Modularity is considered a prerequisite for the evolvability of biological systems. This is because in theory, individual modules can follow quasi-independent evolutionary trajectories or evolve at ...different rates compared to other aspects of the organism. This may influence the potential of some modules to diverge, leading to differences in disparity. Here, we investigated this relationship between modularity, rates of morphological evolution and disparity using a phylogenetically diverse sample of ray-finned fishes. We compared the support for multiple hypotheses of evolutionary modularity and asked if the partitions delimited by the best-fitting models were also characterized by the highest evolutionary rate differentials. We found that an evolutionary module incorporating the dorsal, anal and paired fins was well supported by the data, and that this module evolves more rapidly and consequently generates more disparity than other modules. This suggests that modularity may indeed promote morphological disparity through differences in evolutionary rates across modules.
Fishes are extremely speciose and also highly disparate in their fin configurations, more specifically in the number of fins present as well as their structure, shape, and size. How they achieved ...this remarkable disparity is difficult to explain in the absence of any comprehensive overview of the evolutionary history of fish appendages. Fin modularity could provide an explanation for both the observed disparity in fin configurations and the sequential appearance of new fins. Modularity is considered as an important prerequisite for the evolvability of living systems, enabling individual modules to be optimized without interfering with others. Similarities in developmental patterns between some of the fins already suggest that they form developmental modules during ontogeny. At a macroevolutionary scale, these developmental modules could act as evolutionary units of change and contribute to the disparity in fin configurations. This study addresses fin disparity in a phylogenetic perspective, while focusing on the presence/absence and number of each of the median and paired fins.
Patterns of fin morphological disparity were assessed by mapping fin characters on a new phylogenetic supertree of fish orders. Among agnathans, disparity in fin configurations results from the sequential appearance of novel fins forming various combinations. Both median and paired fins would have appeared first as elongated ribbon-like structures, which were the precursors for more constricted appendages. Among chondrichthyans, disparity in fin configurations relates mostly to median fin losses. Among actinopterygians, fin disparity involves fin losses, the addition of novel fins (e.g., the adipose fin), and coordinated duplications of the dorsal and anal fins. Furthermore, some pairs of fins, notably the dorsal/anal and pectoral/pelvic fins, show non-independence in their character distribution, supporting expectations based on developmental and morphological evidence that these fin pairs form evolutionary modules.
Our results suggest that the pectoral/pelvic fins and the dorsal/anal fins form two distinct evolutionary modules, and that the latter is nested within a more inclusive median fins module. Because the modularity hypotheses that we are testing are also supported by developmental and variational data, this constitutes a striking example linking developmental, variational, and evolutionary modules.
Fishes are both extremely diverse and morphologically disparate. Part of this disparity can be observed in the numerous possible fin configurations that may differ in terms of the number of fins as ...well as fin shapes, sizes and relative positions on the body. Here, we thoroughly review the major patterns of disparity in fin configurations for each major group of fishes and discuss how median and paired fin homologies have been interpreted over time. When taking into account the entire span of fish diversity, including both extant and fossil taxa, the disparity in fin morphologies greatly complicates inferring homologies for individual fins. Given the phylogenetic scope of this review, structural and topological criteria appear to be the most useful indicators of fin identity. We further suggest that it may be advantageous to consider some of these fin homologies as nested within the larger framework of homologous fin‐forming morphogenetic fields. We also discuss scenarios of appendage evolution and suggest that modularity may have played a key role in appendage disparification. Fin modules re‐expressed within the boundaries of fin‐forming fields could explain how some fins may have evolved numerous times independently in separate lineages (e.g., adipose fin), or how new fins may have evolved over time (e.g., anterior and posterior dorsal fins, pectoral and pelvic fins). We favour an evolutionary scenario whereby median appendages appeared from a unique field of competence first positioned throughout the dorsal and ventral midlines, which was then redeployed laterally leading to paired appendages.
