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Axel Meyer - One of the best experts on this subject based on the ideXlab platform.
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transcriptomics of two evolutionary novelties how to make a sperm transfer organ out of an anal fin and a sexually selected sword out of a caudal fin
Ecology and Evolution, 2015Co-Authors: Ji Hyoun Kang, Tereza Manousaki, Paolo Franchini, Susanne Kneitz, Manfred Schartl, Axel MeyerAbstract:Swords are exaggerated male ornaments of Swordtail fishes that have been of great interest to evolutionary biologists ever since Darwin described them in the Descent of Man (1871). They are a novel sexually selected trait derived from modified ventral caudal fin rays and are only found in the genus Xiphophorus. Another phylogenetically more widespread and older male trait is the gonopodium, an intromittent organ found in all poeciliid fishes, that is derived from a modified anal fin. Despite many evolutionary and behavioral studies on both traits, little is known so far about the molecular mechanisms underlying their development. By investigating transcriptomic changes (utilizing a RNA-Seq approach) in response to testosterone treatment in the Swordtail fish, Xiphophorus hellerii, we aimed to better understand the architecture of the gene regulatory networks underpinning the development of these two evolutionary novelties. Large numbers of genes with tissue-specific expression patterns were identified. Among the “sword genes” those involved in embryonic organ development, sexual character development and coloration were highly expressed, while in the gonopodium rather more morphogenesis-related genes were found. Interestingly, many genes and genetic pathways are shared between both developing novel traits derived from median fins: the sword and the gonopodium. Our analyses show that a larger set of gene networks was co-opted during the development and evolution of the “older” gonopodium than in the “younger,” and morphologically less complex trait, the sword. We provide a catalog of candidate genes for future efforts to dissect the development of those sexually selected exaggerated male traits in Swordtails.
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Transcriptomics of two evolutionary novelties: how to make a sperm‐transfer organ out of an anal fin and a sexually selected “sword” out of a caudal fin
Ecology and evolution, 2015Co-Authors: Ji Hyoun Kang, Tereza Manousaki, Paolo Franchini, Susanne Kneitz, Manfred Schartl, Axel MeyerAbstract:Swords are exaggerated male ornaments of Swordtail fishes that have been of great interest to evolutionary biologists ever since Darwin described them in the Descent of Man (1871). They are a novel sexually selected trait derived from modified ventral caudal fin rays and are only found in the genus Xiphophorus. Another phylogenetically more widespread and older male trait is the gonopodium, an intromittent organ found in all poeciliid fishes, that is derived from a modified anal fin. Despite many evolutionary and behavioral studies on both traits, little is known so far about the molecular mechanisms underlying their development. By investigating transcriptomic changes (utilizing a RNA-Seq approach) in response to testosterone treatment in the Swordtail fish, Xiphophorus hellerii, we aimed to better understand the architecture of the gene regulatory networks underpinning the development of these two evolutionary novelties. Large numbers of genes with tissue-specific expression patterns were identified. Among the “sword genes” those involved in embryonic organ development, sexual character development and coloration were highly expressed, while in the gonopodium rather more morphogenesis-related genes were found. Interestingly, many genes and genetic pathways are shared between both developing novel traits derived from median fins: the sword and the gonopodium. Our analyses show that a larger set of gene networks was co-opted during the development and evolution of the “older” gonopodium than in the “younger,” and morphologically less complex trait, the sword. We provide a catalog of candidate genes for future efforts to dissect the development of those sexually selected exaggerated male traits in Swordtails.
