Sulcus Acusticus Research Articles

The multifaceted diversification of the sagitta otolith across the fish tree of life

Abstract Otoliths of actinopterygians are calcified structures playing a key role in hearing and equilibrium functions. To understand their morphological diversification, we quantified the shape of otoliths in both lateral and dorsal view from 697 and 323 species, respectively, using geometric morphometrics. We then combined form (i.e. size and shape) information with ecological data and phylogenetically informed comparative methods to test our hypotheses. Initially, the exploration of morphospaces revealed that the main variations are related to sulcus acusticus shape, elongation and lateral curvature. We also found strong integration between otolith and sulcus shape, suggesting that they are closely mirroring each other, reinforcing a shape-dependent mechanism crucial for otolith motion relative to its epithelium and validating the functional significance of otolith morphology in auditory and vestibular processes. After revealing that otolith shape and size retained a low phylogenetic signal, we showed that the disparity of otolith size and shape is decoupled from order age and from the level of functional diversity across clades. Finally, some traits in otolith disparity are correlated with their morphological evolutionary rate and the order speciation rate. Overall, we observed that the pattern of diversification of otoliths across the fish tree of life is highly complex and likely to be multifactorial.

Otolith Shape Analysis of Five Sillaginidae Species from the Persian Gulf and the Oman Sea

The discrimination power of sagittal otolith shape analysis is evaluated for five closely related sillaginid species from the Persian Gulf and the Oman Sea; (Sillago arabica, Sillago attenuata, Sillago indica, Sillago sihama and Sillaginopodys chondropus) besides the description of morphological characters using scanning electron microscopy (SEM). The identification of sillaginids is difficult due to the limited reliable diagnostic morphological characters. The otolith shape was described by six shape indices (Roundness, Rectangularity, Circularity, Ellipticity, Form factor and Aspect ratio) and Elliptic Fourier Descriptors (EFD). For all shape indices, there was at least an overlap between the two species and no one was significantly different among the five species. Based on EFD analysis all five species were discriminated (91.7%) evidencing the high taxonomic value of sagittal otolith for the studied taxa. SEM images revealed sulcus acusticus as homosulcoid with an inframedian position in all five species. S. arabica and S. sihama are characterized by having a pseudo-ostiocaudal, while S. indica, S. attenuate and Sillaginopodys chondropus have ostial mode of opening. The ostium was tubular and slightly curved in all studied species, which was more strongly curved in S. arabica. These findings suggest that the sagittal otolith shape is a reliable tool to recognize inter-specific diagnosis for sillginid species in the Persian Gulf and Oman Sea.

The developmental changes in the morphology of the otolith of the mullet Chelon auratus (Risso, 1810) (Mugiliformes, Mugilidae) collected from Köyceğiz Lagoon, Aegean Sea, Türkiye

ABSTRACT Nineteen traits were described to define the shapes of the otoliths. The outcomes of this study display ontogenetic variations for different age groups based on the recorded shapes. Otoliths of the young individuals belonging to fish length groups GI and GII have shown differences in the otolith shape from those of the older individuals of the remaining seven length groups examined. A comparison with earlier published otolith description on C. auratus collected from other areas showed some interspecific variation across larger geographic distances, making some characters useless for diagnostic purposes. Other otolith features were shown to be consistent in otoliths from different length groups and such characteristics could be considered for species identification purposes. These characteristics are otolith width, depth, shape of the mesial and the lateral surfaces, shape of the sulcus acusticus, shape of the ostium and cauda and shape of the ostio-caudal differentiation.

Form function of sulcus acusticus of the sagittal otolith in seven Sciaenidae (Acanthuriformes) species using geometric morphometrics (southwestern Atlantic).

