The utility of micro-computed tomography for the non-destructive study of eye microstructure in snails

Molluscan eyes exhibit an enormous range of morphological variation, ranging from tiny pigment-cup eyes in limpets, compound eyes in ark clams and pinhole eyes in Nautilus, through to concave mirror eyes in scallops and the large camera-type eyes of the more derived cephalopods. Here we assess the potential of non-destructive micro-computed tomography (µ-CT) for investigating the anatomy of molluscan eyes in three species of the family Solariellidae, a group of small, deep-sea gastropods. We compare our results directly with those from traditional histological methods applied to the same specimens, and show not only that eye microstructure can be visualised in sufficient detail for meaningful comparison even in very small animals, but also that μ-CT can provide additional insight into gross neuroanatomy without damaging rare and precious specimens. Data from μ-CT scans also show that neurological innervation of eyes is reduced in dark-adapted snails when compared with the innervation of cephalic tentacles, which are involved in mechanoreception and possibly chemoreception. Molecular tests also show that the use of µ-CT and phosphotungstic acid stain do not prevent successful downstream DNA extraction, PCR amplification or sequencing. The use of µ-CT methods is therefore highly recommended for the investigation of difficult-to-collect or unique specimens.Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. The attached file is the published pdf

Ontogenetic changes in the body plan of the sauropodomorph dinosaur Mussaurus patagonicus reveal shifts of locomotor stance during growth

Ontogenetic information is crucial to understand life histories and represents a true challenge in dinosaurs due to the scarcity of growth series available. Mussaurus patagonicus was a sauropodomorph dinosaur close to the origin of Sauropoda known from hatchling, juvenile and mature specimens, providing a sufficiently complete ontogenetic series to reconstruct general patterns of ontogeny. Here, in order to quantify how body shape and its relationship with locomotor stance (quadruped/biped) changed in ontogeny, hatchling, juvenile (~1 year old) and adult (8+ years old) individuals were studied using digital models. Our results show that Mussaurus rapidly grew from about 60 g at hatching to ~7 kg at one year old, reaching >1000 kg at adulthood. During this time, the body’s centre of mass moved from a position in the mid-thorax to a more caudal position nearer to the pelvis. We infer that these changes of body shape and centre of mass reflect a shift from quadrupedalism to bipedalism occurred early in ontogeny in Mussaurus. Our study indicates that relative development of the tail and neck was more influential in determining the locomotor stance in Sauropodomorpha during ontogeny, challenging previous studies, which have emphasized the influence of hindlimb vs. forelimb lengths on sauropodomorph stance

Flying Squirrel–associated Typhus, United States

In March 2002, typhus fever was diagnosed in two patients residing in West Virginia and Georgia. Both patients were hospitalized with severe febrile illnesses, and both had been recently exposed to or had physical contact with flying squirrels or flying squirrel nests. Laboratory results indicated Rickettsia prowazekii infection

Flying Squirrel–associated Typhus, United States

In March 2002, typhus fever was diagnosed in two patients residing in West Virginia and Georgia. Both patients were hospitalized with severe febrile illnesses, and both had been recently exposed to or had physical contact with flying squirrels or flying squirrel nests. Laboratory results indicated Rickettsia prowazekii infection

Evolution in the dark: unifying our understanding of eye loss

The evolution of eye loss in subterranean, deep sea and nocturnal habitats has fascinated biologists since Darwin wrestled with it in On the Origin of Species. This phenomenon appears consistently throughout the animal kingdom, in groups as diverse as crustaceans, salamanders, gastropods, spiders and the well-known Mexican cave fish, but the nature, extent and evolutionary processes behind eye loss remain elusive. With the advantage of new imaging, molecular, and developmental tools, eye loss has once again become the subject of intense research focus. To advance our understanding of eye loss as a taxonomically widespread and repeated evolutionary trajectory, we organized a cross-disciplinary group of researchers working on the historic question, ‘how does eye loss evolve in the dark?’. The resulting set of papers showcase new progress made in understanding eye loss from the diverse fields of molecular biology, phylogenetics, development, comparative anatomy, paleontology, ecology and behaviour in a wide range of study organisms and habitats. Through the integration of these approaches, methods and results, common themes begin to emerge across the field. For the first time, we hope researchers can exploit this new synthesis to identify the broader challenges and key evolutionary questions surrounding eye evolution and so-called regressive evolution and collectively work to address them in future research

Do chitons have a brain? New evidence for diversity and complexity in the polyplacophoran central nervous system