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comprehensive phylogenetic analysis of all species of Swordtails and platies pisces genus xiphophorus uncovers a hybrid origin of a Swordtail fish xiphophorus monticolus and demonstrates that the sexually selected sword originated in the ancestral li
BMC Evolutionary Biology, 2013Co-Authors: Ji Hyoun Kang, Manfred Schartl, Ronald B Walter, Axel MeyerAbstract:Males in some species of the genus Xiphophorus, small freshwater fishes from Meso-America, have an extended caudal fin, or sword – hence their common name “Swordtails”. Longer swords are preferred by females from both sworded and – surprisingly also, non-sworded (platyfish) species that belong to the same genus. Swordtails have been studied widely as models in research on sexual selection. Specifically, the pre-existing bias hypothesis was interpreted to best explain the observed bias of females in presumed ancestral lineages of swordless species that show a preference for assumed derived males with swords over their conspecific swordless males. However, many of the phylogenetic relationships within this genus still remained unresolved. Here we construct a comprehensive molecular phylogeny of all 26 known Xiphophorus species, including the four recently described species (X. kallmani, X. mayae, X. mixei and X. monticolus). We use two mitochondrial and six new nuclear markers in an effort to increase the understanding of the evolutionary relationships among the species in this genus. Based on the phylogeny, the evolutionary history and character state evolution of the sword was reconstructed and found to have originated in the common ancestral lineage of the genus Xiphophorus and that it was lost again secondarily. We estimated the evolutionary relationships among all known species of the genus Xiphophorus based on the largest set of DNA markers so far. The phylogeny indicates that one of the newly described Swordtail species, Xiphophorus monticolus, is likely to have arisen through hybridization since it is placed with the southern platyfish in the mitochondrial phylogeny, but with the southern Swordtails in the nuclear phylogeny. Such discordance between these two types of markers is a strong indication for a hybrid origin. Additionally, by using a maximum likelihood approach the possession of the sexually selected sword trait is shown to be the most likely ancestral state for the genus Xiphophorus. Further, we provide a well supported estimation of the phylogenetic relationships between the previously unresolved northern Swordtail groups. This comprehensive molecular phylogeny of the entire genus Xiphophorus provides evidence that a second Swordtail species, X. monticolus, arose through hybridization. Previously, we demonstrated that X. clemenciae, another southern Swordtail species, arose via hybridization. These findings highlight the potential key role of hybridization in the evolution of this genus and suggest the need for further investigations into how hybridization contributes to speciation more generally.
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A phylogeographic investigation of the hybrid origin of a species of Swordtail fish from Mexico.
Molecular ecology, 2012Co-Authors: Julia C. Jones, Juan-antonio Perez-sato, Axel MeyerAbstract:Hybrid speciation may contribute significantly to generating biodiversity, but only a few well-documented examples for it exist so far that do not involve polyploidization as a mechanism. The Swordtail fish, Xiphophorus clemenciae, shows common hallmarks of a hybrid origin and still overlaps in its current geographic distribution with its putative ancestral species (Xiphophorus hellerii and Xiphophorus maculatus). Xiphophorus clemenciae provides an ideal system for investigating the possible continued genetic interactions between a hybrid and its parental species. Here, we use microsatellite and mitochondrial markers to investigate the population structure of these species of Swordtails and search for signs of recent hybridization. Individuals were sampled from 21 localities across the known range of X. clemenciae- the Isthmus of Tehuantepec (IT) Mexico, and several environmental parameters that might represent barriers to dispersal were recorded. The hybridization event that gave rise to X. clemenciae appears to be rather ancient, and a single origin is likely. We find negligible evidence for ongoing hybridization and introgression between the putative ancestral species, because they now occupy distinct ecological niches, and a common haplotype is shared by most populations of X. clemenciae. The population structure within these species shows an isolation-by-distance (IBD) pattern and genetic differentiation between most populations is significant and high. We infer that tectonic evolution in the Isthmus has greatly restricted gene flow between the southern and central IT populations of X. clemenciae and X. helleriii and provide preliminary information to aid in conservation management of this geographically restricted hybrid species, X. clemenciae.
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An organizer controls the development of the "sword," a sexually selected trait in Swordtail fish.
Evolution & development, 2008Co-Authors: Cornelius Eibner, Axel Meyer, Silke Pittlik, Gerrit BegemannAbstract:SUMMARY Male Swordtail fish of the genus Xiphophorus (Poeciliidae) possess a ‘‘sword’’ that is composed of several colored elongated ventral fin rays of the caudal fin. The sword is a secondary sexual trait that evolved through sexual selection by female preference. To uncover the developmental mechanisms underlying the metamorphosis from a juvenile caudal fin to the sword, we have devised a transplantation protocol to assay the fate of single transplanted fin rays and their interactions with flanking rays. These experiments provide evidence for the existence of a previously unrecognized inductive signal that originates in those rays that develop into the two longest sword rays. This ‘‘sword organizer’’ causes adjacent fin rays to grow and become integrated into the sword and induces the development of an additional, typically pigmented sword in grafts to the dorsal part of the caudal fin. We show that the potential to develop a sword is restricted to certain parts of the caudal fin. Our findings suggest that the evolution of swords in Swordtails required the acquisition of two developmental mechanisms: the establishment of signaling competence in prospective sword rays in the embryo or early larva, and its activation through androgen signaling in adult male fish.
Grant E. Brown - One of the best experts on this subject based on the ideXlab platform.