The morphology of otoliths determines the function they perform, and it is influenced by genetic and environmental factors. Knowing those relationships is necessary to understand the role of hearing in fish. The objectives of this work were: exploring the shape of the sulcus of the sagittal otolith in seven species of Sciaenidae, in relation to sound production, and analyzing whether the shape and size of the sulcus can be used as a phylogenetic character. For this purpose, geometric morphometry analysis was carried out using landmarks data. It was found that there is an influence of size on the shape of the sulcus, and significant differences were found between the shapes of the sulcus (permutational multivariate analysis of variance). Three general shapes of the sulcus were identified (using principal component analysis, canonical variate analysis, and clustering): (1) in species that produce sounds at dominant frequencies <350 Hz, the deformation of the sulcus showed a tendency towards circularity of the ostium; (2) in those species that produce sounds at frequencies >350 Hz, the ostium showed a flattened ovoid shape, and the cauda increased its length; (3) the species that do not produce sounds, did not show any modifications, relative to the form of consensus. Despite finding sister species that presented similar sulcus shapes in the phylogeny, the results did not confirm that this can be used as a phylogenetic character. This work discusses whether the combined effects of phylogenetic legacy and natural functional selection have led to convergent evolution for the sulcus form. The differences presented by the sulcus of species that occupy the same clade, could indicate that there is a displacement of characters. The sagittal otolith and the sensory macula associated with the sulcus acusticus are highly plastic structures that are subject to strong evolutionary pressure in relation to environmental and behavioral factors, resulting in great variability in shapes that can be associated with a specific character. The variation in the shape of the sulcus would allow the analysed species to coexist in the same coastal soundscapes, without losing their particular hearing needs, even in case of overlapping their spatial and temporal distribution areas.

Insights of Otoliths Morphology to Reveal Patterns of Teleostean Fishes in the Southern Atlantic

The sagitta otoliths of teleostean fishes are usually used in diverse studies. Their shapes are species-specific, and the qualitative description of their morphological features seems to be a simple task, despite its subjectivity. On the other hand, morphometric techniques have been developed with a focus on objectivity, reproducibility, and accuracy. Considering this, the otoliths morphology was reviewed and evaluated in terms of robustness as a taxonomic tool and to highlight ecomorphological patterns. The otoliths morphology of 179 teleostean fishes from the Southern Atlantic were analyzed. For each species, the fish total length range, eighteen otolith morphological features (OMFs), and relative proportions were annotated. Species habitat and habit were also recorded. Data analyses were based on exploratory analysis, correlation, nonmetric multidimensional scaling, and a two-way permutational analysis of variance. The most descriptive OMFs were: colliculum, sulcus acusticus (morphology, position, orientation, and opening), and otolith profile. The otolith morphology was significantly related to species habitat and habit, with a new pattern described for deep-ocean pelagic species. In conclusion, otoliths morphology is robust whenever it is based on the comparative method application (otoliths among otoliths), considering the constant updates of fishes’ taxonomy and the use of proper sample sizes linked to morphometric techniques.

Scales and otoliths as identity cards of the Indian oil sardine Sardinella longiceps (Teleostei: Clupeiformes) populations: Ultrastructure and ornamentation characteristics using light and scanning electron microscopy

AbstractScale and otolith morphology and morphometry of Indian oil sardine Sardinella longiceps (Clupeidae) were investigated and described using light and scanning electron microscopy from eight different body regions for scales and the right and left otoliths. Scales of the Indian oil sardine show general characteristics of the other studied clupeids sand that are easily distinguishable from other fish groups, by having striae in the posterior field. The studied cycloid scales of S. longiceps were classified into three types based on the overall shape including circular (e.g. true circular and cordate), pentagonal and quadrilateral in the different body regions. The circular shape was the most common shape (87.5%), while the quadrilateral and pentagonal forms constituted 6.25% each. The results also showed that the relative scale size (J‐index) plays a desirable contribution in separating the examined populations. The results showed that the mean (or relative) scale size for all the eight regions in the Oman Sea population is larger than the Arabian Sea population. Also, another scale variable, the scale shape index (Si index), demonstrated variation (a mean of 0.86 to 1.1) in different regions of both populations from the Oman and Arabian Seas. Interestingly, here, we found that scale characters of S. longiceps not only differ from its other congeneric species, but also differ in the populations from both sides of the Oman Sea (Iran and Oman) and the Arabian Sea. It shows a positive signal for the presence of different taxonomic and management unit in the Oman and Arabian Seas. The idea should be approved by using integrated molecular and morphological traits. The otolith morphology of S. longiceps from the Oman and Arabian Seas was more conservative than the scales, which can be due to its function actin primarily as a balance organ and also enhancing hearing. The overall shape of S. longiceps otolith was lanceolate, with an elongated morphology and a well‐developed rostrum, an ostial sulcus acusticus that opens to the anterior/ dorsal margin. These morphological characters are also found in the Iranian population of S. longiceps. However, otolith displayed variation in biometric parameters among two populations and left and right otoliths and the RRL parameter were important characters to discriminate the Oman and Arabian Sea populations. Thus, the structural/biometrical variability of the otoliths may be used for population distinctness, especially in water bodies with various environmental factors, and the otolith has turned out to be a useful tool to track the life history of teleostean fishes in environments with physicochemical gradients.

