Saccadic head rotations during walking in the stalk-eyed fly (Cyrtodiopsis dalmanni).
ABSTRACT: In stalk-eyed flies (Diopsidae), the eyes are positioned at the end of rigid peduncles protruding laterally from the head. Sexual selection for eye span in male Cyrtodiopsis dalmanni results in eye span that exceeds body length and exceeds the eye span of females. We studied whether the twofold higher moment of inertia (MOI) of the male head results in a reduced head rotation velocity during turning. We analysed films of flies performing walking turns and compared the head kinematics between the sexes. The significance of head rotation to turning was evaluated from the turning kinematics of flies with immobilized (glued) heads. Male and female C. dalmanni rotated their heads relative to the surrounding environment 1.55-fold (male) and 1.65-fold (female) faster than the angular velocity of the body by performing rapid head saccades. During the larger turns, flies with immobilized heads were unable to reorient gaze as fast as the control flies. Despite the larger MOI of the head, male C. dalmanni match the head saccade of females suggesting that eye span elongation is coupled by an adaptation of the neck apparatus to rotate the wider head.
Project description:Drosophila melanogaster structures its optic flow during flight by interspersing translational movements with abrupt body rotations. Whether these "body saccades" are accompanied by steering movements of the head is a matter of debate. By tracking single flies moving freely in an arena, we now discovered that walking Drosophila also perform saccades. Movement analysis revealed that the flies separate rotational from translational movements by quickly turning their bodies by 15 degrees within a tenth of a second. Although walking flies moved their heads by up to 20 degrees about their bodies, their heads moved with the bodies during saccadic turns. This saccadic strategy contrasts with the head saccades reported for e.g., blowflies and honeybees, presumably reflecting optical constraints: modeling revealed that head saccades as described for these latter insects would hardly affect the retinal input in Drosophila because of the lower acuity of its compound eye. The absence of head saccades in Drosophila was associated with the absence of haltere oscillations, which seem to guide head movements in other flies. In addition to adding new twists to Drosophila walking behavior, our analysis shows that Drosophila does not turn its head relative to its body when turning during walking.
Project description:Stalk-eyed flies (family Diopsidae) are a model system for studying sexual selection due to the elongated and sexually dimorphic eye-stalks found in many species. These flies are of additional interest because their X chromosome is derived largely from an autosomal arm in other flies. To identify candidate genes required for development of dimorphic eyestalks and investigate how sex-biased expression arose on the novel X, we compared gene expression between males and females using oligonucleotide microarrays and RNA from developing eyestalk tissue or adult heads in the dimorphic diopsid, Teleopsis dalmanni. Microarray analysis revealed sex-biased expression for 26% of 3,748 genes expressed in eye-antennal imaginal discs and concordant sex-biased expression for 86 genes in adult heads. Overall, 415 female-biased and 482 male-biased genes were associated with dimorphic eyestalk development but not differential expression in the adult head. Functional analysis revealed that male-biased genes are disproportionately associated with growth and mitochondrial function while female-biased genes are associated with cell differentiation and patterning or are novel transcripts. With regard to chromosomal effects, dosage compensation occurs by elevated expression of X-linked genes in males. Genes with female-biased expression were more common on the X and less common on autosomes than expected, while male-biased genes exhibited no chromosomal pattern. Rates of protein evolution were lower for female-biased genes but higher for genes that moved on or off the novel X chromosome. These findings cannot be due to meiotic sex chromosome inactivation or by constraints associated with dosage compensation. Instead, they could be consistent with sexual conflict in which female-biased genes on the novel X act primarily to reduce eyespan in females while other genes increase eyespan in both sexes. Additional information on sex-biased gene expression in other tissues and related sexually monomorphic species could confirm this interpretation.
