Browsing by Author "Baker, Robert J. (TTU)"
Now showing 1 - 11 of 11
- Results Per Page
- Sort Options
Item Chromosomal evolution among leaf-nosed nectarivorous bats - Evidence from cross-species chromosome painting (Phyllostomidae, Chiroptera)(2013) Sotero-Caio, Cibele G. (TTU); Volleth, Marianne; Gollahon, Lauren S. (TTU); Fu, Beiyuan; Cheng, William; Ng, Bee L.; Yang, Fengtang; Baker, Robert J. (TTU)Background: New World leaf-nosed bats, Phyllostomidae, represent a lineage of Chiroptera marked by unprecedented morphological/ecological diversity and extensive intergeneric chromosomal reorganization. There are still disagreements regarding their systematic relationships due to morphological convergence among some groups. Their history of karyotypic evolution also remains to be documented. Results: To better understand the evolutionary relationships within Phyllostomidae, we developed chromosome paints from the bat species Macrotus californicus. We tested the potential of these paints as phylogenetic tools by looking for chromosomal signatures in two lineages of nectarivorous phyllostomids whose independent origins have been statistically supported by molecular phylogenies. By examining the chromosomal homologies defined by chromosome painting among two representatives of the subfamily Glossophaginae (Glossophaga soricina and Anoura cultrata) and one species from the subfamily Lonchophyllinae (Lonchophylla concava), we found chromosomal correspondence in regions not previously detected by other comparative cytogenetic techniques. We proposed the corresponding human chromosomal segments for chromosomes of the investigated species and found two syntenic associations shared by G. soricina and A. cultrata. Conclusion: Comparative painting with whole chromosome-specific paints of M. californicus demonstrates an extensive chromosomal reorganization within the two lineages of nectarivorous phyllostomids, with a large number of chromosomes shared between M. californicus and G. soricina. We show that the evolution of nectar-feeding bats occurs mainly by reshuffling of chiropteran Evolutionarily Conserved Units (ECUs). Robertsonian fusions/fissions and inversions seem to be important modifiers of phyllostomid karyotypes, and autapomorphic character states are common within species. Macrotus californicus chromosome paints will be a valuable tool for documenting the pattern of karyotypic evolution within Phyllostomidae radiation. © 2013 Sotero-Caio et al.; licensee BioMed Central Ltd.Item Conflicting Evolutionary Histories of the Mitochondrial and Nuclear Genomes in New World Myotis Bats(2018) Platt, Roy N. (TTU); Faircloth, Brant C.; Sullivan, Kevin A.M. (TTU); Kieran, Troy J.; Glenn, Travis C.; Vandewege, Michael W. (TTU); Lee, Thomas E.; Baker, Robert J. (TTU); Stevens, Richard D. (TTU); Ray, David A. (TTU)The rapid diversification of Myotis bats into more than 100 species is one of the most extensive mammalian radiations available for study. Efforts to understand relationships within Myotis have primarily utilized mitochondrial markers and trees inferred from nuclear markers lacked resolution.Our current understanding of relationships within Myotis is therefore biased towards a set of phylogenetic markers that may not reflect the history of the nuclear genome. To resolve this, we sequenced the full mitochondrial genomes of 37 representative Myotis, primarily from the NewWorld, in conjunction with targeted sequencing of 3648 ultraconserved elements (UCEs). We inferred the phylogeny and explored the effects of concatenation and summary phylogenetic methods, as well as combinations of markers based on informativeness or levels of missing data, on our results. Of the 294 phylogenies generated from the nuclear UCE data, all are significantly different from phylogenies inferred using mitochondrial genomes. Even within the nuclear data, quartet frequencies indicate that around half of all UCE loci conflict with the estimated species tree. Several factors can drive such conflict, including incomplete lineage sorting, introgressive hybridization, or even phylogenetic error. Despite the degree of discordance between nuclear UCE loci and the mitochondrial genome and among UCE loci themselves, the most common nuclear topology is recovered in one quarter of all analyses with strong nodal support. Based on these results, we re-examine the evolutionary history of Myotis to better understand the phenomena driving their unique nuclear, mitochondrial, and biogeographic histories.Item Contrasting Evolutionary Dynamics of the Developmental Regulator PAX9, among Bats, with Evidence