Flatfishes, Turtles, and Bolyerine Snakes: Evolution by Small Steps or Large, or Both?

A biphasic relational approach to the evolution of human consciousness: Un enfoque relacional bifásico para la evolución de la conciencia humana

Background/objective

Human consciousness is arguably unique, and its features are hard to explain. Continuous and discrete accounts of consciousness are commonly viewed as incompatible, but both have limitations. Continuous accounts cannot readily account for what appears to be unique about human consciousness; discrete accounts have a hard time explaining how human consciousness could have evolved. The present position paper shows how both continuous and discontinuously elements can be combined.

Method

A biphasic model is constructed by unifying complex systems theory, the evolution of symbolic reasoning as a relational extension of human cooperation, and evolutionary science. The application of this approach to modern views of consciousness is then explored.

Results

Our analysis suggests that human consciousness may be viewed as a discontinuous event, that emerged from continuous foundations. This biphasic account contains processes that can be targeted clinically. For example, developmentally delayed children with problems in consciousness may be helped by targeting the processes the present account suggests are important at different levels of complexity.

Conclusions

This biphasic relational approach fits with the evolutionary record and with data on human cognitive development. It may be useful in guiding clinical intervention.

The postembryonic transformation of the shell in emydine box turtles

A key trend in the 210-million-year-old history of modern turtles was the evolution of shell kinesis, that is, shell movement during neck and limb retraction. Kinesis is hypothesized to enhance predator defense in small terrestrial and semiaquatic turtles and has evolved multiple times since the early Cretaceous. This complex phenotype is nonfunctional and far from fully differentiated following embryogenesis. Instead, kinesis develops slowly in juveniles, providing a unique opportunity to illustrate the postembryonic origins of an adaptive trait. To this end, we examined ventral shell (plastral) kinesis in emydine box turtles and found that hatchling plastron shape differs from that of akinetic-shelled relatives, particularly where the hinge that enables kinesis differentiates. We also demonstrated shape changes relative to plastron size in juveniles, coinciding with a shift in the carapace-plastron structural connection, rearrangement of ectodermal plates, and bone repatterning. Furthermore, because the shell grows larger relative to the head, complete concealment of the head and extremities is only achieved after relative shell proportions increase. Structural alterations that facilitate the box turtle's transformation are probably prepatterned in embryos but require function-induced changes to differentiate in juveniles. This mode of delayed trait differentiation is essential to phenotypic diversification in turtles and perhaps other tetrapods.

Phenotypic Novelty in EvoDevo: The Distinction Between Continuous and Discontinuous Variation and Its Importance in Evolutionary Theory

The introduction of novel phenotypic structures is one of the most significant aspects of organismal evolution. Yet the concept of evolutionary novelty is used with drastically different connotations in various fields of research, and debate exists about whether novelties represent features that are distinct from standard forms of phenotypic variation. This article contrasts four separate uses for novelty in genetics, population genetics, morphology, and behavioral science, before establishing how novelties are used in evolutionary developmental biology (EvoDevo). In particular, it is detailed how an EvoDevo-specific research approach to novelty produces insight distinct from other fields, gives the concept explanatory power with predictive capacities, and brings new consequences to evolutionary theory. This includes the outlining of research strategies that draw attention to productive areas of inquiry, such as threshold dynamics in development. It is argued that an EvoDevo-based approach to novelty is inherently mechanistic, treats the phenotype as an agent with generative potential, and prompts a distinction between continuous and discontinuous variation in evolutionary theory.

Sampling diverse characters improves phylogenies: Craniodental and postcranial characters of vertebrates often imply different trees

Morphological cladograms of vertebrates are often inferred from greater numbers of characters describing the skull and teeth than from postcranial characters. This is either because the skull is believed to yield characters with a stronger phylogenetic signal (i.e., contain less homoplasy), because morphological variation therein is more readily atomized, or because craniodental material is more widely available (particularly in the palaeontological case). An analysis of 85 vertebrate datasets published between 2000 and 2013 confirms that craniodental characters are significantly more numerous than postcranial characters, but finds no evidence that levels of homoplasy differ in the two partitions. However, a new partition test, based on tree-to-tree distances (as measured by the Robinson Foulds metric) rather than tree length, reveals that relationships inferred from the partitions are significantly different about one time in three, much more often than expected. Such differences may reflect divergent selective pressures in different body regions, resulting in different localized patterns of homoplasy. Most systematists attempt to sample characters broadly across body regions, but this is not always possible. We conclude that trees inferred largely from either craniodental or postcranial characters in isolation may differ significantly from those that would result from a more holistic approach. We urge the latter.

