Subtle Morphological Differences Research Articles

Polymorphism and multiple correlated characters: Do flatfish asymmetry morphs also differ in swimming performance and metabolic rate?

Phenotypic polymorphisms often differ in multiple correlated traits including morphology, behavior, and physiology, all of which can affect performance. How selection acts on these suites of traits can be complex and difficult to discern. Starry flounder (Platichthys stellatus) is a pleuronectid flatfish that exhibits rare polymorphism for the direction of eye migration and resulting whole‐body asymmetry. P. stellatus asymmetry morphs differ subtly in several anatomical traits, foraging behavior, and stable isotope signatures, suggesting they may be ecologically segregated, yet performance and metabolic differences are unknown.Here we tested the hypothesis that sinistral and dextral P. stellatus asymmetry morphs diverge in performance and routine metabolic rate (RMR) by comparing prolonged swimming endurance (time to exhaustion at a constant swimming speed), fast‐start swimming velocity and acceleration, and rate of oxygen consumption. Based on subtle morphological differences in caudal tail size, we expected sinistral P. stellatus to have superior prolonged swimming endurance relative to dextral fish, but inferior fast‐start performance.Sinistral P. stellatus exhibited both significantly greater prolonged swimming performance and fast‐start swimming performance. However, sinistral P. stellatus also exhibited greater RMR, suggesting that their general swimming performance could be enhanced by an elevated metabolic rate.Divergence between P. stellatus asymmetry morphs in swimming performance and metabolic rates contributes to growing evidence of ecological segregation between them, as well as our understanding of possible ecological consequences of asymmetry direction in flatfishes. These data provide an example of the complexity of polymorphisms associated with multiple correlated traits in a rare case of asymmetry polymorphism in a marine flatfish species.

Sibling sex, but not androgens, shapes phenotypes in perinatal common marmosets (Callithrix jacchus)

When offspring share a womb, interactions among fetuses can impart lasting impressions on phenotypic outcomes. Such intrauterine interactions often are mediated by sex steroids (estrogens and androgens) produced by the developing fetuses. In many mammals, intrauterine interactions between brothers and sisters lead to masculinization of females, which can induce fitness consequences. Many litter-bearing primates, though, seem to escape androgen-mediated litter effects, begging why? Here, we investigated how the sex composition (i.e., same- or mixed-sex) of litters influences perinatal outcomes in the common marmoset monkey (Callithrix jacchus), using a combination of physiological, morphological, and behavioural assays. We hypothesized that androgens from male fetuses would mediate developmental differences across litter types. We found that newborns (24–36 hours old) from same- and mixed-sex litters were indistinguishable by urinary androgen profiles, birth weights, morphometrics, and behaviour. However, monkeys born into same- and mixed-sex litters exhibited subtle morphological and neurobehavioral differences later in the perinatal period, independent of their androgen profiles. Our findings suggest that while androgens from male fetuses likely do not organize their siblings’ phenotypes, perinatal stimuli may initiate divergent developmental trajectories among siblings, which, in turn, promotes inter-individual variability within families.

Techniques and tools for species identification in ciliates: a review.

Ciliates are highly divergent unicellular eukaryotic organisms with nuclear dualism and a highly specialized ciliary pattern. They inhabit all biotopes and play crucial roles in regulating microbial food webs as they prey on bacteria, protists and even on microscopic animals. Nevertheless, subtle morphological differences and tiny sizes hinder proper species identification for many ciliates. In the present review, an attempt has been made to elaborate the various approaches used by modern day ciliate taxonomists for species identification. The different approaches involved in taxonomic characterization of ciliates such as classical (using live-cell observations, staining techniques, etc.), molecular (involving various marker genes) and statistical (delimitation of cryptic species) methods have been reviewed. Ecological and behavioural aspects in species identification have also been discussed. In present-day taxonomy, it is important to use a 'total evidence' approach in identifying ciliates, relying on both classical and molecular information whenever possible. This integrative approach will help in the mergence of classical methods with modern-day tools for comprehensive species description in future.

