Morphological Variability Research Articles

Fifty shades of white: morphological and molecular diversity of the Cadlina laevis species complex (Gastropoda: Nudibranchia) in the North-West Pacific

We provide a morphological examination and a barcoding study to investigate the species identity and variation limits within the Cadlina laevis species complex. Our molecular analysis based on the COI marker revealed seven new clades in the North-West Pacific Cadlina diversity. The distances between these clades are low in some cases (2.08-7.51% overall), and the species delimitation tests gave controversial results (1, 2, 13, 14 groups, depending on the analysis method). This does not allow to conclusively classify this diversity as interspecific or intraspecific. Morphological analysis showed a significant similarity of all examined groups, with minor differences found in the morphology of the central tooth of the radula and the reproductive system. However, these variations fit into the morphological variability of the North Atlantic species Cadlina laevis s.str. and cannot serve as evidence of the isolation of these identified groups. The discovered diversity may represent both a complex of at least 11 very close and cryptic species with not well-established species boundaries, or be a part of a single amphiboreal species Cadlina laevis s.l. This indicates an extremely complex evolutionary history of Cadlina laevis species complex, making this group is an interesting model object for studying speciation in boreal and Arctic communities.

An artificial intelligence-enabled Holter algorithm to identify patients with ventricular tachycardia by analysing their electrocardiogram during sinus rhythm.

Ventricular tachycardia (VT) is a dangerous cardiac arrhythmia that can lead to sudden cardiac death. Early detection and management of VT is thus of high clinical importance. We hypothesize that it is possible to identify patients with VT during sinus rhythm by leveraging a continuous 24 h Holter electrocardiogram and artificial intelligence. We analysed a retrospective Holter data set from the Rambam Health Care Campus, Haifa, Israel, which included 1773 Holter recordings from 1570 non-VT patients and 52 recordings from 49 VT patients. Morphological and heart rate variability features were engineered from the raw electrocardiogram signal and fed, together with demographical features, to a data-driven model for the task of classifying a patient as either VT or non-VT. The model obtained an area under the receiving operative curve of 0.76 ± 0.07. Feature importance suggested that the proportion of premature ventricular beats and beat-to-beat interval variability was discriminative of VT, while demographic features were not. This original study demonstrates the feasibility of VT identification from sinus rhythm in Holter.

The double-headed accessory iliacus muscle: a case report.

Numerous accessory muscles are present in the human body, many of which are clinically significant. We present a case of an anomalous accessory iliacus composed of two heads, whose occurrence and anatomical location indicate a high probability of causing femoral nerve compression. During a routine dissection of the posterior abdominal wall of a xx-year-old cadaver, a double headed accessory muscle was noted, measured and photographed. In addition to the normal anatomy of dissected structures from the posterior abdominal wall, an accessory iliacus muscle composed of superficial and deep heads was identified. In addition, the inferior roots of the divided femoral nerve located between the heads was found to follow an unusual course. It is important to be aware of morphological variability around structures such as double-headed accessory iliacus muscle presented in this study, due to their association with neurovascular bundles and hip joint. The reported atypical morphology is not widely known in the literature but might be of great clinical significance, therefore knowledge of such variability might be regarded in order to diagnose properly and introduce accurate treatment.

A three-headed psoas major muscle: a case report.

Multiple anatomical variations, from anomalous courses to additional structures, have been reported in muscles from different compartments of the human body. We report an extremely rare case of a psoas major muscle presenting as a three-headed structure with variable morphology. During a routine dissection of the posterior abdominal wall of a 82-year-old male cadaver, an anomalous PM muscle with supernumerary head was identified, photographed and subjected to further measurement. Although the anatomy of the dissected posterior abdominal wall structures was typical, a three-headed psoas major muscle composed of superficial, intermediate and deep heads was identified. It is important to be aware of morphological variability of muscles, especially those considered to be constant, since an anomalous structure might interfere not only with their functions, but also lead to further clinical consequences.

