Heterogeneity in the preferential diet of neotropical bats impacts the pancreatic islet mass and α and β cell distribution

Whether there is a relationship between bats' dietary patterns and evolutionary endocrine pancreas adaptation is not clearly understood. Aiming to contribute to this topic, we evaluated some metabolic and structural parameters in the following adult bats: the frugivorous Artibeus lituratus, the nectarivorous Anoura caudifer, the hematophagous Desmodus rotundus, and the insectivorous Molossus molossus. A. lituratus and A. caudifer diets consist of high amounts of simple carbohydrates, while D. rotundus and M. molossus diets consist of high amounts of proteins or protein and fat, respectively. In our results, A. lituratus and A. caudifer bats exhibited the highest values of relative islet mass (%), islet density (number of islets per pancreas area), and the lowest values of intestinal length among the four species. When adjusted by the body mass (mg/g of body mass), both D. rotundus and A. caudifer bats exhibited the highest islet mass values among the groups. Blood glucose was similar between A. lituratus, D. rotundus, and M. molossus, with the lowest values for the A. caudifer bats. M. molossus bats had the highest plasma cholesterol values among the studied species but exhibited similar plasma triacylglycerol with D. rotundus and A. caudifer bats. β- and α-cell distribution within A. lituratus, A. caudifer, and M. molossus islets achieved an approximate average value of ∼ 66% and ∼ 28%, respectively, a pattern inverted in D. rotundus islets (53% of α cells and 40% of β cells). A. caudifer and D. rotundus exhibited the highest and the lowest β/α-cells ratio per islet, respectively. We conclude that the macronutrient predominance in each bat-eating niche correlates with the morphophysiological pancreas features being the nectarivorous A. caudifer the species with the highest islet mass per body mass and β/α-cells ratio, while the hematophagous D. rotundus showed the highest α-cells apparatus.

High disparity in repellent gland anatomy across major lineages of stick and leaf insects (Insecta: Phasmatodea)

BACKGROUND

Phasmatodea are well known for their ability to disguise themselves by mimicking twigs, leaves, or bark, and are therefore commonly referred to as stick and leaf insects. In addition to this and other defensive strategies, many phasmatodean species use paired prothoracic repellent glands to release defensive chemicals when disturbed by predators or parasites. These glands are considered as an autapomorphic trait of the Phasmatodea. However, detailed knowledge of the gland anatomy and chemical compounds is scarce and only a few species were studied until now. We investigated the repellent glands for a global sampling of stick and leaf insects that represents all major phasmatodean lineages morphologically via µCT scans and analyzed the anatomical traits in a phylogenetic context.

RESULTS

All twelve investigated species possess prothoracic repellent glands that we classify into four distinct gland types. 1: lobe-like glands, 2: sac-like glands without ejaculatory duct, 3: sac-like glands with ejaculatory duct and 4: tube-like glands. Lobe-like glands are exclusively present in Timema, sac-like glands without ejaculatory duct are only found in Orthomeria, whereas the other two types are distributed across all other taxa (= Neophasmatodea). The relative size differences of these glands vary significantly between species, with some glands not exceeding in length the anterior quarter of the prothorax, and other glands extending to the end of the metathorax.

CONCLUSIONS

We could not detect any strong correlation between aposematic or cryptic coloration of the examined phasmatodeans and gland type or size. We hypothesize that a comparatively small gland was present in the last common ancestor of Phasmatodea and Euphasmatodea, and that the gland volume increased independently in subordinate lineages of the Occidophasmata and Oriophasmata. Alternatively, the stem species of Neophasmatodea already developed large glands that were reduced in size several times independently. In any case, our results indicate a convergent evolution of the gland types, which was probably closely linked to properties of the chemical components and different predator selection pressures. Our study is the first showing the great anatomical variability of repellent glands in stick and leaf insects.

The marine gastropod Conomurex luhuanus (Strombidae) has high-resolution spatial vision and eyes with complex retinas

All species within the conch snail family Strombidae possess large camera-type eyes that are surprisingly well-developed compared with those found in most other gastropods. Although these eyes are known to be structurally complex, very little research on their visual function has been conducted. Here, we use isoluminant expanding visual stimuli to measure the spatial resolution and contrast sensitivity of a strombid, Conomurex luhuanus. Using these stimuli, we show that this species responds to objects as small as 1.06 deg in its visual field. We also show that C. luhuanus responds to Michelson contrasts of 0.07, a low contrast sensitivity between object and background. The defensive withdrawal response elicited by visual stimuli of such small angular size and low contrast suggests that conch snails may use spatial vision for the early detection of potential predators. We support these findings with morphological estimations of spatial resolution of 1.04 deg. These anatomical data therefore agree with the behavioural measures and highlight the benefits of integrating behavioural and morphological approaches in animal vision studies. Using contemporary imaging techniques [serial block-face scanning electron microscopy (SBF-SEM), in conjunction with transmission electron microscopy (TEM)], we found that C. luhuanus have more complex retinas, in terms of cell type diversity, than expected based on previous studies of the group using TEM alone. We find the C. luhuanus retina comprises six cell types, including a newly identified ganglion cell and accessory photoreceptor, rather than the previously described four cell types.

