Cephalic Morphology Research Articles

Morphological, functional, and phylogenetic aspects of the head capsule of the cockroach Ergaula capucina (Insecta/Blattodea).

BackgroundCockroaches are usually typical omnivorous detritivores and their cephalic morphology is considered to be ancestral in various aspects. Thus, several studies addressed the morphology and function of the blattodean head, and the cockroach usually serves as a model for standard mouthparts in text books. However, so far only two of the three major lineages of Blattodea have been studied and no detailed information for the head of any Corydioidea was available. The present study closes this gap by providing a detailed morphological description of the head of Ergaula capucina, studying some important functional parameters of the mandible and discussing it in a phylogenetic framework.MethodsThe cephalic morphology of Ergaula studied in detail using a broad set of different techniques including digital microscopy, µ-computed tomography, and 3-dimensional reconstructions. Concerning the functional morphology of the mandible, we compared the volume and effective cross sections of the eight compartments of the primary mandibular adductor muscle for Ergaula, Blattella germanica, and Salganea rossi and measured the mechanical advantage, i.e., the force transmission ratio for all teeth of the mandible of Ergaula.ResultsThe head capsule of Ergaula is characterized by a strong sexual dimorphism and typical orthopteran mouthparts. It resembles the head capsule of other roaches in several respects and confirms oesotendons, the reduction of the mesal occelus, and bipartite M. verticopharyngealis and M. hypopharyngosalivaris as blattodean apomorphies. But it also shows some unique adaptations. It is the first described cockroach that lacks the dorsal tentorial arms which has various consequences for the cephalic musculature. On the maxillary lacinia, Ergaula is the first described blattodean to show strong and blunt setae instead of a lacinula, which might be homologues to the dentisetae of dragonflies and mayflies. Like other corydiid roaches that inhabit xeric areas, Ergaula has an atmospheric water-vapor absorption mechanism that includes a gland and a ductus on the epipharnyx and bladders on the hypopharynx. The mandibular adductor is in cockroaches asymmetric, a pattern not found in termites, mantids, or other closely related insects.

Evolution of cephalic structures in extreme myrmecophiles: a lesson from Clavigeritae (Coleoptera: Staphylinidae: Pselaphinae).

Pselaphinae is a large subfamily, comprising over 10 000 species of the megadiverse Staphylinidae (rove beetles). A remarkable feature of this group is the extreme structural diversity of different body regions, especially the head and its appendages. Within Pselaphinae, Clavigeritae stand out as a clade of highly specialized myrmecophiles. We examined internal and external head structures of the clavigerite species Diartiger kubotai Nomura, using state-of-the-art techniques. The cephalic morphology indicates in a phylogenetic context that the loss of eyes in some Clavigeritae was the latest of major evolutionary changes. We compiled the largest set of morphological data ever scored for the subfamily, comprising 155 characters of the head. Parsimony analyses and Bayesian inference yielded a similar phylogenetic pattern, largely congruent with results published previously. We retrieved Pselaphinae as a clade, and Faronitae as sister to all remaining groups of the subfamily. Faronitae are followed by a "Euplectitae grade" and non-monophyletic Goniaceritae, Batrisitae and Pselaphitae. Clavigeritae are monophyletic, but have evolved within the pselaphite grade. The enigmatic Colilodion Besuchet, recently shifted from Clavigeritae to a paraphyletic Pselaphitae, was placed as sister to extant clavigerites based on an array of cephalic synapomorphies. The current classification of Pselaphinae is unstable and deep changes should be made maintaining only monophyletic units, whereas most of the supertribes are paraphyletic. Characters of the head, with a concentration of mouthparts and sensory structures, and essential parts of the digestive tract and the nervous system, are highly informative phylogenetically. Study of internal structures, presently still at a very preliminary stage, obviously is essential for understanding the evolution of Pselaphinae. Future genetic investigations may reveal mechanisms behind the unique structural megadiversity in this exceptional group of rove beetles.

Exploration of the Influences of Temporary Velum Paralysis on Auditory-Perceptual, Acoustic, and Tomographical Markers.

