterior (AP) axis formation of limb buds, mechanisms that specify digit identities along the AP axis remain obscure. Using the four-digit chick leg as a model, we report here that Tbx2 and Tbx3 specify the digit identities of digits IV and III, respectively. Misexpression of Tbx2 and Tbx3 induced posterior homeotic transformation of digit III to digit IV and digit II to digit III, respectively. Conversely, misexpression of their mutants VP16 Delta Tbx2 and VP16 Delta Tbx3 induced anterior transformation. In both cases, alterations in the expression of several markers (e.g., BMP2, Shh, and HoxD genes) were observed. In addition, Tbx2 and Tbx3 rescued Noggin-mediated inhibition of interdigital BMP signaling, signaling which is pivotal in establishing digit identities. Hence, we conclude that Tbx3 specifies digit III, and the combination of Tbx2 and Tbx3 specifies digit IV, acting together with the interdigital BMP signaling cascade.     

Complex I Controls Mitochondrial and Plasma Membrane Potentials in Nerve Terminals

Reductions in the activities of mitochondrial electron transport chain (ETC) enzymes have been implicated in the pathogenesis of numerous chronic neurodegenerative disorders. Maintenance of the mitochondrial membrane potential (Δψ_m) is a primary function of these enzyme complexes, and is essential for ATP production and neuronal survival. We examined the effects of inhibition of mitochondrial ETC complexes I, II/III, III and IV activities by titrations of respective inhibitors on Δψ_m in synaptosomal mitochondria. Small perturbations in the activity of complex I, brought about by low concentrations of rotenone (1–50 nM), caused depolarisation of Δψ_m. Small decreases in complex I activity caused an immediate and partial Δψ_m depolarisation, whereas inhibition of complex II/III activity by more than 70% with antimycin A was required to affect Δψ_m. A similarly high threshold of inhibition was found when complex III was inhibited with myxothiazol, and inhibition of complex IV by more than 90% with KCN was required. The plasma membrane potential (Δψ_p) had a complex I inhibition threshold of 40% whereas complex III and IV had to be inhibited by more than 90% before changes in Δψ_p were registered. These data indicate that in synaptosomes, both Δψ_m and Δψ_p are more susceptible to reductions in complex I activity than reductions in the other ETC complexes. These findings may be of relevance to the mechanism of neuronal cell death in Parkinson’s disease in particular, where such reductions in complex I activity are present.