Summary: Behavioural trials indicate the eyes of conch snail Conomurex luhuanus provide high-resolution spatial vision, and morphological examination reveals the retina contains more cell types than those of other gastropods.

Archigetes Leuckart, 1878 (Cestoda, Caryophyllidea): diversity of enigmatic fish tapeworms with monoxenic life cycles

The caryophyllidean genus Archigetes Leuckart, 1878 is unique among all tapeworms in that its species can mature in invertebrate hosts (Oligochaeta), i.e., have a monoxenic (direct) life cycle. All five species were described as progenetic plerocercoids in oligochaetes and two of them also as adults from cypriniform fishes. Two species, A. sieboldi Leuckart, 1878 and A. iowensis Calentine, 1962, were found in North America in non-native common carp (Cyprinus carpio). A molecular study of caryophyllideans from the southern United States has revealed the occurrence of three new species in native freshwater fishes (Catostomidae, Ictiobinae): Archigetes loculotruncatus n. sp. from Ictiobus bubalus, I. niger and Carpiodes cyprinus is the largest representative of the genus and differs by a loculotruncate scolex. Archigetes megacephalus n. sp. from Ictiobus niger, I. bubalus and I. cyprinellus is characterised by a prominent, bothrioloculodiscate scolex. Archigetes vadosus n. sp. from I. bubalus is typified by a globular scolex with very shallow loculi; it differs from the closely related A. sieboldi in the shape of the body, with a distinct neck region and a scolex wider than the remaining body. Archigetes iowensis Calentine, 1962 becomes a junior synonym of Paraglaridacris limnodrili (Yamaguti, 1934). The generic diagnosis of Archigetes is amended and a key to identification of North American taxa is provided. Species of Archigetes and Paraglaridacris differ from each other most conspicuously in the structure of the ovary, which is follicular in Archigetes versus compact in Paraglaridacris.

Mating behavior and reproductive morphology predict macroevolution of sex allocation in hermaphroditic flatworms

Background

Sex allocation is the distribution of resources to male or female reproduction. In hermaphrodites, this concerns an individual’s resource allocation to, for example, the production of male or female gametes. Macroevolutionary studies across hermaphroditic plants have revealed that the self-pollination rate and the pollination mode are strong predictors of sex allocation. Consequently, we expect similar factors such as the selfing rate and aspects of the reproductive biology, like the mating behaviour and the intensity of postcopulatory sexual selection, to predict sex allocation in hermaphroditic animals. However, comparative work on hermaphroditic animals is limited. Here, we study sex allocation in 120 species of the hermaphroditic free-living flatworm genus Macrostomum. We ask how hypodermic insemination, a convergently evolved mating behaviour where sperm are traumatically injected through the partner’s epidermis, affects the evolution of sex allocation. We also test the commonly-made assumption that investment into male and female reproduction should trade-off. Finally, we ask if morphological indicators of the intensity of postcopulatory sexual selection (female genital complexity, male copulatory organ length, and sperm length) can predict sex allocation.

Results

We find that the repeated evolution of hypodermic insemination predicts a more female-biased sex allocation (i.e., a relative shift towards female allocation). Moreover, transcriptome-based estimates of heterozygosity reveal reduced heterozygosity in hypodermically mating species, indicating that this mating behavior is linked to increased selfing or biparental inbreeding. Therefore, hypodermic insemination could represent a selfing syndrome. Furthermore, across the genus, allocation to male and female gametes is negatively related, and larger species have a more female-biased sex allocation. Finally, increased female genital complexity, longer sperm, and a longer male copulatory organ predict a more male-biased sex allocation.

Conclusions

Selfing syndromes have repeatedly originated in plants. Remarkably, this macroevolutionary pattern is replicated in Macrostomum flatworms and linked to repeated shifts in reproductive behavior. We also find a trade-off between male and female reproduction, a fundamental assumption of most theories of sex allocation. Beyond that, no theory predicts a more female-biased allocation in larger species, suggesting avenues for future work. Finally, morphological indicators of more intense postcopulatory sexual selection appear to predict more intense sperm competition.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01234-1.