Purpose To better understand hypernasality (HN), we explored the relations between velopharyngeal orifice, auditory perception of HN, and acoustic-spectral measures in an in vivo within-subject design: (a) with a normally functioning velum as the control condition and (b) with a temporarily paralyzed velum as the experimental condition. Method The velum of eight volunteers was injected with ropivacaine hydrochloride (Naropin) in the area of the levator veli palatini and tensor veli palatini muscles to induce temporary velopharyngeal inadequacy (VPI) and HN. Sustained [a] and [i] and oronasal text readings were recorded, and 3D cone-beam computed tomography images of the vocal tract were built before and during velar anesthesia. Differences between conditions and correlations in normal-to-numb differences between velopharyngeal cross-sectional area (VParea), mean ratings of HN severity, and nine acoustic-spectral measures were determined. Results Three subjects already had some incomplete velopharyngeal closure in the control condition. Temporary motor nerve blockage of the velum (increased VParea) was accomplished in seven subjects, leading to increased HN and changes in three acoustic-spectral measures. Furthermore, significant correlations only emerged between VParea, HN, and ModelKataoka. Conclusions In most of the participants, it was possible to temporarily increase the velopharyngeal orifice to investigate HN while controlling other speech variables and cephalic morphology. Although this study was exploratory and its are findings preliminary, it provided additional evidence for the possible clinical value of ModelKataoka, A 3-P 0, and B F1 for the objective measurement of VPI or HN.

Influence of Morphometry on Echocardiographic Measurements in Cavalier King Charles Spaniels: An Inverse Probability Weighting Analysis.

The development and progression of myxomatous mitral valve disease (MMVD) in Cavalier King Charles Spaniels (CKCS) are difficult to predict. Thus, the identification of dogs with a morphotype associated with more severe mitral disease at a young age is desirable. The aims of this study were to: (1) describe the physical, morphometric, and echocardiographic features of class B1 MMVD-affected Cavalier King Charles Spaniels (CKCS) according to the American College of Veterinary Internal Medicine (ACVIM) guidelines; (2) evaluate the influence of morphometric physical measurements on murmur intensity, mitral valve prolapse (MVP), regurgitant jet size, and indexed mitral valve and annulus measurements. Fifty-two MMVD-affected CKCS were included in the ACVIM class B1. This is a prospective clinical cross-sectional study. Morphometric measurements, which included the body, thorax, and head sizes of each dog, were investigated to establish the association with heart murmur intensity, valvular and annular echocardiographic measurements, MVP, and regurgitant jet size, using inverse probability weighting (IPW) analyses to adjust for confounding. The IPW analyses showed that when the head length and nose length decreased, dogs had a more severe regurgitant jet size. Furthermore, subjects with a more pronounced head stop angle had thicker anterior mitral valve leaflets. A brachycephalic morphotype, as seen in dogs similar to the King Charles Spaniel breed in terms of cephalic morphology, is associated with a more severe regurgitant jet size and with valvular characteristics that are related to the most severe forms of MMVD.

The cephalic morphology of Morinoia japonica (Talitridae, Amphipoda, Malacostraca) and its implications of terrestrial adaptation and phylogeny

The cephalic anatomical structures of Morinoia japonica were examined using X-ray micro-computed tomography (micro-CT), 3D reconstruction and scanning electron microscopy (SEM), to improve understanding of terrestrial adaptation and phylogenetic inferences. The cerebral nerves, skeletons and musculatures were described in detail based on the observation results. As observed with other terrestrial amphipoids, M. japonica has a reduction in size of the olfactory lobes in the small deutocerebrum and the antenna 1 nerve (in short antennae 1), which might be the apomorphies of Talitridae. Organ of Bellonci is absent in M. japonica. The unfused tentorial arms of M. japonica might be a plesiomorphic state in Amphipoda. The fusion of both peduncular articles 1 and 2 of antenna 2 is another apomorphy of Talitridae, which is also the taxonomic diagnosis of the family. The cephalic musculatures of M. japonica, another amphipod species Gammarus minus (Gammaridae), Daphnia (Branchiopoda), Godzilliognomus frondosus (Remipedia) and Dicondylia (Insecta) were homologized. The markedly reduced foregut muscles of M. japonica are suggested to be associated with its feeding on soft moss.

Female calling, life cycle, and microstructures of the parasitic beetle Ripidius quadriceps Abeille de Perrin.