The morphological variability of the pelvic girdle muscles: a potential trap during ultrasound.

The muscles present in the pelvic girdle compartment demonstrate clinically significant anatomical variation regarding both their site of attachment and additions, such as accessory heads, muscles or tendinous slips. Many of those variations might be considered potential traps during ultrasound examination that may result in misdiagnosis. The aim of this study was to raise awareness of such possibility. A comprehensive search for morphological variations was performed in PubMed and NIH. Relevant papers were listed and citation tracking was accomplished. Although several anatomical variations of pelvic girdle muscles have been presented, few studies have examined their relevance in ultrasound imaging. The morphological variability of the pelvic girdle muscles does not vary from such incidence in other regions of the human body; however further ultrasound studies are needed of the numerous morphological variants that can be found in this region.

Epitypification and emended description of Cyclotella hubeiana, a centric diatom from Central China, with remarks on its distribution and ecology

Since its description by Chen and Zhu in 1985 from samples collected in a river and reservoir from Hubei Province (Central China), Cyclotella hubeiana has been reported from several sites in central and southern China. Only line drawings were provided with the original description and the same drawings were used in the subsequent diatom floras from China. The more recent reports of this species come from limnological studies which generally do not provide illustrations. There is therefore a need to better illustrate this taxon. As the type material could not be retrieved, new material was collected from the type locality (Xionghe Reservoir) to elucidate its ultrastructure using light and electron microscopy. The figures published by Chen and Zhu in 1985 are designed as lectotype and the new material as epitype to the lectotype. Characteristics of the valve such as the position of the rimoportula (on a costa, within the ring of marginal fultoportulae) and the absence of central fultoportulae on the valve face suggest that this species is best placed within the genus Cyclotella as presently defined. Its morphology is compared with similar species of Cyclotella and Pantocsekiella. In addition, in a study on Qiandao Lake, a reservoir from Zhejiang Province (eastern China), a large population of this taxon was found in down-core assemblages within 20 years of the reservoir being impounded. This abundant material allowed a better assessment of the size range and morphological variability of this species. Besides emending the description and validating the taxonomic status of this species, this study also discusses its ecology and distribution.

The GRAVITY young stellar object survey

Context. Temporal variability in the photometric and spectroscopic properties of protoplanetary disks is common in young stellar objects. However, evidence pointing toward changes in their morphology over short timescales has only been found for a few sources, mainly due to a lack of high-cadence observations at high angular resolution. Understanding this type of variation could be important for our understanding of phenomena related to disk evolution. Aims. We study the morphological variability of the innermost circumstellar environment of HD 98922, focusing on its dust and gas content. Methods. Multi-epoch observations of HD 98922 at milliarcsecond resolution with VLTI/GRAVITY in the K-band at low (R = 20) and high (R = 4000) spectral resolution are combined with VLTI/PIONIER archival data covering a total time span of 11 yr. We interpret the interferometric visibilities and spectral energy distribution with geometrical models and through radiative transfer techniques using the code MCMax. We investigated high-spectral-resolution quantities (visibilities and differential phases) to obtain information on the properties of the HI Brackett-γ (Brγ)-line-emitting region. Results. Comparing observations taken with similar (u,v) plane coverage, we find that the squared visibilities do not vary significantly, whereas we find strong variability in the closure phases, suggesting temporal variations in the asymmetric brightness distribution associated to the disk. Our observations are best fitted by a model of a crescent-like asymmetric dust feature located at ~1 au and accounting for ~70 % of the near-infrared (NIR) emission. The feature has an almost constant magnitude and orbits the central star with a possible sub-Keplerian period of ~12 months, although a 9 month period is another, albeit less probable, solution. The radiative transfer models show that the emission originates from a small amount of carbon-rich (25%) silicates, or quantum-heated particles located in a low-density region. Among different possible scenarios, we favor hydrodynamical instabilities in the inner disk that can create a large vortex. The high spectral resolution differential phases in the Brγ line show that the hot-gas compact component is offset from the star and in some cases is located between the star and the crescent feature. The scale of the emission does not favor magnetospheric accretion as a driving mechanism. The scenario of an asymmetric disk wind or a massive accreting substellar or planetary companion is discussed. Conclusions. With this unique observational data set for HD 98922, we reveal morphological variability in the innermost 2 au of its disk region. This property is possibly common to many other protoplanetary disks, but is not commonly observed due to a lack of high-cadence observation. It is therefore important to pursue this approach with other sources for which an extended dataset with PIONIER, GRAVITY, and possibly MATISSE is available.

