Development Mode Research Articles

Ecological Advantages and Evolutionary Limitations of Aggregative Multicellular Development

All multicellular organisms develop through one of two basic routes: they either aggregate from free-living cells, creating potentially chimeric multicellular collectives, or they develop clonally via mother-daughter cellular adhesion. Although evolutionary theory makes clear predictions about trade-offs between these developmental modes, these have never been experimentally tested in otherwise genetically identical organisms. We engineered unicellular baker's yeast (Saccharomyces cerevisiae) to develop either clonally ("snowflake"; Δace2) or aggregatively ("floc"; GAL1p::FLO1) and examined their fitness in a fluctuating environment characterized by periods of growth and selection for rapid sedimentation. When cultured independently, aggregation was far superior to clonal development, providing a 35% advantage during growth and a 2.5-fold advantage during settling selection. Yet when competed directly, clonally developing snowflake yeast rapidly displaced aggregative floc. This was due to unexpected social exploitation: snowflake yeast, which do not produce adhesive FLO1, nonetheless become incorporated into flocs at a higher frequency than floc cells themselves. Populations of chimeric clusters settle much faster than floc alone, providing snowflake yeast with a fitness advantage during competition. Mathematical modeling suggests that such developmental cheating may be difficult to circumvent; hypothetical "choosy floc" that avoid exploitation by maintaining clonality pay an ecological cost when rare, often leading to their extinction. Our results highlight the conflict at the heart of aggregative development: non-specific cellular binding provides a strong ecological advantage-the ability to quickly form groups-but this very feature leads to its exploitation.

Comparing shape along growth trajectories in two marine snail ecotypes of Littorina saxatilis: a test of evolution by paedomorphosis

ABSTRACT Two sympatric ecotypes (‘crab’ and ‘wave’) of Littorina saxatilis are adapted to different microhabitats. It has been claimed, based on the comparison of proteomic differentiation across ontogeny, that the wave ecotype may have evolved by paedomorphosis from an ancestor more similar to the crab ecotype. Here, we test the paedomorphosis hypothesis at a morphological level by comparing crab and wave specimens from two localities using the pattern of shell shape differentiation across ontogeny. The results obtained show a pattern of shell shape differentiation similar to the one observed in previous proteomic studies, but such a pattern could be caused by different modes of evolution, and not necessarily by paedomorphosis. This study emphasizes that in addition to studying the pattern of differentiation, the direction of the evolutionary change across ontogeny has to be analysed before conclusions can be drawn on particular developmental modes of evolution.

Ancestral form and function of larval feeding structures are retained during the development of non-planktotrophic gastropods.

Mode of development (MOD) is a key feature that influences the rate and direction of evolution of marine invertebrates. Although many groups include species with different MODs, the evolutionary loss of feeding larvae is thought to be irreversible, as the complex structures used for larval feeding and swimming are lost, reduced, or modified in many species lacking feeding larvae. This view is largely based on observations of echinoderms. Phylogenetic analysis suggests that feeding larvae have been re-gained in at least one species of calyptraeid gastropod. Further, its sister species has retained the velum, the structure used for larval feeding and swimming. Here, we document velar morphology and function in calyptraeids with 4 different MODs. Embryos of Crepidula navicella, Crepidula atrasolea, Bostrycapulus aculeatus, Bostrycapulus odites, Bostrycapulus urraca, Crepipatella dilatata, Crepipatella occulta, Crucibulum quiriquinae and Crepidula coquimbensis all hatch as crawling juveniles, yet only Crepidula coquimbensis does not make a well-formed velum during intracapsular development. The velar dimensions of 6 species with non-planktotrophic development were similar to those of planktotrophic species, while the body sizes were significantly larger. All of the species studied were able to capture and ingest particles from suspension, but several non-planktotrophic species may ingest captured particles only occasionally. Video footage suggests that some species with adelphophagic direct development capture but frequently fail to ingest particles compared to species with the other MODs. Together these lines of evidence show that, among calyptraeids at least, species that lack planktotrophic larvae often retain the structures and functions necessary to successfully capture and ingest particles, reducing the barriers to the re-evolution of planktotrophy.

