Postmetamorphic Development Research Articles

The people behind the papers - Gabriela Krejčová and Adam Bajgar.

Macrophages maintain tissue homeostasis by removing old, damaged and apoptotic cells. During metamorphosis, the fruit fly larval fat body undergoes cell death and is eventually replaced by the adult fat body. In a new study, Adam Bajgar and colleagues find that macrophages convert dying larval adipocytes into nutrients to be utilised by other tissues during post-metamorphic development. To find out more about the story behind the paper, we caught up with first author Gabriela Krejčová and corresponding author Adam Bajgar, Associate Professor at the University of South Bohemia.

Macrophages play a nutritive role in post-metamorphic maturation in Drosophila.

In the body of multicellular organisms, macrophages play an indispensable role in maintaining tissue homeostasis by removing old, apoptotic and damaged cells. In addition, macrophages allow significant remodeling of body plans during embryonic morphogenesis, regeneration and metamorphosis. Although the huge amount of organic matter that must be removed during these processes represents a potential source of nutrients, their further use by the organism has not yet been addressed. Here, we document that, during metamorphosis, Drosophila larval adipose tissue is infiltrated by macrophages, which remove dying adipocytes by efferocytosis and engulf leaking RNA-protein granules and lipids. Consequently, the infiltrating macrophages transiently adopt the adipocyte-like metabolic profile to convert remnants of dying adipocytes to lipoproteins and storage peptides that nutritionally support post-metamorphic development. This process is fundamental for the full maturation of ovaries and the achievement of early fecundity of individuals. Whether macrophages play an analogous role in other situations of apoptotic cell removal remains to be elucidated.

Carotenoid intake during early life mediates ontogenetic colour shifts and dynamic colour change during adulthood

Carotenoids play an import role as one of the most prevalent pigments in animals. Carotenoid-based coloration accounts for striking sexually and naturally selected colour adaptations. Several anurans (frogs and toads) change body coloration either slowly and permanently between life stages (ontogenetic colour change), or rapidly and temporarily within minutes or hours (dynamic colour change). We investigated ontogenetic colour change from orange to green morphs in the Wallace's flying frog, Rhacophorus nigropalmatus , and tested the influence of dietary carotenoids on colour change during postmetamorphic development. At the age of 9 months, while all individuals still possessed orange-red body coloration, a 20-week-long feeding experiment was performed by supplying the frogs with either no carotenoid supplements or dietary carotenoids once or four times per week. A high carotenoid diet resulted in a faster increase in green colour chroma as well as higher levels of green and carotenoid chroma of back coloration. Less or no carotenoid supplementation led to an increase in UV-blue chroma, contributing to a dull turquoise appearance often observed in captive-bred and captive-raised anurans. In addition, we showed for the first time that Wallace's flying frogs also perform dynamic colour changes. We tested dynamic changes triggered either by 2 min tactile handling or varying 1 h dark and light conditions. Our results demonstrate that a high carotenoid diet facilitates rapid and reversible change of body coloration in response to a tactile stressor, an adaptation absent in frogs receiving no carotenoids. Dynamic colour changes were likewise observed in response to changing light conditions presumably camouflaging individuals and providing protection from UV irradiation. The ontogenetic and dynamic pigmentation changes are discussed in relation to mechanism and as a likely strategy to avoid predation both at different life stages and in different environments. • Dietary carotenoids impact the development of the green back coloration of frogs. • Lack of carotenoids increase UV-blue chroma, contributing to turquoise appearance. • Early life acquisition of carotenoids regulates dynamic colour change behaviour. • Light conditions mediate reversible full and partial body colour change of frogs.

Does dietary β-carotene influence ontogenetic colour change in the southern corroboree frog?