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Are all signals the same? Ontogenetic change in the response to conspecific and heterospecific chemical alarm signals by juvenile green sunfish (Lepomis cyanellus)
Behavioral Ecology and Sociobiology, 2003Co-Authors: Justin L. Golub, Grant E. BrownAbstract:Within aquatic communities, individuals may gain survival benefits by responding to the chemical alarm signals of heterospecific prey guild members. Piscivorous individuals, however, should be selected to use such chemical signals as foraging cues. A variety of centrarchid species, such as largemouth bass (Micropterus salmoides), undergo an ontogenetic change in their response to the chemical alarm cues of heterospecific guild members, switching from antipredator to foraging responses. This ontogenetic shift should occur when potential foraging benefits outweigh any survival advantage gained from an antipredator response. To test this model, we exposed juvenile green sunfish (Lepomis cyanellus) to the skin extracts of conspecifics, a heterospecific prey guild member (finescale dace, Phoxinus neogeaus) or an allopatric heterospecific (green Swordtails, Xiphophorus helleri). Juvenile sunfish exhibited a significant positive relationship between standard length and time spent moving and a significant negative relationship between length and time in a spine-erect posture, when exposed to dace skin extract, but not to either Swordtail or conspecific skin extracts. Smaller individuals of less than 90 mm standard length (SL) decreased time moving and increased time with spines erect (indicating an antipredator response) while larger individuals (>90 mm SL) increased time moving and decreased time with spines erect (indicating a foraging response), when exposed to dace skin extract. Conversely, juvenile sunfish, regardless of size tested, always exhibited an antipredator response to conspecific skin extract. Sunfish exhibited no change in behaviour in response to Swordtail skin extracts. These data further support our model of a threat sensitive trade-off in the response to chemical alarm signals by juvenile centrarchids.
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Attack Cone Avoidance During Predator Inspection Visits by Wild Finescale Dace (Phoxinus neogaeus): The Effects of Predator Diet
Journal of chemical ecology, 2001Co-Authors: Grant E. Brown, Justin L. Golub, Desiree L. PlataAbstract:When confronted by potential predators, many prey fishes engage in predator inspection behavior. Previous authors have argued that by selectively avoiding the predator's head during an inspection visit (attack cone avoidance), individual inspectors may reduce their local risk of predation. In field trials, we investigated the effects of predator diet cues on the presence of ‘attack cone avoidance’ during predator inspection visits. Wild, free-ranging finescale dace (Phoxinus neogaeus) were exposed to the combined cues of a model predator and a distilled water control or the odor of a yellow perch (Perca flavescens) fed dace (with alarm pheromone), Swordtail (Xiphophorus helleri) (lacking Ostariophysan alarm pheromone), or perch that were food deprived for four days. Finescale dace modified their predator inspection behavior following exposure to the odor of a perch fed dace (fewer dace present, reduced frequency of inspections, and an increased per capita inspection rate) compared to those exposed to the odor of a perch fed Swordtails, perch that were food deprived, or a distilled water control. In addition, dace inspected the tail region more often only when the model predator was paired with the odor of a perch fed dace. In all other treatments, dace inspected the head region of the model predator more often. These data suggest that attack cone avoidance of inspecting prey fishes may be more likely to occur in high-risk situations, such as in the presence of conspecific alarm pheromones in the diet of potential predators.
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Chemical Alarm Signals in Juvenile Green Sunfish (Lepomis cyanellus, Centrarchidae)
Copeia, 2000Co-Authors: Grant E. Brown, Scott BrennanAbstract:We investigated the presence of chemical alarm signals in juvenile Green Sunfish (Lepomis cyanellus) under laboratory conditions. We exposed individual sunfish to skin extracts of conspecifics and Swordtails (Xiphophorus helleri), a species not known to possess alarm pheromones and that is phylogenetically distant and allopatric from green sunfish. Sunfish significantly increased time spent freezing and time with dorsal fin rays erect (known antipredator postures) in response to conspecific skin extract but not to Swordtail skin extract. No significant difference was noted in change in area use for sunfish exposed to conspecific versus Swordtail skin extract. These results suggest that juvenile green sunfish possess chemical alarm signals. This is the first such demonstration in a centrarchid species.
