Deep mtDNA divergences indicate cryptic species in a fig-pollinating wasp

Eleanor R Haine, Joanne Martin and James M Cook

This study is important because it calls into question the previous theories and beliefs of coevolution and the rule of 1:1 partner specificity. It also raises questions as to the possible impact the bacteria Wolbachia plays in the evolutionary development of the fig wasps. The fig-wasp symbiosis has been looked at by the scientific community as an excellent example of the 1:1 partner specificity vital to the co-evolution of species. By examining the wasps present in collected samples of fig trees along the East coast of Australia, they were successfully able to obtain evidence of cryptic species. They found four separate clades of the fig wasp species to be populating the fig trees along the coast, with some clades more prevalent in certain areas than others. More importantly to their goals, these different clades of the wasps were found to cohabit the same fig tree, breaking the previously accepted rule of 1:1 specificity. In addition, the authors discovered that every one of the fig wasps carried at least one of three strains of the Wolbachia bacteria. By sequencing a portion of the collected wasps, it was revealed that at least some of the differences found between the clades were related to the strain of Wolbachia infecting the insect. Combined with the break in the rule of specificity, the presence of four clades of wasp among only one species of fig tree, these findings suggest a greater influence by the Wolbachia bacteria in the evolution of the fig wasp than previously assumed. The authors also managed to do this via more expansive and deeper study than their forebears.

Although the study was well explored and more detailed than its predecessors, some of the conclusions they come to seem premature or unsupported by their data. One such conclusion, when explaining their evidence against a role for host shifts, the authors make leaps in logic that are not fully explained nor supported by their data. Another conclusion involves the possibilities to reconcile what is occurring in the evolutionary process with the evidence against parallel divergences of the fig and fig wasps. They provide a few scenarios for what could be happening, but the two they suggest to be most likely are in direct contradiction with each other. Clearly further evidence is needed before any conclusion can be drawn for that situation. The main problem revealed in this study, however, is not a problem with the study. Instead it is that, with the results and conclusions that can be drawn from the collected data, the previous theories concerning co-evolution, especially those that hold up the fig-wasp symbiosis as an exemplary portrait, must be reconsidered and possibly even thrown out. This study of the fig-wasp symbiosis and the effect of Wolbachia in the course of wasp evolution raises more questions than answers regarding the co-evolution of symbiotic species.