Tritrophic interactions involving a dioecious fig tree, its fig pollinating wasp and fig nematodes

Abstract

24 25 Many species of fig trees (Ficus spp., Moraceae) have nematodes that develop 26 inside their inflorescences (figs). Nematodes are carried into young figs by females of the 27 trees' host-specific pollinating fig wasps (Agaonidae) that enter the figs to lay their eggs. 28 The majority of Asian fig trees are functionally dioecious. Pollinators that enter figs on 29 female trees cannot reproduce and offspring of any nematodes they carry will also be 30 trapped inside. The biology of the nematodes is diverse, but poorly understood. We 31 contrasted the development of nematodes carried by the pollinating fig wasp Ceratosolen 32 solmsi marchali into figs on male and female trees of Ficus hispida in Sumatra, Indonesia. 33 Figs were sampled from both male and female trees over a six-month period, with the 34 nematodes extracted to record their development of their populations inside the figs. 35 Populations of three species of nematodes developed routinely inside figs of both sexes: 36 Caenorhabditis sp. (Rhabditidae), Ficophagus cf. centerae and Martininema baculum 37 (both Aphelenchoididae). This is the first record of a Caenorhabditis sp. associated with 38 F. hispida. Mean numbers of nematodes reached around 120-140 in both male and 39 female figs. These peak population sizes coincided with the emergence of the new 40 generation of adult fig wasps in male fig trees. We conclude that figs on female trees can 3 41 support development and reproduction of some nematode species, but the absence of 42 vectors means that their populations cannot persist beyond the lifetime of a single fig. 43 Just like their fig wasp vectors, the nematodes cannot avoid this routine source of 44 mortality. 45 46

Association of Fig Pollinating Wasps and Fig Nematodes inside Male and Female Figs of a Dioecious Fig Tree in Sumatra, Indonesia

“…Most research on nematodes in dioecious fig trees has concentrated on male trees that generate new generations of fig wasps [32,36]. The nematode life cycles in F. hispida figs were mainly similar to those previously described in male figs of other fig trees of both dioecious and monoecious species [4,14,37,38]. However, our research demonstrated that nematodes associated with F. hispida can grow and reproduce within figs from female trees, as shown by a recent study in China [39].…”

“…The Five to six figs from each tree, including their contents, were then placed separately in a Baermann extraction funnel using a method described previously [29] and adjusted later [14]. Each fig was later cut into eight pieces and set on a fine fabric sheet before being submerged in 60 mL distilled water.…”

“…The nematodes are classified into several different families, implying multiple independent fig colonisations accompanied by widespread radiation in some lineages [20]. Nematodes from several different species can grow and develop in one fig tree species, and it has been found that in Indonesia, F. racemosa can support up to eight species of nematodes [14], with more than one species sometimes present inside a single fig. The figs support nematodes to grow and reproduce offspring that are ready to be transported by a new generation of adult female pollinators that come out of their natal figs [3,10].…”

“…During their developments, figs from the subgenus Sycomorus are often partially filled with liquid [25], and they have diverse nematode fauna. These free-swimming nematodes can prey on other nematodes or protistans found abundantly in the fig liquid [14].…”