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fin flicking behaviour a visual antipredator alarm signal in a characin fish hemigrammus erythrozonus
Animal Behaviour, 1999Co-Authors: Grant E. Brown, Jean-guy J. Godin, Jessica PedersenAbstract:Abstract Glowlight tetras, Hemigrammus erythrozonus, show a conspicuous visual display (‘fin flicking’) upon detecting a conspecific chemical alarm signal (alarm pheromone). We conducted laboratory studies to test two, nonmutually exclusive hypotheses regarding the function of this behaviour. To test the hypothesis that fin flicking acts as a visual alarm signal to conspecifics, we paired shoals of tetras with a stimulus tetra in an adjacent tank (separated by a one-way mirror) and exposed the stimulus tetras to conspecific skin extract (with alarm pheromone) or Swordtail skin extract (which lacks ostariophysan alarm pheromone). Stimulus tetras significantly increased their frequency of fin flicking when exposed to conspecific skin extract, but not to the Swordtail skin extract control. The test shoals showed a significant increase in antipredator behaviour in response to fin-flicking stimulus tetras, but not to stimulus tetras that did not fin-flick. To test the hypothesis that fin flicking serves as a predator deterrent, we paired predatory Jack Dempsey cichlids, Cichlasoma octofaciatum, with tetras in adjacent tanks and exposed the tetras to either conspecific or Swordtail skin extract. Predators remained further away from the stimulus tetra, took longer to initiate a bite and displayed fewer bites towards tetras that fin-flicked compared with tetras that did not fin-flick. These results support our hypothesis that fin flicking in tetras serves as both a visual alarm signal to conspecifics and a deterring signal to predators, and suggest that individual tetras may reduce their risk of predation by fin flicking upon detecting a predation threat.
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who dares learns chemical inspection behaviour and acquired predator recognition in a characin fish
Animal Behaviour, 1999Co-Authors: Grant E. Brown, Jean-guy J. GodinAbstract:Abstract Individuals that dare approach predators (predator inspection behaviour) may benefit by acquiring information regarding the potential threat of predation. Although information acquisition based on visual cues has been demonstrated for fish, it is unknown whether fish will inspect predators on the basis of chemical cues or whether such inspection behaviour results in information acquisition. Here, we first ascertained whether predator inspection behaviour can be mediated by chemical cues from predators by exposing groups of predator-naive glowlight tetras (Hemigrammus erythrozonus) to the chemical cues of a potential fish predator (convict cichlidCichlasoma nigrofasciatum) that had been fed either tetras (which possess an alarm pheromone) or Swordtails (Xiphophorus helleri, which lack Ostariophysan alarm pheromones). Tetras showed a significant increase in antipredator behaviour when exposed to the tetra-diet cue, but not when exposed to the Swordtail-diet cue. Chemically mediated predator inspection behaviour was also affected. Both the latency to inspect and the minimum approach distance to the predator significantly increased, and the mean number of inspectors per predator inspection visit significantly decreased when tetras were exposed to the tetra-diet versus the Swordtail-diet chemical cues. We then examined a potential benefit associated with chemically mediated predator inspection behaviour. Only tetras that were initially exposed to the tetra-diet cue and that had inspected the predator acquired the visual recognition of a convict cichlid as a predation threat. Our results thus demonstrate that (1) predator inspection behaviour in the glowlight tetra can be initiated by chemical cues, (2) chemically mediated inspection behaviour is affected by the presence of alarm pheromone, and (3) inspectors benefit by acquiring the recognition of novel predators.
Manfred Schartl - One of the best experts on this subject based on the ideXlab platform.
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transcriptomics of two evolutionary novelties how to make a sperm transfer organ out of an anal fin and a sexually selected sword out of a caudal fin
Ecology and Evolution, 2015Co-Authors: Ji Hyoun Kang, Tereza Manousaki, Paolo Franchini, Susanne Kneitz, Manfred Schartl, Axel MeyerAbstract:Swords are exaggerated male ornaments of Swordtail fishes that have been of great interest to evolutionary biologists ever since Darwin described them in the Descent of Man (1871). They are a novel sexually selected trait derived from modified ventral caudal fin rays and are only found in the genus Xiphophorus. Another phylogenetically more widespread and older male trait is the gonopodium, an intromittent organ found in all poeciliid fishes, that is derived from a modified anal fin. Despite many evolutionary and behavioral studies on both traits, little is known so far about the molecular mechanisms underlying their development. By investigating transcriptomic changes (utilizing a RNA-Seq approach) in response to testosterone treatment in the Swordtail fish, Xiphophorus hellerii, we aimed to better understand the architecture of the gene regulatory networks underpinning the development of these two evolutionary novelties. Large numbers of genes with tissue-specific expression patterns were identified. Among the “sword genes” those involved in embryonic organ development, sexual character development and coloration were highly expressed, while in the gonopodium rather more morphogenesis-related genes were found. Interestingly, many genes and genetic pathways are shared between both developing novel traits derived from median fins: the sword and the gonopodium. Our analyses show that a larger set of gene networks was co-opted during the development and evolution of the “older” gonopodium than in the “younger,” and morphologically less complex trait, the sword. We provide a catalog of candidate genes for future efforts to dissect the development of those sexually selected exaggerated male traits in Swordtails.
