In the comments, Rob Clack asks:
I’ve just read about Martialis on Panda’s Thumb and have a question. If I interpret it correctly, your cladogram shows Martialis to be the sister group of all living ants. Since it was blind and many living genera are not, that presumably implies that vision evolved independently within modern ants. I would therefore expect there to be some significant differences between modern ant eyes and those of other hymenoptera.
I assume I’m missing something.
Rob is referring to this post, going straight to the problem that Martialis seemingly poses for our understanding of ant evolution. Was the ancestor of all ants blind?
The honest answer is that we don’t know. There are, however, a couple observations relevant to Rob’s comment.
First, most “eyeless” ant species are blind only in the worker caste. In these ants the reproductive males and females commonly have eyes used for orientation while mating and dispersing. As way of an example, check out Antweb’s gallery of Centromyrmex bequearti.
Although the workers are blind, they retain the requisite genetic machinery for functional eyes. They must, because their parents have eyes, as do their brothers and some of their sisters. The workers have just turned off the eye program during development.
In theory then, it is possible that a blind species could re-evolve normal eyed workers just by up-regulating the existing eye developmental program. A much easier task than creating eyes de novo.
Second, we have excellent examples of ants that have re-evolved eyes from a blind ancestor. And as Rob suggests, the re-created eyes are indeed odd. Consider the army ant Eciton burchelli:
The eyes of worker Eciton are made of a single enlarged lens like those of, say, spiders. Most other sighted ants have the “normal” insect condition of multi-faceted eyes with many lenses:
We know from studies of the evolution of army ants that Eciton, although it forages in the open, descended from ants that were largely subterranean and almost certainly blind. The oddness of Eciton’s eyes could be a consequence of a circuitous route evolution took when proto- Eciton emerged above ground and needed to see again.
These two observations, the sightedness of reproductive ants and the weirdness of re-evolved eyes, are somewhat at odds with respect to their implications for Martialis. After all, Eciton males have normal multi-faceted eyes. So why didn’t Eciton workers recruit the male eye program when they needed eyes? Is there something about the developmental process that precludes it? And if so, does this mean that an eyeless Martialis really does pose difficulties for our understanding of ant evolution?
Of course, whatever we know or don’t know about ant evolution, it’s worth noting that Martialis is not the Ur-Ant. Martialis is quite likely to have lost its eyes somewhere in the intervening 120 or so million years. If so, then the question is moot anyway. All the same, we have a lot yet to learn about the eyesight of ants.