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Research Progress

Natal Locations of Foundresses Fig Wasps Modify Offspring Sex Ratios

Oct 31, 2014

Ceratosolen solmsi is an obligate pollinator of the functionally dioecious fig Ficus hispida in Xishuangbanna. The pollinating fig wasps are widely used in researches on sex ratio and local mate competition (LMC). Under local mate competition conditions, foundress females are predicted to produce a female-biased offspring sex ratio because it reduces competition between sibling males for mates, but as foundress numbers increase a less female-biased offspring sex ratio becomes optimal. 

Prof. YANG Darong and his team of Xishuangbanna Tropical Botanical Garden (XTBG) of Chinese Academy of Sciences conducted a study to examine the relationship between the location of natal flowers within figs and the fig wasps that emerged from them. The researchers compared components of fitness of female fig wasps developing in central and peripheral flowers and whether this influenced the sex ratios of their offspring. 

The researchers used a dissecting microscope to observe the mating behavior of male pollinators. Observations confirmed that the chewing of mating holes was almost always followed by the male inserting its abdomen into the female's gall, but direct confirmation of mating and insemination was not possible.  

This study found that in F. hispida, most females of the pollinator C. solmsi marchali mated at most only once, as indicated by the presence of a single mating hole in their galls. Some galls, however, had as many as four mating holes, created by different males, providing females with the opportunity to mate up to four times. The female fig wasps that developed in more central locations had a higher frequency of mating opportunities and a larger body size. Those females also produced more offspring and more female-biased sex ratios. Multiple matings increased the number of female genotypes represented among the offspring that develop within each fig and decreased the frequency of sib matings (i.e. mating between brothers and sisters). The researchers further found that foundress mating frequency obscured sex ratio adjustment to foundress numbers. 

The research results extended the understanding of sex ratio adjustment in fig wasps and implied that realized sex ratios among fig wasps may rarely, if ever, be truly optimal. 

The study entitled “Fig wasps from the centre of figs have more chances to mate, more offspring and more female-biased offspring sex ratios” has been published online in Animal Behavior.  

 

Ficus hispida fig showing the mating holes made by male Ceratosolen solmsi marchali in galled ovules that contain conspecific females. (Image by PENG Yanqiong) 

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