Genetic variation in

While examining herbarium specimens of Trithuria inconspicua Cheeseman, we observed differences in the stigmatic hairs among plants from New Zealand’s North and South Islands. This motivated us to assess genetic and morphological variation within this species and its sister T. filamentosa Rodway from Tasmania. Samples were collected from lakes in the three disjunct geographic areas where the two species occur. Genetic variation in both species was assessed with simple sequence-repeat (SSR, microsatellite) markers and analyses of genetic distances. We also compared the morphology of northern and southern New Zealand T. inconspicua using fresh material. Samples of each species clustered together in a minimum evolution tree built from genetic distances. Trithuria filamentosa had more genetic diversity than did T. inconspicua. Within T. inconspicua, plants from lakes in the North Island and the South Island formed discrete genetic groups diagnosable by subtle morphological differences. Low levels of heterozygosity in both species are consistent with a high level of selfing, as suggested for other co-sexual Trithuria species, but unusual for a putative apomict. On the basis of genetic and morphological variation, we propose recognition of the northern New Zealand and southern New Zealand lineages of T. inconspicua at subspecies rank.

Increasing the digital repository of DNA barcoding sequences of sand flies (Psychodidae: Phlebotominae).

Sand fly identification is complex because it depends on the expertise of the taxonomist. The females show subtle morphological differences and the occurrence of the species complexes are usual in this taxon. Therefore, a fragment of the cytochrome c oxidase subunit I (COI) gene is used for taxon barcoding to resolve this kind of problem. This study incorporates barcode sequences, for the first time, for Evandromyia cortelezzii and Migonemyia migonei from Argentina. The nucleotide sequence divergences were estimated to generate a neighbour-joining (NJ) tree. The automatic barcode gap discovery (ABGD) approach was employed to find the barcode gaps and the operational taxonomic unit (OTU) delimitation. Other species of the subtribe were included. The frequency histogram of divergences showed a barcoding gap. The ABGD analysis identified 14 operational taxonomic units (OTUs) from 13 morphological species. Sequences of Ev. cortelezzii and Mg. migonei formed well supported clusters and were diagnosed as primary species. These sequences are useful tools for molecular identification of the sand flies of the New World.

Epitypification of Fusarium oxysporum - clearing the taxonomic chaos.

Fusarium oxysporum is the most economically important and commonly encountered species of Fusarium. This soil-borne fungus is known to harbour both pathogenic (plant, animal and human) and non-pathogenic strains. However, in its current concept F. oxysporum is a species complex consisting of numerous cryptic species. Identification and naming these cryptic species is complicated by multiple subspecific classification systems and the lack of living ex-type material to serve as basic reference point for phylogenetic inference. Therefore, to advance and stabilise the taxonomic position of F. oxysporum as a species and allow naming of the multiple cryptic species recognised in this species complex, an epitype is designated for F. oxysporum. Using multi-locus phylogenetic inference and subtle morphological differences with the newly established epitype of F. oxysporum as reference point, 15 cryptic taxa are resolved in this study and described as species.

Remarkable morphological variation in the proboscis of Neorhadinorhynchus nudus (Harada, 1938) (Acanthocephala: Echinorhynchida).

The acanthocephalans are characterized by a retractible proboscis, armed with rows of recurved hooks, which serves as the primary organ for attachment of the adult worm to the intestinal wall of the vertebrate definitive host. Whilst there is a considerable variation in the size, shape and armature of the proboscis across the phylum, intraspecific variation is generally regarded to be minimal. Consequently, subtle differences in proboscis morphology are often used to delimit congeneric species. In this study, striking variability in proboscis morphology was observed among individuals of Neorhadinorhynchus nudus (Harada, 1938) collected from the frigate tuna Auxis thazard Lacépède (Perciformes: Scombridae) in the South China Sea. Based on the length of the proboscis, and number of hooks per longitudinal row, these specimens of N. nudus were readily grouped into three distinct morphotypes, which might be considered separate taxa under the morphospecies concept. However, analysis of nuclear and mitochondrial DNA sequences revealed a level of nucleotide divergence typical of an intraspecific comparison. Moreover, the three morphotypes do not represent three separate genetic lineages. The surprising, and previously undocumented level of intraspecific variation in proboscis morphology found in the present study, underscores the need to use molecular markers for delimiting acanthocephalan species.

