Variability of Hybridization in Topminnows

Pairs of species that exhibit broadly overlapping distributions, and multiple geographically isolated contact zones, provide opportunities to investigate the mechanisms of reproductive isolation. Such naturally replicated systems have demonstrated that hybridization rates can vary substantially among populations, raising important questions about the genetic basis of reproductive isolation. The topminnows, Fundulus notatus and F. olivaceus, are reciprocally monophyletic, and co-occur in drainages throughout much of the central and southern United States. Hybridization rates vary substantially among populations in isolated drainage systems. We employed genome-wide sampling to investigate geographic variation in hybridization, and to assess the possible importance of chromosome fusions to reproductive isolation among nine separate contact zones. The species differ by chromosomal rearrangements resulting from Robertsonian (Rb) fusions, so we hypothesized that Rb fusion chromosomes would serve as reproductive barriers, exhibiting steeper genomic clines than the rest of the genome. We observed variation in hybridization dynamics among drainages that ranged from nearly random mating to complete absence of hybridization. Contrary to predictions, our use of genomic cline analyses on mapped species-diagnostic SNP markers did not indicate consistent patterns of variable introgression across linkage groups, or an association between Rb fusions and genomic clines that would be indicative of reproductive isolation. We did observe a relationship between hybridization rates and population phylogeography, with the lowest rates of hybridization tending to be found in populations inferred to have had the longest histories of drainage sympatry. Our results, combined with previous studies of contact zones between the species, support population history as an important factor in explaining variation in hybridization rates

Status of the Blackstripe (Fundulus notatus) and Blackspotted (F. olivaceus) Topminnows in the Ozark uplands of Central Missouri

The topminnow species Fundulus notatus and F. olivaceus have broadly overlapping geographic distributions that extend throughout much of the central and southern United States. In the northern portion of their respective ranges, in Missouri, the regional distributions of the two species coincide largely with recognized ecoregions. In the unglaciated southern half of Missouri, F. olivaceus is distributed throughout Ozark upland habitats while F. notatus is abundant in marginal large river and prairie habitats along the Ozark borders. An exception to this partitioning is the historical report of abundant F. notatus in the Bourbeuse and upper Meramec River drainages within the Ozark uplands ecoregion. We conducted an extensive survey of the Bourbeuse and Dry Fork Meramec Rivers to determine topminnow species composition in these systems. Our surveys found abundant F. olivaceus populations throughout these drainages and failed to uncover any F. notatus individuals. A review of museum accessions from the 1940s and 1960s confirms the historical presence of F. notatus in these river drainages, suggesting that a significant shift in topminnow species abundance has occurred in the past half century

Variable Rates Of Hybridization Among Contact Zones Between A Pair Of Topminnow Species, Fundulus Notatus And F. Olivaceus

Pairs of species that exhibit broadly overlapping distributions, and multiple geographically isolated contact zones, provide opportunities to investigate the mechanisms of reproductive isolation. Such naturally replicated systems have demonstrated that hybridization rates can vary substantially among populations, raising important questions about the genetic basis of reproductive isolation. The topminnows, Fundulus notatus and F. olivaceus, are reciprocally monophyletic, and co-occur in drainages throughout much of the central and southern United States. Hybridization rates vary substantially among populations in isolated drainage systems. We employed genome-wide sampling to investigate geographic variation in hybridization, and to assess the possible importance of chromosome fusions to reproductive isolation among nine separate contact zones. The species differ by chromosomal rearrangements resulting from Robertsonian (Rb) fusions, so we hypothesized that Rb fusion chromosomes would serve as reproductive barriers, exhibiting steeper genomic clines than the rest of the genome. We observed variation in hybridization dynamics among drainages that ranged from nearly random mating to complete absence of hybridization. Contrary to predictions, our use of genomic cline analyses on mapped species-diagnostic SNP markers did not indicate consistent patterns of variable introgression across linkage groups, or an association between Rb fusions and genomic clines that would be indicative of reproductive isolation. We did observe a relationship between hybridization rates and population phylogeography, with the lowest rates of hybridization tending to be found in populations inferred to have had the longest histories of drainage sympatry. Our results, combined with previous studies of contact zones between the species, support population history as an important factor in explaining variation in hybridization rates

Evolution of a Sexually Dimorphic Trait In a Broadly Distributed Topminnow (\u3ci\u3eFundulus olivaceus\u3c/i\u3e)

Understanding the interaction between sexual and natural selection within variable environments is crucial to our understanding of evolutionary processes. The handicap principle predicts females will prefer males with exaggerated traits provided those traits are indicators of male quality to ensure direct or indirect female benefits. Spatial variability in ecological factors is expected to alter the balance between sexual and natural selection that defines the evolution of such traits. Male and female blackspotted topminnows (Fundulidae: Fundulus olivaceus) display prominent black dorsolateral spots that are variable in number across its broad range. We investigated variability in spot phenotypes at 117 sites across 13 river systems and asked if the trait was sexually dimorphic and positively correlated with measures of fitness (condition and gonadosomatic index [GSI]). Laboratory and mesocosm experiments assessed femalemate choice and predation pressure on spot phenotypes. Environmental and community data collected at sampling locations were used to assess predictive models of spot density at the individual, site, and river system level. Greater number of spots was positively correlated with measures of fitness in males. Males with more spots were preferred by females and suffered greater mortality due to predation. Water clarity (turbidity) was the best predictor of spot density on the drainage scale, indicating that sexual and natural selection for the trait may be mediated by local light environments

