A review of the taxonomy, phylogeny, distribution and co-evolution of Schistonchus Cobb, 1927 with proposal of Ficophagus n. gen. and Martininema n. gen. (Nematoda: Aphelenchoididae)

Abstract

The purposes of this paper are to clarify the taxonomic status of the fig-pollinating wasp associate Schistonchus sensu lato (Nematoda: Aphelenchoididae) and to suggest directions for future research on the systematics, life history and ecology of the group. Molecular phylogenetic analyses suggest that Schistonchus s.l. is polyphyletic, and the composition of the three major clades is outlined, together with information on nematode morphology, plant host species, associated pollinating wasp species, and distribution. Biological information and collection data is presented for Schistonchus s.l. from Ficus sycones (Moracea) in Africa, Australia, Asia and Central America, and its putative phylogeny is discussed based on molecular and morphological evidence. Both wasps and figs are millions of years old and have worldwide distribution in tropical areas, i.e., opportunities for Schistonchus s.l.-like nematodes to have evolved could have occurred more than once. In addition, figs and their pollinating wasps have variable life histories, which could have provided opportunities for Schistonchus s.l. to also develop different life histories. However, these histories occur inside fig sycones and in association with wasps, which has apparently led to evolutionary convergence and extreme morphological conservatism. Diagnostic characters and their states, derived from examination of described species and morphospecies of Schistonchus s.l. and informed by molecular phylogenetic inferences, are discussed and illustrated. Schistonchus sensu stricto is redefined, and Ficophagus n. gen. and Martininema n. gen. are proposed. Schistonchus s.s. is morphologically characterised by having the excretory pore opening in the region of, or posterior to, the metacorpus; Ficophagus n. gen. by having the excretory pore opening very near the cephalic region; and Martininema n. gen. by having it opening at the anterior end of the metacorpus. Several species of Schistonchus s.s. have a labial disc, but there is no evidence of this in either Ficophagus n. gen. or Martininema n. gen.