Symbiotic Speciation: Concepts, Causes and Consequences

"Especiação simbionte: conceitos, causas e consequências"

Current standard models of speciation disregard potential impacts of microbial reproductive

tract symbionts fostering host speciation. Based on numerous theoretical models but limited

experimental data, prime candidates driving symbiotic speciation in arthropods are

intracellular bacteria belonging to the genus Wolbachia. They are inherited symbionts of

many arthropods capable of manipulating host reproductive biology for their own benefits.

However, it is an ongoing debate as to whether or not reproductive symbionts are capable

of triggering host speciation in nature and if so, to what extent (COYNE & ORR 2004).

Hence we applied the classic model system of symbiotic speciation manifest in neotropical

Drosophila paulistorum semispecies by means of present-day molecular approaches and

artificial symbiont-depletion experiments. This superspecies, consisting of at least six

reproductively isolated semispecies, has been the object of attention of an array of

researchers since at least 1955, when it was initially trapped mid-evolution in flagrant statu

nascendi (DOBZHANSKY & SPASSKY 1959). In this system it has been proposed that

microbial endosymbionts foster incipient speciation (KERNAGHAN & EHRMAN 1970).

We have recently demonstrated the α-proteobacteria Wolbachia as the maternally

transmitted core endosymbiont of D. paulistorum semispecies that presently foster

symbiotic speciation by triggering pre- and postmating isolation mechanisms (MILLER ET AL.

2010; MILLER & SCHNEIDER 2012). Here we will report on (i) the impact of Wolbachia on

driving artificial de novo reproductive isolation in D. paulistorum, (ii) their effects on host

pheromone expression patterns and sexual behaviour, and (iii) unorthodox transmission

modes of mitochondria in hybrids.

Finally we will introduce a second symbiotic speciation system in statu nascendi, i.e., the

Glossina morsitans species group of tsetse flies, where conspecific but incompatible

Wolbachia infections trigger postmating isolation in nature (SCHNEIDER ET AL. 2012).