Julián Torres-Dowdall

Julián Torres-Dowdall
Universität Konstanz | Uni-Konstanz · Department of Biology

PhD

About

62
Publications
14,794
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1,012
Citations
Additional affiliations
January 2008 - present
January 2005 - present
Colorado State University

Publications

Publications (62)
Article
Full-text available
Abstract Nonparallel evolution, where independent populations occupy similar environments but show phenotypic differences, can uncover previously ignored selective factors. We investigated a nonparallelism in the life-history strategy of a Trinidadian guppy population, a system famous for parallel adaptation to differences in predation risk. We tes...
Article
Identifying the environmental factors responsible for the formation of a species' distribution limit is challenging because organisms interact in complex ways with their environments. However, the use of statistical niche models in combination with the analysis of phenotypic variation along environmental gradients can help to reduce such complexity...
Article
Full-text available
Predation and parasitism are two of the most important sources of mortality in nature. By forming groups, individuals can gain protection against predators but may increase their risk of being infected with contagious parasites. Animals might resolve this conflict by forming mixed-species groups thereby reducing the costs associated with parasites...
Article
1. Theoretical models of life-history evolution predict a continuum of fast to slow life histories, yet most of empirical support for this theory comes from studies that have considered dichotomous environments (i.e. high vs. low food, presence or absence of major predators). Although this approach has been very successful in identifying the signat...
Article
Divergent selection pressures across environments can result in phenotypic differentiation that is due to local adaptation, phenotypic plasticity, or both. Trinidadian guppies exhibit local adaptation to the presence or absence of predators, but the degree to which predator-induced plasticity contributes to population differentiation is less clear....
Article
Phylogenetic comparative studies suggest that the direction of deviation from bilateral symmetry (sidedness) might evolve through genetic assimilation; however, the changes in sidedness inheritance remain largely unknown. We investigated the evolution of genital asymmetry in fish of the family Anablepidae, in which males' intromittent organ (the go...
Article
Full-text available
Vision is critical for most vertebrates, including fish. One challenge that aquatic habitats pose is the high variability in spectral properties depending on depth and the inherent optical properties of the water. By altering opsin gene expression and chromophore usage, cichlid fish modulate visual sensitivities to maximize sensory input from the a...
Article
Full-text available
Understanding the ecological factors that shape geographic range limits and the evolutionary constraints that prevent populations from adaptively evolving beyond these limits is an unresolved question. Here, we investigated why the euryhaline fish, Poecila reticulata, is confined to freshwater within its native range, despite being tolerant of brac...
Article
Full-text available
Characterizing biological communities and knowledge on the distribution of biodiversity allows the assessment of ecological quality. This provides valuable information for conservation biology and monitoring purposes. While obtaining such data has been challenging in the past, environmental DNA (eDNA) sampling represents a promising tool to describ...
Article
Full-text available
Exaggerated secondary sexual characteristics are apparently costly and seem to defy natural selection. This conundrum promoted the theory of sexual selection. Accordingly, exaggerated secondary sexual characteristics might be ornaments on which female choice is based and/or armaments used during male–male competition. Males of many cichlid fish spe...
Chapter
The Nicaraguan Midas cichlid species complex is a natural experiment where fish from a large source population from turbid and shallow great lakes very recently (<20,000 years ago) colonized eight small crater lakes. The colonizers experienced completely novel environments in the clear and deep calderas. So far, 13 Midas cichlid species have been d...
Article
Full-text available
The visual system of vertebrates has greatly contributed to our understanding of how different molecular mechanisms shape adaptive phenotypic diversity. Extensive work on African cichlid fishes has shown how variation in opsin gene expression mediates diversification as well as convergent evolution in color vision. This trait has received less atte...
Article
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The transition from ‘well-marked varieties’ of a single species into ‘well-defined species’—especially in the absence of geographic barriers to gene flow (sympatric speciation)—has puzzled evolutionary biologists ever since Darwin1,2. Gene flow counteracts the buildup of genome-wide differentiation, which is a hallmark of speciation and increases t...
