Fig 12 - uploaded by Kory M Evans
Content may be subject to copyright.
Photographs heads of live specimens of four syntopic species of Sternarchella from the vicinity of Tefé, Amazonas, Brazil. a. Sternarchella rex holotype (MCP 49422). b. Sternarchella schotti (MCP 49429. c. Sternarchella calhamazon (MCP 49420. d. Sternarchella orthos (MCP 49436). Scale bar = 10 mm. The flanks of this fish were considerably paler moments before this photograph was taken.
Source publication
This paper provides a taxonomic revision of the Neotropical electric fish genus Sternarchella, with redescriptions of seven valid species and descriptions of two new species. A maximum parsimony analysis of 76 morphological characters from seven ingroup and seven outgroup taxa recovered a non-monophyletic Sternarchella, in which a clade comprising...
Similar publications
Eigenmannia is one of the more taxonomically complex genera within the Gymnotiformes. Here we adopt an integrative taxonomic approach, combining osteology, COI gene sequences, and geometric morphometrics to describe three new species belonging to the E. trilineata species group from Colombian trans-Andean region. These new species increase the numb...
The banded knife fish Gymnotus carapo is among the most widely distributed, broadly adapted (eurytopic), and phenotypically variable fish species in South America, with a geographic range of about 14 million km2, from the Llanos of Ven- ezuela to the Pampas of northern Argentina. Here we assess the structure of phenotypic variation in G. carapo acr...
Citations
... References. Evans et al. 2017. Figure 5I New records. ...
Gymnotiform electric knifefishes are an important yet undersampled component of the Neotropical aquatic biota. We report on the gymnotiform fauna of the Tres Fronteras region located at the triple border of Brazil, Colombia, and Peru in the biodiverse western Amazon. The presence of at least 33 species of gymnotiforms in the Tres Fronteras region is validated from recent sampling efforts and the review of previously collected materials. A key is provided for the identification of the species that have been collected from the region. We comment on the diversity of habitat utilization and intraspecific colour variation of some species.
... Gymnotiform electric fishes are a clade of approximately 262 species that inhabit most lowland aquatic habitats across tropical South and Central America (Albert, 2001(Albert, , 2003Crampton, 2006, 2009;Ivanyisky and Albert, 2014;Evans et al., 2017a;Bernt et al., 2018Bernt et al., , 2020Dagosta and de Pinna, 2019;Albert et al., 2020). The family of ghost electric knifefishes (Apteronotidae) is a dominant component of the species diversity and biomass in large and deep (to 100 m) lowland river channels of Greater Amazonia (Lundberg et al., 1987;Crampton et al., 2004;Correa et al., 2006;Duarte et al., 2019). ...
Ghost electric knifefishes (Gymnotiformes: Apteronotidae) are a dominant component of the species diversity and biomass of large lowland rivers in Greater Amazonia, including 77 species that exhibit diverse craniofacial morphologies associated with trophic and secondary sexual traits. Here we use open-source computed micro-tomography (CT) scans to generate 3D reconstructions for a majority of apteronotid species and almost all valid genera, and geometric morphometric and phylogenetic analyses to explore patterns of skull evolution. As with most vertebrates, principal component 1 (PC1) summarizes variance from brachycephalic to dolichocephalic morphologies, previously described as heterocephaly, and PC2 summarizes variance from recurved (upturned) to decurved (downturned) snout morphologies, described here as heterorhynchy. Phylomorphospace and traitogram analyses found instances of both convergent and divergent evolution along both of the first two PC axes, as well as a preponderance of clades characterized by morphological stasis or phylogenetic conservatism. Certain phenotypic combinations predominate among species and clades, including elongated-downturned snouts and foreshortened-upturned snouts, while other phenotypic combinations are not observed, including elongated-upturned snouts and foreshortened-downturned snouts. These results highlight the power of 3D geometric morphometrics in the study of craniofacial evolution and indicate developmental or functional constraints in the evolution of craniofacial phenotypes in an ecologically dominant clade of riverine Amazonian fishes.
