Biology subjects

Ian Dworkin

Publications and source records attributed to Ian Dworkin.

6 recordsLinked to original sources

bioRxiv2016

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

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 - {beta} (TGF-{beta}) 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.

Genetics↗

bioRxiv2015

Dis-integrating the fly: A mutational perspective on phenotypic integration and covariation

The structure of environmentally induced phenotypic covariation can influence the effective strength and magnitude of natural selection. Yet our understanding of the factors that contribute to and influence the evolutionary lability of such covariation is poor. Most studies have either examined environmental variation without accounting for covariation, or examined phenotypic and genetic covariation without distinguishing the environmental component. In this study we examined the effect of mutational perturbations on different properties of environmental covariation, as well as mean shape. We use strains of Drosophila melanogaster bearing well-characterized mutations known to influence wing shape, as well as naturally-derived strains, all reared under carefully-controlled conditions and with the same genetic background. We find that mean shape changes more freely than the covariance structure, and that different properties of the covariance matrix change independently from each other. The perturbations affect matrix orientation more than they affect matrix eccentricity or total variance. Yet, mutational effects on matrix orientation do not cluster according to the developmental pathway that they target. These results suggest that it might be useful to consider a more general concept of decanalization, involving all aspects of variation and covariation.

Evolutionary Biology↗

bioRxiv2014

How predator hunting-modes affect prey behaviour: Capture deterrence in Drosophila melanogaster

Hunting mode, the distinct set of behavioural strategies that a predator employs while hunting, can be an important determinant of the prey organisms behavioural response. However, few studies have considered how a predators hunting mode influences anti-predatory behaviours of a prey species. Here we document the influence of active hunters (zebra jumping spiders, Salticus scenicus) and ambush predators (Chinese praying mantids, Tenodera aridifolia sinensis) on the capture deterrence anti-predatory behavioural repertoire of the model organism, Drosophila melanogaster. We hypothesized that D. melanogaster would reduce overall locomotory activity in the presence of ambush predators, and increase activity with active hunters. First we observed and described the behavioural repertoire of D. melanogaster in the presence of the predators. We documented three previously undescribed behaviours-abdominal lifting, stopping and retreat-which were performed at higher frequency by D. melanogaster in the presence of predators, and may aid in capture deterrence. Consistent with our predictions, we observed an increase in the overall activity of D. melanogaster in the presence of jumping spiders (active hunter). However, counter to our prediction, mantids (ambush hunter) had only a modest influence on activity. We also observed considerable intra and inter-individual variation in response to both predator types. Given these new insights into Drosophila behaviour, and with the genetic tools available, dissecting the molecular mechanisms of anti-predator behaviours may now be feasible in this system.

Animal Behavior and Cognition↗

bioRxiv2014

Adaptation to a novel predator in Drosophila melanogaster: How well are we able to predict evolutionary responses?

Evolutionary theory is sufficiently well developed to allow for short-term prediction of evolutionary trajectories. In addition to the presence of heritable variation, prediction requires knowledge of the form of natural selection on relevant traits. While many studies estimate the form of natural selection, few examine the degree to which traits evolve in the predicted direction. In this study we examine the form of natural selection imposed by mantid predation on wing size and shape in the fruitfly, Drosophila melanogaster. We then evolve populations of D. melanogaster under predation pressure, and examine the extent to which wing size and shape have responded in the predicted direction. We demonstrate that wing form partially evolves along the predicted vector from selection, more so than for control lineages. Furthermore, we re-examined phenotypic selection after [~]30 generations of experimental evolution. We observed that the magnitude of selection on wing size and shape was diminished in populations evolving with mantid predators, while the direction of the selection vector differed from that of the ancestral population for shape. We discuss these findings in the context of the predictability of evolutionary responses, and the need for fully multivariate approaches.

Evolutionary Biology↗

bioRxiv2014

Evolutionary rates for multivariate traits: the role of selection and genetic variation

A fundamental question in evolutionary biology is the relative importance of selection and genetic architecture in determining evolutionary rates. Adaptive evolution can be described by the multivariate breeders equation [Formula], which predicts evolutionary change for a suite of phenotypic traits [Formula] as a product of directional selection acting on them ({beta}) and the genetic variance-covariance matrix for those traits (G). Despite being empirically challenging to estimate, there are enough published estimates of G and {beta} to allow for synthesis of general patterns across species. We use published estimates to test the hypotheses that there are systematic differences in the rate of evolution among trait types, and that these differences are in part due to genetic architecture. We find evidence some evidence that sexually selected traits exhibit faster rates of evolution compared to life-history or morphological traits. This difference does not appear to be related to stronger selection on sexually selected traits. Using numerous proposed approaches to quantifying the shape, size and structure of G we examine how these parameters relate to one another, and how they vary among taxonomic and trait groupings. Despite considerable variation, they do not explain the observed differences in evolutionary rates.

Evolutionary Biology↗

bioRxiv2014

The roles of standing genetic variation and evolutionary history in determining the evolvability of anti-predator strategies

Standing genetic variation and the historical environment in which that variation arises (evolutionary history) are both potentially significant determinants of a populations capacity for evolutionary response to a changing environment. We evaluated the relative importance of these two factors in influencing the evolutionary trajectories in the face of sudden environmental change. We used the open-ended digital evolution software Avida to examine how historic exposure to predation pressures, different levels of genetic variation, and combinations of the two, impact anti-predator strategies and competitive abilities evolved in the face of threats from new, invasive, predator populations. We show that while standing genetic variation plays some role in determining evolutionary responses, evolutionary history has the greater influence on a populations capacity to evolve effective anti-predator traits. This adaptability likely reflects the relative ease of repurposing existing, relevant genes and traits, and the broader potential value of the generation and maintenance of adaptively flexible traits in evolving populations.

Evolutionary Biology↗