Ontogenetic colour change occurs in a diversity of vertebrate taxa and may be closely linked to dietary changes throughout development. In various species, red, orange and yellow colouration can be enhanced by the consumption of carotenoids. However, a paucity of long-term dietary manipulation studies means that little is known of the role of individual carotenoid compounds in ontogenetic colour change. We know even less about the influence of individual compounds at different doses (dose effects). The present study aimed to use a large dietary manipulation experiment to investigate the effect of dietary β-carotene supplementation on colouration in southern corroboree frogs (Pseudophryne corroboree) during early post-metamorphic development. Frogs were reared on four dietary treatments with four β-carotene concentrations (0, 1, 2 and 3mgg-1), with frog colour measured every 8 weeks for 32 weeks. β-Carotene was not found to influence colouration at any dose. However, colouration was found to become more conspicuous over time, including in the control treatment. Moreover, all frogs expressed colour maximally at a similar point in development. These results imply that, for our study species, (1) β-carotene may contribute little or nothing to colouration, (2) frogs can manufacture their own colour, (3) colour development is a continual process and (4) there may have been selection for synchronised development of colour expression. We discuss the potential adaptive benefit of ontogenetic colour change in P. corroboree. More broadly, we draw attention to the potential for adaptive developmental synchrony in the expression of colouration in aposematic species.

Evaluating a developmental endocrine toxicity assay for Blanchard's cricket frog (Acris blanchardi) in outdoor enclosures

A developmental toxicity testing design was evaluated for larval and post-metamorphic Blanchard's cricket frogs (Acris blanchardi) raised in outdoor enclosures. Larvae were chronically exposed to 17β-estradiol (0.0–2.3 μg/L E2) from free swimming (Gosner stage 26) until metamorphosis. Juvenile frogs were allowed to mature within the enclosures for 60 days to assess effects of larval exposure on development, including body mass, snout-vent length (SVL), sex ratio, gonad size, and gonadal histopathology. Forty-eight percent of the initial 600 animals were recovered at the end of the study. Recovery was not influenced by E2 exposure, but larval losses were negatively impacted by unusually high spring rain events that flooded some larval tanks, and heat-related mortality of late stage larvae during summer. All surviving larvae completed metamorphosis within an average of 47 days. Overall, E2 exposure did not influence sex ratio, or the body mass, SVL, or gonad size of either males or females. Development of testes was not influenced by E2 exposure, but oviduct development in males was 4.5-fold greater in the highest treatment. Oviduct and ovary development in females exposed to the two highest E2 treatments were half that of control females. Although not treatment related and despite ad-lib feeding, variation in terminal body mass and SVL within enclosures was pronounced, with minimum – maximum differences ranging from 207 to 1442 mg for body mass and 1 mm to 15 mm for SVL. This design allowed us to assess the effects of larval exposure to a contaminant on post-metamorphic development of a native amphibian in a semirealistic field environment. With modifications to decrease flooding or overheating, this enclosure design and species is a good test system for assessing contaminant effects on development of an amphibian from early larval stages through reproductive maturity.

Amphibian thalamic nuclear organization during larval development and in the adult frog Xenopus laevis: Genoarchitecture and hodological analysis.

The early patterning of the thalamus during embryonic development defines rostral and caudal progenitor domains, which are conserved from fishes to mammals. However, the subsequent developmental mechanisms that lead to the adult thalamic configuration have only been investigated for mammals and other amniotes. In this study, we have analyzed in the anuran amphibian Xenopus laevis (an anamniote vertebrate), through larval and postmetamorphic development, the progressive regional expression of specific markers for the rostral (GABA, GAD67, Lhx1, and Nkx2.2) and caudal (Gbx2, VGlut2, Lhx2, Lhx9, and Sox2) domains. In addition, the regional distributions at different developmental stages of other markers such as calcium binding proteins and neuropeptides, helped the identification of thalamic nuclei. It was observed that the two embryonic domains were progressively specified and compartmentalized during premetamorphosis, and cell subpopulations characterized by particular gene expression combinations were located in periventricular, intermediate and superficial strata. During prometamorphosis, three dorsoventral tiers formed from the caudal domain and most pronuclei were defined, which were modified into the definitive nuclear configuration through the metamorphic climax. Mixed cell populations originated from the rostral and caudal domains constitute most of the final nuclei and allowed us to propose additional subdivisions in the adult thalamus, whose main afferent and efferent connections were assessed by tracing techniques under in vitro conditions. This study corroborates shared features of early gene expression patterns in the thalamus between Xenopus and mouse, however, the dynamic changes in gene expression observed at later stages in the amphibian support mechanisms different from those of mammals.

