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1.
Cell Tissue Res ; 377(3): 415-443, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31270611

RESUMO

The digestive system of the malacostracan crustaceans, namely the decapods, isopods, amphipods and mysids, is among the most complex organ systems of the animal kingdom serving multiple functions such as food processing, absorption and storage of nutrients, synthesis of digestive enzymes and blood proteins, detoxification of xenobiotics and osmoregulation. It is rather well investigated compared to other invertebrates because the Malacostraca include many ecological keystone species and food items for humans. The Decapoda and Peracarida share food processing with chewing and filtering structures of the stomach but differ with respect to morphology and ultrastructure of the digestive glands. In the Peracarida, the digestive glands are composed of few, relatively large lateral caeca, whereas in the Decapoda, hundreds to thousands of blindly ending tubules form a voluminous hepatopancreas. Morphogenesis and onset of functionality of the digestive system strongly depend on the mode of development. The digestive system is early developed in species with feeding planktonic larvae and appears late in species with direct lecithotrophic development. Some structures of the digestive system like the stomach ossicles are rather constant in higher taxa and are of taxonomic value, whereas others like the chewing structures are to some degree adapted to the feeding strategy. The nutrient absorbing and storing cells of the digestive glands show considerable ultrastructural variation during moult cycle, vitellogenesis and starvation. Some of the various functions of the digestive system are already assigned to specific sections of the digestive tract and cell types, but others still await precise localization.


Assuntos
Crustáceos/anatomia & histologia , Crustáceos/fisiologia , Trato Gastrointestinal/anatomia & histologia , Trato Gastrointestinal/crescimento & desenvolvimento , Animais , Morfogênese
2.
Philos Trans A Math Phys Eng Sci ; 377(2138): 20180267, 2019 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-30967062

RESUMO

Many myodocopid ostracods are unusual in that they have well-developed compound eyes yet must view their environment through a shell. The cypridinid Macrocypridina castanea is relatively large among ostracods (about 5-10 mm) and is a pelagic predator. This species possess highly pigmented shells with a transparent region lying just above the eye. Here we examine the ultrastructure and transparency of this window using electron microscopy, serial-block face scanning electron microscopy and X-ray diffraction analysis and optical modelling. An internal, laminar stack was identified within the window region of the shell that formed a more regular half-wave reflector than in non-window regions, and where the distance between molecules in the chitin-protein fibrils decreases as compared to the non-window area. This results in excellent transmission properties-at around 99% transmission-for wavelengths between 350 and 630 nm due to its half-wave reflector organization. Therefore, blue light, common in the mid and deep sea, where this species inhabits, would be near-optimally transmitted as a consequence of the sub-micrometre structuring of the shell, thus optimizing the ostracod's vision. Further, pore canals were identified in the shell that may secrete substances to prevent microbial growth, and subsequently maintain transparency, on the shell surface. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology'.


Assuntos
Crustáceos/anatomia & histologia , Olho , Fenômenos Ópticos , Exoesqueleto/anatomia & histologia , Animais , Feminino
3.
Curr Biol ; 29(1): 171-177.e1, 2019 01 07.
Artigo em Inglês | MEDLINE | ID: mdl-30595518