The precopulatory behaviour of the larviform females of Ripidius quadriceps Abeille de Perrin, 1872 is described. The calling posture of virgin females is documented. The cephalic morphology and microstructures are visualised using scanning electron microscopy, in particular the secretory pores in the cuticle of inflatable maxillary palps. An exhaustive overview of relevant publications revealed that the location of secretory pores on the head of females is unique within the order Coleoptera. Compared to other beetles with sedentary calling females, the calling phase of the short-lived and non-feeding female of Ripidius is exceptionally short. For bioassays, various traps using virgin females of Ripidius were tested. It is likely that the sedentary behaviour of the short-lived female combined with a unique morphology and priority for investing in reproduction is compensated for by the actively flying males with remarkably flabellate antennae. The life cycle of this species, including some of the exceptions recorded at the individual level, is discussed. Perspectives for a biological and morphological survey of this rarely collected western Palaearctic species are outlined. In addition, the calling behaviour, secretory sites and location of pheromone glands in females of Coleoptera producing long range pheromones is reviewed.

Heteromorphosis associated to host-exploitation in an atypical parasitoid, Mallophora ruficauda (Diptera: Asilidae)

In this work, we provide morphological illustration and descriptions of the immature stages of the ectoparasitoid robber fly Mallophora ruficauda. Additionally, we studied the ecological aspects of its life cycle through the correlation between the morphology and function performed in each phase of the consumption of their host, the white grub Cyclocephala signaticollis. For the morphological description and quantification of length and width of the egg and larval instars I–II, images were used through optical and scanning electron microscopy. Individuals from larval instars III–V were weighed and measured with digital calibre directly. Finally, images were taken of the cephalic structures of the larval instars and through the use of image processing software we measured in each instar the size of cephalic structures. In addition, the changes in the width of cephalic capsule and the relative size of the maxillary palps and labrum with respect to the width of cephalic capsule were studied for each larval instar through GLMs, to relate the morphology of the cephalic structures with the function they perform. We found that the cephalic structures of the larva undergo changes when moulting to the next instar, according to their relationship with the host, matching with the stage of development where the processes of orientation to the host and attachment to its cuticle take place. These observations reveal, for the first time in a parasitoid asilid larva, the correlation between cephalic morphology and ecological function during the parasitism process and host use.

Profound head modifications in Claviger testaceus (Pselaphinae, Staphylinidae, Coleoptera) facilitate integration into communities of ants.

Clavigeritae is a group of obligate myrmecophiles of the rove beetle subfamily Pselaphinae (Staphylinidae). Some are blind and wingless, and all are believed to depend on ant hosts through feeding by trophallaxis. Phylogenetic hypotheses suggest that their ancestors, as are most pselaphines today, were free-living predators. Morphological alterations required to transform such beetles into extreme myrmecophiles were poorly understood. By studying the cephalic morphology of Claviger testaceus, we demonstrate that profound changes in all mouthpart components took place during this process, with a highly unusual connection of the maxillae to the hypopharynx, and formation of a uniquely transformed labium with a vestigial prementum. The primary sensory function of the modified maxillary and labial palps is reduced, and the ventral mouthparts transformed into a licking/'sponging' device. Many muscles have been reduced, in relation to the coleopteran groundplan or other staphylinoids. The head capsule contains voluminous glands whose appeasement secretions are crucial for the beetle survival in ant colonies. The brain, in turn, has been shifted into the neck region. The prepharyngeal dilator is composed of an entire series of bundles. However, the pharynx does not show any peculiar adaptations to taking up liquid food. We demonstrate that far-reaching cephalic modifications characterize C. testaceus, and that the development of appeasement glands and adaptation of the mouthparts to trophallaxis determine the head architecture of this extreme myrmecophile.

First description of male worms of Enterobius (Colobenterobius) serratus (Nematoda: Oxyuridae), the pinworm parasite of proboscis monkeys

Males of Enterobius (Colobenterobius) serratus Hasegawa et al., 2003 (Nematoda: Oxyuridae) are described for the first time based on six individuals collected from the feces of proboscis monkeys, Nasalis larvatus, in the Lower Kinabatangan Wildlife Sanctuary, Sabah, Malaysian Borneo. The males show identical cephalic morphology to females, being readily distinguishable from their congeners by the serrated inner margins of the lips. The bicolored esophageal corpus, long thin spicule and developed spicular pouch with paired muscular bands are also remarkable characteristics, presumably shared by other Asian members of the subgenus.

