In the course of evolution, crustaceans adapted to a large variety of habitats. Probably the most extreme habitat shift was the transition from water to land, which occurred independently in at least five crustacean lineages. This substantial change in life style required adaptations in sensory organs, as the medium conveying stimuli changed in both chemical and physical properties. One important sensory organ in crustaceans is the first pair of antennae, housing their sense of smell. Previous studies on the crustacean transition from water to land focused on morphological, behavioral and physiological aspects but did not analyze gene expression. Our goal was to scrutinize the molecular makeup of the crustacean antennulae, comparing the terrestrial Coenobita clypeatus and the marine Pagurus bernhardus. We sequenced and analyzed the antennal transcriptomes of two hermit crab species. Comparison to previously published datasets of similar tissues revealed a comparable quality and GO annotation confirmed a highly similar set of expressed genes in both datasets. The chemosensory gene repertoire of both species displayed a similar set of ionotropic receptors (IRs), most of them belonging to the divergent IR subtype. No binding proteins, gustatory receptors (GRs) or insect-like olfactory receptors (ORs) were present. Additionally to their olfactory function, the antennules were equipped with a variety of pathogen defense mechanisms, producing relevant substances on site. The overall similarity of both transcriptomes is high and does not indicate a general shift in genetic makeup connected to the change in habitat. Ionotropic receptors seem to perform the task of olfactory detection in both hermit crab species studied.
Article Figures and data Abstract eLife digest Introduction Results and discussion Materials and methods References Decision letter Author response Article and author information Metrics Abstract Many insect species are host-obligate specialists. The evolutionary mechanism driving the adaptation of a species to a toxic host is, however, intriguing. We analyzed the tight association of Drosophila sechellia to its sole host, the fruit of Morinda citrifolia, which is toxic to other members of the melanogaster species group. Molecular polymorphisms in the dopamine regulatory protein Catsup cause infertility in D. sechellia due to maternal arrest of oogenesis. In its natural host, the fruit compensates for the impaired maternal dopamine metabolism with the precursor l-DOPA, resuming oogenesis and stimulating egg production. l-DOPA present in morinda additionally increases the size of D. sechellia eggs, what in turn enhances early fitness. We argue that the need of l-DOPA for successful reproduction has driven D. sechellia to become an M. citrifolia obligate specialist. This study illustrates how an insect's dopaminergic system can sustain ecological adaptations by modulating ontogenesis and development. https://doi.org/10.7554/eLife.03785.001 eLife digest Many insect species rely on another animal or plant species for their own reproduction. For example, a fruit fly called Drosophila sechellia—which is found in the Seychelles—will only feed and lay its eggs on the fruit of a species of tree called Morinda citrifolia. This pairing is particularly unusual because these fruits, commonly called morinda, are toxic to all other Drosophila species. Female Drosophila sechellia flies produce fewer eggs than other Drosophila species, which makes it difficult to raise this species in the laboratory. However providing these flies with morinda fruit, or chemicals from this fruit, was known to increase the expression of many genes involved in egg production and stimulate the flies to lay more eggs. Nevertheless, the reasons why this species of fruit fly depends on the toxic morinda fruit were unclear. Now Lavista-Llanos et al. have confirmed that feeding Drosophila sechellia flies a diet of morinda fruit—instead of a typical laboratory diet—causes these flies to produce six-times as many eggs. Furthermore, this morinda diet had effects that went beyond the previously reported stimulatory effects of acidic chemicals in the fruits triggering