RESUMO

Pancrustaceans boast impressive diversity, abundance, and ecological impact in the biosphere throughout the Phanerozoic [1]. Molecular clock estimates suggest an early Cambrian divergence for pancrustaceans [2, 3]. Despite the wealth of Palaeozoic exceptional fossiliferous deposits [4-7], the early evolution of Pancrustacea remains elusive given the difficulty of recognizing synapomorphies between Cambrian forms and extant representatives. Although early studies suggested crustacean affinities for Cambrian bivalved euarthropods [8-11], this view has fallen out of favor by recent reappraisals of their morphology [12-16]. The best evidence for total-group pancrustaceans comes from Cambrian microfossils preserved as three-dimensional phosphatic replicates in Orsten-type assemblages [4, 17-19] or as "small carbonaceous fossils" (SCFs) [20, 21]. Although these taphonomic windows capture minute morphology enabling detailed comparisons with extant representatives, these microfossils are limited to larval stages (Orsten) or recalcitrant fragmentary remains (SCFs) restricting their phylogenetic precision [5, 12, 19, 20, 22, 23]. We employed X-ray computed tomography [24] to reveal the three-dimensionally appendage morphology of the Chengjiang bivalved euarthropod Ercaicunia multinodosa [25] from the early Cambrian of China. E. multinodosa possesses characters uniquely shared with extant crustaceans, including differentiated tritocerebral antennae and epipodite-bearing biramous trunk appendages. Similarities between E. multinodosa with clypecaridids [9], waptiids [16] and hymenocarines [11, 14] suggest that these euarthropods may also possess similarly differentiated appendages, but these details are obstructed by the limits of preservation of compacted macrofossils. E. multinodosa illuminates the early evolution of pancrustacean appendage differentiation and represents the oldest unequivocal crown-group mandibulate known from complete macrofossils [22].


Assuntos
Evolução Biológica , Crustáceos/anatomia & histologia , Extremidades/anatomia & histologia , Fósseis/anatomia & histologia , Animais , China , Crustáceos/crescimento & desenvolvimento , Larva/anatomia & histologia , Larva/crescimento & desenvolvimento , Filogenia , Tomografia Computadorizada por Raios X
4.
Sci Rep ; 8(1): 17876, 2018 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-30552339

RESUMO

Intensive trawling activities in Hong Kong waters have seriously depleted fishery resources and damaged marine benthic habitats over the last four decades. To minimize further destruction and rehabilitate fishery resources, the Hong Kong Government implemented a permanent territory-wide trawling closure on 31 December 2012. Such a trawl ban creates a unique opportunity to investigate recoveries in ecosystem structure and function following a major shift in disturbance regime by removing impacts from a major gear. This study was designed to test the hypothesis that dominant predatory mantis shrimps, including Harpiosquilla harpax, Miyakella nepa, Oratosquillina interrupta, and Oratosquilla oratoria would show signs of recovery following the trawl ban. Their population dynamics were investigated before and after the trawl ban. The results showed that their mean weight, mean carapace length and proportion of large-sized individuals increased significantly 3.5 years after the trawl ban, whilst their abundance, biomass and maximum length remained unchanged. This study suggests that the stomatopod assemblage in the human-dominated Hong Kong waters shows some initial signs of possible recovery following the trawl ban but also highlights the complexity of implementing fishery management and detecting changes resulted from management measures in a heavily urbanized seascape where many biotic and abiotic factors can influence their population dynamics.


Assuntos
Organismos Aquáticos/crescimento & desenvolvimento , Crustáceos/crescimento & desenvolvimento , Ecossistema , Atividades Humanas , Dinâmica Populacional , Animais , Biomassa , Biometria , Tamanho Corporal , Peso Corporal , Conservação dos Recursos Naturais , Crustáceos/anatomia & histologia , Hong Kong , Água do Mar
5.
Biol Lett ; 14(11)2018 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-30404865

RESUMO

Ostracod crustaceans are diverse and ubiquitous in aqueous environments today but relatively few known species have gills. Ostracods are the most abundant fossil arthropods but examples of soft-part preservation, especially of gills, are exceptionally rare. A new ostracod, Spiricopia aurita (Myodocopa), from the marine Silurian Herefordshire Lagerstätte (430 Mya), UK, preserves appendages, lateral eyes and gills. The respiratory system includes five pairs of gill lamellae with hypobranchial and epibranchial canals that conveyed haemolymph. A heart and associated vessels had likely evolved in ostracods by the Mid-Silurian.