<p class="HeadingRunIn"><strong>Arrangement and size variation of intra-gonadal offspring in a viviparous asterinid sea star</strong></p>

Sibling competition and developmental asynchrony may greatly influence the arrangement and size of offspring of marine invertebrates that care for their young. In Parvulastra parvivipara, an asterinid sea star that incubates its young in the gonads, sibling cannibalism supports post-metamorphic development. Offspring size varies within (coefficient of variation, CV = 22.6 %) and among (CV = 17.7%) the gonads. Confocal microscopy was used to visualize early embryos and oocytes, and revealed the presence of several developmental stages within individual gonads. The eggs were a mean diameter of 84 μm. The observation of a gastrula at 86 µm smaller than the largest egg observed (134 µm) suggests that terminal egg size varies. The appearance of early embryos surrounded by somatic cells suggests that they may receive nutrients through histotrophy. Sibling competition intensifies once the digestive tract is functional in the tiny juveniles which then start to consume siblings. The arrangement of the offspring in the gonads was observed using micro-computed tomography. The juveniles were oriented with their oral surface facing each other, presumably as a defensive strategy to protect themselves from being eaten. Periodic release of offspring in single or several cohorts indicates continual reproduction. Released and retained juveniles varied in size. It is not known what initiates birth but it may be mediated by sibling competition. Larger adults had a greater allocation to female reproductive output than smaller adults.

A comparative analysis of egg provisioning using mass spectrometry during rapid life history evolution in sea urchins.

A dramatic life history switch that has evolved numerous times in marine invertebrates is the transition from planktotrophic (feeding) to lecithotrophic (nonfeeding) larval development-an evolutionary tradeoff with many important developmental and ecological consequences. To attain a more comprehensive understanding of the molecular basis for this switch, we performed untargeted lipidomic and proteomic liquid chromatography-tandem mass spectrometry on eggs and larvae from three sea urchin species: the lecithotroph Heliocidaris erythrogramma, the closely related planktotroph Heliocidaris tuberculata, and the distantly related planktotroph Lytechinus variegatus. We identify numerous molecular-level changes possibly associated with the evolution of lecithotrophy in H. erythrogramma. We find the massive lipid stores of H. erythrogramma eggs are largely composed of low-density, diacylglycerol ether lipids that, contrary to expectations, appear to support postmetamorphic development and survivorship. Rapid premetamorphic development in this species may instead be powered by upregulated carbohydrate metabolism or triacylglycerol metabolism. We also find proteins involved in oxidative stress regulation are upregulated in H. erythrogramma eggs, and apoB-like lipid transfer proteins may be important for echinoid oogenic nutrient provisioning. These results demonstrate how mass spectrometry can enrich our understanding of life history evolution and organismal diversity by identifying specific molecules associated with distinct life history strategies and prompt new hypotheses about how and why these adaptations evolve.

Food Restrictions Affect the Larval Metamorphosis and Early Juvenile Performance in a Neotropical Mangrove Fiddler Crab (Leptuca cumulanta).

Sporadic fluctuations in food availability may affect larval biology and post-metamorphic development in many marine invertebrates. In an experimental study in the laboratory, we investigated whether different regimes (1, 3, and 5 days) of initial starvation or feeding affect the survival and duration of the last planktotrophic larval stage (i.e., megalopa) of the neotropical mangrove fiddler crab Leptuca cumulanta. Newly metamorphosed crabs originating from megalopae starved for 1 and 3 days were cultured through the first 5 juvenile stages to further evaluate whether prior nutritional experience affects the post-larval performance of this species. All megalopae that were starved continuously died, while 80% of the larvae that were fed constantly metamorphosed successfully into the juvenile stage. Megalopae initially starved for 3 and 5 days exhibited lower survival (55% and 30% of larval metamorphosis, respectively) than larvae starved for only 1 day (85%) or fed constantly. The starvation periods (1, 3, and 5 days) also significantly prolonged the mean megalopal stage duration (12.8, 13.9, and 14.3 days, respectively) compared to the continuous feeding regime (10.6 days). Survival of the megalopae subjected to different periods of initial feeding (1, 3, and 5 days) was significantly lower (15.0%, 57.5%, and 62.5%, respectively) than survival of the larvae fed constantly. The mean megalopal stage duration, by contrast, did not vary among megalopae initially fed for 3 and 5 days or fed continuously (10.4 days). The larval starvation did not affect survival and carapace shape of juveniles, but it did alter their intermolt period, growth, and body size. These carryover effects were stronger in the first juvenile crab stage than in other juvenile stages. Our results indicate that the timing and duration of the starvation or feeding regime experienced by the megalopae may affect their successful survival and developmental period until metamorphosis to juvenile life. In addition, the preceding larval starvation associated with a prolonged larval period may also affect early juvenile performance in specific crab stages of L. cumulanta.

