Developmental modularity and phenotypic novelty within a biphasic life cycle: morphogenesis of a cone snail venom gland

The venom gland of predatory cone snails (Conus spp.), which secretes neurotoxic peptides that rapidly immobilize prey, is a proposed key innovation for facilitating the extraordinary feeding behaviour of these gastropod molluscs. Nevertheless, the unusual morphology of this gland has generated controversy about its evolutionary origin and possible homologues in other gastropods. I cultured feeding larvae of Conus lividus and cut serial histological sections through the developing foregut during larval and metamorphic stages to examine the development of the venom gland. Results support the hypothesis of homology between the venom gland and the mid-oesophageal gland of other gastropods. They also suggest that the mid-region of the gastropod foregut, like the anterior region, is divisible into dorsal and ventral developmental modules that have different morphological, functional and ontogenetic fates. In larvae of C. lividus, the ventral module of the middle foregut transformed into the anatomically novel venom gland of the post-metamorphic stage by rapidly pinching-off from the main dorsal channel of the mid-oesophagus, an epithelial remodelling process that may be similar to other cases where epithelial tubes and vesicles arise from a pre-existing epithelial sheet. The developmental remodelling mechanism could have facilitated an abrupt evolutionary transition to the derived morphology of this important gastropod feeding innovation.     

The larval head structures of Podagricomela shirahatai (Chûjô) (Chrysomelidae,Galerucinae, Alticini) and morphological effects of leaf mining

Head structures of the leaf mining larva of the chrysomelid species Podagricomela shirahatai are described and illustrated. Internal and external structures were reconstructed three dimensionally based on image stacks obtained with microcomputed tomography. The larval head is characterized by prognathism, a dorsoventrally compressed shape, a flattened maxillolabial complex, a completely reduced coronal suture, and the presence of a deep, V‐shaped posterior emargination of the head capsule. Internal structures are not distinctly affected by leaf mining. The cephalic features are compared with conditions found in surface feeding and root feeding alticine larvae and also with characters of chrysomeline larvae of Chrysomela populi Linnaeus. Possible correlations between modifications of the larval head and different feeding behaviors are discussed. Characters are also discussed with respect to possible phylogenetic implications. Some derived features are apparently due to phylogenetic constraints. Apomorphies characterizing alticine larvae with distinctly different life habits are the loss of M. frontoepharyngalis (M. 9), the origin of M. tentoriostipitalis (M. 18) from the head capsule, two insertions of M. tentoriopraementalis inferior (M. 29) and the reduction of stemmata. The study underlines that the anatomical study of chrysomeloid larvae is not only highly desirable in a phylogenetic context, but also crucial for understanding the evolution of different life strategies in this extremely successful group of Coleoptera. J. Morphol. 276:446–457, 2015. © 2014 Wiley Periodicals, Inc.     

Development and metamorphic loss of the musculature in larvae of the nudibranch Phestilla sibogae: A functional ontogeny

Developmental programmes for many marine invertebrates include the assembly of muscular systems appropriate to the functions of swimming and feeding in pelagic larvae. Upon metamorphosis, that musculature is often radically re-organized to meet very different demands of post-larval life. To investigate the development and fate of musculature in the nudibranch Phestilla sibogae, embryos, larvae and metamorphosing stages were fixed, labelled with phalloidin and examined with confocal microscopy. The resultant images revealed the sequential development of both large retractor muscles and numerous finer muscles that allow the larva to manipulate the velum, foot and operculum. Observations of living specimens at the same stages as those fixed for microscopy revealed the actions of the muscles as they developed. During metamorphosis, muscles with shell attachments disintegrate as the larva transforms into a shell-less juvenile. Notably, the massive velar, pedal and opercular retractor muscles disappear during metamorphosis in a sequence that corresponds to their loss of function. Other muscles, however, that appear to be important to the embryo and free-swimming larva persist into juvenile life. The comprehensive and detailed observations of the musculature presented here provide a solid foundation for comparisons with other species with different phylogenies and life histories.     

