A Functional Genetic Study of Sexual Dimorphism and Behavioral Ecology in Chrysomya rufifacies (Diptera: Calliphoridae)
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Date
2015-08-05
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Abstract
Chrysomya rufifacies Macquart (Diptera: Calliphoridae) is a blow fly of medical, veterinary, and forensic relevance. This species is native to the Australo-Pacific region and invasive in the New World. A unique characteristic of this species is that it lacks obvious sex chromosomes and possesses a poorly understood monogenic sex determination system in which females produce all male or female clutches. This species also engages in facultative predation on other blow fly species, but the proximate causes of this behavior remain unstudied. The unusual sex determination mechanism employed by this species was leveraged to study sexually dimorphic patterns of gene expression throughout immature development, expression of genes between sexes and sex-producers, and to evaluate the genes correlated with predation.
The exact mechanism leading to monogenic sex determination in C. rufifacies was not identified in this work, though many genes were differentially expressed between females relative to the sex of their offspring. Gene expression results, coupled with the observation that sex ratios deviate from a binomial distribution, suggest there may be neurological, physiological, or behavioral differences between female-types. Three specific genetic hypotheses related to the primary signal establishing sex determination in this species are raised by this work: transformer, Sex-lethal, daughterless. Genetic tools are now available to investigate differential expression and the effect of these genes on sexual development, but do not preclude the possibility of a gene unique to this species or non-coding RNA in directing sexual fate as hypothesized in other taxa.
The results show that sexual dimorphism in gene expression can be observed at all stages of development, with a female bias in differentially expressed nodes in egg and adult stages and male bias in the larval and pupal stages. Male up-regulated genes tended to be those related to neurogenesis and behavior, whereas female enriched genes were involved in metabolic processes, muscle development, and oogenesis.
Several genes were differentially expressed between actively predating and non-predating individuals, including those involved in growth regulation, response to starvation, dehydration, and neurogenesis. There was also weak evidence of sexual-dimorphism in predation rates and gene expression.
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Entomology, Sex determination, Transcriptome, Calliphoridae, Molecular ecology