Molluscs demonstrate an astonishing degree of morphological diversity, and the relationships among molluscan clades have been debated for more than a century. Molluscan nervous systems range from simple 'ladder-like' arrangements of nerve cords to the complex brains of cephalopods. Chitons (Polyplacophora) are assumed to retain many molluscan plesiomorphies, lacking neural condensation and ganglionic structure, and therefore a brain. We reconstructed three-dimensional anatomical models of the nervous system in eight species of chitons in an attempt to clarify chiton neuroarchitecture and its variability. The specimen material incorporated both new data and digitised historic slide material originally used in the work of malacologist Johannes Thiele (1860-1935). Reconstructions of whole nervous systems in Acanthochitona fascicularis, Callochiton septemvalvis, Chiton olivaceus, Hemiarthrum setulosum, Lepidochitona cinerea, Lepidopleurus cajetanus, and Leptochiton asellus, and the anterior nervous system of Schizoplax brandtii, demonstrated a consistent and substantial anterior concentration of nervous tissue in the circumoesophageal nerve ring. This neural mass is further organised into three concentric tracts, corresponding to the paired lateral, ventral, and (putatively) cerebral nerve cords. These represent homologues to the three main pairs of ganglia found in other molluscs. The relative size, shape and organisation of these components is highly variable among the examined taxa, but consistent with previous studies of select species, and we formulated a set of neuroanatomical characters for chitons. These characters are parsimony-informative for reconstructing chiton phylogeny at the ordinal and subordinal levels; the identification of robust detailed homologies in neural architecture will be central to future comparisons among all molluscs, and more broadly in Lophotrochozoa. Modern evolutionary thinking, and modern tomographic technology, bring new light to an old problem. Contrary to almost all previous descriptions, the size and structure of the chiton anterior nerve ring unambiguously qualify it as a true brain with cordal substructure

Evolution in the dark: unifying our understanding of eye loss

The evolution of eye loss in subterranean, deep sea and nocturnal habitats has fascinated biologists since Darwin wrestled with it in On the Origin of Species. This phenomenon appears consistently throughout the animal kingdom, in groups as diverse as crustaceans, salamanders, gastropods, spiders and the well-known Mexican cave fish, but the nature, extent and evolutionary processes behind eye loss remain elusive. With the advantage of new imaging, molecular, and developmental tools, eye loss has once again become the subject of intense research focus. To advance our understanding of eye loss as a taxonomically widespread and repeated evolutionary trajectory, we organized a cross-disciplinary group of researchers working on the historic question, ‘how does eye loss evolve in the dark?’. The resulting set of papers showcase new progress made in understanding eye loss from the diverse fields of molecular biology, phylogenetics, development, comparative anatomy, paleontology, ecology and behaviour in a wide range of study organisms and habitats. Through the integration of these approaches, methods and results, common themes begin to emerge across the field. For the first time, we hope researchers can exploit this new synthesis to identify the broader challenges and key evolutionary questions surrounding eye evolution and so-called regressive evolution and collectively work to address them in future research

Continuous and regular expansion of a distributed visual system in the eyed chiton Tonicia lebruni Rocheburne, 1884

Chitons have a distinctive armature of eight articulating dorsal shells. In all living species, the shell valves are covered by a dense array of sensory pores called aesthetes; but in some taxa, a subset of these are elaborated into lensed eyes, which are capable of spatial vision. We collected a complete ontogenetic series of the eyed chiton Tonicia lebruni de Rochebrune, 1884 to examine the growth of this visual network and found that it expands continuously as eyes are added at the margin during shell growth. Our dataset ranged from a 2.58-mm juvenile with only 16 eyes to adults of 25–31 mm with up to 557 eyes each. This allowed us to investigate the organization (and potential constraints therein) of these sensory structures and their development. Chiton eyes are constrained to a narrowly defined region of the shell, and data from T. lebruni indicate that they are arranged roughly bilaterally symmetrically. We found deviations from symmetry of up to 10%, similar to irregularity reported in some other animals with multiplied eyes. Distances separating successive eyes indicate that, while shell growth slows during the life of an individual chiton, eyes are generated at regular time intervals. Although we could not identify a specific eye-producing tissue or organ, we propose that the generation of new eyes is controlled by a clock-like mechanism with a stable periodicity. The apparent regularity and organization of the chiton visual system are far greater than previously appreciated. This does not imply the integration of shell eyes to form composite images, but symmetry and regular organization could be equally beneficial to a highly duplicated system by ensuring even and comprehensive sampling of the total field of view