Recent genetic, phenetic and ecological divergence across the Mesoamerican highlands: a study case with Diglossa baritula (Aves: Thraupidae).

The topographical, geological, climatic and biodiversity complexity of Mesoamerica has made it a primary research focus. The Mesoamerican highlands is a region with particularly high species richness and within-species variation. The Cinnamon-bellied Flowerpiercer, Diglossa baritula (Wagler, 1832), is a species endemic to the Mesoamerican highlands, with three allopatric subspecies currently recognized. To characterize divergence within this species, we integrated genomics, morphology, coloration and ecological niche modeling approaches, obtained from sampling individuals across the entire geographic distribution of the species. Our results revealed a clear genomic divergence between the populations to the east versus the west of the Isthmus of Tehuantepec. In contrast to the genomic results, morphology and coloration analyses showed intermediate levels of differentiation, indicating that population groups within D. baritula have probably been under similar selective pressures. Our morphology results indicated that the only sexually dimorphic morphological variable is the wing chord, with males having a longer wing chord than females. Finally, ecological data indicated that there are differences in ecological niche within D. baritula. Our data suggest that D. baritula could contain two or more incipient species at the intermediate phase of the speciation continuum. These results highlight the importance of the geographical barrier of the Isthmus of Tehuantepec and Pleistocene climatic events in driving isolation and population divergence in D. baritula. The present investigation illustrates the speciation potential of the D. baritula complex and the capacity of Mesoamerican highlands to create cryptic biodiversity and endemism.

Biogeographic factors contributing to the diversification of Euphoniinae (Aves, Passeriformes, Fringillidae): a phylogenetic and ancestral areas analysis.

Factors such as the Andean uplift, Isthmus of Panama, and climate changes have influenced bird diversity in the Neotropical region. Studying bird species that are widespread in Neotropical highlands and lowlands can help us understand the impact of these factors on taxa diversification. Our main objectives were to determine the biogeographic factors that contributed to the diversification of Euphoniinae and re-evaluate their phylogenetic relationships. The nextRAD and mitochondrial data were utilized to construct phylogenies. The ancestral distribution range was then estimated using a time-calibrated phylogeny, current species ranges, and neotropical regionalization. The phylogenies revealed two main Euphoniinae clades, Chlorophonia and Euphonia, similar to previous findings. Furthermore, each genus has distinctive subclades corresponding to morphology and geography. The biogeographic results suggest that the Andean uplift and the establishment of the western Amazon drove the vicariance of Chlorophonia and Euphonia during the Miocene. The Chlorophonia lineage originated in the Andes mountains and spread to Central America and the Mesoamerican highlands after the formation of the Isthmus of Panama. Meanwhile, the ancestral area of Euphonia was the Amazonas, from which it spread to trans-Andean areas during the Pliocene and Pleistocene due to the separation of the west lowlands from Amazonas due to the Northern Andean uplift. Chlorophonia and Euphonia species migrated to the Atlantic Forest during the Pleistocene through corridors from the East Andean Humid Forest and Amazonas. These two genera had Caribbean invasions with distinct geographic origins and ages. Finally, we suggested taxonomic changes in the genus Euphonia based on the study's phylogenetic, morphological, and biogeographic findings.

Enhancing debris removal in curved canals: a comparative evaluation of XP-endo Finisher and Passive Ultrasonic Irrigation.

