Eyespot Formation Research Articles

Exploring Alternatives for Marine Toxicity Testing: Initial Evaluation of Fish Embryo and Mysid Tests.

Current regulations require that toxicity assessments be performed using standardized toxicity testing methods, often using fish. Recent legislation in both the European Union and United States has mandated that toxicity testing alternatives implement the 3Rs of animal research (replacement, reduction, and refinement) whenever possible. There have been advances in the development of alternatives for freshwater assessments, but there is a lack of analogous developments for marine assessments. One potential alternative testing method is the fish embryo toxicity (FET) test, which uses fish embryos rather than older fish. In the present study, FET methods were applied to two marine model organisms, the sheepshead minnow and the inland silverside. Another potential alternative is the mysid shrimp survival and growth test, which uses an invertebrate model. The primary objective of the present study was to compare the sensitivity of these three potential alternative testing methods to two standardized fish-based tests using 3,4-dichloroaniline (DCA), a common reference toxicant. A secondary objective was to characterize the ontogeny of sheepshead minnows and inland silversides. This provided a temporal and visual guide that can be used to identify appropriately staged embryos for inclusion in FET tests and delineate key developmental events (e.g., somite development, eyespot formation, etc.). Comparison of the testing strategies for assessing DCA indicated that: (1) the standardized fish tests possessed comparable sensitivity to each other; (2) the mysid shrimp tests possessed comparable sensitivity to the standardized fish tests; (3) the sheepshead minnow and inland silverside FET tests were the least sensitive testing strategies employed; and (4) inclusion of sublethal endpoints (i.e., hatchability and pericardial edema) in the marine FETs increased their sensitivity. Environ Toxicol Chem 2024;43:1285-1299. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Wing pattern diversity in Eunica butterflies (Nymphalidae: Biblidinae): phylogenetic analysis implies decoupled adaptive trends in dorsal sexual dimorphism and ventral eyespot evolution.

Butterfly eyespots are wing patterns reminiscent of vertebrate eyes, formed by concentric rings of contrastingly coloured scales. Eyespots are usually located close to the wing margin and often regarded as the single most conspicuous pattern element of butterfly wing colour displays. Recent efforts to understand the processes involved in the formation of eyespots have been driven mainly by evo-devo approaches focused on model species. However, patterns of change implied by phylogenetic relationships can also inform hypotheses about the underlying developmental mechanisms associated with the formation or disappearance of eyespots, and the limits of phenotypic diversity occurring in nature. Here we present a combined evidence phylogenetic hypothesis for the genus Eunica, a prominent member of diverse Neotropical butterfly communities, that features notable variation among species in eyespot patterns on the ventral hind wing surface. The data matrix consists of one mitochondrial gene region (COI), four nuclear gene regions (GAPDH, RPS5, EF1a and Wingless) and 68 morphological characters. A combined cladistic analysis with all the characters concatenated produced a single most parsimonious tree that, although fully resolved, includes many nodes with modest branch support. The phylogenetic hypothesis presented corroborates a previously proposed morphological trend leading to the loss of eyespots, together with an increase in the size of the conserved eyespots, relative to outgroup taxa. Furthermore, wing colour pattern dimorphism and the presence of androconia suggest that the most remarkable instances of sexual dimorphism are present in the species of Eunica with the most derived eyespot patterns, and are in most cases accompanied by autapomorphic combinations of scent scales and "hair pencils". We discuss natural and sexual selection as potential adaptive explanations for dorsal and ventral wing patterns.

Zeaxanthin is required for eyespot formation and phototaxis in Euglena gracilis.