Continued development of auditory ability in autism spectrum disorder children: A clinical study on click-evoked auditory brainstem response

ObjectivesThe study aimed to analyze the developmental mode of auditory at the level of brainstem in preschool autistic children using click-evoked auditory brainstem response (click-ABR). Methods: Twenty children with autism spectrum disorder (ASD) and 20 age matched typical development children (TD) were recruited. The detail data recorded from click-ABR were collected at two time periods (T1 and T2). ResultsThere was no significant change in TD group at two time periods. In ASD group, wave V latency was significantly shortened at T2 compared to that recorded at T1. The interpeak latency of I–V was short at T2 versus at T1 in the autistic children. Compared to the TD group, ASD was associated with longer latencies for waves V and longer interpeak latencies of I-III, I–V at T1. In addition, ASD group also indicated longer latencies of wave III and wave V, longer interpeak latencies of I-III and I–V at T2 compared to the TD group. ConclusionsASD group had immature and dysfunction developmental mode in auditory stimuli perception at the level of brainstem. The performance of auditory ability in children with ASD improved gradually with ages. However, there are still differences compared with TD children.

Avian developmental rates are constrained by latitude and migratoriness – A global analysis

AbstractAimIt has long been recognized that tropical bird species demonstrate a wide range of traits characteristic for slow life histories, as indicated by lower investment in reproduction, slower senescence or slower physiological pace of life. Nevertheless, evidence for latitudinal variation in avian developmental rates has, so far, been inconclusive and based on limited geographic or phylogenetic sampling. The aim of this study was to test for global associations of avian developmental rates with latitude and migratoriness.LocationGlobal.TaxonBirds.MethodsWe compiled data on developmental (incubation and fledging) periods of 3,500 passerine and non‐passerine bird species distributed worldwide, which represented nearly all extant avian orders and families. Associations of developmental periods with latitude and migratoriness were analysed with phylogenetically informed comparative models that controlled for major sources of variation in developmental rates (body mass, clutch size, and developmental mode across altricial‐precocial spectrum).ResultsOur analyses provided support for a negative latitudinal gradient in the duration of fledging, but not incubation period. After controlling for latitude, we also found that migratory birds showed faster developmental rates than resident species. Finally, we found that developmental rates were nonlinearly associated with clutch size (fastest developmental rates at intermediate clutch size) and that duration of fledging period had higher evolutionary lability than incubation period.Main conclusionsOur global comparative analysis provided convincing and phylogenetically robust evidence for a long‐held hypothesis on latitudinal variation in avian developmental rates, although the pattern was apparent only at the post‐embryonic stage of development (fledging period). This challenges a common belief on longer incubation periods in tropics and indicates that incubation and fledging periods may differently respond to external environmental factors, which can possibly be driven by their different evolutionary lability. The results may contribute to our understanding of biogeographic variation in species diversity.

Incorporation of in vitro techniques for botanicals dietary supplement safety assessment – Towards evaluation of developmental and reproductive toxicity (DART)

As complex mixtures, botanicals present unique challenges when assessing safe use, particularly when endpoint gaps exist that cannot be fully resolved by existing toxicological literature. Here we explore in vitro gene expression as well receptor binding and enzyme activity as alternative assays to inform on developmental and reproductive toxicity (DART) relevant modes of action, since DART data gaps are common for botanicals. Specifically, botanicals suspected to have DART effects, in addition to those with a significant history of use, were tested in these assays. Gene expression changes in a number of different cell types were analysed using the connectivity mapping approach (CMap) to identify modes of action through a functional read across approach. Taken together with ligand affinity data obtained using a set of molecular targets customised towards known DART relevant modes of action, it was possible to inform DART risk using functional analogues, potency comparisons and a margin of internal exposure approach.

Effects of embryo energy, egg size, and larval food supply on the development of asteroid echinoderms.

