Identification of a reptile lyssavirus in Anolis allogus provided novel insights into lyssavirus evolution.

Lyssaviruses (genus Lyssavirus) are negative-strand RNA viruses belonging to the family Rhabdoviridae. Although a lyssa-like virus (frog lyssa-like virus 1 [FLLV-1]), which is distantly related to lyssaviruses, was recently identified in frogs, a large phylogenetic gap exists between those viruses, and thus the evolution of lyssaviruses is unclear. In this study, we detected a lyssa-like virus from publicly available RNA-seq data obtained using the brain and skin of Anolis allogus (Spanish flag anole), which was designated anole lyssa-like virus 1 (ALLV-1), and determined its complete coding sequence. Via mapping analysis, we demonstrated that ALLV-1 was actively replicating in the original brain and skin samples. Phylogenetic analyses revealed that ALLV-1 is more closely related to lyssaviruses than FLLV-1. Overall, the topology of the tree is compatible with that of hosts, suggesting the long-term co-divergence of lyssa-like and lyssaviruses and vertebrates. The ψ region, which is a long 3' untranslated region of unknown origin present in the G mRNA of lyssaviruses (approximately 400-700 nucleotides), is also present in the genome of ALLV-1, but it is much shorter (approximately 180 nucleotides) than those of lyssaviruses. Interestingly, FLLV-1 lacks the ψ region, suggesting that the ψ region was acquired after the divergence of the FLLV-1 and ALLV-1/lyssavirus lineages. To the best of our knowledge, this is the first report to identify a lyssa-like virus in reptiles, and thus, our findings provide novel insights into the evolution of lyssaviruses.

Characterization of G protein-coupled estrogen receptors in Japanese medaka, Oryzias latipes.

The G protein-coupled estrogen receptor 1 (Gper1) is a membrane-bound estrogen receptor that mediates non-genomic action of estrogens. A Gper1-mediating pathway has been implicated in reproductive activities in fish, including oocyte growth, but Gper1 has been characterized in only a very limited number of fish species. In this study, we cloned and characterized two genes encoding medaka (Oryzias latipes) Gper1s, namely, Gper1a and Gper1b, and phylogenic and synteny analyses suggest that these genes originate through a teleost-specific whole genome duplication event. We found that Gper1a induced phosphorylation of mitogen-activated protein kinase (MAPK) in 293T cells transfected with medaka Gper1s on exposure to the natural estrogen, 17ß-estradiol (E2) and a synthetic Gper1 agonist (G-1), and treatment with both E2 and G-1 also decreased the rate of spontaneous maturation in medaka oocytes. These findings show that the processes for oocyte growth and maturation are sensitive to estrogens and are possibly mediated through Gper1a in medaka. We also show that 17α-ethinylestradiol (EE2), one of the most potent estrogenic endocrine-disrupting chemicals, and bisphenol A (BPA, a weak environmental estrogen) augmented phosphorylation of MAPK through medaka Gper1s in 293T cells. Interestingly, however, treatment with EE2 or BPA did not attenuate maturation of medaka oocytes. Our findings support that Gper1-mediated effects on oocytes are conserved among fish species, but effects of estrogenic endocrine-disrupting chemicals on oocytes acting through Gper1 may be divergent among fish species.

Comprehensive thermal performance curves for yellow dung fly life history traits and the temperature-size-rule.

