Revealing the mechanisms of the rostral shift of pelvic fins among teleost fishes

In teleost fishes, the position of the pelvic fins shift during evolution; this positional shift seems to have diversified their locomotion and feeding behavior, thereby expanding the habitats of these fishes. Thus, such a positional shift of the pelvic fins is one of the significant features of teleost fishes from evolutionary, embryological, and taxonomic viewpoints, but no studies to date have investigated the mechanism for the rostral shift of the pelvic fins from the anal region in teleosts. Examining the fate of the prospective pelvic fin cells of the zebrafish Danio rerio and the Nile tilapia Oreochromis niloticus embryos demonstrates that the prospective pelvic fin cells are originally located near the anus, as seen in tetrapods, but their position shifts with respect to the body trunk after its protrusion from the yolk surface. In this article, we highlight such recent findings and discuss the mechanisms of pelvic fin evolution among teleost fishes.     

A developmental transition in growth control during zebrafish caudal fin development

A long-standing question in developmental biology is how do growing and developing animals achieve form and then maintain it. We have revealed a critical transition in growth control during zebrafish caudal fin development, wherein a switch from allometric to isometric growth occurs. This morphological transition led us to hypothesize additional physiological changes in growth control pathways. To test this, we fasted juvenile and adult zebrafish. Juvenile fins continued allometric growth until development of the mature bi-lobed shape was completed. In contrast, the isometric growth of mature adult fins arrested within days of initiating a fast. We explored the biochemical basis of this difference in physiology between the two phases by assessing the sensitivity to rapamycin, a drug that blocks a nutrient-sensing pathway. We show that the nutrition-independent, allometric growth phase is resistant to rapamycin at 10-fold higher concentrations than are effective at arresting growth in the nutrition-dependent, isometric growth phase. We thus link a morphological transition in growth control between allometric and isometric growth mechanisms to different physiological responses to nutritional state of the animal and finally to different pharmacological responses to a drug (rapamycin) that affects the nutrition-sensing mechanism described from yeast to human.     

Function and structure in the paired fins of scorpaeniform fishes

Synopsis The paired fins of the basic, ancestral type of free-swimming acanthopterygian teleost serve primarily in guiding the forward course of movement and in maneuvering within the water column. In various scorpaeniform fishes the paired fins have taken on a number of other functions associated with a bottom-living mode of life. Among these are: defense against predation, probing for food items, propping the forward part of the body away from the bottom, progressing over it, digging into it, and the development of a suction disc for attachment to it. The relationship between these developments and paired-fin structure is the subject of the paper.     

Correlated evolution of body and fin morphology in the cichlid fishes

Body and fin shapes are chief determinants of swimming performance in fishes. Different configurations of body and fin shapes can suit different locomotor specializations. The success of any configuration is dependent upon the hydrodynamic interactions between body and fins. Despite the importance of body–fin interactions for swimming, there are few data indicating whether body and fin configurations evolve in concert, or whether these structures vary independently. The cichlid fishes are a diverse family whose well‐studied phylogenetic relationships make them ideal for the study of macroevolution of ecomorphology. This study measured body, and caudal and median fin morphology from radiographs of 131 cichlid genera, using morphometrics and phylogenetic comparative methods to determine whether these traits exhibit correlated evolution. Partial least squares canonical analysis revealed that body, caudal fin, dorsal fin, and anal fin shapes all exhibited strong correlated evolution consistent with locomotor ecomorphology. Major patterns included the evolution of deep body profiles with long fins, suggestive of maneuvering specialization; and the evolution of narrow, elongate caudal peduncles with concave tails, a combination that characterizes economical cruisers. These results demonstrate that body shape evolution does not occur independently of other traits, but among a suite of other morphological changes that augment locomotor specialization.     

Structure of supporting elements in the dorsal fin of percid fishes

The dorsal fin is one of the most varied swimming structures in Acanthomorpha, the spiny‐finned fishes. This fin can be present as a single contiguous structure supported by bony spines and soft lepidotrichia, or it may be divided into an anterior, spiny dorsal fin and a posterior, soft dorsal fin. The freshwater fish family Percidae exhibits especially great variation in dorsal fin spacing, including fishes with separated fins of varying gap length and fishes with contiguous fins. We hypothesized that fishes with separated dorsal fins, especially those with large gaps between fins, would have stiffened fin elements at the leading edge of the soft dorsal fin to resist hydrodynamic loading during locomotion. For 10 percid species, we measured the spacing between dorsal fins and calculated the second moment of area of selected spines and lepidotrichia from museum specimens. There was no significant relationship between the spacing between dorsal fins and the second moment of area of the leading edge of the soft dorsal fin.     