OBJECTIVES: The study aimed to compare the efficacy of XP-endo Finisher and Passive Ultrasonic Irrigation (PUI) in removing hard tissue debris from curved canals. MATERIALS AND METHODS: Thirty-four mandibular molars with Vertucci's type II mesial canals were scanned in microcomputed tomography before and after preparation with HyFlex EDM, and accumulated hard tissue debris was quantified. Subsequently, the teeth were randomly divided into two groups according to the supplementary procedure: PUI with the Ultra-X insert or XP-endo Finisher. After the intervention, the specimens underwent another scanning. Two separate analyses were conducted, one for the total canal and another for the isthmus area. Unpaired and paired T-tests were used for inter- and intergroup comparisons, with a significance level set at 5%. RESULTS: Both supplementary methods reduced the amount of debris compared to the initial volume. Remarkably, the XP-endo Finisher achieved a significantly higher percentage of debris removal (71% for the total canal and 74% for the isthmus areas) compared to PUI (41% for the total canal and 52% for the isthmus area) (P < 0.05). CONCLUSIONS: Both supplementary approaches reduced the amount of hard tissue debris from canal preparation, still XP-endo Finisher showed a higher reduction compared to PUI (p < 0.05). CLINICAL RELEVANCE: None of the supplementary methods rendered canals completely free of hard tissue debris. However, the supplementary approach with XP-endo Finisher resulted in lower levels of hard tissue debris than PUI in curved canals with isthmuses.

External Auditory Canal: Computed Tomography Analysis and Classification.

Introduction Computed tomography (CT) details of the external auditory canal (EAC) are not fully covered in the literature, so building up base for the CT evaluation and description is important. Preoperative details of the EAC are mandatory before any approach or procedure involving the canal. Objective To determine the different dimensions, measurements, and grading of the EAC by CT scan that were not previously published. Methods The CT scans of 100 temporal bones (200 sides) were included. Axial images were acquired with multiplanar reformates to obtain delicate details in coronal and sagittal planes for all subjects. Results At the EAC entry, the mean vertical length (height) was 7.75 ± 1 mm, and its mean horizontal length (width) was 6.1 ± 0.8. At the bony cartilaginous junction of the EAC, the mean vertical length was 7.88 ± 1 mm, and its mean horizontal length was 6.22 ± 0.9. At the EAC isthmus, the mean vertical length was 6.8 ± 0.97 mm, and its mean horizontal length was 5.2 ± 0.76. At the medial end of the EAC, the mean vertical length was 7.1 ± 0.9 mm, and its mean horizontal length was 5.4 ± 0.85. There were no reported significant differences between right and left sides in all dimensions. Males showed significantly longer vertical and horizontal dimensions of the EAC entry, vertical dimension of the isthmus, and vertical dimension of the medial end of the EAC than females. Conclusion This study improves otologists and radiologists' awareness of EAC variations in the ear field and can be of help to residents in training.

Unraveling the complex phylogeographic history of freshwater fishes in Lower Central America: A study of the electric fish Brachyhypopomus occidentalis.

Lower Central America (LCA) has a complex biogeographic history shaped by the rise of the Isthmus of Panama and the global climatic oscillations of the Pleistocene. These events have been crucial in structuring biodiversity in LCA, but their consequences for the distribution and partitions of genetic diversity across the region remain to be elucidated. We combined complete mitochondrial genomes and nuclear ultraconserved elements (UCEs) to study the phylogeographic history and population genetic structure of the electric fish Brachyhypopomus occidentalis in LCA. Our results are consistent with the known phylogeographic history of B. occidentalis in LCA, but we update this history in several important ways that help illuminate the phylogeographic history of freshwater fishes in the region. We provide: i) support for three waves of colonization, two of which occurred prior to the final closure of the Panama Isthmus; ii) a more precise understanding of each colonization event, with evidence for a larger footprint of the first event, as well as genetic exchange across the continental divide in subsequent events; and iii) evidence for high levels of previously unrecognized population genetic structure across LCA. This updated model of colonization and diversification of B. occidentalis consists of three waves of dispersal and colonization, which triggered the evolution of geographic breaks in both nuclear and mitochondrial genomes across LCA. These processes are tightly linked to the dynamic uplift of the Isthmus, recent volcanic activity in the region, and the sea-level oscillations of the Pleistocene. These results improve previous phylogeographic inferences regarding the distribution and diversification of freshwater fishes in LCA, and generate testable hypotheses to guide future research exploring the factors shaping biodiversity in the region.