The eyespot apparatus is an organelle that forms carotenoid-rich globules in diverse flagellated microalgae and functions in phototaxis. The euglenophytes have structurally and functionally distinct eyespot apparatuses from chlorophytes. β-Carotene is the most abundant pigment detected in chlorophytes' eyespots, while xanthophylls such as zeaxanthin and diadinoxanthin have been suggested to function in euglenophytes' eyespots. Here, we investigated the association between carotenoid composition and eyespot formation via pathway-scale mutagenesis using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-mediated genome editing in the euglenophyte Euglena gracilis. Lycopene cyclase (lcy) mutants exhibited sole lycopene accumulation, defective red eyespots, and phototactic insensitivity. Conversely, β-carotene hydroxylase (cytochrome P450 97h1, cyp97h1) mutants accumulated β-carotene and its hydroxylated products β-cryptoxanthin and zeaxanthin and formed phototactic eyespot apparatuses, while cyp97h1 cyp97f2 double mutants were deficient in β-carotene hydroxylation and mostly lacked functional eyespots. Thus, zeaxanthin is required for the stable formation of functional eyespots in E. gracilis, highlighting evolutionary differences between euglenophytes and chlorophytes in the metabolic regulation of photoreactive organelle formation.

Mathematical modeling of the eyespots in butterfly wings

Butterfly wing color patterns are a representative model system for studying biological pattern formation, due to their two-dimensional simple structural and high inter- and intra-specific variabilities. Moreover, butterfly color patterns have demonstrated roles in mate choice, thermoregulation, and predator avoidance via disruptive coloration, attack deflection, aposematism, mimicry, and masquerade. Because of the importance of color patterns to many aspects of butterfly biology and their apparent tractability for study, color patterns have been the subjects of many attempts to model their development. Early attempts focused on generalized mechanisms of pattern formation such as reaction-diffusion, diffusion gradient, lateral inhibition, and threshold responses, without reference to any specific gene products. As candidate genes with expression patterns that resembled incipient color patterns were identified, genetic regulatory networks were proposed for color pattern formation based on gene functions inferred from other insects with wings, such as Drosophila. Particularly detailed networks incorporating the gene products, Distal-less (Dll), Engrailed (En), Hedgehog (Hh), Cubitus interruptus (Ci), Transforming growth factor-β (TGF-β), and Wingless (Wg), have been proposed for butterfly border ocelli (eyespots) which helps the investigation of the formation of these patterns. Thus, in this work, we develop a mathematical model including the gene products En, Hh, Ci, TGF-β, and Wg to mimic and investigate the eyespot formation in butterflies. Our simulations show that the level of En has peaks in the inner and outer rings and the level of Ci has peaks in the inner and middle rings. The interactions among these peaks activate cells to produce white, black, and yellow pigments in the inner, middle, and outer rings, respectively, which captures the eyespot pattern of wild type Bicyclus anynana butterflies. Additionally, our simulations suggest that lack of En generates a single black spot and lack of Hh or Ci generates a single white spot, and a deficiency of TGF-β or Wg will cause the loss of the outer yellow ring. These deficient patterns are similar to those observed in the eyespots of Vanessa atalanta, Vanessa altissima, and Chlosyne nycteis. Thus, our model also provides a hypothesis to explain the mechanism of generating the deficient patterns in these species.

Neurological and regenerative defects in fresh water planarian exposed to lead

Lead (Pb) is a major heavy metal that augments environmental pollution and is a health risk to living organisms. This study was performed to investigate the effect of lead on characteristics of planarian, Dugesia japonica. Briefly, planarians were cultivated in water containing different concentrations (0–400 mg/L) of Pb, and incubated for varying durations (1, 3, and 5 hr). After termination of the incubation time, motility and seizure-like behaviors (c-like, head-bop, snake-like, and screw-like) of the planarians were counted in fresh water. Results showed that increasing Pb concentration and time resulted in decreased motility of the planarians (p<0.05). Increasing concentrations of Pb also resulted in significant increase in the seizure-like behavioral patterns, in particular the c-like and head-bop behaviors. In order to examine eye regeneration, the head region was cut, and rest of the body was incubated in water in the absence or presence of Pb, until emergence of the eye extrusion. Formation of eye spots was initiated in amputated fragments of the control group (without Pb) on day 4 after incubation, whereas appearance of the eye spots was delayed in planarian exposed to 200 mg/L Pb. Moreover, immunohistochemistry revealed that formation of the optic nerve was delayed in planarians exposed to Pb. Thus, our studies determined that planarians exposed to high concentrations of Pb resulted in decreasing motility and induction of seizure-like behaviors, as well as delayed eye regeneration. Results of the current study therefore validate that exposure to lead has a negative effect on the lifespan of aquatic organisms and can cause disturbance of the nervous system in animals, thereby implying the possibility of threatening health.