for a Novel Post-Transcriptional Regulatory Mechanism(2013) Phillips, Caleb D. (TTU); Butler, Boyd (TTU); Fondon, John W.; Mantilla-Meluk, Hugo (TTU); Baker, Robert J. (TTU)Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways. However, little is known about the genetic basis of such phenotypic diversity. Understanding these mechanisms is difficult for numerous reasons, yet studies in model organisms often provide clues about the major developmental pathways involved. The paired-domain gene, PAX9, is known to be a key regulator of development, particularly of the face and teeth. In this study, using a comparative genetics approach, we investigate PAX9 molecular evolution among mammals, focusing on craniofacially diversified (Phyllostomidae) and conserved (Vespertilionidae) bat families, and extend our comparison to other orders of mammal. Open-reading frame analysis disclosed signatures of selection, in which a small percentage of residues vary, and lineages acquire different combinations of variation through recurrent substitution and lineage specific changes. A few instances of convergence for specific residues were observed between morphologically convergent bat lineages. Bioinformatic analysis for unknown PAX9 regulatory motifs indicated a novel post-transcriptional regulatory mechanism involving a Musashi protein. This regulation was assessed through fluorescent reporter assays and gene knockdowns. Results are compatible with the hypothesis that the number of Musashi binding-elements in PAX9 mRNA proportionally regulates protein translation rate. Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but be static among conserved species. Under this model, Musashi's regulatory control of alternative human PAX9 isoforms would also vary. The presence of Musashi-binding elements within PAX9 of all mammals examined, chicken, zebrafish, and the fly homolog of PAX9, indicates this regulatory mechanism is ancient, originating basal to much of the animal phylogeny. © 2013 Phillips et al.Item Dietary and flight energetic adaptations in a salivary gland transcriptome of an insectivorous bat(2014) Phillips, Carleton J. (TTU); Phillips, Caleb D. (TTU); Goecks, Jeremy; Lessa, Enrique P.; Sotero-Caio, Cibele G. (TTU); Tandler, Bernard; Gannon, Michael R.; Baker, Robert J. (TTU)We hypothesized that evolution of salivary gland secretory proteome has been important in adaptation to insectivory, the most common dietary strategy among Chiroptera. A submandibular salivary gland (SMG) transcriptome was sequenced for the little brown bat, Myotis lucifugus. The likely secretory proteome of 23 genes included seven (RETNLB, PSAP, CLU, APOE, LCN2, C3, CEL) related to M. lucifugus insectivorous diet and metabolism. Six of the secretory proteins probably are endocrine, whereas one (CEL) most likely is exocrine. The encoded proteins are associated with lipid hydrolysis, regulation of lipid metabolism, lipid transport, and insulin resistance. They are capable of processing exogenous lipids for flight metabolism while foraging. Salivary carboxyl ester lipase (CEL) is thought to hydrolyze insect lipophorins, which probably are absorbed across the gastric mucosa during feeding. The other six proteins are predicted either to maintain these lipids at high blood concentrations or to facilitate transport and uptake by flight muscles. Expression of these seven genes and coordinated secretion from a single organ is novel to this insectivorous bat, and apparently has evolved through instances of gene duplication, gene recruitment, and nucleotide selection. Four of the recruited genes are single-copy in the Myotis genome, whereas three have undergone duplication(s) with two of these genes exhibiting evolutionary 'bursts' of duplication resulting in multiple paralogs. Evidence for episodic directional selection was found for six of seven genes, reinforcing the conclusion that the recruited genes have important roles in adaptation to insectivory and the metabolic demands of flight. Intragenic frequencies of mobile- element-like sequences differed from frequencies in the whole M. lucifugus genome. Differences among recruited genes imply separate evolutionary trajectories and that adaptation was not a single, coordinated event. © 2014 Phillips et al.Item Elevated mitochondrial genome variation after 50 generations of radiation exposure in a wild rodent(2017) Baker, Robert J. (TTU); Dickins, Benjamin; Wickliffe, Jeffrey K.; Khan, Faisal A.A. (TTU); Gaschak, Sergey; Makova, Kateryna D.; Phillips, Caleb D. (TTU)Currently, the effects of chronic, continuous low dose environmental irradiation