Mark J Margres

Mark J Margres
University of South Florida | USF · Department of Integrative Biology

Ph.D.

About

41
Publications
9,914
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1,415
Citations
Citations since 2016
30 Research Items
1243 Citations
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2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250
2016201720182019202020212022050100150200250

Publications

Publications (41)
Article
Full-text available
Spontaneous tumor regression has been documented in a small proportion of human cancer patients, but the specific mechanisms underlying tumor regression without treatment are not well-understood. Tasmanian devils are threatened with extinction from a transmissible cancer due to universal susceptibility and a near 100% case fatality rate. In over 10...
Article
Emergence to endemism The emergence of a devastating transmissible facial cancer among Tasmanian devils over the past few decades has caused substantial concern for their future because these animals are already threatened by a regional distribution and other stressors. Little is known about the overall history and trajectory of this disease. Patto...
Article
Significance A central question in biology is whether trait differences are the result of variation in gene number, sequence, or regulation. Snake venoms are an excellent system for addressing this question because of their genetic tractability, contributions to fitness, and high evolutionary rates. We sequenced and assembled the genome of the Tige...
Article
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Ecologically divergent selection can lead to the evolution of reproductive isolation through the process of ecological speciation, but the balance of responsible evolutionary forces is often obscured by an inadequate assessment of demographic history and the genetics of traits under selection. Snake venoms have emerged as a system for studying the...
Article
On 17 June 2019, we collected a unique juvenile rattlesnake from a wildlife response call on Jekyll Island State Park, GA. The snake exhibited intermediate color patterns and gross anatomical features suggesting potential hybridization between Crotalus horridus (Canebrake/Timber Rattlesnake) and Crotalus adamanteus (Eastern Diamond-back Rattlesnake...
Article
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Background Transmissible cancers lie at the intersection of oncology and infectious disease, two traditionally divergent fields for which gene expression studies are particularly useful for identifying the molecular basis of phenotypic variation. In oncology, transcriptomics studies, which characterize the expression of thousands of genes, have ide...
Article
Full-text available
Tasmanian devils ( Sarcophilus harrisii ) are evolving in response to a unique transmissible cancer, devil facial tumour disease (DFTD), first described in 1996. Persistence of wild populations and the recent emergence of a second independently evolved transmissible cancer suggest that transmissible cancers may be a recurrent feature in devils. Her...
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Significance Why biological complexity evolves is a major question in the life sciences, but the specific selection pressures favoring simple or complex traits remain unclear. Using high-resolution measurements of venom complexity in North American pitvipers, we link changes in complexity to natural history via phylogenetic diversity of snake diets...
Preprint
Full-text available
Background Transmissible cancers lie at the intersection of oncology and infectious disease, two traditionally divergent fields for which gene expression studies are particularly useful for identifying the molecular basis of phenotypic variation. In oncology, transcriptomics studies, which characterize the expression of thousands of genes, have ide...
Article
Full-text available
Ontogenetic shifts in venom occur in many snakes but establishing their nature as gradual or discrete processes required additional study. We profiled shifts in venom expression from the neonate to adult sizes of two rattlesnake species, the eastern diamondback and the timber rattlesnake. We used serial sampling and venom chromatographic profiling...
Article
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The migration-selection balance often governs the evolution of lineages, and speciation with gene flow is now considered common across the tree of life. Ecological speciation is a process that can facilitate divergence despite gene flow due to strong selective pressures caused by ecological differences; however, the exact traits under selection are...
Article
Genetic structure in host species is often used to predict disease spread. However, host and pathogen genetic variation may be incongruent. Understanding landscape factors that have either concordant or divergent influence on host and pathogen genetic structuring is crucial for wildlife disease management. Devil facial tumor disease (DFTD) was firs...
Article
Landscape genomics studies focus on identifying candidate genes under selection via spatial variation in abiotic environmental variables, but rarely by biotic factors (i.e., disease). The Tasmanian devil (Sarcophilus harrisii ) is found only on the environmentally heterogeneous island of Tasmania and is threatened with extinction by a transmissible...
Article
Full-text available
Whether hybridization generates or erodes species diversity has long been debated, but to date most studies have been conducted at small taxonomic scales. Salamanders (order Caudata) represent a taxonomic order in which hybridization plays a prevalent ecological and evolutionary role. We employed a recently developed model of trait-dependent divers...
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Background: Modularity is the tendency for systems to organize into semi-independent units and can be a key to the evolution and diversification of complex biological systems. Snake venoms are highly variable modular systems that exhibit extreme diversification even across very short time scales. One well-studied venom phenotype dichotomy is a tra...
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In an era of unprecedented global change, exploring patterns of gene expression among wild populations across their geographic range is crucial for characterizing adaptive potential. RNA-sequencing studies have successfully characterized gene expression differences among populations experiencing divergent environmental conditions in a wide variety...
Preprint
Full-text available
Landscape genomics studies focus on identifying candidate genes under selection via spatial variation in abiotic environmental variables, but rarely by biotic factors such as disease. The Tasmanian devil (Sarcophilus harrisii) is found only on the environmentally heterogeneous island of Tasmania and is threatened with extinction by a nearly 100% fa...
Preprint
Full-text available
Whether hybridization generates or erodes species diversity has long been debated, but to date most studies have been conducted at small taxonomic scales. Salamanders (order Caudata) represent a taxonomic order in which hybridization plays a prevalent ecological and evolutionary role. We employed a recently developed model of trait-dependent divers...
Article
Full-text available
Reconstructing species' demographic histories is a central focus of molecular ecology and evolution. Recently, an expanding suite of methods leveraging either the sequentially Markovian coalescent (SMC) or the site-frequency spectrum (SFS) have been developed to reconstruct population size histories from genomic sequence data. However, few studies...
Article