Assuntos
Crustáceos/anatomia & histologia , Fósseis/anatomia & histologia , Animais , Crustáceos/classificação , Inglaterra , Sistema Respiratório/anatomia & histologia
6.
Arthropod Struct Dev ; 47(6): 563-613, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30419291

RESUMO

No consensus exists for the homology and terminology of the male genitalia of the Hexapoda despite over a century of debate. Based on dissections and the literature, genital skeletomusculature was compared across the Hexapoda and contrasted with the Remipedia, the closest pancrustacean outgroup. The pattern of origin and insertion for extrinsic and intrinsic genitalic musculature was found to be consistent among the Ectognatha, Protura, and the Remipedia, allowing for the inference of homologies given recent phylogenomic studies. The penis of the Hexapoda is inferred to be derived from medially-fused primary gonopods (gonopore-bearing limbs), while the genitalia of the Ectognatha are inferred to include both the tenth-segmental penis and the ninth-segmental secondary gonopods, similar to the genitalia of female insects which comprise gonopods of the eighth and ninth segments. A new nomenclatural system for hexapodan genitalic musculature is presented and applied, and a general list of anatomical concepts is provided. Novel and refined homologies are proposed for all hexapodan orders, and a series of groundplans are postulated. Emphasis is placed on the Endopterygota, for which fine-grained transition series are hypothesized given observed skeletomuscular correspondences.


Assuntos
Artrópodes/anatomia & histologia , Evolução Biológica , Animais , Crustáceos/anatomia & histologia , Feminino , Genitália/anatomia & histologia , Insetos/anatomia & histologia , Masculino , Filogenia , Terminologia como Assunto
7.
Elife ; 72018 08 09.
Artigo em Inglês | MEDLINE | ID: mdl-30091704

RESUMO

The influence of biomechanics on the tempo and mode of morphological evolution is unresolved, yet is fundamental to organismal diversification. Across multiple four-bar linkage systems in animals, we discovered that rapid morphological evolution (tempo) is associated with mechanical sensitivity (strong correlation between a mechanical system's output and one or more of its components). Mechanical sensitivity is explained by size: the smallest link(s) are disproportionately affected by length changes and most strongly influence mechanical output. Rate of evolutionary change (tempo) is greatest in the smallest links and trait shifts across phylogeny (mode) occur exclusively via the influential, small links. Our findings illuminate the paradigms of many-to-one mapping, mechanical sensitivity, and constraints: tempo and mode are dominated by strong correlations that exemplify mechanical sensitivity, even in linkage systems known for exhibiting many-to-one mapping. Amidst myriad influences, mechanical sensitivity imparts distinct, predictable footprints on morphological diversity.


Assuntos
Evolução Biológica , Fenômenos Biomecânicos , Crustáceos/anatomia & histologia , Peixes/anatomia & histologia , Animais
8.
Nature ; 556(7701): 366-369, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29643505

RESUMO

Sexual selection favours traits that confer advantages in the competition for mates. In many cases, such traits are costly to produce and maintain, because the costs help to enforce the honesty of these signals and cues 1 . Some evolutionary models predict that sexual selection also produces costs at the population level, which could limit the ability of populations to adapt to changing conditions and thus increase the risk of extinction2-4. Other models, however, suggest that sexual selection should increase rates of adaptation and enhance the removal of deleterious mutations, thus protecting populations against extinction3, 5, 6. Resolving the conflict between these models is not only important for explaining the history of biodiversity, but also relevant to understanding the mechanisms of the current biodiversity crisis. Previous attempts to test the conflicting predictions produced by these models have been limited to extant species and have thus relied on indirect proxies for species extinction. Here we use the informative fossil record of cytheroid ostracods-small, bivalved crustaceans with sexually dimorphic carapaces-to test how sexual selection relates to actual species extinction. We show that species with more pronounced sexual dimorphism, indicating the highest levels of male investment in reproduction, had estimated extinction rates that were ten times higher than those of the species with the lowest investment. These results indicate that sexual selection can be a substantial risk factor for extinction.