Marine habitats vary widely in structure, from incredibly complex coral reefs to simpler deep water and open ocean habitats. Hydromechanical models of swimming kinematics and microevolutionary ...studies suggest that these habitats select for different body shape characteristics. Fishes living in simple habitats are predicted to experience selection for energy-efficient sustained swimming, which can be achieved by fusiform body shapes. In contrast, fishes living in complex habitats are predicted to be under selection for maneuverability, which can be enhanced by deep-bodied and laterally compressed forms. To look for a signature of these processes at a broad macroevolutionary scale, we quantified the body shapes of 3322 species of marine teleostean fishes using a series of linear measurements. We scored each species for whether they were reef-associated or not and tested for morphological differences using a phylogenetic framework. Our results confirmed significant overall shape differences between reef-associated teleosts and those occupying structurally simpler marine habitats. Reef-associated species have, on average, deeper bodies and higher depth-to-width ratios, while non-reef species are more streamlined with narrower and shallower caudal peduncles. Despite the numerous evolutionary forces that may influence body shapes on a broad macroevolutionary scale, our results reveal differences in body shapes between reef-associated and non-reef species that are consistent with hydromechanical models of swimming kinematics as well as with microevolutionary patterns.
Actinopterygians demonstrate high levels of morphological disparity, especially in the variation of fin positions, sizes and shapes. One hypothesis to explain the diversity of fin morphologies is ...that it is facilitated by a modular organization. According to this hypothesis, fin modules would be quasi-independent during ontogeny or evolution, facilitating their evolvability. We investigated variational modularity of fins in two cyprinid species, the zebrafish (
Danio rerio
) and the Northern redbelly dace (
Chrosomus eos
), to determine which subsets of fins are quasi-independent and which are most highly integrated in positioning. Hypotheses of modularity were evaluated using a combination of methods suitable for analyses of landmarks. The hypothesis that the dorsal and anal fins belong to a posterior trunk and tail module is strongly supported, a finding that can be explained by the use of subcarangiform locomotion in these two species. There is also some support for the hypothesis that the paired fins and head region each constitute variational modules. The support for fin variational modules is weaker than expected considering the wealth of developmental evidence supporting fin modularity. This might be related to a dissociation of the fin positioning modules during actinopterygian evolution, a process that had already been suggested for the dorsal and anal fins. Alternatively, the fin modules inferred from developmental data might not directly translate into variational modules: variational modules can incorporate the signals from numerous partially overlapping developmental processes so that one to one correspondence between developmental and variational modules is not always expected.
Androgens are major regulators of prostate cell growth and physiology. In the human prostate, androgens are inactivated in the form of hydrophilic glucuronide conjugates. These metabolites are formed ...by the two human UGT2B15 UGT (UDP-glucuronosyltransferase) 2B15 and UGT2B17 enzymes. The FXR (farnesoid X receptor) is a bile acid sensor controlling hepatic and/or intestinal cholesterol, lipid and glucose metabolism. In the present study, we report the expression of FXR in normal and cancer prostate epithelial cells, and we demonstrate that its activation by chenodeoxycholic acid or GW4064 negatively interferes with the levels of UGT2B15 and UGT2B17 mRNA and protein in prostate cancer LNCaP cells. FXR activation also causes a drastic reduction of androgen glucuronidation in these cells. These results point out activators of FXR as negative regulators of androgen-conjugating UGT expression in the prostate. Finally, the androgen metabolite androsterone, which is also an activator of FXR, dose-dependently reduces the glucuronidation of androgens catalysed by UGT2B15 and UGT2B17 in an FXR-dependent manner in LNCaP cells. In conclusion, the present study identifies for the first time the activators of FXR as important regulators of androgen metabolism in human prostate cancer cells.