β-Thymosin is an essential regulator of stem cell proliferation and neuron regeneration in planarian (Dugesia japonica)

β-Thymosin is a multifunctional peptide ubiquitously expressed in vertebrates and invertebrates. Many studies have found β-thymosin is critical for wound healing, angiogenesis, cardiac repair, hair regrowth, and anti-fibrosis in vertebrates, and plays an important role in antimicrobial immunity in invertebrates. However, whether β-thymosin participates in the regeneration of organisms is still poorly understood. In this study, we identified a β-thymosin gene in Dugesia japonica which played an important role in stem cell proliferation and neuron regeneration during the tissue repair process in D. japonica. Sequencing analysis showed that β-thymosin contained two conserved β-thymosin domains and two actin-binding motifs, and had a high similarity with other β-thymosins of invertebrates. In situ or fluorescence in situ hybridization analysis revealed that Djβ-thymosin was co-localized with DjPiWi in the neoblast cells of intact adult planarians and the blastema of regenerating planarians, suggesting Djβ-thymosin has a potential function of regeneration. Disruption Djβ-thymosin by RNA interference results in a slightly curled up head of planarian and stem cell proliferation defects. Additionally, we found that, upon amputation, Djβ-thymosin RNAi-treated animals had impaired regeneration ability, including impaired blastema formation, delayed eyespot formation, decreased brain area, and disrupted central CNS formation, implying Djβ-thymosin is an essential regulator of stem cell proliferation and neuron regeneration.

Neural and endocrine responses to social stress differ during actual and virtual aggressive interactions or physiological sign stimuli

Neural and endocrine responses provide quantitative measures that can be used for discriminating behavioral output analyses. Experimental design differences often make it difficult to compare results with respect to the mechanisms producing behavioral actions. We hypothesize that comparisons of distinctive behavioral paradigms or modification of social signals can aid in teasing apart the subtle differences in animal responses to social stress. Eyespots are a unique sympathetically activated sign stimulus of the lizard Anolis carolinensis that influence aggression and social dominance. Eyespot formation along with measurements of central and plasma monoamines enable comparison of paired male aggressive interactions with those provoked by a mirror image. The results suggest that experiments employing artificial application of sign stimuli in dyadic interactions amplify behavioral, neural and endocrine responses, and foreshorten behavioral interactions compared to those that develop among pairs naturally. While the use of mirrors to induce aggressive behavior produces simulated interactions that appear normal, some behavioral, neural, and endocrine responses are amplified in these experiments as well. In contrast, mirror image interactions also limit the level of certain behavioral and neuroendocrine responses. As true social communication does not occur during interaction with mirror images, rank relationships can never be established. Multiple experimental approaches, such as combining naturalistic social interactions with virtual exchanges and/or manipulation of sign stimuli, can often provide added depth to understanding the motivation, context, and mechanisms that produce specific behaviors. The addition of endocrine and neural measurements helps identify the contributions of specific behavioral elements to the social processes proceeding.

Carotenoid accumulation in the eyespot apparatus required for phototaxis is independent of chloroplast development in Euglena gracilis

Euglena gracilis exhibits photomovements in response to various light stimuli, such as phototactic and photophobic responses. Our recent study revealed that carotenoids in the eyespot apparatus are required for triggering phototaxis in this alga. However, the role of chloroplasts in eyespot formation is not understood. Here, we isolated carotenoid-less (cl) strains of E. gracilis from cells silenced gene expression of phytoene synthase (EgcrtB). Unlike WT, the culture colors of cl1, cl3, and the non-photosynthetic mutant SM-ZK were orange, while that of cl4 was white. Electron microscope observations showed that SM-ZK, cl1, and cl3 had no developed chloroplast and formed a normal eyespot apparatus, similar to that of WT, but this was not the case for cl4. Carotenoids detected in WT were diadinoxanthin, neoxanthin, and β-carotene. However, the most abundant species of SM-ZK, cl1, and cl3 was zeaxanthin, and there was no diadinoxanthin or neoxanthin. Photomovement analysis showed that SM-ZK, cl1, and cl3 exhibited negative phototactic and photophobic responses, similar to those of WT, whereas cl4 lacked negative phototaxis. Taken together, the formation of the eyespot apparatus required for phototaxis is independent of chloroplast development in E. gracilis, suggesting that this property is different from other photosynthetic flagellates.