Ambient temperature strongly determines the behaviour, physiology, and life history of all organisms. The technical assessment of organismal thermal niches in form of now so-called thermal performance curves (TPC) thus has a long tradition in biological research. Nevertheless, several traits do not display the idealized, intuitive dome-shaped TPC, and in practice assessments often do not cover the entire realistic or natural temperature range of an organism. We here illustrate this by presenting comprehensive sex-specific TPCs for the major (juvenile) life history traits of yellow dung flies (Scathophaga stercoraria; Diptera: Scathophagidae). This concerns estimation of prominent biogeographic rules, such as the temperature-size-rule (TSR), the common phenomenon in ectothermic organisms that body size decreases as temperature increases. S. stercoraria shows an untypical asymptotic TPC of continuous body size increase with decreasing temperature without a peak (optimum), thus following the TSR throughout their entire thermal range (unlike several other insects presented here). Egg-to-adult mortality (our best fitness estimator) also shows no intermediate maximum. Both may relate to this fly entering pupal winter diapause below 12 °C. While development time presents a negative exponential relationship with temperature, development rate and growth rate typify the classic TPC form for this fly. The hitherto largely unexplored close relative S. suilla with an even more arctic distribution showed very similar responses, demonstrating large overlap among two ecologically similar, coexisting dung fly species, thus implying limited utility of even complete TPCs for predicting species distribution and coexistence.

Comparisons of behavioural and TRPA1 heat sensitivities in three sympatric Cuban Anolis lizards.

Thermal tolerances of organisms play a role in defining geographic ranges and occurrence of species. In Cuba, three sympatric species of Anolis lizards (Anolis allogus, Anolis homolechis and Anolis sagrei) inhabit different thermal microhabitats. A previous study found that these species showed distinct gene expression patterns in response to temperature stimuli, suggesting the genetically distinct thermal physiology among species. To investigate whether the Anolis species inhabiting locally distinct thermal habitats diverge their thermal tolerances, we first conducted behavioural experiments to analyse the temperatures at which the three Anolis species escape from heat source. Then, for each of the three species, we isolated cDNA encoding a putative molecular heat sensor, transient receptor potential ion channel ankyrin 1 (TRPA1), which has been suggested to play a role on eliciting behavioural responses to heat stimuli. We performed electrophysiological analysis to quantify activation temperature of Anolis TRPA1 to see whether the pattern of divergence in TRPA1 responses is congruent with that of divergence in behavioural responses. We found that temperatures triggering behavioural and TRPA1 responses were significantly lower for shade-dwelling species (A. allogus) than for sun-dwelling species (A. homolechis and A. sagrei). The ambient temperature of shade habitats where A. allogus occurs stays relatively cool compared to that of open habitats where A. homolechis and A. sagrei occur and bask. The high temperature thresholds of A. homolechis and A. sagrei may reflect their heat tolerances that would benefit these species to inhabit the open habitats.

Physiological responses of ionotropic histamine receptors, PxHCLA and PxHCLB, to neurotransmitter candidates in a butterfly, Papilio xuthus.

Histamine is the only known neurotransmitter released by arthropod photoreceptors. Synaptic transmission from photoreceptors to second-order neurons is mediated by the activation of histamine-gated chloride channels (HCLs). These histaminergic synapses have been assumed to be conserved among insect visual systems. However, our understanding of the channels in question has thus far been based on studies in flies. In the butterfly Papilio xuthus, we have identified two candidate histamine-gated chloride channels, PxHCLA and PxHCLB, and studied their physiological properties using a whole-cell patch-clamp technique. We studied the responses of channels expressed in cultured cells to histamine as well as to other neurotransmitter candidates, namely GABA, tyramine, serotonin, d-/l-glutamate and glycine. We found that histamine and GABA activated both PxHCLA and PxHCLB, while the other molecules did not. The sensitivity to histamine and GABA was consistently higher in PxHCLB than in PxHCLA. Interestingly, simultaneous application of histamine and GABA activated both PxHCLA and PxHCLB more strongly than either neurotransmitter individually; histamine and GABA may have synergistic effects on PxHCLs in the regions where they co-localize. Our results suggest that the physiological properties of the histamine receptors are basically conserved among insects, but that the response to GABA differs between butterflies and flies, implying variation in early visual processing among species.

Codon Usage Selection Can Bias Estimation of the Fraction of Adaptive Amino Acid Fixations.