Actinopterygians are the most diversified clade of extant vertebrates. Their impressive morphological disparity bears witness to tremendous ecological diversity. Modularity, the organization of ...biological systems into quasi-independent anatomical/morphological units, is thought to increase evolvability of organisms and facilitate morphological diversification. Our study aims to quantify patterns of variational modularity in a model actinopterygian, the zebrafish (
), using three-dimensional geometric morphometrics on osteological structures isolated from micro-CT scans. A total of 72 landmarks were digitized along cranial and postcranial ossified regions of 30 adult zebrafishes. Two methods were used to test modularity hypotheses, the covariance ratio and the distance matrix approach. We find strong support for two modules, one comprised paired fins and the other comprised median fins, that are best explained by functional properties of subcarangiform swimming. While the skull is tightly integrated with the rest of the body, its intrinsic integration is relatively weak supporting previous findings that the fish skull is a modular structure. Our results provide additional support for the recognition of similar hypotheses of modularity identified based on external morphology in various teleosts, and at least two variational modules are proposed. Thus, our results hint at the possibility that internal and external modularity patterns may be congruent.
Regionalization of the vertebral column occurred early during vertebrate evolution and has been extensively investigated in mammals. However, less data are available on vertebral regions of crown ...gnathostomes. This is particularly true for batoids (skates, sawfishes, guitarfishes, and rays) whose vertebral column has long been considered to be composed of the same two regions as in teleost fishes despite the presence of a synarcual. However, the numerous vertebral units in chondrichthyans may display a more complex regionalization pattern than previously assumed and the intraspecific variation of such pattern deserves a thorough investigation. In this study, we use micro‐computed tomography (µCT) scans of vertebral columns of a growth series of thorny skates Amblyraja radiata to provide the first fine‐scale morphological description of vertebral units in a batoids species. We further investigate axial regionalization using a replicable clustering analysis on presence/absence of vertebral elements to decipher the regionalization of the vertebral column of A. radiata. We identify four vertebral regions in this species. The two anteriormost regions, named synarcual and thoracic, may undergo strong developmental or functional constraints because they display stable patterns of shapes and numbers of vertebral units across all growth stages. The third region, named hemal transitional, is characterized by high inter‐individual morphological variation and displays a transition between the monospondylous (one centrum per somite) to diplospondylous (two centra per somite) conditions. The posteriormost region, named caudal, is subdivided into three sub‐regions with shapes changing gradually along the anteroposterior axis. These regionalized patterns are discussed in light of ecological habits of skates.
The vertebral column of a skate species is described in details for different ontogenetic stages. Four regions are recognized: the synarcual and the thoracic regions display few inter‐individual variability, as opposed to the hemal transitional and caudal regions. The importance of describing transitional vertebrae is highlighted to better understand functional and developmental aspects of the vertebral column.
Abstract
Modularity is a ubiquitous feature of organismal design that plays an important role in structuring patterns of morphological diversification. Modularity can facilitate evolutionary changes ...by allowing subsets of traits to coevolve as integrated units and follow quasi-independent evolutionary trajectories, a pattern that may be particularly consequential in the case of highly complex morphological structures. Here we examine modularity in a complex and highly kinetic structure, the teleost skull, and ask if a modular organization of the skull has influenced the diversification dynamics of the shapes of its osteological components across the labrid phylogeny. We compiled one of the largest 3D morphological data sets of fishes to date and used geometric morphometrics to quantify patterns of cranial shape evolution across 184 species of wrasses (Labridae). We then tested several hypotheses of modularity inspired by functional and developmental relationships between cranial bones and compared phenotypic rates among modules. We also compared the fit of models of trait evolution for the entire skull and the various articulated bones that it comprises. Our analyses indicated strong support for a 2-module hypothesis, one that encompasses the oral and pharyngeal jaws and another module comprised of the neurocranium, hyoid apparatus, and operculum. This functional hypothesis yielded one of the highest significant rate differentials across modules, yet we also found that the best-fitting models of trait evolution differed among skull bones. These results suggest that modularity can influence morphological diversification in complex biological structures via differences in both the tempo and mode of evolutionary change. 3D geometric morphometrics, cranial morphology, evolutionary modularity, Labridae, phenotypic rates, structural complexity.
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