Corresponding author: Alfonso A. González-Díaz ( agonzalez@ecosur.mx ) Academic editor: Felipe Ottoni
© 2021 Yanet Elizabeth Aguilar-Contreras, Alfonso A. González-Díaz, Omar Mejía, Rocío Rodiles-Hernández.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Aguilar-Contreras YE, González-Díaz AA, Mejía O, Rodiles-Hernández R (2021) Morphometric variation of Middle-American cichlids: Theraps– Paraneetroplus clade (Actinopterygii: Cichliformes: Cichlidae). Acta Ichthyologica et Piscatoria 51(4): 403-412. https://doi.org/10.3897/aiep.51.69363
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This study assesses the patterns of variation in body shape, and relations of morphological similarity among species of the Theraps–Paraneetroplus clade in order to determine whether body shape may be a trait in phylogenetic relations. A total of 208 specimens belonging to 10 species of the Theraps–Paraneetroplus clade were examined. The left side of each specimen was photographed; in each photograph, 27 fixed landmarks were placed to identify patterns in body shape variation. Images were processed by using geometric morphometrics, followed by a phylogenetic principal component analysis. The phylogenetic signal for body shape was then calculated. To determine the relations in morphological similarity, a dendrogram was created using the unweighted pair group method and arithmetic mean values, while a Procrustes ANOVA and post-hoc test were used to evaluate significant differences between species and habitats. We found three morphological groups that differed in body length and depth, head size, and the position of the mouth and eyes. The body shape analysis recovered the morphotypes of seven species, and statistical differences were demonstrated in eight species. Based on traits associated with cranial morphology, Wajpamheros nourissati (Allgayer, 1989) differed the most among the species examined. No phylogenetic signal was found for body shape; this trait shows independence from ancestral relatedness, indicating that there is little congruence between morphological and genetic interspecific patterns. As evidenced by the consistently convergent morphology of the species in the Theraps–Paraneetroplus clade, the diversification of the group is related to an ecological opportunity for habitat use and the exploitation of food resources. Although no phylogenetic signal was detected for body shape, there appears to be an order associated with cranial morphology-based phylogeny. However, it is important to evaluate the intraspecific morphologic plasticity produced by ecological segregation or partitioning of resources. Therefore, future morphological evolutionary studies should consider cranial structures related to the capture and processing of food.
diversification, geometric morphometrics, morphological convergence, phylogenetic signal, Usumacinta province
Among Neotropical freshwater fishes, evidence of diversity suggests that allopatric speciation models frequently apply to several clades and that there are few cases of sympatric speciation stemming from adaptive processes (
In Neotropical cichlids, the ability to use new or newly available resources (i.e., ecological opportunity) has been an important mechanism in diversification (
Despite advances in knowledge regarding the evolution of diverse groups of cichlids worldwide, there are still lineages with incipient research, such as Middle American heroine cichlids. Middle America harbors approximately 124 cichlid species (
Among Middle American cichlids, the Theraps–Paraneetroplus clade (sensu
In addition to ecomorphological evidence indicating that the phenotypic expression of morphological attributes in some clade members is associated with habitat type and feeding (
In the Theraps–Paraneetroplus clade, convergent morphological characteristics seem to support the hypothesis of diversification via ecological opportunity and resource partitioning, which contrasts with the hypothesis proposed by phylogenetic systematics and the theory of evolutionary non-independence (
For this purpose, geometric morphometrics and comparative phylogenetic methods are used as analytical tools because they are commonly used to study the evolution of biological morphology. Geometric morphometrics can be used to identify variation in the pure shape of organisms, and separate the variation and size of individuals by analyzing shapes in multivariate space (
To analyze the morphological variation among members of the Theraps–Paraneetroplus clade, the presently reported study included a total of 208 specimens (females and males of similar size) that correspond to 10 species, representative of each genus in the clade. All the specimens were deposited at the Fish Collection of El Colegio de la Frontera Sur, San Cristóbal (ECOSC). Theraps clade: Chuco intermedium (Günther, 1862) (abbreviation and number of specimens: Chin, n = 21); Cincelichthys pearsei (Hubbs, 1936) (Cipe, n = 24); Kihnichthys ufermanni (Allgayer, 2002) (Kiuf, n = 23); Theraps irregularis Günther, 1862 (Thir, n = 20); Wajpamheros nourissati (Allgayer, 1989) (Wano, n = 24); Paraneetroplus clade: Maskaheros argenteus (Allgayer, 1991) (Maar, n = 25); Oscura heterospila (Hubbs, 1936) (Oshe, n = 20); Paraneetroplus bulleri Regan, 1905 (Pabu, n = 3); Rheoheros lentiginosus (Steindachner, 1864) (Rhle, n = 25); Vieja hartwegi (Taylor et Miller, 1980) (Viha, n = 23).