Sinistral snail shells in the sea: developmental causes and consequences

The paucity of sinistral (left-coiling) relative to dextral (right-coiling) species of gastropods in the marine realm is an enigma. In Conus , one of the most diverse marine animal genera, sinistral shell coiling has evolved as a species-wide character only once. Fossils of this species, Conus adversarius , are found in Upper Pliocene and lowermost Pleistocene deposits in the southeastern USA. Conus adversarius had nonplanktonic larval development; this may have been a critical factor for the early establishment of the species, as well as sinistral marine species in other clades. Notably, most specimens of aberrantly sinistral modern Conus are derived from typically dextral species that have nonplanktonic development. If C. adversarius was reproductively isolated from dextral conspecifics, then this species may provide an example of nearly instantaneous sympatric speciation in the fossil record. Furthermore, the common and widespread – while geologically short-lived – fossil shells of C. adversarius show large amounts of variability in form and this variation may be related, at least in part, to a pleiotropic effect associated with the reversed coiling direction of this species.     

Fluctuating asymmetry and age in children: evolutionary implications for the control of developmental stability

Fluctuating asymmetry (FA) is small deviations from perfect symmetry which reflect one component of fitness, i.e. developmental stability. There is accumulating evidence that low FA is important in inter- and intra-sexual selection in humans. However, there is little information on the pattern of FA in children. Data from cross-sectional studies of 680 participants from 2–18 years suggests that (1) both absolute and relative FA reduces with age until 10 years (2) there is an increase in FA in adolescents (11–15 years) with a peak at 13 years for males and 14 years for females (3) after 15 years there is reduction in FA which is maintained until 18 years. The importance of growth rate, metabolic maintenance and sex steroids on developmental stability is discussed.     

Development and validation of a generic 3D model of the distal femur

The development and validation of a virtual generic 3D model of the distal femur using computer graphical methods is presented. The synthesis of the generic model requires the following steps: acquisition of bony 3D morphology using standard computed tomography (CT) imaging; alignment of 3D models reconstructed from CT images with a common coordinate system; computer graphical sectioning of the models; extraction of bone contours from the image sections; combining and averaging of extracted contours; and 3D reconstruction of the averaged contours.

The generic models reconstructed from the averaged contours of six cadaver femora were validated by comparing their surface geometry on a point to point basis with that of the CT reconstructed reference models. The mean errors ranged from 0.99 to 2.5 mm and were in agreement with the qualitative assessment of the models.     

中国亚洲玉米螟发育历期的地理变异

广布种昆虫可调节其生活史以适应栖息地的条件变化,如可以通过调节自身的生长发育和繁殖期,使其发生与栖息地的物候(如食料、气温和降雨等)同步,这对昆虫在栖息地的繁衍具有十分重要的意义。亚洲玉米螟Ostrinia furnacalis为玉米主要害虫,在中国从南到北都有分布,栖息地气候也不同,不同地理种群生活史发生了分化,如化性、临界光周期、滞育后羽化时间、体重和体型、繁殖力和抗寒力等均不同。然而该虫发育历期的地理变异尚未见系统报道。为此,详细比较了来自5个亚洲玉米螟不同地理种群即广西阳朔(YS)、江西南昌(NC)、山东泰安(TA)、河北廊坊(LF)和黑龙江哈尔滨(HEB)在20—31℃下卵、幼虫、蛹发育历期及其与栖息地纬度的关系。结果表明:不同温度下的不同地理种群的卵期不存在显著差异,在20、22和25℃下,卵期从南到北稍有延长,卵期与其栖息地纬度呈正相关;但在28℃下,不同地理种群的卵期基本相等,与纬度相关性不显著。在31℃下,不同地理种群的幼虫期不存在显著差异,而在其他温度下,不同地理种群的幼虫期存在显著差异;在22、25和28℃下,幼虫期与其栖息地纬度呈正相关,而在20和31℃下,幼虫期与其栖息地纬度呈负相关,在20、22和25℃下,最北的哈尔滨种群的幼虫期变幅不大,而其他4个种群的幼虫期随着温度的升高明显缩短。各地理种群20℃下的雌蛹、28℃下的雄蛹和31℃下的雌雄蛹期差异均不显著,其他雌或雄蛹期差异显著;各温度下的雌雄蛹期与其栖息地纬度存在正相关关系。这些研究结果揭示了广布种昆虫可以调节其自身发育历期以适应栖息地环境条件。     

The Onset of the Juvenile Period in Carp, Cyprinus Carpio: a Literature Survey

Literature data on the relative growth of body parts, functional morphology, feeding behaviour and differential growth capacity in 0+ carp, Cyprinus carpio, were relatively consistent with respect to the onset of the juvenile period in this species, which occurs at 20-25 mm standard length (20-30 days after hatching), when the process of metamorphosis (larva-juvenile transition) is regarded as complete and the definitive phenotype is attained. However, changes in metabolic rate, development of social interactions and shifts in habitat use suggest that carp are not small adults until they attain a greater size and age. Problems relative to the global heterogeneity of carp stocks, including wild and domesticated morphs, and the importance of an holistic approach to the study of metamorphosis in carp, and fish in general, are also discussed.     

