Asymmetry In Fish Research Articles

Genetic assimilation and the evolution of direction of genital asymmetry in anablepid fishes.

Phylogenetic comparative studies suggest that the direction of deviation from bilateral symmetry (sidedness) might evolve through genetic assimilation; however, the changes in sidedness inheritance remain largely unknown. We investigated the evolution of genital asymmetry in fish of the family Anablepidae, in which males' intromittent organ (the gonopodium, a modified anal fin) bends asymmetrically to the left or the right. In most species, males show a 1 : 1 ratio of left-to-right-sided gonopodia. However, we found that in three species left-sided males are significantly more abundant than right-sided ones. We mapped sidedness onto a new molecular phylogeny, finding that this left-sided bias likely evolved independently three times. Our breeding experiment in a species with an excess of left-sided males showed that sires produced more left-sided offspring independently of their own sidedness. We propose that sidedness might be inherited as a threshold trait, with different thresholds across species. This resolves the apparent paradox that, while there is evidence for the evolution of sidedness, commonly there is a lack of support for its heritability and no response to artificial selection. Focusing on the heritability of the left : right ratio of offspring, rather than on individual sidedness, is key for understanding how the direction of asymmetry becomes genetically assimilated.

How much fluctuating asymmetry in fish is affected by mercury concentration in the Guanabara Bay, Brazil?

This study aims to analyze if the fluctuating asymmetry (FA) of the Corocoro grunt Orthopristis ruber is affected by mercury concentration in Brazilian Southeastern eutrophicated bay. The O. ruber fishes were collected in two areas of the Guanabara Bay, Rio de Janeiro, Brazil: Vermelha Beach, influenced to ocean waters, and Paquetá Island, for greater freshwater loads of the rivers of the region, both in wet and dry seasons. Possibly availability of food resources, exposure to other pollutants and harmful agents (pesticide, algal toxicity, among others), and environmental and oceanographic factors may be reflecting on the FA detected for the O. ruber population. Mercury (Hg) is a harmful trace metal when present in the food, because of the high toxicity, high levels of absorption, and low excretion rate. Hg accumulates in human organisms through fish consumption, which may represent a risk to health. Analytical determinations of THg were performed by Direct Mercury Analyzer, following the manufacture's recommendations and following the procedure proposed by Guimarães et al. (Food Sci Nutr 4:398-408, 2015). No evidenced in the influence of THg on FA. In turn, the THg was significantly different between areas. Higher THg levels were found in O. ruber populations in the Vermelha Beach, with mean values ​​of HgT 0.08 ± 0.01mg/kg-1, and the Paquetá Island with HgT 0.05 ± 0.01mg/kg-1. Likely higher THg on the Vermelha Beach occurred due to hydrodynamic factors, increasing the bioavailability of THg from the sediment and incorporated into the food web. This indicates that the higher THg levels in the outermost area of the Guanabara Bay can directly influence the bioaccumulation of this metal in the commercially important species present in this region, through the trophic chain because O. ruber constitutes an important part of the diet of themselves.

Evaluating Morphological Asymmetry in Three Species of the Genus <i>Hydrocynus</i> from the White Nile in Sudan

The present study aimed to determine and evaluate the level of fluctuating asymmetry (FA) of morphological characters for three species of Hydrocynus from the White Nile. In H. vittatus 41% of morphological characters fluctuated to the right side and 59% to left side. In H. brevis 50% fluctuated to right and 50% to left side, while in H. forskalii 34% fluctuated to right and 66% fluctuated to left side. More scales were recorded along the lateral line on the right side of H. vittatus and H. brevis compared to H. forskalii , while more gill rakers were recorded on the left side of H. vittatus . The smallest asymmetry index was found for PVFL of the three species and the largest index was found for POL of H. brevis . Mean asymmetry index was (3.5%) in H. forskalii , (5.1%) and (4.9%) in H. vittatus and H. brevis , respectively. Absolute asymmetry values were significantly correlated with character size for the number of lateral line scales, head length, pectoral fin length and ventral fin length (P>0.05) and highly correlated for snout length and caudal peduncle length (P>0.001) in the three species. Correlations between means of bilateral characters and body size were significant (P>0.05) for the head length, pelvic fin length and pectoral spine length of the three species. This study is the first of its kind in species of the Nile fish. The present result can be a base line for further study of fluctuating asymmetry in fish and as indicators to detect the level of pollutants in the Nile and the condition of the environment and the organisms.

