Evolution of insect behavior driven by human activity

• Calcagno V, Bonhomme V, Thomas Y, Singer MC & Bourguet D (2010) Divergence in behaviour between the European corn borer, Ostrinia nubilalis, and its sibling species Ostrinia scapulalis: adaptation to human harvesting? Proc. R. Soc. Lond. B (published online)

This paper describes a behavioral difference between two sibling species of moths (Ostrinia nubilalis and Ostrinia scapulalis). During larval periods, these insects live inside the stalks of their host plants. When they develop to the final stage of larva, they undergo diapause. The position in which O. nubilalis undergo diapause is closer to the ground compared to O. scapulalis. What generated such difference? O. nubilalis feeds only on maize while O. scapulalis feeds on various plants including maize. The authors also showed that, in the two moth species, the selective force of maize harvesting by humans is so strong that diapausing position in maize stalks is a crucial factor for their survival. Based on these results, the authors hypothesize that human harvesting on maize triggered the evolution of geotactic behavior in O. nubilalis. Very interesting!

Sexy or not sexy?

In insects, sex determination is cell autonomous. That is, a single cell determines its sex independently following its own chromosome constitution. Thus, it has long been assumed that every cell is either male or female. The following paper demonstrates that this is not the case. The spatio-temporal expression of sex determining genes clearly shows that many of the cells are not sexually differentiated and only a portion of the cells (particularly those that display sexually dimorphic morphology) are sexually differentiated. This is a more complex system than we expected. Would an integrated understanding of sex determination across animal kingdom be possible? 

• Robinett CC, Vaughan AG, Knapp J-M, Baker BS (2010) Sex and the single cell. II. There is a time and place for sex. PLoS Biology 8: e1000365. [link]

Speciation by a selfish genetic element?

Phadnis N, Orr HA (2009) A single gene causes both male sterility and segregation distortion in Drosophila hybrids. Science 323: 376-379. [link]


Segregation distorter (also referred to as meiotic drive) is a selfish genetic element that is preferentially transmitted to subsequent generation by distorting the 50:50 Medelian segregation. If such gene is located on X chromosome, offspring sex ratio of the XY male would be biased toward female. If such alleles spread in the population, suppressors against segregation distortion become easier to spread. So, segregation distorter and its suppressor can be both fixed in the population. In such situation, violation against Mendelian rule can never be observed unless hybridization between different populations occurs.

In the fruitfly Drosophila pseudoobscura, segregation distortion of the X chromosome is observed by hybridization between different subspecies. This is never observed within subspecies.

In this paper, a single gene, called overdrive, was found to cause hybrid male sterility (a kind of post-mating reproductive isolation) between subspecies, and this very gene was also found to cause segregation distortion.

Although this result is not a proof for speciation by the selfish genetic element, such scenario seems very likely.

Readers who are interested in this paper may also be interested in the following paper:

• Bordenstein SR, O'Hara FP, Werren JH (2001) Wolbachia-induced incompatibility precedes other hybrid incompatibilities in Nasonia. Nature 409: 707-710. [link]

細菌Wolbachiaによって引き起こされる細胞質不和合のメカニズムに関する論文を紹介しました。

Landmann F, Orsi GA, Loppin B, Sullivan W (2009) Wolbachia-mediated cytoplasmic incompatibility is associated with impaired histone deposition in the male pronucleus. PLoS Pathogen 5(3): e1000343.

「H1N1型インフルエンザAウイルスの進化」についての文献を紹介しました。

Nelson MI, Viboud C, Simonsen L, Bennett RT, Griesemer SB, et al. (2008) Multiple reassortment events in the evolutionary history of H1N1 influenza A virus since 1918. PLoS Pathog 4(2): e1000012.