Recent sympatric speciation involving habitat-associated nuptial colour polymorphism in a crater lake cichlid

Even though the idea that modes of speciation other than allopatric speciation are possible in nature is now widespread, compelling examples of ecological speciation in sympatry remain rare. We studied an undescribed radiation of haplochromine cichlids in a young crater lake in western Uganda, and in the small river that is nearby but has currently no known surface connection to the lake. We describe two different modes of speciation that occurred in this cichlid lineage within the past 1,500–10,000 years. Not constrained by gene flow, allopatric divergence between river and lake cichlids affects many different morphological traits as well as nuptial colouration—muted in the river, but intensified and polymorphic in lake cichlids—and neutral genetic differentiation. More surprisingly, we demonstrate a case for sympatric speciation within the small lake that is associated with dramatic differences in male breeding colouration (yellow with bright red-chest versus bright blue) and subtle differences in microhabitat, feeding regime and morphology. Reproductive isolation by assortative mating is suggested by significant differentiation between yellow and blue males in neutral markers of gene flow despite complete sympatry. We hypothesize speciation is mediated by divergent selection on sexual signalling between microhabitats.

Abstract 335: Introducing a Multiwell Cardiac μGMEA Platform for Action Potential Recordings From Human iPSC Derived Cardiomyocyte Constructs

Multielectrode array technology utilizing iPSC derived cardiomyocytes has proven useful for drug screening and arrhythmia studies. However, its application for direct action potential (AP) measurements from multicellular preparations remains limiting. We report a novel platform for high temporal resolution AP recordings from human iPSC-derived cardiomyocyte (hiPSC-CM) constructs. Derivation of high purity hiPSC-CMs yielded syncytial monolayers when cultured on a PEDOT-coated micro-gold multielectrode array (μGMEA). We gained intracellular access via 30 seconds of localized electroporation causing a revertible transition of extracellular field potential signals to quasi-APs to APs. We recorded a total of 492 AP waveforms within and across 9 constructs simultaneously and classified their morphologies based on action potential duration ratio (APD 50 /APD 90 ) and difference (APD 90 –APD 50 ). The vast majority of the waveforms (90.8%) were found to be ventricular-like with APD 50 /APD 90 and APD 90 –APD 50 of 0.75-0.95 and 52-166ms respectively. APD 30 displayed a wider variability within individual constructs when compared to the APD 80 distribution. The variability in fractional repolarization (APD 80 – APD 30 /APD 80 ) and triangulation (APD 80 – APD 30 ), parameters widely used for drug screening and arrhythmogenesis, ranged from 0.1- 0.8 and 100- 550ms respectively. The Gaussian distribution produced a single peak across these parameters confirming the ventricular-like properties of all the constructs. We confirmed the reliability of the system by recapitulating known drug induced responses on APs. Norepinephrine and isoproterenol associated with β-adrenergic stimulation produced a dose dependent increase in beating rate and shortening of APD. E4031, a hERG channel blocker, elicited a dose dependent prolongation of the APD and produced arrhythmic early afterdepolarizations (EADs) thus modulating AP waveforms via external factors. Our cardiac μGMEA model has the capability to distinguish subtle differences in AP morphology for identifying novel cardio-factors and for drug screening.

A Functional Comparison of Swimming Behavior in Two Temperate Forest Ants (Camponotus pennsylvanicus and Formica subsericea) (Hymenoptera: Formicidae)

Water is a dangerous and often lethal obstacle for small terrestrial animals like insects. However, some ants survive this hazard by efficiently traversing the water surface. Swimming performance (velocity, acceleration, and efficiency) differs dramatically among ant species, yet the factors that affect performance remain unclear. Here, we investigate the relative importance of behavior and morphology to swimming performance using a comparative study of two temperate forest ant species having superficially similar morphology: Camponotus pennsylvanicus (De Geer, 1773) (Hymenoptera: Formicidae) and Formica subsericea (Say, 1836) (Hymenoptera: Formicidae). We also investigated how water surface tension and ant morphology enable some F. subsericea workers to walk across the water surface, whereas others swim partially submerged. Leg ablation experiments demonstrated that both species use their forelegs for propulsion and hind legs as stabilizers, whereas their midlegs effect both propulsion and stabilization during swimming. C. pennsylvanicus workers swam faster than F. subsericea workers, probably reflecting the larger body size and longer relative foreleg length of C. pennsylvanicus workers. F. subsericea workers that walked on water were somewhat smaller than swimming conspecifics, and no workers were able to walk on water when surface tension was reduced with ethanol. Collectively, these results and those of related studies suggest that, within a clade of ants, differences in swimming performance arise mainly from subtle morphological differences. The importance of ant ecology and cuticular chemistry in this context remains to be explored.