Laterality is Universal Among Fishes but Increasingly Cryptic Among Derived Groups.

Laterality has been studied in several vertebrates, mainly in terms of brain lateralization and behavioral laterality, but morphological asymmetry has not been extensively investigated. Asymmetry in fishes was first described in scale-eating cichlids from Lake Tanganyika, in the form of bilateral dimorphism in which some individuals, when opening their mouths, twist them to the right and others to the left. This asymmetry has a genetic basis, and is correlated with lateralized attack behaviors. This has subsequently been found in fishes from numerous taxa with various feeding habits. The generality of such morphological laterality should thus be investigated in as wide a range of fishes as possible. Using specific indicators of lateral differences in mandibles and head inclination, we find that representative species from all 60 orders of extant gnathostome fishes (both bony and cartilaginous) possess morphological laterality. Furthermore, we identify the same laterality in agnathans (hagfish and lamprey), suggesting that this trait appeared early in fish evolution and has been maintained across fish lineages. However, a comparison of asymmetry among groups of bony fishes reveals, unexpectedly, that phylogenetically more recent-groups possess less asymmetry in body structures. The universality of laterality in fishes indicates a monophyletic origin, and may have been present in the ancestors of vertebrates. Ecological factors, predator-prey interactions in particular, may be key drivers in the evolution and maintenance of dimorphism, and may also be responsible for the cryptic trend of asymmetry in derived groups. Because lungfish and coelacanths share this trait, it is likely that tetrapods also inherited it. We believe that study of this morphological laterality will provide insights into the behavioral and sensory lateralization of vertebrates.

BAC Recombineering of the Agouti Loci from Spotted Gar and Zebrafish Reveals the Evolutionary Ancestry of Dorsal-Ventral Pigment Asymmetry in Fish.

Dorsoventral pigment patterning, characterized by a light ventrum and a dark dorsum, is one of the most widespread chromatic adaptations in vertebrate body coloration. In mammals, this countershading depends on differential expression of agouti-signaling protein (ASIP), which drives a switch of synthesis of one type of melanin to another within melanocytes. Teleost fish share countershading, but the pattern results from a differential distribution of multiple types of chromatophores, with black-brown melanophores most abundant in the dorsal body and reflective iridophores most abundant in the ventral body. We previously showed that Asip1 (a fish ortholog of mammalian ASIP) plays a role in patterning melanophores. This observation leads to the surprising hypothesis that agouti may control an evolutionarily conserved pigment pattern by regulating different mechanisms in mammals and fish. To test this hypothesis, we compared two ray-finned fishes: the teleost zebrafish and the nonteleost spotted gar (Lepisosteus oculatus). By examining the endogenous pattern of asip1 expression in gar, we demonstrate a dorsoventral-graded distribution of asip1 expression that is highest ventrally, similar to teleosts. Additionally, in the first reported experiments to generate zebrafish transgenic lines carrying a bacterial artificial chromosome (BAC) from spotted gar, we show that both transgenic zebrafish lines embryos replicate the endogenous asip1 expression pattern in adult zebrafish, showing that BAC transgenes from both species contain all of the regulatory elements required for regular asip1 expression within adult ray-finned fishes. These experiments provide evidence that the mechanism leading to an environmentally important pigment pattern was likely in place before the origin of teleosts.

New case of lateral asymmetry in fishes: A new subfamily, genus and species of deep water clingfishes from Papua New Guinea, western Pacific Ocean

The unusual clingfish Protogobiesox asymmetricus n. gen, n. sp. is described on the basis of four specimens collected in deep water off the north coast of Papua New Guinea in 2012. The species is characterized by its 9–10 dorsal rays, 8 anal rays, 17–24 pectoral-fin rays, 15 principal caudal-fin rays, 3 gills, third arch with 3 gill rakers, 34–35 total vertebrae, with asymmetrical lateral bending starting behind the skull, bent at an angle of 85°–92°; skull asymmetrical in frontal view; skin naked, surface of head and body without striae; disc without adhesive papillae. A new subfamily Protogobiesocinae is described for this species and Lepadicyathus mendeleevi Prokofiev, 2005, which is redescribed. The new subfamily is compared within the family; keys to the subfamilies of Gobiesocidae and the species within the new subfamily are presented; its phylogenetic relationship to other gobiesocids is inferred based on a multi-locus DNA dataset.