the flies to lay more eggs. Egg production in flies is controlled by dopamine, and a lack of this hormone is known to reduce the size of other fruit flies' ovaries and the number of eggs that they produce. Lavista-Llanos et al. went on to feed female Drosophila sechellia flies the chemical building blocks that make up the dopamine hormone, and one such chemical (called l-DOPA) caused the flies to produce more eggs. This did not occur when the flies were fed dopamine itself. Lavista-Llanos et al. discovered that Drosophila sechellia flies have very high levels of dopamine but much lower levels of l-DOPA than other Drosophila fly species; and revealed that this was because a gene called Catsup is mutated in Drosophila sechellia. When Lavista-Llanos et al. mutated the same gene in another Drosophila species, the mutant flies produced fewer eggs and abnormally accumulated an enzyme (which makes l-DOPA) inside their developing eggs—just like Drosophila sechellia. The presence of l-DOPA in morinda fruit partly compensates for the reduced fertility of Drosophila sechellia and the other flies with mutations in the Catsup gene. Lavista-Llanos et al. discovered that removing or replacing l-DOPA in the morinda fruit caused the flies to produce fewer eggs. Furthermore, the l-DOPA present in morinda increases the size of Drosophila sechellia eggs, which in turn helps them to survive their toxic environment. Lavista-Llanos et al. also discovered that feeding dopamine to vulnerable Drosophila species helps them to cope with the toxic effects of a morinda diet. One of the next challenges will be to uncover how chemicals from the morinda fruit affect the dopamine system of the flies. It is also unknown if the dopamine hormone also influences the strong attraction that Drosophila sechellia feels towards its only host, the morinda fruit. https://doi.org/10.7554/eLife.03785.002 Introduction Morinda citrifolia fruit (morinda) is the sole host of Drosophila sechellia (Tsacas and Baechli, 1981), a close relative of Drosophila melanogaster and endemic to the Seychelles archipelago (Louis and David, 1986). A peculiar aspect of the specialization is that morinda fruits are toxic to all other drosophilids (Legal et al., 1992). The toxicity stems from a high content of carboxylic acids (primarily octanoic and hexanoic acid) (Legal et al., 1994), to which D. sechellia appears to be resistant (Farine et al., 1996). The chemosensory system of D. sechellia is specialized in detecting and coding key volatiles produced by morinda (Dekker et al., 2006) while devoid of the repellence towards the acids (Matsuo et al., 2007). On the other hand, D. sechellia females exhibit a low reproductive potential, partly because of a low ovariole number and partly because of fairly low egg production (R'Kha et al., 1991; R'kha et al., 1997), making it difficult to raise D. sechellia under laboratory conditions. In turn, morinda stimulates egg production (R'kha et al., 1997), and D. sechellia clearly prefers to oviposit in medium containing morinda carboxylic acids (Amlou et al., 1998). On its host, D. sechellia increases expression of genes involved with oogenesis and fatty acid metabolism (Dworkin and Jones, 2009). Thus, we here examined the dependence of Drosophila sechellia on morinda, for optimal reproduction. All animal embryos rely on maternally provided gene products for their initial development prior to zygotic genetic synthesis. Maternal effects can thus act as a form of cross-generational phenotypic plasticity, playing a role in an animal's adaptation to toxic environments. Embryonic survival in morinda is a maternally inherited trait and does not depend on the genotype of the embryo (R'Kha et al., 1991). We therefore considered if maternal effects sustained the evolutionary process that has driven the specialization of D. sechellia. Results enhance our understanding of the reproductive behaviour of Drosophila and suggest an ontogenetic mechanism of insect adaptation to a toxic host. Results and discussion We first examined the influence of chemicals found in morinda on the reproductive system of D. sechellia by testing the effect of diet on egg production. We raised