Integration and modularity of teleostean pectoral fin shape and its role in the diversification of acanthomorph fishes

Phenotypic integration and modularity describe the strength and pattern of interdependencies between traits. Integration and modularity have been proposed to influence the trajectory of evolution, either acting as constraints or facilitators. Here, we examine trends in the integration and modularity of pectoral fin morphology in teleost fishes using geometric morphometrics. We compare the fin shapes of the highly diverse radiation of acanthomorph fishes to lower teleosts. Integration and modularity are measured using two‐block partial least squares analysis and the covariance ratio coefficient between the radial bones and lepidotrichia of the pectoral fins. We show that the fins of acanthomorph fishes are more tightly integrated but also more morphologically diverse and faster evolving compared to nonacanthomorph fishes. The main pattern of shape covariation in nonacanthomorphs is concordant with the main trajectory of evolution between nonacanthomorphs and acanthomorphs. Our findings support a facilitating role for integration during the acanthomorph diversification. Potential functional consequences and developmental mechanisms of fin integration are discussed.     

Cloning and embryonic expression of six wnt genes in the medaka (Oryzias latipes) with special reference to expression of wnt5a in the pectoral fin buds

WNTs are secreted signaling molecules which control cell differentiation and proliferation. They are known to play essential roles in various developmental processes. Wnt genes have been identified in a variety of animals, and it has been shown that their amino acid sequences are highly conserved throughout evolution. To investigate the role of wnt genes during fish development from the evolutionary viewpoint, six medaka wnt genes (wnt4, wnt5a, wnt6, wnt7b, wnt8b and wnt8-like) were isolated and their embryonic expression was examined. These wnt genes were expressed in various tissues during embryonic development, and most of their expression patterns were conserved or comparable to those of other vertebrates. Thus, these wnt genes may be useful as molecular markers to investigate development and organogenesis using the medaka. Focus was on wnt5a, which was expressed in the pectoral fin buds, because its expression pattern was particularly comparable to that in tetrapod limbs. Its detailed expression pattern was further examined during pectoral fin bud development. The conservation and diversification of Wnt5a expression through the evolutionary transition from fish fins to tetrapod limbs is discussed.     

Saltatory control of isometric growth in the zebrafish caudal fin is disrupted in long fin and rapunzel mutants

Zebrafish fins grow by sequentially adding new segments of bone to the distal end of each fin ray. In wild type zebrafish, segment addition is regulated such that an isometric relationship is maintained between fin length and body length over the lifespan of the growing fish. Using a novel, surrogate marker for fin growth in conjunction with cell proliferation assays, we demonstrate here that segment addition is not continuous, but rather proceeds by saltation. Saltation is a fundamental growth mechanism shared by disparate vertebrates, including humans. We further demonstrate that segment addition proceeds in conjunction with cyclic bursts of cell proliferation in the distal fin ray mesenchyme. In contrast, cells in the distal fin epidermis proliferate at a constant rate throughout the fin ray growth cycle. Finally, we show that two separate fin overgrowth mutants, long fin and rapunzel, bypass the stasis phase of the fin ray growth cycle to develop asymmetrical and symmetrical fin overgrowth, respectively.     

bmp1 and mini fin are functionally redundant in regulating formation of the zebrafish dorsoventral axis

Drosophila metalloproteinase Tolloid (TLD) is responsible for cleaving the antagonist Short gastrulation (SOG), thereby regulating signaling by the bone morphogenetic protein (BMP) Decapentaplegic (DPP). In mice there are four TLD-related proteinases, two of which, BMP1 and mammalian Tolloid-like 1 (mTLL1), are responsible for cleaving the SOG orthologue Chordin, thereby regulating signaling by DPP orthologues BMP2 and 4. However, although TLD mutations markedly dorsalize Drosophila embryos, mice doubly homozygous null for BMP1 and mTLL1 genes are not dorsalized in early development. Only a single TLD-related proteinase has previously been reported for zebrafish, and mutation of the zebrafish TLD gene (mini fin) results only in mild dorsalization, manifested by loss of the most ventral cell types of the tail. Here we identify and map the zebrafish BMP1 gene bmp1. Knockdown of BMP1 expression results in a mild tail phenotype. However, simultaneous knockdown of mini fin and bmp1 results in severe dorsalization resembling the Swirl (swr) and Snailhouse (snh) phenotypes; caused by defects in major zebrafish ventralizing genes bmp2b and bmp7, respectively. We conclude that bmp1 and mfn gene products functionally overlap and are together responsible for a key portion of the Chordin processing activity necessary to formation of the zebrafish dorsoventral axis.     

