Geographic variation, null hypotheses, and subspecies limits in the California Gnatcatcher: A response to McCormack and Maley

We interpreted the results of nuclear DNA sequencing to be inconsistent with the recognition of California Gnatcatcher (Polioptila californica) subspecies. McCormack and Maley (2015) suggested that our data did support 2 taxa, one of which was P. c. californica, listed as Threatened under the Endangered Species Act (ESA). We summarize here how 2 sets of researchers with access to the same data reached different conclusions by including different analyses. We included the southern subspecies’ boundary from the taxonomy of Atwood (1991), the taxonomic basis for the ESA listing, which resulted in an Analysis of Molecular Variance that provided no support for subspecies. In contrast, using a novel taxonomic hypothesis without precedent in the literature, McCormack and Maley (2015) found statistically significant FST values for 2 loci, which they suggested supports P. c. californica. We propose that our mitochondrial and nuclear data had sufficient power to capture geographical structure at either the phylogenetic (monophyly) or traditional ‘‘75% rule’’ level. McCormack and Maley (2015) suggested that finding an absence of population structure was a ‘‘negative result,’’ whereas we consider it to be the null hypothesis for a species with gene flow and no geographical barriers. We interpret the unstructured mtDNA and nuclear DNA trees, the STRUCTURE analysis supporting one group, the identification of just 26% (and not 75%) of individuals of P. c. californica with the most diagnostic nuclear locus, the overall GST that suggests that over 98% of the variation is explained by nontaxonomic sources, and the lack of evidence of ecological differentiation to indicate that P. c. californica is not a valid subspecies. McCormack and Maley (2015) suggest that statistically significant differences at 2 loci that explained ,6% of the genetic variation, and previous morphological data, support recognition of P. c. californica. If ornithology continues to recognize subspecies, these different standards should be reconciled

PHYLOGEOGRAPHY OF THE CALIFORNIA GNATCATCHER (POLIOPTILA CALIFORNICA) USING MULTILOCUS DNA SEQUENCES AND ECOLOGICAL NICHE MODELING: IMPLICATIONS FOR CONSERVATION

An important step in conservation is to identify whether threatened populations are evolutionarily discrete and significant to the species. A prior mitochondrial DNA (mtDNA) phylogeographic study of the California Gnatcatcher (Polioptila californica) revealed no geographic structure and, thus, did not support the subspecies validity of the threatened coastal California Gnatcatcher (P. c. californica). The U.S. Fish and Wildlife Service concluded that mtDNA data alone were insufficient to test subspecies taxonomy. We sequenced eight nuclear loci to search for historically discrete groupings that might have been missed by the mtDNA study (which we confirmed with new ND2 sequences). Phylogenetic analyses of the nuclear loci revealed no historically significant groupings and a low level of divergence (GST = 0.013). Sequence data suggested an older population increase in southern populations, consistent with niche modeling that suggested a northward range expansion following the Last Glacial Maximum (LGM). The signal of population increase was most evident in the mtDNA data, revealing the importance of including loci with short coalescence times. The threatened subspecies inhabits the distinctive Coastal Sage Scrub ecosystem, which might indicate ecological differentiation, but a test of niche divergence was insignificant. The best available genetic, morphological, and ecological data indicate a southward population displacement during the LGM followed by northward range expansion, without the occurrence of significant isolating barriers having led to the existence of evolutionarily discrete subspecies or distinct population segments that would qualify as listable units under the Endangered Species Act

Transcriptomic effects of dispersed oil in a non-model decapod crustacean

Background. Oil spills are major environmental disasters. Dispersants help control spills, as they emulsify oil into droplets to speed bioremediation. Although dispersant toxicity is controversial, the genetic consequences and damages of dispersed oil exposure are poorly understood. We used RNA-seq to measure gene expression of flatback mudcrabs (Eurypanopeus depressus, Decapoda, Brachyura, Panopeidae) exposed to dispersed oil. Methods. Our experimental design included two control types, oil-only, and oil-dispersant treatments with three replicates each. We prepared 100 base pair-ended libraries from total RNA and sequenced them in one Illumina HiSeq2000 lane. We assembled a reference transcriptome with all replicates per treatment, assessed quality with novel metrics, identified transcripts, and quantified gene expression with open source software. Results. Our mudcrab transcriptome included 500,008 transcripts from 347,082,962 pairend raw reads. In oil-only treatments, we found few significant differences. However, in oildispersant treatments, over 4000 genes involved with cellular differentiation, primordial cellular component upkeep, apoptosis, and immune response were downregulated. A few muscle structure and development genes were upregulated. Discussion. Our results provide evidence that exposure to chemically dispersed oil causes a generalized cellular shutdown and muscular repair attempts. Our results suggest current oil-spill treatment procedures could be detrimental to crustaceans and indicate additional research is needed to evaluate the impact of oil spills in gene expression. Finally, traditional quality metrics such as N50s have limitations to explain the nature of RNA-seq compared to new methods in non-model decapod crustaceans