Fetal echocardiography in B and M modes for to standardize morphological and functional cardiovascular variables of canine fetuses in the final third of gestation: fetal echocardiographic measurements

Fetal echocardiography allows early diagnosis of cardiovascular changes. However, few studies have described physiological values that allow a quantitative evaluation for this test in dogs. The objective was to describe the presumed physiological values of echocardiographic variables obtained in B and M modes, and cardiac function, by canine fetal echocardiography in the last trimester of pregnancy. Twenty fetuses were submitted to fetal echocardiography. The variables that showed a statistically significant correlation coefficient in relation to fetal age were the diameter of the aorta and the thickness of the interventricular septum in systole and in diastole. The morphological evaluation allowed the observation and determination that the heart occupied an average of one third of the thorax, most of it located in the left hemithorax and with the apex turned to the left. By identifying the spine, the anterior wall of the chest was observed opposite to it, represented by the sternum. The right ventricle was found just below, separated from the right atrium by the tricuspid valve. Both ventricles showed similar size, thickness and contractility. The measurement of ejection fractions and shortening allowed the determination of the left ventricular systolic function. This study determined physiological values for the main echocardiographic variables obtained in B and M modes for the investigated group.

Taxonomic characterization, morphological variability, and geographic patterns of Juniperus turbinata Guss. in Algeria

A biometric study of cones, seeds, needles, and branchlets was conducted in 15 natural populations of Juniperus turbinata Guss. within its Algerian range. Each population was represented by 20-30 individuals. A total of 386 individuals were examined to evaluate inter- and intraspecific variation, and its geographic patterns, confirming the status of J. turbinata in Algerian populations. Maritime and mainland (Atlas Mountains) populations differed significantly. Cones in the seaside areas tended to be longer and more turbinate, with fewer seeds (mean 4.80) and leaves on the terminal 5-mm section of lateral branchlets (mean 27.87), compared to those from the Atlas, with 5.75 seeds and 29.00 leaves on average. The Aurès Mountain populations had more leaves than other scale-like junipers and other species of the Cupressaceae. Furthermore, maritime popula­tions stood out for having the most turbinated cones among recorded Juniperus phoenicea s.l. populations. Costal populations were more related to those located on oriental Mediterranean shores, while Atlas Mountain populations seemed to be related to Moroccan Atlas ones. A negative gradient of leaf number from east to west was identified in the Atlas group, extending into Morocco. The distinct separation between the 2 geographic patterns supports the hypothesis of migration of J. turbinata along 2 routes and relaunches the proposal of possible varieties within the group.

The Use of Virtual Tissue Constructs That Include Morphological Variability to Assess the Potential of Electrical Impedance Spectroscopy to Differentiate between Thyroid and Parathyroid Tissues during Surgery.