The cephalic morphology of free-living and cave-dwelling species of trechine ground beetles from China (Coleoptera, Carabidae)

Morphological adaptations of cave-dwelling organisms including different groups of Coleoptera have fascinated researchers since a long time. Nevertheless, very few detailed documentations of the anatomy of cave beetles using modern techniques are available. In this study, we describe and illustrate external and internal cephalic features of free-living and cave-dwelling trechine carabid beetles using digital microscopy, SEM, micro-CT, and computer-based 3D reconstruction. Morphological characteristics found in three selected species with different habitat preferences are compared. The following derived features distinguish a troglobite species (Sinaphaenops wangorum Ueno et Ran 1998) from a species living in the entrance of caves (Trechiotes perroti Jeannel 1954) and from a fully epigean species (Bembidion sp.): (1) the optic lobes are completely missing; (2) the head capsule, mouth parts, and antennae are distinctly elongated; (3) some muscle attachment areas are shifted; and (4) an additional dilator of the pharynx is present. Despite of conspicuous differences likely related with subterranean habits, the link of some cephalic features to this specific habitat preference remains uncertain.

The cephalic morphology of the American cockroach Periplaneta americana (Blattodea)

The skeleto-muscular system of the head of the American cockroach Periplaneta americana is described in detail. The results are compared with previous partial descriptions of the cephalic morphology of this species and other dictyopterans. The head of Periplaneta is, as in other cockroaches, mostly characterized by plesiomorphies such as the typical orthopteroid mouthparts, the lateral position of the compound eyes, 5-segmented maxillary palps and 3-segmented labial palps, as well as long antennae. Periplaneta shows sexual dimorphism with the compound eyes of the males reaching further ventrally. The epistomal ridge is medially interrupted so that the frons and the clypeus are confluent. The cephalic musculature is typical for a polyneopteran insect and includes 59 muscles. Potential apomorphies for Blattodea in the cephalic area include the absence of the median ocellus, the bipartite condition of M. verticopharyngealis (0ph1) and of M. hypopharyngosalivaris (0hy12), and the presence of oesotendons. The lacinula, a subapical lobelet on the lacinia, is present in almost all studied blattodeans but its potential homology to the dentisetae of Palaeoptera or the lamellae of apterygotes cannot be addressed at the moment. A “perforate” tentorium, a membranous postmola, and a lacinia that fits into the concave mesal wall of the galea are confirmed as autapomorphies of Dictyoptera.

Cephalic anatomy and three-dimensional reconstruction of the head of Catops ventricosus (Weise, 1877) (Coleoptera: Leiodidae: Cholevinae)

Adult head structures are well known in the coleopteran suborders Archostemata and Adephaga, whereas the available information is very fragmentary in the megadiverse Polyphaga, including the successful superfamily Staphylinoidea. In the present study, the cephalic morphology of the cholevine species Catops ventricosus is described in detail and documented. The results were compared to conditions occurring in other polyphagan lineages, especially staphylinoid and scarabaeoid representatives. Specific external features documented in Catops and potential autapomorphies of Leiodidae include a five-segmented antennal club with a reduced eighth antennomere and the presence of periarticular grooves filled with sensilla on antennomeres 7, 9, and 10. The firm connection of the head and pronotum is possibly an apomorphy of Cholevinae. The monophyly of Cholevinae excluding Eucatopini and Oritocatopini is supported by the apical maxillary palpomere as long as or shorter than the subapical one, and the presence of cryptic pore plates on the surface of these palpomeres—a feature described and documented here for the first time. The internal cephalic structures of Catops are mostly plesiomorphic, as for instance the complete tentorium. The pattern of the muscles is similar to what is found in other staphylinoid taxa. The unusual maxillary muscle “Mx” is likely a groundplan apomorphy of the clade Staphyliniformia + Scarabaeoidea. M. hypopharyngomandibularis (M13) was identified in Catops and is ancestral for Coleoptera, even though it is often missing. The same applies to M. tentoriohypopharyngalis (M42).

Catching prey with the antennae – The larval head of Corethrella appendiculata (Diptera: Corethrellidae)

The larval cephalic morphology of Corethrella appendiculata Grabham, 1906 is described and documented in detail. The observed features are compared to conditions found in Chaoboridae, Culicidae, and other culicomorph families. The function of antennae, mouthparts and associated muscles is interpreted based on the morphological results. The prey catching mechanism is compared to what occurs in other predaceous larvae of Culicomorpha. The cephalic larval morphology is discussed with respect to homology and possible phylogenetic implications. The horizontal frontoclypeal antennal grooves and the lateral rows of strongly developed bristles are likely larval autapomorphies of Corethrellidae. The presence of raptorial antennae is a highly unusual apomorphy shared with Chaoboridae. The systematic position of Corethrellidae remains ambiguous.