Geographic variation, null hypotheses, and subspecies limits in the California Gnatcatcher: A response to McCormack and Maley

We interpreted the results of nuclear DNA sequencing to be inconsistent with the recognition of California Gnatcatcher (Polioptila californica) subspecies. McCormack and Maley (2015) suggested that our data did support 2 taxa, one of which was P. c. californica, listed as Threatened under the Endangered Species Act (ESA). We summarize here how 2 sets of researchers with access to the same data reached different conclusions by including different analyses. We included the southern subspecies’ boundary from the taxonomy of Atwood (1991), the taxonomic basis for the ESA listing, which resulted in an Analysis of Molecular Variance that provided no support for subspecies. In contrast, using a novel taxonomic hypothesis without precedent in the literature, McCormack and Maley (2015) found statistically significant FST values for 2 loci, which they suggested supports P. c. californica. We propose that our mitochondrial and nuclear data had sufficient power to capture geographical structure at either the phylogenetic (monophyly) or traditional ‘‘75% rule’’ level. McCormack and Maley (2015) suggested that finding an absence of population structure was a ‘‘negative result,’’ whereas we consider it to be the null hypothesis for a species with gene flow and no geographical barriers. We interpret the unstructured mtDNA and nuclear DNA trees, the STRUCTURE analysis supporting one group, the identification of just 26% (and not 75%) of individuals of P. c. californica with the most diagnostic nuclear locus, the overall GST that suggests that over 98% of the variation is explained by nontaxonomic sources, and the lack of evidence of ecological differentiation to indicate that P. c. californica is not a valid subspecies. McCormack and Maley (2015) suggest that statistically significant differences at 2 loci that explained ,6% of the genetic variation, and previous morphological data, support recognition of P. c. californica. If ornithology continues to recognize subspecies, these different standards should be reconciled

PHYLOGEOGRAPHY OF THE CALIFORNIA GNATCATCHER (POLIOPTILA CALIFORNICA) USING MULTILOCUS DNA SEQUENCES AND ECOLOGICAL NICHE MODELING: IMPLICATIONS FOR CONSERVATION

An important step in conservation is to identify whether threatened populations are evolutionarily discrete and significant to the species. A prior mitochondrial DNA (mtDNA) phylogeographic study of the California Gnatcatcher (Polioptila californica) revealed no geographic structure and, thus, did not support the subspecies validity of the threatened coastal California Gnatcatcher (P. c. californica). The U.S. Fish and Wildlife Service concluded that mtDNA data alone were insufficient to test subspecies taxonomy. We sequenced eight nuclear loci to search for historically discrete groupings that might have been missed by the mtDNA study (which we confirmed with new ND2 sequences). Phylogenetic analyses of the nuclear loci revealed no historically significant groupings and a low level of divergence (GST = 0.013). Sequence data suggested an older population increase in southern populations, consistent with niche modeling that suggested a northward range expansion following the Last Glacial Maximum (LGM). The signal of population increase was most evident in the mtDNA data, revealing the importance of including loci with short coalescence times. The threatened subspecies inhabits the distinctive Coastal Sage Scrub ecosystem, which might indicate ecological differentiation, but a test of niche divergence was insignificant. The best available genetic, morphological, and ecological data indicate a southward population displacement during the LGM followed by northward range expansion, without the occurrence of significant isolating barriers having led to the existence of evolutionarily discrete subspecies or distinct population segments that would qualify as listable units under the Endangered Species Act

Fluctuating fire regimes and their historical effects on genetic variation in an endangered shrubland specialist