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Transcriptomics of two evolutionary novelties: how to make a sperm‐transfer organ out of an anal fin and a sexually selected “sword” out of a caudal fin
Ecology and evolution, 2015Co-Authors: Ji Hyoun Kang, Tereza Manousaki, Paolo Franchini, Susanne Kneitz, Manfred Schartl, Axel MeyerAbstract:Swords are exaggerated male ornaments of Swordtail fishes that have been of great interest to evolutionary biologists ever since Darwin described them in the Descent of Man (1871). They are a novel sexually selected trait derived from modified ventral caudal fin rays and are only found in the genus Xiphophorus. Another phylogenetically more widespread and older male trait is the gonopodium, an intromittent organ found in all poeciliid fishes, that is derived from a modified anal fin. Despite many evolutionary and behavioral studies on both traits, little is known so far about the molecular mechanisms underlying their development. By investigating transcriptomic changes (utilizing a RNA-Seq approach) in response to testosterone treatment in the Swordtail fish, Xiphophorus hellerii, we aimed to better understand the architecture of the gene regulatory networks underpinning the development of these two evolutionary novelties. Large numbers of genes with tissue-specific expression patterns were identified. Among the “sword genes” those involved in embryonic organ development, sexual character development and coloration were highly expressed, while in the gonopodium rather more morphogenesis-related genes were found. Interestingly, many genes and genetic pathways are shared between both developing novel traits derived from median fins: the sword and the gonopodium. Our analyses show that a larger set of gene networks was co-opted during the development and evolution of the “older” gonopodium than in the “younger,” and morphologically less complex trait, the sword. We provide a catalog of candidate genes for future efforts to dissect the development of those sexually selected exaggerated male traits in Swordtails.
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comprehensive phylogenetic analysis of all species of Swordtails and platies pisces genus xiphophorus uncovers a hybrid origin of a Swordtail fish xiphophorus monticolus and demonstrates that the sexually selected sword originated in the ancestral li
BMC Evolutionary Biology, 2013Co-Authors: Ji Hyoun Kang, Manfred Schartl, Ronald B Walter, Axel MeyerAbstract:Males in some species of the genus Xiphophorus, small freshwater fishes from Meso-America, have an extended caudal fin, or sword – hence their common name “Swordtails”. Longer swords are preferred by females from both sworded and – surprisingly also, non-sworded (platyfish) species that belong to the same genus. Swordtails have been studied widely as models in research on sexual selection. Specifically, the pre-existing bias hypothesis was interpreted to best explain the observed bias of females in presumed ancestral lineages of swordless species that show a preference for assumed derived males with swords over their conspecific swordless males. However, many of the phylogenetic relationships within this genus still remained unresolved. Here we construct a comprehensive molecular phylogeny of all 26 known Xiphophorus species, including the four recently described species (X. kallmani, X. mayae, X. mixei and X. monticolus). We use two mitochondrial and six new nuclear markers in an effort to increase the understanding of the evolutionary relationships among the species in this genus. Based on the phylogeny, the evolutionary history and character state evolution of the sword was reconstructed and found to have originated in the common ancestral lineage of the genus Xiphophorus and that it was lost again secondarily. We estimated the evolutionary relationships among all known species of the genus Xiphophorus based on the largest set of DNA markers so far. The phylogeny indicates that one of the newly described Swordtail species, Xiphophorus monticolus, is likely to have arisen through hybridization since it is placed with the southern platyfish in the mitochondrial phylogeny, but with the southern Swordtails in the nuclear phylogeny. Such discordance between these two types of markers is a strong indication for a hybrid origin. Additionally, by using a maximum likelihood approach the possession of the sexually selected sword trait is shown to be the most likely ancestral state for the genus Xiphophorus. Further, we provide a well supported estimation of the phylogenetic relationships between the previously unresolved northern Swordtail groups. This comprehensive molecular phylogeny of the entire genus Xiphophorus provides evidence that a second Swordtail species, X. monticolus, arose through hybridization. Previously, we demonstrated that X. clemenciae, another southern Swordtail species, arose via hybridization. These findings highlight the potential key role of hybridization in the evolution of this genus and suggest the need for further investigations into how hybridization contributes to speciation more generally.