Assuntos
Crustáceos/fisiologia , Extinção Biológica , Fósseis , Preferência de Acasalamento Animal , Seleção Genética , Adaptação Fisiológica , Animais , Tamanho Corporal , Crustáceos/anatomia & histologia , Crustáceos/classificação , Feminino , Masculino , Modelos Biológicos , Reprodução , Fatores de Risco , Caracteres Sexuais
9.
Sci Rep ; 8(1): 1365, 2018 01 22.
Artigo em Inglês | MEDLINE | ID: mdl-29358761

RESUMO

The mid-Cretaceous Burmese amber (~99 Ma, Myanmar), widely known for exquisite preservation of theropods, also yields microfossils, which can provide important contextual information on paleoenvironment and amber formation. We report the first Cretaceous ostracod in amber-the gigantic (12.9 mm) right valve of an exclusively marine group (Myodocopa: Myodocopida) preserved in Burmese amber. Ostracods are usually small (0.5-2 mm), with well-calcified carapaces that provide an excellent fossil record extending to at least the Ordovician (~485 million years ago), but they are rarely encountered in amber. The new specimen effectively doubles the age of the ostracod amber record, offering the first representative of the Myodocopa, a weakly calcified group with a poor fossil record. Its carapace morphology is atypical and likely plesiomorphic. The preserved valve appears to be either a moulted exuvium or a dead and disarticulated specimen, and subsequent resin flows contain forest floor inclusions with terrestrial arthropods, i.e., fragmentary remains of spiders, and insect frass. These features resolve an enigmatic taphonomic pathway, and support a marginal marine setting for resin production.


Assuntos
Crustáceos/anatomia & histologia , Fósseis/anatomia & histologia , Animais , Crustáceos/classificação , Mianmar
10.
J Comp Neurol ; 526(7): 1148-1165, 2018 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-29377111

RESUMO

Stomatopods have an elaborate visual system served by a retina that is unique to this class of pancrustaceans. Its upper and lower eye hemispheres encode luminance and linear polarization while an equatorial band of photoreceptors termed the midband detects color, circularly polarized light and linear polarization in the ultraviolet. In common with many malacostracan crustaceans, stomatopods have stalked eyes, but they can move these independently within three degrees of rotational freedom. Both eyes separately use saccadic and scanning movements but they can also move in a coordinated fashion to track selected targets or maintain a forward eyestalk posture during swimming. Visual information is initially processed in the first two optic neuropils, the lamina and the medulla, where the eye's midband is represented by enlarged regions within each neuropil that contain populations of neurons, the axons of which are segregated from the neuropil regions subtending the hemispheres. Neuronal channels representing the midband extend from the medulla to the lobula where populations of putative inhibitory glutamic acid decarboxylase-positive neurons and tyrosine hydroxylase-positive neurons intrinsic to the lobula have specific associations with the midband. Here we investigate the organization of the midband representation in the medulla and the lobula in the context of their overall architecture. We discuss the implications of observed arrangements, in which midband inputs to the lobula send out collaterals that extend across the retinotopic mosaic pertaining to the hemispheres. This organization suggests an integrative design that diverges from the eumalacostracan ground pattern and, for the stomatopod, enables color and polarization information to be integrated with luminance information that presumably encodes shape and motion.


Assuntos
Percepção de Cores/fisiologia , Crustáceos/anatomia & histologia , Neurônios/fisiologia , Lobo Óptico de Animais não Mamíferos/anatomia & histologia , Retina/citologia , Animais , Dextranos/metabolismo , Microscopia Eletrônica , Neurônios/ultraestrutura , Neurópilo/fisiologia , Lobo Óptico de Animais não Mamíferos/metabolismo , Células Fotorreceptoras , Coloração pela Prata , Sinapsinas/metabolismo , Tirosina 3-Mono-Oxigenase/metabolismo , Visão Ocular
11.
Mol Phylogenet Evol ; 121: 86-97, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29258880