The Pleistocene was characterized by worldwide shifts in community compositions. Some of these shifts were a result of changes in fire regimes, which influenced the distribution of species belonging to fire-dependent communities. We studied an endangered juniper–oak shrubland specialist, the black-capped vireo (Vireo atricapilla). This species was locally extirpated in parts of Texas and Oklahoma by the end of the 1980s as a result of habitat change and loss, predation, brood parasitism, and anthropogenic fire suppression. We sequenced multiple nuclear loci and used coalescence methods to obtain a deeper understanding of historical population trends than that typically available from microsatellites or mtDNA. We compared our estimated population history, a long-term history of the fire regime and ecological niche models representing the mid-Holocene, last glacial maximum, and last interglacial. Our Bayesian skyline plots showed a pattern of historical population fluctuation that was consistent with changing fire regimes. Genetic data suggest that the species is genetically unstructured, and that the current population should be orders of magnitude larger than it is at present. We suggest that fire suppression and habitat loss are primary factors contributing to the recent decline of the BCVI, although the role of climate change since the last glacial maximum is unclear at present

Transcriptomic effects of dispersed oil in a non-model decapod crustacean

Background. Oil spills are major environmental disasters. Dispersants help control spills, as they emulsify oil into droplets to speed bioremediation. Although dispersant toxicity is controversial, the genetic consequences and damages of dispersed oil exposure are poorly understood. We used RNA-seq to measure gene expression of flatback mudcrabs (Eurypanopeus depressus, Decapoda, Brachyura, Panopeidae) exposed to dispersed oil. Methods. Our experimental design included two control types, oil-only, and oil-dispersant treatments with three replicates each. We prepared 100 base pair-ended libraries from total RNA and sequenced them in one Illumina HiSeq2000 lane. We assembled a reference transcriptome with all replicates per treatment, assessed quality with novel metrics, identified transcripts, and quantified gene expression with open source software. Results. Our mudcrab transcriptome included 500,008 transcripts from 347,082,962 pairend raw reads. In oil-only treatments, we found few significant differences. However, in oildispersant treatments, over 4000 genes involved with cellular differentiation, primordial cellular component upkeep, apoptosis, and immune response were downregulated. A few muscle structure and development genes were upregulated. Discussion. Our results provide evidence that exposure to chemically dispersed oil causes a generalized cellular shutdown and muscular repair attempts. Our results suggest current oil-spill treatment procedures could be detrimental to crustaceans and indicate additional research is needed to evaluate the impact of oil spills in gene expression. Finally, traditional quality metrics such as N50s have limitations to explain the nature of RNA-seq compared to new methods in non-model decapod crustaceans

Stoma-free survival after anastomotic leak following rectal cancer resection: worldwide cohort of 2470 patients

Background: The optimal treatment of anastomotic leak after rectal cancer resection is unclear. This worldwide cohort study aimed to provide an overview of four treatment strategies applied. Methods: Patients from 216 centres and 45 countries with anastomotic leak after rectal cancer resection between 2014 and 2018 were included. Treatment was categorized as salvage surgery, faecal diversion with passive or active (vacuum) drainage, and no primary/secondary faecal diversion. The primary outcome was 1-year stoma-free survival. In addition, passive and active drainage were compared using propensity score matching (2: 1). Results: Of 2470 evaluable patients, 388 (16.0 per cent) underwent salvage surgery, 1524 (62.0 per cent) passive drainage, 278 (11.0 per cent) active drainage, and 280 (11.0 per cent) had no faecal diversion. One-year stoma-free survival rates were 13.7, 48.3, 48.2, and 65.4 per cent respectively. Propensity score matching resulted in 556 patients with passive and 278 with active drainage. There was no statistically significant difference between these groups in 1-year stoma-free survival (OR 0.95, 95 per cent c.i. 0.66 to 1.33), with a risk difference of -1.1 (95 per cent c.i. -9.0 to 7.0) per cent. After active drainage, more patients required secondary salvage surgery (OR 2.32, 1.49 to 3.59), prolonged hospital admission (an additional 6 (95 per cent c.i. 2 to 10) days), and ICU admission (OR 1.41, 1.02 to 1.94). Mean duration of leak healing did not differ significantly (an additional 12 (-28 to 52) days). Conclusion: Primary salvage surgery or omission of faecal diversion likely correspond to the most severe and least severe leaks respectively. In patients with diverted leaks, stoma-free survival did not differ statistically between passive and active drainage, although the increased risk of secondary salvage surgery and ICU admission suggests residual confounding