two geographically different populations of D. sechellia on standard Drosophila cornmeal medium (standard diet), on morinda fruit (morinda diet), or on a non-host fruit (banana diet). For comparison, we also raised two strains of D. melanogaster (wild-type Berlin and Canton-S) on the same media (see ‘Materials and methods’). To score the rate of egg production, we transferred the flies to oviposition cages containing agar plates devoid of oviposition stimuli (i.e., yeast or morinda carboxylic acids). In agreement with previous reports, D. sechellia raised on standard diet produced few eggs compared to D. melanogaster wild-type Berlin and D. melanogaster Canton-S (Figure 1A and Figure 1—figure supplement 1), raised on the same media. The addition of morinda carboxylic acids to the standard diet did not increase egg production in D. sechellia (Figure 1B). D. sechellia raised on a non-host fruit (banana diet) showed a slight increase in the number of eggs laid (Figure 1B), but this number did not increase further with the addition of morinda carboxylic acids (Figure 1B). D. sechellia raised on morinda diet, however, showed a sixfold increase in egg production (Figure 1B and Figure 1—figure supplement 1). Morinda diet did not affect the number of eggs produced by D. melanogaster wild-type Berlin and slightly reduced those of D. melanogaster Canton-S (Figure 1C and Figure 1—figure supplement 1), as did the addition of morinda carboxylic acids to the standard diet (Figure 1C). Banana, however, tripled egg production in D. melanogaster wild-type Berlin (Figure 1C). This increase could be inhibited by the addition of morinda carboxylic acids to the banana (Figure 1C). These results demonstrate that the presence of a natural host modulates the reproductive capacity of Drosophila. In particular, morinda has a strong effect on D. sechellia egg production that goes beyond the reported stimulatory effect of the carboxylic acids on oviposition (Amlou et al., 1998). Figure 1 with 3 supplements see all Download asset Open asset Morinda increases egg production in D. sechellia. (A–C) Egg production (egg/female/day) (N > 20) (A) and its relative change (N > 5) (B and C) in D. sechellia (14021–0248.25, sec) and D. melanogaster wild-type Berlin (wtB) fed a standard diet (sd), or morinda diet (md), or banana diet (bd), or diets supplemented with morinda carboxylic acids (+OA:HA). (D) Confocal images showing the surface (top) or the interior (middle) of ovarioles stained with nucleic acid specific dyes (sytox orange (SO) and TOTO) of D. sechellia (14021–0248.25) fed a standard diet (sec-sd) or a morinda diet (sec-md). The follicle cells (f) surrounding the oocyte (o) or stretched over the nurse cells (n) (arrow) are indicated for early (S8). Scale bar 100 μm. (E) Rate of vitellogenesis (>S8/ 8) in D. sechellia (14021–0248.25, sec) and D. melanogaster wild-type Berlin (wtB) fed a standard diet (sd), or a morinda diet (md), or a diet supplemented with morinda carboxylic acids (+OA:HA). Different letters denote significant differences (p < 0.01) using ANOVA followed by Tukey's test (B–E); ****p < 0.00001 using Student's t test to compare species (A). Error bars represent s.e.m. https://doi.org/10.7554/eLife.03785.003 To study the mechanism behind the dietary modulation of egg production, we next examined oocyte development. The germarium in each ovariole continuously produces oocyte-cysts, each composed of 15 nurse cells and one oocyte, surrounded by a layer of follicular cells (Figure 1D). Each oocyte-cyst follows 14 stereotypical consecutive stages of pre-vitellogenic (S1–S7) and vitellogenic (S8–S14) growth, each easily distinguishable by morphological criteria (Spradling et al., 1997). Mated D. melanogaster females typically exhibit multiple ovarioles carrying vitellogenic cysts (Spradling et al., 1997). Females of D. sechellia had cysts normally composed of 15 nurse cells and one oocyte, surrounded by follicular cells (Figure 1D). Kept on standard diet, mated D. sechellia held oocytes in early developmental stages (S8), what resulted in a significantly lowered rate of vitellogenesis (calculated as >S8/ 6) (B) quantification of apoptosis (apoptotic