Coding characters from different life stages for phylogenetic reconstruction: a case study on dragonfly adults and larvae, including a description of the larval head anatomy ofEpiophlebia superstes(Odonata: Epiophlebiidae)

The exclusive use of characters coding for specific life stages may bias tree reconstruction. If characters from several life stages are coded, the type of coding becomes important. Here, we simulate the influence on tree reconstruction of morphological characters of Odonata larvae incorporated into a data matrix based on the adult body under different coding schemes. For testing purposes, our analysis is focused on a well-supported hypothesis: the relationships of the suborders Zygoptera, ‘Anisozygoptera’, and Anisoptera. We studied the cephalic morphology of Epiophlebia, a key taxon among Odonata, and compared it with representatives of Zygoptera and Anisoptera in order to complement the data matrix. Odonate larvae are characterized by a peculiar morphology, such as the specific head form, mouthpart configuration, ridge configuration, cephalic musculature, and leg and gill morphology. Four coding strategies were used to incorporate the larval data: artificial coding (AC), treating larvae as independent terminal taxa; non-multistate coding (NMC), preferring the adult life stage; multistate coding (MC); and coding larval and adult characters separately (SC) within the same taxon. As expected, larvae are ‘monophyletic’ in the AC strategy, but with anisopteran and zygopteran larvae as sister groups. Excluding larvae in the NMC approach leads to strong support for both monophyletic Odonata and Epiprocta, whereas MC erodes phylogenetic signal completely. This is an obvious result of the larval morphology leading to many multistate characters. SC results in the strongest support for Odonata, and Epiprocta receives the same support as with NMC. Our results show the deleterious effects of larval morphology on tree reconstruction when multistate coding is applied. Coding larval characters separately is still the best approach in a phylogenetic framework.

Mandibles with two joints evolved much earlier in the history of insects: dicondyly is a synapomorphy of bristletails, silverfish and winged insects

AbstractThe evolution of two‐jointed mandibles is considered to be a major step during the evolution of early insects enabling the exploration of new types of food. Two‐jointed – or dicondylic – mandibles are believed to be a groundplan characteristic for winged insects and silverfish. Jumping bristletails are thought to possess mandibles with one joint and are the sistergroup of winged insects + silverfish. However, our knowledge of the cephalic morphology of bristletails is limited to data from a few species and thus fragmentary. We investigated the cephalic morphology of both families of bristletails, Meinertellidae and Machilidae. We focused on skeletal elements and the musculature and compared them with the corresponding structures found in silverfish and winged insects. Bristletails show a previously unknown coupling structure between the maxillary palps and the mandibles and an additional anterior articulation of the mandibles in the region of the anterior tentorial pits. The articulation can be homologised with the anterior articulation in silverfish and winged insects. Together with a description of the functional morphology of the mandible system of bristletails and a discussion of the homology of mandibular articulations and related characters, we provide conclusive evidence that bristletails are, in fact, dicondylic insects.

Ontogeny and intraspecific variation of the early Cambrian trilobite Olenellus gilberti, with implications for olenelline phylogeny and macroevolutionary trends in phenotypic canalization

Morphological variation within the Early Cambrian olenelline trilobite Olenellus gilberti from the Pioche Formation of Nevada is partitioned into ontogenetic, static (non-ontogenetic), and taphonomic components, providing clearer understanding of the nature and sources of the variation. Such understanding is crucial for improved systematic, phylogenetic and evolutionary analyses of early trilobites. Compaction caused a significant change in mean form and an increase in shape variance, distorting many aspects of biological shape and shape variation. Morphologically mature specimens exhibited variation in many quantitative and qualitative aspects of cephalic morphology, in the distribution of prothoracic axial nodes, and in the number of opisthothoracic segments. The variance of two log-transformed size measures does not significantly increase over the first five sampled instars, a pattern interpretable either as the oldest known case of targeted growth in animal history, or as evidence of strong selection during early ontogeny. The magnitude of static cephalic shape variation does not significantly change during late ontogeny, also indicative either of developmental regulation of form or of selection against deviant phenotypes. The dominant structure of cephalic static shape variation is similar to the pattern of shape change during late portions of ontogeny: intraspecific heterochrony might therefore have been an important contributor to size-independent shape variation. For many traits, the developmental system was not well buffered against internal and/or external variation so that the resulting phenotype was not tightly canalized in the condition of those traits. Intraspecific variation in such traits is rarely documented in later (especially post-Cambrian) trilobites, consistent with the claim that developmental systems of early trilobites were relatively poorly canalized. However, other aspects of cephalic growth are consistent with having been under tight developmental regulation, which would not be indicative of general developmental ‘sloppiness’. This cautions against generalizing observations from a limited number of traits to the entire organism.