On a New Species of Pseudocypretta Klie, 1932 (Crustacea, Ostracoda) from the Neotropical Region, with a Discussion on the Position of the Genus

Pseudocypretta amor sp. nov. (named after the carapace spots resembling the word "Love") is here described from all-female populations from the four major floodplains in Brazil. The new species is compared to the other two known species in the genus, P. maculata Klie (1932), the type species, and P. lineata Ma and Yu (2020). As the latter two species are thus far found exclusively in South East Asia and China, respectively, the present extension of the area of the genus to South America is considerable. Several morphological characters in this genus and species are discussed, especially the presence of marginal septa in the valves, the candonid type T3 with 3^rd and 4^th segment separated (candonid type) and the caudal ramus which is reduced to a flagellum (cypridopsine type) or is fully absent. Based on the combination of these and other characters, the genus Pseudocypretta is here transferred from the Cyprettinae to the tribe Cyprettadopsini in the Cypridopsinae, as it is closely related to the genus Cyprettadopsis Savatenalinton, 2020. The presence of the candonid type T3 in Cyprididae and Notodromadidae, where the T3 generally has a pincer-shaped tip by the fusion of the 3^rd and the 4^th segment, is further discussed.

Morphology and ultrastructure of the epithelial femoral gland in cicadas (Hemiptera: Cicadidae)

Exocrine glands in the legs of social insects are found throughout all leg segments, but studies of exocrine glands in legs of solitary insects are very limited. We discovered a novel gland at the apex of the fore, mid and hind femurs from six representative species of Cicadidae, which we propose to name as the epithelial femoral gland. The epithelial femoral gland is located between the paired apodemes and the articulation membrane within the apex of the femur, which faces the proximal articulation region of the tibia. The epithelial femoral gland in the midlegs is less developed than that in the fore- and hindlegs within a species. The glandular cells belong to class-1, which contain a large amount of rough endoplasmic reticulum, secretory vesicles and Golgi bodies, indicating that these cells may produce a proteinaceous secretion. Details of the epithelial femoral gland at the ultrastructural level suggest that it may function to produce nourishing substances to the joint between femur and tibia. The less developed epithelial femoral gland in the midlegs and the slight difference in the glands between fore- and hindlegs within a species could be related to the functional differentiation of the corresponding legs in cicadas. Further studies of exocrine glands in the legs of cicadas and other Cicadomorpha insects may improve our understanding of the structural and functional divergence of legs in hemipteran insects.

External structures of the metathoracic scent gland efferent system in the true bug superfamily Pyrrhocoroidea (Hemiptera: Heteroptera: Pentatomomorpha)

Pyrrhocoroidea represents an important group of true bugs (Insecta: Hemiptera: Heteroptera) which includes fire bugs, cotton stainers and other taxa widely used in experimental studies or known as pests. However, the morphology and phylogeny of Pyrrhocoroidea have been only poorly studied so far. Here, structures of the external scent efferent system of the metathoracic scent glands are examined in 64 out of 71 currently valid genera of Pyrrhocoroidea and scanning electron micrographs are provided for most taxa. Several characters are revealed which define each of the three higher taxa within Pyrrhocoroidea: Larginae (small auriculate peritreme lacking manubrium and median furrow; metathoracic spiracle never surrounded by evaporatorium), Physopeltinae (large, widely open ostiole; large peritremal disc with manubrium [new term], lacking median furrow; mace-like mycoid filter processes of equal shape and size on both anterior and posterior margins of metathoracic spiracle), and Pyrrhocoridae (elongate auriculate peritreme with deep median furrow). Within Pyrrhocoridae, three main types (A, B and C) of the external scent efferent system are distinguished, differring in the amount of reductions. The findings are interpreted in the context of phylogenetic hypotheses available for Pyrrhocoroidea and their close relatives, Coreoidea and Lygaeoidea. An updated identification key to the families and subfamilies of Pyrrhocoroidea applicable for both sexes is provided.