cysts/ovary) (N > 6) and (C) rate of vitellogenesis (>S8/ 12) in D. sechellia (14021–0248.25) flies fed a non-supplemented (−) standard diet (sd) or a standard diet supplemented with L-3,4-dihydroxyphenylalanine (1 mg/ml, l-DOPA); dopamine (1 mg/ml, DA); tyramine (2 mg/ml, TA) or octopamine (2 mg/ml, OA); or a non- pretreated morinda diet (md) or a morinda diet pre-treated with catechol-O-methyltransferase (2.5 U per gram of fruit, md + COMT). Different letters denote significant differences (p < 0.01) using ANOVA followed by Tukey's test. Error bars represent s.e.m. (D) The total ion chromatogram (top trace) shows all compounds present in morinda extract, and the extracted ion chromatogram (lower trace) corresponds to the exact mass of sum formula of L-3,4-dihydroxyphenylalanine (l-DOPA) present in the fruit; as analysed by UHPLC-MS. (E) Egg production (eggs/female/day) (N > 3) in D. sechellia (14021–0248.25) flies fed a morinda diet (md) non-pre-treated (−), pre-treated with catechol-O-methyltransferase (2.5 U per gram of fruit, COMT) or α-methyl-DOPA (0.4 mM, mDp). Different letters denote significant differences (p < 0.01) using ANOVA followed by Tukey's test. Error bars represent s.e.m. https://doi.org/10.7554/eLife.03785.007 The findings so far thus led us to speculate that morinda contains monoamines, which stimulate oogenesis in D. sechellia. Indeed, we detected 180.4 ± 3.5 ng l-DOPA (mean ± s.e.m; N = 3) per gram of fruit pulp (Figure 2D) in morinda extracts analysed by ultra-high-performance liquid chromatography coupled to mass spectrometry (UHPLC-MS). Notably, we did not detect DA, OA or TA in morinda. Unripe (150.99 ± 8 ng l-DOPA [mean ± s.e.m; N = 3] per gram of fruit) and overripe (147.47 ± 8 ng l-DOPA [mean ± s.e.m; N = 3] per gram of fruit) morinda fruits contained l-DOPA in equal amounts, what suggests that oxidisation, known to occur commonly in monoamines through atmospherical exposure, is prevented in morinda. The preservation of l-DOPA is likely due to the high carboxylic acid content—octanoic and hexanoic acids have been shown to inhibit diphenol oxidase activity (Guo et al., 2010)—and the ensuing low pH of the fruit (4.1 ± 0.1 [N = 7] and 3.6 ± 0.1 [N = 5] [mean ± s.e.m.], ripe and overripe morinda, respectively; for comparison, 5.7 ± 0.2 [mean ± s.e.m.], [N = 4], ripe banana; p = 0.0001; one-way ANOVA), known for its antioxidant properties. Banana is reported to contain up to 1 mg DA per gram of fresh weight (Kanazawa and Sakakibara, 2000). Notably, DA in banana is synthesized directly from TA (Deacon and Marsh, 1971) and not via synthesis of l-DOPA. Presumably, the absence of l-DOPA in banana renders this non-host fruit unable to stimulate egg production in D. sechellia (see Figure 1B). Is the presence of l-DOPA in morinda then necessary for the stimulatory effect on egg production? To address this question, we depleted levels of l-DOPA in morinda by pre-incubating fruit pulp with catechol-O-methyltransferase (COMT, 2.5 U/g morinda), an enzyme that catabolises l-DOPA into an unusable product (Gordonsmith et al., 1982). Treatment with COMT suppressed the anti-apoptotic effects of morinda (Figure 2B) and hindered the fruit from stimulating vitellogenesis (Figure 2—figure supplement 1) and egg production in D. sechellia (Figure 2E), reducing the number of eggs to levels in a standard diet (compare Figure 2A and Figure 2E). Additionally, we added α-methyl-DOPA (mDp, 0.4 mM), a non-hydrolysable l-DOPA analogue and a competitive inhibitor of the enzyme dopa decarboxylase that converts l-DOPA into DA, separately to the fruit. The presence of mDp in morinda strongly reduced egg production (Figure 2E); feeding a corresponding mDp-supplemented diet to D. melanogaster wild-type Berlin did not have such an effect (not shown). Notably, mDp in the fruit did not hinder oogenesis; instead, eggs were retained in the ovaries (Figure 2—figure supplement 1). This halt in ovulation was completely reversed one day after flies were moved to fresh medium (Figure 2—figure supplement 1), and, remarkably, oviposition was significantly enhanced when morinda was offered as an oviposition substrate (Figure 2—figure supplement 1). We