Organisms have limited resources available to invest in reproduction, causing a trade‐off between the number and size of offspring. One consequence of this trade‐off is the evolution of disparate egg sizes and, by extension, developmental modes. In particular, echinoid echinoderms (sea urchins and sand dollars) have been widely used to experimentally manipulate how changes in egg size affect development. Here, we test the generality of the echinoid results by (a) using laser ablations of blastomeres to experimentally reduce embryo energy in the asteroid echinoderms (sea stars), Pisaster ochraceus and Asterias forbesi and (b) comparing naturally produced, variably sized eggs (1.7‐fold volume difference between large and small eggs) in A. forbesi. In P. ochraceus and A. forbesi, there were no significant differences between juveniles from both experimentally reduced embryos and naturally produced eggs of variable size. However, in both embryo reduction and egg size variation experiments, simultaneous reductions in larval food had a significant and large effect on larval and juvenile development. These results indicate that (a) food levels are more important than embryo energy or egg size in determining larval and juvenile quality in sea stars and (b) the relative importance of embryo energy or egg size to fundamental life history parameters (time to and size at metamorphosis) does not appear to be consistent within echinoderms.

One species, two developmental modes: a case of geographic poecilogony in marine gastropods

BackgroundPoecilogony, the presence of two developmental modes in the same animal species, is a rare phenomenon. Few cases of poecilogony have been suggested for marine invertebrates including molluscs and even less stood extensive testing, mostly revealing a species pair with differing developmental modes. We studied a textbook example of poecilogony in the viviparous snail Planaxis sulcatus (Gastropoda: Planaxidae), for the first time throughout its entire distribution range.ResultsIn the Western Indian Ocean and Red Sea this intertidal species is observed to have large, shelled juveniles, whereas in the Indo-West Pacific planktotrophic veliger larvae are released from a subhaemocoelic brood pouch. We uncovered a shift in developmental modes across its range: from west to east successively earlier developmental stages are released. Furthermore, genetic data based on mitochondrial DNA suggests to recognize P. sulcatus as a single species rather than a group of cryptic species. A reconstruction of the ancestral area of P. sulcatus based on molecular data outlines the Western Indian Ocean and the Indo-West Pacific as area of origin.ConclusionThe findings supporting Planaxis sulcatus as a single widespread species and the geographical shift from one reproductive mode to another suggest for this species to truly represent a case of geographic poecilogony, i.e. differing developmental modes between populations of the same species. Furthermore, the results of our ancestral range estimation imply the release of planktotrophic larvae as the ancestral developmental mode.

Skeletal development and adult osteology of Hypsiboas pulchellus (Anura: Hylidae)

Osteological and skeletal characters have long been proven to be particularly informative in taxonomic and systematic research. Furthermore, ossification sequences are assumed to be a potential tool to investigate developmental states and developmental modes of fossil and extant skeletal specimens. Herein, we provide a detailed account on adult osteology and skeletogenesis in the Montevideo treefrog, Hypsiboas pulchellus (Anura: Hylidae) based on evaluation of a series of cleared and stained specimens. A consensus sequence of ossification, i.e., the order of appearance of mineralized elements until early metamorphosis could be determined as (parasphenoid, presacral vertebrae I-VII, frontoparietal, exoccipital) – transverse processes of presacral vertebrae I-VIII – sacral vertebra – (humerus, radioulna, ilium, femur, tibiofibula, scapula) – (cleithrum, clavicle, coracoids, metacarpals, tarsals, metatarsals, phalanges, hypochord) – (prootic, angulosplenial, dentary, maxilla, premaxilla, squamosal). Comparing the state of mineralized elements in individual specimens, a number of skeletal elements, including the exoccipital, frontoparietal, parasphenoid and prootic, as well as elements of the shoulder and pelvic girdles, and the phalanges, were found to vary intraspecifically regarding the relative time of their ossification within the ossification sequence.