A Multiwell Cardiac μGMEA Platform for Action Potential Recordings from Human iPSC-Derived Cardiomyocyte Constructs.

SummaryMultielectrode array (MEA) technology has been extensively used for field potential recordings from excitable cells. However, its application for action potential (AP) measurements has not been harnessed. Here, we report a novel platform for high-resolution intracellular AP recordings from induced pluripotent stem cell-cardiomyocyte constructs derived from human cardiac fibroblasts. To gain intracellular access, micro-gold MEAs were used to electroporate multiple constructs simultaneously. High-throughput AP measurements were obtained from 41 multicellular constructs. Repeated electroporations of the same cells did not affect the signal stability. Our model has the capability to distinguish subtle differences in AP morphology to characterize the network profile. Furthermore, we confirm the reliability of the system by recapitulating known drug-induced physiological and arrhythmogenic responses. Overall, the model provides a unique cardio-electronic interface for non-invasive measurements of AP dynamics for drug screening and disease modeling. This technology opens the door for identifying novel cardio-factors to enhance electrophysiological maturation.

Quantifying High-Performance Material Microstructure Using Nanomechanical Tools with Visual and Frequency Analysis.

High-performance materials like ballistic fibers have remarkable mechanical properties owing to specific patterns of organization ranging from the molecular scale, to the micro scale and macro scale. Understanding these strategies for material organization is critical to improving the mechanical properties of these high-performance materials. In this work, atomic force microscopy (AFM) was used to detect changes in material composition at an extremely high resolution with transverse-stiffness scanning. New methods for direct quantification of material morphology were developed, and applied as an example to these AFM scans, although these methods can be applied to any spatially-resolved scans. These techniques were used to delineate between subtle morphological differences in commercial ultra-high-molecular-weight polyethylene (UHMWPE) fibers that have different processing conditions and mechanical properties as well as quantify morphology in commercial Kevlar®, a high-performance material with an entirely different organization strategy. Both frequency analysis and visual processing methods were used to systematically quantify the microstructure of the fiber samples in this study. These techniques are the first step in establishing structure-property relationships that can be used to inform synthesis and processing techniques to achieve desired morphologies, and thus superior mechanical performance.

Molecular phylogeny, morphology, and distribution of Polygordius (Polychaeta: Polygordiidae) in the Atlantic and Mediterranean

Low morphological diversity among interstitial taxa makes it difficult to delimit species and their geographic boundaries based solely on morphology and molecular data often reveal cryptic species. Polygordius (Annelida, Polygordiidae) have low morphological diversity, but are unusual among interstitial species in their comparatively large size due to their elongated form, high fecundity, and potential for long-distance dispersal via a planktotrophic larval stage. Polygordius species collected from 14 localities in the Northwest Atlantic, Mediterranean Sea, and Southwest Atlantic including several of the respective type localities were analysed. This study presents the first phylogeny of the genus Polygordius and combines molecular data, sequences of COI, 16S and ITS1/2 genes, and morphological data for a systematic re-evaluation focusing on Atlantic species, with an emphasis on populations from European waters. Phylogenetic analyses recovered six valid species (P. appendiculatus, P. lacteus, P. neapolitanus, P. triestinus, P. jouinae, and P. eschaturus) and their distinctness is confirmed by haplotype network analyses. Thus, molecular data supported the validity of the previously recognized morpho-species and no new species were present. P. erythrophthalmus and P. villoti are invalid species being synonymous with P. lacteus. Subtle differences in head and pygidial morphology and larval type (endolarva vs. exolarva), were useful characters for discrimination. Yet seemingly significant variation in characters among individuals in some species was not diagnostic (e.g., number of pygidial cirri). Highly similar species based on adult morphology were shown to be sister taxa occurring in allopatry. Present day distribution patterns of species are summarized in light of this study.

Descriptions of two new endemic and cryptic species of Sitana Cuvier, 1829from peninsular India.