A Comparison of the Egg Development and Hatching Success of Two Molecularly Delineated Species of Diplostomum (Digenea)

The life cycles of many species of Diplostomum (Digenea) have been elucidated; however, few studies include the details of egg development and hatching success. Here the eggs of 2 molecularly delineated sympatric species of Diplostomum were observed for differences in developmental parameters. These parameters included prepatent period, time required for first visible eyespot formation, hatching time, and hatching success. There was no significant difference in the mean prepatent period, total number of miracidia that developed eyespots, or number of days to hatch between the 2 species. There was a significant difference in the average time for first visible eyespots to appear and hatching success. These data highlight the need for further studies investigating sympatric species of Diplostomum to document and understand differences in life history traits during the various phases of their life cycles and their role in transmission success.

Wound healing, calcium signaling, and other novel pathways are associated with the formation of butterfly eyespots

BackgroundOne hypothesis surrounding the origin of novel traits is that they originate from the co-option of pre-existing genes or larger gene regulatory networks into novel developmental contexts. Insights into a trait’s evolutionary origins can, thus, be gained via identification of the genes underlying trait development, and exploring whether those genes also function in other developmental contexts. Here we investigate the set of genes associated with the development of eyespot color patterns, a trait that originated once within the Nymphalid family of butterflies. Although several genes associated with eyespot development have been identified, the eyespot gene regulatory network remains largely unknown.ResultsIn this study, next-generation sequencing and transcriptome analyses were used to identify a large set of genes associated with eyespot development of Bicyclus anynana butterflies, at 3-6 h after pupation, prior to the differentiation of the color rings. Eyespot-associated genes were identified by comparing the transcriptomes of homologous micro-dissected wing tissues that either develop or do not develop eyespots in wild-type and a mutant line of butterflies, Spotty, with extra eyespots. Overall, 186 genes were significantly up and down-regulated in wing tissues that develop eyespots compared to wing tissues that do not. Many of the differentially expressed genes have yet to be annotated. New signaling pathways, including the Toll, Fibroblast Growth Factor (FGF), extracellular signal–regulated kinase (ERK) and/or Jun N-terminal kinase (JNK) signaling pathways are associated for the first time with eyespot development. In addition, several genes involved in wound healing and calcium signaling were also found to be associated with eyespots.ConclusionsOverall, this study provides the identity of many new genes and signaling pathways associated with eyespots, and suggests that the ancient wound healing gene regulatory network may have been co-opted to cells at the center of the pattern to aid in eyespot origins. New transcription factors that may be providing different identities to distinct wing sectors, and genes with sexually dimorphic expression in the eyespots were also identified.

Distal-less induces elemental color patterns in Junonia butterfly wings.

BackgroundThe border ocellus, or eyespot, is a conspicuous color pattern element in butterfly wings. For two decades, it has been hypothesized that transcription factors such as Distal-less (Dll) are responsible for eyespot pattern development in butterfly wings, based on their expression in the prospective eyespots. In particular, it has been suggested that Dll is a determinant for eyespot size. However, functional evidence for this hypothesis has remained incomplete, due to technical difficulties.ResultsHere, we show that ectopically expressed Dll induces ectopic elemental color patterns in the adult wings of the blue pansy butterfly, Junonia orithya (Lepidoptera, Nymphalidae). Using baculovirus-mediated gene transfer, we misexpressed Dll protein fused with green fluorescent protein (GFP) in pupal wings, resulting in ectopic color patterns, but not the formation of intact eyespots. Induced changes included clusters of black and orange scales (a basic feature of eyespot patterns), black and gray scales, and inhibition of cover scale development. In contrast, ectopic expression of GFP alone did not induce any color pattern changes using the same baculovirus-mediated gene transfer system.ConclusionsThese results suggest that Dll plays an instructive role in the development of color pattern elements in butterfly wings, although Dll alone may not be sufficient to induce a complete eyespot. This study thus experimentally supports the hypothesis of Dll function in eyespot development.