Article
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Detecting contemporary evolution requires demonstrating that genetic change has occurred. Mixed effects models allow estimation of quantitative genetic parameters and are widely used to study evolution in wild populations. However, predictions of evolution based on these parameters frequently fail to match observations. Here, we applied three comm...
Article
Full-text available
Background: Recent increases in understanding the ecological and evolutionary roles of microbial communities have underscored the importance of their hosts’ biology. Yet, little is known about gut microbiota dynamics during the early stages of ecological diversification and speciation. We sequenced the V4 region of the 16s rRNA gene to study the gu...
Article
Full-text available
Cichlid fishes are exceptionally species-rich, speciated at explosive rates and, hence, are a model system in speciation research. Yet, their reproductive isolating barriers have, so far, not been comprehensively studied. Here, we review current knowledge on pre-and postzygotic mechanisms in cichlids. While premating isolation is the norm in cichli...
Article
Animal genitalia vary considerably across taxa, with divergence in many morphological traits, including striking departures from symmetry. Different mechanisms have been proposed to explain this diversity, mostly assuming that at least some of the phenotypic variation is heritable. However, heritability of the direction of genital asymmetry has bee...
Preprint
Full-text available
Background: Recent increases in understanding the ecological and evolutionary roles of microbial communities has underscored the importance for their hosts’ biology. Yet, little is known about gut microbiota dynamics during early stages of ecological diversification and speciation. We sequenced the V4 region of the 16s rRNA gene to study the gut mi...
Preprint
Full-text available
Background: Recent increases in understanding the ecological and evolutionary roles of microbial communities has underscored the importance for their hosts’ biology. Yet, little is known about gut microbiota dynamics during early stages of ecological diversification and speciation. We sequenced the V4 region of the 16s rRNA gene to study the gut mi...
Preprint
Full-text available
Background: Recent increases in understanding the ecological and evolutionary roles of microbial communities has underscored the importance for their hosts’ biology. Yet, little is known about gut microbiota dynamics during early stages of ecological diversification and speciation. We sequenced the V4 region of the 16s rRNA gene to study the gut mi...
Article
Full-text available
Cichlid fishes’ famous diversity in body coloration is accompanied by a highly diverse and complex visual system. Although cichlids possess an unusually high number of seven cone opsin genes, they express only a subset of these during their ontogeny, accounting for their astonishing interspecific variation in visual sensitivities. Much of this dive...
Article
Full-text available
Color patterns in African cichlid fishes vary spectacularly. While phylogenetic analysis showed already 30 years ago that many color patterns evolved repeatedly in these adaptive radiations, only recently have we begun to understand the genic basis of color variation. Horizontal stripe patterns evolved and were lost several times independently acro...
Preprint
Full-text available
Recent increases in understanding the ecological and evolutionary roles of microbial communities has underscored their importance for their hosts' biology. Yet, little is known about gut microbiota dynamics during early stages of ecological diversification and speciation. We studied the gut microbiota of extremely young adaptive radiations of Nicar...
Article
Full-text available
Phenotypic plasticity, particularly during development, allows organisms to rapidly adjust to different environmental conditions. Yet, it is often unclear whether the extent and direction of plastic changes are restricted by an individual's ontogeny. Many species of cichlid fishes go through ontogenetic changes in visual sensitivity, from short to...
Article
Full-text available
Freshwater sulfide springs have extreme environmental conditions that only few vertebrate species can tolerate. These species often develop a series of morphological and molecular adaptations to cope with the challenges of life under the toxic and hypoxic conditions of sul-fide springs. In this paper, we described a new fish species of the genus Je...
Article
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Organisms can change their environment and in doing so change the selection they experience and how they evolve. Population density is one potential mediator of such interactions because high population densities can impact the ecosystem and reduce resource availability. At present, such interactions are best known from theory and laboratory experi...
Article
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Asymmetries in bilateral organisms attract a lot of curiosity given that they are conspicuous departures from the norm. They allow the investigation of the integration at different levels of biological organization. Here we study whether and how behavioral and asymmetrical anatomical traits co-evolved and work together. We ask if asymmetry is deter...