Two new cryptic species of the agamid genus Sitana Cuvier, 1829 from Peninsular India are described herein. Sitana gokakensis sp. nov. from Gokak, Karnataka closely resembles Sitana thondalu sp. nov. from Nagarjuna Sagar, Andhra Pradesh. The two species can be distinguished based on their subtle morphological differences, genetic difference and geographic distribution. Sitana gokakensis sp. nov. have a relatively depressed head compared to Sitana thondalu sp. nov. Additionally, the vertebral scale counts differ in females of the two new species (Sitana gokakensis sp. nov. 45-47 vs Sitana thondalu sp. nov. 49-53). Genetic divergence between them is comparable to those between previously described Sitana species. Furthermore, the two new species are distributed ca. 500 km apart and are endemic to their respective landscapes that lie in similar latitudes of peninsular India. We urge the use of large sample size in new species descriptions especially those dealing with cryptic species like Sitana. The discovery of the two new cryptic species from these rocky terrains in peninsular India highlights need for more herpetological exploration in this region.

Taxonomic status and epidemiology of the mesoparasitic copepod Pennella balaenoptera in cetaceans from the western Mediterranean.

Pennella balaenoptera is a mesoparasitic copepod that has been reported in at least 17 cetacean species. Subtle morphological differences in the first antennae of adult females have been used to discriminate this species from P. filosa, a species infecting fishes. Other morphological traits are unreliable because of their high plasticity, and no molecular data are available to confirm the taxonomic status of P. balaenoptera as an independent species. We found no consistent morphological differences of the first antennae between P. balaenoptera and P. filosa collected from cetaceans and fish in the western Mediterranean. Molecular data on the mitochondrial cytochrome oxidase subunit I failed to show reciprocal monophyly for the 2 species, and nucleotide divergence between them was low (mean ± SD [range]: 4.1 ± 0.006% [0.5-8.9]). Thus, P. balaenoptera and P. filosa are considered conspecific. We also obtained data on infection parameters of P. balaenoptera based on 450 individuals of 6 cetacean species stranded on the Spanish Mediterranean coast between 1980 and 2017. Prevalence was significantly lowest in the most coastal species, the bottlenose dolphin Tursiops truncatus (3.6%) and highest in the most oceanic species, Cuvier's beaked whale Ziphius cavirostris (100%). This suggests that the life cycle of P. balaenoptera is primarily oceanic. Interestingly, P. filosa also occurs in the oceanic realm infecting large fishes. This ecological similarity further supports the hypothesis that P. balaenoptera and P. filosa are conspecific.

Incomplete Reproductive Isolation Between Genetically Distinct Sympatric Clades of the Pennate Model Diatom Seminavis robusta

Incomplete reproductive isolation between genetically distinct taxa provides an interesting opportunity for speciation and adaptation studies. This phenomenon is well-described in macro-organisms, but less experimental evidence is available for unicellular eukaryotes. Here, we document the sympatric occurrence of genetically differentiated populations of the pennate model diatom Seminavis robusta in coastal subtidal biofilm communities and show widespread potential for gene flow between them. Based on sequence variation in the plastid-encoded rbcL gene, three distinct clades were identified. Morphological variation between the clades reflected their phylogenetic relationships, with subtle differences in valve morphology in the most distant clade compared to the other two clades, which were indistinguishable. Using a large number of experimental crosses we showed that, although reproductive output was significantly lower compared to the majority of within-clade crosses, approximately 34.5% of the inter-clade crosses resulted in viable and fertile progeny. While the nature of the incomplete reproductive isolation remains unknown, its occurrence in natural diatom populations represents an additional mechanism contributing to population genetic structuring and adaptation and can spur further research into the mechanisms of species divergence and the maintenance of species identity in the presence of gene flow.

Prevalence of disruptive selection predicts extent of species differentiation in Lake Victoria cichlids.

Theory suggests that speciation with gene flow is most likely when both sexual and ecological selection are divergent or disruptive. Divergent sexual and natural selection on the visual system have been demonstrated before in sympatric, morphologically similar sister species of Lake Victoria cichlids, but this does not explain the subtle morphological differences between them. To investigate the significance of natural selection on morphology during speciation, we here ask whether the prevalence of disruptive ecological selection differs between sympatric sister species that are at different stages of speciation. Some of our species pairs do (Pundamilia) and others do not (Neochromis) differ distinctively in sexually selected male nuptial coloration. We find that (i) evidence for disruptive selection, and for evolutionary response to it, is prevalent in traits that are differentiated between sister species; (ii) prevalence of both predicts the extent of genetic differentiation; and (iii) genetic differentiation is weaker in species pairs with conserved male nuptial coloration. Our results speak to the existence of two different mechanisms of speciation with gene flow: speciation mainly by sexual selection tightly followed by ecological character displacement in some cases and speciation mainly by divergent ecological selection in others.