Evidence for Overlapping and Distinct Biological Activities and Transcriptional Targets Triggered by Fibroblast Growth Factor Receptor 2b Signaling between Mid- and Early Pseudoglandular Stages of Mouse Lung Development.

Branching morphogenesis is the basic developmental mode common to organs such as the lungs that undergo a process of ramification from a rudimentary tree. However, the precise molecular and cellular bases underlying the formation of branching organs are still unclear. As inactivation of fibroblast growth factor receptor 2b (Fgfr2b) signaling during early development leads to lung agenesis, thereby preventing the analysis of this pathway at later developmental stages, we used transgenic mice to induce expression of a soluble form of Fgfr2b to inactivate Fgfr2b ligands at embryonic day (E) 14.5, corresponding to the mid-pseudoglandular stage of lung development. We identified an Fgfr2b signaling signature comprised of 46 genes enriched in the epithelium, some of which were common to, but most of them distinct from, the previously identified Fgfr2b signaling signature at E12.5. Our results indicate that Fgfr2b signaling at E14.5 controls mostly proliferation and alveolar type 2 cell (AT2) differentiation. In addition, inhibition of Fgfr2b signaling at E14.5 leads to morphological and cellular impairment at E18.5, with defective alveolar lineage formation. Further studies will have to be conducted to elucidate the role of Fgfr2b signaling at successive stages (canalicular/saccular/alveolar) of lung development as well as during homeostasis and regeneration and repair after injury.

Nutrition-responsive gene expression and the developmental evolution of insect polyphenism.

Nutrition-responsive development is a ubiquitous and highly diversified example of phenotypic plasticity, yet its underlying molecular and developmental mechanisms and modes of evolutionary diversification remain poorly understood. We measured genome-wide transcription in three closely related species of horned beetles exhibiting strikingly diverse degrees of nutrition responsiveness in the development of male weaponry. We show that (1) counts of differentially expressed genes between low- and high-nutritional backgrounds mirror species-specific degrees of morphological nutrition responsiveness; (2) evolutionary exaggeration of morphological responsiveness is underlain by both amplification of ancestral nutrition-responsive gene expression and recruitment of formerly low nutritionally responsive genes; and (3) secondary loss of morphological responsiveness to nutrition coincides with a dramatic reduction in gene expression plasticity. Our results further implicate genetic accommodation of ancestrally high variability of gene expression plasticity in both exaggeration and loss of nutritional plasticity, yet reject a major role of taxon-restricted genes in the developmental regulation and evolution of nutritional plasticity.

An automated aquatic rack system for rearing marine invertebrates

BackgroundOne hundred years ago, marine organisms were the dominant systems for the study of developmental biology. The challenges in rearing these organisms outside of a marine setting ultimately contributed to a shift towards work on a smaller number of so-called model systems. Those animals are typically non-marine organisms with advantages afforded by short life cycles, high fecundity, and relative ease in laboratory culture. However, a full understanding of biodiversity, evolution, and anthropogenic effects on biological systems requires a broader survey of development in the animal kingdom. To this day, marine organisms remain relatively understudied, particularly the members of the Lophotrochozoa (Spiralia), which include well over one third of the metazoan phyla (such as the annelids, mollusks, flatworms) and exhibit a tremendous diversity of body plans and developmental modes. To facilitate studies of this group, we have previously described the development and culture of one lophotrochozoan representative, the slipper snail Crepidula atrasolea, which is easy to rear in recirculating marine aquaria. Lab-based culture and rearing of larger populations of animals remain a general challenge for many marine organisms, particularly for inland laboratories.ResultsHere, we describe the development of an automated marine aquatic rack system for the high-density culture of marine species, which is particularly well suited for rearing filter-feeding animals. Based on existing freshwater recirculating aquatic rack systems, our system is specific to the needs of marine organisms and incorporates robust filtration measures to eliminate wastes, reducing the need for regular water changes. In addition, this system incorporates sensors and associated equipment for automated assessment and adjustment of water quality. An automated feeding system permits precise delivery of liquid food (e.g., phytoplankton) throughout the day, mimicking real-life feeding conditions that contribute to increased growth rates and fecundity.ConclusionThis automated system makes laboratory culture of marine animals feasible for both large and small research groups, significantly reducing the time, labor, and overall costs needed to rear these organisms.