conclude that morinda contains l-DOPA and that its presence in the fruit pulp is both sufficient and necessary to stimulate egg production in D. sechellia. Morinda, accordingly, provides D. sechellia with the DA precursor necessary for the progression of oogenesis. Although providing a critical chemical, the acidity of the fruit, which helps preserve l-DOPA by preventing oxidisation, creates a hostile environment for the eggs to develop in. How do flies ensure that the eggs survive in this toxic environment? An interesting observation provides one clue. Eggs of D. sechellia are characteristically large compared to those of sibling species D. melanogaster, D. simulans, Drosophila ananassae, Drosophila erecta, Drosophila mojavensis, Drosophila persimilis, Drosophila pseudoobscura, Drosophila virilis, Drosophila willistoni and Drosophila yakuba (Markow et al., 2009). In accordance, we observed D. sechellia eggs to be 45% larger in size compared to eggs of D. melanogaster wild-type Berlin (Figure 3A), in a standard diet condition. Upon being fed a morinda diet, eggs of D. sechellia increased in volume twofold compared to eggs of conspecifics fed standard medium (Figure 3A and Figure 3—figure supplement 1); the resulting eggs had an almost threefold larger volume than did D. melanogaster wild-type Berlin eggs in standard conditions (Figure 3A). This effect could be replicated by supplementing standard diet with l-DOPA or, notably, DA (Figure 3B). On the other hand, adding COMT or mDp to a morinda diet prevented the fruit from having any effect on the volume of eggs (Figure 3C). These results indicate that egg size is also under a dopaminergic control regime during egg development. The increased size may provide buffering capacity to the eggs, helping them to cope with the toxic environment of the host. Indeed, the hatching rate of eggs transferred onto a morinda-containing medium was significantly higher in the enlarged eggs of flies fed morinda than in the smaller eggs of individuals fed only standard medium (Figure 3D). The low number of ovarioles of D. sechellia (R'kha et al., 1997) thus seems to be a result of a trade-off between number and size (Figure 3—figure supplement 2), favouring the enlarged eggs of females fed morinda. Figure 3 with 2 supplements see all Download asset Open asset Morinda enhances early fitness. (A–C) Volume (mm3(10−3)) of D. melanogaster wild-type Berlin (wtB) and D. sechellia (14021–0248.25, sec) eggs produced by flies fed a standard diet (sd) or morinda diet (md) (N > 15) (A); D. sechellia (14021–0248.25) flies fed a non-supplemented (−) standard diet (sd), or supplemented with L-3,4-dihydroxyphenylalanine (1 mg/ml, l-DOPA) or dopamine (1 mg/ml, DA) (N > 23) (B); D. sechellia (14021–0248.25) flies fed a non-pre-treated (−) morinda diet (md), or pre-treated with catechol-O-methyltransferase (2.5 U per gram of fruit, COMT) or α-methyl-DOPA (0.4 mM, mDp) (N > 10) (C). (D) Egg hatching rate (N > 5) in D. sechellia (14021–0248.25) fed (feed) a standard diet (sd) or morinda diet (md), ovipositing (ovip.) in either media. Different letters denote significant differences (p < 0.01) using ANOVA followed by Tukey's test. Error bars represent s.e.m. https://doi.org/10.7554/eLife.03785.009 Genetic changes in a single gene of the steroid hormone biosynthetic pathway made Drosophila pachea dependent on the uncommon sterols of its host plant, the toxic senita cactus (Lang et al., 2012). Likewise, the requirement of dietary l-DOPA suggests that its metabolism is impaired in D. sechellia. We next quantified l-DOPA in fly-tissue extracts by UHPLC-MS. D. sechellia—kept on standard diet—showed significantly lower levels of l-DOPA in whole flies, bodies and ovaries than did D. melanogaster wild-type Berlin (Figure 4A). However, in D. sechellia fed a morinda diet, l-DOPA levels were significantly increased compared to levels in conspecifics fed a standard diet, and surpassing those of D. melanogaster wild-type Berlin in standard diet (Figure 4B). In short, these results demonstrate that under laboratory conditions, l-DOPA is greatly reduced in D. sechellia, and that this l-DOPA deficiency can be remedied by a diet supplemented