External Auditory Canal: Computed Tomography Analysis and Classification

Abstract Introduction Computed tomography (CT) details of the external auditory canal (EAC) are not fully covered in the literature, so building up base for the CT evaluation and description is important. Preoperative details of the EAC are mandatory before any approach or procedure involving the canal. Objective To determine the different dimensions, measurements, and grading of the EAC by CT scan that were not previously published. Methods The CTscans of 100 temporal bones (200 sides) were included. Axial images were acquired with multiplanar reformates to obtain delicate details in coronal and sagittal planes for all subjects. Results At the EAC entry, the mean vertical length (height) was 7.75 ± 1 mm, and its mean horizontal length (width) was 6.1 ±0.8. At the bony cartilaginous junction of the EAC, the mean vertical length was 7.88 ±1 mm, and its mean horizontal length was 6.22 ± 0.9. At the EAC isthmus, the mean vertical length was 6.8 ± 0.97 mm, and its mean horizontal length was 5.2 ± 0.76. At the medial end of the EAC, the mean vertical length was 7.1 ±0.9 mm, and its mean horizontal length was 5.4 ± 0.85. There were no reported significant differences between right and left sides in all dimensions. Males showed significantly longer vertical and horizontal dimensions of the EAC entry, vertical dimension of the isthmus, and vertical dimension of the medial end of the EAC than females. Conclusion This study improves otologists and radiologists' awareness of EAC variations in the ear field and can be of help to residents in training.

Nonlinear Statistical Features of the Seismicity in the Subduction Zone of Tehuantepec Isthmus, Southern México.

After the M8.2 main-shock occurred on 7 September 2017 at the Isthmus of Tehuantepec, Mexico, the spatial distribution of seismicity has showed a clear clusterization of earthquakes along the collision region of the Tehuantepec Transform/Ridge with the Middle America Trench off Chiapas. Furthermore, nowadays, the temporal rate of occurrence in the number of earthquakes has also showed a pronounced increase. On the basis of this behavior, we studied the sequence of magnitudes of the earthquakes which occurred within the Isthmus of Tehuantepec in southern Mexico from 2010 to 2020. Since big earthquakes are considered as a phase transition, after the M8.2 main-shock, one must expect changes in the Tehuantepec ridge dynamics, which can be observed considering that the b-value in the Gutenberg-Richter law, has also showed changes in time. The goal of this paper is to characterize the behavior of the seismic activity by using the Gutenberg-Richter law, multifractal detrended fluctuation analysis, visibility graph and nowcasting method. Those methods have showed important parameters in order to assess risk, the multifractality and connectivity. Our findings indicate, first that b-value shows a dependency on time, which is clearly described by our analyses based on nowcasting method, multifractality and visibility graph.

Plasticity in the hippocampal formation of shorebirds during the wintering period: Stereological analysis of parvalbumin neurons in Actitis macularius.

The number of parvalbumin neurons can be modified by social, multisensory, and cognitive stimuli in both mammals and birds, but nothing is known about their plasticity in long-distance migratory shorebirds. Here, in the spotted sandpiper (Actitis macularius), we investigated the plasticity of parvalbumin neurons of two brain areas during this species' wintering period at a lower latitude. We compared individuals in a nonmigratory rest period (November-January) and premigration (May-July) period. We used parvalbumin as a marker for counting a subpopulation of inhibitory neurons in the hippocampal formation (HF), with the magnocellular nucleus of the tectal isthmus (IMC) as a control area. Because the HF is involved in learning and memory and social interaction and the IMC is essential for control of head, neck, and eye movements, we hypothesized that parvalbumin neurons would increase in the HF and remain unchanged in the IMC. We used an optical fractionator to estimate cell numbers. Compared with the nonmigratory rest birds, parvalbumin neuron count estimates in the premigration birds increased significantly in the HF but remained unchanged in IMC. We suggest that the greater number of parvalbuminergic neurons in the HF of A. macularius in the premigration period represents adaptive circuitry changes involved in the migration back to reproductive niches in the northern hemisphere.