Electrical impedance spectroscopy (EIS) has been proposed as a promising noninvasive method to differentiate healthy thyroid from parathyroid tissues during thyroidectomy. However, previously reported similarities in the in vivo measured spectra of these tissues during a pilot study suggest that this separation may not be straightforward. We utilise computational modelling as a method to elucidate the distinguishing characteristics in the EIS signal and explore the features of the tissue that contribute to the observed electrical behaviour. Firstly, multiscale finite element models (or 'virtual tissue constructs') of thyroid and parathyroid tissues were developed and verified against in vivo tissue measurements. A global sensitivity analysis was performed to investigate the impact of physiological micro-, meso- and macroscale tissue morphological features of both tissue types on the computed macroscale EIS spectra and explore the separability of the two tissue types. Our results suggest that the presence of a surface fascia layer could obstruct tissue differentiation, but an analysis of the separability of simulated spectra without the surface fascia layer suggests that differentiation of the two tissue types should be possible if this layer is completely removed by the surgeon. Comprehensive in vivo measurements are required to fully determine the potential for EIS as a method in distinguishing between thyroid and parathyroid tissues.

Variability in morphology of soot particles during non-cloud and in-cloud processes

The morphology of soot particle influences their optical properties and their ability to act as cloud condensation nuclei (CCN). However, the morphology of soot particles has not been thoroughly examined from non-cloud to in-cloud processes. This study analyzed the morphology and mixing structures of cloud interstitial (INT) and cloud residual (RES) soot particles collected at three mountain sites. Soot particles were classified into four categories based on their mixing structures: INT-Bare, INT-Thinly coated, INT-Thickly coated, and RES soot particles. The fractal dimensions (Df) of INT-Thinly coated (1.93) and INT-Thickly coated (1.99) are larger than those of INT-Bare (1.86) soot particles, indicating significant soot compaction due to non-cloud atmospheric aging processes. Interestingly, we found that the Df of RES soot particles (1.95) is close to that of non-cloud internally mixed soot particles in this study (1.97) and previous literature (1.96). Our results indicate that cloud processing may not further compact the soot particles. This discovery has significant implications for the accurate portrayal of soot morphology within cloud droplets in models, ultimately impacting the modeling of radiative and climate effects. Additionally, our study highlights the potential significance of coating density as a factor influencing soot compaction.

Scale morphology is a promising, additional tool for exploring the taxonomy and ecology of freshwater fishes

AbstractIt has long been recognized that presence–absence, localisation, size, number and shape of fish scales can be important taxonomic features. Although there are some notes on the relationship between scale morphology and ecological needs, in the absence of a sufficiently large and detailed database, the morphological variability of fish scales and the factors responsible for this variability have not yet been explored in detail. For this reason, a database—which contains the shape and relative size data of 193 freshwater fish taxa of 14 orders, originated from five biogeographic realms—has been built. Database analyses showed that both the scale shape and relative size are proper taxonomic indicators. They can be used to separate higher taxonomic categories (e.g., orders), and by the simultaneous analysis of shape and size scale morphology, we showed increased sensitivity for species‐level detachments. Our results suggest that while both the shape and the size of the fish scales are genetically determined, they are also useful descriptors of the niche segregation (habitat use, flow preference) of close relative species. Scale morphology is a promising additional tool to specify the environmental preferences of lesser known or close relative recent and extinct fish species. And also can be of great help in such cases when only the scales are available for taxonomic identification, for example, in the research field of archaeology and palaeontology.

The superior frontal sulcus in the human brain: Morphology and probability maps.

The superior frontal sulcus (SFS) is the major sulcus on the dorsolateral frontal cortex that defines the lateral limit of the superior frontal gyrus. Caudally, it originates near the superior precentral sulcus (SPRS) and, rostrally, it terminates near the frontal pole. The advent of structural neuroimaging has demonstrated significant variability in this sulcus that is not captured by the classic sulcal maps. The present investigation examined the morphological variability of the SFS in 50 individual magnetic resonance imaging (MRI) scans of the human brain that were registered to the Montreal Neurological Institute (MNI) standard stereotaxic space. Two primary morphological patterns were identified: (i) the SFS was classified as a continuous sulcus or (ii) the SFS was a complex of sulcal segments. The SFS showed a high probability of merging with neighbouring sulci on the superior and middle frontal gyri and these patterns were documented. In addition, the morphological variability and spatial extent of the SFS were quantified using volumetric and surface spatial probability maps. The results from the current investigation provide an anatomical framework for understanding the morphology of the SFS, which is critical for the interpretation of structural and functional neuroimaging data in the dorsolateral frontal region, as well as for improving the accuracy of neurosurgical interventions.