Otolith shape analysis supports three cryptic species in the Stellifer punctatissimus complex (Acanthuriformes: Sciaenidae)

Abstract Sciaenidae species (croakers and drums) are known for specializations in their sensory apparatus, such as otoliths and lateral line. Within this family, some Stelliferinae members remain taxonomically unresolved due to their cryptic aspects and low phenotypic disparities. Stellifer punctatissimus comprises a species complex putatively formed by three species on morphological grounds, but molecular data have indicated only two evolutionary lineages. Herein, we tested the hypothesis that this complex is composed of Stellifer gomezi (GM), S. menezesi (MN), and S. punctatissimus (PC), using the otolith shape and morphology to differentiate them. Seventy-seven sagittal otoliths (GM = 30, MN = 30, PC = 17) were photographed to outline the otolith contour by Elliptical Fourier descriptors. Ten otoliths for each group were used to detect shape variation in the sulcus acusticus through semilandmarks. Differences in otolith shape contour were recorded among the species by PERMANOVA (Pseudo-F = 4.02, df = 2, p &lt; 0.001) and corroborated by the Linear Discriminant Analysis, which demonstrated three partially segregated groups with satisfactory re-classification rates. A larger sulcus acusticus (GM and MN), rounded projection (PC), and distinct rectangularity pattern were also recorded. Our results support the morphological hypothesis and thus contribute to narrowing the taxonomic gaps in Sciaenidae.

Intra- and interspecific variability among congeneric Pagellus otoliths

Otolith features are useful tools for studying taxonomy, ecology, paleontology, and fish biology since they represent a permanent record of life history. Nevertheless, the functional morphology of otoliths remains an open research question that is useful to completely understand their eco-morphology. This study aims to deepen the knowledge of intra- and interspecific variation in sagitta morphology in three congeneric seabreams, to understand how such variability could be related to the lifestyles of each species. Therefore, the sagittae (n = 161) of 24 Pagellus bogaraveo, 24 Pagellus acarne, and 37 Pagellus erythrinus specimens, collected from the south Tyrrhenian Sea, were analyzed using scanning electron microscopy and a stereomicroscope to assess morphometric features, variability between otolith pairs and the external crystalline structure the of sulcus acusticus. Statistical analysis demonstrated that, between the species, variability in sagittal otolith rostral length growth and sulcus acusticus features, correlated with increased fish total length and body weight. Moreover, slight differences between otolith pairs were detected in P. acarne and P. erythrinus (P < 0.05). The results confirm changes in otolith morphometry and morphology between different congeneric species and populations of the same species from different habitats.

