Coevolution with parasites drive reproductive isolation

Reproductive isolation entails a set of mechanisms, behaviors, and physiological processes that prevent members of two different species from mating and producing fertile offspring (Barton 1986). Over time, these barriers block gene flow between populations and act as reproductive boundaries that leads to the evolution of new species. Reproductive isolation can evolve in species whose geographic distribution overlaps (sympatric speciation) or when species are subdivided into geographically isolated populations (allopatric speciation).

Credit: Pearson Education, Inc.

For species with populations isolated by geographical barriers, variation in host-parasite interactions can potentially lead to rapid host population divergence. Parasites might represent at least 50% of the known biodiversity and this ubiquity makes parasites a major force in shaping genetic diversity (Schmid-Hempel 2011). The co-evolution of hosts and parasites may contribute considerably to host population diversification and eventually speciation.

Berenos et al., from the Institute of Integrative Biology – Zurich, conducted a study to test whether the biotic interactions in host-parasite co-evolution can lead to reproductive isolation via local adaptation. The experiment paired five lines of our beloved red flour beetle (Tribolium castaneum) with their respective  microsporidia, Nosema whitei. After 17 generations of species host-parasite interactions between these five lines, virgin females and males from each line were selected to mate with others from each of the four different lines and within their respective lines.

Light microscopy of N. whitei

The research team found that mating pairs from different lines had, on average, 16% fewer offspring than pairs from the same respective line. The number of offspring from the mixed mating pair was significantly lower compared to the related mating pair.

Positive correlation between coevolution and reproductive isolation.

The findings of this study suggest a role for co-evolution with parasites in in host reproductive isolation. And because reproductive isolation is a decisive step towards speciation, parasites may also accelerate population differentiation and ultimately lead to speciation.

References:

Berenos, C., Schmid-Hepel, P., Wegner, K.M. 2012. Antagonistic Coevolution Accelerates the Evolution of Reproductive Isolation in Tribolium Castaneum. Am Soc Nat, 180(4): 520-528.

Barton N., Bengtsson B. O. 1986. The barrier to genetic exchange between hybridising populations. Heredity 57 (3): 357–376.

Schmid-Hempel, P. 2011. Evolutionary parasitology: the integrated study of infections, immunology, ecology and genetics. Oxford
University Press, Oxford.