Article
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Lake Tanganyika is the oldest and phenotypically most diverse of the three East African cichlid fish adaptive radiations. It is also the cradle for the younger parallel haplochromine cichlid radiations in Lakes Malawi and Victoria. Despite its evolutionary significance, the relationships among the main Lake Tanganyika lineages remained unresolved,...
Article
Full-text available
How predictable is evolution? This remains a fundamental but contested issue in evolutionary biology. When independent lineages colonize the same environment, we are presented with a natural experiment that allows us to ask if genetic and ecological differences promote species‐specific evolutionary outcomes or whether species phenotypically evolve...
Data
Figure 1: Proportional expression of six cone opsins based on quantitative Real‐Time PCR (qPCR; y‐axes) and RNA‐Seq (x‐axes) data. Figure 2: Hypothetical data of two species to illustrate our vector analysis for convergent evolution. Figure 3: As previously shown with quantitative Real‐Time PCR (Härer et al. 2017; Torres‐Dowdall et al. 2017), Mid...
Article
During early ontogeny, visual opsin gene expression in cichlids is influenced by prevailing light reg-imen. Red light, for example, leads to an early switch from the expression of short-wavelength sensitive to long-wavelength sensitive opsins. Here, we address the influence of light deprivation on opsin expression. Individuals reared in constant da...
Article
Only few fish species have successfully colonized subterranean habitats, but the underlying biological constraints associated with this are still poorly understood. Here, we investigated the influence of permanent darkness on spinal-column development in one species (Midas cichlid, Amphilophus citrinellus) with no known cave form, and one (Atlantic...
Article
ON THE COVER: The cover image, by Nidal Karagic et al., is based on the Research Article Heterochronic opsin expression due to early light deprivation results in drastically shifted visual sensitivity in a cichlid fish: Possible role of thyroid hormone signaling, DOI 10.1002/jez.b.22806.
Article
Full-text available
Theory predicts that gene flow will decrease phenotypic differences among populations. Correlational studies have in some cases documented constraining effects of gene flow on phenotypic divergence and/or have also provided evidence for local differentiation despite high gene flow. However, correlative studies are unable to evaluate how gene flow a...
Article
Colonization of novel habitats is typically challenging to organisms. In the initial stage after colonization, approximation to fitness optima in the new environment can occur by selection acting on standing genetic variation, modification of developmental patterns or phenotypic plasticity. Midas cichlids have recently colonized crater Lake Apoyo f...
Article
1.Genetically based stable colour polymorphisms provide a unique opportunity to study the evolutionary processes that preserve genetic variability in the wild. Different mechanisms are proposed to promote the stability of polymorphisms, but only few empirical examples have been documented, resulting in an incomplete understanding of these mechanism...
Presentation
Full-text available
Unnoticed by the public, initiatives for oil exploration are advanced in Africa’s largest freshwater reservoirs, including Lakes Tanganyika, Malawi and lately Albert, threatening their ecosystems and biota. It is imperative that environmental impact assessments are conducted by independent organizations to ensure that decisions on this matter are b...
Article
Full-text available
Midas cichlid fish are a Central American species flock containing 13 described species that has been dated to only few thousand years old, a historical timescale infrequently associated with speciation. Their radiation involved the colonization of several clear water crater lakes from two turbid great lakes. Therefore, Midas cichlids have been sub...
Data
Numbers of described Cichlidae, Characidae, and Poeciliidae species; ecology and reproductive features of our study species; sample sizes and sampling locations; cytochrome b primers; GenBank accession numbers of Poecilia spp.; a list of species occurring in Punta Gorda and San Juan Basins; FST values among populations; nucleotide and haplotype div...
Article
Full-text available
Sympatric speciation has been debated in evolutionary biology for decades. Although it has gained in acceptance recently, still only a handful of empirical examples are seen as valid (e.g. crater lake cichlids). In this study, we disentangle the role of hypertrophied lips in the repeated adaptive radiations of Nicaraguan crater lake cichlid fish. W...
