Species- and sex-specific chemical composition from an internal gland-like tissue of an African frog family.

Intraspecific chemical communication in frogs is understudied and the few published cases are limited to externally visible and male-specific breeding glands. Frogs of the family Odontobatrachidae, a West African endemic complex of five morphologically cryptic species, have large, fatty gland-like strands along their lower mandible. We investigated the general anatomy of this gland-like strand and analysed its chemical composition. We found the strand to be present in males and females of all species. The strand varies in markedness, with well-developed strands usually found in reproductively active individuals. The strands are situated under particularly thin skin sections, the vocal sac in male frogs and a respective area in females. Gas-chromatography/mass spectrometry and multivariate analysis revealed that the strands contain sex- and species-specific chemical profiles, which are consistent across geographically distant populations. The profiles varied between reproductive and non-reproductive individuals. These results indicate that the mandibular strands in the Odontobatrachidae comprise a so far overlooked structure (potentially a gland) that most likely plays a role in the mating and/or breeding behaviour of the five Odontobatrachus species. Our results highlight the relevance of multimodal signalling in anurans, and indicate that chemical communication in frogs may not be restricted to sexually dimorphic, apparent skin glands.

Cellular development and evolution of the mammalian cerebellum.

The expansion of the neocortex, a hallmark of mammalian evolution1,2, was accompanied by an increase in cerebellar neuron numbers3. However, little is known about the evolution of the cellular programmes underlying the development of the cerebellum in mammals. In this study we generated single-nucleus RNA-sequencing data for around 400,000 cells to trace the development of the cerebellum from early neurogenesis to adulthood in human, mouse and the marsupial opossum. We established a consensus classification of the cellular diversity in the developing mammalian cerebellum and validated it by spatial mapping in the fetal human cerebellum. Our cross-species analyses revealed largely conserved developmental dynamics of cell-type generation, except for Purkinje cells, for which we observed an expansion of early-born subtypes in the human lineage. Global transcriptome profiles, conserved cell-state markers and gene-expression trajectories across neuronal differentiation show that cerebellar cell-type-defining programmes have been overall preserved for at least 160 million years. However, we also identified many orthologous genes that gained or lost expression in cerebellar neural cell types in one of the species or evolved new expression trajectories during neuronal differentiation, indicating widespread gene repurposing at the cell-type level. In sum, our study unveils shared and lineage-specific gene-expression programmes governing the development of cerebellar cells and expands our understanding of mammalian brain evolution.

Lacunae rostralis: A new structure on the rostrum of sailfish Istiophorus platypterus.

Recent comparative studies of billfishes (Istiophoridae and Xiphiidae) have provided evidence of differences in the form and function of the rostra (bill) among species. Here, we report the discovery of a new structure, lacuna rostralis, on the rostra of sailfish Istiophorus platypterus, which is absent on the rostra of swordfish Xiphias gladius, striped marlin Kajikia audax and blue marlin Makaira nigricans. The lacunae rostralis are small cavities that contain teeth. They were found on the ventral rostrum surface of all I. platypterus specimens examined and dorsally in half of them. Ventrally, the lacunae rostralis were most prominent in the mid-section of the rostrum. Dorsally, they occurred closer to the tip. The density of lacunae rostralis increased towards the rostrum tip but, because they are smaller in size, the percentage of rostrum coverage decreased. The teeth located within the lacunae rostralis were found to be different in size, location and orientation from the previously identified micro-teeth of billfish. We propose two potential functions of the lacunae rostralis that both relate to the use of the bill in feeding: mechanoreception of prey before tapping it with the bill and more efficient prey handling via the creation of suction, or physical grip.

Roots Structure and Development of Austrobaileya scandens (Austrobaileyaceae) and Implications for Their Evolution in Angiosperms.