Functional design of the feeding mechanism in lower vertebrates: unidirectional and bidirectional flow systems in the tiger salamander

There are two basic designs of the aquatic feeding mechanism in lower vertebrates: unidirectional and bidirectional flow systems. Larval salamanders and most fishes posses a unidirectional flow design in which water drawn into the mouth with the prey passes over the gills and exits posteriorly. Metamorphosed salamanders and all other aquatic vertebrates possess a bidirectional system in which water flows into and out of the mouth during a single feeding cycle. We investigated the functional consequences of these two feeding designs in larval and metamorphosed tiger salamanders ( Ambystoma tigrinum ) feeding in the water. Buccal cavity pressures were measured during feeding and 11 variables measured from the pressure traces. Significant differences were found between the larval and metamorphosed salamanders in eight variables. Larval salamanders generate significantly greater negative pressures than do metamorphosed individuals and a principal components analysis of the 11 pressure variables completely separates larval from metamorphosed salamanders. Larval individuals are significantly better at capturing elusive prey than are metamorphosed salamanders, apparently because of changes in the structure of the feeding mechanism and the concomitant functional modifications.     

Development of feeding structures in larval fish with different life histories: winter flounder and Atlantic cod

The size at which feeding structures developed and shifts in head proportions occurred, differed between Atlantic cod Gadus morhua and winter flounder Pseudopleuronectes americanus. The sequence and timing of the development of feeding structures may not be dependent on size, but may occur because they are necessary to meet specific requirements offish larvae feeding in the plankton. In early larval stages development of feeding structures was similar in number and type and was necessary for first-feeding in both species. In later stages, significant differences between species occurred in the timing of the development of feeding structures. In cod differentiation of new structures and changes in head proportions occurred at about two-thirds of the way through larval life, which coincided with an increase in growth. In flounder changes in feeding morphology did not occur during the symmetrical larval stage, but occurred only after metamorphosis to the asymmetrical demersal juvenile stage. Differences between cod and flounder in the size at which feeding structures develop may reflect life history adaptations expressed in the duration of the pelagic larval stage, as well as differences in juvenile habitat and feeding ecology.     

Structure of the caudal neural tube in an ascidian larva: Vestiges of its possible evolutionary origin from a ciliated band

Ultrastructural analysis and differential immunocytochemical staining with two antitubulin monoclonal antibodies were used to reexamine the organization and development of the neural tube in the larva of an ascidian, Ciona intestinalis, in appraisal of a theory that the dorsal tubular nervous system of the chordates evolved from two halves of a ciliated band in an auricularia-like larva of the kind found in echinoderms and hemichordates. One of the antibodies stained cilia in the nervous system and elsewhere; the other reacted primarily with neuronal axons. The caudal neural tube consists of four rows of large ciliated ependymal-glial cells enclosing an axial neural canal into which their single cilia extend. Two ventrolateral nerve tracts, containing axons, arise in the posterior brain region and extend along the length of the caudal tube, partially surrounded by the ependymal cells. The nonnervous, ciliated, ependymal neural tube of the ascidian larva with its two associated nerve tracts survives as a primitive early condition that could result from a ciliated band transformation. Tissues in the distal-most part of the ascidian larval tail have cell lineage origins that indicate an evolutionary history different from those in the proximal majority of the tail. The ependymal cells in this presumed later addition to the tail are not ciliated, although all of the others in the caudal ependymal tube appear to be.     

Nucleolar apparatus in the macronucleus of Didinium nasutum (Ciliata): EM and 3D reconstruction

The three-dimensional (3D) organization of nucleoli in the somatic nuclei (macronuclei) of recently fed and starved Didinium nasutum was reconstructed on the basis of serial ultra-thin sections. It was shown that nucleoli, looking on the single sections like individual separate structures, appeared to be parts of the large complicated branchy nucleolar networks. A 30 h starvation did not lead to disintegration of this network, but stimulated formation of numerous vacuoles in the granular component of nucleoli, which becomes more condensed. Unlike starved D. nasutum, in fed ciliates numerous holes appeared in the fibrillar component located at the periphery of nucleoli. These holes may presumably serve as channels for transporting newly synthesized rRNA. To our knowledge, this is the first report of a 3D reconstruction of the nucleolar apparatus in ciliates.     