A new species of Characidium (Characiformes: Crenuchidae) from the rio Doce basin, Brazil

A new species of Characidium is described from the tributaries of the upper and middle rio Doce basin, Minas Gerais, Brazil. The new species is distinguished from most congeners, except C. cricarense, C. hasemani, C. helmeri, C. kalunga, C. pterostictum, C. schubarti, C. summus, and C. travassosi by lacking scales in the area between the anterior limit of the isthmus and the anterior margin of cleithrum. The new species differs from the aforementioned species by a series of characters, including the presence of the adipose fin, 2­-4 scales between the anus and anal fin, two rows of dentary teeth, presence of the parietal branch of the supraorbital canal, 4 scale rows above the lateral line, and absence of two conspicuous inclined dark bands on each caudal-fin lobe. The new species further differs from most congeners with an unscaled ventral surface of the isthmus by the presence of 33-34 pored scales on the lateral line and by the dark dashes on the caudal fin-rays not forming well-defined bands.(AU)

Uma nova espécie de Characidium é descrita de afluentes do alto e médio curso da bacia do rio Doce, Minas Gerais, Brasil. A nova espécie se distingue da maioria das congêneres, exceto C. cricarense, C. hasemani, C. helmeri, C. kalunga, C. pterostictum, C. schubarti, C. summus e C. travassosi pela falta de escamas na área entre o limite anterior do istmo e a margem anterior do cleitro. A nova espécie difere das espécies acima mencionadas por uma série de caracteres, incluindo a presença de nadadeira adiposa, 2-4 escamas entre o ânus e a nadadeira anal, duas séries de dentes no dentário, ramo parietal do canal supraorbital presente, 4 séries de escamas acima da linha lateral e ausência de duas bandas escuras inclinadas em cada lobo da nadadeira caudal. A nova espécie difere ainda mais da maioria das congêneres com superfície ventral sem escamas no istmo por ter 33-34 escamas perfuradas na linha lateral e traços escuros nos raios da nadadeira caudal não formando bandas bem definidas.(AU)

Weaving Mitochondrial DNA and Y-Chromosome Variation in the Panamanian Genetic Canvas.

The Isthmus of Panama was a crossroads between North and South America during the continent's first peopling (and subsequent movements) also playing a pivotal role during European colonization and the African slave trade. Previous analyses of uniparental systems revealed significant sex biases in the genetic history of Panamanians, as testified by the high proportions of Indigenous and sub-Saharan mitochondrial DNAs (mtDNAs) and by the prevalence of Western European/northern African Y chromosomes. Those studies were conducted on the general population without considering any self-reported ethnic affiliations. Here, we compared the mtDNA and Y-chromosome lineages of a new sample collection from 431 individuals (301 males and 130 females) belonging to either the general population, mixed groups, or one of five Indigenous groups currently living in Panama. We found different proportions of paternal and maternal lineages in the Indigenous groups testifying to pre-contact demographic events and genetic inputs (some dated to Pleistocene times) that created genetic structure. Then, while the local mitochondrial gene pool was marginally involved in post-contact admixtures, the Indigenous Y chromosomes were differentially replaced, mostly by lineages of western Eurasian origin. Finally, our new estimates of the sub-Saharan contribution, on a more accurately defined general population, reduce an apparent divergence between genetic and historical data.

Blunt aortic injury: Surgical treatment of the ascending and descending aorta.

Traumatic aortic injury is potentially fatal. Although uncommon, involvement of the aortic arch and the ascending aorta can occur. This case shows concomitant dissection of the ascending and descending sections of the aorta after blunt chest trauma where the open surgical approach was successfully performed to treat both aortic injuries.