Mitochondrial genomic investigation of flatfish monophyly

We present the first study to use whole mitochondrial genome sequences to examine phylogenetic affinities of the flatfishes (Pleuronectiformes). Flatfishes have attracted attention in evolutionary biology since the early history of the field because understanding the evolutionary history and patterns of diversification of the group will shed light on the evolution of novel body plans. Because recent molecular studies based primarily on DNA sequences from nuclear loci have yielded conflicting results, it is important to examine phylogenetic signal in different genomes and genome regions. We aligned and analyzed mitochondrial genome sequences from thirty-nine pleuronectiforms including nine that are newly reported here, and sixty-six non-pleuronectiforms (twenty additional clade L taxa [Carangimorpha or Carangimorpharia] and forty-six secondary outgroup taxa). The analyses yield strong support for clade L and weak support for the monophyly of Pleuronectiformes. The suborder Pleuronectoidei receives moderate support, and as with other molecular studies the putatively basal lineage of Pleuronectiformes, the Psettodoidei is frequently not most closely related to other pleuronectiforms. Within the Pleuronectoidei, the basal lineages in the group are poorly resolved, however several flatfish subclades receive consistent support. The affinities of Lepidoblepharon and Citharoides among pleuronectoids are particularly uncertain with these data.

Are flatfishes (Pleuronectiformes) monophyletic?

All extant species of flatfish (order Pleuronectiformes) are thought to descend from a common ancestor, and therefore to represent a monophyletic group. This hypothesis is based largely on the dramatic bilateral asymmetry and associated ocular migration characteristics of all flatfish. Yet, molecular-based phylogenetic studies have been inconclusive on this premise. Support for flatfish monophyly has varied with differences in taxonomic and gene region sampling schemes. Notably, the genus Psettodes has been found to be more related to non-flatfishes than to other flatfishes in many recent studies. The polyphyletic nature of the Pleuronectiformes is often inferred to be the result of weak historical signal and/or artifact of phylogenetic inference due to a bias in the data. In this study, we address the question of pleuronectiform monophyly with a broad set of markers (from six phylogenetically informative nuclear loci) and inference methods designed to limit the influence of phylogenetic artifacts. Concomitant with a character-rich analytical strategy, an extensive taxonomic sampling of flatfish and potential close relatives is used to increase power and resolution. Results of our analyses are most consistent with a non-monophyletic Pleuronectiformes with Psettodes always being excluded. A fossil-calibrated Bayesian relaxed clock analysis estimates the age of Pleuronectoidei to be 73 Ma, and the time to most recent common ancestor of Pleuronectoidei, Psettodes, and other relative taxa to be 77 Ma. The ages are much older than the records of any fossil pleuronectiform currently recognized. We discuss our findings in the context of the available morphological evidence and discuss the compatibility of our molecular hypothesis with morphological data regarding extinct and extant flatfish forms.

'Monster… -omics': on segmentation, re-segmentation, and vertebrae formation in amphibians and other vertebrates

Background

The axial skeleton is one of the defining evolutionary landmarks of vertebrates. How this structure develops and how it has evolved in the different vertebrate lineages is, however, a matter of debate. Vertebrae and vertebral structures are derived from the embryonic somites, although the mechanisms of development are different between lineages.

Discussion

Using the anecdotal description of a teratological newt (Triturus dobrogicus) with an unusual malformation in its axial skeleton, we review, compare, and discuss the development of vertebral structures and, in particular, the development of centra from somitic cellular domains in different vertebrate groups. Vertebrae development through re-segmentation of the somitic sclerotomal cells is considered the general mechanism among vertebrates, which has been generalized from studies in amniotic model organisms. The prevalence of this mechanism among anamniotes is, however, controversial. We propose alternative developmental mechanisms for vertebrae formation that should be experimentally tested.

Summary

Research in model organisms, especially amniotes, is laying the foundations for a thorough understanding of the mechanisms of development of the axial skeleton in vertebrates, foundations that should expand the extent of future comparative studies. Although immersed in the ‘-omics’ era, we emphasize the need for an integrative and organismal approach in evolutionary developmental biology for a better understanding of the causal role of development in the evolution of morphological diversity in nature.