Post-metamorphic ontogenetic changes in head size and shape of the pool frog (Pelophylax lessonae, Ranidae)

Post-metamorphic ontogenetic variations of head size and shape were investigated in the pool frog (Pelophylax lessonae, Ranidae). We showed that allometry is an important aspect of the post-metamorphic ontogeny of the pool frog as most of the differences between the head shape of subadults and adults were size-related adjustments. The largest changes affected by size variations included the posterior part of the head and the snout and eye region. In comparison to subadults, adults have wider heads, shorter snouts and relatively smaller eyes. Analyses of the relationships between head size and shape and the maximum size of the prey indicated the absence of correlations in adults. A positive correlation was found in subadults, but only between head width and the maximum size of the prey. Further studies will allow us to draw more generalized conclusions about the ecological relevance of the variations in head size and shape during post-metamorphic development of the pool frog.

Amino acid digestibility of animal protein ingredients for bullfrogs in different phases of post-metamorphic development

The development of diets that economically and ecologically meet the requirements of bullfrogs (Lithobates catesbeianus) is important for frog farming. Therefore, the objective of this study was to determine the apparent digestibility coefficients for essential amino acids of eight animal feed ingredients (poultry byproduct meal, meat and bone meal, salmon byproduct meal, tilapia byproduct meal, spray-dried blood meal, powered red blood cells, feather meal and sardine meal) used in the diets of bullfrogs. Additionally, the limiting digestible amino acids were determined for each ingredient. Bullfrogs in different phases of post-metamorphic development were used: 810 animals in the early phase (mean weight: 40 ± 10 g), 405 animals in the growing phase (95 ± 15 g) and 243 animals in the finishing phase (175 ± 25 g). Poultry byproduct meal, salmon byproduct meal and blood meal exhibited the largest number of high apparent digestibility coefficients for essential amino acids (>70%) in the early, growing and finishing phases, respectively. The animal protein ingredients were well digested by the bullfrogs and could be used in practical diets for this species, respecting the limits of inclusion and digestibility values for each developmental phase.

Metamorphosis of the edible mangrove crab Ucides cordatus (Ucididae) in response to benthic microbial biofilms

Benthic microbial communities can play an important role in the induction of larval metamorphosis in marine invertebrates. The role of biofilms in recognizing the parental habitat is unknown for the ecologically and economically important mangrove crab Ucides cordatus, a species suffering from environmental pressures such as habitat degradation and disease. In the laboratory, we experimentally tested the influence of biofilms grown in offshore and estuarine waters on the moulting rates and developmental time to metamorphosis (TTM) of the last larval stage (megalopa) of U. cordatus. Here, we specifically studied whether: (i) megalopae of this larval-exporting species respond differently to marine (MB) and estuarine biofilms (EB), (ii) biofilms previously immersed (24h) in adult crab-conditioned seawater (ACSW; i.e. conspecific chemical cues) exhibit a greater effectiveness (i.e. by inducing higher moulting rates and shorter TTM) on larval metamorphosis than non-immersed ones and (iii) biofilms pre-immersed (24h) in ACSW decrease their effectiveness when incubated (24h) in pure filtered seawater (FSW) before offering them to megalopae. U. cordatus megalopae metamorphosed to the first juvenile crab stage (JI) in response to both MB and EB, however the moulting rates were significantly higher and development TTM shorter in the presence of EB compared to MB. The metamorphosis-inducing effects were significantly enhanced when both types of biofilms were pre-immersed in ACSW, suggesting that conspecific cues can be absorbed and stored by microbial matrix. The higher inductiveness of EB compared to MB persisted after previous contact with ACSW. Furthermore, EB exhibited a significantly greater biomass production (measured as dry weight) than MB, and when immersed in ACSW, both groups of biofilms significantly increased in biomass (maintaining the hierarchy EB>MB), suggesting that water-soluble chemical substances emitted by the adult crabs may have been absorbed and metabolized by the biofilms. The metamorphic inductiveness and biomass production decreased when both groups of biofilms that were previously kept (24h) in ACSW were thereafter immersed (24h) in FSW. All megalopae successfully moulted to JI after accelerated TTM when reared in ACSW, regardless of presence or absence of biofilms, corroborating that conspecific stimuli are the most effective metamorphosis-stimulating cues tested so far in U. cordatus. The fact that EB improved the moulting rates and shortened the development TTM indicates that megalopae can recognize and respond to microbial assemblages typical for specific environments. This should be ecologically important during larval recruitment by facilitating settlement in appropriate habitats for the post-metamorphic development of early benthic recruits. In addition, the influence of EB could encourage colonization of new estuarine areas and aid natural recovery of U. cordatus in mangrove habitats where crab populations have suffered significant reduction due to deforestation, fishing pressure or diseases.