A growing number of molecular evolutionary studies are estimating the proportion of adaptive amino acid substitutions (α) from comparisons of ratios of polymorphic and fixed DNA mutations. Here, we examine how violations of two of the model assumptions, neutral evolution of synonymous mutations and stationary base composition, affect α estimation. We simulated the evolution of coding sequences assuming weak selection on synonymous codon usage bias and neutral protein evolution, α = 0. We show that weak selection on synonymous mutations can give polymorphism/divergence ratios that yield α-hat (estimated α) considerably larger than its true value. Nonstationary evolution (changes in population size, selection, or mutation) can exacerbate such biases or, in some scenarios, give biases in the opposite direction, α-hat < α. These results demonstrate that two factors that appear to be prevalent among taxa, weak selection on synonymous mutations and non-steady-state nucleotide composition, should be considered when estimating α. Estimates of the proportion of adaptive amino acid fixations from large-scale analyses of Drosophila melanogaster polymorphism and divergence data are positively correlated with codon usage bias. Such patterns are consistent with α-hat inflation from weak selection on synonymous mutations and/or mutational changes within the examined gene trees.

Assembly constraints drive co-evolution among ribosomal constituents.

Ribosome biogenesis, a central and essential cellular process, occurs through sequential association and mutual co-folding of protein-RNA constituents in a well-defined assembly pathway. Here, we construct a network of co-evolving nucleotide/amino acid residues within the ribosome and demonstrate that assembly constraints are strong predictors of co-evolutionary patterns. Predictors of co-evolution include a wide spectrum of structural reconstitution events, such as cooperativity phenomenon, protein-induced rRNA reconstitutions, molecular packing of different rRNA domains, protein-rRNA recognition, etc. A correlation between folding rate of small globular proteins and their topological features is known. We have introduced an analogous topological characteristic for co-evolutionary network of ribosome, which allows us to differentiate between rRNA regions subjected to rapid reconstitutions from those hindered by kinetic traps. Furthermore, co-evolutionary patterns provide a biological basis for deleterious mutation sites and further allow prediction of potential antibiotic targeting sites. Understanding assembly pathways of multicomponent macromolecules remains a key challenge in biophysics. Our study provides a 'proof of concept' that directly relates co-evolution to biophysical interactions during multicomponent assembly and suggests predictive power to identify candidates for critical functional interactions as well as for assembly-blocking antibiotic target sites.

Differentially expressed genes associated with adaptation to different thermal environments in three sympatric Cuban Anolis lizards.

How animals achieve evolutionary adaptation to different thermal environments is an important issue for evolutionary biology as well as for biodiversity conservation in the context of recent global warming. In Cuba, three sympatric species of Anolis lizards (Anolis allogus, A. homolechis and A. sagrei) inhabit different thermal microhabitats, thereby providing an excellent opportunity to examine how they have adapted to different environmental temperatures. Here, we performed RNA-seq on the brain, liver and skin tissues from these three species to analyse their transcriptional responses at two different temperatures. In total, we identified 400, 816 and 781 differentially expressed genes (DEGs) between the two temperatures in A. allogus, A. homolechis and A. sagrei, respectively. Only 62 of these DEGs were shared across the three species, indicating that global transcriptional responses have diverged among these species. Gene ontology (GO) analysis showed that large numbers of ribosomal protein genes were DEGs in the warm-adapted A. homolechis, suggesting that the upregulation of protein synthesis is an important physiological mechanism in the adaptation of this species to hotter environments. GO analysis also showed that GO terms associated with circadian regulation were enriched in all three species. A gene associated with circadian regulation, Nr1d1, was detected as a DEG with opposite expression patterns between the cool-adapted A. allogus and the hot-adapted A. sagrei. Because the environmental temperature fluctuates more widely in open habitats than in forests throughout the day, the circadian thermoregulation could also be important for adaptation to distinct thermal habitats.

Understanding the role of environmental temperature on sex determination through comparative studies in reptiles and amphibians.

