Genomic conflict in scale insects: the causes and consequences of bizarre genetic systems

  title={Genomic conflict in scale insects: the causes and consequences of bizarre genetic systems},
  author={Laura Ross and Ido Pen and David M. Shuker},
  journal={Biological Reviews},
It is now clear that mechanisms of sex determination are extraordinarily labile, with considerable variation across all taxonomic levels. This variation is often expressed through differences in the genetic system (XX‐XY, XX‐XO, haplodiploidy, and so on). Why there is so much variation in such a seemingly fundamental process has attracted much attention, with recent ideas concentrating on the possible role of genomic conflicts of interest. Here we consider the role of inter‐ and intra‐genomic… 

Diversity of Modes of Reproduction and Sex Determination Systems in Invertebrates, and the Putative Contribution of Genetic Conflict

The different modes of reproduction among invertebrate species, highlighting sexual reproduction as the probable ancestral state; the paradoxical diversity of sex determination systems; and the different types of genetic conflicts that could drive the evolution of such different systems are reviewed.

Genetic conflict, kin and the origins of novel genetic systems

  • B. NormarkL. Ross
  • Biology
    Philosophical Transactions of the Royal Society B: Biological Sciences
  • 2014
Asymmetric genetic systems are much more common in terrestrial and freshwater taxa than in marine taxa, and an environment of asymmetric kinship (with neighbours more closely related by maternal alleles than by paternal alleles) may have helped to drive asymmetries in expression and transmission.

Gene-rich X chromosomes implicate intragenomic conflict in the evolution of bizarre genetic systems

High increased X-linkage in modern and ancestral genomes of gPGE+X species, with an estimated 30 times more X-linked genes than in non-gPGE-X relatives, suggests a general role for intragenomic conflict in the origins of PGE/HD.

Are asymmetric inheritance systems an evolutionary trap? Transitions in the mechanism of genome loss in the scale insect family Eriococcidae

Broadly, it is failed to find evidence for a reversion from PGE to Mendelian inheritance in Eriococcidae, supporting the idea that asymmetric inheritance systems such as PGE may be an evolutionary trap.

The role of endosymbionts in the evolution of haploid-male genetic systems in scale insects (Coccoidea)

It is shown that species harboring endosymbionts are indeed more likely to have a genetic system with male haploidy, which supports the idea that intergenomic conflict can drive the evolution of novel genetic systems and affect host reproduction.

Sexual antagonism in haplodiploids

A series of evolutionary-genetic models of sexual antagonism for haplodiploids are developed, incorporating details of their molecular biology and social ecology, and it is found that PGE promotes female-beneficial alleles more than arrhenotoky.

Genomic conflict over reproduction in a booklouse (Psocodea: Liposcelis): consequences of a maternally transmitted reproductive manipulator on host ecology and genetics

It is found that the Distorting element is able to stably persist in L. bostrychophila populations, both in the wild and in the laboratory, and this is partially due to the fact that females that carry the distorting element have a shorter lifespan and do not produce as many offspring as females that do not carry the element.

No evidence for an intragenomic arms race under paternal genome elimination in Planococcus mealybugs

It is concluded that there is scope for intragenomic conflict between parental genomes in mealybugs and how these paternal escapes can occur and what these findings may reveal about the evolutionary dynamics of this bizarre genetic system.

Small but mighty: the evolutionary dynamics of W and Y sex chromosomes

  • J. Mank
  • Biology
    Chromosome Research
  • 2011
Although sex chromosomes have been the focus of a great deal of scientific scrutiny, most interest has centred on understanding the evolution and relative importance of X and Z chromosomes. By

Sex Determination, Sex Chromosomes, and Karyotype Evolution in Insects

A large database on karyotypes and sex chromosomes in insects, containing information on over 13000 species covering 29 orders of insects, is established, which constitutes a unique starting point to report phylogenetic patterns on the distribution of sex determination mechanisms, sex chromosomes, and karyotype among insects.



The evolution of unusual chromosomal systems in coccoids: extraordinary sex ratios revisited

A model of the evolution of paternal genome loss in coccoids from an ancestral system of XX‐XO sex determination is presented, based on Hamilton's (1967) theory that different genetic elements within the genome have different unbeatable sex ratios.

Can maternally transmitted endosymbionts facilitate the evolution of haplodiploidy?

It is found that both with male‐killers and CI‐inducing endosymbionts, the hosts are likely to develop increased viability of haploid males, which can be considered a preadaptation to haplodiploidy.

Maternal-zygotic gene conflict over sex determination: effects of inbreeding.

It is shown that maternal-effect and zygotic genes are subject to conflicting selective pressures over sex determination in species with partial inbreeding or subdivided populations.


There is growing evidence that genetic conflict could be important in the evolution of sex-determining mechanisms, including sex chromosome drive, cytoplasmic sex-ratio distortion, and cytop lasmic male sterility in plants.

Turnover of sex chromosomes induced by sexual conflict

In this theoretical study, it is shown that an autosomal gene under sexually antagonistic selection can cause the spread of a new sex-determining gene linked to it, which can account for the origin of newSex-Determining loci, the transposition of an ancestral sex-D determining gene to an autosome, and the maintenance of multiple sex- determining factors in species that lack heteromorphic sex chromosomes.


  • B. Normark
  • Biology
    Evolution; international journal of organic evolution
  • 2004
This hypothesis helps to explain the ecological correlates of the origins of haplodiploidsy, as well as such otherwise puzzling phenomena as obligate cannibalism by male Micromalthus beetles, reversion to diploidy by aposymbiotic male stictococcid scale insects, and the bizarre genomic constitution of scale insect bacteriomes.

The evolution of alternative genetic systems in insects.

A classification of the genetic systems of insects and the number of evolutionary transitions between them is presented and available evidence tends to support W.D. Hamilton's hypothesis that maternally transmitted endosymbionts have been involved in the origins of haplodiploidy.

Sexual conflict, sex allocation and the genetic system

This work considers how biased gene transmission, as expressed in different genetic systems, enhances the opportunity for sex ratio conflict and gives empirical examples that confirm that males and females have the opportunity to influence sex ratios.

Haploidploidy and the evolution of the social insect.

Evidence is presented from 20 species that the ratio of investment in monogynous ants is, indeed, about 1 : 3, and this discovery is subject to a series of tests, which provide quantitative evidence in support of kinship theory, sex ratio theory, and the assumption that the offspring is capable of acting counter to its parents' best interests.

Adaptations in scale insects.

The sedentary lifestyle of female scale insects has favored the evolution of appendage reduction or loss, gross changes in body shape, and protective wax secretions, tests, and other scale covers, while Crawlers have evolved as the main agents of dispersal.