Capacidad de Penetración y Difusión de la Medicación, Intraconducto en Túbulos Dentinales, Conductos Laterales e Istmos. Una Revisión Sistemática / Penetration and Diffusion Capacity of Intra-duct Medication in Dentinal Tubules, Lateral Canals and Isthmus. A Systematic Review

El objetivo de la terapia endodóntica consiste en tratar o prevenir la periodontitis apical. La efectiva eliminación o disminución de microbiota es esencial para la reparación periapical. Debido a esto, se utiliza el empleo de medicamentos intraconductos para tratar químicamente el sistema de conductos radiculares, y cobra relevancia la capacidad de penetración y difusión de dicho medicamento para entrar en contacto directo con los microorganismos que penetren dentro de los túbulos dentinales, conductos laterales e itsmos. Se realizó una revisión de la literatura en bases de datos electrónicas con los buscadores "Pubmed, Scielo y Google Académico", utilizando palabras clave para identificar la literatura publicada relevante en inglés. El análisis y los criterios de elegibilidad se documentaron de acuerdo con los elementos de informe para revisiones sistemáticas y meta-análisis (Preferred Reporting Items for Systematic Reviews and Meta-Analysis, PRISMA). No se impusieron restricciones sobre la fecha de publicación. Se recogieron datos sobre capacidad de difusión de medicación intraconductos en túbulos dentinales, conductos laterales e itsmos radiculares y se sometieron a análisis descriptivo de datos. La búsqueda bibliográfica en bases de datos electrónicas según los criterios de inclusión arrojó 45 títulos y resúmenes. Entre ellos, 7 artículos fueron seleccionados. Se determinó un rango de penetración del medicamento muy variable, entre 27,7 - 2350 μm y rango de difusión de 200-500 μm. Hay pocos estudios publicados que reporten la capacidad de penetración y difusión de la medicación intraconductos. El vehículo empleado y diámetro de las partículas en la preparación del medicamento y la eliminación de la capa de desecho aumentaría la capacidad de penetración/difusión del medicamento intraconductos dentro del túbulo dentinal, conductos laterales e itsmo.

The objective of endodontic therapy is to treat or prevent apical periodontitis. The effective elimination or reduction of the microbiota is essential for periapical repair. Due to this, the use of intracanal drugs is used to chemically treat the root canal system, and the penetration and diffusion capacity of said drug becomes relevant to come into direct contact with the microorganisms that penetrate inside the dentinal tubules, lateral canals and isthmus. A literature review was carried out in electronic databases with the search engines "Pubmed, Scielo and Google Academic", using keywords to identify the relevant published literature in English. The analysis and eligibility criteria were documented according to the reporting items for systematic reviews and meta-analyzes (Preferred Reporting Items for Systematic Reviews and Meta-Analysis, PRISMA). No restrictions were placed on the date of publication. Data on intracanal drug diffusion capacity in dentinal tubules, lateral canals and root isthmus were collected and subjected to descriptive data analysis. The bibliographic search in electronic databases according to the inclusion criteria yielded 45 titles and abstracts. Among them, 7 articles were selected. A highly variable drug penetration range was determined, between 27.7 - 2350 μm and a diffusion range of 200-500 μm. There are few published studies that report the penetration and diffusion capacity of intracanal medication. The vehicle used and the diameter of the particles in the preparation of the drug and the elimination of the waste layer would increase the penetration / diffusion capacity of the drug within the dentinal tubule, lateral canals and isthmus.

Are clinicopathological features of the isthmic thyroid nodule different from nodules in thyroid lobes? A single center experience

