@article {45716, title = {Pupariation site preference within and between Drosophila sibling species.}, journal = {Evolution}, volume = {67}, year = {2013}, month = {2013 Sep}, pages = {2714-27}, abstract = {

Holometabolous insects pass through a sedentary pupal stage and often choose a location for pupation that is different from the site of larval feeding. We have characterized a difference in pupariation site choice within and between sibling species of Drosophila. We found that, in nature, Drosophila sechellia pupariate within their host fruit, Morinda citrifolia, and that they perform this behavior in laboratory assays. In contrast, in the laboratory, geographically diverse strains of Drosophila simulans vary in their pupariation site preference; D. simulans lines from the ancestral range in southeast Africa pupariate on fruit, or a fruit substitute, whereas populations from Europe or the New World select sites off of fruit. We explored the genetic basis for the evolved preference in puariation site preference by performing quantitative trait locus mapping within and between species. We found that the interspecific difference is controlled largely by loci on chromosomes X and II. In contrast, variation between two strains of D. simulans appears to be highly polygenic, with the majority of phenotypic effects due to loci on chromosome III. These data address the genetic basis of how new traits arise as species diverge and populations disperse.

}, keywords = {Africa, Animal Distribution, Animals, Chromosomes, Insect, Drosophila, Europe, Evolution, Molecular, Genetic Speciation, Genetic Variation, Morinda, Phylogeography, Pupa, Quantitative Trait Loci, X Chromosome}, issn = {1558-5646}, doi = {10.1111/evo.12146}, author = {Erezyilmaz, Deniz F and Stern, David L} } @article {4650, title = {Morphological evolution caused by many subtle-effect substitutions in regulatory DNA.}, journal = {Nature}, volume = {474}, year = {2011}, month = {2011 Jun 30}, pages = {598-603}, abstract = {

Morphology evolves often through changes in developmental genes, but the causal mutations, and their effects, remain largely unknown. The evolution of naked cuticle on larvae of Drosophila sechellia resulted from changes in five transcriptional enhancers of shavenbaby (svb), a transcript of the ovo locus that encodes a transcription factor that governs morphogenesis of microtrichiae, hereafter called {\textquoteright}trichomes{\textquoteright}. Here we show that the function of one of these enhancers evolved through multiple single-nucleotide substitutions that altered both the timing and level of svb expression. The consequences of these nucleotide substitutions on larval morphology were quantified with a novel functional assay. We found that each substitution had a relatively small phenotypic effect, and that many nucleotide changes account for this large morphological difference. In addition, we observed that the substitutions had non-additive effects. These data provide unprecedented resolution of the phenotypic effects of substitutions and show how individual nucleotide changes in a transcriptional enhancer have caused morphological evolution.

}, keywords = {Animals, Base Sequence, Biological Evolution, Developmental, DNA-Binding Proteins, Drosophila, Drosophila melanogaster, Drosophila Proteins, Embryo, Enhancer Elements, Female, Gene Expression Regulation, Genetic, Larva, Male, Nonmammalian, Nucleic Acid, Phenotype, Sequence Alignment, Sequence Homology, Transcription Factors}, issn = {1476-4687}, doi = {10.1038/nature10200}, author = {Frankel, Nicol{\'a}s and Erezyilmaz, Deniz F and McGregor, Alistair P and Wang, Shu and Payre, Fran\c cois and Stern, David L} } @article {2501, title = {The nuclear receptor E75A has a novel pair-rule-like function in patterning the milkweed bug, Oncopeltus fasciatus.}, journal = {Developmental Biology}, volume = {334}, year = {2009}, month = {2009 Oct 1}, pages = {300-10}, abstract = {

Genetic studies of the fruit fly Drosophila have revealed a hierarchy of segmentation genes (maternal, gap, pair-rule and HOX) that subdivide the syncytial blastoderm into sequentially finer-scale coordinates. Within this hierarchy, the pair-rule genes translate gradients of information into periodic stripes of expression. How pair-rule genes function during the progressive mode of segmentation seen in short and intermediate-germ insects is an ongoing question. Here we report that the nuclear receptor Of{\textquoteright}E75A is expressed with double segment periodicity in the head and thorax. In the abdomen, Of{\textquoteright}E75A is expressed in a unique pattern during posterior elongation, and briefly resembles a sequence that is typical of pair-rule genes. Depletion of Of{\textquoteright}E75A mRNA caused loss of a subset of odd-numbered parasegments, as well as parasegment 6. Because these parasegments straddle segment boundaries, we observe fusions between adjacent segments. Finally, expression of Of{\textquoteright}E75A in the blastoderm requires even-skipped, which is a gap gene in Oncopeltus. These data show that the function of Of{\textquoteright}E75A during embryogenesis shares many properties with canonical pair-rule genes in other insects. They further suggest that parasegment specification may occur through irregular and episodic pair-rule-like activity.