Post-metamorphic development of skin glands in a true toad: Parotoids versus dorsal skin.

Chemical defenses in amphibians are a common antipredatory and antimicrobial strategy related to the presence of dermal glands that synthesize and store toxic or unpalatable substances. Glands are either distributed throughout the skin or aggregated in multiglandular structures, being the parotoids the most ubiquitous macrogland in toads of Bufonidae. Even though dermal glands begin to develop during late-larval stages, many species, including Rhinella arenarum, have immature glands by the end of metamorphosis, and their post-metamorphic growth is unknown. Herein, we compared the post-metamorphic development of parotoids and dorsal glands by histological and allometric studies in a size series of R. arenarum. Histological and histochemical studies to detect proteins, acidic glycoconjugates, and catecholamines, showed that both, parotoids and dorsal glands, acquire characteristics of adults in individuals larger than 50 mm; that is, a moment in which the cryptic coloration disappears. Parotoid height increased allometrically as a function of body size, whereas the size of small dorsal glands decreased with body size. The number of glands in the dorsum was not linearly related to body size, appearing to be an individual characteristic. Only adult specimens had intraepithelial granular glands in the duct of the largest glands of the parotoids. Since toxic secretions accumulate in the central glands of parotoids, allometric growth of parotoids may translate into greater protection from predators in the largest animals. Conversely, large glands in the dorsum, which produce a proteinaceous secretion of unknown function, grow isometrically to body size. Some characteristics, like intraepithelial glands in the ducts and basophilic glands in the dorsum, are limited to adults.

Landscape influences the morphology of male common toads (Bufo bufo)

In Europe, the recent agricultural intensification has strongly homogenised the landscape. This loss in habitat diversity and the use of agrochemicals are considered as major causes of the global erosion of biodiversity. Landscape changes may also favour phenotypic variation with divergences between populations even at a small spatial scale. We investigated this notion in the common toad (Bufo bufo), a species that inhabits a wide variety of rural habitats. Specifically, we compared the morphology of male adult toads from three contrasting landscapes: forests, traditional farming landscape and intensive farmlands. Overall, individuals from open landscapes were larger and heavier, had longer hind legs and larger parotoid glands than their forest counterparts; suggesting that open landscapes positively influence body size in this species. However, toads from intensive farmland were less symmetrical, suggesting that these individuals may have experienced environmental stress during larval and/or post-metamorphic development. Overall, our results suggest that landscape-specific traits can influence the morphology of male toads in complex ways. Further studies are required to comprehensively assess the impacts of environmental and anthropogenic pressures on amphibians in agroecosystems.

Development and morphological variation of the axial and appendicular skeleton in hylidae (Lissamphibia, Anura).