RESUMO

Cladogenesis is often driven by the interplay of dispersal and vicariance. The importance of long-distance dispersal in biogeography and speciation is increasingly recognised, but still ill-understood. Here, we study faunal interconnectivity between four large Brazilian floodplains, namely the Amazon, Araguaia, Pantanal (on Paraguay River) and Upper Paraná River floodplains, investigating a species complex of the non-marine ostracod genus Strandesia. We use DNA sequence data from the mitochondrial COI and the nuclear Elongation Factor 1 alpha genes to construct molecular phylogenies and minimum spanning networks, to identify genetic species, analyse biogeographic histories and provide preliminary age estimates of this species complex. The Strandesia species complex includes five morphological and eleven genetic species, which doubles the known diversity in this lineage. The evolutionary history of this species complex appears to comprise sequences of dispersal and vicariance events. Faunal and genetic patterns of connectivity between floodplains in some genetic species are mirrored in modern hydrological connections. This could explain why we find evidence for (aquatic) long-distance dispersal between floodplains, thousands of kilometres apart. Our phylogenetic reconstructions seem to mostly indicate recent dispersal and vicariance events, but the evolution of the present Strandesia species complex could span up to 25 Myr, which by far exceeds the age of the floodplains and the rivers in their current forms.


Assuntos
Migração Animal/fisiologia , Organismos Aquáticos/fisiologia , Crustáceos/anatomia & histologia , Crustáceos/fisiologia , Animais , Teorema de Bayes , Brasil , Complexo IV da Cadeia de Transporte de Elétrons/genética , Evolução Molecular , Especiação Genética , Geografia , Paraguai , Filogenia , Análise de Sequência de DNA , Especificidade da Espécie
12.
Prog Neurobiol ; 161: 23-60, 2018 02.
Artigo em Inglês | MEDLINE | ID: mdl-29197652

RESUMO

Malacostracan crustaceans display a large diversity of sizes, morphs and life styles. However, only a few representatives of decapod taxa have served as models for analyzing crustacean olfaction, such as crayfish and spiny lobsters. Crustaceans bear multiple parallel chemosensory pathways represented by different populations of unimodal chemosensory and bimodal chemo- and mechanosensory sensilla on the mouthparts, the walking limbs and primarily on their two pairs of antennae. Here, we focus on the olfactory pathway associated with the unimodal chemosensory sensilla on the first antennal pair, the aesthetascs. We explore the diverse arrangement of these sensilla across malacostracan taxa and point out evolutionary transformations which occurred in the central olfactory pathway. We discuss the evolution of chemoreceptor proteins, comparative aspects of active chemoreception and the temporal resolution of crustacean olfactory system. Viewing the evolution of crustacean brains in light of energetic constraints can help us understand their functional morphology and suggests that in various crustacean lineages, the brains were simplified convergently because of metabolic limitations. Comparing the wiring of afferents, interneurons and output neurons within the olfactory glomeruli suggests a deep homology of insect and crustacean olfactory systems. However, both taxa followed distinct lineages during the evolutionary elaboration of their olfactory systems. A comparison with insects suggests their olfactory systems ö especially that of the vinegar fly ö to be superb examples for "economy of design". Such a comparison also inspires new thoughts about olfactory coding and the functioning of malacostracan olfactory systems in general.


Assuntos
Células Quimiorreceptoras/fisiologia , Crustáceos/anatomia & histologia , Condutos Olfatórios/fisiologia , Olfato/fisiologia , Animais , Condutos Olfatórios/citologia
13.
Dev Neurobiol ; 78(1): 3-14, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29082670

RESUMO

The compound eyes of adult stomatopod crustaceans have two to six ommatidial rows at the equator, called the midband, that are often specialized for color and polarization vision. Beneath the retina, this midband specialization is represented as enlarged optic lobe lamina cartridges and a hernia-like expansion in the medulla. We studied how the optic lobe transforms from the larvae, which possess typical crustacean larval compound eyes without a specialized midband, through metamorphosis into the adults with the midband in a two midband-row species Alima pacifica. Using histological staining, immunolabeling, and 3D reconstruction, we show that the last-stage stomatopod larvae possess double-retina eyes, in which the developing adult visual system forms adjacent to, but separate from, the larval visual system. Beneath the two retinas, the optic lobe also contains two sets of optic neuropils, comprising of a larval lamina, medulla, and lobula, as well as an adult lamina, medulla, and lobula. The larval eye and all larval optic neuropils degenerate and disappear approximately a week after metamorphosis. In stomatopods, the unique adult visual system and all optic neuropils develop alongside the larval system in the eyestalk of last-stage larvae, where two visual systems and two independent visual processing pathways coexist. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 3-14, 2018.


