Figs and fig wasps have lived in symbioses for centuries — wasps lay their eggs in figs, and pollinate the trees as recompense. Pollination of figs is either passive, or more commonly it is active. Only one species of pollinator is required to maintain host plant populations and situations where a Ficus species is actively pollinated by more than one fig wasp species, provide opportunities for the evolution of ‘cheating’ behavior, where agaonids fail to pollinate their hosts and there is a transition in them. However, cheating agaonid wasps are very rare. A cost in terms of reduced reproductive success among cheaters could be one explanation.
Prof. YANG Darong and his team of Xishuangbanna Tropical Botanical Garden (XTBG) compared the behavior and reproductive biology of the pollinator and cheater agaonids associated with Ficus altissima, in order to discover whether costs associated with a loss of active pollination could be detected. The study was conducted at the Xishuangbanna Tropical Botanical Garden (101°15′E, 21°55′N, at about 555 m a.s.l.), located in SW China at the northern margin of tropical SE Asia.
They asked: (i) Do the pollinator (Eupristina altissima) and cheater (an undescribed Eupristina sp) have similar body sizes and egg loads? (ii) Do adult females of the two species compete when attempting to enter the same figs? (iii) Do they produce similar numbers of offspring? (iv)How does their reproductive success respond to intraspecific and interspecific competition?
The study found that adult females of both species fought with conspecifics when they were seeking entry through the ostiole into receptive figs, but there was no fighting with heterospecifics. Despite a similar body size, female pollinators contained more eggs than female cheaters. Cheaters that shared a fig with pollinators failed to produce more offspring than figs containing only cheaters. Their results suggested that the disadvantages resulting from a failure to pollinate their host figs also extended to cheater species that had lost their ability to actively pollinate.
The researchers thus concluded that there were significant costs associated with abandoning the mutualism.
The study entitled “A switch from mutualist to exploiter is reflected in smaller egg loads and increased larval mortalities in a ‘cheater’ fig wasp” has been published in Acta Oecologica.