... S. duccis and S. raptor ["S. duccis clade" sensu Evans et al., 2017] Adductor mandibulae. The malaris arises from the mid-dorsal portion of the hyomandibula, quadrate, and preopercle, converging anteriorly to the buccopalatal membrane, where the anterodorsal portion differentiates into an endomaxilar ligament, equal to the fibrous portion of the malaris, to a insertion at the mesethmoid, premaxilla and the connective tissue between the anterior margin of the premaxilla and upper lip; and the anteroventral fibers converges into an ectomaxillary ligament that inserts at the posterolateral face of the maxilla. ...
... Conflicting ideas about the most basal taxon in Eigenmanniinae have been recurrent, regardless of the kind of data employed. Some analyses place Rhabdolichops in that Albert, 2014;Tagliacollo et al., 2016;Evans et al., 2017; or to a clade composed of Compsaraia + Melanosternarchus (Bernt et al., , 2020. Again, at odds with previous proposals, our analysis places Compsaraia as sister to clade PA. ...
... Clade MS includes species traditionally allocated in Sternarchella (S. schotti and S. orthos) and species previously in Magosternarchus (M. raptor and M. duccis; the genus was recently considered as a junior synonym of Sternarchella by Ferraris et al., 2017 andEvans et al., 2017). Clade MS is one of the few groups unanimously supported in all previous hypotheses of relationships among Apteronotidae (e.g., Albert, Campos-da-Paz, 1998;Albert, 2001;Triques, 2005;Tagliacollo et al., 2016;Ivanyisky III, Albert, 2014;Evans et al., 2017;Bernt et al., , 2020 and is also supported here. ...
The present study offers a broad comparative analysis of the dorsolateral head musculature in the Gymnotiformes, with detailed descriptions and illustrations of the dorsolateral head muscles of 83 species representing combined all valid genera. Results permit a detailed assessment of primary homologies and taxonomically-relevant variation across the order. This provides the basis for a myological synonymy, which organizes 33 previously proposed names for 15 recognized muscles. Morphological variation derived from dorsolateral head musculature was coded into 56 characters. When analyzed in isolation, that set of characters results in Gymnotidae as the sister group of remaining gymnotiforms, and all other currently recognized families as monophyletic groups. In a second analysis, myological characters were concatenated with other previously proposed characters into a phenotypic matrix. Results of that analysis reveal new myological synapomorphies for nearly all taxonomic categories within Gymnotiformes. A Partitioned Bremer Support (PBS) was used to asses the significance of comparative myology in elucidating phylogenetic relationships. PBS values show strongly non-uniform distributions on the tree, with positive scores skewed towards more inclusive taxa, and negative PBS values concentrated on less inclusive clades. Our results provide background for future studies on biomechanical constraints evolved in the early stages of gymnotiform evolution.
... Meristic data for species in Apteronotus and other Gymnotiformes genera were taken by direct examination and/or from the literature (Albert, 2001;Bernt & Albert, 2017;Bernt et al., 2018Bernt et al., , 2020Campos-da-Paz, 1995, 1999Evans et al., 2017a;Fernández-Yépez, 1968;Hulen et al., 2005;Hilton et al., 2007;Hilton & Cox Fernandes, 2017;Lundberg et al., 2013;Mago-Leccia, 1994;Maldonado-Ocampo et al., 2011;de Santana, 2002de Santana, , 2003, 2005de Santana & Cox Fernandes, 2012;de Santana & Lehmann, 2006;de Santana & Crampton, 2007, 2010, 2011de Santana & Vari, 2009, 2010Schultz, 1949;Steindachner, 1881;Triques, 2011;. ...
