Multi-Allelic Major Effect Genes Interact with Minor Effect QTLs to Control Adaptive Color Pattern Variation in Heliconius erato

Recent studies indicate that relatively few genomic regions are repeatedly involved in the evolution of Heliconius butterfly wing patterns. Although this work demonstrates a number of cases where homologous loci underlie both convergent and divergent wing pattern change among different Heliconius species, it is still unclear exactly how many loci underlie pattern variation across the genus. To address this question for Heliconius erato, we created fifteen independent crosses utilizing the four most distinct color pattern races and analyzed color pattern segregation across a total of 1271 F2 and backcross offspring. Additionally, we used the most variable brood, an F2 cross between H. himera and the east Ecuadorian H. erato notabilis, to perform a quantitative genetic analysis of color pattern variation and produce a detailed map of the loci likely involved in the H. erato color pattern radiation. Using AFLP and gene based markers, we show that fewer major genes than previously envisioned control the color pattern variation in H. erato. We describe for the first time the genetic architecture of H. erato wing color pattern by assessing quantitative variation in addition to traditional linkage mapping. In particular, our data suggest three genomic intervals modulate the bulk of the observed variation in color. Furthermore, we also identify several modifier loci of moderate effect size that contribute to the quantitative wing pattern variation. Our results are consistent with the two-step model for the evolution of mimetic wing patterns in Heliconius and support a growing body of empirical data demonstrating the importance of major effect loci in adaptive change.     

Role of superoxide dismutases (SODs) in controlling oxidative stress in plants

Reactive O(2) species (ROS) are produced in both unstressed and stressed cells. Plants have well-developed defence systems against ROS, involving both limiting the formation of ROS as well as instituting its removal. Under unstressed conditions, the formation and removal of O(2) are in balance. However, the defence system, when presented with increased ROS formation under stress conditions, can be overwhelmed. Within a cell, the superoxide dismutases (SODs) constitute the first line of defence against ROS. Specialization of function among the SODs may be due to a combination of the influence of subcellular location of the enzyme and upstream sequences in the genomic sequence. The commonality of elements in the upstream sequences of Fe, Mn and Cu/Zn SODs suggests a relatively recent origin for those regulatory regions. The differences in the upstream regions of the three FeSOD genes suggest differing regulatory control which is borne out in the research literature. The finding that the upstream sequences of Mn and peroxisomal Cu/Zn SODs have three common elements suggests a common regulatory pathway. The tools are available to dissect further the molecular basis for antioxidant defence responses in plant cells. SODs are clearly among the most important of those defences, when coupled with the necessary downstream events for full detoxification of ROS.     

Developmental expression of neuromodulators in the central complex of the grasshopper Schistocerca gregaria

The central complex is a major integrative region within the insect brain with demonstrated roles in spatial orientation, the regulation of locomotor behavior, and sound production. In the hemimetabolous grasshopper, the central complex comprises the protocerebral bridge, central body (CB), ellipsoid body, noduli, and accessory lobes, and this modular organization develops entirely during embryogenesis. From a biochemical perspective, a range of neuroactive substances has been demonstrated in these modules of the adult central complex, but little is known about their developmental expression. In this study, we use matrix‐assisted laser desorption/ionization‐imaging mass spectrometry on single brain slices to confirm the presence of several peptide families (tachykinin, allatostatin, periviscerokinin/pyrokinin, FLRFamide, and neuropeptide F) in the adult central complex and then use immunohistochemistry and histology to examine their developmental expression, together with that of the indolamin serotonin, and the endogenous messenger nitric oxide (NO; via its synthesizing enzyme). We find that each neuromodulator is expressed according to a unique, stereotypic, pattern within the various modules making up the central complex. Neuropeptides such as tachykinin (55%) and allatostatin (65%), and the NO‐synthesizing enzyme diaphorase (70%), are expressed earlier during embryonic development than the biogenic amine serotonin (80%), whereas periviscerokinin‐like peptides and FLRFamide‐like peptides begin to be expressed only postembryonically. Within the CB, these neuroactive substances are present in tangential projection neurons before they appear in columnar neurons. There is also no colocalization of serotonin‐positive and peptide‐positive projections up to the third larval instar during development, consistent with the clear dorsoventral layering of the neuropil we observe. Our results provide the first neurochemical fingerprint of the developing central complex in an hemimetabolous insect. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Mosquito vector‐associated microbiota: Metabarcoding bacteria and eukaryotic symbionts across habitat types in Thailand endemic for dengue and other arthropod‐borne diseases

Vector‐borne diseases are a major health burden, yet factors affecting their spread are only partially understood. For example, microbial symbionts can impact mosquito reproduction, survival, and vectorial capacity, and hence affect disease transmission. Nonetheless, current knowledge of mosquito‐associated microbial communities is limited. To characterize the bacterial and eukaryotic microbial communities of multiple vector species collected from different habitat types in disease endemic areas, we employed next‐generation 454 pyrosequencing of 16S and 18S rRNA amplicon libraries, also known as metabarcoding. We investigated pooled whole adult mosquitoes of three medically important vectors, Aedes aegypti, Ae. albopictus, and Culex quinquefasciatus, collected from different habitats across central Thailand where we previously characterized mosquito diversity. Our results indicate that diversity within the mosquito microbiota is low, with the majority of microbes assigned to one or a few taxa. Two of the most common eukaryotic and bacterial genera recovered (Ascogregarina and Wolbachia, respectively) are known mosquito endosymbionts with potentially parasitic and long evolutionary relationships with their hosts. Patterns of microbial composition and diversity appeared to differ by both vector species and habitat for a given species, although high variability between samples suggests a strong stochastic element to microbiota assembly. In general, our findings suggest that multiple factors, such as habitat condition and mosquito species identity, may influence overall microbial community composition, and thus provide a basis for further investigations into the interactions between vectors, their microbial communities, and human‐impacted landscapes that may ultimately affect vector‐borne disease risk.     