Differentiating morpho-functional patterns of the five most common deep-sea benthic anglerfishes (Lophiiformes) from Andaman and Nicobar Islands (eastern Indian Ocean)

Anglerfishes are widely distributed from shallow to deep-water habitats occupying different ecological niches. To explain this adaptability, we performed a morpho-functional study on common benthic anglerfishes inhabiting the Indian deep-sea waters. Sensory capabilities of species were examined using the morphology and morphometry of sagitta otoliths (related to detection sound and hearing) and eye size (related to visual communication). We also performed an analysis of the degree of functional niche overlap using fish body traits to understand the coexistence of species. Otoliths showed a morphological pattern similar to that of other anglerfishes: an archaesulcoid sulcus acusticus and variability in the irregularity of the dorsal margin. This last feature affected the allometric relationships between the otolith morphometry and fish length, as well as the otolith relative sizes of each species. The findings suggested that bigger otoliths are associated with the increase of depth distribution of species up to 1000 m, from which it decreases. Our hypothesis is that anglerfishes with irregular otolith shapes could be linked to more nocturnal feeding behaviour because they were characterized by greater eye sizes. The results also indicated interspecific significant differences in functional traits providing a low niche overlap. Therefore, our study supports the hypothesis of an environmental and ecological specialization of benthic anglerfishes.

Delineation of seven species of genus Channa from upper Assam region, India using sagittal otolith morphology

Morphology of sagittal otoliths of seven species of genus Channa from upper Assam, India was studied to obtain baseline information for their prospective role in taxonomic studies. In the present study, variations were recorded in morphological characteristics of sagittal otolith among the studied species. Of all the studied parameters, otolith shape, sulcus acusticus, ostium, and cauda, in particular, were found to be taxonomically important features for the identification of the species. The pentagonal shape of sagitta in Channa punctata, pseudo-ostiocaudal sulcus acusticus in C. marulius, bent concave ostium in C. stewartii, straight cauda in C. bleheri were found to be species-specific features. Sagitta size was smallest in C. gachua while the largest was recorded in C. striata. The proposed taxonomic keys enumerated through the combination of different otolith characters from the present investigation will be useful in the identification of these species when standard methodologies fail to deliver satisfactory results.

Fourier-based contour descriptors to relax positional standardization of the otolith images in AFORO queries

The otolith digital catalogue AFORO allows unknown otoliths to be classified automatically by using a comparison with its classified records. To do this, the otolith’s contour, which is extracted from an image, is used. In AFORO, otolith images follow a strict positional normalization. Only the left sagitta is considered, and the images must show the internal side of the whole otolith, with the sulcus acusticus visible, the dorsal side (D) placed in the dorsal position and the rostral side (R) placed on the right. The otolith in the incoming image to be classified must also follow the same positional normalization. Variations from the reference position worsen the classification results. In this article, robust contour descriptors are proposed to extend this functionality of AFORO to the images of otoliths that are poorly normalized, contain rotations, are entirely inverted or came from the right rather than the left sagitta. These descriptors are based on the discrete Fourier transform and could extend the classification functionality to incoming images that are taken and sent, for instance, from smartphones in a wide range of working conditions.

Ontogenetic and sexual variation in the sagitta otolith of Menticirrhus americanus (Teleostei; Sciaenidae) (Linnaeus, 1758) in a subtropical environment

This study aimed to verify variations in the form of the sagitta otolith of Menticirrhus americanus as to their ontogeny, sex and stage of such structure. Ontogenetically were found significant differences (p &lt; 0.05) for all shape indices (aspect ratios, shape factor, rectangularity, ellipticity, relative surface of sulcus acusticus) and also in the wavelet of the otolith. The CVA presented a 98.6% correct reclassification of the otolith between interval class. Sexual variations were found in the wavelet and in the relative surface of sulcus acusticus index. Between adult females and young females, differences were not detected in the wavelet and rectangularity, but significant differences were found in all other shape indices. The CVA presented a 79.6% correct reclassification of the otolith of the sexes and stages of life sampled. Young females and adults females showed highest correct percentage of classification. The results of this study demonstrate for the first time the influence of the ontogenetic variation and sexual in the form of the otoliths.