Predominance of parallel- and cross-predation in anglerfish

Several studies in the last 20 years have revealed that morphological asymmetry in fish can be characterized as ‘antisymmetry’. Antisymmetry is a lateral dimorphism in which each population consists of individuals with well-developed left sides (lefties) and well-developed right sides (righties). This dimorphism influences predator–prey interactions. In some piscivorous fishes, it has been found that predators can catch more prey of the opposite morphological type to themselves (cross-predation) than of the same morphological type (parallel-predation). Our previous work clarified that the predominance of cross-predation is caused by lateralized behaviors of predators and prey that correspond to their morphological antisymmetry. Moreover, based on the results of our behavioral observations, we hypothesized that parallel-predation can predominate when predators encounter the potential prey frontally. To test this hypothesis, in the present study we investigated the relationship between lateral morphological types of anglerfish (Lophiomus setigerus) and those of the prey fishes found in their stomachs. Anglerfish attract potential prey using their first dorsal fin (illicium) as a lure, and their frontal encounters with potential prey fishes were photographed in situ and observed in an aquarium. The results of a stomach contents analysis indicated that parallel-predation predominated in five benthopelagic prey fish species (perches and eels). By contrast, five benthic prey fishes (gobies and weevers) exhibited the predominance of cross-predation. These results not only demonstrate the predominance of parallel-predation in a natural fish community, but also suggest that the relationship between morphological types of predator and prey species can be reversed depending on the lifestyle of prey.

Measuring and evaluating morphological asymmetry in fish: distinct lateral dimorphism in the jaws of scale‐eating cichlids

The left–right asymmetry of scale-eating Tanganyikan cichlids is described as a unilateral topographical shift of the quadratomandibular joints. This morphological laterality has a genetic basis and has therefore been used as a model for studying negative frequency-dependent selection and the resulting oscillation in frequencies of two genotypes, lefty and righty, in a population. This study aims were to confirm this laterality in Perissodus microlepis Boulenger and P. straeleni (Poll) and evaluate an appropriate method for measuring and testing the asymmetry. Left–right differences in the height of the mandible posterior ends (HMPE) and the angle between the neurocranium and vertebrae of P. microlepis and P. straeleni were measured on skeletal specimens. Snout-bending angle was also measured using a dorsal image of the same individuals following a previous method. To define which distribution model, fluctuating asymmetry (FA), directional asymmetry (DA), or antisymmetry (AS), best fit to the lateral asymmetry of the traits, we provided an R package, IASD. As a result, HMPE and neurocranium–vertebrae angle of both species were best fitted to AS, suggesting that P. microlepis and P. straeleni showed a distinct dimorphism in these traits, although snout-bending angle of P. microlepis was best fitted to FA. Measurement error was low for HMPE comparing the snout-bending angle in P. microlepis, indicating that measuring HMPE is a more accurate method. The scale-eating tribe Perissodini showed distinct antisymmetry in the jaw skeleton and neurocranium–vertebrae angle, and this laterality remains a valid marker for further evolutionary studies.

Laterality of the initial stage of escape response in roach (Rutilus rutilus) upon impact of alternating electric current

The initial stage of the escape response (C-bend of the body) upon sudden impact of electric current on free-swimming fish was studied in young roach (Rutilus rutilus). More than half of the fish showed distinct behavioral laterality. i.e., a stabile tendency to bend either to the left or to the right, and retained it until the next test conducted 10 days later. The majority of fish bent to the left, but the difference between the proportions of individuals that showed opposite lateralities lacked statistical significance. This response and the type of laterality are stable and simple to record, which makes the C-bend a convenient experimental model for studying behavioral asymmetry in fishes.