Sedimentary environment and organic matter accumulation of Neoproterozoic black shale in the North China Craton: A case study of the Tonian Baishugou Formation in the Luonan area

With acceleration of “oil exploration near the source” in the petroleum industry, black shales (BS) play an increasingly important role in oil and gas exploration. Meso-Neoproterozoic BS are well developed in the North China Craton (NCC), China, many of which are identified as potential hydrocarbon source rocks. Although BS from the Mesoproterozoic Era has been widely investigated, few studies were focused on the Neoproterozoic BS so far. Based on petrology and geochemistry analysis, the sedimentary environment, provenance and organic matter accumulation of two BS layers in the Tonian Baishugou Formation from Sujiacun section, Luonan Area, southern NCC were investigated. It suggests that the lower BS (LB) was deposited in a shallow and non-stratified cratonic-interior sea environment with unstable dysoxic or suboxic conditions. The seawater salinity increased from brackish to marine facies conditions due to the decrease of runoff caused by climate cooling. The Upper BS (UB) was deposited in an open paleomarine environment with stable suboxic conditions and brackish salinity in continuously humid and hot paleoclimate. Both BS were derived from granitoids formed by the ca.2.5 Ga collisional-thermal events in the NCC. The OM accumulation rate of UB is higher than that of UB while LB records lower OM loss rate. On these bases, two developmental modes for the BS from the Baishugou Formation were established.

ПЕДАГОГІЧНІ УМОВИ ПРОФЕСІЙНОЇ ПІДГОТОВКИ МАЙБУТНІХ ЛОГОПЕДІВ В ІНФОРМАЦІЙНО-ОСВІТНЬОМУ СЕРЕДОВИЩІ УНІВЕРСИТЕТУ

У статті обґрунтовано комплекс педагогічних умов професійної підготовки майбутніх логопедів в інформаційно-освітньому середовищі закладів вищої освіти. Подано трактування комплексу педагогічних умов, під якими розуміємо сукупність взаємопов’язаних чинників та заходів освітнього процесу, дотримання яких забезпечує досягнення студентами більш високого рівня готовності до професійної діяльності. Визначено такі групи умов: перша група, що відображає процес цілеспрямованого використання потенціалу фахових дисциплін у професійній підготовці майбутніх логопедів через теоретичну підготовку та практичну діяльність, спрямовану на роботу з дітьми з порушенням мовлення; друга – орієнтує на формування в майбутніх логопедів готовності до роботи в розвивально-корекційному режимі (мотивації, потреби, здатності, рішучості до саморозвитку, рефлексії, емпатії, творчої активності) з використанням інноваційних форм, активних методів та інформаційно-комунікаційних технологій; третя – спрямована на розвиток професійних умінь і навичок, зокрема через корекційно-логопедичну роботу засобами моделювання артикуляції звуків.

Postembryonic development of Nymphon australe Hodgson, 1902 (Pycnogonida, Nymphonidae) from Antarctica

Developmental modes in pycnogonids are variable, even between congeneric species. Most of our previous knowledge of pycnogonid life history stages is based on morphological descriptions of the larval and those postlarval instars still retained on male ovigers, whereas the free-living instars are largely unknown. In this paper, a combination of morphological and molecular tools is used in order to link those postlarval instars retained on male ovigers to free-living specimens representing putatively later stages in the postembryonic development of a sea spider species. Male specimens of Nymphon australe carrying postembryonic instars were collected from localities off the South Shetland Islands, the Weddell Sea, the Drake Passage, the Bransfield Strait, and the Ross Sea. Three subsequent free-living instars were collected from Drake Passage. Nymphon australe hatch as a postlarval instar with two-articled palps and limb buds of the two first-walking legs. Postlarval instars 1 and 2 (both carried on the ovigers of males), postlarval instars 3 and 4, and a juvenile (all three free living) are all described and illustrated. A molecular phylogenetic based on the cox1 gene links all free-living stages to N. australe populations from the Antarctic Peninsula. The postlarval development of N. australe is discussed here and compared with those known from other pycnogonid species with similar development pathways.

