San Martin, G. | Search bioRxiv

bioRxiv2018

Molecular phylogeny of Odontosyllis (Annelida, Syllidae): A recent and rapid radiation of marine bioluminescent worms.

Marine worms of the genus Odontosyllis (Syllidae, Annelida) are well known for their spectacular bioluminescent courtship rituals. During the reproductive period, the benthic marine worms leave the ocean floor and swim to the surface to spawn, using bioluminescent light for mate attraction. The behavioral aspects of the courtship ritual have been extensively investigated, but little is known about the origin and evolution of light production in Odontosyllis, which might in fact be a key factor shaping the natural history of the group, as bioluminescent courtship might promote speciation. To investigate the speciation patterns and evolutionary history of Odontosyllis and to trace the origin of bioluminescence within the group, we inferred phylogenies using both gene concatenation and multispecies coalescent species-tree approaches with a multilocus molecular dataset (18S rRNA, 16S rRNA and COI). We also used this dataset to estimate divergence times and diversification rates in a relaxed molecular clock Bayesian framework. Our results suggest that Odontosyllis has undergone a recent rapid radiation, possibly triggered by the origin of bioluminescent courtship, which might have increased speciation rates and lineage divergence through sexual selection. Additionally, our analyses reveal that the genus Odontosyllis as currently delineated is a paraphyletic group that needs to be reorganized to reflect evolutionary relationships.

evolutionary biology↗

bioRxiv2017

Partial restoration of mutational robustness after addition of genetic polymorphism and in the presence of sexual selection

The interaction between mutational (i.e. genetic) robustness, cryptic genetic variation and epistasis is currently under much debate, as is the question whether mutational robustness evolved under direct selection or as a by-product of environmental robustness. Here we report that mutational robustness was restored in a mutant line of the butterfly Bicyclus anynana after the spontaneous mutation, comet, appeared in a genetically polymorphic wild type population. The comet mutation modified two phenotypic traits known to be under sexual selection in this butterfly: the dorsal forewing eyespot, which is normally round, but became comet-shaped, and the androconia, the structures producing the male sex pheromone, which were reduced in size. The comet mutant line remained phenotypically stable for [~]7 seven years, but when outcrossed to the genetically polymorphic wild type population, the outcrossed comet line surprisingly recovered the wild type phenotype within 8 generations. This suggests that mutational robustness against the comet mutation was recovered in the comet outcrossed line by epistatic interactions with the genetic polymorphism originating from wild types. The extent of wild type phenotype recovery in the comet outcrossed line was trait- and developmental temperature-dependent, such that mutational robustness was partially recovered at high, but not at low developmental temperatures. We hypothesized that sexual selection through mate choice, which is sex-reversed between developmental temperatures in this butterfly, could produce mutational robustness at a high (but not at a low) temperature. Females are the choosy sex and exert stabilizing or directional selection on male secondary sexual wing traits but only at higher temperatures. Male mating success experiments under semi-natural conditions then revealed that males with the typical comet mutant phenotype suffered from lower mating success compared to wild type males, while mating success of comet males resembling wild types was partially restored. Altogether, we document the roles of cryptic genetic variation and epistasis in restoration of mutational robustness against a spontaneous mutation with known fitness effects, and we provide experimental evidence, for the first time to our knowledge, that sexual selection can produce mutational robustness.

evolutionary biology↗