Disentangling taxonomy of Biacetabulum (Cestoda, Caryophyllidea), parasites of catostomid fishes in North America: proposal of Megancestus gen. n. to accommodate B. carpiodi

A new genus, Megancestus n. gen., is proposed to accommodate the caryophyllidean tapeworm Biacetabulum carpiodi Mackiewicz, 1969 from carpsuckers and quillback (Carpiodes spp.) in North America. This species is not closely related to other species of Biacetabulum Hunter, 1927 and is transferred to a newly erected genus. This new genus is typified by the possession of a small body (total length of 3.1-7.5 mm) with a scolex that bears a pair of large acetabulum-like loculi, two pairs of shallow lateral loculi, and a slightly convex apical disc, testes arranged in one or two layers, oval, thick-walled cirrus-sac, well-developed external seminal vesicle, separate gonopores, H-shaped ovary, few median vitelline follicles, and the uterus extending by a single loop anterior to the cirrus-sac. Megancestus differs from all Nearctic caryophyllidean genera (family Capingentidae), including Biacetabulum, by vitelline follicles dorsal to the ovary that connect the preovarian and postovarian vitelline fields. The most closely related Hunterella Mackiewicz et McCrae, 1962 differs by shape of the scolex (tholate, i.e., devoid of any loculi), dumbbell-shaped ovary and the uterus not extending anterior to the cirrus-sac. Megancestus carpiodi (Mackiewicz, 1969) n. comb. is the only species of the genus and it is a stenoxenous parasite, which has been found only in the river carpsucker (Carpiodes carpio-type host), quillback (Carpiodes cyprinus) and highfin carpsucker (Carpiodes velifer) (Catostomidae: Ictiobinae) in the lower and middle Mississippi basin.

Male postabdomen reveals ancestral traits of Megasecoptera among winged insects

External male genitalia of insects are greatly diverse in form and frequently used in evolutionary context and taxonomy. Therefore, our proper recognition of homologous structures among various groups from Paleozoic and extant insect taxa is of crucial interest, allowing to understand the key steps in insect evolution. Here, we reveal structural details of two Late Carboniferous representatives of Megasecoptera (families Bardohymenidae and Brodiopteridae), such as the presence of separated coxal plates VIII and ventral expansions of coxal lobes IX. Together with the confirmed presence of abdominal styli in some other members of Palaeodictyopterida (Diaphanopterodea) this suggests that early pterygotes may have had traits more archaic than expected. Whether or not these traits point to a stem-group relationship of Palaeodictyopterida to all other Pterygota as suspected by earlier authors remains unclear at this stage. Furthermore, the present study provides an updated comparison of male postabdomen morphology among extant species of wingless Archaeognatha and representatives of early diverging groups of Pterygota from the Late Carboniferous and Early Permian, the Megasecoptera (Palaeodictyopterida), Permoplectoptera (Ephemeroptera) and Meganisoptera (Odonatoptera).

Comparative cranial morphology of the Late Cretaceous protostegid sea turtle Desmatochelys lowii

BACKGROUND

The phylogenetic placement of Cretaceous marine turtles, especially Protostegidae, is still under debate among paleontologists. Whereas protostegids were traditionally thought to be situated within the clade of recent marine turtles (Chelonioidea), some recent morphological and molecular studies suggest placement along the stem of Cryptodira. The main reason why the evolution of marine turtles is still poorly understood, is in part due to a lack of insights into the cranial anatomy of protostegids. However, a general availability of high-quality fossil material, combined with modern analysis techniques, such as X-ray microtomography, provide ample opportunity to improve this situation. The scope of this study is to help resolve its phylogenetic relationships by providing a detailed description of the external and internal cranial morphology of the extinct protostegid sea turtle Desmatochelys lowii Williston, 1894.

MATERIAL AND METHODS

This study is based on the well-preserved holotype of Desmatochelys lowii from the Late Cretaceous (middle Cenomanian to early Turonian) Greenhorn Limestone of Jefferson County, Nebraska. The skulls of two recent marine turtles, Eretmochelys imbricata (Linnaeus, 1766) (Cheloniidae) and Dermochelys coriacea Lydekker, 1889 (Dermochelyidae), as well as the snapping turtle Chelydra serpentina (Linnaeus, 1758) (Chelydridae) provide a comparative basis. All skulls were scanned using regular or micro CT scanners and the scans were then processed with the software program Amira to create 3D isosurface models. In total, 81 bones are virtually isolated, figured, and described, including the nature of their contacts. The novel bone contact data is compiled and utilized in a preliminary phenetic study. In addition, an update phylogenetic analysis is conduced that utilizes newly obtained anatomical insights.

RESULTS

The detailed examination of the morphology of the herein used specimens allowed to explore some features of the skull, to refine the scoring of Desmatochelys lowii in the recent global matrix of turtles, and develop five new characters. The alleged pineal foramen in the type skull of Desmatochelys lowii is shown to be the result of damage. Instead, it appears that the pineal gland only approached the skull surface, as it is in Dermochelys coriacea. Whereas the parasphenoid in confirmed to be absent in hard-shelled sea turtles, ist possible presence in Desmatochelys lowii is unclear. The results of the phenetic study show that Desmatochelys lowii is least similar to the other examined taxa in regards to the nature of its bone contacts, and therefore suggests a placement outside Americhelydia for this protostegid sea turtle. The phylogenetic study results in a placement of Protostegidae along the stem of Chelonioidea, which is a novel position for the group.