Museum catalogue information. Chuco intermedium (Chin) ECOSC 103, 314(4), 334, 395(5), 440, 473(3), 815(2), 12747(2), 4892(2); Cincelichthys pearsei (Cipe) ECOSC 204, 229(2), 299, 300, 337, 444, 719(4), 849, 1049, 1512(3), 1055, 2352, 2546, 2575, 4422(2), 4436 (2); Kihnichthys ufermanni (Kiuf) ECOSC 90, 186, 233, 406, 409, 613, 675, 769, 1729, 1230, 1536(3), 1548, 1557(2), 1867, 1873, 2118(2), 2298, 4687, 7618; Maskaheros argenteus (Maar) ECOSC 386, 698, 741, 1280, 1448,1472, 1481, 1502, 1606, 1747, 1771, 1998, 2020, 2163, 2174, 2395, 2555, 2577, 4716, 4747(2), 4806(2), 4821, 7774; Oscura heterospila (Oshe) ECOSC 2338, 2720, 3053, 3054, 3491, 3505, 3777, 4563, 6709, 7826, 8465, 9070, 9080, 9267, 9318, 9816, 9849, 10164, 10165, 13757; Paraneetroplus bulleri (Pabu) ECOSC 12018(3); Rheoheros lentiginosus (Rhle) ECOSC 646, 853(3), 869(2), 1471(2), 1503(2), 1874, 1900, 2296(4), 2389, 2515(3), 2549, 2559, 7789, 4695, 12748; Theraps irregularis (Thir) ECOSC 245, 254, 817(2), 1255, 1780, 1967, 2133, 2626, 4725, 4729, 4809(9); Vieja hartwegi (Viha) ECOSC 4445(3), 4546, 6838, 6857(4), 7468, 7542(4), 7543(4), 7548(2), 7549(2), 12340; Wajpamheros nourissati (Wano) ECOSC 532(2), 684(2), 820(2), 893, 1237, 1288(2), 1546(2), 1847, 1289(2), 2082(2), 2105, 2280, 2651, 4744, 4888, 7336, 7453.
Morphometric analysis. Specimens were photographed on their left side using a Canon (EOS 70D) digital camera. The camera was mounted on a tripod to standardize the distance from the specimen. A 1-cm scale was placed on each photograph. To describe and compare body shapes, a geometric morphometric analysis was performed. In each photo, 27 fixed landmarks were placed using the configuration provided by
Then, in order to eliminate variation caused by the size, rotation, and displacement of the specimens, a generalized Procrustes analysis (
Location of fixed landmarks in species of the Theraps–Paraneetroplus clade (image modified from
Shape analysis. To reduce morphological variation related to phylogeny and differences in specimen size (allometry), regression of the Procrustes coordinates and centroid size was conducted using the “phyl.resid” function of the Phytools package ver. 0.7–80 in R software (
Additionally, the phylogenetic signal for body shape was computed by using the Kmult statistic (K) across 1000 permutations via the Geomorph package 4.0.0 in R software (
Finally, to determine whether significant differences in body shape exist among species and between lentic (LE) and lotic (LO) habitats, a Procrustes ANOVA was used as implemented in Geomorph 4.0.0 (
The pPCA indicated that the first three components explained 80% of the total variance (PC1: 52.6%; PC2: 17.6%; PC3: 11.6%). Species located on the positive axis of PC1 include T. irregularis, P. bulleri, and R. lentiginosus; O. heterospila, M. argenteus, C. pearsei, and K. ufermanni were located on the negative axis; and C. intermedium, V. hartwegi, and W. nourissati were located on the middle axis. The deformation grids showed variation among species on the positive axis related to decreased body height, elongation of the caudal peduncle, a convex base of the anal fin, and a narrow distal section. Species on the negative axis showed a deep body height, shortened caudal peduncle, and concave base of the anal fin. According to the morphotypes, the lotic species T. irregularis, P. bulleri, and R. lentiginosus were on the positive axis, while lentic species on the negative axis included O. heterospila, M. argenteus, C. pearsei, and K. ufermanni. However, the lotic species C. intermedium and W. nourissati, as well as the lentic species V. hartwegi, were in the middle of the axis (Fig.