Project description:Stalk-eyed flies (family Diopsidae) are a model system for studying sexual selection due to the elongated and sexually dimorphic eye-stalks found in some species. These flies are of additional interest because their X chromosome is derived largely from an autosomal arm in other flies. To investigate how sex-biased expression arose on the novel X we compared gene expression between males and females using oligonucleotide microarrays and RNA from developing eyestalk tissue in the sexually monomorphic diopsid, Teleopsis quinqueguttata. We use probe sequence divergence to evaluate cross-species ascertainment bias and chromosome assignment to determine if sex linkage influence expression. Microarray analysis revealed sex-biased expression for only 1.9% of 3,748 genes expressed in eye-antennal imaginal discs. Analysis of probe sequences between species indicates that the lack of sex-biased expression is not due to ascertainment bias. These findings indicate that the the majority of sex-biased gene expression observed in developing heads of the dimorphic species, T. dalmanni, is causally related to development of dimorphic head shape. Two-condition experiment, female vs. male RNA using larval eye discs and adult heads for one species (Teleopsis quinqueguttata)
Project description:Background: Stalk-eyed flies (family Diopsidae) are a model system for studying sexual selection due to the presence of elongated and sexually dimorphic eye-stalks in many species. Recent genomic studies on these flies have revealed a neo-X chromosome and evidence of gene movement onto or off of this X chromosome. To determine if sex linkage and gene movement are related to sexual dimorphism and sexual conflict, we compared gene expression between males and females using oligonucleotide microarrays and RNA from either developing eyestalk tissue or adult heads from a dimorphic species, Teleopsis dalmanni, or from developing eyestalk tissue in a congeneric monomorphic species, T. quinqueguttata. Results: Comparison of gene expression between the sexes for 3,748 genes indicates that dosage compensation is present due to elevated expression of X-linked genes in males. However, sex-biased expression was detected in 26% of the genes present in eye-antennal imaginal discs of larval T. dalmanni. Functional annotation reveals that female-biased genes are associated with transcription, anatomical development and cell communication in the nucleus, while male-biased genes are associated with metabolism and the mitochondria. Comparison of gene expression between experiments identified 140 genes with concordant sex-biased expression in the larval and adult tissues of T. dalmanni and 17 genes with identical sex-biased expression between species. There were only five reversals of sex-biased expression across experiments. In T. dalmanni, male-biased genes are more common on autosomes than on the X while female-biased genes are more common on the X in T. quinqueguttata. Female-biased expression is especially common among genes that moved onto the ancestral X while male-biased expression is more common among genes that moved onto an autosome. Conclusions: Genes with sex-biased expression exhibit different functions in each sex as expected if sexual conflict has influenced their evolution. The strong relationship between sex-biased expression and gene movement found in this study is consistent with resolution of sexual conflict by an RNA- or DNA-mediated process that moves genes between chromosomes. Measurement of gene expression in additional species should provide a more complete picture of how gene expression change occurs over evolutionary time in these extraordinary flies. Two-condition experiment, female vs. male RNA using larval eye discs for two species (Teleopsis dalmanni, Teleopsis quinqueguttata), and adult heads for one species (Teleopsis dalmanni).
Project description:Stalk-eyed flies of the family Diopsidae have proven to be an excellent model organism for studying the evolution of ornamental sexual traits. In diopsid flies the eyes and antennae are borne at the end of lateral head projections called 'eye-stalks'. Eyespan, the distance between the eyes, and the degree of sexual dimorphism in eyespan vary considerably between species and several sexually dimorphic species show sexual selection through female mate preference for males with exaggerated eyespan. Relatively little is known about the molecular genetic basis of intra- or inter-species variation in eyespan, eye-stalk development or growth regulation in diopsids. Molecular approaches including comparative developmental analyses, EST screening and QTL mapping have identified potential candidate loci for eyespan regulation in the model species Teleopsis dalmanni. Functional analyses of these genes to confirm and fully characterise their roles in eye-stalk growth require the development of techniques such as germline transformation to manipulate gene activity in vivo.We used in vivo excision assays to identify transposon vector systems with the activity required to mediate transgenesis in T. dalmanni. Mariner based vectors showed no detectable excision while both Minos and piggyBac were active in stalk-eyed fly embryos. Germline transformation with an overall efficiency of 4% was achieved using a Minos based vector and the 3xP3-EGFP marker construct. Chromosomal insertion of constructs was confirmed by Southern blot analysis. Both autosomal and X-linked inserts were recovered. A homozygous stock, established from one of the X-linked inserts, has maintained stable expression for eight generations.We have performed stable germline transformation of a stalk-eyed fly, T. dalmanni. This is the first transgenic protocol to be developed in an insect species that exhibits an exaggerated male sexual trait. Transgenesis will enable the development of a range of techniques for analysing gene function in this species and so provide insight into the mechanisms underlying the development of a morphological trait subject to sexual selection. Our X-linked insertion line will permit the sex of live larvae to be determined. This will greatly facilitate the identification of genes which are differentially expressed during eye-stalk development in males and females.