In vertebrates, species exhibit phenotypic plasticity of sex determination that the sex can plastically be determined by the external environmental temperature through a mechanism, temperature-dependent sex determination (TSD). Temperature exerts influence over the direction of sexual differentiation pathways, resulting in distinct primary sex ratios in a temperature-dependent manner. This review provides a summary of the thermal sensitivities associated with sex determination in reptiles and amphibians, with a focus on the pattern of TSD, gonadal differentiation, temperature sensing, and the molecular basis underlying thermal sensitivity in sex determination. Comparative studies across diverse lineages offer valuable insights into comprehending the evolution of sex determination as a phenotypic plasticity. While evidence of molecular mechanisms governing sexual differentiation pathways continues to accumulate, the intracellular signaling linking temperature sensing and sexual differentiation pathways remains elusive. We emphasize that uncovering these links is a key for understanding species-specific thermal sensitivities in TSD and will contribute to a more comprehensive understanding of ecosystem and biodiversity conservations.

Mitochondrial-nuclear interactions and accelerated compensatory evolution: evidence from the primate cytochrome C oxidase complex.

Accelerated rates of mitochondrial protein evolution have been proposed to reflect Darwinian coadaptation for efficient energy production for mammalian flight and brain activity. However, several features of mammalian mtDNA (absence of recombination, small effective population size, and high mutation rate) promote genome degradation through the accumulation of weakly deleterious mutations. Here, we present evidence for "compensatory" adaptive substitutions in nuclear DNA- (nDNA) encoded mitochondrial proteins to prevent fitness decline in primate mitochondrial protein complexes. We show that high mutation rate and small effective population size, key features of primate mitochondrial genomes, can accelerate compensatory adaptive evolution in nDNA-encoded genes. We combine phylogenetic information and the 3D structure of the cytochrome c oxidase (COX) complex to test for accelerated compensatory changes among interacting sites. Physical interactions among mtDNA- and nDNA-encoded components are critical in COX evolution; amino acids in close physical proximity in the 3D structure show a strong tendency for correlated evolution among lineages. Only nuclear-encoded components of COX show evidence for positive selection and adaptive nDNA-encoded changes tend to follow mtDNA-encoded amino acid changes at nearby sites in the 3D structure. This bias in the temporal order of substitutions supports compensatory weak selection as a major factor in accelerated primate COX evolution.

Evolution of genes and genomes on the Drosophila phylogeny.

Comparative analysis of multiple genomes in a phylogenetic framework dramatically improves the precision and sensitivity of evolutionary inference, producing more robust results than single-genome analyses can provide. The genomes of 12 Drosophila species, ten of which are presented here for the first time (sechellia, simulans, yakuba, erecta, ananassae, persimilis, willistoni, mojavensis, virilis and grimshawi), illustrate how rates and patterns of sequence divergence across taxa can illuminate evolutionary processes on a genomic scale. These genome sequences augment the formidable genetic tools that have made Drosophila melanogaster a pre-eminent model for animal genetics, and will further catalyse fundamental research on mechanisms of development, cell biology, genetics, disease, neurobiology, behaviour, physiology and evolution. Despite remarkable similarities among these Drosophila species, we identified many putatively non-neutral changes in protein-coding genes, non-coding RNA genes, and cis-regulatory regions. These may prove to underlie differences in the ecology and behaviour of these diverse species.

Sexual dimorphic eyestalk transcriptome of kuruma prawn Marsupenaeus japonicus.

