Of Crucial Ecological and Cultural Significance

As its sole pollinator, Platyscapa quadraticeps exhibits a reciprocal mutualistic relationship with Ficus religiosa.³ The fig of F. religiosa is monoecious, meaning the syconium (hollow, fleshy receptacle that develops into fruit) is functionally male and female.⁴ When the almost ripe fig is in the male phase, impregnated female wasps will lay their eggs and pollinate the syconium through swift foreleg motions.⁵ P. quadraticeps has an adult lifespan of less than two days, within which time they must pollinate the fig ovaries where wasp larvae are raised.⁶ In the wasp’s scientific name, ‘scapa’, from Latin meaning ‘to drop’, likely references pollen deposition while ‘quad’ hints at the wasp’s foreleg motions, and the root ‘-cep-’, meaning to take or receive, alludes to the wasp’s mutualistic relationship with the fig tree.⁷

Ficus religiosa, reliant on Platyscapa quadraticeps, possesses significant cultural value in Singapore and across Asia. Moreover, valued for its nutritional qualities, figs are not only a popular snack but also used in traditional Chinese medicine prevalent in Singapore.⁸ Dried figs are a common ingredient in respiratory related tonics, and fig bark and leaves can be used for wound treatment.⁹ Platyscapa quadraticeps thus plays a hidden but crucial part in maintaining Ficus religiosa’s important cultural roles.

Situating Platyscapa quadraticeps in Singapore’s Dense Cityscape

Platyscapa quadraticeps exhibits wide dispersal patterns, and the population in Singapore is likely part of a continuous regional population spanning temperate and tropical Asia.¹⁰ Platyscapa quadraticeps follows the spontaneous distribution of F. religiosa in Singapore across both primary and secondary forests like Bukit Timah Nature Reserve, as well as in the city’s urban green spaces – from the Japanese Garden in Jurong East to Duxton Plain Park in the CBD to Tanah Merah MRT station.¹¹

Urban green spaces in Singapore cover over 47% of the city, reflecting its “city in nature” (originally “garden city” and then “city in a garden”) moniker.¹² Urban green spaces are integrated into Singapore’s hot and air, light, and noise-polluted landscape, and are affected by continuous urban development.¹³ Pearl’s Hill City Park’s (PHCP) ecosystem exemplifies that of a typical urban green space in Singapore. Located near Outram Park and Chinatown, PHCP was the site of a gambier plantation and hospital in the 1800s before becoming a public park.¹⁴ Today, PHCP is dominated by non-native birds that are omnivorous generalists such as the Javan Myna (Acridotheres javanicus) and Eurasian Tree Sparrow (Passer montanus). The park also features a Bodhi tree that has been designated as a heritage tree, meaning Platyscapa quadraticeps also inhabits the park.¹⁵

The diversity of species inhabiting the park shapes how the Singaporean public perceives and uses urban green spaces. These spaces provide cultural ecosystem services by facilitating recreation (e.g., birdwatching, hiking) and providing a respite from city life.¹⁶ Indeed, the presence of the heritage Bodhi tree provides a meditative space that the public can enjoy.¹⁷ However, while the Bodhi tree in the park may be valued, the fig wasps silently serving this cultural good are often undervalued and are likely viewed as a nuisance based on prevailing negative sentiments surrounding wasps. Any lack in addressing threats to the fig wasp’s survivability, however, will also impact the fig tree’s future.

From Flight to Plight: Future Challenges to Platyscapa quadraticeps

As the climate crisis worsens alongside continual urban development and other escalating anthropogenic environmental pressures, the quality of Singapore’s UGS is at risk. This poses challenges to P. quadraticeps, with cascading effects including the potential for a breakdown of the mutualistic relationship between the wasp and tree, which may have drastic effects for urban green spaces that rely on F. religiosa as a keystone species.¹⁸

Increasing Temperatures

Increasing ambient air temperatures in urban green spaces are a threat to fig wasp fitness in Singapore. Singapore’s dense cityscape activates the urban heat island effect, wherein features of the city—including impervious dark surfaces that absorb heat and trapped waste heat that seeps through from vehicles, buildings, and appliances—lead to higher temperatures of up to a 7°C difference compared to the island’s less built-up areas.¹⁹ While urban green spaces alleviate the urban heat island effect, they are simultaneously exposed to these heightened temperatures.²⁰ Moreover, temperatures in Singapore are projected to increase by 1.4°C to 4.6°C by the end of the century, with the brunt to be felt in urban areas.²¹ A recent study found that multiple fig wasp species²² suffered average reduced life spans of two to ten hours when temperatures rose to 36°C, compared to the average adult lifespan of 1-2 days.²³ This corroborates earlier Singaporean findings that an increase of over 3°C would significantly decrease the adult lifespan of all studied fig wasp species.²⁴

Ozone Pollution

In addition to temperature, ozone pollution is a rising threat to fig wasps in Singapore. Ozone is a key component of ‘smog’, and in recent years, certain episodes of harmful air quality in Singapore have been attributed to ozone-induced smog, not haze, contrary to common assumptions.²⁵ In a study of a fig wasp in the Platyscapa genus in the sub-tropical French Mediterranean, ozone induced abnormal motility at even low concentrations, impacting pollinator behaviour and success.²⁶ There are suggestions that ozone episodes in the French Mediterranean may already be affecting fig wasp and fig tree mutualism, as fig wasp females search for receptive figs at midday which coincides with maximum ozone concentrations, hindering wasp motility and reproductive success.²⁷ Worsening ozone pollution in Singapore is thus likely to implicate P. quadraticeps’ motility.