Essential oil composition, morphological characterization, phenolic content and antioxidant activity of Iranian populations of Hymenocrater longiflorus Benth. (Lamiaceae)

The study focused on the morphological and chemical characteristics of 200 Hymenocrater longiflorus Benth. genotypes found in natural habitats of eight regions in west of Iran. The primary objective of the study was to assess the morphological and phytochemical variability within populations grown in their natural habitats, with the aim of identifying their potential for domestication and utilization in pre-breeding programs. The plant height (PH) ranged from 50.32 to 69.65 cm, with the highest observed in population P8. The internode distances ranged from 4.7 to 6.47 cm, with the maximum distance found in P4. Flower lengths varied from 1.95 to 2.45 cm, with the minimum and maximum values observed in P4 and P3, respectively. The highest leaf length (5.20 cm) and width (3.87 cm) were recorded in P2. The aerial parts of the plant were utilized to extraction and determine the essential oil (EO) content and composition, which ranged from 0.40 to 0.78% (v/w). The analysis of EO by gas chromatography (GC) and gas chromatography mass spectrometry (GC/MS) identified 26 compounds, constituting 99–99.5% of the EOs. The main compounds in the EO and their percentage range (v/w DW) were tau-cadinol (0.62–55.56), mono (2-ethylhexyl) phthalate (8.10–94.70), elemol (0.21–19.11), β-spathulenol (0.08–14.39), 4-terpineol (0.23–10.19), and β-eudesmol (0.21–9.94). The main chemical groups found in EOs included oxygenated sesquiterpenes (1.12–68.43), and phthalates (9.73–94.72). Cluster analysis revealed three distinct chemotypes: chemotype I (populations 1 and 2) with major components of mono (2-ethylhexyl) phthalate, tau-cadinol, and α-elemol; chemotype II (population 5) rich in mono (2-ethylhexyl) phthalate; and chemotype III (populations 3, 4, 6–8) containing tau-cadinol, β-eudesmol, and 4-terpineol. The study also evaluated total phenolic, total flavonoid, and DPPH free radical scavenging activity in the fifty percent inhibitory concentration (IC50) in leaf and flower samples of the genotypes, along with estimating total anthocyanin content in the flower samples. The total phenolic content (TPC) in leaf and flower samples ranged from 7.89 to 107.18 mg GAE/g DW and 39.98 to 86.62 mg gallic acid equivalent (GAE)/g DW, respectively. Total flavonoid content (TFC) ranged from 81.04 to 143.46 mg QUE/g DW in leaf samples and from 94.82 to 133.26 mg quercetin equivalent (QUE)/g DW in flower samples. DPPHsc IC50 (µg/mL) ranged from 0.65 to 78.74 in leaf samples and from 4.38 to 7.71 in flower samples. Anthocyanin content ranged from 1.89 to 3.75 mg cyanidin-3-glucoside equivalent (C3GE)/g DW among populations. Canonical correspondence analysis and simple correlation demonstrated a strong association and correlations among the studied attributes. The negative correlations between leaf DPPH (DPPH L) IC50 and TFC (− 0.73), TPC (− 0.63), Elemol (− 0.90), and EO (− 0.85) indicate that these compounds have a significant impact on the antioxidant activity of the leaves. Furthermore, Fruit DPPH (DPPH F) IC50 showed a negative correlation with TPC (− 0.79) and TFC (− 0.78), but a positive correlation with flower anthocyanins (0.51), (Z)-β-Farnesene (0.66), and 4-Terpineol (0.57). Circular cluster analysis categorized the genotypes of all individuals in the eight studied populations into three main categories based on all the studied traits, indicating significant variation in phytochemical and morphological traits among populations, surpassing the within-populations variation.