Man Bites Mosquito: Understanding the Contribution of Human Movement to Vector-Borne Disease Dynamics

In metropolitan areas people travel frequently and extensively but often in highly structured commuting patterns. We investigate the role of this type of human movement in the epidemiology of vector-borne pathogens such as dengue. Analysis is based on a metapopulation model where mobile humans connect static mosquito subpopulations. We find that, due to frequency dependent biting, infection incidence in the human and mosquito populations is almost independent of the duration of contact. If the mosquito population is not uniformly distributed between patches the transmission potential of the pathogen at the metapopulation level, as summarized by the basic reproductive number, is determined by the size of the largest subpopulation and reduced by stronger connectivity. Global extinction of the pathogen is less likely when increased human movement enhances the rescue effect but, in contrast to classical theory, it is not minimized at an intermediate level of connectivity. We conclude that hubs and reservoirs of infection can be places people visit frequently but briefly and the relative importance of human and mosquito populations in maintaining the pathogen depends on the distribution of the mosquito population and the variability in human travel patterns. These results offer an insight in to the paradoxical observation of resurgent urban vector-borne disease despite increased investment in vector control and suggest that successful public health intervention may require a dual approach. Prospective studies can be used to identify areas with large mosquito populations that are also visited by a large fraction of the human population. Retrospective studies can be used to map recent movements of infected people, pinpointing the mosquito subpopulation from which they acquired the infection and others to which they may have transmitted it.     

First-generation linkage map of the warningly colored butterfly Heliconius erato

We report the first genetic linkage map of Heliconius erato, a species that shows remarkable variation in its warningly colored wing patterns. We use crosses between H. erato and its sister species, H. himera, to place two major color pattern genes, D and Cr, on a linkage map containing AFLP, allozyme, microsatellite and single-copy nuclear loci. We identified all 21 linkage groups in an initial genetic screen of 22 progeny from an F1 female x male H. himera family. Of the 229 markers, 87 used to identify linkage groups were also informative in 35 progeny from a sibling backcross (H. himera female x F1 male). With these, and an additional 33 markers informative in the second family, we constructed recombinational maps for 19 of the 21 linkage groups. These maps varied in length from 18.1 to 431.1 centimorgans (cM) and yielded an estimated total length of 2400 cM. The average distance between markers was 23 cM, and eight of the 19 linkage groups, including the sex chromosome (Z) and the chromosome containing the Cr locus, contained two or more codominant anchor loci. Of the three potential candidate genes mapped here, Cubitus interruptus (Ci), Decapentaplegic (Dpp) and Wingless (Wg), only Ci was linked, although loosely, to a known Heliconius color pattern locus. This work is an important first step for constructing a denser genetic map of the H. erato color pattern radiation and for a comparative genomic study of the architecture of mimicry in Heliconius butterflies.     

Parallel genetic architecture of parallel adaptive radiations in mimetic Heliconius butterflies

It is unknown whether homologous loci underlie the independent and parallel wing pattern radiations of Heliconius butterflies. By comparing the locations of color patterning genes on linkage maps we show that three loci that act similarly in the two radiations are in similar positions on homologous chromosomes.     

Insulin signaling, lifespan and stress resistance are modulated by metabotropic GABA receptors on insulin producing cells in the brain of Drosophila

Insulin-like peptides (ILPs) regulate growth, reproduction, metabolic homeostasis, life span and stress resistance in worms, flies and mammals. A set of insulin producing cells (IPCs) in the Drosophila brain that express three ILPs (DILP2, 3 and 5) have been the main focus of interest in hormonal DILP signaling. Little is, however, known about factors that regulate DILP production and release by these IPCs. Here we show that the IPCs express the metabotropic GABA(B) receptor (GBR), but not the ionotropic GABA(A) receptor subunit RDL. Diminishing the GBR expression on these cells by targeted RNA interference abbreviates life span, decreases metabolic stress resistance and alters carbohydrate and lipid metabolism at stress, but not growth in Drosophila. A direct effect of diminishing GBR on IPCs is an increase in DILP immunofluorescence in these cells, an effect that is accentuated at starvation. Knockdown of irk3, possibly part of a G protein-activated inwardly rectifying K(+) channel that may link to GBRs, phenocopies GBR knockdown in starvation experiments. Our experiments suggest that the GBR is involved in inhibitory control of DILP production and release in adult flies at metabolic stress and that this receptor mediates a GABA signal from brain interneurons that may convey nutritional signals. This is the first demonstration of a neurotransmitter that inhibits insulin signaling in its regulation of metabolism, stress and life span in an invertebrate brain.