Suspension of Egg Hatching Caused by High Humidity and Submergence in Spider Mites.

We tested the effects of high humidity and submergence on egg hatching of spider mites. In both the high humidity and submergence treatments, many Tetranychus and Panonychus eggs did not hatch until after the hatching peak of the lower humidity or unsubmerged controls. However, after humidity decreased or water was drained, many eggs hatched within 1-3 h. This was observed regardless of when high humidity or submergence treatments were implemented: either immediately after oviposition or immediately before hatching was due. Normal eyespot formation was observed in most eggs in the high humidity and submergence treatments, which indicates that spider mite embryos develop even when eggs are underwater. Therefore, delays in hatching are not caused by delayed embryonic development. A delay in hatching was always observed in Panonychus citri (McGregor) but was more variable in Tetranychus urticae Koch and Tetranychus kanzawai Kishida. The high humidity and submergence treatments affected but did not suppress larval development in these species. In contrast, many Oligonychus eggs died following the high humidity treatments. In Tetranychus and Panonychus spider mites, suspension of egg hatching may mitigate the adverse effects of rainfall.

The transcription factor Apontic-like controls diverse colouration pattern in caterpillars.

Genetic polymorphisms underlie the convergent and divergent evolution of various phenotypes. Diverse colour patterns on caterpillars, which are ecologically important, are good models for understanding the molecular backgrounds of phenotypic diversity. Here we show that a single evolutionarily conserved gene apontic-like (apt-like) encoding for a putative transcription factor accounts for the silkworm p locus, which causes at least 15 different larval markings involved in branch-like markings and eye-spot formation. The expression of apt-like and melanin synthesis genes are upregulated in association with pigmented areas of marking mutants Striped (p(S)) and normal (+(p)) but not in the non-marking allele plain (p). Functional analyses, ectopic expression, RNAi and TALEN, demonstrate that apt-like causes melanin pigmentation in a cell-autonomous manner. These results suggest that variation in p alleles is caused by the differential expression of the gene apt-like which induces targeted elevation of gene expressions in the melanin synthesis pathway.

Evolutionary history of the recruitment of conserved developmental genes in association to the formation and diversification of a novel trait

BackgroundThe origin and modification of novel traits are important aspects of biological diversification. Studies combining concepts and approaches of developmental genetics and evolutionary biology have uncovered many examples of the recruitment, or co-option, of genes conserved across lineages for the formation of novel, lineage-restricted traits. However, little is known about the evolutionary history of the recruitment of those genes, and of the relationship between them -for example, whether the co-option involves whole or parts of existing networks, or whether it occurs by redeployment of individual genes with de novo rewiring. We use a model novel trait, color pattern elements on butterfly wings called eyespots, to explore these questions. Eyespots have greatly diversified under natural and sexual selection, and their formation involves genetic circuitries shared across insects.ResultsWe investigated the evolutionary history of the recruitment and co-recruitment of four conserved transcription regulators to the larval wing disc region where circular pattern elements develop. The co-localization of Antennapedia, Notch, Distal-less, and Spalt with presumptive (eye)spot organizers was examined in 13 butterfly species, providing the largest comparative dataset available for the system. We found variation between families, between subfamilies, and between tribes. Phylogenetic reconstructions by parsimony and maximum likelihood methods revealed an unambiguous evolutionary history only for Antennapedia, with a resolved single origin of eyespot-associated expression, and many homoplastic events for Notch, Distal-less, and Spalt. The flexibility in the (co-)recruitment of the targeted genes includes cases where different gene combinations are associated with morphologically similar eyespots, as well as cases where identical protein combinations are associated with very different phenotypes.ConclusionsThe evolutionary history of gene (co-)recruitment is consistent with both divergence from a recruited putative ancestral network, and with independent co-option of individual genes. The diversity in the combinations of genes expressed in association with eyespot formation does not parallel diversity in characteristics of the adult phenotype. We discuss these results in the context of inferring homology. Our study underscores the importance of widening the representation of phylogenetic, morphological, and genetic diversity in order to establish general principles about the mechanisms behind the evolution of novel traits.