The influence of temperature and light on larval pre-settlement metamorphosis: a study of the effects of environmental factors on pre-settlement metamorphosis of the solitary ascidian Styela canopus

This study investigated the effects of two environmental factors, temperature and light, on larval settlement and metamorphosis in the solitary ascidian Styela canopus. The results revealed that larval settlement rates decreased with increasing temperature in the range 12–30°C. We also demonstrated for the first time that pre-settlement metamorphosis of ascidian larvae can occur as a function of temperature. We suggest this could be an adaptation to avoid the greater energetic cost of active larval swimming, presumably resulting from the increasing temperature. They are able to metamorphose into passive drifting post-larvae and to continue planktonic life. This finding has implications for larval dispersal, especially under conditions of ocean warming. In addition, the effect of light intensity on larval settlement and metamorphosis was significantly different between photoperiods of 24 L : 0 D and 12 L : 12 D. These results provide some insight into the complex cues affecting settlement and metamorphosis of ascidian larvae and ascidian distribution in nature.     

Evolution of a giant intromittent organ in Scydmaeninae (Coleoptera: Staphylinidae): Functional morphology of the male postabdomen in Mastigini

We compared the postabdominal architecture of Mastigini with extremely long (Stenomastigus) or short (Palaeostigus) aedeagus. A novel mode of copulation was discovered: males of Stenomastigus insert a paramere between the female's abdomen and elytra, and the intromission is stabilized by several structures of both sexes. The intrinsic aedeagal mechanism is indicated as responsible for inflating the endophallus, and the long flagellum does not penetrate the ductus spermathecae during copulation. The structure of the flagellum suggests that it is primarily responsible for the sperm transfer. Asymmetrical postabdominal rotators of the aedeagus were only found in Stenomastigus; they presumably facilitate the withdrawal of the genitalia; their origin as bundles separated from larger muscles is postulated. We discuss a scenario in which the evolution of elongated genitalia was facilitated by the lack of structural constraints and existing preadaptations. Benefits of stabilizing the copulation and intromission are indicated as the driving force for the evolution of extremely long aedeagi, while the short aedeagi might have the advantage of freedom of movements facilitating the initiation of copulation by males. Disruptive selection is suggested as a working hypothesis to further investigate mechanisms that have played a role in the evolution of genital structures of Mastigini.     

麦红吸浆虫3-羟基-3-甲基戊二酰辅酶A还原酶基因SmHMGR的克隆及在滞育与发育变态过程中的表达动态

【目的】3-羟基-3-甲基戊二酰辅酶A还原酶(HMGR)是保幼激素(JH)合成途径的限速酶。麦红吸浆虫Sitodiplosis mosellana是一种典型的专性幼虫滞育昆虫。本研究旨在探讨HMGR基因在麦红吸浆虫滞育和发育变态过程中的作用。【方法】通过RT-PCR和RACE技术克隆麦红吸浆虫滞育前幼虫HMGR基因全长cDNA序列;利用生物信息学软件分析HMGR基因核苷酸和其编码的蛋白氨基酸序列特性;采用qPCR技术测定其在麦红吸浆虫滞育不同时期3龄幼虫及不同发育阶段(1-2龄幼虫、预蛹、初蛹、中蛹和后蛹以及雌雄成虫)中的mRNA表达水平。【结果】克隆获得一条麦红吸浆虫HMGR基因全长cDNA序列,命名为SmHMGR(GenBank登录号: MG876766)。该基因全长2 548 bp,其中开放阅读框长2 328 bp,编码775个氨基酸,预测的蛋白分子量为84.16 kD,理论等电点为8.29。序列分析发现该基因编码的蛋白具有HMGR蛋白家族典型的HMG-CoA-reductase-classⅠ催化功能域及其他保守功能基序;序列比对和系统发育分析表明,SmHMGR与达氏按蚊Anopheles darling等长角亚目(Nematocera)昆虫HMGR的相似性最高、亲缘关系最近。SmHMGR在麦红吸浆虫滞育前的3龄早期幼虫中表达量显著升高,进入滞育后一直维持较高水平,并在滞育后静息阶段的当年12月至翌年1月达到最高。SmHMGR在蛹期表达量低于幼虫期,预蛹期表达量最低;在雌成虫中表达量显著高于在蛹和雄成虫中的表达量。【结论】SmHMGR的表达与麦红吸浆虫发育密切相关,可能在滞育诱导、维持及滞育后静息状态的维持及生殖中发挥作用,其表达量的降低可能参与了幼虫到蛹的变态。