Habitat Fragmentation

Beyond climatic changes, habitat fragmentation is also a concern to fig wasps in Singapore. Fragmentation will continue as Singapore develops, and projects like the upcoming Cross Island MRT line passing underneath the Central Catchment Nature Reserve may have uncertain ecological effects.²⁸ Studies reveal that highly fragmented forests have a lower proportion of pollinator wasps compared to non-pollinator wasps, wherein the latter may become pests to the fig tree.²⁹ Further, fragmentation contextualised in Singapore’s urban cityscape increases the risk of road mortality, which has been implicated in pollinating insects’ deaths worldwide.³⁰ Fig wasps can be responsible for dispersing pollen up to 160km from the source tree, and flying over increasingly fragmented and busy urban traffic exacerbates the difficulty and danger of pollination journeys.³¹

Everything, Everywhere, All at Once

Further, the synergistic culmination of multiple pressures is likely to present an even greater challenge than each of these threats in isolation. On top of fragmentation, increased temperatures and ozone pollution also make it more difficult for wasps to travel long distances to the trees they pollinate and navigate their way to the syconium.³² Indeed, other air pollutants not yet studied are likely to have similar detrimental effects to fig wasp fitness.³³ Together, these factors will escalate the difficulty of successful pollination and thus reproduction of P. quadraticeps.

The Possibility of a Relationship Breakdown

Reduced reproductive success may contribute to a breakdown in the mutualistic relationship between P. quadraticeps and F. religiosa. The strong mutualistic relationship between the fig wasp and fig tree has been evolutionary solidified, which includes safeguards to prevent ‘cheating’ in the relationship.³⁴ Indeed, fig wasps that failed to pollinate the fig tree Ficus perforate experienced a reduced fitness of 0.59 compared to successful wasps.³⁵ Breakdown is prevented in the short-term as an unpollinated syconium can remain receptive for long periods; however, one study found that older figs produced fewer seeds and fig wasp offspring when eventually pollinated.³⁶ This leads to a slow reduction in the fig wasp population, eroding fitness and activity.³⁷ It has also been noted that fig wasps tend to experience faster speciation than fig trees, which may lead to decoupled speciation dynamics driven by these anthropogenic pressures.³⁸ The species-specific nature of the relationship between P. quadraticeps and F. religiosa thus also implicates the latter’s outlook, despite its ability to thrive in urban Singapore. This then has cascading effects on organisms that rely on F. religiosa as a keystone species given its yearlong fruit production, including native birds like the Jambu Fruit Dove (Ptilinopus jambu) and Yellow-vented Bulbul (Pycnonotus goiavier).³⁹

The Future of Fig Wasps in Singapore

Therefore, while the existence of Singapore’s urban green spaces is not under threat, and indeed there are plans to develop more, the quality of these spaces faces inevitable challenges amidst anthropogenic climate change and continual urban development, both of which can only be mitigated within broader policies.⁴⁰ To combat urban fragmentation’s specific impact on fig wasps, alongside temperature and air pollution that may decrease the wasp’s ability to travel long distances, it may be helpful to consider intentional planting of F. religiosa in urban spaces that are not parks (e.g., on the roadside) which may expand the accessibility of trees to fig wasps that prevents the need to travel long distances exposed to increasingly harsh urban conditions.⁴¹ Plans to expand eco-links may also alleviate the effects of fragmentation and road mortality by connecting isolated urban green spaces to each other and other habitats.⁴² However, these bridges are a mitigation strategy with indeterminate success rates for different species on different time scales, with uncertain benefits to P. quadraticeps.⁴³

Ultimately, any breakdown in the relationship between F. religiosa and P. quadraticeps has significant ecological implications for a range of organisms. ⁴⁴ Efforts to mitigate the impending challenges to the fig wasp are thus oriented towards an ecosystem-based outlook grounded in addressing broader pollution concerns and creating ecological bridges and links that may combat fragmentation. This will ease Platyscapa quadraticeps’ plight against such changes to uphold its mutualistic relationship with Ficus religiosa, which is a cornerstone of Singapore’s urban green spaces. However, it is important to be mindful that simply creating urban green spaces is insufficient to mitigate the effects of climate change or pollution on different species and the habitats they rely on, and the future of often forgotten non-native species is at stake in both our ecological and cultural futures.

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