Fish otolith asymmetry: Morphometry and modeling

Mathematical modeling suggests that relatively large values of otolith mass asymmetry in fishes can alter acoustic functionality and may be responsible for abnormal fish behavior when subjected to weightlessness during parabolic or space flight [D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17–34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55–69]. The results of morphometric studies of otolith mass asymmetry suppose that the absolute value and the sign of the otolith mass asymmetry can change many times during the growth of individual fish within the range ±20% [D.V. Lychakov, Y.T. Rebane, Otolith mass asymmetry in 18 species of fish and pigeon, J. Grav. Physiol. 11 (3) (2004) 17–34; D.V. Lychakov, Y.T. Rebane, Fish otolith mass asymmetry: morphometry and influence on acoustic functionality, Hear. Res. 201 (2005) 55–69]. This implies that the adverse effects of otolith asymmetry on acoustic and vestibular functionality could change during the lifetime of an individual fish. The aims of the present article were to examine the nature of otolith mass asymmetry fluctuation and to quantify otolith mass asymmetry in a large number of teleost fishes to verify our previous measurements. A dimensionless measure of otolith mass asymmetry, χ, was calculated as the difference between the masses of the right and left paired otoliths divided by average otolith mass. Saccular otolith mass asymmetry was studied in 59 Mediterranean teleost species (395 otolith pairs), 14 Black Sea teleost species (42 otolith pairs), red drum (196 otolith pairs) and guppy (30 otolith pairs). Utricular otolith mass asymmetry was studied in carp (103 otolith pairs) and goldfish (45 otolith pairs). In accordance with our previous results the value of χ did not depend on fish size (length or mass), systematic or ecological position of the fish, or otolith growth rate. In the great majority of the fishes studied, the saccular otolith χ was small ∣ χ∣ < 0.05 (or <5%). Mathematical modeling indicates that values of χ vary among individual fish, but that the value is probably stable during a fish’s lifetime.

Elevated fluctuating asymmetry in eastern mosquitofish (Gambusia holbrooki) from a river receiving paper mill effluent

The present study investigated whether fluctuating asymmetry can serve as a useful biomarker of environmental stress in the eastern mosquitofish (Gambusia holbrooki). Fluctuating asymmetry was measured in sexually mature females sampled from two Florida, USA, coastal streams: The Fenholloway River, which is dominated by effluent from a paper mill, and Spring Creek, a tributary to the Fenholloway River (Taylor County, FL, USA) that does not receive paper mill effluent. Nine morphometric (lengths of the A and B scales, fifth pectoral fin ray, supraorbital canal, and preorbital canal and the sixth gill raker on the first brachial arch; orbit diameter; distance from the dorsal-ventral midpoint of the eye socket to the base of the pectoral fin; and distance from the postorbital canal to the operculum) and five meristic traits (numbers of scales in the lateral line, radii on the A and B scales, pectoral fin rays, and gill rakers on the first brachial arch) were included. For each of the three indexes of fluctuating asymmetry that were used, the majority of the traits showed a higher level of fluctuating asymmetry in fish from the Fenholloway River than in fish from Spring Creek. For two of the indexes, the difference was significant. Comparisons of mean values for fluctuating asymmetry (over all traits) for each fish and the means of a composite index of asymmetry both indicated that fish from the Fenholloway River had significantly greater overall fluctuating asymmetry than those from Spring Creek. Results of the present study are consistent with the hypothesis that environmental stress increased the level of fluctuating asymmetry in fish from the Fenholloway River. Thus, fluctuating asymmetry appears to be a useful biomarker for stress-induced developmental instability in the eastern mosquitofish.