on the mitochondrial genome of resident small mammals are unknown. Using the bank vole (Myodes glareolus) as a model system, we tested the hypothesis that approximately 50 generations of exposure to the Chernobyl environment has significantly altered genetic diversity of the mitochondrial genome. Using deep sequencing, we compared mitochondrial genomes from 131 individuals from reference sites with radioactive contamination comparable to that present in northern Ukraine before the 26 April 1986 meltdown, to populations where substantial fallout was deposited following the nuclear accident. Population genetic variables revealed significant differences among populations from contaminated and uncontaminated localities. Therefore, we rejected the null hypothesis of no significant genetic effect from 50 generations of exposure to the environment created by the Chernobyl meltdown. Samples from contaminated localities exhibited significantly higher numbers of haplotypes and polymorphic loci, elevated genetic diversity, and a significantly higher average number of substitutions per site across mitochondrial gene regions. Observed genetic variation was dominated by synonymous mutations, which may indicate a history of purify selection against nonsynonymous or insertion/deletion mutations. These significant differences were not attributable to sample size artifacts. The observed increase in mitochondrial genomic diversity in voles from radioactive sites is consistent with the possibility that chronic, continuous irradiation resulting from the Chernobyl disaster has produced an accelerated mutation rate in this species over the last 25 years. Our results, being the first to demonstrate this phenomenon in a wild mammalian species, are important for understanding genetic consequences of exposure to low-dose radiation sources.Item Genetic Diversity of Neotropical Myotis (Chiroptera: Vespertilionidae) with an Emphasis on South American Species(2012) Larsen, Roxanne J. (TTU); Knapp, Michelle C. (TTU); Genoways, Hugh H.; Khan, Faisal Ali Anwarali (TTU); Larsen, Peter A. (TTU); Wilson, Don E.; Baker, Robert J. (TTU)Background: Cryptic morphological variation in the Chiropteran genus Myotis limits the understanding of species boundaries and species richness within the genus. Several authors have suggested that it is likely there are unrecognized species-level lineages of Myotis in the Neotropics. This study provides an assessment of the diversity in New World Myotis by analyzing cytochrome-b gene variation from an expansive sample ranging throughout North, Central, and South America. We provide baseline genetic data for researchers investigating phylogeographic and phylogenetic patterns of Myotis in these regions, with an emphasis on South America. Methodology and Principal Findings: Cytochrome-b sequences were generated and phylogenetically analyzed from 215 specimens, providing DNA sequence data for the most species of New World Myotis to date. Based on genetic data in our sample, and on comparisons with available DNA sequence data from GenBank, we estimate the number of species-level genetic lineages in South America alone to be at least 18, rather than the 15 species currently recognized. Conclusions: Our findings provide evidence that the perception of lower species richness in South American Myotis is largely due to a combination of cryptic morphological variation and insufficient sampling coverage in genetic-based systematic studies. A more accurate assessment of the level of diversity and species richness in New World Myotis is not only helpful for delimiting species boundaries, but also for understanding evolutionary processes within this globally distributed bat genus. © 2012 Larsen et al.Item Human-modified habitats change patterns of population genetic structure and group relatedness in Peter's tent-roosting bats(2016) Sagot, Maria; Phillips, Caleb D. (TTU); Baker, Robert J. (TTU); Stevens, Richard D. (TTU)Although coloniality is widespread among mammals, it is still not clear what factors influence composition of social groups. As animals need to adapt to multiple habitat and environmental conditions throughout their range, variation in group composition should be influenced by adaptive adjustment to different ecological factors. Relevant to anthropogenic disturbance, increased habitat modification by humans can alter species’ presence, density, and population structure. Therefore, it is important to understand the consequences of changes to landscape composition, in particular how habitat modification affects social structure of group-forming organisms. Here, we