with morinda fruit. Figure 4 with 5 supplements see all Download asset Open asset Dopamine metabolism is impaired in D. sechellia. (A) L-3,4-dihydroxyphenylalanine quantification (l-DOPA pg/fly) (N = 3) in whole fly, bodies and ovaries of female D. melanogaster wild-type Berlin (wtB) and D. sechellia (14021–0248.25, sec) fed a standard diet (sd). *p < 0.05 and **p < 0.002 using Student's t test. (B) Relative L-3,4-dihydroxyphenylalanine (% pg l-DOPA per mg body, % l-DOPA) (N = 3) in female D. melanogaster wild-type Berlin (wtB) and D. sechellia (14021–0248.25, sec) fed a standard diet (sd) or morinda diet (md). p = 0.0062 and p = 0.018 using Student's t test D. melanogaster vs D. sechellia fed, respectively, a standard diet or morinda diet. (C) Western blots of total protein whole-fly extracts for TH-PLE, CATSUP, and α-TUBULIN as a loading control, in D. melanogaster wild-type Berlin (wtB) and D. sechellia (14021–0248.25, sec) fed a standard diet (sd) or morinda diet (md). The numbers under TH-PLE and CATSUP protein lanes indicate the relative protein levels (normalised to α-TUBULIN). (D) Ratios of L-3,4-dihydroxyphenylalanine (l-DOPA/tyr) (N = 3) and dopamine (DA/tyr) (N = 3) to tyrosine substrate in female D. melanogaster wild-type Berlin (wtB) and D. sechellia (14021–0248.25, sec) fed a standard diet (sd). **p < 0.007 and ***p < 0.000007 using Student's t test. (E) Drosophila CATSUP protein structure scheme showing a signal peptide (grey box) and six trans-membrane domains (black boxes). Deletions (dash) and exchanges (grey or white) of amino acids in D. sechellia (14021–0248.25, sec) compared to in D. melanogaster wild-type Berlin (wtB) and in D. melanogaster DGRP-357 (DGRP-357) CATSUP are indicated. (F–H) Dopamine (DA ng/fly) (N = 3) (F), relative rate of vitellogenesis (% >S8/ 10) (G), and egg-volume (% mm3(10−3)) (n > 10) (H) in D. sechellia (14021–0248.25, sec), D. melanogaster wild-type Berlin (wtB) and D. melanogaster DGRP-357 (DGRP-357) fed a standard diet (sd). (I) Egg production (egg/female/day) (N > 3) in D. melanogaster wild-type Berlin (wtB), heterozygote flies (Catsup1/CyO), D. melanogaster DGRP-357 (CatsupIn270Del/CatsupIn270Del), trans heterozygote flies (CatsupIn270Del/Catsup1) and D. sechellia (14021–0248.25, sec), fed a standard diet (sd). Different letters denote significant differences (p < 0.05) using ANOVA followed by Tukey's test (F–I). Error bars represent s.e.m. https://doi.org/10.7554/eLife.03785.012 The oxidation of the precursor amino acid tyrosine into l-DOPA is the first and rate-limiting step in the DA biosynthetic pathway (Levitt et al., 1965). This oxidation is catalysed by the enzyme tyrosine hydroxylase (TH), which is encoded by the pale (ple) locus in Drosophila (Neckameyer and White, 1993). The whole-fly expression of TH-PLE was increased in D. sechellia relative to in D. melanogaster wild-type Berlin (Figure 4C) and Canton-S (Figure 4—figure supplement 1), as revealed by Western blots. Thus, l-DOPA impairment in D. sechellia seems not to result from a low expression of its synthesizing enzyme. To assess if the activity of TH-PLE was altered in D. sechellia, we compared the ratios of product (l-DOPA and DA) to substrate (tyrosine) in whole-fly extracts. D. sechellia showed a 3.3-fold decrease in the l-DOPA/tyrosine ratio as compared to in D. melanogaster wild-type Berlin (Figure 4D) with a 1.4-fold increase in tyrosine content (Figure 4—figure supplement 2). However, in D. sechellia the DA/tyrosine ratio was increased 2.4 times with respect to in D. melanogaster wild-type Berlin (Figure 4D). DA itself was increased 4.8 times in D. sechellia (Figure 4F). In sum, we conclude that TH-PLE is active; in fact, DA levels are drastically enhanced in D. sechellia. TH-PLE activity is negatively regulated via direct physical interactions with the protein Catecholamines up (Catsup) (Stathakis et al., 1999). Interestingly, Catsup loss-of-function mutations cause hyperactivation of TH-PLE and abnormally high levels of catecholamines (Stathakis et al., 1999), as well as infertility due to maternal arrest of oogenesis (Schupbach and Wieschaus, 1991; Stathakis et al., 1999). These phenotypes prompted us to