1 / 18

Sex Allocation Distorters: Understanding the Interplay and Consequences of Sex Ratio Distorters

This chapter explores the mechanisms and consequences of sex ratio distorters, including nuclear genes, cytoplasmic elements, and genomic imprinting. It discusses their impact on sex allocation, the spread of distorters, and their effects on host biology. The chapter concludes with the need for empirical data and further research on the interplay between different distorters.

jodee
Download Presentation

Sex Allocation Distorters: Understanding the Interplay and Consequences of Sex Ratio Distorters

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 9 Sex allocation/(ratio) distorters

  2. Sex ratio distorters • The ESS SR may differ between the point of view of different genes within an individual conflict over SR • SR distorting elements: • Nuclear genes • Cytoplasmatic elements

  3. Nuclear genes Sex chromosome meiotic drive: • Y chromosome drive leads to male bias: Y chromosome only transmitted by males so a gene on Y that will lead to more male offspring will spread • X chromosome drive leads to female bias: X drive at the cost of Y Spread slower Commonly found in Diptera More common than Y drive Aedes aegypti

  4. B chromosomes • Supernumerary chromosome, not required for fitness • Generally no effect on SR but: • PSR in Nasonia vitripennis, only male offspring produced • Ultimate selfish element, ensures own transmission at cost of the rest of the genome

  5. Cytoplasmic genes • Only transmitted trough the maternal line > selection for SR distortion • Include mitochondria and micro-organisms (Wolbachia, cardinium) • Several mechanism found to increase the amount of female offspring produced

  6. Feminizers • Override the nuclear sex determination • Found in woodlice, mites, parasitoids and shrimp • Frequency often lower than expected, might be caused by risk of producing intersexes

  7. Maternal Sex Ratio • Influences the fertilization rate • Found in some parasitoids • Should rapidly spread to fixation ? ?

  8. Male killers • Two types: early and late • Early: resources allocated to sons can be used by daughters with related bacteria • Late: males used as vectors for horizontal transfer

  9. Parthenogenesis induction • In haplodiploids: unfertilized eggs develop into females • Genome duplication • Found in several insect taxa

  10. Cytoplasmic incompatibility • Not strictly SR distorter • In haploids male unaffected >leads to male biased SR /only males

  11. Genomic imprinting • Differential expression alleles dependent on parental origin • Alleles from different backgrounds can disagree over SR • Imprinting as a battle ground for conflict over SR

  12. Spread of SR distorters • Often not fixed in populations • Possible explanation: • Balancing selection • Reduced fertility/survival infected individuals • Sexual selection, avoiding infected individuals • Suppressors • Sex chromosome linked • Autosomal: Fisherian selection

  13. PSR • Spread dependent on fertilization rate • It can only invade when FR > 0.5 • LMC causes female biased SR, but small patch size selects against PSR • Presence of MSR, although PSR selects against MSR

  14. Male killing • Spread dependent on transmission rate • High transmission: fixation, population extinction • Low transmission: intermediate frequency • Resource reallocation among offspring • Survival cost • Mating preference • Selection for nuclear suppression because of • Increase in fecundity • Fisherian advantage of rare sex

  15. The consequences of SR distorters • Compensatory SR adjustment Only under imperfect transmission Under high transmission, no selection >no gene flow between infected and uninfected part population

  16. Other effects of SR distorters • Sex role reversal, due to biased SR • The evolution of new sex determination systems e.g haplodiploidy • Adjustment of breeding system e.g. larger clutches, multiple mating, reallocation of resources among offspring • Selective sweep, hitchhiking effect, reduced recombination (X drive)

  17. Conclusion • Main topics for future research: • What controls variation across taxa • The interplay between different distorters • Consequences for host biology Lots of theory, but need for empirical data

  18. Final thoughts • Why so often in haplodiploids? • Mechanisms: how does the drive work, details of mechanisms might influence effects

More Related