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Hybrid origin of a Swordtail species (Teleostei: Xiphophorus clemenciae) driven by sexual selection
Molecular ecology, 2006Co-Authors: Axel Meyer, Walter Salzburger, Manfred SchartlAbstract:The swordlike exaggerated caudal fin extensions of male Swordtails are conspicuous traits that are selected for through female choice. Swords are one of only few examples where the hypothesis of a pre-existing bias is believed to apply for the evolution of a male trait. Previous laboratory experiments demonstrated that females prefer males with longer swords and even females from some swordless species show an affiliation for males of sworded species. Earlier phylogenetic studies based on maternally inherited mitochondrial DNA placed the sworded southern Swordtail Xiphophorus clemenciae with swordless platies, contradicting its morphology-based evolutionary affinities. The analyses of new nuclear DNA markers now recover its traditional phylogenetic placement with other southern Swordtails, suggesting that this species was formed by an ancient hybridization event. We propose that sexual selection through female choice was the likely process of hybrid speciation, by mating of platy females with males of an ancestral Swordtail lineage. In artificial crosses of descendent species from the two potential ancestral lineages of X. clemenciae the hybrid and backcross males have swords of intermediate lengths. Additionally, mate choice experiments demonstrate that hybrid females prefer sworded males. These experimental lines of evidence make hybridization through xeno-specific sexual selection by female choice the likely mechanism of speciation.
Ji Hyoun Kang - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Open Access Comprehensive
2016Co-Authors: Ji Hyoun KangAbstract:phylogenetic analysis of all species of Swordtails and platies (Pisces: Genus Xiphophorus) uncovers a hybrid origin of a Swordtail fish, Xiphophorus monticolus, and construct a comprehensive molecular phylogeny of all 26 known Xiphophorus species, including the four recently Kang et al. BMC Evolutionary Biology 2013, 13:2
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transcriptomics of two evolutionary novelties how to make a sperm transfer organ out of an anal fin and a sexually selected sword out of a caudal fin
Ecology and Evolution, 2015Co-Authors: Ji Hyoun Kang, Tereza Manousaki, Paolo Franchini, Susanne Kneitz, Manfred Schartl, Axel MeyerAbstract:Swords are exaggerated male ornaments of Swordtail fishes that have been of great interest to evolutionary biologists ever since Darwin described them in the Descent of Man (1871). They are a novel sexually selected trait derived from modified ventral caudal fin rays and are only found in the genus Xiphophorus. Another phylogenetically more widespread and older male trait is the gonopodium, an intromittent organ found in all poeciliid fishes, that is derived from a modified anal fin. Despite many evolutionary and behavioral studies on both traits, little is known so far about the molecular mechanisms underlying their development. By investigating transcriptomic changes (utilizing a RNA-Seq approach) in response to testosterone treatment in the Swordtail fish, Xiphophorus hellerii, we aimed to better understand the architecture of the gene regulatory networks underpinning the development of these two evolutionary novelties. Large numbers of genes with tissue-specific expression patterns were identified. Among the “sword genes” those involved in embryonic organ development, sexual character development and coloration were highly expressed, while in the gonopodium rather more morphogenesis-related genes were found. Interestingly, many genes and genetic pathways are shared between both developing novel traits derived from median fins: the sword and the gonopodium. Our analyses show that a larger set of gene networks was co-opted during the development and evolution of the “older” gonopodium than in the “younger,” and morphologically less complex trait, the sword. We provide a catalog of candidate genes for future efforts to dissect the development of those sexually selected exaggerated male traits in Swordtails.
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Transcriptomics of two evolutionary novelties: how to make a sperm‐transfer organ out of an anal fin and a sexually selected “sword” out of a caudal fin
Ecology and evolution, 2015Co-Authors: Ji Hyoun Kang, Tereza Manousaki, Paolo Franchini, Susanne Kneitz, Manfred Schartl, Axel MeyerAbstract:Swords are exaggerated male ornaments of Swordtail fishes that have been of great interest to evolutionary biologists ever since Darwin described them in the Descent of Man (1871). They are a novel sexually selected trait derived from modified ventral caudal fin rays and are only found in the genus Xiphophorus. Another phylogenetically more widespread and older male trait is the gonopodium, an intromittent organ found in all poeciliid fishes, that is derived from a modified anal fin. Despite many evolutionary and behavioral studies on both traits, little is known so far about the molecular mechanisms underlying their development. By investigating transcriptomic changes (utilizing a RNA-Seq approach) in response to testosterone treatment in the Swordtail fish, Xiphophorus hellerii, we aimed to better understand the architecture of the gene regulatory networks underpinning the development of these two evolutionary novelties. Large numbers of genes with tissue-specific expression patterns were identified. Among the “sword genes” those involved in embryonic organ development, sexual character development and coloration were highly expressed, while in the gonopodium rather more morphogenesis-related genes were found. Interestingly, many genes and genetic pathways are shared between both developing novel traits derived from median fins: the sword and the gonopodium. Our analyses show that a larger set of gene networks was co-opted during the development and evolution of the “older” gonopodium than in the “younger,” and morphologically less complex trait, the sword. We provide a catalog of candidate genes for future efforts to dissect the development of those sexually selected exaggerated male traits in Swordtails.