Cephalic Morphology of Ariosoma gilberti (Bathymyrinae: Congridae)

The head bones and relevant muscles are important elements composing the feeding and respiration apparatus and can be considered as highly important structures for giving rise to evolutionary specializations. The eels of the Anguilloidei is a diverse group and structural diversity in their cranial musculoskeletal system is thus to be expected. Ariosoma gilberti is a member of Bathymyrinae (Congridae) with a hydraulic based prey transport and closely related to muraenid family with mechanical prey transport system. Since there is no information about the cephalic morphology of A. gilbert, hence this study was conducted to provide detailed description of its cranial osteology and myology. The immobile maxillary with large pointed teeth, an anterior moderate mouth gape, large jaw closing muscles and large lateral and ventral bony elements, providing more room for the orobranchial cavity of A. gilberti suggesting the presence of a hydraulic and suction-based mechanism.

Unique rostrate larvae and basidiomycophagy in the beetle family Corylophidae

The head morphology of larvae of two undescribed species of the corylophid genus Holopsis were examined. Both are associated with the same basidiomycete host Ganoderma cf applanatum. Whereas the round and convex adults are very similar, one of the disc-shaped larvae is characterized by an elongate weevil-like snout, which is a unique feature in larval beetles. The posterior head region, the mouthparts and the general configuration of the musculature are similar in the larvae of both species. However, in the rostrate Holopsis sp. 1 most muscles are either widened along the longitudinal axis or elongated. Moreover, an additional bundle of M. frontobuccalis posterior is present, which strengthens the pharyngeal pumping apparatus. Both species share an unusual connection between the prepharynx and pharynx. This is a potential autapomorphy of the genus. The larval cephalic morphology of Holopsis sp. 2 and the corylophine genus Sericoderus is quite similar. However, they differ in some muscular features and in the configuration of the foregut. Holopsis species are associated with Basidiomycetes. Whether this is an ancestral condition in Corylophidae remains ambiguous due to conflicting phylogenetic hypotheses and the largely unknown biology of the Australian subfamily Periptyctinae. Several features of Holopsis are likely plesiomorphic and possibly related with the association with basidiomycetes. However, the larval rostrum of sp. 1 is doubtlessly derived, and could have a performance advantage over other species feeding on the spores of Ganoderma cf applanatum including Holopsis sp. 2.

The adult head of Axymyia furcata (Insecta: Diptera: Axymyiidae)

The external and internal cephalic morphology of males and females of Axymyia furcata is described and illustrated in detail. The documented features are compared with those of potentially related groups. Axymyia displays a number of apomorphic features of the adult head, like the subdivision of the compound eyes, the absence of several mucles (M. clypeolabralis, M. stipitopalpalis externus, M. palpopalpalis maxillae primus, Mm. palpopalpalis maxillae primus and secundus), the absence of both maxillary endites, and the loss of the salivary pump musculature (M. hypopharyngosalivarialis). Another apomorphic character is the origin of M. tentorioscapalis anterior on the head capsule. Some features are plesiomorphic and probably belong to the groundplan of Diptera: the orthognathous head, three ocelli, 5-segmented maxillary palps, 2-segmented labial palps transformed into medially fused labella, one premental retractor, a dense vestiture of microtrichia on all exposed parts of the head except the labrum, and the presence of an epipharyngeal food channel. The systematic position of Axymyiidae is discussed. Our findings do not provide support for the phylogenetic position of Axymyiidae.

Cephalic morphological variation in freshwater silversides Odontesthes hatcheri and Odontesthes bonariensis in Patagonia: introgression and ecological relationships

Based on geometric morphometrics and discriminant analysis, the percentage of silverside Odontesthes hatcheri and Odontesthes bonariensis individuals identified by a taxonomic key and misclassified by discriminant analysis was obtained and a negative correlation between the percentage of misclassified individuals of O. hatcheri and the distance to the nearest hatchery stocking silversides was found, suggesting a genetic introgression. Morphological analyses between species, between populations and within populations pointed to the same anatomical structures, suggesting a nested variation related to environmental cues such as availability of littoral shelter. The dependence between the cephalic morphology of O. hatcheri and body size would be in agreement with the trophic niche shifts of the species. Introgression adds a new threat to the already observed decline of populations of O. hatcheri and suggests that this species deserves particular consideration in terms of conservation guidelines.