Geometric morphometrics in the sulcus acusticus of the sagittae otolith as tool to discriminate species of the genus Centropomus (Centropomidae: Perciformes) from the southeastern Gulf of California

Due to the limited morphological differentiation among species of the genus Centropomus and the increased overlap of their meristic characters, in this study, we examined 114 sagittae otoliths by geometric morphometrics. Otoliths belonged to four species: Centropomus robalito (Jordan and Gilbert, 1881) Centropomus medius (Gunter, 1864), Centropomus nigrescens (Gunter, 1864), and Centropomus viridis (Lockington, 1877) collected by artisanal fishing carried out in the “Marismas Nacionales Nayarit” Biosphere Reserve and the continental shelf of the state of Nayarit. According to the canonical variate analysis, all four species were discriminated (100% correct) evidencing the high taxonomic value of sagittae otolith for these taxa. In our study, the morphology of sagittae otolith of four species of the genus Centropomus is documented for the first time.

Insights into fish auditory structure–function relationships from morphological and behavioural ontogeny in a maturing sciaenid

Knowledge of the relationship between auditory form and function is necessary to understand the role of hearing in fish ecology, as well as the potential impacts of anthropogenic noise and environmental change on hearing-mediated functions. We explored the functional significance of otolith (ear stone) morphology in a large predatory sciaenid, Argyrosomus japonicus (Temminck and Schlegel), by comparing ontogenetic changes in otolith structure to changes in habitat, diet and swimming activity. We examined an otolith metric that has previously been linked to habitat use and activity in fishes, the relative sensory area (sulcus to otolith area ratio, S:O), and a new metric that quantifies the protuberant structure (calcareous concrescence) found on the distal surface of sciaenid otoliths (otolith perimeter to area ratio, P:SA). Strong allometric growth of the sulcus acusticus was detected in the sagitta of A. japonicus ranging from 7 to 80 cm TL. Both S:O and P:SA changed rapidly until A. japonicus reached 50 cm TL, after which only a gradual increase in relative sensory area was detected. The aspect ratio of the caudal fin (CAR, an index of swimming activity) abruptly increased in A. japonicus at 41–50 cm TL. These changes coincide with an observed shift in diet from benthic invertebrates to pelagic fish, a shift in foraging habitat and an increase in foraging activity.

A geometric morphometric approach for disparity of the sulcus acusticus of sagitta in species of Gerreidae (Teleostei: Perciformes)

This paper explores shape disparity in the sulcus acusticus of saccular otolith using geometric morphometric methods in selected Gerreidae species. First, multivariate linear regressions between size (CS-log-transformed) and shape were implemented to uncover allometry in the variation of the sulcus acusticus at three levels: intraspecific, intrageneric, and interspecific. Second, we assessed species disparity to investigate if differences in disparity are associated with three biologically contrasting ecological or historical processes within the family. Specifically, we asked: (1) How has disparity changed as a result of an ecological shift from marine to freshwater habitat? (2) How has disparity changed in genera with increasing taxonomic richness? and (3) How did a vicariant event across the Panama isthmus changed disparity in a pair of sister species? Our results indicate that the disparity of the sulcus acusticus shape of the single freshwater species (Eugerres mexicanus) is in the middle of the range of values of the 17 marine species compared. This suggests that the change to a freshwater environment did not influence the variability of the sulcus acusticus. In the taxonomic comparisons, as expected, disparity is lowest in the monotypic Deckertichthys, while it increases with species number in Diapterus. In the vicariant pair, the Pacific basin species (Diapterus brevirostris) has a disparity value almost twice the value than in the Atlantic taxon (D. rhombeus). It remains to be investigated if the same disparity patterns documented here are associated to marine-freshwater ecological shifts and vicariant events in other fish families.

Comparison of otolith morphology of invasive big-scale sand smelt (Atherina boyeri) from natural and artificial lakes in Turkey.