Traits can evolve rapidly through changes in gene expression or protein-coding sequences. However, these forms of genetic variation can be correlated and changes to one can influence the other. As a result,we might expect traits lacking differential expression to preferentially evolve through changes in protein sequences or morphological adaptation...
Article
Full-text available
The migration-selection interaction is the strongest determinant of whether a beneficial allele increases in frequency within a population. Results of empirical studies examining the role of gene flow in an adaptive context, however, have largely been equivocal, with examples of opposing outcomes being repeatedly documented (e.g., local adaptation...
Article
Full-text available
Understanding the genetic basis of disease-related phenotypes, such as cancer susceptibility, is crucial for the advancement of personalized medicine. Although most cancers are somatic in origin, a small number of transmissible cancers have been documented. Two such cancers have emerged in the Tasmanian devil (Sarcophilus harrisii) and now threaten...
Article
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Identifying the genetic architecture of complex phenotypes is a central goal of modern biology, particularly for disease‐related traits. Genome‐wide association methods are a classical approach for identifying the genomic basis of variation in disease phenotypes, but such analyses are particularly challenging in natural populations due to sample si...
Article
Identifying the environmental correlates of divergence in functional traits between populations can provide insights into the evolutionary mechanisms that generate local adaptation. Here, we assess patterns of population differentiation in expressed venom proteins in Northern Pacific rattlesnakes (Crotalus oreganus) from 13 locations across Califor...
Article
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Venom-gland transcriptomics is a key tool in the study of the evolution, ecology, function, and pharmacology of animal venoms. In particular, gene-expression variation and coding sequences gained through transcriptomics provide key information for explaining functional venom variation over both ecological and evolutionary timescales. The accuracy a...
Article
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A trait’s genomic architecture can affect the rate and mechanism of adaptation, and although many ecologically-important traits are polygenic, most studies connecting genotype, phenotype, and fitness in natural populations have focused on traits with relatively simple genetic bases. To understand the genetic basis of polygenic adaptation, we must i...
Article
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Gene duplication is the primary mechanism leading to new genes and phenotypic novelty, but the proximate evolutionary processes underlying gene family origin, maintenance, and expansion are poorly understood. Although sub- and neofunctionalization provide clear long-term advantages, selection does not act with foresight, and unless a redundant gene...
Article
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The same selective forces that give rise to rapid inter-and intraspecific divergence in snake venoms can also favor differences in venoms across life-history stages. Ontogenetic changes in venom composition are well known and widespread in snakes but have not been investigated to the level of unambiguously identifying the specific loci involved. Th...
Article
Phenotypes frequently vary across and within species. The connection between specific phenotypic effects and function, however, is less understood despite being essential to our understanding of the adaptive process. Snake venoms are ideal for identifying functionally important phenotypic variation because venom variation is common, and venoms can...
Article
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Protein expression level is one of the strongest predictors of protein sequence evolutionary rate, with high-expression protein sequences evolving at slower rates than low-expression protein sequences, largely because of constraints on protein folding and function. Expression evolutionary rates have also been shown to be negatively correlated with...
Article
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Protein expression is a major link in the genotype-phenotype relationship, and processes affecting protein abundances, such as rates of transcription and translation, could contribute to phenotypic evolution if they generate heritable variation. Recent work has suggested that mRNA abundances do not accurately predict final protein abundances, which...
Article
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Selection can vary geographically across environments and temporally over the lifetime of an individual. Unlike geographic contexts, where different selective regimes can act on different alleles, age-specific selection is constrained to act on the same genome by altering age-specific expression. Snake venoms are exceptional traits for studying ont...
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The genetics underlying adaptive trait evolution describes the intersection between the probability that particular types of mutation are beneficial and the rates they arise. Snake venoms can vary in a directly meaningful manner through coding mutations and regulatory mutations. The amounts of different components determine venom efficacy, but poin...
Article
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Largely because of their direct, negative impacts on human health, the venoms of front-fanged snakesof the families Viperidae and Elapidae have been extensively characterized proteomically, transcriptomically,and pharmacologically. However, relatively little is known about the molecular complexityand evolution of the venoms of rear-fanged colubrid...
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Selection is predicted to drive diversification within species and lead to local adaptation, but understanding the mechanistic details underlying this process, and thus the genetic basis of adaptive evolution, requires the mapping of genotype to phenotype. Venom is complex and involves many genes, but the specialization of the venom-gland towards t...
Article
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Unlabelled: Understanding the molecular basis of the phenotype is key to understanding adaptation, and the relationship between genes and specific traits is represented by the genotype-phenotype map. The specialization of the venom-gland towards toxin production enables the use of transcriptomics to identify a large number of loci that contribute...
Article
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Snake venom is shaped by the ecology and evolution of venomous species, and signals of positive selection in toxins have been consistently documented, reflecting the role of venoms as an ecologically critical phenotype. New World coral snakes (Elapidae) are represented by three genera and over 120 species and sub-species that are capable of causing...
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Background Snake venoms generally show sequence and quantitative variation within and between species, but some rattlesnakes have undergone exceptionally rapid, dramatic shifts in the composition, lethality, and pharmacological effects of their venoms. Such shifts have occurred within species, most notably in Mojave (Crotalus scutulatus), South Ame...
Article
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Snake venoms have significant impacts on human populations through the morbidity and mortality associated with snakebites and as sources of drugs, drug leads, and physiological research tools. Genes expressed by venom-gland tissue, including those encoding toxic proteins, have therefore been sequenced but only with relatively sparse coverage result...

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