Abstract: Since the resolution of the ANA grade [Amborellales, Nymphaeales, Austrobaileyales] as sister to all other flowering plants, a few comparative studies of root structure have suggested that some of their anatomical traits could be of importance to understanding root evolutionary development and angiosperm phylogeny. However, there is still a paucity of information on root structure and apical meristems (RAMs) in these lineages and especially the sister to all other Austrobaileyales, Austrobaileya scandens. We used microtome sections and bright field, epifluorescence, laser confocal, and scanning electron microscopy to study adventitious root RAMs and tissues of A. scandens. Our results indicate that root structure is relatively simple in A. scandens. The epidermis has a thick cuticle and lacks root hairs. The stele is typically diarch, or some modification thereof, and surrounded by a cortex differentiated into a uniseriate endodermis, a middle region sometimes packed with starch, some oil cells, and colonized by arbuscular mycorrhizal fungi, and a multiseriate exodermis. Secondary growth produced many vessel elements in the secondary xylem and scattered sclerenchymatous fibers in secondary phloem. The absence of distinct patterning within the RAM and between the RAM and derivative differentiating tissues shows that the RAM is open and characterized by common initials. Roots structure and anatomy of A. scandens are thus essentially similar to some previously described in Amborella or Illicium in the ANA grade and many magnoliids, and suggest that the first woody flowering plants likely had an open RAM with common initials. Their functional and evolutionary significance in woody early-diverging and basal lineages of flowering plants and gymnosperms remains unclear, but they are clearly ancestral traits.

Refinement of the dopaminergic system of anuran amphibians based on connectivity with habenula, basal ganglia, limbic system, pallium, and spinal cord.

Whereas our understanding of the dopaminergic system in mammals allows for a distinction between ventral tegmental area (VTA) and substantia nigra pars compacta (SNc), no clear evidence for separate structures in anamniotes has been presented to date. To broaden the insight into the organization and regulation of neuromodulatory systems in anuran amphibians, tracing and immunohistochemical investigations were performed in the Oriental fire-bellied toad, Bombina orientalis. Topographically organized catecholaminergic "nigrostriatal," "mesolimbic," "mesocortical," and spinal cord projections arising from the posterior tubercle and mesencephalic tegmentum were identified. We compared these results with published data from lampreys, chondrichthyes, teleosts, amphibians, reptiles, birds, and mammals. Based on the pattern of organization, as well as the differential innervation by the habenular nuclei, domains gradually comparable to the mammalian paranigral VTA, ventral tier of the SNc, interfascicular nucleus of the VTA, and supramamillary/retromamillary area were identified. Additionally, we could demonstrate topographic separate populations of habenula neurons projecting via a direct excitatory or indirect GABAergic pathway onto the catecholaminergic VTA/SNc homologs and serotonergic raphe nuclei. The indirect GABAergic habenula pathway derives from neurons in the superficial mamillary area, which in terms of its connectivity and chemoarchitecture resembles the mammalian rostromedial tegmental nucleus. These results demonstrate a much more elaborate interconnection principle of the anuran dopaminergic system than previously assumed. Based on the data presented it seems that most features of the dopaminergic system of amniotes had already evolved when the amphibian line of evolution diverged from that leading up to mammals, reptiles, and birds.

Individual Dopaminergic Neurons of Lamprey SNc/VTA Project to Both the Striatum and Optic Tectum but Restrict Co-release of Glutamate to Striatum Only.

Dopaminergic neurons in the substantia nigra (SNc) innervate both striatum and the superior colliculus in mammals, as well as its homolog the optic tectum in lampreys, belonging to the oldest group of living vertebrates [1-3]. In the lamprey, we have previously shown that the same neuron sends axonal branches to both striatum and the optic tectum [3]. Here, we show that most neurons in the lamprey SNc and ventral tegmental area (VTA) (also referred to as the nucleus of the posterior tuberculum) express not only tyrosine hydroxylase (TH), in lamprey a marker of dopaminergic neurons [4], but also the vesicular glutamate transporter (vGluT), suggesting that glutamate is a co-transmitter. Remarkably, the axonal branches that project to striatum elicit both dopaminergic and glutamatergic synaptic effects on striatal neurons, whereas the axonal projections to the optic tectum only evoke dopaminergic effects. Thus, axonal branches from the same neuron can use two transmitters in one branch and only one in the other. Previous studies suggest that, along an individual dopaminergic axon, there can be microdomains of either TH or vGluT [5-8]. In addition, the present results demonstrate that entire axonal branches to one target structure can differ from that of branches to another target, both originating from the same dopamine neuron. This implies that a given dopamine neuron can exert different effects on two different target structures. The combined release of dopamine and glutamate may be appropriate in striatum, whereas the effects exerted on the tectal motor center may be better served with a selective dopaminergic modulation.