Comparative analysis reveals the complex role of histoblast nest size in the evolution of novel insect abdominal appendages in Sepsidae (Diptera)

BACKGROUND

The males of some sepsid species (Sepsidae: Diptera) have abdominal appendages that are remarkable in several ways. They are sexually dimorphic, have a complex evolutionary history of gain and loss, and can be jointed and thus highly mobile. The sternite brushes are used extensively in complex courtship behaviors that differ considerably between species and during mating. The abdominal appendages have a novel developmental pathway developing from histoblast nests rather than imaginal discs.

RESULTS

We focus on the evolution of cell number, nest area, and segment length in both sexes to understand how this tissue relates to the formation of novel abdominal appendages. We map histoblast nest size of wandering-phase larvae of 17 species across 10 genera to a phylogenetic tree of Sepsidae and demonstrate that abdominal appendages require significant increases of histoblast nest size and cell number in most species while one species produces small appendages even without such modifications. In species with particularly large appendages, not only the nests on the fourth, but nests in neighboring segments are enlarged (Themira biloba, Themira putris). The loss of abdominal appendages corresponds to the loss of an enlarged fourth histoblast nest, although one species showed an exception to this pattern. One species that constitutes an independent origin of abdominal appendages (Perochaeta dikowi) uses an unusual developmental mechanism in that the histoblast nest sizes are not sexually dimorphic.

CONCLUSIONS

The surprisingly high diversity in histoblast size and degree of sexual dimorphism suggests that the developmental mechanism used for abdominal appendage formation in sepsids is highly adaptable. The presence of appendages usually correlate with increased histoblast cell number and in most cases appendage loss results in a return to ancestral histoblast morphology. However, we also identify several exceptions that indicate the abdominal appendages have a malleable developmental origin that is responsive to selection.

Evidence for spatial vision in Chiton tuberculatus, a chiton with eyespots

To better understand relationships between the structures and functions of the distributed visual systems of chitons, we compare how morphological differences between the light-sensing structures of these animals relate to their visually guided behaviors. All chitons have sensory organs - termed aesthetes - embedded within their protective shell plates. In some species, the aesthetes are interspersed with small, image-forming eyes. In other species, the aesthetes are paired with pigmented eyespots. Previously, we compared the visually influenced behaviors of chitons with aesthetes to those of chitons with both aesthetes and eyes. Here, we characterize the visually influenced behaviors of chitons with aesthetes and eyespots. We find that chitons with eyespots engage in behaviors consistent with spatial vision, but appear to use spatial vision for different tasks than chitons with eyes. Unlike chitons with eyes, Chiton tuberculatus and C. marmoratus fail to distinguish between sudden appearances of overhead objects and equivalent, uniform changes in light levels. We also find that C. tuberculatus orients to static objects with angular sizes as small as 10 deg. Thus, C. tuberculatus demonstrates spatial resolution that is at least as fine as that demonstrated by chitons with eyes. The eyespots of Chiton are smaller and more numerous than the eyes found in other chitons and they are separated by angles of <0.5 deg, suggesting that the light-influenced behaviors of Chiton may be more accurately predicted by the network properties of their distributed visual system than by the structural properties of their individual light-detecting organs.

Ultrastructure of the midgut in Heteroptera (Hemiptera) with different feeding habits

Heteroptera have diverse feeding habits with phytophagous, zoophagous, and haematophagous species. This dietary diversity associated with the monophyly of Heteroptera makes these insects a good object for comparative studies of the digestive tract. This work compares the ultrastructure of the middle midgut region in the phytophagous Coptosoma scutellatum (Plataspidae), Graphosoma lineatum (Pentatomidae), Kleidocerys resedae (Lygaeidae), and zoophagous Rhynocoris iracundus (Reduviidae), Nabis rugosus (Nabidae), and Himacerus apterus (Nabidae), to verify if diet affects midgut cells in phylogenetically related insects. The middle region of the midgut was used for comparison because it is the main site for digestion and absorption of the midgut. The digestive cell ultrastructure was similar in the six species, with features of secretory, absorptive, transport, storage, and excretory cells, suggesting a stronger correlation of middle digestive cell ultrastructure with the phylogeny of these species than with the different heteropteran feeding habits.