Kuruma prawn (Marsupenaeus japonicus) is a benthic decapod crustacean that is widely distributed in the Indo-West Pacific region. It is one of the most important fishery resources in Japan, but its annual catches have declined sharply since the 1990s. To increase stocks, various approaches such as seed production and aquaculture were attempted. Since the demand for important fishery species, including kuruma prawn, is expected to increase worldwide in the future, there is a need to develop new technologies that will make aquaculture more efficient. Historically, the eyestalk endocrine organ is known to consist of the X-organ and sinus gland (XO/SG) complex that synthesizes and secrets various neuropeptide hormones that regulate growth, molt, sexual maturation, reproduction, and changes in body color. In the current study, eyestalk-derived neuropeptides were identified in the transcriptome. In addition, most orthologs of sex-determination genes were expressed in eyestalks. We identified two doublesex genes (MjapDsx1 and MjapDsx2) and found that MjapDsx1 showed male-biased expression in the eyestalk ganglion with no sex-specific splicing, unlike insect species. Therefore, this study will provide an opportunity to advance the research of neuropeptides and sex determination in the kuruma prawn.

Comparative analysis of gonadal transcriptomes between turtle and alligator identifies common molecular cues activated during the temperature-sensitive period for sex determination.

The mode of sex determination in vertebrates can be categorized as genotypic or environmental. In the case of genotypic sex determination (GSD), the sexual fate of an organism is determined by the chromosome composition with some having dominant genes, named sex-determining genes, that drive the sex phenotypes. By contrast, many reptiles exhibit environmental sex determination (ESD), whereby environmental stimuli drive sex determination, and most notably temperature. To date, temperature-dependent sex determination (TSD) has been found in most turtles, some lizards, and all crocodylians, but commonalities in the controlling processes are not well established. Recent innovative sequencing technology has enabled investigations into gonadal transcriptomic profiles during temperature-sensitive periods (TSP) in various TSD species which can help elucidate the controlling mechanisms. In this study, we conducted a time-course analysis of the gonadal transcriptome during the male-producing temperature (26℃) of the Reeve's turtle (Chinese three-keeled pond turtle) Mauremys reevesii. We then compared the transcriptome profiles for this turtle species during the TSP with that for the American alligator Alligator mississippiensis to identify conserved reptilian TSD-related genes. Our transcriptome-based findings provide an opportunity to retrieve the candidate molecular cues that are activated during TSP and compare these target responses between TSD and GSD turtle species, and between TSD species.

Chronology of embryonic and gonadal development in the Reeves' turtle, Mauremys reevesii.

Temperature-dependent sex determination (TSD) is a mechanism in which environmental temperature, rather than innate zygotic genotype, determines the fate of sexual differentiation during embryonic development. Reeves' turtle (also known as the Chinese three-keeled pond turtle, Mauremys reevesii) exhibits TSD and is the only species whose genome has been determined in Geoemydidae to date. Thus, M. reevesii occupy phylogenetically important position for the study of TSD and can be compared to other TSD species to elucidate the underlying molecular mechanism of this process. Nevertheless, neither embryogenesis nor gonadogenesis has been described in this species. Therefore, herein, we investigated the chronology of normal embryonic development and gonadal structures in M. reevesii under both female- and male-producing incubation temperatures (FPT 31 °C or MPT 26 °C, respectively). External morphology remains indistinct between the two temperature regimes throughout the studied embryonic stages. However, the gonadal ridges present on the mesonephros at stage 16 develop and sexually differentiate at FPT and MPT. Ovarian and testicular structures begin to develop at stages 18-19 at FPT and stages 20-21 at MPT, respectively, and thus, the sexual differentiation of gonadal structures began earlier in the embryos at FPT than at MPT. Our results suggest that temperature sensitive period, at which the gonadal structures remain sexually undifferentiated, spans from stage 16 (or earlier) to stages 18-19 at FPT and to stages 20-21 at MPT. Understanding the temperature-dependent differentiation in gonadal structures during embryonic development is a prerequisite for investigating molecular basis underlying TSD. Thus, the result of the present study will facilitate further developmental studies on TSD in M. reevesii.

Estrogen Receptor 1 (ESR1) Agonist Induces Ovarian Differentiation and Aberrant Müllerian Duct Development in the Chinese Soft-shelled Turtle, Pelodiscus sinensi.