Assuntos
Crustáceos/crescimento & desenvolvimento , Metamorfose Biológica , Lobo Óptico de Animais não Mamíferos/crescimento & desenvolvimento , Animais , Crustáceos/anatomia & histologia , Olho/anatomia & histologia , Olho/crescimento & desenvolvimento , Imageamento Tridimensional , Larva/anatomia & histologia , Larva/crescimento & desenvolvimento , Microscopia Confocal , Lobo Óptico de Animais não Mamíferos/anatomia & histologia , Vias Visuais/anatomia & histologia , Vias Visuais/crescimento & desenvolvimento
14.
Integr Comp Biol ; 57(5): 1139-1150, 2017 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-29155966

RESUMO

We review the visual systems of crustacean larvae, concentrating on the compound eyes of decapod and stomatopod larvae as well as the functional and behavioral aspects of their vision. Larval compound eyes of these macrurans are all built on fundamentally the same optical plan, the transparent apposition eye, which is eminently suitable for modification into the abundantly diverse optical systems of the adults. Many of these eyes contain a layer of reflective structures overlying the retina that produces a counterilluminating eyeshine, so they are unique in being camouflaged both by their transparency and by their reflection of light spectrally similar to background light to conceal the opaque retina. Besides the pair of compound eyes, at least some crustacean larvae have a non-imaging photoreceptor system based on a naupliar eye and possibly other frontal eyes. Larval compound-eye photoreceptors send axons to a large and well-developed optic lobe consisting of a series of neuropils that are similar to those of adult crustaceans and insects, implying sophisticated analysis of visual stimuli. The visual system fosters a number of advanced and flexible behaviors that permit crustacean larvae to survive extended periods in the plankton and allows them to reach acceptable adult habitats, within which to metamorphose.


Assuntos
Crustáceos/anatomia & histologia , Crustáceos/fisiologia , Visão Ocular , Percepção Visual , Animais , Crustáceos/crescimento & desenvolvimento , /crescimento & desenvolvimento , Larva/anatomia & histologia , Larva/crescimento & desenvolvimento , Larva/fisiologia , Zooplâncton/crescimento & desenvolvimento , Zooplâncton/fisiologia
15.
Elife ; 62017 09 26.
Artigo em Inglês | MEDLINE | ID: mdl-28949916

RESUMO

Mushroom bodies are the iconic learning and memory centers of insects. No previously described crustacean possesses a mushroom body as defined by strict morphological criteria although crustacean centers called hemiellipsoid bodies, which serve functions in sensory integration, have been viewed as evolutionarily convergent with mushroom bodies. Here, using key identifiers to characterize neural arrangements, we demonstrate insect-like mushroom bodies in stomatopod crustaceans (mantis shrimps). More than any other crustacean taxon, mantis shrimps display sophisticated behaviors relating to predation, spatial memory, and visual recognition comparable to those of insects. However, neuroanatomy-based cladistics suggesting close phylogenetic proximity of insects and stomatopod crustaceans conflicts with genomic evidence showing hexapods closely related to simple crustaceans called remipedes. We discuss whether corresponding anatomical phenotypes described here reflect the cerebral morphology of a common ancestor of Pancrustacea or an extraordinary example of convergent evolution.