The axial and appendicular skeleton, the associated musculature and tendons form a functional system related to specific modes of locomotion in anurans. Many transformations in the structures linked with the locomotor function of the adult occur during larval stages and metamorphosis. In this study, we present the larval ontogeny and adult morphology of the axial and appendicular skeletons of 14 species of frogs in the family Hylidae with different locomotor modes and habitat uses. Among Hylidae, a diversity of shapes, locomotory types occurs (e.g., walker, swimmer, jumper, hopper) and different habitat types occupied (shrubby, terrestrial, aquatic, arboreal). Many elements complete differentiation at the end of metamorphosis; others, such as sesamoids, still show an incomplete development at that stage. Sixty seven characters were scored and optimized in an available phylogeny. Nine characters of developmental timing and adult osteology are optimized as synapomorphies of specific groups. Some characters appear to be related to the locomotor type (e.g., the sacro-urostyle region configuration is highly linked with the jumping mode; nonexpanded diapophyses would related to aquatic habitat use). Nevertheless, the functional interpretations are quite particular to this family. Monophyletic clades are also groups with shared locomotory modes or habitat uses. Hence, the hypothesis of common ancestry or adaptation can be evaluated, taking into account the analysis level of the phylogenetic context, so that, when a character is inherited via common ancestry, it necessarily means that functional constraints could also be inherited. Here, we outline the basis for further work on: postmetamorphic development as a fundamental period for the complete differentiation of structures related to a full locomotor functionality; the biomechanical performance in relationship to the variation in ligaments and sesamoids; the importance of analyzing these topics within the frame of heterochrony. J. Morphol. 277:786-813, 2016. © 2016 Wiley Periodicals, Inc.

Post-metamorphic impact of brief hyposaline stress on recently hatched veligers of the gastropod Crepipatella peruviana (Calyptraeidae)

Intertidal environments experience low salinity during heavy rainfall, creating stressful conditions for organisms, including invertebrate pelagic larvae, which can affect post-metamorphic development. Salinity in tide pools was monitored at low tide during a rainfall event in November 2013 at Puerto Montt, southern Chile. Water samples were taken to identify the presence and size of veligers of the gastropod Crepipatella peruviana. In addition, newly hatched veligers were exposed to different salinities [32 (control), 25, 20, and 15] in the laboratory for 6 h and then cultured at the control salinity until metamorphosis. Shell length (SL), oxygen consumption (OCR) and clearance (CR) rates of juveniles, and survival and growth in the first 2 weeks post-metamorphosis were quantified. The salinity of tide pools decreased to ten during heavy rains and yet contained an abundance of living veliger larvae; more than 85 % of the C. peruviana veligers collected had a SL ≤400 µm, which implies that they had only recently hatched. Exposing early veligers to low salinities (15 and 20) decreased size at metamorphosis and early juvenile survival by approximately 10 and 20 %, respectively. Also, the CR was lower at 5 days post-metamorphosis, decreasing by 30 % in individuals that had been exposed to salinity 15 as larvae. However, the OCR (5 and 15 days post-metamorphosis) and CR (15 days post-metamorphosis) were not different from the control treatment with an average value of 1.7 (×10−2 mg O2 h−1 juv−1) and 0.07 (L h−1 juv−1) for OCR and CR at 15 days post-metamorphosis, respectively. Also there was no effect on juvenile growth rate. This study shows that short hyposaline events suffered by early veligers of C. peruviana can cause reduced size at metamorphosis and potentially reduce juvenile survival, factors that could affect the fitness of future adult populations.

From complex to simple: myogenesis in an aplacophoran mollusk reveals key traits in aculiferan evolution.

BackgroundRecent studies suggest a bifurcation at the base of Mollusca, resulting in the primarily single-shelled Conchifera (Bivalvia, Gastropoda, Scaphopoda, Monoplacophora, Cephalopoda) and the spicule-bearing Aculifera (Polyplacophora, Neomeniomorpha, Chaetodermomorpha). A recent study revealed a complex larval musculature exclusively shared by Neomeniomorpha and Polyplacophora, supporting a close relationship of both taxa. However, the ontogenetic transition from the complex larval to the simple adult neomeniomorph musculature, which mainly consists of a three-layered body-wall musculature and serially iterated dorsoventral muscles, remains unknown. To close this gap in knowledge, we studied remodeling of the larval musculature during metamorphosis in the neomeniomorph Wirenia argentea. A comparative analysis with a novel data set of a polyplacophoran, Leptochiton asellus, allows us to infer the morphology of the last common ancestor of Aculifera and the evolution of its subclades therefrom.ResultsThe complex larval musculature of Wirenia argentea persists through metamorphosis and becomes modified to form two of the three muscle layers of the adult body wall. The innermost longitudinal layer of the three-layered body wall musculature is generated by transformation and expansion of distinct larval longitudinal muscle bundles. The larval ventrolateral muscle strands are remodeled and eventually become the most ventral part of the adult longitudinal layer of the body wall musculature. The paired larval enrolling muscle forms the lateral parts and the former rectus muscle is destined to become the most dorsal part of the longitudinal layer of the body wall musculature. The transient ventromedian muscle is lost during postmetamorphic development.ConclusionsPostmetamorphic remodeling in W. argentea supports the hypothesis of a complex myoanatomy rather than a three-layered body wall musculature at the base of Aculifera, and thus argues against homology of the body wall musculature of adult Neomeniomorpha and other potential molluscan sister groups. Our data show that the neomeniomorph body wall musculature is a derived condition and not an aculiferan or molluscan plesiomorphy.