Mammal coloration as a social signal

AbstractOtherwise, apparently cryptic mammals often have conspicuous patches of colour on distal regions of their body, possibly for signalling. To investigate ideas about communication within sociosexual contexts, we used a comparative dataset for 2726 terrestrial mammals to match the coloration and patterning of distal body areas (head, chest, rump and tail) to activity cycle, group size, sexual size dimorphism, mating system and congener overlap at both Class and Order levels. Using phylogenetic controls, we uncovered repeated associations between white colour patches and nocturnality, conspicuous rump patches and sexual selection and multicoloured, complex patterning on distal regions of the body being associated with small group size. Overall, however, we found rather few associations between conspicuous coloration and behavioural, social and morphological variables, suggesting that visual signalling is not a key driver of communication in mammals, perhaps because the majority are nocturnal and solitary, and rely on olfactory signalling.

The use of geometric morphometry and traditional methods to analyze intraspecific variability of the first lower molar (m1) of Alexandromys fortis (Arvicolinae) in island and continental populations of Primorye, Russia

The complexity of the structure of the dental surface of the first lower molar (m1) of mainland and island populations of the reed vole Alexandromys fortis (Büchner, 1889) was assessed using two different methods. Using the traditional approach and methods of geometric morphometry (GM), the morphological variability of the anteroconid m1 of this species of the mainland (the south of Primorsky Krai) and the islands of the Peter the Great Gulf was analyzed. The traditional approach was based on describing the folding of the occlusal surface using three features: 1) folding of the lingual side of the anterior unpaired anteroconid loop (AC); 2) the shape of the labial side of the AC; 3) the shape of the fourth lingual reentrant angle. On the mainland part of the species' range, the highest occurrence was shown by morphotype III-C-a, which also predominated in the Late Pleistocene samples of the species in Primorye. The research revealed increased morphotypic diversity in island populations of the reed vole, which is probably due to the phenotypic and genotypic characteristics of the founders of island populations, as well as inbreeding, which can cause the release of hidden diversity and an increase in the number of rare morphotypes. The most numerous morphotype on the De Livrona – Durnovo Islands was II-C-a, rare for the mainland. In general, the most complex forms are present on the islands. Using a geometric morphometry approach, the anteroconid was divided into two separately studied structures: the anterior unpaired loop of the anteroconid (AC) and the base of the anteroconid (AB). The distribution of AC configurations in the space of the two principal components took on an arcuate shape, revealing a “forbidden zone.” The main changes occur on the lingual side of the AC. Regression analysis showed a direct relationship between the length of the contour (mm) and the complication of the shape of the anterior unpaired loop. The base of the anteroconid (AC) also undergoes transformation: it either stretches or contracts, while if the anterior unpaired loop of the anteroconid (AB) is more complex, then simplification and compression of its base is observed (negative regression). Analysis of the results of using two approaches, traditional and GM methods, in the analysis of the variability of the anteroconid section m1 of A. fortis showed extreme subjectivity in the use of the first one and the wide possibilities of the second one for identifying different aspects of molare transformation using mathematical methods.