investigate whether Catsup is impaired in D. sechellia. We cloned the ortholog of Catsup from D. sechellia, which revealed a 45 bp in-frame deletion of 15 amino acids in a predicted zinc-binding region of the protein (O'Donnell et al., 2002) and seven single amino acid exchanges (Figure 4E). Additionally, Western blots of whole-fly extracts revealed 2- to 3.7-fold decrease in CATSUP expression in D. sechellia compared to CATSUP expression in D. melanogaster wild-type Berlin (Figure 4C) and Canton-S (Figure 4—figure supplement 1). The reduced expression of D. sechellia CATSUP would explain the high DA levels in D. sechellia (see Figure 4F). Is Catsup then responsible for the reproductive phenotypes in D. sechellia? An allele (In270Del) similar to D. sechellia Catsup has been described for a natural D. melanogaster population (DGRP-357) (Carbone et al., 2006) (Figure 4E). CatsupIn270Del has been associated with polymorphisms in the number of sensory bristles, starvation resistance and locomotor behavior (Carbone et al., 2006). As for D. sechellia, we found increased DA levels in adult D. melanogaster DGRP-357 compared to in D. melanogaster wild-type Berlin (Figure 4F). Reciprocally, D. sechellia showed an increased number of sensory bristles that were present in flies of three geographically different populations (Figure 4—figure supplement 3). To test if CatsupIn270Del was sufficient to generate egg phenotypes on par with those of D. sechellia, we next examined egg growth in D. melanogaster DGRP-357 females. Both D. sechellia traits—low levels of vitellogenesis (Figure 4G) and enlarged eggs (Figure 4H)—were present in D. melanogaster DGRP-357. Furthermore, D. melanogaster DGRP-357 produced fewer eggs than did D. melanogaster wild-type Berlin (Figure 4I), and the ovariole rate of egg production in D. melanogaster DGRP-357 females did not differ significa
Abstract For centuries the wonderful looking, but foul smelling, Arum lilies have fascinated botanists. The floral odour of many species is believed to mimic faeces—the oviposition substrate of their pollinators, mainly coprophilous flies and beetles. But not all of the 29 Arum species produce a bad floral smell. The genus has evolved a variety of pollination mechanisms, including sweet and wine–like odours, and maybe even pheromone mimicry. In order to study the evolution of the pollination syndromes in Arum , a detailed and reliable phylogeny is a crucial basis. Here we present the first detailed molecular phylogeny of the genus Arum . By combining three chloroplast and one nuclear loci, as well as AFLPs, a highly resolved tree with good statistical support was obtained. The phylogeny is in most parts in congruence with the traditional classification of the genus. By comparing the phylogeny with the data on the pollination biology of the genus we could show that the mimicry of faeces is the oldest and most basal pollination mechanism, but is also present in the youngest and most derived species. The phylogeny presented here will help to study the evolution of deceptive pollination mechanisms in Arum .
The olfactory sense detects a plethora of behaviorally relevant odor molecules; gene families involved in olfaction exhibit high diversity in different animal phyla. Insects detect volatile molecules using olfactory (OR) or ionotropic receptors (IR) and in some cases gustatory receptors (GRs). While IRs are expressed in olfactory organs across Protostomia, ORs have been hypothesized to be an adaptation to a terrestrial insect lifestyle. We investigated the olfactory system of the primary wingless bristletail Lepismachilis y-signata (Archaeognatha), the firebrat Thermobia domestica (Zygentoma) and the neopteran leaf insect Phyllium siccifolium (Phasmatodea). ORs and the olfactory coreceptor (Orco) are with very high probability lacking in Lepismachilis; in Thermobia we have identified three Orco candidates, and in Phyllium a fully developed OR/Orco-based system. We suggest that ORs did not arise as an adaptation to a terrestrial lifestyle, but evolved later in insect evolution, with Orco being present before the appearance of ORs.
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