ABSTRACT Objectives: Thyroid nodules located in isthmus were found less prevalent, although papillary thyroid cancer in this location was reported to be more aggressive behaviour in some studies. Our aim was to evaluate hormonal,ultrasonographic, and cytopathologic features of nodules located in isthmus (isthmic nodules). Subjects and methods: Patients who underwent thyroidectomy between 2006-2014 reviewed retrospectively. Hormonal, ultrasonographic, and cytopathologic features compared between patients with isthmic (Group-1) and with lober (non-isthmic, Group-2) nodules. Results: Group-1 and Group-2 consisted of 251 and 2076 patients, respectively. 260 isthmic (5.5%) and 4433 non-isthmic (94.5%) nodules were compared.However,most ultrasonographical features such as presence of microcalcification and halo, diameters, echogenicity, texture, margin, and vascularity were similar between groups, macrocalcification rate was lower in isthmic nodules (18.8%, 25.9%; p = 0.012). Cytologic results were also similar.Although malignancy rate was lower in isthmic nodules (6.2%, 12.5%; p = 0.002), type of thyroid cancer was similar in isthmic and non-isthmic nodules.When malignant isthmic (n = 16,2.8%) and malignant non-isthmic nodules (n = 553, 97.2%) were compared, diameter and type of tumor, lymphovascular and capsular invasions, extrathyroidal extension and multifocality rates were not statistically significant.Malignant isthmic nodules (n = 16, 6.2%) had smaller size [10.1 (7.5-34.5) mm, 19.95 (8.4-74.1) mm; p = 0.002], and higher hypoechogenicity rate (31.3%, 5.7%, p = 0.003) compared to benign isthmic nodules (n = 244, 93.8%). Negative predictive value was higher and positive predictive value was lower in isthmic nodules compared to non-isthmic nodules (p = 0.033, p = 0.047, respectively). Conclusion: Isthmic nodules appear to be indolent because of having lower malignancy rate. FNAB might be required in isthmic nodules even if it has relatively small size.The surgery with limited extent or follow-up might seem to be reliable in the management of patients having isthmic nodules especially with indeterminate cytology.

Base-substitution mutation rate across the nuclear genome of Alpheus snapping shrimp and the timing of isolation by the Isthmus of Panama.

BACKGROUND: The formation of the Isthmus of Panama and final closure of the Central American Seaway (CAS) provides an independent calibration point for examining the rate of DNA substitutions. This vicariant event has been widely used to estimate the substitution rate across mitochondrial genomes and to date evolutionary events in other taxonomic groups. Nuclear sequence data is increasingly being used to complement mitochondrial datasets for phylogenetic and evolutionary investigations; these studies would benefit from information regarding the rate and pattern of DNA substitutions derived from the nuclear genome. RESULTS: To estimate the genome-wide neutral mutation rate (µ), genotype-by-sequencing (GBS) datasets were generated for three transisthmian species pairs in Alpheus snapping shrimp. A range of bioinformatic filtering parameters were evaluated in order to minimize potential bias in mutation rate estimates that may result from SNP filtering. Using a Bayesian coalescent approach (G-PhoCS) applied to 44,960 GBS loci, we estimated µ to be 2.64E-9 substitutions/site/year, when calibrated with the closure of the CAS at 3 Ma. Post-divergence gene flow was detected in one species pair. Failure to account for this post-split migration inflates our substitution rate estimates, emphasizing the importance of demographic methods that can accommodate gene flow. CONCLUSIONS: Results from our study, both parameter estimates and bioinformatic explorations, have broad-ranging implications for phylogeographic studies in other non-model taxa using reduced representation datasets. Our best estimate of µ that accounts for coalescent and demographic processes is remarkably similar to experimentally derived mutation rates in model arthropod systems. These results contradicted recent suggestions that the closure of the Isthmus was completed much earlier (around 10 Ma), as mutation rates based on an early calibration resulted in uncharacteristically low genomic mutation rates. Also, stricter filtering parameters resulted in biased datasets that generated lower mutation rate estimates and influenced demographic parameters, serving as a cautionary tale for the adherence to conservative bioinformatic strategies when generating reduced-representation datasets at the species level. To our knowledge this is the first use of transisthmian species pairs to calibrate the rate of molecular evolution from GBS data.

Are clinicopathological features of the isthmic thyroid nodule different from nodules in thyroid lobes? A single center experience.

