Molecular diversity and relationships of fig associated nematodes from South Africa

Nematodes of figs and fig wasps have received limited attention in Africa since their discovery in 1973. Sixteen of the 25 species of native South African figs were sampled for nematode associates using molecular barcoding with three loci (SSU, LSU D2-D3 and mtCOI) and fourteen (93%) were positive for at least one nematode species. Thirty-three putative species of nematodes were identified and classified according to the loci that were amplified and successfully sequenced. Fourteen putative nematode species were classified as Aphelenchoididae, of which nine were identified as Ficophagus from four species of Ficus from the section Galoglychia (i.e., five ex F. burkei including one shared with F. natalensis, one ex F. glumosa, one ex F. lutea, and one ex F. stuhlmannii) and one species ex F. sur from the section Sycomorus. In addition, there were four nematode species classified as Schistonchus s.s. from section Galoglychia figs (i.e., one ex F. burkei, two ex F. trichopoda, and one ex F. glumosa). There was also one species of Bursaphelenchus nematode recovered from F. sur from the section Sycomorus. Sixteen putative nematode species were classified as Diplogastridae, of which eight occurred in two clades of what is currently called Parasitodiplogaster with one (P. salicifoliae) being recovered from two Ficus species in the section Urostigma (F. salicifolia and F. ingens) and seven diplogastrids being associated with six species of Ficus from the section Galoglychia (i.e., two ex F. burkei including P. sycophilon, one ex F. stuhlmannii, one ex F. burtt-davyi, one ex F. trichopoda, one ex F. abutilifolia and one ex F. sansibarica). Three Acrostichus spp., a Teratodiplogaster and a Pristionchus species were recovered from F. sur and two Teratodiplogaster spp. and Pristionchus sycomori were recovered from F. sycomorus with both Ficus species belonging to the subgenus and section Sycomorus. The identities of the previously described T. martini and Parasitodiplogaster doliostoma (= Pristionchus sp. 35) are discussed. Lastly, there was a panagrolaimid identified from F. petersii.

The Scent of Life: Phoretic Nematodes Use Wasp Volatiles and Carbon Dioxide to Choose Functional Vehicles for Dispersal

Hitchhikers (phoretic organisms) need vehicles to disperse out of unsuitable habitats. Therefore, finding vehicles with the right functional attributes is essential for phoretic organisms. To locate these vehicles, phoretic organisms employ cues within modalities, ranging from visual to chemical senses. However, how hitchhikers discriminate between individual vehicles has rarely been investigated. Using a phoretic nematode community associated with an obligate fig-fig wasp pollination mutualism, we had earlier established that hitchhiking nematodes make decisions based on vehicle species identity and number of conspecific hitchhikers already present on the vehicle. Here we investigate if hitchhikers can differentiate between physiological states of vehicles. We asked whether phoretic nematodes choose between live or dead vehicles present in a chemically crowded environment and we investigated the basis for any discrimination. We conducted two-choice and single-choice behavioral assays using single nematodes and found that plant- and animal-parasitic nematodes preferred live over dead vehicles and used volatiles as a sensory cue to make this decision. However, in single-choice assays, animal-parasitic nematodes were also attracted towards naturally dead or freeze-killed wasps. The volatile profile of the wasps was dominated by terpenes and spiroketals. We examined the volatile blend emitted by the different wasp physiological states and determined a set of volatiles that the phoretic nematodes might use to discriminate between these states which is likely coupled with respired CO₂. We determined that CO₂ levels emitted by single wasps are sufficient to attract nematodes, demonstrating the high sensitivity of nematodes to this metabolic product.