}, keywords = {Animals, Blastoderm, Body Patterning, Cytoplasmic and Nuclear, Embryo, Hemiptera, Insect Proteins, Nonmammalian, Receptors, RNA Interference}, issn = {1095-564X}, doi = {10.1016/j.ydbio.2009.06.038}, author = {Erezyilmaz, Deniz F and Kelstrup, Hans C and Riddiford, Lynn M} } @article {2500, title = {The role of the pupal determinant broad during embryonic development of a direct-developing insect.}, journal = {Development Genes \& Evolution}, volume = {219}, year = {2009}, month = {2009 Dec 30}, pages = {535-44}, abstract = {

Metamorphosis is one of the most common, yet dramatic of life history strategies. In insects, complete metamorphosis with morphologically distinct larval stages arose from hemimetabolous ancestors that were more direct developing. Over the past century, several ideas have emerged that suggest the holometabolous pupa is developmentally homologous to the embryonic stages of the hemimetabolous ancestor. Other theories consider the pupal stage to be a modification of a hemimetabolous nymph. To address this question, we have isolated an ortholog of the pupal determinant, broad (br), from the hemimetabolous milkweed bug and examined its role during embryonic development. We show that Oncopeltus fasciatus br (Of{\textquoteright}br) is expressed in two phases. The first occurs during germ band invagination and segmentation when Of{\textquoteright}br is expressed ubiquitously in the embryonic tissues. The second phase of Of{\textquoteright}br expression appears during the pronymphal phase of embryogenesis and persists through nymphal differentiation to decline just before hatching. Knock-down of Of{\textquoteright}br transcripts results in defects that range from posterior truncations in the least-affected phenotypes to completely fragmented embryonic tissues in the most severe cases. Analysis of the patterning genes engrailed and hunchback reveal loss of segments and a failure in neural differentiation after Of{\textquoteright}br depletion. Finally, we show that br is constitutively expressed during embyrogenesis of the ametabolous firebrat, Thermobia domestica. This suggests that br expression is prominent during embryonic development of ametabolous and hemimetabolous insects but was lost with the emergence of the completely metamorphosing insects.

}, keywords = {Animals, Biological, Biological Evolution, Body Patterning, Cloning, Developmental, DNA Primers, Drosophila Proteins, Gene Expression Regulation, Heteroptera, In Situ Hybridization, Insect Proteins, Metamorphosis, Molecular, Reverse Transcriptase Polymerase Chain Reaction, Transcription Factors}, issn = {1432-041X}, doi = {10.1007/s00427-009-0315-7}, author = {Erezyilmaz, Deniz F and Rynerson, Melody R and Truman, James W and Riddiford, Lynn M} } @article {2446, title = {The pupal specifier broad directs progressive morphogenesis in a direct-developing insect.}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {103}, year = {2006}, month = {2006 May 2}, pages = {6925-30}, abstract = {

A key regulatory gene in metamorphosing (holometabolous) insect life histories is the transcription factor broad (br), which specifies pupal development. To determine the role of br in a direct-developing (hemimetabolous) insect that lacks a pupal stage, we cloned br from the milkweed bug, Oncopeltus fasciatus (Of{\textquoteright}br). We find that, unlike metamorphosing insects, in which br expression is restricted to the larval-pupal transition, Of{\textquoteright}br mRNA is expressed during embryonic development and is maintained at each nymphal molt but then disappears at the molt to the adult. Induction of a supernumerary nymphal stage with a juvenile hormone (JH) mimic prevented the disappearance of br mRNA. In contrast, induction of a precocious adult molt by application of precocene II to third-stage nymphs caused a loss of br mRNA at the precocious adult molt. Thus, JH is necessary to maintain br expression during the nymphal stages. Injection of Of{\textquoteright}br dsRNA into either early third- or fourth-stage nymphs caused a repetition of stage-specific pigmentation patterns and prevented the normal anisometric growth of the wing pads without affecting isometric growth or molting. Therefore, br is necessary for the mutable (heteromorphic) changes that occur during hemimetabolous development. Our results suggest that metamorphosis in insects arose as expression of br, which conveys competence for change, became restricted to one postembryonic instar. After this shift in br expression, the progressive changes that occur within the nymphal series in basal insects became compressed to the one short period of morphogenesis seen in the larva-to-pupa transition of holometabolous insects.

}, keywords = {Animals, Biological, Drosophila Proteins, Heteroptera, Insect Proteins, Juvenile Hormones, Metamorphosis, Molecular Sequence Data, Morphogenesis, Nymph, Pigmentation, RNA, Transcription Factors, Wing}, issn = {0027-8424}, doi = {10.1073/pnas.0509983103}, author = {Erezyilmaz, Deniz F and Riddiford, Lynn M and Truman, James W} }