In this study, otolith morphology and otolith contour from big-scale sand smelt, Atherina boyeri were analyzed in Lake Egirdir and Lake Iznik (natural lakes), and Hirfanli Dam Lake (artificial lake). The otolith contour and sixteen otolith morphological characters such as width, depth, shape, sulcus acusticus shape, ostium, cauda, rostrum size-shape, and thickness, antirostrum size-shape, and thickness, anterior and posterior regions, mesial and lateral surfaces were successfully investigated for three total length groups of A. boyeri inhabiting the lakes. Intraspecific variation in rostrum shape, rostrum size, rostrum thickness, antirostrum, anterior region, mesial and lateral surfaces were observed for the three total length groups of three A. boyeri populations. In the three different lakes, saccular otoliths surface morphology of A. boyeri were detected such as flatten surface for Lake Egirdir, rough surface for Lake Iznik, and relatively smooth surface for Hirfanli Dam Lake using the Scanning Electron Microscope. The otolith contours were noticeable difference in the three total length groups of A. boyeri from the different lakes. Intraspecific variability of the otolith characters and morphology consist of the otolith surface morphology and otolith contour were presented and compared for the three total length groups of the A. boyeri from the different lakes.

Otolith shape index: is it a tool for trophic ecology studies?

AbstractThe aim of this study was to test the effective separation of shape indices of otoliths of three species belonging to the family Sciaenidae before and afterin vitrodigestion. We measured 328 sagittal otoliths and applied six shape indices. Before the experiment, the aspect ratio (otolith height/otolith length%), circularity, ellipticity and relative surface of the sulcus acusticus were suitable for differentiating the species of genera Paralonchurus and Stellifer. Among the species of Stellifer, the aspect ratio and rectangularity were suitable. Otoliths exposed toin vitrodigestion showed no significant differences in their morphometry before and after the experiment. Afterin vitrodigestion, the aspect ratio and circularity were effective in separating Paralonchurus and Stellifer. However, none of the indices used in the present study were efficient to separate otoliths of congeneric species afterin vitrodigestion.

Otolith Morphology of Amur Sleeper Perccottus glenii (Odontobutidae)

Morphology of the sagitta, lapillus, and asteriscus is described in Amur sleeper Perccottus glenii, 19–245 mm TL. The sagitta is characterized by an almost quadratic shape. In the majority of individuals, the largest sagitta height along the dorsoventral axis (OH) is larger than the largest sagitta length along the anteroposterior axis (OL); and the average OH/OL index in the fishes above 60 mm TL is 1.18 (n = 191). The sagitta differs from the sagittae of recent and fossil representatives of the suborder Gobioidei (described until now) in the irregular rims with several dorsal lobes, well-developed postrostrum, and undefined sulcus acusticus. A negative allometry of the sagitta growth in relation to body length and lapillus and asteriscus growth in relation to body length and sagitta height is observed.

Geometric morphometrics for the analysis of character variation in size and shape of the sulcus acusticus of sagittae otolith in species of Gerreidae (Teleostei: Perciformes)

Sagittal otoliths are a useful structure to distinguish teleostean fishes. However, character variation in size and shape of the sulcus acusticus has not been tested among Gerreidae Gunther, 1862 species. For the first time, this paper explores the size and shape variation in the sulcus acusticus using landmark data and geometric morphometric methods. Variation in the sulcus acusticus size, as estimated with centroid size, is not a useful feature to distinguish neither the five genera nor all species in this study. However, since analyses of variance followed by Tukey a posteriori tests detect differences among groups of species, it is possible that the size of the sulcus acusticus will still be useful as a phylogenetic character. As expected, the pattern of variation in the shape of the sulcus acusticus consists of well-defined character states exclusive of each of the 18 species of Gerreidae included. All comparisons in multivariate analyses of variance of semi-landmark configurations with a CVA were statistically significant, and the rates for correct posterior classifications were all above 79%. Discriminant axes allowed to locate variation in particular regions of the sulcus acusticus outline that contribute most to the distinction among genera. Results revealed species in the same genus share a particular shape in the ostium and posterior extension of the cauda. Variation in the shape of the sulcus acusticus is, therefore, a very useful character to identify species in Gerreidae.

Do upwellings produce specific morphologic and chemical signatures in Sardinella brasiliensis otoliths?

Do upwellings produce specific morphologic and chemical signatures in Sardinella brasiliensis otoliths?