A genetic basis for intraspecific differences in developmental timing?

Heterochrony, altered developmental timing between ancestors and their descendents, has been proposed as a pervasive evolutionary feature and recent analytical approaches have confirmed its existence as an evolutionary pattern. Yet, the mechanistic basis for heterochrony remains unclear and, in particular, whether intraspecific variation in the timing of developmental events generates, or has the potential to generate, future between-species differences. Here we make a key step in linking heterochrony at the inter- and intraspecific level by reporting an association between interindividual variation in both the absolute and relative timing (position within the sequence of developmental events) of key embryonic developmental events and genetic distance for the pond snail, Radix balthica. We report significant differences in the genetic distance of individuals exhibiting different levels of dissimilarity in their absolute and relative timing of developmental events such as spinning activity, eyespot formation, heart ontogeny, and hatching. This relationship between genetic and developmental dissimilarity is consistent with there being a genetic basis for variation in developmental timing and so suggests that intraspecific heterochrony could provide the raw material for natural selection to produce speciation.

Artificially induced changes of butterfly wing colour patterns: dynamic signal interactions in eyespot development

Eyespot formation in butterfly wings has been explained by the concentration gradient model. However, this model has recently been questioned, and dynamic interactions between the black-inducing signal and its inhibitory signal have been proposed. Here, the validity of these models was examined using a nymphalid butterfly Junonia almana. Early focal damage to the major eyespots often made them smaller, whereas the late damage made the outer ring larger and the inner ring smaller in a single eyespot. Non-focal damage at the outer ring not only attracted the whole eyespot structure toward the damaged site but also reduced the overall size of the eyespot. Surprisingly, a reduction of the major eyespot was accompanied by an enlargement of the associated miniature eyespots. These results demonstrate limitations of the conventional gradient model and support a dynamic interactive nature of morphogenic signals for colour-pattern determination in butterfly wings.

Involvement of the conserved Hox gene Antennapedia in the development and evolution of a novel trait

BackgroundHox proteins specify segment identity during embryogenesis and have typical associated expression patterns. Changes in embryonic expression and activity of Hox genes were crucial in the evolution of animal body plans, but their role in the post-embryonic development of lineage-specific traits remains largely unexplored. Here, we focus on the insect Hox genes Ultrabithorax (Ubx) and Antennapedia (Antp), and implicate the latter in the formation and diversification of novel, butterfly-specific wing patterns.ResultsFirst, we describe a conserved pattern of Ubx expression and a novel pattern of Antp expression in wing discs of Bicyclus anynana butterflies. The discrete, reiterated domains of Antp contrast with the typical expression of Hox genes in single continuous regions in arthropod embryos. Second, we show that this pattern is associated with the establishment of the organizing centres of eyespots. Antp upregulation is the earliest event in organizer development described to date, and in contrast to all genes implicated in eyespot formation, is exclusive to those centres. Third, our comparative analysis of gene expression across nymphalids reveals unexpected differences in organizer determination.ConclusionsWe show that the Antp's recruitment for the formation of novel traits in butterfly wing discs involved the evolution of new expression domains, and is restricted to a particular lineage. This study contributes novel insights into the evolution of Antp expression, as well as into the genetic mechanisms underlying morphological diversification. Our results also underscore how a wider representation of morphological and phylogenetic diversity is essential in evolutionary developmental biology.

Salinity-induced heterokairy in an upper-estuarine population of the snail Radix balthica (Mollusca: Pulmonata)