Heterochronically early decline of Hox expression prior to cartilage formation in the avian hindlimb zeugopod

The fibula, a zeugopod bone in the hindlimb, exhibits various morphologies in tetrapod species. The fibula in some species has a similar length with the other zeugopod element, the tibia, while other species have obvious differences in the sizes of the two elements. In the avian hindlimb, for example, the fibula is extremely short, thin, and truncated. Basic morphology of the fibula is established during development, and cartilage primordium of the bone emerges in a certain region defined by a distinct combination of expression of Hox genes (Hox code). In order to elucidate how the different morphologies are produced from a region that is defined as the fixed Hox code, we examined spatial and temporal patterns of Hoxd11/Hoxd12 expression in the developing limb bud, which defines the region from which the fibula emerges, in comparison with the sites of precartilaginous mesenchymal condensations representing regions for cartilage formation among chick, mouse, and gecko embryos. We found that in the chick hindlimb, expression of Hoxd11/Hoxd12 decreased and disappeared from the presumptive zeugopod region before cartilage formation. This heterochronically early decline of expression of Hox genes is strongly correlated with the peculiar trait of the fibula in the avian hindlimb, since in the other species examined, expression of those genes continued after the onset of cartilage formation. This is morphological phenotype-related because the early disappearance was not seen in the chick forelimb. Our results suggest that temporal change of the Hox code governs diversification in morphology of homologous structures among related species.     

Developmental genetic basis for the evolution of pelvic fin loss in the pufferfish Takifugu rubripes

Paired appendages were a key developmental innovation among vertebrates and they eventually evolved into limbs. Ancient developmental control systems for paired fins and limbs are broadly conserved among gnathostome vertebrates. Some lineages including whales, some salamanders, snakes, and many ray-fin fish, independently lost the pectoral, pelvic, or both appendages over evolutionary time. When different taxa independently evolve similar developmental morphologies, do they use the same molecular genetic mechanisms? To determine the developmental genetic basis for the evolution of pelvis loss in the pufferfish Takifugu rubripes (fugu), we isolated fugu orthologs of genes thought to be essential for limb development in tetrapods, including limb positioning (Hoxc6, Hoxd9), limb bud initiation (Pitx1, Tbx4, Tbx5), and limb bud outgrowth (Shh, Fgf10), and studied their expression patterns during fugu development. Results showed that bud outgrowth and initiation fail to occur in fugu, and that pelvis loss is associated with altered expression of Hoxd9a, which we show to be a marker for pelvic fin position in three-spine stickleback Gasterosteus aculeatus. These results rule out changes in appendage outgrowth and initiation genes as the earliest developmental defect in pufferfish pelvic fin loss and suggest that altered Hoxd9a expression in the lateral mesoderm may account for pelvis loss in fugu. This mechanism appears to be different from the mechanism for pelvic loss in stickleback, showing that different taxa can evolve similar phenotypes by different mechanisms.     

The duplication of the <Emphasis Type="Italic">Hox</Emphasis> gene clusters in teleost fishes

Higher teleost fishes, including zebrafish and fugu, have duplicated their Hox genes relative to the gene inventory of other gnathostome lineages. The most widely accepted theory contends that the duplicate Hox clusters orginated synchronously during a single genome duplication event in the early history of ray-finned fishes. In this contribution we collect and re-evaluate all publicly available sequence information. In particular, we show that the short Hox gene fragments from published PCR surveys of the killifish Fundulus heteroclitus, the medaka Oryzias latipes and the goldfish Carassius auratus can be used to determine with little ambiguity not only their paralog group but also their membership in a particular cluster. Together with a survey of the genomic sequence data from the pufferfish Tetraodon nigroviridis we show that at least percomorpha, and possibly all eutelosts, share a system of 7 or 8 orthologous Hox gene clusters. There is little doubt about the orthology of the two teleost duplicates of the HoxA and HoxB clusters. A careful analysis of both the coding sequence of Hox genes and of conserved non-coding sequences provides additional support for the “duplication early” hypothesis that the Hox clusters in teleosts are derived from eight ancestral clusters by means of subsequent gene loss; the data remain ambiguous, however, in particular for the HoxC clusters. Assuming the “duplication early” hypothesis we use the new evidence on the Hox gene complements to determine the phylogenetic positions of gene-loss events in the wake of the cluster duplication. Surprisingly, we find that the resolution of redundancy seems to be a slow process that is still ongoing. A few suggestions on which additional sequence data would be most informative for resolving the history of the teleostean Hox genes are discussed. Supplemental material is available at http://www.bioinf.uni-leipzig.de/Publications/SUPPLEMENTS/04-006/.     