Project description:<h4>Background</h4>Polymorphisms of single amino acid repeats (SARPs) are a potential source of genetic variation for rapidly evolving morphological traits. Here, we characterize variation in and test for an association between SARPs and head shape, a trait under strong sexual selection, in the stalk-eyed fly, Teleopsis dalmanni. Using an annotated expressed sequence tag database developed from eye-antennal imaginal disc tissues in T. dalmanni we identified 98 genes containing nine or more consecutive copies of a single amino acid. We then quantify variation in length and allelic diversity for 32 codon and 15 noncodon repeat regions in a large outbred population. We also assessed the frequency with which amino acid repeats are either gained or lost by identifying sequence similarities between T. dalmanni SARP loci and their orthologs in Drosophila melanogaster. Finally, to identify SARP containing genes that may influence head development we conducted a two-generation association study after assortatively mating for extreme relative eyespan.<h4>Results</h4>We found that glutamine repeats occur more often than expected by amino acid abundance among 3,400 head development genes in T. dalmanni and D. melanogaster. Furthermore, glutamine repeats occur disproportionately in transcription factors. Loci with glutamine repeats exhibit heterozygosities and allelic diversities that do not differ from noncoding dinucleotide microsatellites, including greater variation among X-linked than autosomal regions. In the majority of cases, repeat tracts did not overlap between T. dalmanni and D. melanogaster indicating that large glutamine repeats are gained or lost frequently during Dipteran evolution. Analysis of covariance reveals a significant effect of parental genotype on mean progeny eyespan, with body length as a covariate, at six SARP loci [CG33692, ptip, band4.1 inhibitor LRP interactor, corto, 3531953:1, and ecdysone-induced protein 75B (Eip75B)]. Mixed model analysis of covariance using the eyespan of siblings segregating for repeat length variation confirms that significant genotype-phenotype associations exist for at least one sex at five of these loci and for one gene, CG33692, longer repeats were associated with longer relative eyespan in both sexes.<h4>Conclusion</h4>Among genes expressed during head development in stalk-eyed flies, long codon repeats typically contain glutamine, occur in transcription factors and exhibit high levels of heterozygosity. Furthermore, the presence of significant associations within families between repeat length and head shape indicates that six genes, or genes linked to them, contribute genetic variation to the development of this extremely sexually dimorphic trait.