combine information on roosting associations with genetic structure of Peter's tent-roosting bats, Uroderma bilobatum to address how different habitat characteristics at different scales affect structure of social groups. By dividing analyses by age and sex, we determined that genetic structure was greater for adult females than adult males or offspring. Habitat variables explained 80% of the variation in group relatedness (mainly influenced by female relatedness) with roost characteristics contributing the most explained variation. This suggests that females using roosts of specific characteristics exhibit higher relatedness and seem to be philopatric. These females mate with more males than do more labile female groups. Results describe ecological and microevolutionary processes, which affect relatedness and social structure; findings are highly relevant to species distributions in both natural and human-modified environments.Item Integration of molecular cytogenetics, dated molecular phylogeny, and model-based predictions to understand the extreme chromosome reorganization in the Neotropical genus Tonatia (Chiroptera: Phyllostomidae)(2015) Sotero-Caio, Cibele G. (TTU); Volleth, Marianne; Hoffmann, Federico G.; Scott, Lu Ann; Wichman, Holly A.; Yang, Fengtang; Baker, Robert J. (TTU)Background: Defining factors that contributed to the fixation of a high number of underdominant chromosomal rearrangements is a complex task because not only molecular mechanisms must be considered, but also the uniqueness of natural history attributes of each taxon. Ideally, detailed investigation of the chromosome architecture of an organism and related groups, placed within a phylogenetic context, is required. We used multiple approaches to investigate the dynamics of chromosomal evolution in lineages of bats with considerable karyotypic variation, focusing on the different facets contributing to fixation of the exceptional chromosomal changes in Tonatia saurophila. Integration of empirical data with proposed models of chromosome evolution was performed to understand the probable conditions for Tonatia's karyotypic evolution. Results: The trajectory of reorganization of chromosome blocks since the common ancestor of Glossophaginae and Phyllostominae subfamilies suggests that multiple tandem fusions, as well as disruption and fusions of conserved phyllostomid chromosomes were major drivers of karyotypic reshuffling in Tonatia. Considerable variation in the rates of chromosomal evolution between phyllostomid lineages was observed. Thirty-nine unique fusions and fission events reached fixation in Tonatia over a short period of time, followed by ~12 million years of chromosomal stasis. Physical mapping of repetitive DNA revealed an unusual accumulation of LINE-1 sequences on centromeric regions, probably associated with the chromosomal dynamics of this genus. Conclusions: Multiple rearrangements have reached fixation in a wave-like fashion in phyllostomid bats. Different biological features of Tonatia support distinct models of rearrangement fixation, and it is unlikely that the fixations were a result of solely stochastic processes in small ancient populations. Increased recombination rates were probably facilitated by expansion of repetitive DNA, reinforced by aspects of taxon reproduction and ecology.Item Natural hybridization generates mammalian lineage with species characteristics(2010) Larsen, Peter A. (TTU); Marchán-Rivadeneira, María R. (TTU); Baker, Robert J. (TTU)Most diploid species arise from single-species ancestors. Hybrid origins of new species are uncommon (except among polyploids) and are documented infrequently in animals. Examples of natural hybridization leading to speciation in mammals are exceedingly rare. Here, we show a Caribbean species of bat (Artibeus schwartzi) has a nuclear genome derived from two nonsister but congeneric species (A. jamaicensis and A. planirostris) and a mitochondrial genome that is from a third extinct or uncharacterized congener. Artibeus schwartzi is self-sustaining, morphologically distinct, and exists in near geographic isolation of its known parent species. Island effects (i.e., area, reduced habitat variability, and geographic isolation) likely have restricted gene flowfrom parental species into the Caribbean populations of this hybrid lineage, thus contributing to local adaptation and isolation of this newly produced taxon. We hypothesize differential rates of the development of reproductive isolation within the genus and estimate that 2.5 million years was an insufficient amount of time for the development