The fine structure of the fin musculature in two teleost species with different swimming modes,the puffer,Tetraodon steindachneri,and the goldfish,Carassius auratus

Summary Puffer fish (Tetraodon steindachneri) can execute precise maneuvers due to their highly specialized mode of propulsion. In the conventional locomotion exemplified by the goldfish (Carassius auratus), the fish thrusts are generated by lateral beating of the caudal fin. In contrast, the puffer generates its propulsive force by very rapid undulating movements of the pectoral, dorsal and anal fins. The fine structure of the fin muscles is identical in the two species of fishes, despite the differences in fin movement; cytologically, the fibers are intermediate between those of red and of white muscle. On the other hand, both the fusion frequency and the number of motor endplates are considerably higher in the fin muscles of the puffer than in those of the goldfish.     

Postembryonal growth and its variability of the three marine fishes with special reference to the mechanism of growth variation in fishes

1. To study the relation of growth variation to the behaviour pattern, newly hatched Hemiramphus sajori, Chrysophrys major and Zebrias zebra were reared in 30 litter aquaria during one month, and body length was measured four times.
2. In Hemiramphus sajori coefficient of variation of body length (CV) first increased but showed a tendency to decrease with development of schooling behaviour.
3. In Chrysophrys major CV markedly increased and mode of the distribution curve of body length inclined towards the left side, associated with appearance of aggression and cannibalism.
4. In Zebrias zebra, when behaviour pattern changed from planktonic to demersal some of the small individuals nearly ceased growing. At that time CV of body length remarkably increased and the mode of the distribution curve of body length shifted towards the right side.
5. In all the species a positive correlation was seem between specific growth rate and initial body length soon after intensive feeding began. An negative correlation was observed in most of individuals of Hemiramphus sajori after the appearance of schooling behaviour. When a conspicuous increase in CV and skewness in distribution curve took place, a separate type of correlation was seen in large and small group in the population.
6. Based on above mentioned and other materials a general mechanism of growth variation in fishes was discussed.

     

Deficiency of a transmembrane prolyl 4-hydroxylase in the zebrafish leads to basement membrane defects and compromised kidney function

Prolyl 4-hydroxylases (P4Hs) catalyze the hydroxylation of collagens and hypoxia-inducible factor (HIF)-α subunits. We studied the zebrafish homologue of the recently characterized human transmembrane P4H (P4H-TM) that can hydroxylate HIF-α, but not collagens, in vitro and influence HIF-α levels in cellulo. The zebrafish P4H-TM mRNA had its highest expression in the eye and brain and lower levels in other tissues, including the kidney. Morpholino knockdown of P4H-TM in embryos resulted in a reduction in the size of the eye and head and morphological alterations in the head from 2 days postfertilization onward. In addition, pericardial edema, regarded as a sign of kidney dysfunction, developed from 3 days postfertilization onward. The phenotype was dependent on the P4H-TM catalytic activity because similar results were obtained with morpholinos targeting either translation initiation or catalytic residues of the enzyme. Structural and functional analyses of the morphant pronephric kidneys revealed fragmented glomerular basement membranes (BMs), disorganized podocyte foot processes, and severely compromised pronephric kidney function leading to proteinuria. The opacity of the eye lens was increased due to the presence of extra nuclei and deposits, and the structure of the lens capsule BM was altered. Our data suggest that P4H-TM catalytic activity is required for the proper development of the glomerular and lens capsule BMs. Many HIF target genes were induced in the P4H-TM-deficient morphants, but the observed phenotype is not likely to be mediated at least solely via the HIF pathway, and thus P4H-TM probably has additional, as yet unknown, substrates.     

Knockdown of connexin43-mediated regulation of the zone of polarizing activity in the developing chick limb leads to digit truncation

In the developing chick wing, the use of antisense oligodeoxynucleotides to transiently knock down the expression of the gap junction protein, connexin43 (Cx43), results in limb patterning defects, including deletion of the anterior digits. To understand more about how such defects arise, the effects of transient Cx43 knockdown on the expression patterns of several genes known to play pivotal roles in limb formation were examined. Sonic hedgehog (Shh), which is normally expressed in the zone of polarizing activity (ZPA) and is required to maintain both the ZPA and the apical ectodermal ridge (AER), was found to be downregulated in treated limbs within 30 h. Bone morphogenetic protein-2 (Bmp-2), a gene downstream of Shh, was similarly downregulated. Fibroblast growth factor-8 expression, however, was unaltered 30 h after treatment but was greatly reduced at 48 h post-treatment, when the AER begins to regress. Expressions of Bmp-4 and Muscle segment homeobox-like gene (Msx-1) were not affected at any of the time points examined. Cx43 expression is therefore involved in some, but not all patterning cascades, and appears to play a role in the regulation of ZPA activity.     