Estrogens play critical roles in ovarian and reproductive organ development, but the molecular signaling pathways in non-mammalian vertebrates are not well understood. Studies of reptiles have indicated that administration of exogenous estrogens during embryonic development causes ovarian differentiation and presumptive male to female sex-reversal. The Chinese soft-shelled turtle, Pelodiscus sinensis, belongs to the family Trionychidae and exhibits genotypic sex determination system with ZZ/ZW sex chromosomes. In order to assess the role of estrogens and their signaling pathway on sex determination and differentiation, P. sinensis eggs were given a single administration of endogenous estrogen,17ß-estradiol (E2) or a synthetic estrogen receptor 1 (ESR1) agonist, 4,4',4"-(4-propyl-[1H]-pyrazole-1,3,5-triyl) trisphenol (PPT) in ovo during gonadal differentiation, and the subsequent effects were examined during a final developmental stage prior to hatching. The administration of both E2 and PPT induced ovarian differentiation in genetic male embryos. Intriguingly, PPT but not E2 induced the Müllerian duct enlargement and aberrant glandular development. These data suggest that ovarian differentiation and reproductive tract anomalies induced by the exogenous estrogen exposure act through ESR1 in the Chinese soft-shelled turtles.

Distinguishing Among Evolutionary Forces Acting on Genome-Wide Base Composition: Computer Simulation Analysis of Approximate Methods for Inferring Site Frequency Spectra of Derived Mutations.

Inferred ancestral nucleotide states are increasingly employed in analyses of within- and between -species genome variation. Although numerous studies have focused on ancestral inference among distantly related lineages, approaches to infer ancestral states in polymorphism data have received less attention. Recently developed approaches that employ complex transition matrices allow us to infer ancestral nucleotide sequence in various evolutionary scenarios of base composition. However, the requirement of a single gene tree to calculate a likelihood is an important limitation for conducting ancestral inference using within-species variation in recombining genomes. To resolve this problem, and to extend the applicability of ancestral inference in studies of base composition evolution, we first evaluate three previously proposed methods to infer ancestral nucleotide sequences among within- and between-species sequence variation data. The methods employ a single allele, bifurcating tree, or a star tree for within-species variation data. Using simulated nucleotide sequences, we employ ancestral inference to infer fixations and polymorphisms. We find that all three methods show biased inference. We modify the bifurcating tree method to include weights to adjust for an expected site frequency spectrum, "bifurcating tree with weighting" (BTW). Our simulation analysis show that the BTW method can substantially improve the reliability and robustness of ancestral inference in a range of scenarios that include non-neutral and/or non-stationary base composition evolution.

Factors affecting interspecific differences in genetic divergence among populations of Anolis lizards in Cuba.

BACKGROUND: Geographical patterns and degrees of genetic divergence among populations differ between species, reflecting relative potentials for speciation or cladogenesis and differing capacities for environmental adaptation. Identification of factors that contribute to genetic divergence among populations is important to the understanding of why some species exhibit greater interpopulation genetic divergence. In this study, we calculated the mean pairwise genetic distances among populations as species' average genetic divergence by a phylogeny using nuclear and mitochondrial genes of 303 individuals from 33 Cuban Anolis species and estimated species ages by another phylogeny using nuclear and mitochondrial genes of 51 Cuban and 47 non-Cuban Anolis species. We identified factors that influence species' differences in genetic divergence among 26 species of Anolis lizards from Cuba. Species ages, environmental heterogeneity within species ranges, and ecomorph types were considered as factors affecting average genetic divergences among populations. RESULTS: The phylogenies presented in this study provide the most comprehensive sampling of Cuban Anolis species to date. The phylogeny showed more conservative evolution of Anolis ecomorphs within Cuba and identified twig anoles as a monophyletic group. Subsequent Phylogenetic Generalized Least Squares (PGLS) analyses showed that species age was positively correlated with species' average genetic divergence among populations. CONCLUSION: Although previous studies have focused on factors affecting genetic divergence within species, the present study showed for the first time that species differences in genetic divergence could be largely affected by species age.