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 9:95-105 (2010) - DOI: https://doi.org/10.3354/ab00231 Salinity-induced heterokairy in an upper-estuarine population of the snail Radix balthica (Mollusca: Pulmonata) Oliver Tills*, John I. Spicer, Simon D. Rundle Marine Biology and Ecology Research Centre, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK *Email: oliver.tills@plymouth.ac.uk ABSTRACT: Climate change is predicted to increase sea level and cause saline intrusion of coastal freshwaters. This will have consequences for freshwater organisms inhabiting such areas; developmental phenotypic plasticity may facilitate the persistence of freshwater species under such scenarios of increased salinity. Here we investigated developmental plasticity under different salinity treatments (S = 2, 5, 7 and 9, with artificial pond water [APW] and deionised water [S = 0] as controls) in embryos from an upper-estuarine population of the gastropod Radix balthica. We focused on plasticity in the timing of developmental events (heterokairy) at different salinities, including the time of onset (relative and absolute) of 10 developmental events and duration of 4 developmental stages; we also assessed whether salinity affected hatchling morphology and embryonic cardiac activity. There were significant differences in the absolute time of onset of several events with increased salinity, including a delayed first heartbeat in S5 and S7 compared with APW and in the relative time of onset of eye spot formation, first heartbeat and foot attachment between treatments. Stage duration also varied between salinity treatments: the hippo developmental stage lasted significantly longer in S7 compared with APW and development overall was prolonged in S7, with embryos in S9 not developing past the trochophore stage. Salinity also affected both shell size and shell shape of hatchlings. Hence salinity influences the time of onset (absolute and relative) of developmental events and duration of several developmental stages and the morphology of hatchling snails, although the mechanistic basis and fitness implications are, as yet, unknown. KEY WORDS: Developmental phenotypic plasticity · Seawater intrusion · Embryonic development · Sequence changes Full text in pdf format PreviousCite this article as: Tills O, Spicer JI, Rundle SD (2010) Salinity-induced heterokairy in an upper-estuarine population of the snail Radix balthica (Mollusca: Pulmonata). Aquat Biol 9:95-105. https://doi.org/10.3354/ab00231 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 9, No. 1. Online publication date: April 06, 2010 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2010 Inter-Research.

Conserved developmental processes and the formation of evolutionary novelties: examples from butterfly wings

The origin and diversification of evolutionary novelties-lineage-specific traits of new adaptive value-is one of the key issues in evolutionary developmental biology. However, comparative analysis of the genetic and developmental bases of such traits can be difficult when they have no obvious homologue in model organisms. The finding that the evolution of morphological novelties often involves the recruitment of pre-existing genes and/or gene networks offers the potential to overcome this challenge. Knowledge about shared developmental processes obtained from extensive studies in model organisms can then be used to understand the origin and diversification of lineage-specific structures. Here, we illustrate this approach in relation to eyespots on the wings of Bicyclus anynana butterflies. A number of spontaneous mutations isolated in the laboratory affect eyespots, lepidopteran-specific features, and also processes that are shared by most insects. We discuss how eyespot mutants with disturbed embryonic development may help elucidate the genetic pathways involved in eyespot formation, and how venation mutants with altered eyespot patterns might shed light on mechanisms of eyespot development.

Developmental and genetic mechanisms for evolutionary diversification of serial repeats: eyespot size in Bicyclus anynana butterflies

Serially repeated pattern elements on butterfly wings offer the opportunity for integrating genetic, developmental, and functional aspects towards understanding morphological diversification and the evolution of individuality. We use captive populations of Bicyclus anynana butterflies, an emerging model in evolutionary developmental biology, to explore the genetic and developmental basis of compartmentalized changes in eyespot patterns. There is much variation for different aspects of eyespot morphology, and knowledge about the genetic pathways and developmental processes involved in eyespot formation. Also, despite the strong correlations across all eyespots in one butterfly, B. anynana shows great potential for independent changes in the size of individual eyespots. It is, however, unclear to what extent the genetic and developmental processes underlying eyespot formation change in a localized manner to enable such individualization. We use micromanipulations of developing wings to dissect the contribution of different components of eyespot development to quantitative differences in eyespot size on one wing surface. Reciprocal transplants of presumptive eyespot foci between artificial selection lines and controls suggest that while localized antagonistic changes in eyespot size rely mostly on localized changes in focal signal strength, concerted changes depend greatly on epidermal response sensitivities. This potentially reflects differences between the signal-response components of eyespot formation in the degrees of compartmentalization and/or the temporal pattern of selection. We also report on the phenotypic analysis of a number of mutant stocks demonstrating how single alleles can affect different eyespots in concert or independently, and thus contribute to the individualization of serially repeated traits.