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comprehensive phylogenetic analysis of all species of Swordtails and platies pisces genus xiphophorus uncovers a hybrid origin of a Swordtail fish xiphophorus monticolus and demonstrates that the sexually selected sword originated in the ancestral li
BMC Evolutionary Biology, 2013Co-Authors: Ji Hyoun Kang, Manfred Schartl, Ronald B Walter, Axel MeyerAbstract:Males in some species of the genus Xiphophorus, small freshwater fishes from Meso-America, have an extended caudal fin, or sword – hence their common name “Swordtails”. Longer swords are preferred by females from both sworded and – surprisingly also, non-sworded (platyfish) species that belong to the same genus. Swordtails have been studied widely as models in research on sexual selection. Specifically, the pre-existing bias hypothesis was interpreted to best explain the observed bias of females in presumed ancestral lineages of swordless species that show a preference for assumed derived males with swords over their conspecific swordless males. However, many of the phylogenetic relationships within this genus still remained unresolved. Here we construct a comprehensive molecular phylogeny of all 26 known Xiphophorus species, including the four recently described species (X. kallmani, X. mayae, X. mixei and X. monticolus). We use two mitochondrial and six new nuclear markers in an effort to increase the understanding of the evolutionary relationships among the species in this genus. Based on the phylogeny, the evolutionary history and character state evolution of the sword was reconstructed and found to have originated in the common ancestral lineage of the genus Xiphophorus and that it was lost again secondarily. We estimated the evolutionary relationships among all known species of the genus Xiphophorus based on the largest set of DNA markers so far. The phylogeny indicates that one of the newly described Swordtail species, Xiphophorus monticolus, is likely to have arisen through hybridization since it is placed with the southern platyfish in the mitochondrial phylogeny, but with the southern Swordtails in the nuclear phylogeny. Such discordance between these two types of markers is a strong indication for a hybrid origin. Additionally, by using a maximum likelihood approach the possession of the sexually selected sword trait is shown to be the most likely ancestral state for the genus Xiphophorus. Further, we provide a well supported estimation of the phylogenetic relationships between the previously unresolved northern Swordtail groups. This comprehensive molecular phylogeny of the entire genus Xiphophorus provides evidence that a second Swordtail species, X. monticolus, arose through hybridization. Previously, we demonstrated that X. clemenciae, another southern Swordtail species, arose via hybridization. These findings highlight the potential key role of hybridization in the evolution of this genus and suggest the need for further investigations into how hybridization contributes to speciation more generally.
Molly R. Morris - One of the best experts on this subject based on the ideXlab platform.
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Male Mating Tactics in the Northern Mountain Swordtail Fish (Xiphophorus nezahualcoyotl): Coaxing and Coercing Females to Mate
Ethology, 2008Co-Authors: Molly R. Morris, Oscar Rios-cardenas, Abby DarrahAbstract:Our understanding of the evolution of alternative male mating tactics would benefit greatly from more comparative studies; however, descriptions of the variation in mating behaviors are often lacking or reported in ways that consider only the role of male–male competition. Here we examine the mating behavior of the Swordtail fish Xiphophorus nezahualcoyotl in relation to male size across different competitive contexts and in relation to coaxing vs. coercing females to mate. We also compare these results with reports for four other species of northern Swordtails. The mating behaviors displayed by X. nezahualcoyotl males were correlated with male size, and were ranked in order from most coaxing to most coercive (a new behavior ‘headstand’, frontal displays, backing and fast chase) based on the probability that a behavior was followed by an attempted forced copulation. The largest males never used the most coercive behavior in the laboratory setting, even in the context of a larger competitor, and the smallest males never used the most coaxing behavior, even when alone with females. We argue, however, that changing the competitive context may not be the best way to expose the full range of behaviors a male may use if circumventing female mate choice is also driving the evolution of the alternative tactics. Finally, when we compared the mating behaviors of X. nezahualcoyotl males to those of the males of four other species of northern Swordtails, they were not most similar to males of the closely related species X. continens .I nX. continens, all males are small and have no morphological traits or behaviors that coax females to mate, where as even the smallest X. nezahualcoyotl males had both morphological and behavioral traits that could coax females to mate.
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Genetic variation and phylogeography of the Swordtail fish Xiphophorus cortezi (Cyprinodontiformes, Poeciliidae).