OBJECTIVE: Thyroid nodules located in isthmus were found less prevalent, although papillary thyroid cancer in this location was reported to be more aggressive behaviour in some studies. Our aim was to evaluate hormonal, ultrasonographic, and cytopathologic features of nodules located in isthmus (isthmic nodules). METHODS: Patients who underwent thyroidectomy between 2006-2014 reviewed retrospectively. Hormonal, ultrasonographic, and cytopathologic features compared between patients with isthmic (Group-1) and with lober (non-isthmic, Group-2) nodules. RESULTS: Group-1 and Group-2 consisted of 251 and 2076 patients, respectively. 260 isthmic (5.5%) and 4433 non-isthmic (94.5%) nodules were compared. However, most ultrasonographical features such as presence of microcalcification and halo, diameters, echogenicity, texture, margin, and vascularity were similar between groups, macrocalcification rate was lower in isthmic nodules (18.8%, 25.9%; p = 0.012). Cytologic results were also similar. Although malignancy rate was lower in isthmic nodules (6.2%, 12.5%; p = 0.002), type of thyroid cancer was similar in isthmic and non-isthmic nodules. When malignant isthmic (n = 16,2.8%) and malignant non-isthmic nodules (n = 553, 97.2%) were compared, diameter and type of tumor, lymphovascular and capsular invasions, extrathyroidal extension and multifocality rates were not statistically significant. Malignant isthmic nodules (n = 16, 6.2%) had smaller size [10.1 (7.5-34.5) mm, 19.95 (8.4-74.1) mm; p = 0.002], and higher hypoechogenicity rate (31.3%, 5.7%, p = 0.003) compared to benign isthmic nodules (n = 244, 93.8%). Negative predictive value was higher and positive predictive value was lower in isthmic nodules compared to non-isthmic nodules (p = 0.033, p = 0.047, respectively). CONCLUSION: Isthmic nodules appear to be indolent because of having lower malignancy rate. FNAB might be required in isthmic nodules even if it has relatively small size. The surgery with limited extent or follow-up might seem to be reliable in the management of patients having isthmic nodules especially with indeterminate cytology.

Biofilm removal from a simulated isthmus and lateral canal during syringe irrigation at various flow rates: a combined experimental and Computational Fluid Dynamics approach.

AIM: (i) To quantify biofilm removal from a simulated isthmus and a lateral canal in an artificial root canal system during syringe irrigation with NaOCl at different concentrations and delivered at various flow rates (ii) to examine whether biofilm removal is further improved by a final high-flow-rate rinse with an inert irrigant following irrigation with NaOCl. (iii) to simulate the irrigant flow in these areas using a computer model (iv) to examine whether the irrigant velocity calculated by the computer model is correlated to biofilm removal. METHODOLOGY: Ninety-six artificial root canals with either a simulated isthmus or lateral canal were used. A dual-species in vitro biofilm was formed in these areas using a Constant Depth Film Fermenter. NaOCl at various concentrations (2, 5 and 10%) or adhesion buffer (control) was delivered for 30 s by a syringe and an open-ended needle at 0.033, 0.083, or 0.166 mL s-1 or passively deposited in the main root canal (phase 1). All specimens were subsequently rinsed for 30 s with adhesion buffer at 0.166 mL s-1 (phase 2). The biofilm was scanned by Optical Coherence Tomography to determine the percentage of the remaining biofilm. Results were analysed by two 3-way mixed-design ANOVAs (α = 0.05). A Computational Fluid Dynamics model was used to simulate the irrigant flow inside the artificial root canal system. RESULTS: The flow rate during phase 1 and additional irrigation during phase 2 had a significant effect on the percentage of the remaining biofilm in the isthmus (P = 0.004 and P < 0.001). Additional irrigation during phase 2 also affected the remaining biofilm in the lateral canal significantly (P ≤ 0.007) but only when preceded by irrigation at medium or high flow rate during phase 1. The effect of NaOCl concentration was not significant (P > 0.05). Irrigant velocity in the isthmus and lateral canal increased with increasing flow rate and it was substantially correlated to biofilm removal from those areas. CONCLUSIONS: The irrigant flow rate affected biofilm removal in vitro more than NaOCl concentration. Irrigant velocity predicted by the computer model corresponded with the pattern of biofilm removal from the simulated isthmus and lateral canal.

Effect of the Central American Isthmus on gene flow and divergence of the American crocodile (Crocodylus acutus).