Hopping on: Conspecific traveller density within a vehicle regulates parasitic hitchhiking between ephemeral microcosms

Hitchhikers (phoretic organisms) identify their vehicles using species-specific visual, chemical and vibrational cues. However, what factors influence their choice between vehicles of the same species has rarely been investigated. Hitchhikers must not only avoid overcrowded vehicles but may also need to travel with conspecifics to ensure mates at their destination. Hence, a trade-off between overcrowding and presence of conspecifics likely determines the choice of a vehicle especially when destination sites are distant, ephemeral and unique. Here, we investigate whether a trade-off between the presence of conspecifics versus overcrowding by conspecifics or heterospecifics on a vehicle affects hitchhiker choice. We also investigate the sensory modality responsible for this choice. We experimentally examine these questions using a phoretic nematode community (containing plant- and animal-parasitic taxa) obligately associated with a brood-site pollination mutualism. In this model system, nematodes co-travel with conspecifics and heterospecifics on pollinators as vehicles, between ephemeral plant brood sites to complete their developmental life cycle. In this system, hitchhiker overcrowding has proven negative impacts on vehicle and plant fitness. We expected nematodes to respond to conspecifics and heterospecific density on offered vehicles when making their choice. We found that animal-parasitic nematodes preferred vehicles containing some conspecifics within a certain density range. However, plant-parasitic nematodes preferentially boarded vehicles that were devoid of conspecifics or had few conspecifics. Plant parasites that preferred empty vehicles likely hitchhiked in pairs. Both nematode types employed volatile cues to discriminate between vehicles with different conspecific nematode densities. Our results suggest that vehicle overcrowding by conspecifics, most likely, guaranteed access to mates at the destination determined hitchhiker choice. Surprisingly, and contrary to our expectations, plant- and animal-parasitic nematodes did not respond to heterospecific crowding on vehicles and did not discriminate between vehicles with different heterospecific nematode densities. The reason for this lack of response to heterospecific presence is unknown. This study not only shows that phoretic organisms use different strategies while choosing a vehicle but also confirms that density-dependent effects can ensure the stability and persistence of phoretic interactions in a mutualism by balancing overcrowding against reproductive assurance.

Morphological and molecular characteristics of Parasitodiplogaster religiosae n. sp. (Nematoda: Diplogastrina) associated with Ficus religiosa in China

A new nematode species of the genus Parasitodiplogaster was recovered from syconia of Ficus religiosa at the Guangxiao Temple, Guangzhou, China. It is described herein as P. religiosae n. sp. and is characterised by possessing the longest and thinnest spicule of all currently described males in the genus, an elongated laterally “ε-shaped” and ventrally rhomboid-like gubernaculum, a stoma without teeth, consisting of a ring-like cheilostom with indistinct anteriolateral projections, a tube-like gymnostom and a funnel-like stegostom, monodelphic with a mean vulval position of 66%. There are three pre-cloacal and six post-cloacal male genital papillae with the arrangement P1, P2, P3, (C, P4), P5, P6d, P7, P8, P9d, Ph. This new species was easily differentiated from other members of the genus by DNA sequences of partial small subunit rRNA gene (SSU) and the D2-D3 expansion segments of the large subunit rRNA gene (LSU). Phylogenetic analysis also corroborated its reasonable placement within a well-supported monophyletic clade with other Parasitodiplogaster species and within the australis-group that includes P. australis and P. salicifoliae that are all associates of fig wasp pollinators (Platyscapa sp.) of figs of the subsection Urostigma.

Two new species and three morphospecies of Ficophagus Davies & Bartholomaeus, 2015 (Nematoda: Aphelenchoididae) from Ficus subgenus Pharmacosycea (Moraceae) in Central America

Aphelenchoidid nematodes were collected from the sycones ofFicussubgenusPharmacosyceafrom Central America. Two new species ofFicophaguswere recovered, and are described herein asF. maximasp. n. andF. yoponensissp. n. fromFicus maximaandF. yoponensis, respectively. They are differentiated from other species of the genus by a combination of morphological characters including having C-shaped females and spiral males, EP opening close to the lips, a short to long post-uterine sac, spicule characters, three pairs of subventral caudal papillae, DNA sequence data, biogeographical range, and host wasp andFicusspecies affiliation. The new species are differentiated from each other by spicule characters, length of the post-uterine sac, spermatheca shape, and female tail shape. In addition, three morphospecies were collected from sycones ofFicus glabrata,F. insipidaandF. tonduzii, respectively. Their morphological descriptions are presented but these taxa are not formally named as they currently lack molecular data.