Modelling seasonal increments in size to determine the onset of annual growth in fishes

A new method based on modelling of seasonal growth increments ( G _SI) in total length was found useful for assessing the date of onset of annual growth for 16 fish species in a temperate fluvial lake. Model comparisons indicated that polynomial (linear or quadratic) functions provided better fits to seasonal growth and were more likely to avoid convergence problems than alternative non-linear models. There was little evidence for differences in the date of onset of growth between years, nor among age classes within individual species. The onset of growth also was to some extent synchronized among species and was concentrated within a narrow temporal window of c. 2 weeks, between 18 May and 2 June, which corresponded to mean water temperatures between 16·1 and 17·3° C. There was no apparent relationship between date of onset and species' thermal preferenda or thermal preferences. By producing a point estimate along with appropriate 95% CI, the G _SI method provides useful information on the onset of growth and the uncertainty about that estimate. The G _SI analyses can contribute to a better understanding of environmental influences on the onset of growth and the length of the growing season, and of thermal thresholds for growth, including their use in calculation of degree-day metrics.     

Relative growth of the limbs and trunk in sifakas: Heterochronic,ecological, and functional considerations

Limb, trunk, and body weight measurements were obtained for growth series of Milne-Edwards's diademed sifaka, Propithecus diadema edwardsi, and the golden-crowned sifaka, Propithecus tattersalli. Similar measures were obtained also for primarily adults of two subspecies of the western sifaka: Propithecus verreauxi coquereli, Coquerel's sifaka, and Propithecus verreauxi verreauxi, Verreaux's sifaka. Ontogenetic series for the larger-bodied P. d. edwardsi and the smaller-bodied P. tattersalli were compared to evaluate whether species-level differences in body proportions result from the differential extension of common patterns of relative growth. In bivariate plots, both subspecies of P. verreauxi were included to examine whether these taxa also lie along a growth trajectory common to all sifakas. Analyses of the data indicate that postcranial proportions for sifakas are ontogenetically scaled, much as demonstrated previously with cranial dimensions for all three species (Ravosa, 1992). As such, P. d. edwardsi apparently develops larger overall size primarily by growing at a faster rate, but not for a longer duration of time, than P. tattersalli and P. verreauxi; this is similar to results based on cranial data. A consideration of Malagasy lemur ecology suggests that regional differences in forage quality and resource availability have strongly influenced the evolutionary development of body-size variation in sifakas. On one hand, the rainforest environment of P. d. edwardsi imposes greater selective pressures for larger body size than the dry-forest environment of P. tattersalli and P. v. coquereli, or the semi-arid climate of P. v. verreauxi. On the other hand, as progressively smaller-bodied adult sifakas are located in the east, west, and northwest, this apparently supports suggestions that adult body size is set by dry-season constraints on food quality and distribution (i. e., smaller taxa are located in more seasonal habitats such as the west and northeast). Moreover, the fact that body-size differentiation occurs primarily via differences in growth rate is also due apparently to differences in resource seasonality (and juvenile mortality risk in turn) between the eastern rainforest and the more temperate northeast and west. Most scaling coefficients for both arm and leg growth range from slight negative allometry to slight positive allometry. Given the low intermembral index for sifakas, which is also an adaptation for propulsive hindlimb-dominated jumping, this suggests that differences in adult limb proportions are largely set prenatally rather than being achieved via higher rates of postnatal hindlimb growth. Our analyses further indicate that the larger-bodied P. d. edwardsi has a higher adult intermembral index than P. tattersalli and P. verreauxi, thus supporting the allometric argument regarding the interspecific scaling of limb proportions in arboreal primates which employ vertical postures (Cartmill, 1974,1985; Jungers, 1978, 1985). Lastly, additional analyses indicate that P. d. edwardsi exhibits significant sexual dimorphism where adult females are larger than adult males in about one-third of all adult comparisons, whereas P. tattersalli exhibits significant sexual dimorphism in about one-fifth of all adult comparisons. Among western sifakas, adult P. v. coquereli exhibit significant sex dimorphism in about one-third of all comparisons, whereas adult P. v. uerreauxi show no significant differences between the sexes. Given that all taxa are ontogenetically scaled, this suggests that sexual dimorphism develops via such processes as well. Interestingly, our data indicate that sex dimorphism is allometric, with larger-bodied taxa like P. d. edwardsi being more dimorphic.