A) Phylomorphospace formed by PC1 and PC2. B) Phylomorphospace formed by PC1 and PC3. Black circles represent the mean body shape configuration for each species, and white circles the ancestral state. Black lines represent Theraps clade, and grey lines Paraneetroplus clade. LE represent lentic ecomorphotype, LO represent lotic ecomorphotype, LE/LO represent both ecomorphotypes. Deformation grids are associated to the most negative and positive values of the PC1 and PC2. Abbreviations: Chin-LO = Chuco intermedium; Cipe-LE = Cincelichthys pearsei; Kiuf-LE = Kihnichthys ufermanni; Thir-LO = Theraps irregularis; Wano-LO = Wajpamheros nourissati; Maar-LE/LO = Maskaheros argenteus; Oshe-LE = Oscura heterospila; Pabu-LE = Paraneetroplus bulleri; Rhle-LO = Rheoheros lentiginosus; Viha-LE = Vieja hartwegi.
In PC2, species found in the positive axis included C. pearsei, K. ufermanni, C. intermedium, T. irregularis, and V. hartwegi, while O. heterospila, W. nourissati, R. lentiginosus, M. argenteus, and P. bulleri were found on the negative axis (Fig.
In PC3, W. nourissati was the most differentiated on the positive axis, exhibiting accentuated variation in the cephalic region with increased head size and a notable anteroventral displacement of the mouth. Additionally, the eyes and pectoral fins of W. nourissati were displaced posteriorly. On the negative axis, the remaining species were equally distributed with short heads, rounded profiles, and small mouths (Fig.
The dendrogram based on Mahalanobis distances showed that C. intermedium differed the most in body shape, followed by the C. pearsei and K. ufermanni groups. The remaining species formed two groups—one composed of P. bulleri, R. lentiginosus, and T. irregularis and another composed of M. argenteus and O. heterospila. The second most similar species were W. nourissati and V. hartwegi. The phylogenetic signal value of the Kmult statistic was 0.765, with a significance value of P = 0.308 and displaying no significant effect of phylogeny on body shape under the Brownian motion evolutionary model (Fig.
The Procrustes ANOVA identified significant differences in body shape among species (F = 34.62, R2 = 0.59, P < 0.01) and habitats for the comparison of Procrustes coordinates (F = 56.24, R2 = 0.20, P < 0.001). However, the comparison using the centroid size of each species failed to recover significant differences among species (F = 1.06, R2 = 0.043, P= 0.181) and habitats (F = 1.20, R2 = 0.005, P = 0.264). However, the pairwise comparison test showed statistical differences between all the species (P < 0.05) excluding V. hartwegi and P. bulleri (P = 0.055) (Table
Procrustes distances (above diagonal) and p values (below diagonal) to pairwise comparison test between all cichlid species of Middle-American Theraps–Paraneetroplus clade. Bold letters indicate no significant differences between species.
Chin | Cipe | Kiuf | Maar | Oshe | Pabu | Rhle | Thir | Viha | Wano | |
Chin | — | 0.047 | 0.051 | 0.059 | 0.079 | 0.061 | 0.071 | 0.085 | 0.045 | 0.068 |
Cipe | 0.001 | — | 0.034 | 0.066 | 0.074 | 0.081 | 0.087 | 0.102 | 0.049 | 0.077 |
Kiuf | 0.001 | 0.004 | — | 0.057 | 0.055 | 0.075 | 0.083 | 0.105 | 0.044 | 0.066 |
Maar | 0.001 | 0.001 | 0.001 | — | 0.052 | 0.058 | 0.077 | 0.111 | 0.049 | 0.071 |
Oshe | 0.001 | 0.001 | 0.001 | 0.001 | — | 0.090 | 0.102 | 0.137 | 0.073 | 0.077 |
Pabu | 0.006 | 0.001 | 0.001 | 0.009 | 0.001 | — | 0.057 | 0.077 | 0.046 | 0.067 |
Rhle | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.011 | — | 0.061 | 0.061 | 0.071 |
Thir | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | — | 0.078 | 0.086 |
Viha | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.055 | 0.001 | 0.001 | — | 0.056 |
Wano | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | — |
In the pPCA, species were placed in morphospace based on body length and depth, followed by variation in the cephalic region based on changes in head size and profile, mouth position, and eye position and size. Additionally, some morphological changes were evident based on the position and size of the fins. The variation observed in these morphological characteristics has been closely associated with the environments, locomotion, and feeding of fish (
In the morphospace and similarity analysis, the most notable groupings were T. irregularis, R. lentiginosus, and P. bulleri, all of which presented elongated bodies and caudal peduncles as well as pelvic fins that were positioned ventrally. Ecomorphological studies have reported that these characteristics are functionally associated with high-velocity current environments (
The group comprising O. heterospila, K. ufermanni, M. argenteus, and C. pearsei occupies another part of the morphospace. These species displayed deep bodies, short heads, shortened caudal peduncles, and mouths that were generally in a terminal position. These morphological characteristics are associated with environments where current velocity ranges from medium to slow, and have different types of substrates (i.e., rock, gravel, sand, and mud) (