of postzygotic isolation among the three species that hybridized to produce A. schwartzi. Reticulated evolution thus has resulted in a genomiccombination from three evolutionary lineages and a transgressive phenotype that is distinct from all other known species of Artibeus. The data herein further demonstrate the phenomenon of speciation by hybridization in mammals is possible in nature.Item Rolling-circle transposons catalyze genomic innovation in a mammalian lineage(2014) Thomas, Jainy; Phillips, Caleb D. (TTU); Baker, Robert J. (TTU); Pritham, Ellen J.Rolling-circle transposons (Helitrons) are a newly discovered group ofmobileDNAwidespread in plant and invertebrate genomes but limited to thebat family Vespertilionidae amongmammals. Little is knownabout thelong-term impact of Helitron activity because the genomeswhere Helitron activity has been extensively studied are predominated by young families. Here,we report a comprehensive catalog of vetted Helitrons from the 7× Myotis lucifugus genome assembly. To estimate the timing of transposition, we scored presence/absence across related vespertilionid genome sequences with estimated divergence times. This analysis revealed that the Helibat family has been a persistent source of genomic innovation throughout the vespertilionid diversification from approximately 30-36 Ma to as recently as approximately 1.8-6 Ma. This is the first report of persistent Helitron transposition over an extended evolutionary timeframe. These findings illustrate that the pattern of Helitron activity is akin to the vertical persistence of LINE retrotransposons in primates and other mammalian lineages. Like retrotransposition in primates, rolling-circle transposition has generated lineage-specific variation and accounts for approximately 110 Mb, approximately 6%of the genome of M. lucifugus. The Helitrons carry a heterogeneous assortment of host sequence including retroposed messenger RNAs, retrotransposons, DNA transposons, as well as introns, exons and regulatory regions (promoters, 50-untranslated regions [UTRs], and 30-UTRs) of which some are evolving in a pattern suggestive of purifying selection. Evidence that Helitrons have contributed putative promoters, exons, splice sites, polyadenylation sites, and microRNA-binding sites to transcripts otherwise conserved across mammals is presented, and the implication of Helitron activity to innovation in these unique mammals is discussed.Item Secretory gene recruitments in vampire bat salivary adaptation and potential convergences with sanguivorous leeches(2015) Phillips, Caleb D. (TTU); Baker, Robert J. (TTU)Regulatory evolution is thought to be fundamental to adaptive evolution. However, the identification of specific regulatory changes responsible for adaptation are sparse. Bats of the family Phyllostomidae, owing to their unparalleled rate of ecological and morphological evolution, represent an ideal system to identify regulatory evolution of adaptive significance. Among ecological niche leaps observed in this family, the most dramatic is the evolution of obligate sanguivory by vampire bats, which due to their highly derived phenotype, the sporadic phylogenetic occurrence of blood-feeding, and the adaptive potential of salivary glands, has enabled the development of hypotheses about adaptive molecular phenotypes. Using comparative transcriptomics of vampire bat, outgroup insectivorous bats, and sanguivorous leeches we identify genes that have been convergently recruited as secretory products of salivary glands of vampire bats and leeches. Comparisons of vampire bat to lineages maintaining the primitive chiropteran condition of insectivory indicated gene recruitment of alternative splice variants, and 5′ exon evolution, as the mechanisms producing secretory expression in vampire bats, but not in the insectivorous bats Macrotus and Myotis. Biochemical functions of hypothesized recruited genes explain adaptive benefits to sanguivory by modulating host hemostasis and neural signaling. It is difficult to identify how complex phenotypic change and rapid ecological transition, such as that observed in vampire bats, evolved over a short evolutionary timescale. Results indicate that regulatory evolution controlling tissue-specific splicing patterns has been important to successful adaptation of this lineage. Future studies that leverage emerging long sequence-read technologies, increased sample sizes, and expression and sequence comparisons across other sanguivore lineages will further elucidate roles of alternative splicing and gene recruitment in the remarkable evolution of sanguivory.