Article
Full-text available
As the world’s demands for hydrocarbons increase, remote areas previously made inaccessible by technological limitations are now being prospected for oil and gas deposits. Virtually unnoticed by the public, such activities are ongoing in the East African Great Lakes region, threatening these ecosystems famed for their hyper-diverse biota, includin...
Article
Full-text available
Understanding how speciation can occur without geographic isolation remains a central objective in evolutionary biology. Generally, some form of disruptive selection and assortative mating are necessary for sympatric speciation to occur. Disruptive selection can arise from intraspecific competition for resources. If this competition leads to the di...
Article
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Large-scale infrastructure projects commonly have strong effects on the environment. Thus, it is of highest importance to evaluate possible impacts on biodiversity and take measures to reduce these. The planned construction of the Nicaragua Canal will irreversibly alter the aquatic environment of Nicaragua in many ways. Two distinct drainage basins...
Article
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Genetic rescue, an increase in population growth owing to the infusion of new alleles, can aid the persistence of small populations, but its use as a management tool is limited by a lack of empirical data geared towards predicting effects of gene flow on local adaptation and demography. Experimental translocations provide an ideal opportunity to mo...
Article
The visual system in the colorful cichlid fishes from the African great lakes is believed to be important for their adaptive radiations. However, few studies have attempted to compare the visual system of radiating cichlid lineages to that of cichlids that have not undergone recent radiations. One such study published in this journal (Schott et al....
Article
Full-text available
Colonization of novel environments can alter selective pressures and act as a catalyst for rapid evolution in nature. Theory and empirical studies suggest that the ability of a population to exhibit an adaptive evolutionary response to novel selection pressures should reflect the presence of sufficient additive genetic variance and covariance for i...
Article
Predation can play an important role in the evolution and maintenance of prey colour polymorphisms. Several factors are known to affect predator choice, including the prey's relative abundance and conspicuousness. In polymorphic prey species, predators often target the most common or most visible morphs. To test if predator choice can explain why i...
Presentation
Background/Question/Methods Although individuals tend to prefer forming groups with conspecifics, mixed-species groups occur in various taxa and are thought to be adaptive. The two main explanations proposed for the formation of mixed-species groups are increased defense against predators through dilution of individual risk and increased resource a...
Article
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Composición, estructura y variación estacional de la comunidad de aves del Jardín Botánico de la Fundación Miguel Lillo, Tucumán, Argentina R e s u m e n — Resumen-Las alteraciones ambientales causadas por las actividades humanas impactan negativamente en la biodiversidad. Entre ellas, se espera que la transfor-mación de ambientes naturales en urba...
Article
Full-text available
Trace-element analysis has been suggested as a tool for the study of migratory connectivity because (1) trace-element abundance varies spatially in the environment, (2) trace elements are assimilated into animals' tissues through the diet, and (3) current technology permits the analysis of multiple trace elements in a small tissue sample, allowing...
Article
Full-text available
Stable isotope analyses have revolutionized the study of migratory connectivity. However, as with all tools, their limitations must, be understood in order to derive the maximum benefit of a particular application. The goal of this study was to evaluate the efficacy of stable isotopes of C, N, H, O and S for assigning known-origin feathers to the m...
Article
Deuterium isotope analyses have revolutionized the study of migratory connectivity because global gradients of deuterium in precipitation (deltaD(P)) are expressed on a continental scale. Several authors have constructed continental scale base maps of deltaD(P) to provide a spatial reference for studying the movement patterns of migratory species a...
Article
Full-text available
Organophosphorus (OP) and carbamate (CB) pesticides are commonly used agrochemicals throughout the Western Hemisphere. These pesticides have caused mortalities in migratory birds and adverse physiological effects in trials with captive birds. Migratory shorebirds use a variety, of habitats during the austral summer in temperate South America and du...
Article
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Sephanoides sephaniodes es el picaflor más austral del mundo, encontrándose desde el sur del desierto de Atacama en Chile y desde Neuquén hasta Santa Cruz en Argentina, presentándose incluso en Tierra del Fuego, Islas Malvinas y archipiélago de Juan Fernández. Nidifica en bosques austrosudamericanos entre septiembre y diciembre, encontrándose excep...