Fishes are both extremely diverse and morphologically disparate. Part of this disparity can be ob... more 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 appenda...
Modularity is considered a prerequisite for the evolvability of biological systems. This is becau... more 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 ...
Actinopterygians demonstrate high levels of morphological disparity, especially in the variation ... more 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.
Developmental systems determine whether selectively useful variation arises (eg, Maynard Smith et... more Developmental systems determine whether selectively useful variation arises (eg, Maynard Smith et a/., I985; Wagner, I988; Gerhart and Kirschner, 2007). They can reduce that variation via canalization or by structuring it into integrated complexes, thereby preventing ...
Modularity is considered a prerequisite for the evolvability of biological systems. This is becau... more 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.
Background: Fishes are extremely speciose and also highly disparate in their fin configurations, ... more Background: 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. Results: 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 f ins.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. Conclusions: 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 .
The semi-dominant Br mutation affects presphenoid growth, producing the facial retrognathism and ... more The semi-dominant Br mutation affects presphenoid growth, producing the facial retrognathism and globular neuro- cranial vault that characterize heterozygotes. We analysed the impact of this mutation on skull shape, comparing heterozygotes to wildtype mice, to determine if the effects are skull-wide or confined to the sphenoid region targeted by the mutation. In addition, we examined patterns of variability of shape for the skull as a whole and for three regions (basicranium, face and neurocranium). We found that the Br mice differed significantly from wildtype mice in skull shape in all three regions as well as in the shape of the skull as a whole. However, the sig- nificant increases in variance and fluctuating asymmetry were found only in the basicranium of mutant mice. These results suggest that the mutation has a significant effect on the underlying developmental architecture of the skull, which produces an increase in phenotypic variability that is localized to the anatomical region in which the mean phenotype is most dramatically affected. These results suggest that the same developmental mechanisms that produce the change in phenotypic mean also produce the change in variance.
Fishes are both extremely diverse and morphologically disparate. Part of this disparity can be ob... more 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 appenda...
Modularity is considered a prerequisite for the evolvability of biological systems. This is becau... more 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 ...
Actinopterygians demonstrate high levels of morphological disparity, especially in the variation ... more 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.
Developmental systems determine whether selectively useful variation arises (eg, Maynard Smith et... more Developmental systems determine whether selectively useful variation arises (eg, Maynard Smith et a/., I985; Wagner, I988; Gerhart and Kirschner, 2007). They can reduce that variation via canalization or by structuring it into integrated complexes, thereby preventing ...
Modularity is considered a prerequisite for the evolvability of biological systems. This is becau... more 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.
Background: Fishes are extremely speciose and also highly disparate in their fin configurations, ... more Background: 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. Results: 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 f ins.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. Conclusions: 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 .
The semi-dominant Br mutation affects presphenoid growth, producing the facial retrognathism and ... more The semi-dominant Br mutation affects presphenoid growth, producing the facial retrognathism and globular neuro- cranial vault that characterize heterozygotes. We analysed the impact of this mutation on skull shape, comparing heterozygotes to wildtype mice, to determine if the effects are skull-wide or confined to the sphenoid region targeted by the mutation. In addition, we examined patterns of variability of shape for the skull as a whole and for three regions (basicranium, face and neurocranium). We found that the Br mice differed significantly from wildtype mice in skull shape in all three regions as well as in the shape of the skull as a whole. However, the sig- nificant increases in variance and fluctuating asymmetry were found only in the basicranium of mutant mice. These results suggest that the mutation has a significant effect on the underlying developmental architecture of the skull, which produces an increase in phenotypic variability that is localized to the anatomical region in which the mean phenotype is most dramatically affected. These results suggest that the same developmental mechanisms that produce the change in phenotypic mean also produce the change in variance.
Les fossiles comme outils dans l’interprétation de l’évolution des nageoires chez les poissons
A... more Les fossiles comme outils dans l’interprétation de l’évolution des nageoires chez les poissons
Auteurs : Olivier Larouche(1), Miriam L. Zelditch(2) et Richard Cloutier(1) (1) Laboratoire de Paléontologie et de Biologie évolutive, Université du Québec à Rimouski; Membres du CSBQ. (2) Museum of Paleontology, University of Michigan.
Les poissons constituent un groupe à la fois très riche en espèces mais aussi en diversité de formes corporelles, notamment en raison de différences dans la configuration des nageoires. Afin de mieux comprendre l’origine de ces différences, il est nécessaire de clarifier le scénario évolutif traduisant l’apparition séquentielle des nageoires. Celui-ci n’est pas bien compris pour deux raisons principales : (1) les relations phylogénétiques entre les agnathes (poissons sans mâchoires) et les gnathostomes (poissons avec mâchoires) ne font pas l’objet d’un consensus, et (2) les relations d’homologie entre les nageoires des agnathes et celles des gnathostomes sont incertaines. Or, la majorité des agnathes ne sont connus que par des taxons fossiles. De ce fait, une bonne connaissance des états de caractères de ces taxons fossiles est essentielle pour interpréter la séquence évolutive d’apparition des nageoires. À ces fins, un super-arbre phylogénétique a été produit, synthétisant les résultats de 118 analyses phylogénétiques récentes, puis les données de présence/absence et de nombre des nageoires ont été superposées sur ce super-arbre. La répartition des caractères dans le super-arbre suggère entre autres que les nageoires médianes et paires seraient toutes deux apparues d’abord sous la forme de structures allongées qui auraient donc été les précurseurs des nageoires aux insertions plus exigües que l’on retrouve chez les poissons plus avancés.
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Papers by Miriam Zelditch
Results: 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 f ins.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.
Conclusions: 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 .
Results: 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 f ins.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.
Conclusions: 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 .
Auteurs : Olivier Larouche(1), Miriam L. Zelditch(2) et Richard Cloutier(1)
(1) Laboratoire de Paléontologie et de Biologie évolutive, Université du Québec à Rimouski; Membres du CSBQ.
(2) Museum of Paleontology, University of Michigan.
Les poissons constituent un groupe à la fois très riche en espèces mais aussi en diversité de formes corporelles, notamment en raison de différences dans la configuration des nageoires. Afin de mieux comprendre l’origine de ces différences, il est nécessaire de clarifier le scénario évolutif traduisant l’apparition séquentielle des nageoires. Celui-ci n’est pas bien compris pour deux raisons principales : (1) les relations phylogénétiques entre les agnathes (poissons sans mâchoires) et les gnathostomes (poissons avec mâchoires) ne font pas l’objet d’un consensus, et (2) les relations d’homologie entre les nageoires des agnathes et celles des gnathostomes sont incertaines. Or, la majorité des agnathes ne sont connus que par des taxons fossiles. De ce fait, une bonne connaissance des états de caractères de ces taxons fossiles est essentielle pour interpréter la séquence évolutive d’apparition des nageoires. À ces fins, un super-arbre phylogénétique a été produit, synthétisant les résultats de 118 analyses phylogénétiques récentes, puis les données de présence/absence et de nombre des nageoires ont été superposées sur ce super-arbre. La répartition des caractères dans le super-arbre suggère entre autres que les nageoires médianes et paires seraient toutes deux apparues d’abord sous la forme de structures allongées qui auraient donc été les précurseurs des nageoires aux insertions plus exigües que l’on retrouve chez les poissons plus avancés.