Quaternary ice sheets and sea level regression drove divergence in a marine gastropod along Eastern and Western coasts of South America

The southern coastline of South America is a remarkable area to evaluate how Quaternary glacial processes impacted the demography of the near-shore marine biota. Here we present new phylogeographic analyses in the pulmonate Siphonaria lessonii across its distribution, from northern Chile in the Pacific to Uruguay in the Atlantic. Contrary to our expectations, populations from the southwestern Atlantic, an area that was less impacted by ice during glacial maxima, showed low genetic diversity and evidence of recent expansion, similar to the patterns recorded in this study across heavily ice-impacted areas in the Pacific Magellan margin. We propose that Atlantic and Pacific shallow marine hard-substrate benthic species were both affected during the Quaternary in South America, but by different processes. At higher latitudes of the southeast Pacific, ice-scouring drastically affected S. lessonii populations compared to non-glaciated areas along the Chile-Peru province where the species was resilient. In the southwest Atlantic, S. lessonii populations would have been dramatically impacted by the reduction of near-shore rocky habitat availability as a consequence of glacio-eustatic movements. The increase of gravelly and rocky shore substrates in the southwest Atlantic supports a hypothesis of glacial refugia from where the species recolonized lower latitudes across the Atlantic and Pacific margins. Our results suggest that current patterns of genetic diversity and structure in near-shore marine benthic species do not solely depend on the impact of Quaternary glacial ice expansions but also on the availability of suitable habitats and life-history traits, including developmental mode, bathymetry and the likelihood of dispersal by rafting.

Do differences in developmental mode shape the potential for local adaptation?

Future climate change is leading to the redistribution of life on Earth as species struggle to cope with rising temperatures. Local adaptation allows species to become locally optimized and persist despite environmental selection, but the extent to which this occurs in nature may be limited by dispersal and gene flow. Congeneric marine gastropod species (Littorina littorea and L.saxatilis) with markedly different developmental modes were collected from across a latitudinal thermal gradient to explore the prevalence of local adaptation to temperature. The acute response of metabolic rate (using oxygen consumption as a proxy) to up-ramping and down-ramping temperature regimes between 6°C and 36°C was quantified for five populations of each species. The highly dispersive L.littorea exhibited minimal evidence of local adaptation to the thermal gradient, with no change in thermal optimum (Topt ) or thermal breadth (Tbr ) and a decline in maximal performance (max ) with increasing latitude. In contrast, the direct developing L.saxatilis displayed evidence of local optimization, although these varied idiosyncratically with latitude, suggesting a suite of selective pressures may be involved in shaping thermal physiology in this relatively sedentary species. Our results show that the biogeography of thermal traits can differ significantly between related species, and show that interpopulation differences in thermal performance do not necessarily follow simple patterns that may be predicted based on latitudinal changes in environmental temperatures. Further research is clearly required to understand the mechanisms that can lead to the emergence of local adaptation in marine systems better and allow improved predictions of species redistribution in response to climate change.

Embryonic development of the false limpet Siphonaria lateralis from Atlantic Patagonia