Wajpamheros nourissati
, the outlier of the cichlids analyzed, is the only species that has long and thick lips. This is a characteristic associated with feeding between cracks, on rock surfaces, and on the substrate (
The variation associated with the cephalic region revealed that the majority of species occupy a position in the morphospace that corresponds to their respective clades. For example, members of the Theraps clade (i.e., C. pearsei, C. intermedium, K. ufermanni, and T. irregularis) are positioned toward the superior part of the morphospace, while members of the Paraneetroplus clade (i.e., M. argenteus, O. heterospila, P. bulleri, and R. lentiginosus) are located toward the lower region. However, convergence between the two clades was also observed, largely in the variation of the cephalic characteristics of V. hartwegi and W. nourissati. This notably coincides with the variation of the cephalic characteristic in members of the opposite clade in both cases. Comparative studies have revealed patterns of rapid diversification between lineages and phenotypes through habitat- and diet-related morphological diversity (
Evidence of the low phylogenetic signal of the body shape thus disproves the hypothesis of evolutionary non-independence. However, as the value of the phylogenetic signal can be determined by several processes and evolutionary rates (
In this context, some species of both clades (Theraps–Paraneetroplus) exhibited high convergence in the variation associated with body length and depth, fins position, and eye size and position. This is evident in C. intermedium, V. hartwegi, and W. nourissati, which showed similar body shapes despite being considered as different ecomorphotypes. The remaining species exhibited a morphological pattern consistent with what was expected from the corresponding habitat. The lentic species (C. pearsei, K. ufermanni, M. argenteus, and O. heterospila) showed a clear morphologically divergent pattern with respect to the lotic species (R. lentiginosus, T. irregularis, and P. bulleri). In the case of C. intermedium, V. hartwegi, and W. nourissati, it is probable that habitat preference is determined by other morphological traits that are likely linked to the cephalic region and associated with feeding behavior. This adaptive process has been documented in other fish groups; for example, in the Pomacentridae family, variations in cephalic traits explain feeding behavior and diet and are an important predictor of trophic habit (
Based on the analysis of body shape and head characteristics, the lack of congruence in the order of species in morphospace does not fully support the ecomorphological classification described by
Species of the Theraps–Paraneetroplus clade show highly varied and convergent morphologies that are largely promoted by ecological opportunities associated with habitat and feeding preferences (
In this paper, the morphological variation of the Theraps–Paraneetroplus clade was divided into three groups within the morphospace. These variations are related to body length, body height, head shape, mouth position, and eye size and position. In particular, W. nourissati was the most divergent species due to its cranial characteristics, which are largely related to the shape of the head and the position of the mouth. Body size and height were the variables that best described the position of the species in the morphospace. This facilitates the recovery of lotic and lentic ecomorphotypes for seven species, with only C. intermedium, V. hartwegi, and W. nourissati showing incongruity. The presence of the phylogenetic signal disproves the non-independence hypothesis, but evidence suggests that body shape results from adaptive processes related to ecological opportunity. Although the results of the ANOVA with Procrustes distances and size of the centroid were contradictory, groupings in the morphospace and dendrogram were consistent with the ecomorphotypes and phylogeny. The pairwise comparison test showed statistical differences between all species, with the exception of V. hartwegi–P. bulleri. The morphological patterns found support the taxonomical validity of each species and can be used to describe body shape at the genus level. Future morphological evolution studies should consider cranial structures related to the capture and processing of food.
We thank the anonymous reviewers who provided helpful comments that improved the manuscript. Financial support for this study was received from the Project: “Conectividad y diversidad funcional de la cuenca del río Usumacinta” (Fondo de Investigación Científica y Desarrollo Tecnológico de El Colegio de la Frontera Sur, FID-784), coordinated by RRH. This manuscript is the result of the master thesis of YEAC.