Re-visiting Al Feng’s contributions toward understanding the peripheral basis of acoustic communication in frogs

Al has made substantial contributions toward understanding the peripheral auditory mechanisms underlying acoustic communication in frogs. Al was the first to demonstrate that the basilar papilla is innervated by high-frequency auditory nerve fibers, while the amphibian papilla gives rise to low- and mid-frequency fibers. As his graduate student, we subsequently showed that the tuning of these end organs changes during post-metamorphic development. Al developed a dorsal surgical approach to the auditory nerve, which allowed the coupling between the ears to be studied. He demonstrated that both the monaural directivity patterns and the coupling between ears are frequency dependent. In a follow-up study, we manipulated the coupling between ears and concluded that the frog’s ear functions as a combination pressure/pressure gradient receiver. In this talk, I will re-visit the frequency-dependent crosstalk between the ears first described by Al in 1980. The crosstalk function is analyzed using an acoustic model of a tube with a side branch. This analysis shows the mouth cavity as the side branch is insufficient and yields a lowpass crosstalk function. Including the nares in parallel with the mouth cavity as a side branch yields a bandpass function for sound transmission that accounts for Al’s empirical crosstalk data.

Explorations of the unique anuran ear: The contributions of Al Feng

The anuran inner ear is unique among vertebrate ears in containing three organs for sound detection—the amphibian papilla, the basilar papilla, and the saccule (a mixed auditory/vestibular organ). Al’s anatomical, physiological, and behavioral work in several different anuran species, from the American bullfrog to the Chinese torrent frog, has significantly furthered our understanding of the evolution and operation of this unusual ear. In this talk, I will review this species diversity in inner ear systems and I will further discuss how this diversity emerges over ontogenetic (metamorphic) development. Following up on Al’s research into the post-metamorphic development of the amphibian and basilar papillae in bullfrogs, I will present anatomical data on the larval development of the inner ear in two anuran species, the bullfrog and the African clawed frog, which are adapted to live in different biomes as adults. These results focus attention on how differences in post-metamorphic habitats are reflected in developmental timetables of the maturation of the ear during tadpole life.

Mantle margin morphogenesis in Nodipecten nodosus (Mollusca: Bivalvia): new insights into the development and the roles of bivalve pallial folds.

BackgroundDespite extensive knowledge on bivalve anatomy and development, the formation and differentiation of the mantle margin and its associated organs remain largely unclear. Bivalves from the family Pectinidae (scallops) are particularly promising to cast some light on these issues, because they exhibit a complex mantle margin and their developmental stages are easily obtained from scallop farms. We investigated the mantle margin of the scallop Nodipecten nodosus (L. 1758) during larval and postmetamorphic development.MethodsA thorough analysis of the mantle margin development in Nodipecten nodosus, from veliger larvae to mature adults, was conducted by means of integrative microscopy techniques, i.e., light, electron, and confocal microscopy.ResultsInitially unfolded, the pallial margin is divided into distal and proximal regions by the periostracum-forming zone. The emergence of the pallial musculature and its neural innervation are crucial steps during bivalve larval development. By the late pediveliger stage, the margin becomes folded, resulting in a bilobed condition (i.e., outer and inner folds), a periostracal groove, and the development of different types of cilia. After metamorphosis, a second outgrowth process is responsible for emergence of the middle mantle fold from the outer surface of the inner fold. Once the three-folded condition is established, the general adult features are rapidly formed.ConclusionsOur data show that the middle mantle fold forms from the outer surface of the inner fold after metamorphosis and that the initial unfolded mantle margin may represent a common condition among bivalves. The first outgrowth process, which gives rise to the outer and inner folds, and the emergence of the pallial musculature and innervation occur during larval stages, highlighting the importance of the larval period for mantle margin morphogenesis in Bivalvia.