Pollinating fig wasp Ceratosolen solmsi adjusts the offspring sex ratio to other foundresses

Abstract

Local mate competition theory predicts that offspring sex ratio in pollinating fig wasps is female-biased when there is only one foundress, and increased foundress density results in increased offspring sex ratio. Information of other foundresses and clutch size have been suggested to be the main proximate explanations for sex ratio adjustment under local mate competition. Our focus was to show the mechanism of sex ratio adjustment in a pollinating fig wasp, Ceratosolen solmsi Mayr, an obligate pollinator of the functionally dioecious fig, Ficus hispida Linn., with controlled experiments in the field. First, we obtained offspring from one pollinator and offspring at different oviposition sequences, and found that offspring sex ratio decreased with clutch size, and pollinators produced most of their male offspring at the start of bouts, followed by mostly females. Second, we found that offspring sex ratio increased with foundress density, and pollinators did adjust their offspring sex ratio to other females in the oviposition patches. We suggest that when oviposition sites are not limited, pollinators will mainly adjust their offspring sex ratio to other foundresses independent of clutch size changes, whereas adjusting clutch size may be used to adjust sex ratio when oviposition sites are limited.

Delimitation and description of the immature stages of a pollinating fig wasp,Ceratosolen solmsi marchaliMayr (Hymenoptera: Agaonidae)

“…The results showed that all the offspring of virgin females were males, and most offspring of mated females were females (female/total offspring was 0.89±0.06, n =9). This was consistent with the previous reports that in one-foundress figs, offspring sex ratios of C. solmsi were highly female-biased (Hu et al , 2013). In addition, we did more than 20 sets (30 eggs or larvae per set) of morphologic comparisons on the eggs and larvae between the male offspring of virgin females and sex-unknown offspring of mated females.…”

Evolutionary stable sex ratios with non‐facultative male‐eggs first sex allocation in fig wasps

“…While the assumed mechanism in our model yields sex ratios or male numbers that maximize fitness on average without the need to invoke facultative sex ratio adjustment (and would also explain a number of observed patterns of fig wasp clutch size, foundress density and sex ratios), we do not expect this mechanism to apply to all species that experience LMC. In particular, we would predict facultative sex ratio adjustment strategies to be more common among species that regularly experience higher, and more variable foundress numbers (Hu et al ). Nonetheless, our model adds to theoretical tools used to understand sex allocation as an adaptation, and suggests that selection for a male first strategy may be a real phenomenon in at least some species of fig wasp, and possibly in other species that fit the ‘biofacies’ outlined by Hamilton ().…”

“…These models were adaptations of a model by Stubblefied and Seger (1990), that assumed that mothers use only knowledge of their own fecundity to adjust sex allocation. Furthermore, studies have reported that in several fig wasp species, the eggs initially oviposited are male (Nefdt and Compton 1996, Kathuria et al , Kinoshita et al , Raja et al , Hu et al , Wang et al ). Such initial deposition of male eggs is also known from other organisms, such as the spider mite, Tetranychus urticae (Macke et al ).…”

Offspring sex ratio shifts of the solitary parasitoid wasp, Trichopria drosophilae (Hymenoptera: Diapriidae), under local mate competition

“…Trichopria drosophilae produced a greater proportion of sons on the first day of oviposition than on the second to fifth day. This may result from a male-first strategy (Bayram et al 2004, Hu et al 2012; that is, in some species, male offspring tend to be produced at the start of oviposition bouts, followed by mostly females, as seen for some pollinating fig wasps (Kjellberg et al 2005, Raja et al 2008, Hu et al 2013). An egg parasitoid wasp, Telenomus busseolae Gahan (Scelionidae), also has a higher proportion of females with increasing egg mass size (Bayram et al 2004).…”

“…Ceratosolen solmsi (Mayr), the pollinator of Ficus hispida L. f., has wingless males, which mate with females in the figs and then dig holes through the wall of the figs to allow females to disperse. Mating always happens between relatives, and a female-biased sex ratio evolved in the manner predicted by LMC models (Hu et al 2013). Such a strict subpopulation is classic in theories, but is unusual in nature.…”