Temporal variation in sex allocation in the mealybug Planococcus citri: adaptation, constraint, or both?

Abstract

Sex ratio theory has been very successful in predicting under which circumstances parents should bias their investment towards a particular offspring sex. However, most examples of adaptive sex ratio bias come from species with well-defined mating systems and sex determining mechanisms, while in many other groups there is still an ongoing debate about the adaptive nature of sex allocation. Here we study the sex allocation in the mealybug Planococcus citri, a species in which it is currently unclear how females adjust their sex ratio, even though experiments have shown support for facultative sex ratio adjustment. Previous work has shown that the sex ratio females produce changes over the oviposition period, with males being overproduced early and late in the laying sequence. Here we investigate this complex pattern further, examining both the robustness of the pattern and possible explanations for it. We first show that this sex allocation behaviour is indeed consistent across lines from three geographical regions. Second, we test whether females produce sons first in order to synchronize reproductive maturation of her offspring, although our data provide little evidence for this adaptive explanation. Finally we test the age at which females are able to mate successfully and show that females are able to mate and store sperm before adult eclosion. Whilst early-male production may still function in promoting protandry in mealybugs, we discuss whether mechanistic constraints limit how female allocate sex across their lifetime.

Paternal Genome Elimination inLiposcelisBooklice (Insecta: Psocodea)

“…Additionally, species with PGE often have female biased sex ratios with maternal control over the offspring sex ratio. This has been studied best in mites (Helle et al 1978, Nagelkerke andSabelis 1998) and scale insects (Varndell and Godfray 1996;Ross et al 2010bRoss et al , 2012. The results from our controlled laboratory experiments point toward maternal control of sex ratio in Liposcelis sp.…”

Lateral Thinking: How Histone Modifications Regulate Gene Expression

“…Total RNA was extracted from inbred male and female P. citri at key developmental stages: male-and female-biased embryos, 3rd instar males and females, adult males, virgin and mated females (Table 1). Females' first broods are known to be male-biased while embryos laid on day 3 are femalebiased (Ross et al, 2012). As there is no way to identify the sex of an embryo without destroying it, I used first broods as a proxy for male embryos and third-day broods as a proxy for female embryos.…”

Development and longevity of Citrus mealybug Planococcus citri (Risso, 1813) (Insecta: Homoptera: Pseudococcidae) associated with grapevine

“…The small size and great mobility of the nymphs is a notable characteristic of the first two instars, favoring their spreading to other structures of the host plants, thereby hindering their location (Daane et al, 2008;Cid et al, 2010;Ross et al, 2010Ross et al, , 2012.…”

“…The leaf discs containing second and third instar male nymphs were transferred to plates without water agar because at this stage the insect's mouthparts atrophy and it does not drink (Correa et al, 2005;Santa-Cecilia et al, 2009;Ross et al, 2012).…”