Project description:BACKGROUND: Many species of stalk-eyed flies (Diopsidae) possess highly-exaggerated, sexually dimorphic eye-stalks that play an important role in the mating system of these flies. Eye-stalks are increasingly being used as a model system for studying sexual selection, but little is known about the genetic mechanisms producing variation in these ornamental traits. Therefore, we constructed an EST database of genes expressed in the developing eye-antennal imaginal disc of the highly dimorphic species Teleopsis dalmanni. We used this set of genes to construct microarray slides and compare patterns of gene expression between lines of flies with divergent eyespan. RESULTS: We generated 33,229 high-quality ESTs from three non-normalized libraries made from the developing eye-stalk tissue at different developmental stages. EST assembly and annotation produced a total of 7,066 clusters comprising 3,424 unique genes with significant sequence similarity to a protein in either Drosophila melanogaster or Anopheles gambiae. Comparisons of the transcript profiles at different stages reveal a developmental shift in relative expression from genes involved in anatomical structure formation, transcription, and cell proliferation at the larval stage to genes involved in neurological processes and cuticle production during the pupal stages. Based on alignments of the EST fragments to homologous sequences in Drosophila and Anopheles, we identified 20 putative gene duplication events in T. dalmanni and numerous genes undergoing significantly faster rates of evolution in T. dalmanni relative to the other Dipteran species. Microarray experiments identified over 350 genes with significant differential expression between flies from lines selected for high and low relative eyespan but did not reveal any primary biological process or pathway that is driving the expression differences. CONCLUSION: The catalogue of genes identified in the EST database provides a valuable framework for a comprehensive examination of the genetic basis of eye-stalk variation. Several candidate genes, such as crooked legs, cdc2, CG31917 and CG11577, emerge from the analysis of gene duplication, protein evolution and microarray gene expression. Additional comparisons of expression profiles between, for example, males and females, and species that differ in eye-stalk sexual dimorphism, are now enabled by these resources.
Project description:Eye-stalks of some flies exhibit extreme sexual dimorphism, but little is known about the genetic mechanisms producing variation in these ornamental traits. Therefore, we constructed an EST database of genes expressed in the developing eye-antennal imaginal disc of the highly dimorphic species, Teleopsis dalmanni, and used this set of genes to construct high density oligoarrays and compare patterns of gene expression between lines of flies selected for divergent eyespan. Microarray experiments using eye-antennal disc tissue identified over 350 genes with significant differential expression between male flies from lines selected for high and low relative eyespan but did not reveal any primary biological process or pathway that is driving the expression differences. Overall design: Custom 4x44K Agilent arrays were designed for approximately 3600 unique genes. Each gene was represented by three 60 bp oligo probes and each probe was printed in triplicate on each array. Each oligoarray was hybridized with two biological samples labeled either with cy3 or cy5. Each sample came from 25 sets of eye-antennal imaginal discs that were dissected from gut-purged male larvae. Samples were from lines of flies that had been under directional selection on males to either increase or decrease relative eyespan for 65 generations. Dye labeling was switched between lines for every other array. Ratios of median intensities were averaged across probes for each gene and then analyzed by SAM to identify genes with differential expression between lines.
Project description:We performed RNA-seq to profile gene expression in the heads and whole bodies of 32 isofemale fly lines from two divergent microclimates at 'Evolution Canyon' in Israel (16 fly lines from each microclimate). We also measured RNA editing levels in the head tissue of these flies. Overall design: For each of the 32 isofemale fly lines from 'Evolution Canyon', gene expression profiles of whole bodies and heads, along with RNA editing profiles of heads of 3-5 day old male flies through RNA-seq.
Project description:Persons with Parkinson disease (PD) experience turning difficulty, often leading to freezing of gait and falls. Visual information plays a significant role in locomotion and turning, and while the effects of deep brain stimulation (DBS) on oculomotor function have been well documented, the effects of DBS on oculomotor function during turning and on turning itself have yet to be fully elucidated.To determine the effects of STN DBS on turning performance and related oculomotor performance in PD.Eleven subjects with PD and DBS of the subthalamic nucleus performed a seated voluntary saccade task and standing 180° turns in DBS OFF and DBS ON conditions. Oculomotor data were captured using an infrared eye tracking system while segment rotations were measured using 3-D motion capture.During the seated saccade task, DBS did not improve saccade amplitude or latency. DBS also did not improve gait velocity and stride length during forward walking. During turning, DBS improved turn performance (turn duration), reduced the number of saccades performed during the turns, and increased the amplitude and velocity of the saccade initiating the turn. DBS decreased the intersegmental latencies (eye-head, eye-foot, and head-trunk) but this effect was lost for eye-head and eye-foot after controlling for the duration of the first gait cycle.DBS significantly improves turn performance and related oculomotor performance. These findings add to the growing list of therapeutic benefits offered by DBS.