Molecular phylogenetics and evolution, 2006Co-Authors: Carla Gutiérrez-rodríguez, Molly R. Morris, Natalie S. Dubois, Kevin De QueirozAbstract:Swordtail fish have been studied extensively in relation to diverse aspects of biology; however, little attention has been paid to the patterns of genetic variation within and among populations of Swordtails. In this study, we sequenced the mtDNA control region from 65 individuals and 10 populations of Xiphophorus cortezi to investigate the genetic variation within and among populations, including tests for correlations between genetic and geographic distances and tests for species monophyly. We found low gene and nucleotide diversity within populations and high degrees of genetic differentiation among populations. Significant and positive correlations between genetic distance and both river and straight-line geographic distance indicate that genetic differentiation among X. cortezi populations can be explained, to some extent, by an isolation-by-distance model and provide evidence of stream capture. Phylogenetic analyses suggest that X. cortezi is paraphyletic relative to X. malinche, raising questions concerning the status of these taxa as separate species.
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The role of sexual selection in the loss of sexually selected traits in the Swordtail fish Xiphophorus continens
Animal Behaviour, 2005Co-Authors: Molly R. Morris, Jason A. Moretz, Kristen Farley, Paul F. NicolettoAbstract:Swordtail fish have been studied extensively in relation to several exaggerated male traits that have evolved due to sexual selection. However, one species of Swordtail fish, Xiphophorus continens, lacks all of these traits. Males in this species are relatively small, lack swords and do not possess any of the pigment patterns found throughout the Swordtails and platyfish. In this study we compared the mating behaviour of X. continens to the mating behaviours of other Swordtail fish to determine whether a relaxation of sexual selection may have played a role in the loss of large male size and the pigment pattern vertical bars. We found that X. continens lacked the courtship behaviours present in other Swordtail species, and that female mating preference for male size and male response to the pigment pattern vertical bars were significantly weaker than in other Swordtails we have tested. In addition, results of staged male–male interactions suggested that neither male size nor vertical bars are under strong selection due to male–male competition. However, we did detect a polymorphism in female preference for vertical bars, suggesting that the response of female X. continens to vertical bars has been evolutionarily retained even though the trait was lost. Based on what is known about female preference for body size and bars, and male response to body size and bars across the northern Swordtails, we hypothesize that the loss of large male size was due to a relaxation of sexual selection, whereas the loss of vertical bars was not.
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Phylogenetic Relationships among Populations of Northern Swordtails (Xiphophorus) as Inferred from Allozyme Data
Copeia, 2001Co-Authors: Molly R. Morris, Kevin De Queiroz, Don C. MorizotAbstract:Abstract Twenty-nine populations of Xiphophorus fishes representing nine species of northern Swordtails, one southern Swordtail and a platyfish were assayed electrophoretically for allozyme variation. Phylogenetic relationships were inferred using parsimony and likelihood analysis of gene frequency characters, as well as Fitch-Margoliash, minimum evolution and neighbor-joining analyses of genetic distances. The phylogenetic relationships among species that were well supported in all analyses included (1) monophyly of the northern Swordtails, (2) the pygmaeus clade of Xiphophorus nigrensis, X. multilineatus, and X. pygmaeus, and (3) the clade of X. nigrensis and X. multilineatus. Of those species represented by more than one population, all analyses supported monophyly of X. montezumae and weakly supported monophyly of X. nezahualcoyotl and X. birchmanni. Only the distance analyses supported monophyly of X. cortezi, and the support was weak. Finally, all analyses supported a clade including X. nezahualcoyo...
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large body size in the pygmy Swordtail xiphophorus pygmaeus
Biological Journal of The Linnean Society, 1995Co-Authors: Molly R. Morris, Michael J. RyanAbstract:Fishes in the genus Xiphophorus (Swordtails and platyfishes) are well known for the influence of the pituitary (P) locus on variation of male size at maturity both within and among species. We report the discovery of large male size ( >29 mm SL) in several populations of the Swordtail X. pygmaeus, a species previously thought to consist of only small males (<29 mm SL). Large size is geographically restricted, and average male size varies significantly by site and year sampled in a pattern suggesting a recent origin and slow spreading of the large male phenotype. However, large male size is not strongly patternally inherited in this species, as it is in its two closest relatives, X. nigrensis and X. multilineatus, showing that large size does not result from the same genetic (P locus) mechanism. Large X. pygmaeus males do not court, can exhibit the gold morph, do not possess swords and have slender body shape. In these traits they resemble small conspecific males and small males of X. nigrensis and X. multilineatus rather than large males of these latter two species. This shows that correlations between morphological and behavioural traits that occur in X. nigrensis and X. multilineatus are absent in X. pygmaeus.