Strong regional heterogeneity in base composition evolution on the Drosophila X chromosome.

Fluctuations in base composition appear to be prevalent in Drosophila and mammal genome evolution, but their timescale, genomic breadth, and causes remain obscure. Here, we study base composition evolution within the X chromosomes of Drosophila melanogaster and five of its close relatives. Substitutions were inferred on six extant and two ancestral lineages for 14 near-telomeric and 9 nontelomeric genes. GC content evolution is highly variable both within the genome and within the phylogenetic tree. In the lineages leading to D. yakuba and D. orena, GC content at silent sites has increased rapidly near telomeres, but has decreased in more proximal (nontelomeric) regions. D. orena shows a 17-fold excess of GC-increasing vs. AT-increasing synonymous changes within a small (approximately 130-kb) region close to the telomeric end. Base composition changes within introns are consistent with changes in mutation patterns, but stronger GC elevation at synonymous sites suggests contributions of natural selection or biased gene conversion. The Drosophila yakuba lineage shows a less extreme elevation of GC content distributed over a wider genetic region (approximately 1.2 Mb). A lack of change in GC content for most introns within this region suggests a role of natural selection in localized base composition fluctuations.

Molecular evolution in the Drosophila melanogaster species subgroup: frequent parameter fluctuations on the timescale of molecular divergence.

Although mutation, genetic drift, and natural selection are well established as determinants of genome evolution, the importance (frequency and magnitude) of parameter fluctuations in molecular evolution is less understood. DNA sequence comparisons among closely related species allow specific substitutions to be assigned to lineages on a phylogenetic tree. In this study, we compare patterns of codon usage and protein evolution in 22 genes (>11,000 codons) among Drosophila melanogaster and five relatives within the D. melanogaster subgroup. We assign changes to eight lineages using a maximum-likelihood approach to infer ancestral states. Uncertainty in ancestral reconstructions is taken into account, at least to some extent, by weighting reconstructions by their posterior probabilities. Four of the eight lineages show potentially genomewide departures from equilibrium synonymous codon usage; three are decreasing and one is increasing in major codon usage. Several of these departures are consistent with lineage-specific changes in selection intensity (selection coefficients scaled to effective population size) at silent sites. Intron base composition and rates and patterns of protein evolution are also heterogeneous among these lineages. The magnitude of forces governing silent, intron, and protein evolution appears to have varied frequently, and in a lineage-specific manner, within the D. melanogaster subgroup.

Red-shift of spectral sensitivity due to screening pigment migration in the eyes of a moth, Adoxophyes orana.

BACKGROUND: We have found that the spectral sensitivity of the compound eye in the summer fruit tortrix moth (Adoxophyes orana) differs in laboratory strains originating from different regions of Japan. We have investigated the mechanisms underlying this anomalous spectral sensitivity. METHODS: We applied electrophysiology, light and electron microscopy, opsin gene cloning, mathematical modeling, and behavioral analysis. RESULTS: The ERG-determined spectral sensitivity of dark-adapted individuals of all strains peaks around 520 nm. When light-adapted, the spectral sensitivity of the Nagano strain narrows and its peak shifts to 580 nm, while that in other strains remains unchanged. All tested strains appear to be identical in terms of the basic structure of the eye, the pigment migration in response to light- and dark-adaptation, and the molecular structure of long-wavelength absorbing visual pigments. However, the color of the perirhabdomal pigment clearly differs; it is orange in the Nagano strain and purple in the others. The action spectrum of phototaxis appears to be shifted towards longer wavelengths in the Nagano individuals. CONCLUSIONS: The spectral sensitivities of light-adapted eyes can be modeled under the assumption that this screening pigment plays a crucial role in determining the spectral sensitivity. The action spectrum of phototaxis indicates that the change in the eye spectral sensitivity is behaviorally relevant.