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The sex-limited effects of mutations in the EGFR and TGF-? signaling pathways on shape and size sexual dimorphism and allometry in the Drosophila wing.

ABSTRACT: Much of the morphological diversity in nature-including among sexes within a species-is a direct consequence of variation in size and shape. However, disentangling variation in sexual dimorphism for both shape (SShD), size (SSD), and their relationship with one another remains complex. Understanding how genetic variation influences both size and shape together, and how this in turn influences SSD and SShD, is challenging. In this study, we utilize Drosophila wing size and shape as a model system to investigate how mutations influence size and shape as modulated by sex. Previous work has demonstrated that mutations in epidermal growth factor receptor (EGFR) and transforming growth factor-? (TGF-?) signaling components can influence both wing size and shape. In this study, we re-analyze this data to specifically address how they impact the relationship between size and shape in a sex-specific manner, in turn altering the pattern of sexual dimorphism. While most mutations influence shape overall, only a subset have a genotypic specific effect that influences SShD. Furthermore, while we observe sex-specific patterns of allometric shape variation, the effects of most mutations on allometry tend to be small. We discuss this within the context of using mutational analysis to understand sexual size and shape dimorphism.

SUBMITTER: Testa ND

PROVIDER: S-EPMC4899140 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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The sex-limited effects of mutations in the EGFR and TGF-β signaling pathways on shape and size sexual dimorphism and allometry in the Drosophila wing.

Testa Nicholas D ND Dworkin Ian I

Development genes and evolution 20160401 3

Much of the morphological diversity in nature-including among sexes within a species-is a direct consequence of variation in size and shape. However, disentangling variation in sexual dimorphism for both shape (SShD), size (SSD), and their relationship with one another remains complex. Understanding how genetic variation influences both size and shape together, and how this in turn influences SSD and SShD, is challenging. In this study, we utilize Drosophila wing size and shape as a model system ...[more]

PMID: 27038022

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Project description:Sexual differences in morphology, ranging from subtle to extravagant, occur commonly in many animal species. These differences can encompass overall body size (sexual size dimorphism, SSD) or the size and/or shape of specific body parts (sexual body component dimorphism, SBCD). Interacting forces of natural and sexual selection shape much of the expression of dimorphism we see, though non-adaptive processes may be involved. Differential scaling of individual features can result when selection favors either exaggerated (positive allometry) or reduced (negative allometry) size during growth. Studies of sexual dimorphism and character scaling rely on multivariate models that ideally use an unbiased reference character as an overall measure of body size. We explored several candidate reference characters in a cryptically dimorphic taxon, Hadrurus arizonensis. In this scorpion, essentially every body component among the 16 we examined could be interpreted as dimorphic, but identification of SSD and SBCD depended on which character was used as the reference (prosoma length, prosoma area, total length, principal component 1, or metasoma segment 1 width). Of these characters, discriminant function analysis suggested that metasoma segment 1 width was the most appropriate. The pattern of dimorphism in H. arizonensis mirrored that seen in other more obviously dimorphic scorpions, with static allometry trending towards isometry in most characters. Our findings are consistent with the conclusions of others that fecundity selection likely favors a larger prosoma in female scorpions, whereas sexual selection may favor other body parts being larger in males, especially the metasoma, pectines, and possibly the chela. For this scorpion and probably most other organisms, the choice of reference character profoundly affects interpretations of SSD, SBCD, and allometry. Thus, researchers need to broaden their consideration of an appropriate reference and exercise caution in interpreting findings. We highly recommend use of discriminant function analysis to identify the least-biased reference character.

Project description:BackgroundThe evolution of sexual size dimorphism (SSD) is likely constrained by life history. Using phylogenetic comparative methods, we examined correlations between SSD among anurans and their life history traits, including egg size, clutch size, mating combat, and parental care behaviour. We used sexual dimorphism index (SDI = Body-size(female) /Body-size(male) -1) as the measurement for SSD. Body size, life history and phylogenetic data were collected from published literature. Data were analysed at two levels: all anuran species and within individual families.ResultsFemale-biased SSD is the predominant form in anurans. SSD decreases along with the body size increase, following the prediction of Rensch's rule, but the magnitude of decrease is very small. More importantly, female body size is positively correlated with both fecundity related traits, egg size and clutch size, and SDI is also positively correlated with clutch size, suggesting fecundity advantage may have driven the evolution of female body size and consequently leads to the evolution of female-biased SSD. Furthermore, the presence of parental care, male parental care in particular, is negatively correlated with SDI, indicating that species with parental care tend to have a smaller SDI. A negative correlation between clutch size and parental care further suggests that parental care likely reduces the fecundity selection pressure on female body size. On the other hand, there is a general lack of significant correlation between SDI and the presence of male combat behaviour, which is surprising and contradictory to previous studies.ConclusionsWe find clear evidence to support the 'fecundity advantage hypothesis' and the 'parental care hypothesis' in shaping SSD in anurans. Nevertheless, the relationships of both parental care and combat behaviour to the evolution of SSD are complex in anurans and the extreme diversity of life history traits may have masked some potential interesting relationships. Our study represents the most comprehensive study of SSD in anurans to date.

Project description:BackgroundThe Drosophila wing represents a particularly appropriate model to investigate the developmental control of phenotypic variation. Previous studies which aimed to identify candidate genes for wing morphology demonstrated that the genetic basis of wing shape variation in D. melanogaster is composed of numerous genetic factors causing small, additive effects. In this study, we analyzed wing shape in males and females from 191 lines of D. melanogaster, homozygous for a single P-element insertion, using geometric morphometrics techniques. The analysis allowed us to identify known and novel candidate genes that may contribute to the expression of wing shape in each sex separately and to compare them to candidate genes affecting wing size which have been identified previously using the same lines.ResultsOur results indicate that more than 63% of induced mutations affected wing shape in one or both sexes, although only 33% showed significant differences in both males and females. The joint analysis of wing size and shape revealed that only 19% of the P-element insertions caused coincident effects on both components of wing form in one or both sexes. Further morphometrical analyses revealed that the intersection between veins showed the smallest displacements in the proximal region of the wing. Finally, we observed that mutations causing general deformations were more common than expected in both sexes whereas the opposite occurred with those generating local changes. For most of the 94 candidate genes identified, this seems to be the first record relating them with wing shape variation.ConclusionsOur results support the idea that the genetic architecture of wing shape is complex with many different genes contributing to the trait in a sexually dimorphic manner. This polygenic basis, which is relatively independent from that of wing size, is composed of genes generally involved in development and/or metabolic functions, especially related to the regulation of different cellular processes such as motility, adhesion, communication and signal transduction. This study suggests that understanding the genetic basis of wing shape requires merging the regulation of vein patterning by signalling pathways with processes that occur during wing development at the cellular level.

Dataset Information

The sex-limited effects of mutations in the EGFR and TGF-? signaling pathways on shape and size sexual dimorphism and allometry in the Drosophila wing.

Publications

The sex-limited effects of mutations in the EGFR and TGF-β signaling pathways on shape and size sexual dimorphism and allometry in the Drosophila wing.

Similar Datasets

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