Assuntos
Crustáceos/anatomia & histologia , Corpos Pedunculados/anatomia & histologia , Animais , Evolução Biológica , Encéfalo/anatomia & histologia
16.
J Morphol ; 278(11): 1570-1576, 2017 11.
Artigo em Inglês | MEDLINE | ID: mdl-28691246

RESUMO

The crescent sculpture of the so-called "Xestoleberis-spot" develops inside the calcified valve of the family Xestoleberididae. Electron microscopic observations on both, intermoult and postmoult stages of Xestoleberis species reveal that the "Xestoleberis-spot" system consists of three elements; two calcified chambers, a vesicle of electron-dense material and an uncalcified procuticle. The formation and function of the "Xestoleberis-spot" system are discussed. In conclusion, the "Xestoleberis-spot" system functions as the muscle attachment site for several antennal muscles, and provides the material for chitinous fibers in the exocuticle of outer lamella. The unique cuticular structures of the family Xestoleberididae are due to the "Xestoleberis-spot" system.


Assuntos
Crustáceos/anatomia & histologia , Crustáceos/fisiologia , Animais , Calcificação Fisiológica , Crustáceos/ultraestrutura , Muda/fisiologia
17.
PLoS One ; 12(7): e0177791, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28678866

RESUMO

Assessing the long-term macroevolutionary consequences of sexual selection has been hampered by the difficulty of studying this process in the fossil record. Cytheroid ostracodes offer an excellent system to explore sexual selection in the fossil record because their readily fossilized carapaces are sexually dimorphic. Specifically, males are relatively more elongate than females in this superfamily. This sexual shape difference is thought to arise so that males carapaces can accommodate their very large copulatory apparatus, which can account for up to one-third of body volume. Here we test this widely held explanation for sexual dimorphism in cytheroid ostracodes by correlating investment in male genitalia, a trait in which sexual selection is seen as the main evolutionary driver, with sexual dimorphism of carapace in the genus Cyprideis. We analyzed specimens collected in the field (C. salebrosa, USA; C. torosa, UK) and from collections of the National Museum of Natural History, Washington, DC (C. mexicana). We digitized valve outlines in lateral view to obtain measures of size (valve area) and shape (elongation, measured as length to height ratio), and obtained several dimensions from two components of the hemipenis: the muscular basal capsule, which functions as a sperm pump, and the section that includes the intromittent organ (terminal extension). In addition to the assessment of this primary sexual trait, we also quantified two dimensions of the male secondary sexual trait-where the transformed right walking leg functions as a clasping organ during mating. We also measured linear dimensions from four limbs as indicators of overall (soft-part) body size, and assessed allometry of the soft anatomy. We observed significant correlations in males between valve size, but not elongation, and distinct structural parts of the hemipenis, even after accounting for their shared correlation with overall body size. We also found weak but significant positive correlation between valve elongation and the degree of sexual dimorphism of the walking leg, but only in C. torosa. The correlation between the hemipenis parts, especially basal capsule size and male valve size dimorphism suggests that sexual selection on sperm size, quantity, and/or efficiency of transfer may drive sexual size dimorphism in these species, although we cannot exclude other aspects of sexual and natural selection.


Assuntos
Crustáceos/fisiologia , Fósseis , Genitália/fisiologia , Caracteres Sexuais , Comportamento Sexual Animal/fisiologia , Animais , Tamanho Corporal , Crustáceos/anatomia & histologia , Crustáceos/classificação , Feminino , Genitália/anatomia & histologia , Masculino , Tamanho do Órgão , Especificidade da Espécie
18.
J Mech Behav Biomed Mater ; 76: 38-57, 2017 12.
Artigo em Inglês | MEDLINE | ID: mdl-28629739