The final formation of the Central American Isthmus (CAI) about 3.5 million years ago altered global ocean circulation, connected North and South America terrestrial biotas, and established the Caribbean Sea. The nature of this event creates a natural scenario to test vicariance, divergence, and speciation by allopatry. Studies have shown the effect of the CAI on marine and terrestrial species, but none have examined a large-bodied amphibious taxon. We used RAD sequencing on populations of the American crocodile (Crocodylus acutus) to study the genomic variation of C. acutus on both sides of the CAI, infer its demographic history, and measure the effect of the opening of the Panama Canal. Our results showed three genomic clusters: (1) Caribbean and the Panama Canal, (2) Pacific coast, and (3) Coiba island. The estimated divergence times between the Caribbean and Pacific populations are about 20,000 years ago, which is younger than the formation of the CAI, coinciding with the Last Glacial Maximum. We hypothesize the glacial/interglacial cycles facilitated gene flow between the Caribbean and Pacific crocodile populations after the formation of the CAI, masking any genomic divergence the CAI may have caused. There is no evidence of gene flow associated with the opening of the Panama Canal.

A new species of long-tailed shrew of the genus Sorex (Eulipotyphla: Soricidae) from Sierra de Omoa, Honduras.

The only known species of the genus Sorex in Honduras is Sorex mccarthyi Matson Ordóñez-Garza, which is endemic to Celaque National Park. This species shows the presence of a postmandibular foramen and canal, a characteristic that is useful to distinguish between species south of the Isthmus of Tehuantepec and unique to the Sorex salvini species group. Recently, two specimens of Sorex were collected in 2018 at Cusuco National Park, northwestern Honduras. These specimens lack the distinctive characteristics possessed by the S. salvini species group and belong to the Sorex veraepacis species group. Previously, the S. veraepacis species group was only known from the highlands of the southern Mexican state of Chiapas and Guatemala. Principal component analysis shows that specimens from Sierra de Omoa are different in size and shape with respect to other known species (i.e., S. veraepacis Alston, S. ibarrai Matson McCarthy and S. madrensis Matson Ordóñez-Garza). We describe these two specimens, currently known only from an isolated cloud forest in the Sierra de Omoa, Honduras, as a new species.

The unknown diversity of the genus Characidium (Characiformes: Crenuchidae) in the Chocó biogeographic region, Colombian Andes: Two new species supported by morphological and molecular data.

Two new species of Characidium, C. tatama and C. dule, are described from the biogeographic Chocó region in western Colombia. Both new species are supported by both morphological and molecular data. C. tatama from the San Juan River in the Pacific and C. dule from the Atrato River in the Caribbean portion of Colombia are both distributed in the upper and lower portions of these basins. An extensive comparison with other trans- and cis-Andean species of Characidium was made, in addition to species delimitation, using COI sequences by distinct methods (GMYC, ABGD, bPTP).

Niche conservatism promotes speciation in cycads: the case of Dioon merolae (Zamiaceae) in Mexico.

Niche conservatism is the tendency of lineages to retain the same niche as their ancestors. It constrains biological groups and prevents ecological divergence. However, theory predicts that niche conservatism can hinder gene flow, strengthen drift and increase local adaptation: does it mean that it also can facilitate speciation? Why does this happen? We aim to answer these questions. We examined the variation of chloroplast DNA, genome-wide single nucleotide polymorphisms, morphological traits and environmental variables across the Dioon merolae cycad populations. We tested geographical structure, scenarios of demographic history, and niche conservatism between population groups. Lineage divergence is associated with the presence of a geographical barrier consisting of unsuitable habitats for cycads. There is a clear genetic and morphological distinction between the geographical groups, suggesting allopatric divergence. However, even in contrasting available environmental conditions, groups retain their ancestral niche, supporting niche conservatism. Niche conservatism is a process that can promote speciation. In D. merolae, lineage divergence occurred because unsuitable habitats represented a barrier against gene flow, incurring populations to experience isolated demographic histories and disparate environmental conditions. This study explains why cycads, despite their ancient lineage origin and biological stasis, have been able to diversify into modern ecosystems worldwide.