Position-Associated GC Asymmetry of Gene Duplicates

It is well known that repositioning of a gene often exerts a strong impact on its own expression and whole development. Here we report the results of genome-wide analyses suggesting that repositioning may also radically change the evolutionary fate of gene duplicates. As an indicator of these changes, we used the GC content of gene pairs which originated by duplication. This indicator turned out to be duplicate-asymmetric, which means that genes in a pair differ significantly in GC content despite their apparent origin from a common ancestor. Such an asymmetry necessarily implies that after duplication two originally identical genes mutated in opposite directions-toward GC-rich and GC-poor content, respectively. In mammalian genomes, this trend is definitely associated with presumably methylated hypermutable CpG sites, and in a typical GC-asymmetric gene pair, its two member genes are embedded in GC-contrasting isochores. However, we unexpectedly found similar significant GC asymmetry in fish, fly, worm, and yeast. This means that neither methylation alone nor methylation in combination with isochores can be counted as a primary cause of the GC asymmetry; rather they represent specific realizations of some universal principle of genome evolution. Remarkably, genes from pairs with the greatest GC asymmetry tend to be on different chromosomes, suggesting that the mutational difference between gene duplicates is associated with translocation of a new gene to a different place in the genome, whereas GC symmetric pairs demonstrate the opposite tendency. A recently emerged extra gene copy is usually on the same chromosome as is its parent but quickly, by 0.05 substitution per synonymous site, either has perished or occupies a different chromosome. During this earliest posttranslocation period, the ratio of nonsynonymous/synonymous base substitutions is unusually high, suggesting a rapid adaptive evolution of novel functions. In a general context of evolution by gene duplication, our interpretation of this position-dependent GC asymmetry between duplicated genes is that evolution of redundant genes toward a new function has often been associated with their very early, postduplication repositioning in the genome, with a concomitant abrupt change in epigenetic control of tissue/stage-specific expression and an increase in the mutation rate. Of eight eukaryotic genomes studied, the most distinguished in this respect is the human genome.

Lateralization of aggression in fish

Recent research has suggested that lateralization of aggressive behaviors could follow an homogeneous pattern among all vertebrates. A left eye/right hemisphere dominance in eliciting aggressive responses has been demonstrated for all groups of tetrapods but teleost fish for which data is lacking. Here we studied differential eye use during aggressive interactions in three species of teleosts: Gambusia holbrooki, Xenotoca eiseni and Betta splendens. In the first experiment we checked for lateralization in the use of the eyes while the subject was attacking its own mirror image. In order to confirm the results, other tests were performed on two species and eye preference was scored during attacks or displays directed toward a live rival. All three species showed a marked preference for using the right eye when attacking a mirror image or a live rival. Thus, the direction of asymmetry in fish appears the opposite to that shown by all the other groups of vertebrates. Hypotheses on the origin of the difference are discussed.

Contaminants and bilateral asymmetry in yellow perch

AbstractSeveral studies have shown that contaminants can induce bilateral asymmetry in fishes. In this study five bilateral meristic characters from seven populations of yellow perch (Perca flavescens) from Ohio and Wisconsin were enumerated to determine if there were any relationships among the asymmetries for each character and the body burdens of contaminants. Bilateral characters included scales on, above and below the lateral line, pectoral fin rays and gill rakers. Contaminants found in yellow perch were primarily polychlorinated biphenyls, DDT and dieldrin. All populations were asymmetrical for each bilateral character, but the degree of asymmetry was not related to contaminant levels. Unless a direct relationship between asymmetry and contaminants can be shown, we do not believe that this phenomenon will be a useful biological monitor.

Fluctuating asymmetry in fishes inhabiting acidified and unacidified lakes

Fluctuating asymmetry, the random deviation from perfect bilateral symmetry owing to developmental perturbation, has been used in a number of studies to quantify stress during early life. Decreasing pH and related changes in aquatic environments owing to input of anthropogenic acids have been demonstrated to be physiologically stressful to many fish species. Therefore, a link between environmental acidification and fluctuating asymmetry was postulated. Brook trout (Salvelinus fontinalis), white sucker (Catostomus commersoni), and lake chub (Couesis plumbeus) were collected from lakes over a wide range of pH values. Use of several species allowed separate consideration of environmental and genetic effects. Depending on species, 15 to 20 paired meristic and morphometric characters were scored for the left and right sides of each individual. Differences between sides were calculated and analyzed by a variety of statistical methods. Most characters examined were not significantly more asymmetric in acidified lakes. However, one or two characters in each species were more asymmetric in lakes of lower pH. Relative overall asymmetry in brook trout was related to parameters that changed with acidification. The small number of locations sampled precluded such an analysis in the other two species. The results are consistent with the hypothetical link between environmental stress by acidification and increased fluctuating asymmetry, but the connection is much weaker than expected. This finding, the need for large sample sizes, and the lack of a definite causal link, severely limits the utility of this type of analysis in assessing the level of stress in fish populations.