Precision of sex ratio adjustment in the parasitoid wasp Nasonia vitripennis


Nasonia wild type Nasonia red eye mutant Hamilton's theory of local mate competition (LMC) predicts female biased sex ratios when: (a) a small number of females lay eggs per patch, and (b) the resultant offspring mate amongst themselves before only the females disperses. Some of the clearest support for this prediction has come from the parasitoid wasp N. vitripennis. We are exploiting this previous work to use sex ratio behaviour in this organism as a model trait for examining the constraints that prevent 'perfect' adaptation.

To date we have been focusing on three issues: (A) Mechanistic issues, and especially how individuals are constrained by their ability to process relevant information about the environment. This has been facilitated by the use of eye colour mutants (photo above right) to follow the behaviour of individuals with relative ease. (B) What is happeing in field populations? (C) The importance of genetic architecture (mutation, pleiotropy etc) for constraining sex ratio behaviour. Our main findings include:
  1. The eggs laid by other females are a more important cue for shifting sex ratios then the presence of other females (Shuker & West, 2004 PNAS; Shuker et al 2007 Anim. Behav.).
  2. Females adjust their offspring sex ratios more precisely then previously realised, with adaptive sex ratio variation within a patch, in response to variation in when different broods will emerge (Shuker et al, 2005 Am. Nat.; Shuker et al. 2006 Behav. Ecol.).
  3. Several potentially important factors have negligible effects on offspring sex ratios. Specifically: (i) Females do not adjust their offspring sex ratios as predicted in response to relatedness to their mates or other females - conflict of interest between individuals maybe a constraint preventing this (Reece et al. 2004 J Evo. Biol.; Shuker et al. 2004 Evol. Ecol. Res.; Shuker et al. 2004 Anim. Behav.). (ii) Aysmetric larval competition between male and female larvae is relatively weak (Sykes et al. 2007 Behav. Ecol. Sociobiol.) (iii) Males have either no or a small influence on offspring sex ratios (Shuker et al. 2006 Behav. Ecol.).
  4. The findings of in our laboratory experiments are supported by the data from natural field populations (Burton-Chellew et al. 2009 Am. Nat.).
  5. The genetic variance for sex ratio behaviour in natural populations is to low to be explained by mutation-selction balance and the observed mutability of sex ratio behaviour (one mutation every 5-60 generations that shifts the sex ratio by approximately 0.01), suggesting that sex ratio mutations also have deleterious effects on other traits (Pannebakker et al. 2008 Evolution).
We are also complementing this research with: (A) our wider comparative studies; (B) experimental studies on the lack of sex ratio adjustment in Melittobia parasitoids.

This work is led by Dave Shuker, with Bart Pannebakker, Ed Sykes, Max Burton & Sarah Reece. It also involves collaboration on theoretical modelling with Ido Pen (Groningen University, Netherlands), and field and genetic work with Leo Beukeboom (Groningen) and Juergen Gadeau (Wurzberg, Germany). Ali & Dan developed the Nasonia games. We are particularly interested in gaining students/fellows/collaborators with different backgrounds and skills to ours - we have a trait where we understand the fitness consequences and behavioural cues very well, and have enormous potential to exploit this from all possible angles.

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