Evolution of a Sexually Dimorphic Trait in a Broadly Distributed Topminnow (Fundulus Olivaceus)

Understanding the interaction between sexual and natural selection within variable environments is crucial to our understanding of evolutionary processes. The handicap principle predicts females will prefer males with exaggerated traits provided those traits are indicators of male quality to ensure direct or indirect female benefits. Spatial variability in ecological factors is expected to alter the balance between sexual and natural selection that defines the evolution of such traits. Male and female blackspotted topminnows (Fundulidae: Fundulus olivaceus) display prominent black dorsolateral spots that are variable in number across its broad range. We investigated variability in spot phenotypes at 117 sites across 13 river systems and asked if the trait was sexually dimorphic and positively correlated with measures of fitness (condition and gonadosomatic index [GSI]). Laboratory and mesocosm experiments assessed female mate choice and predation pressure on spot phenotypes. Environmental and community data collected at sampling locations were used to assess predictive models of spot density at the individual, site, and river system level. Greater number of spots was positively correlated with measures of fitness in males. Males with more spots were preferred by females and suffered greater mortality due to predation. Water clarity (turbidity) was the best predictor of spot density on the drainage scale, indicating that sexual and natural selection for the trait may be mediated by local light environments

Characterization of LINE-1 Ribonucleoprotein Particles

The average human genome contains a small cohort of active L1 retrotransposons that encode two proteins (ORF1p and ORF2p) required for their mobility (i.e., retrotransposition). Prior studies demonstrated that human ORF1p, L1 RNA, and an ORF2p-encoded reverse transcriptase activity are present in ribonucleoprotein (RNP) complexes. However, the inability to physically detect ORF2p from engineered human L1 constructs has remained a technical challenge in the field. Here, we have employed an epitope/RNA tagging strategy with engineered human L1 retrotransposons to identify ORF1p, ORF2p, and L1 RNA in a RNP complex. We next used this system to assess how mutations in ORF1p and/or ORF2p impact RNP formation. Importantly, we demonstrate that mutations in the coiled-coil domain and RNA recognition motif of ORF1p, as well as the cysteine-rich domain of ORF2p, reduce the levels of ORF1p and/or ORF2p in L1 RNPs. Finally, we used this tagging strategy to localize the L1–encoded proteins and L1 RNA to cytoplasmic foci that often were associated with stress granules. Thus, we conclude that a precise interplay among ORF1p, ORF2p, and L1 RNA is critical for L1 RNP assembly, function, and L1 retrotransposition

Population Genetics of Death Valley Pupfishes (Cyprinodontidae:Cyprinodon Spp.) and the Identification of a New Retrotransposable Element Family

Study of the genetic relationships and evolutionary histories of pupfish populations (Cyprinodontidae: Cyprinodon spp.) from the remnant aquatic habitats of Death Valley was approached by exploring the genetic structure and divergence within and among populations using mitochondrial and nuclear DNA markers. The findings of these studies illustrate the influences of population size and isolation time in the divergence of small, fragmented populations largely via genetic drift. The information revealed in this study has implications for assessing priorities in the conservation of the unique evolutionary heritage among populations of the Death Valley pupfishes. A new retrotransposable element family was identified and characterized. This family of genetic elements was uncovered during a search of the pupfish genome for transposable elements to be used as molecular markers for population analyses. The description of this element family, named Swimmer 1 (SW1), provides new insights into the evolution of long interspersed nuclear elements (LINEs) in vertebrates. Therefore, a full characterization of the SW1 element family was undertaken in the Japanese medaka (Oryzias latipes) as well as in the pupfish genome. The Japanese medaka is a model organism widely used for genetic and developmental biology studies

Contrasting molecular population genetics of four hexokinases in Drosophila melanogaster, D. simulans and D. yakuba.

As part of a larger study contrasting patterns of variation in regulatory and nonregulatory enzymes of the central metabolic pathways we have examined the molecular variation in four uncharacterized hexokinase genes unique to muscle, fat body, and testis in Drosophila melanogaster, D. simulans, and D. yakuba. Earlier isoenzyme studies had designated these genes as Hex-A, Hex-C, and Hex-t. There are two tightly linked testes-specific genes designated here as Hex-t1 and Hex-t2. Substantial and concordant differences across species are seen in levels of both amino acid and silent polymorphism. The flight muscle form Hex-A is the most conserved followed by the fat body hexokinase Hex-C and testis-specific hexokinases Hex-t1 and Hex-t2. While constraints acting at the amino acid level are expected, the silent polymorphisms follow this pattern as well. All genes are in regions of normal recombination, therefore hitchhiking and background selection are not likely causes of interlocus differences. In D. melanogaster latitudinal clines are seen for amino acid polymorphisms at the Hex-C and Hex-t2 loci. There is evidence for accelerated amino acid substitution in Hex-t1 that has lost residues known to be associated with glucose and glucose-6-phosphate binding. D. simulans shows substantial linkage phase structuring that suggests historical population subdivision