A new species of ghost knifefish, Apteronotus, is described from high‐energy environments in the Rios Mapuera and Trombetas (at Cachoeira Porteira waterfalls), Brazil. X‐ray microcomputed tomography (μCT scan) was employed to access the internal anatomy of the type series. The new species is distinguished from all congeners by the anteriormost position of the anus, with its posterior margin extending less than one eye diameter beyond the vertical through the caudal limit of the posterior nostril, the low number of anal‐fin rays (117–125), and the reduced number of branchiostegal rays (three). A series of modifications associated with secondary sexual dimorphism on the preorbital region of mature males are depicted and discussed. In addition, comments on homologies of the branchiostegal rays in Apteronotidae are provided.
... optima occur on a high-dimensional landscape with both static and dynamic features. Static features of fitness landscapes arise due to negative epistasis within genotypic networks (Whitlock et al. 1995;Weinreich et al. 2005;Wright 1932) and functional trade-offs between different ecological niches or collections of similar niches known as adaptive zones (Simpson 1944;Roughgarden 1972;Higham et al. 2016;Evans et al. 2017). Dynamic features, emphasized by the more recent paradigm of adaptive dynamics originating in game theory (Abrams et al. 1993;Abrams 2001;Bolnick 2004;, arise because the fitness landscape resembles a trampoline: as the relative frequency of phenotypically similar individuals competing for the same limited resources increases, their fitness decreases due to increased competition, whereas rare phenotypes at the extremes of the phenotype distribution should have a fitness advantage due to reduced competition for additional resources that they are able to exploit (Rosenzweig 1978). ...
The effect of the environment on fitness in natural populations is a fundamental question in evolutionary biology. However, experimental manipulations of both environment and phenotype at the same time are rare. Thus, the relative importance of the competitive environment versus intrinsic organismal performance in shaping the location, height, and fluidity of fitness peaks and valleys remains largely unknown. Here, we experimentally tested the effect of competitor frequency on the complex fitness landscape driving adaptive radiation of a generalist and two trophic specialist pupfishes, a scale‐eater and molluscivore, endemic to hypersaline lakes on San Salvador Island (SSI), Bahamas. We manipulated phenotypes, by generating 3407 F4/F5 lab‐reared hybrids, and competitive environment, by altering the frequency of rare transgressive hybrids between field enclosures in two independent lake populations. We then tracked hybrid survival and growth rates across these four field enclosures for 3–11 months. In contrast to competitive speciation theory, we found no evidence that the frequency of hybrid phenotypes affected their survival. Instead, we observed a strikingly similar fitness landscape to a previous independent field experiment, each supporting multiple fitness peaks for generalist and molluscivore phenotypes and a large fitness valley isolating the divergent scale‐eater phenotype. These features of the fitness landscape were stable across manipulated competitive environments, multivariate trait axes, and spatiotemporal heterogeneity. We suggest that absolute performance constraints and divergent gene regulatory networks shape macroevolutionary (interspecific) fitness landscapes in addition to microevolutionary (intraspecific) competitive dynamics. This interplay between organism and environment underlies static and dynamic features of the adaptive landscape.
... During the Neogene, tectonics, and climatic changes resulted on important modifications in geographical connectivity between these mega-wetlands, ranging from more connected in the late Miocene to more fragmented by Pliocene to Recent times (Albert et al., 2018). The above mentioned drainage connections allowed fishes to disperse between northern South America and Parana basins (Albert et al., 2011(Albert et al., , 2018Dias et al., 2014;Evans et al., 2017). ...