Venous valves of the azygos arch: A cadaveric study

PurposeThe existence of valves in the azygos vein are not discussed in depth in the current body of literature. Although the clinical relevance of the valves in these veins are not well understood, these valves may have implications in diagnostic imaging where their appearance on imaging studies can impact interpretation. This study aims to use cadaveric dissections to determine the anatomic prevalence and morphology of valves in the arch of the azygos vein in comparison to current data reported from clinical imaging studies and anatomy textbooks. MethodsApproval of this research study on human cadaveric specimen was sought from the St. George's University Institutional Review Board (IRB) and was deemed exempt from full review (IRB – 16015). This research project involved 47 azygos veins dissected from human cadaveric donor specimen. Azygos veins were harvested from the level of the diaphragm to the inflow into the superior vena cava for gross inspection of valve presence and morphology. The data collected was recorded and sorted by sex, valve presence, number and morphology and valve location. Chi square analysis was performed to assess possible relationships in valve findings based on sex. A brief search of the literature using the keywords “azygos vein” and “valves” was conducted to see the current understanding of azygos valve prevalence. ResultsOf the donor specimen, 53.2% (25 of 47) were male and 46.8% (22 of 47) were female. Of the 47 cadavers that were dissected, 89.3% (42 of 47) were found to have valves in the azygos vein, while 10.6% (5 of 47) were found to have none. The azygos vein contained mostly one valve along its length, mainly located in the arch. The valves were unicuspid (8.5%; 4 of 47), bicuspid (70.2%; 33 of 47) or tricuspid (10.64%; 5 of 47). Dividing the arch of the azygos into quartiles, valves were found most commonly in the third quartile of the distance from the opening of the right superior intercostal vein into the azygos vein to the superior vena cava. Four cadavers had multiple valves, each with varying valve morphology. The length of the cusp of the bicuspid valve ranged from 10 mm to 12 mm. ConclusionThis study shows that the azygos vein contains valves, predominantly within the arch at a prevalence of 89.3%. The presence and variability in morphology of valves in the azygos vein and its potential implications for contrast appearance on imaging studies is clinically important. Radiologists should have a working knowledge of the different appearances of azygos arch valves to minimize the risks of confusing normal variations with thoracic pathology. Though not commonly described in anatomy texts, the findings of this research not only add more detail to the historical cadaveric study information on azygos vein valves, but also shows that the prevalence of azygos arch valves surpasses the numbers reported in clinical studies. As such, it provides support for the inclusion of azygos arch valves in anatomical textbooks and in the teaching of image interpretation.

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.

Second-step lectotypification of Stobaea rigida and reassessment of heterotypic synonyms of Berkheya rigida (Asteraceae, Arctotideae)

As part of a taxonomic reassessment of species that were classified in Berkheya series Rigidae in the most recent monograph of Berkheya, the type material for Berkheya rigida and its putative heterotypic synonyms is reassessed. The original material for the basionym, Stobaea rigida, is heterospecific. Therefore, a second-step lectotype is designated consistent with predominant usage of the name Berkheya rigida. The name Apuleia rigida and its replacement name Stobaea gaertneri apply to a conspicuously radiate species and are excluded from the synonymy of Berkheya rigida. The morphological variability of Berkheya rigida is discussed.

Two new Encyonema species from Europe compared to the type material of E. minutum and E. silesiacum (Gomphonemataceae, Bacillariophyceae)

ABSTRACT Cymbella minuta Hilse and C. silesiaca Bleisch, transferred in 1990 to the genus Encyonema, are two species frequently observed in European rivers. The original material of both species was included in Rabenhorst’s historical exsiccata series (numbers 1261 & 1802) and illustrated by Kurt Krammer in 1997. Despite this publication, the morphological variability of these two species is poorly known, and interpretations of this variability are often too broad or not precise enough. Recently, several populations of Encyonema displaying intermediate morphological features between E. minutum and E. silesiacum have been observed in Europe, making a reliable identification of these taxa impossible. Based on the currently available literature, two taxa that could not be assigned to an existing species are described as new: E. morvanense and E. vandammeanum. The present paper illustrates and discusses the morphology of the type material of E. minutum and E. silesiacum and compares it with both new species. Encyonema morvanense is distinguished by its typically protracted, rostrate apices, a low length/width ratio, the presence of an isolated pore, and areolae that are discernible under LM. In contrast, E. vandammeanum also exhibits protracted apices, but a higher length/width ratio, areolae that are faintly discernible, and the absence of an isolated pore. Comparisons with other Encyonema species, described in 1997 by Krammer (such as E. brevicapitatum, E. minutiforme and E. simile), are added in order to better understand the differences and similarities between these species.