AbstractSiphonariids are pulmonate gastropods inhabiting rocky intertidal habitats, and many studies have focused on these false limpets around the world. In the southern South Atlantic, studies on reproduction and development in species of Siphonaria are scarce. We studied the embryonic development and egg masses of Siphonaria lateralis at its northernmost distribution in Atlantic Patagonia. In S. lateralis, as in most species of Siphonaria, individuals spawn benthic egg masses that strongly attach to intertidal rocky substrata. A single spherical egg that measures ~120 µm develops inside the egg capsule of S. lateralis. Considering the relatively small egg size, and reports from previous studies, the developmental modality of S. lateralis might be expected to include a planktotrophic larval phase. However, we found that hatchlings emerged as 1‐mm crawling juveniles, probably owing to the presence of intracapsular fluid, which may provide the energetic requirements for direct development. The embryonic size changed little from the egg to veliger stages, and then increased rapidly until the hatchling stage. We compared development in S. lateralis with development in the sympatric Siphonaria lessonii, in which egg size was reported to be ~80 µm and hatching occurs as planktotrophic veliger larvae. In these two species, spawn and early intracapsular developmental modes are remarkably different; these differences represent contrasting ways to survive in the harsh and physically stressful intertidal Patagonian coasts.

Candidate cases of poecilogony in Neogastropoda: implications for the systematics of the genus Raphitoma Bellardi, 1847

Poecilogony is the intraspecific variation in developmental mode, with larvae of different types produced by the same individual, population or species. It is very rare among marine invertebrates, and in gastropods has long been described only in a few opisthobranchs. The physiological and regulatory mechanisms underlying larval evolutionary transitions, such as loss of planktotrophy that occurred repeatedly in many caenogastropod lineages, are still largely unknown. We have studied the inter- v. intraspecific variation in larval development in the north-east Atlantic neogastropod genus Raphitoma Bellardi, 1847, starting with an iterative taxonomy approach: 17 morphology-based Preliminary Species Hypotheses were tested against a COI molecular-distance-based method (ABGD), and the retained species hypotheses were eventually inspected for reciprocal monophyly on a multilocus dataset. We subsequently performed an ancestral state reconstruction on an ultrametric tree of the 10 Final Species Hypotheses, time-calibrated by fossils, revealing that the interspecific changes were planktotrophy > lecithotrophy, and all have occurred in the Pleistocene, after 2.5 million years ago. This is suggestive of a major role played by Pleistocene Mediterranean oceanographic conditions – enhanced oligotrophy, unpredictable availability of water column resources – likely to favour loss of planktotrophy. Within this group of species, which has diversified after the Miocene, we identified one pair of sibling species differing in their larval development, Raphitoma cordieri (Payraudeau, 1826) and R. horrida (Monterosato, 1884). However, we also identified two Final Species Hypotheses, each comprising individuals with both larval developmental types. Our working hypothesis is that they correspond to one or two poecilogonous species. If confirmed by other nuclear markers, this would be the first documentation of poecilogony in the Neogastropoda, and the second in the whole Caenogastropoda. Although sibling species with different developmental strategies may offer good models to study some evolutionary aspects, poecilogonous taxa are optimally suited for identifying regulatory and developmental mechanisms underlying evolutionary transitions.

Increasing our knowledge on direct-developing frogs: The ontogeny of Ischnocnema henselii (Anura: Brachycephalidae)

Due to the difficulty in finding newly fresh spawn in natural environments, few embryonic developmental studies have been carried out in anurans with direct development. Here we provide detailed data on the embryonic ontogeny of Ischnocnema henselii, and compare some morphological aspects related to its developmental mode within and outside of the brachycephaloid clade. Embryonic development in I. henselii is characterized by a unicuspid egg tooth (bicuspid in most other Brachycephaloidea), external gills present, open vent tube, and tail fins with dorsoventral orientation throughout the development. We also provide the first account of skin development in direct-developing frogs, revealing that the maturation of the integument has a typical dorsal to ventral sequence of changes as in most biphasic anurans. The early onset of thyroid development seems to be consistent with the hypothesis that the evolution of direct development in anuran amphibians involved precocious activation of the thyroid axis. A comparative analysis with the still few described embryonic ontogenies for direct-developing species reveals variation in the length of the embryonic period, rate of development, size at hatching and presence/absence of external morphological characters, which suggests heterochronic shifts in the rate of species-specific stage progression. All these details reinforce the idea of the high morphological variability among direct-developing frogs.