Recharacterisation of three Parasitodiplogaster species based on morphological and molecular profiles

Three previously described Parasitodiplogaster spp., P. nymphanema, P. obtusinema and P. trigonema were re-isolated from their type locality, Barro Colorado Island Research Station, Smithsonian Tropical Research Institute, in Panama. The re-isolated materials were morphologically observed to compare with the original descriptions and molecularly characterised by DNA sequences of the near-full-length small subunit and D2-D3 expansion segments of the large subunit of the ribosomal RNA genes. Although the male tail characters, i.e., arrangement of genital papillae and spicule and gubernaculum morphologies, were close to the original descriptions, a compressed stoma with two (right subventral and dorsal) teeth was observed for the first time and confirmed in the newly re-isolated materials. The molecular phylogenetic analysis revealed that the three re-isolated species are close to P. laevigata, P. citrinema and P. popenema, forming the P. laevigata group in the genus, and this group was separated into three subgroups, P. citrinema + P. popenema (subgroup 1), P. nymphanema + P. obtusinema (subgroup 2) and P. laevigata + P. trigonema and three undescribed species (subgroup 3). The P. laevigata group is characterised by a relatively compressed stoma with two (right subventral and dorsal) teeth, arrangement of genital papillae (three or four precloacal and four postcloacal pairs), but distinguishable from each other by stomatal morphology, i.e., the shortest and most compressed being in subgroup 3, widest in subgroup 1, and intermediate in subgroup 2. Furthermore, a large and long spicule and gubernaculum were observed in subgroup 2 as its hypothesised apomorphy.

Allodiplogaster josephi n. sp. and A. seani n. sp. (Nematoda: Diplogastridae), associates of soil-dwelling bees in the eastern USA

Two commensal associates of bees,Allodiplogaster josephin. sp. from the Dufour’s gland of a cellophane bee (Colletes thoracicus) from Maryland, USA, andA. seanin. sp. from the abdominal glands of an andrenid bee (Andrena alleghaniensis) from New York, USA, are described and illustrated. Both species were collected as dauers from their respective hosts and cultured on bacteria on tryptic soy broth (TSB) or NGM agar.Allodiplogaster josephin. sp. andA. seanin. sp. are morphologically closer to each other than to other species ofAllodiplogaster, which was recently revised to include 37 valid species. However, the two new species are distinguished by reproductive isolation, shape of the spicule manubrium, host associations and molecular characters, the latter in sequences of the near-full length small subunit (SSU) rRNA gene, D2-D3 expansion segments of the large subunit (LSU) rRNA gene and partial mitochondrial COI. Morphological characterisation was supplemented by scanning electron microscopy (SEM), which revealed furcation of both v5 and v6 male genital papillae, consistent with previous reports for species of thehenrichaegroup ofAllodiplogaster.

Molecular and morphological observations on Parasitodiplogaster sycophilon Poinar, 1979 (Nematoda: Diplogastrina) associated with Ficus burkei in Africa

A Parasitodiplogaster sp. was isolated from syconia of Ficus burkei from Pretoria, South Africa, and determined to be conspecific with P. sycophilon, originally described by Poinar in 1979 from Harare, Zimbabwe, and also from F. burkei. Examination of type material of P. sycophilon revealed inaccuracies in the former description necessitating a redescription which is provided herein. Additionally, the original description lacked molecular data, which is also provided. Originally, the stoma of P. sycophilon was described as reduced without teeth. However, we observed a large dorsal stegostomal tooth and an almost equally-sized right subventral tooth which was typologically similar to the stoma of P. laeviagata from Florida. In addition, a pore-like phasmid was observed in both males and females just above the tail tip. Most other characters were as formerly described. Based upon molecular inferences from sequences of the D2/D3 expansion segments of the rDNA of the large subunit (LSU), P. sycophilon is not clearly defined relative to the neotropical Parasitodiplogaster species that have been described and sequenced from figs in the Section Urostigma, Subsection Americana (i.e., P. laevigata, P. popenema, P. citrinema, and P. trigonema), or to P. australis from Australia ex. F. virens (Section Urostigma, Subsection Urostigma), or to P. maxinema from neotropical figs from the Section Pharmacosycea, Subsection Pharmacosycea. Further work is needed to elucidate the molecular phylogeny of the Parasitodiplogaster lineages that may have co-speciated with the African figs of the Section Urostigma, Subsection Galoglychia.