RESUMO

The Bouligand structure, which is found in many biological materials, is a hierarchical architecture that features uniaxial fiber layers assembled periodically into a helicoidal pattern. Many studies have highlighted the high damage-resistant performance of natural and biomimetic Bouligand structures. One particular species that utilizes the Bouligand structure to achieve outstanding mechanical performance is the smashing Mantis Shrimp, Odontodactylus Scyllarus (or stomatopod). The mantis shrimp generates high speed, high acceleration blows using its raptorial appendage to defeat highly armored preys. The load-bearing part of this appendage, the dactyl club, contains an interior region [16] that consists of a Bouligand structure. This region is capable of developing a significant amount of nested twisting microcracks without exhibiting catastrophic failure. The development and propagation of these microcracks are a source of energy dissipation and stress relaxation that ultimately contributes to the remarkable damage tolerance properties of the dactyl club. We develop a theoretical model to provide additional insights into the local stress intensity factors at the crack front of twisting cracks formed within the Bouligand structure. Our results reveal that changes in the local fracture mode at the crack front leads to a reduction of the local strain energy release rate, hence, increasing the necessary applied energy release rate to propagate the crack, which is quantified by the local toughening factor. Ancillary 3D simulations of the asymptotic crack front field were carried out using a J-integral to validate the theoretical values of the energy release rate and the local stress intensity factors.


Assuntos
Crustáceos/anatomia & histologia , Fenômenos Mecânicos , Animais , Fenômenos Biomecânicos
19.
J Morphol ; 278(8): 1091-1104, 2017 08.
Artigo em Inglês | MEDLINE | ID: mdl-28480519

RESUMO

Pores and sensilla on ostracod shell have often been used in studies of ontogeny, taxonomy, and phylogeny of the group. However, an analysis of sexual dimorphism and variation between valves in the number and distribution of pores is lacking. Also, such studies have never been done on a widely distributed, morphologically variable, and weakly ornamented freshwater ostracod. Here, we survey pores in one such species, Physocypria kraepelini. We choose 27 homologous pores as landmarks for 2D-geometric morphometric analysis, with the aim to assess intersexual and between valves variation in size and shape relative to the Fourier outline analysis. This species has only simple (Type A) pores with and without a lip, and each pore carries an undivided sensory seta. Our results show that the total number of pores varies (from 270 to 296), but this is not associated with a specific valve. Males carry fewer pores than females, however no sex specific pores are found. Small intrapopulation divergence of the Cyt b molecular marker (1%) indicates that morphological variability is not species related. We found that P. kraepelini exhibits directional asymmetry of size and shape, sexual size dimorphism (SSD) but lacks sexual shape dimorphism (SShD). Two geometric morphometrics methods were congruent in the estimation of SSD, SShD, and directional asymmetry of shape but differ in the statistical evaluation of directional asymmetry of size. Contrary to other animal groups, our study suggests that ostracods have more pronounced directional asymmetry of shape compared to directional asymmetry of size.


Assuntos
Exoesqueleto/anatomia & histologia , Crustáceos/anatomia & histologia , Análise de Variância , Exoesqueleto/ultraestrutura , Animais , Crustáceos/ultraestrutura , Feminino , Masculino , Filogenia , Análise de Componente Principal
20.
J Exp Biol ; 220(Pt 7): 1360-1368, 2017 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-28356369

RESUMO

Stomatopods have an extraordinary visual system, incorporating independent movement of their eyes in all three degrees of rotational freedom. In this work, we demonstrate that in the peacock mantis shrimp, Odontodactylus scyllarus, the level of ocular independence is task dependent. During gaze stabilization in the context of optokinesis, there is weak but significant correlation between the left and right eyes in the yaw degree of rotational freedom, but not in pitch and torsion. When one eye is completely occluded, the uncovered eye does not drive the covered eye during gaze stabilization. However, occluding one eye does significantly affect the uncovered eye, lowering its gaze stabilization performance. There is a lateral asymmetry, with the magnitude of the effect depending on the eye (left or right) combined with the direction of motion of the visual field. In contrast, during a startle saccade, the uncovered eye does drive a covered eye. Such disparate levels of independence between the two eyes suggest that responses to individual visual tasks are likely to follow different neural pathways.


Assuntos
Crustáceos/fisiologia , Animais , Crustáceos/anatomia & histologia , Olho/anatomia & histologia , Movimentos Oculares , Movimentos Sacádicos , Visão Ocular , Campos Visuais
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