Sexual selection and the evolution of male pheromone glands in philanthine wasps (Hymenoptera, Crabronidae)

Background

Sexual selection is thought to promote evolutionary changes and diversification. However, the impact of sexual selection in relation to other selective forces is difficult to evaluate. Male digger wasps of the tribe Philanthini (Hymenoptera, Philanthinae) scent mark territories to attract receptive females. Consequently, the organs for production and storage of the marking secretion, the mandibular gland (MG) and the postpharyngeal gland (PPG), are subject to sexual selection. In female Philanthini, these glands are most likely solely subject to natural selection and show very little morphological diversity. According to the hypothesis that sexual selection drives interspecific diversity, we predicted that the MG and PPG show higher interspecific variation in males than in females. Using histological methods, 3D-reconstructions, and multivariate statistical analysis of morphological characters, we conducted a comparative analysis of the MG and the PPG in males of 30 species of Philanthini and three species of the Cercerini and Aphilanthopsini, two related tribes within the Philanthinae.

Results

We found substantial interspecific diversity in gland morphology with regard to gland incidence, size, shape and the type of associated secretory cells. Overall there was a phylogenetic trend: Ensuing from the large MGs and small PPGs of male Cercerini and Aphilanthopsini, the size and complexity of the MG was reduced in male Philanthini, while their PPG became considerably enlarged, substantially more complex, and associated with an apparently novel type of secretory cells. In some clades of the Philanthini the MG was even lost and entirely replaced by the PPG. However, several species showed reversals of and exceptions from this trend. Head gland morphology was significantly more diverse among male than among female Philanthinae.

Conclusion

Our results show considerable variation in male head glands including the loss of an entire gland system and the evolution of a novel kind of secretory cells, confirming the prediction that interspecific diversity in head gland morphology is higher in male than in female Philanthini. We discuss possible causes for the remarkable evolutionary changes in males and we conclude that this high diversity has been caused by sexual selection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-017-0963-6) contains supplementary material, which is available to authorized users.

Changes in segmentation and setation along the anterior/posterior axis of the homonomous trunk limbs of a remipede (Crustacea, Arthropoda)

This study describes the segmentation and setation at different developmental stages of the homonomous trunk limbs of the remipede Speleonectes tulumensisYager, 1987 collected in anchialine caves of the Yucatan Peninsula. Most homonomous trunk limbs originate ventrolaterally and are composed of two protopodal segments, three exopodal segments and four endopodal segments; contralateral limb pairs are united by a sternal bar. However, the last few posterior limbs originate ventrally, are smaller sized, and have regressively fewer segments, suggesting that limb development passes through several intermediate steps beginning with a limb bud. A terminal stage of development is proposed for specimens on which the posterior somite bears a simple bilobate limb bud, and the adjacent somite bears a limb with a protopod comprised of a coxapod and basipod, and with three exopodal and four endopodal segments. On each trunk limb there are 20 serially homologous groups of setae, and the numbers of setae on different limbs usually varies. These groups of setae are arranged linearly and are identified based on the morphology of the setae and their position on the segments. The number of setae in these groups increases gradually from the anterior homonomous limb to a maximum between limbs 8–12; the number then decreases sharply on the more posterior limbs. Changes in the number of setae, which reach a maximum between trunk limbs 8–12, differ from changes in segmentation which vary only over the last few posterior trunk limbs. Following a vector analysis that identified a spatial pattern for these 20 groups of setae among the different homonomous limbs, the hypothesis was confirmed that the number of setae in any given group and any given limb is correlated with the group, with the position of the somite along the body axis, and with the number of somites present on the specimens. This is the first vector analysis used to analyze a pattern of developmental changes in serially homologs of an arthropod. Development of remipede limbs are compared and contrasted with similar copepod limbs. Architecture, particularly the sternal bar uniting contralateral limb pairs, proposed as homologous, and development of trunk limb segmentation of the remipede is generally similar to that of copepods, but the remipede limb differs in several ways including an additional endopodal segment, the proximal, that appears simultaneously with the protopod during development.

Mesoscale morphology at nanoscale resolution: serial block-face scanning electron microscopy reveals fine 3D detail of a novel silk spinneret system in a tube-building tanaid crustacean

Background

The study of morphology is experiencing a renaissance due to rapid improvements in technologies for 3D visualization of complex internal and external structures. But 3D visualization of the internal structure of mesoscale objects — those in the 10–1000 μm range — remains problematic. They are too small for microCT, many lack suitable specific fluorescent markers for confocal microscopy, or they require labor-intensive stacking and smoothing of individual TEM images. Here we illustrate the first comprehensive morphological description of a complete mesoscale biological system at nanoscopic resolution using ultra-modern technology for 3D visualization — serial block-face scanning electron microscopy (SBF-SEM). The SBF-SEM machine combines an in-chamber ultramicrotome, which creates a serial array of exposed surfaces, with an SEM that images each surface as it is exposed. The serial images are then stacked automatically by 3D reconstruction software. We used SBF-SEM to study the spinneret (thread-producing) system of a small, tube-dwelling crustacean that weaves tubes of silk. Thread-producing ability is critical for the survival of many small-bodied animals but the basic morphology of these systems remains mysterious due to the limits of traditional microscopy.