Ficotylus laselvae n. sp. (Tylenchomorpha: Anguinidae) associated with Ficus colubrinae in Costa Rica

Ficotylus laselvaen. sp. was recovered from under the bracts of figs (syconia) ofFicus colubrinaefrom La Selva, Costa Rica, during a survey of nematode rainforest biodiversity and is described herein. This is only the second report of an association between the nematode suborder Tylenchina and the sycones of figs. Previous reports of most nematode associates of the sycones of figs have been from the lumen and involved transmission by female fig wasp pollinators (Agaonidae) during pollination/oviposition (e.g.,SchistonchusandParasitodiplogasterspp.). The association betweenF. laselvaen. sp. andFicus colubrinaemay involve an invertebrate host, but none was recovered from dissections of the bracts during this study. It is also possible that this is a rainforest understory nematode that feeds ectoparasitically in protected areas on the aerial parts ofF. colubrinae. Molecular analysis using near-full-length sequences of the small subunit (SSU) rRNA and D2-D3 expansion segments of the large subunit (LSU) rRNA genes ofFicotylus laselvaen. sp. suggests that it is a member of the suborder Tylenchina (infraorder: Tylenchomorpha; family: Anguinidae) and that the closest sequenced species isF. congestaefrom the lumen of sycones ofFicus congestafrom Queensland, Australia. Although both nematode species are associated with figs, they are morphologically divergent, suggesting that the different micro-niches that they fill provide different selective pressures for evolution of differing morphological characters or they represent different life history morphotypes of a dicyclic genus.

Parasitodiplogaster species associated with Pharmacosycea figs in Panama

Parasitodiplogaster species that are associated with figs in the Ficus subsection Pharmacosycea, i.e., Ficus maxima, F. yoponensis, F. insipida and F. glabrata, were studied using morphological characters and molecular sequences. Some nematodes isolated from the fig sycones were casually observed and recorded as morphospecies according to their morphotype, and were then digested for their DNA, while others were fixed in formalin-glycerin for additional morphological study. High resolution microscopic observation of the morphological materials yielded five morphospecies including two nominal species, P. maxinema and P. pharmaconema. The morphospecies were distinguished from each other by male tail characters. By contrast, five and six genotypes were recognised by D2/D3 expansion segments of the large subunit (LSU) and near-full-length sequences of small subunit (SSU) ribosomal RNA genes, respectively. Except for two nominal species, genotypes and morphospecies were not clearly correlated because of limitations in the microscopic resolution in the initial morphotyping. Although the morphospecies and genotypes were not clearly paired, Pharmacosycea-associated Parasitodiplogaster species, which are tentatively referred to as the ‘P. maxinema group’, formed a monophyletic clade in both D2/D3 LSU and SSU analyses and are morphologically characterised by their stomatal morphology, i.e., a tube-shaped stoma with two stick-like teeth and male tail morphology, presence of nine paired papillae and relatively slender spicule.

Teratodiplogaster variegatae n. sp. (Nematoda: Diplogastridae) isolated from the syconia of Ficus variegata Blume on Ishigaki Island, Okinawa, Japan

Teratodiplogaster variegatae n. sp. is described and illustrated from Ficus variegata on Ishigaki Island, Okinawa, Japan. Teratodiplogaster variegatae n. sp. is characterised by its scoop-like lip, the presence of large sac-like receptaculum seminis in the female gonads, and eight pairs of male genital papillae with an arrangement of (P1, P2, P3, vs, C, (P4, P5d), (P6, P7), P8d, Ph). It is distinguished from its close relatives T. fignewmani and T. martini by its stomatal morphology, spicule and gubernaculum morphology, structure of female reproductive organs, and the characteristic star-shaped appendage on the tail tip of males and females. Molecular phylogenetic analyses based upon near-full-length SSU and D2-D3 expansion segments of LSU corroborate a monophyletic origin of the genus Teratodiplogaster.