... First, a compilation of the records of species originally described based on specimens collected in the Rio Negro basin or that included that basin in their distribution range was made based in the catalogues of Reis et al. (2003), Buckup et al. (2007), Ferraris-Jr (2007, and Ferraris-Jr et al. (2017). Additional information from taxonomic revisions and species descriptions from 2003 to 2019 were also included: Armbruster (2003), Britto and Lima (2003), Costa (2003aCosta ( , 2003b, Vari and Lima (2003), Costa (2004aCosta ( , 2004b, Crampton et al. (2004), Hrbek et al. (2004), Lehmann and Reis (2004), Malabarba (2004), Zanata and Toledo-Piza (2004), Zarske et al. (2004, Kullander and Ferreira (2005), Lundberg and er (2016), , , Tencatt and Britto (2016), Tencatt and Ohara (2016), Britski and Birindelli (2016), Bernt and Albert (2017), Burns et al. (2017), Evans et al. (2017), Ferraris-Jr et al. (2017), Fontenelle and Carvalho (2017), Sabaj and Hernández (2017), Ribeiro et al. (2017), Marinho and Menezes (2017), Melo and Oliveira (2017), Bernt et al. (2018, Bragança (2018), Caires and Toledo-Piza (2018), Henschel et al. (2018), Mateussi et al. (2018), Silva and Rapp Py-Daniel (2018), Urbanski et al. (2018), and Reia and Benine (2019). Information was also collected from publications focusing on biogeographic analyses and large taxonomic fish inventories in specific areas or sub-basins of the Rio Negro drainage system: Knöppel (1970), Henderson and Walker (1986), Goulding et al. (1988), Barletta (1995), Chao and Prada-Pedreros (1995), Silva (1995), Zuanon et al. (1998), Saint-Paul et al. (2000, Chao (2001), Mortati (2004), Thomé-Souza and Chao (2004), Soares and Yamamoto (2005) The second main source of information was composed by a thorough survey for all species that were collected in the Rio Negro basin and that have lots deposited in the INPA Fish Collection, which were personally verified by the authors. ...
This study presents an extensive review of published and unpublished occurrence records of fish species in the Rio Negro drainage system within the Brazilian territory. The data was gathered from two main sources: 1) litterature compilations of species occurrence records, including original descriptions and revisionary studies; and 2) specimens verification at the INPA fish collection. The results reveal a rich and diversified ichthyofauna, with 1,165 species distributed in 17 orders (+ two incertae sedis), 56 families, and 389 genera. A large portion of the fish fauna (54.3% of the species) is composed of small-sized fishes < 10 cm in standard length. The main groups are Characiformes (454 species; 39.0%), Siluriformes (416; 35.7%), Gymnotiformes (105; 9.0%), and Cichliformes (102; 8.8%). The species composition differs between the main aquatic environments, such as: main channel (159 species), lakes (296), tributary rivers (596), small streams (234), seasonal beaches (186), and rapids (41). Part of the ichthyofauna is shared with adjacent basins, such as the Orinoco, rivers of the Guiana Shield, lower Solimões/Amazonas and upper Amazonas, which contributes to the remarkable ichthyofaunal diversity of the basin. A high rate of species endemism was observed in Characidae (24), Loricariidae (18), Cichlidae (18) and Callichthyidae (18), totalling 156 species (13.4%) endemic to the basin. An estimation of the species richness for the Rio Negro basin, considering 23 published references, resulted in 1,466 and 1,759 species (Jackknife 1 and 2, respectively), which seems reasonable when considering the large number of morphotypes left out of the present list and the low sampling effort in many areas of the basin. The results presented herein provide an additional tool for environmental managers and decision makers for conservation purposes of one of the richest and most well-preserved sub-basins of the Rio Amazonas system.
... John and Martin 2019). This specialized niche has evolved more than 19 times in fishes across diverse environments from the deep sea (Nakae and Sasaki 2002) to the Amazon basin (Evans et al. 2017), but to our knowledge scale-eating evolved only once among over 1500 species of atherinomorph and cyprinodontiform fishes Martin and Wainwright 2013a;Kolmann et al. 2018). Thus, the scale-eating pupfish is separated by 168 million years from the most closely related scale-eating specialists (within the East African cichlid radiations), providing a quantitative phylogenetic index of the novelty of this ecological niche relative to other ecological niches (Martin and Wainwright 2013a). ...