Results

SBF-SEM allowed us to describe — in full 3D — well-resolved components (glands, ducts, pores, and associated nerves and muscles) of the spinneret system in the thoracic legs and body segments of Sinelobus sp. (Crustacea, Peracarida, Tanaidacea), a tube-building tanaid only 2 mm in body length. The 3D reconstruction by SBF-SEM revealed at nanoscale resolution a unique structure to the gland and duct systems: In each of three thread-producing thoracic segments, two separate ducts, derived from two separate glands located in the body, run through the entire leg and merge at the leg tip just before the spinneret pore opening. We also resolved nerves connecting to individual setae, spines and pores on the walking legs, and individual muscles within each leg segment.

Conclusions

Our results significantly expand our understanding of the diversity of spinneret systems in the Crustacea by providing the first well-resolved view of spinneret components in the peracarid crustacean order, Tanaidacea. More significantly, our results reveal the great power of SBF-SEM technology for comprehensive studies of the morphology of microscopic animals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-016-0146-0) contains supplementary material, which is available to authorized users.

Comparative morphology of the reproductive system and germ cells of Amblyomma ticks (Acari: Ixodidae): A contribution to Ixodidae systematics

Among arthropods, ticks of the genus Amblyomma are of great medical and veterinary importance and present phylogenetic and taxonomic divergences given polymorphisms and phenotypic plasticity between subpopulations. Generally, the male reproductive system and spermatozoon exhibit diversified morphology and ultrastructure species-specific, bringing new possibilities for phylogenetic and taxonomic issues. Therefore, the present study aimed to describe and compare the morphology of the male reproductive system and its germ cells of Amblyomma aureolatum, A. sculptum, and A. triste, intending to identify possible diagnostic features. Couples of the three tick's species were kept in colony, infested on rabbits and collected over 12 days of feeding. The males had their reproductive systems dissected, fixed and processed for histology and scanning electron microscopy. The results obtained here allowed the description of spermiogenesis stages and the comparison of spermatids morphology in the last stage of development. Furthermore, the testis of A. triste present an isthmus connecting the distal region of both, while in the other two species this structure could not be observed. Some anatomical features were identified which can be used for taxonomic and phylogenetic studies, like the presence or absence of the isthmus connecting testis, spV cell shape, the shape of the operculum and the presence or absence of the rim on its base.

Fine taxonomic sampling of nervous systems within Naididae (Annelida: Clitellata) reveals evolutionary lability and revised homologies of annelid neural components

Introduction

An important goal for understanding how animals have evolved is to reconstruct the ancestral features and evolution of the nervous system. Many inferences about nervous system evolution are weak because of sparse taxonomic sampling and deep phylogenetic distances among species compared. Increasing sampling within clades can strengthen inferences by revealing which features are conserved and which are variable within them. Among the Annelida, the segmented worms, the Clitellata are typically considered as having a largely conserved neural architecture, though this view is based on limited sampling.

Results

To gain better understanding of nervous system evolution within Clitellata, we used immunohistochemistry and confocal laser scanning microscopy to describe the nervous system architecture of 12 species of the basally branching family Naididae. Although we found considerable similarity in the nervous system architecture of naidids and that of other clitellate groups, our study identified a number of features that are variable within this family, including some that are variable even among relatively closely related species. Variable features include the position of the brain, the number of ciliary sense organs, the presence of septate ventral nerve cord ganglia, the distribution of serotonergic cells in the brain and ventral ganglia, and the number of peripheral segmental nerves.

Conclusions

Our analysis of patterns of serotonin immunoreactive perikarya in the central nervous system indicates that segmental units are not structurally homogeneous, and preliminary homology assessments suggest that whole sets of serotonin immunoreactive cells have been gained and lost across the Clitellata. We also found that the relative position of neuroectodermal and mesodermal segmental components is surprisingly evolutionarily labile; in turn, this revealed that scoring segmental nerves by their position relative to segmental ganglia rather than to segmental septa clarifies their homologies across Annelida. We conclude that fine taxonomic sampling in comparative studies aimed at elucidating the evolution of morphological diversity is fundamental for proper assessment of trait variability.