Integrative analyses of Nervilia (Orchidaceae) section Linervia reveal further undescribed cryptic diversity in Thailand

The delimitation of cryptic species is necessary to accurately classify and appropriately conserve biodiversity. Integrative analyses can be incisive in detecting and circumscribing cryptic diversity, especially in species complexes whose members are delineated by minor or overlapping morphological variation. We adopt an integrative approach to assess species relationships and resolve species boundaries in the taxonomically difficult Nervilia adolphi/punctata species alliance of N. sect. Linervia, an Old World complex of reduced, one-flowered terrestrial orchids that is both species-rich and poorly known in tropical and warm temperate Asia. We sampled 12 of the 27 known species of the alliance in Asia, including all four species reported from Thailand and a further 20 plants collected in that country that could not be satisfactorily identified using morphology alone. Phylogenetic analyses using one nuclear (ITS) and two plastid (matK and trnL-F) markers confirmed both N. sect. Linervia and the alliance itself as monophyletic, and corroborated 11 of the 12 sampled species; N. punctata proved polyphyletic, with the Thai samples referred to this Indonesian species falling sister to the Himalayan N. mackinnonii. The 20 unidentified Thai samples formed three distinct, strongly supported clades. STACEY, a Bayesian coalescence approach to species delimitation, resolved the same three clusters, but provided evidence suggesting that one comprised two distinct sub-clades. Building on this genetic evidence, we identify subtle morphological differences and invoke a diagnosable species concept to circumscribe three previously unrecognized cryptic species from Thailand. This objective approach to species delimitation validates ostensibly minor morphological differences as a basis for differentiating species within the alliance, paving the way for a global analysis of species boundaries throughout the genus as a whole.

Southern high latitude squat lobsters II: description of Uroptychus macquariae sp. nov. from Macquarie Ridge.

Squat lobsters have only recently been recorded from the Macquarie Ridge, which extends south between New Zealand and Antarctica. Among these, Uroptychus insignis (Henderson, 1885) was recorded for the first time outside the western Indian Ocean, exhibiting only subtle morphological differences. Reexamination of the Macquarie Ridge and Indian Ocean specimens attributed to U. insignis using morphological and molecular data revealed the Macquarie Ridge form to represent a separate species. Subtle but consistent morphological differences are evident and partial CO1 sequence data indicates that the specimens collected on Macquarie Ridge differ from those collected in the Indian Ocean by more than 7%. The Macquarie Ridge species is described herein as Uroptychus macquariae n.sp. Subtle morphological differences between the new species and U. insignis are discussed.

Molecular Identification of Gambierdiscus and Fukuyoa (Dinophyceae) from Environmental Samples.

Ciguatera Fish Poisoning (CFP) is increasing across the Pacific and the distribution of the causative dinoflagellates appears to be expanding. Subtle differences in thecal plate morphology are used to distinguish dinoflagellate species, which are difficult to determine using light microscopy. For these reasons we sought to develop a Quantitative PCR assay that would detect all species from both Gambierdiscus and Fukuyoa genera in order to rapidly screen environmental samples for potentially toxic species. Additionally, a specific assay for F. paulensis was developed as this species is of concern in New Zealand coastal waters. Using the assays we analyzed 31 samples from three locations around New Zealand and the Kingdom of Tonga. Fourteen samples in total were positive for Gambierdiscus/Fukuyoa and two samples were also positive using the F. paulensis assay. Samples from the Kermadec Islands were further characterized using high-throughput sequencing metabarcoding. The majority of reads corresponded to Gambierdiscus species with three species identified at all sites (G. australes, G. honu and G. polynesiensis). This is the first confirmed identification of G. polynesiensis, a known ciguatoxin producer, in New Zealand waters. Other known toxin-producing genera were also detected, included Alexandrium, Amphidinium, Azadinium, Dinophysis, Ostreopsis, and Prorocentrum.