Synopsis
Biologists are drawn to the most extraordinary adaptations in the natural world, often referred to as evolutionary novelties, yet rarely do we understand the microevolutionary context underlying the origins of novel traits, behaviors, or ecological niches. Here we discuss insights gained into the origins of novelty from a research program spanning biological levels of organization from genotype to fitness in Caribbean pupfishes. We focus on a case study of the origins of novel trophic specialists on San Salvador Island, Bahamas and place this radiation in the context of other rapid radiations. We highlight questions that can be addressed about the origins of novelty at different biological levels, such as measuring the isolation of novel phenotypes on the fitness landscape, locating the spatial and temporal origins of adaptive variation contributing to novelty, detecting dysfunctional gene regulation due to adaptive divergence, and connecting behaviors with novel traits. Evolutionary novelties are rare, almost by definition, and we conclude that integrative case studies can provide insights into this rarity relative to the dynamics of adaptation to more common ecological niches and repeated parallel speciation, such as the relative isolation of novel phenotypes on fitness landscapes and the transient availability of ecological, genetic, and behavioral opportunities.
... Gymnotiform fishes are a moderately diverse (~300 spp.) clade of weakly electric fishes which exhibit elongate eel-like bodies and all possess elongate anal fins for use in a specialized form of locomotion (Albert 2001;van der Sleen and Albert 2017;Evans et al. 2018b). In addition to their derived body shapes, gymnotiform fishes also exhibit a diversity of skull shapes and trophic ecologies, ranging from fishes with elongate tube-snouts that probe the substrate and interstitial spaces to extract aquatic invertebrates, to brachycephalic piscivores who feed primarily on scales and tails of other electric fishes (Marrero and Winemiller 1993;Lundberg et al. 1996;Albert 2001;Albert and Crampton 2005;Bernt and Albert 2017;Evans et al. 2017a). Gymnotiformes have been the subject of several recent studies examining the developmental and evolutionary history of the skull and oral jaws (Evans et al. 2017b;Evans et al. 2017c;Evans et al. 2018a). ...
Synopsis
The relationship between form and function is thought to play an integral role in structuring broad-scale patterns of morphological evolution and resource utilization. In ecomorphological studies, mechanical performance is widely understood to constrain the evolution of form and function. However, the relationship between form, function, and resource utilization is less clear. Additionally, seasonal fluctuations in resource availability may further complicate patterns of resource use. How organisms cope with these complexities, and the effect of these factors on broadscale patterns of morphological evolution is also poorly understood. Here we use three-dimensional geometric morphometrics, biomechanics, stable isotope analysis, and gut-content analysis to study trophic evolution in a clade of riverine-adapted electric fishes from a region with high seasonal variability; the Amazon River. We find significant and phylogenetically structured relationships among measures of trophic ecology and skull shape. We also recover a significant relationship between the mechanical advantage of the mandible and trophic position, where species feeding at higher trophic levels have narrower jaws with lower mechanical advantages, and species feeding at lower trophic levels have deeper jaws with higher mechanical advantages. Our results indicate that selection is driving the evolution of mandible shape and performance toward specialization on different trophic ecologies.
... Electric fishes possess the ability to regenerate a significant portion of their bodies after being damaged by predation. As a result, total length is often a poor estimate of size; to correct for this, dimensions of head length are frequently utilized as a proxy for overall size (Albert, 2001;Bernt & Albert, 2017;Evans et al., 2017aEvans et al., , 2018. ...
The evolution of sexually dimorphic traits is thought to have marked effects on underlying patterns of static allometry. These traits can negatively affect organismal survivability by creating trade-offs between trait size and performance. Here we use three-dimensional geometric morphometrics to study the static allometry of two species of sexually dimorphic electric fishes (Apteronotus rostratus and Compsaraia samueli) in which mature males grow elongate jaws used in agonistic male–male interactions. We also estimate jaw-closing performance between the sexes of both species to track changes in kinematic transmission associated with the development of sexual weaponry. We find significantly different patterns of static allometry between the sexes of both species, with males exhibiting more positive allometric slopes relative to females. We also find a negative relationship between skull shape and mandibular kinematic transmission in C. samueli, suggesting a trade-off where males with longer faces exhibit lower mechanical advantages, suggesting weaker jaw leverage. In contrast, males and females of A. rostratus exhibit no difference between sexes in mechanical advantage associated with facial elongation.