Electronic supplementary material

The online version of this article (doi:10.1186/s12983-015-0100-6) contains supplementary material, which is available to authorized users.

Rotator cuff muscle size and the interpretation of scapular shape in primates

Scapular shape variation among primates is widely viewed as being strongly related to locomotor differences. The relative importance of overhead forelimb elevation in the locomotor repertoire of a species, as reflected in muscular leverage for scapular rotation or in the sizes of attachment areas for muscles involved in glenohumeral elevation, has proven to be a useful organizing principle for understanding this variation. While generally successful in sorting primate scapulae into functional groups, the scapulae of some species do not entirely match predictions based on the perceived importance of forelimb elevation. A recent study has shown that scapular fossa sizes in apes are not as accurate predictors of the sizes of the muscles arising from them as has been assumed. To further explore the degree of correspondence between actual and predicted muscle size based on the perceived importance of forelimb elevation, the current study examines the relative sizes of the rotator cuff muscles in a wider sample of primate taxa using published data on muscle mass and cross-sectional area. The results do not support some of the accepted generalizations about the relative sizes of members of the rotator cuff based on measurements of the sizes of scapular fossae. For example, orthograde apes do not display enlarged supraspinatus muscles compared to pronograde monkeys. Differences in assessments of relative muscle size based on mass compared to those based on cross-sectional area suggest that poor correspondence between muscle size predicted from scapular fossa size and actual muscle size may be related to constraints on scapular form associated with muscular leverage for scapular rotation and with scapular position on the thorax.

Development of the splanchnocranium in Prochilodus argenteus (Teleostei: Characiformes) with a discussion of the basal developmental patterns in the Otophysi

Development of the mandibular, hyoid and gill arches, which constitute the splanchnocranium, are described for Prochilodus argenteus, order Characiformes, one of the basal lineages of the Otophysi. Development was examined from just hatched larvae through juveniles using whole specimens cleared and counterstained for cartilage and bone as well as histological preparations. Observations are compared with the developmental trends reported for Cypriniformes, the basalmost clade of the Otophysi. Shortened developmental sequences for Prochilodus compared to the cypriniform Catostomus were discovered in the ontogeny of the ceratohyals, ceratobranchials 1-5, epibranchials 1-4 and the symplectic portion of the hyosymplectic. Prochilodus also differs from Catostomus in having the basihyal plus the anterior copula appearing at different stages of ontogeny rather than simultaneously. Contrary to previous assumptions, developmental information indicates that hypobranchial 4 as well as likely basibranchial 5 are present in Prochilodus. Various developmental patterns in Prochilodus considered basal for the Otophysi, the predominant component of the Ostariophysi, are likely conserved from patterns prevalent in basal groups in the Actinopterygii.

Holoparasitic Rafflesiaceae possess the most reduced endophytes and yet give rise to the world's largest flowers

BACKGROUND AND AIMS

Species in the holoparasitic plant family Rafflesiaceae exhibit one of the most highly modified vegetative bodies in flowering plants. Apart from the flower shoot and associated bracts, the parasite is a mycelium-like endophyte living inside their grapevine hosts. This study provides a comprehensive treatment of the endophytic vegetative body for all three genera of Rafflesiaceae (Rafflesia, Rhizanthes and Sapria), and reports on the cytology and development of the endophyte, including its structural connection to the host, shedding light on the poorly understood nature of this symbiosis.

METHODS

Serial sectioning and staining with non-specific dyes, periodic-Schiff's reagent and aniline blue were employed in order to characterize the structure of the endophyte across a phylogenetically diverse sampling.

KEY RESULTS

A previously identified difference in the nuclear size between Rafflesiaceae endophytes and their hosts was used to investigate the morphology and development of the endophytic body. The endophytes generally comprise uniseriate filaments oriented radially within the host root. The emergence of the parasite from the host during floral development is arrested in some cases by an apparent host response, but otherwise vegetative growth does not appear to elicit suppression by the host.

CONCLUSIONS

Rafflesiaceae produce greatly reduced and modified vegetative bodies even when compared with the other holoparasitic angiosperms once grouped with Rafflesiaceae, which possess some vegetative differentiation. Based on previous studies of seeds together with these findings, it is concluded that the endophyte probably develops directly from a proembryo, and not from an embryo proper. Similarly, the flowering shoot arises directly from the undifferentiated endophyte. These filaments produce a protocorm in which a shoot apex originates endogenously by formation of a secondary morphological surface. This degree of modification to the vegetative body is exceptional within angiosperms and warrants additional investigation. Furthermore, the study highlights a mechanical isolation mechanism by which the host may defend itself from the parasite.