Biomedical subjects

Giuseppe Fusco

Publications and source records attributed to Giuseppe Fusco.

7 recordsLinked to original sources

PubMed2026

Loss, persistence and reversal of phenotypic traits.

The irreversibility of complex trait loss has long been a tenet of evolutionary biology. However, this idea is increasingly at odds with the numerous documented exceptions across the Tree of Life. We synthesise this growing body of evidence across a diverse array of taxa and traits, exploring the evolutionary conditions that enable evolutionary reversal. By integrating macroevolutionary, genetic, and developmental information, we argue that trait reversal is commonly fostered by some form of persistence in the generative developmental pathway of the lost trait. We identify three overarching modes of trait reversal and support them with multiple case studies: by pleiotropy (the involvement of the same generative components in other traits and/or functions), by plasticity (environment-dependent expression of the trait) and by hemiplasy (persistence in another lineage, followed by reticulate evolution). We also examine important affinities between trait reversal and evolutionary novelties, undermining a neat distinction between what is old and what is new in evolution. This survey may provide a useful framework for future explorations of the developmental mechanisms underlying these still overlooked macroevolutionary dynamics.

Phenotype↗

PubMed2006

Water-flea males from the netherworld.

Simple treatments with hormones could unlock the expression of complex phenotypes not known to occur in nature. Using this method, Kim et al. recently obtained males from all-female populations of water fleas. The novel characters revealed by this work can be used in taxonomic identification and phylogenetic inference. Additionally, these "resurrected" males offer insights into the conservation of traits that are not exposed to natural selection.

Animals↗

PubMed2006

From embryo to adult--beyond the conventional periodization of arthropod development.

The traditional framework for the description of arthropod development takes the molt-to-molt interval as the fundamental unit of periodization, which is similar to the morphological picture of the main body axis as a series of segments. Developmental time is described as the subdivision into a few major stages of one or more instars each, which is similar to the subdivision of the main body axis into regions of one to many segments each. Parallel to recent criticisms to the segment as the fundamental building block of arthropod anatomy, we argue that, while a firm subdivision of development in stages is useful for describing arthropod ontogeny, this is limiting as a starting point for studying its evolution. Evolutionary change affects the association between different developmental processes, some of which are continuous in time whereas others are linked to the molting cycle. Events occurring but once in life (hatching; first achieving sexual maturity) are traditionally used to establish boundaries between major units of arthropod developmental time, but these boundaries are quite labile. The presence of embryonic molts, the 'gray zone' of development accompanying hatching (with the frequent delivery of an immature whose qualification as 'free-embryo' or ordinary postembryonic stage is arbitrary), and the frequent decoupling of growth and molting suggest a different view. Beyond the simple comparison of developmental schedules in terms of heterochrony, the flexible canvas we suggest for the analysis of arthropod development opens new vistas into its evolution. Examples are provided as to the origin of holometaboly and hypermetaboly within the insects.

Animals↗

PubMed2005

Conserved versus innovative features in animal body organization.

The origin of evolutionary novelties is a central topic in evolutionary developmental biology (evo-devo) studies. In any new feature, there is a conserved component that is either structural or related to the underlying genetic control, but it is not always obvious what is really new and what is conserved. Nevertheless, disentangling this blending of old and new features is basic to understanding mechanisms of evolutionary change. The origin of arthropod appendages illustrates the complexity in tracing the origin of evolutionary novelties. At the base of the lineage, the main body axis was already segmented and antero-posteriorly patterned, and the genetic tool kit required to form lateral outgrowths was already available. The novelty was possibly the developmental decision to "read" the available axial information and to exploit it for differentiating segmentally patterned and axially segmented appendages. Some important novelties bridge the gap between what have been traditionally distinguished as systemic and local changes. For example, the origin of the body cavities evolved by several animal groups may have been initiated by simple changes in cell-to-cell adhesive properties. Any possible change in an existing ontogenetic pathway has the potential to generate novelties.

Animals↗

PubMed2004

Evo-devo perspectives on segmentation: model organisms, and beyond.

Bilaterian animals show a diverse array of segmental patterns and segmentation processes. Differences in pattern and process emerge both in comparisons of taxa and among sets of serial structures within one animal. Diversity in developmental mechanisms of segmentation and their genetic control is reflected in the modes in which segmentation evolves, which are difficult to accommodate within the traditional concept of segments as modular building blocks. Thus, in spite of the apparent simplicity of segmental patterns, studying the evolution of segmentation requires an approach that, in an adequate comparative framework, combines the efforts of researchers of genes, cells, embryos and post-embryonic stages.

Journal Article↗

PubMed2003

Exploring developmental modes in a fossil arthropod: growth and trunk segmentation of the trilobite Aulacopleura konincki.

Trilobites offer the opportunity to explore postembryonic development within the fossil record of arthropod evolution. In contrast to most trilobites, the Silurian proetid Aulacopleura konincki from the Czech Republic exhibits marked variation in the mature number of thoracic segments, with five morphs with 18-22 thoracic segments. The combination of abundant articulated specimens available from a narrow stratigraphic interval and segmental intraspecific variation makes this trilobite singularly useful for studying postembryonic growth and segmentation. Trunk segmentation followed a hemianamorphic pattern, as seen in other arthropods and as characteristic of the Trilobita; during a first anamorphic phase, segments were accreted, while in the subsequent epimorphic phase, segmentation did not proceed further despite continued growth. Size increment during the anamorphic phase was targeted and followed Dyar's rule, a geometric progression typical of many arthropods. We consider alternative hypotheses for the control of the switch from anamorphic to epimorphic phases of development. Our analysis favors a scenario in which the mature number of thoracic segments was determined quite early in development rather than at a late stage in association with a critical size threshold. This study demonstrates that hypotheses concerning developmental pattern and control can be tested in organisms belonging to an extinct clade.

Animals↗

PubMedDate not supplied

Trunk segment numbers and sequential segmentation in myriapods.

Sequential segmentation from a posterior "proliferative zone" is considered to be the primitive mechanism of segmentation in arthropods. Several studies of embryonic and post-embryonic development and gene expression suggest that this occurs in all major arthropod taxa. Sequential segmentation is often associated with the idea of posterior production of body units that accumulate along the main body axis. However, the precise mechanism of sequential segmentation has not been identified yet, and, while searching for the genetic circuitry able to generate a first periodic pattern in the embryo, we can at least outline the distinctive role in segmentation of a proliferative zone. A perusal of myriapod segmentation patterns suggests that these patterns result from multi-layered developmental processes, where gene expression and epigenetic mechanisms interact in a nonstrictly hierarchical way. The posterior zone is possibly a zone of periodic signal production, but, in general, the resulting segmental pattern is not completely attributable to the activity of the signal generator. In this sense, a posterior proliferative zone would be more a "segmental organizer" than a "segment generator."

Animals↗