Blog Post 3 - Batesian Mimicry in Papilio polytes

This week I will be using the swallowtail butterfly, Papilio polytes, as an example of Batesian mimcry. The swallowtail butterfly is common throughout Asia and is known to resemble the unpalatable red bodied butterfly, Pachliopta aristolochiae (Katoh et al. 2017). In the swallowtail butterfly there is a single male isoform and two different female isoforms; Interestingly, only the female forms can mimic the red bodied butterfly (Nishikawa et al. 2015). Females occur either in the form of:                                                                                                                                                                                             1 - A male-like, black and white non-mimetic form (Katoh et al. 2017)    OR   2- As a red-spotted form that mimics a toxic species (i.e. the red bodied butterfly) (Katoh et al. 2017)

This female limited mimicry is maternally heritable (Katoh et al. 2018) and is believed that single-locus Mendelian inheritance coded by the autosomal doublesex (dsx) supergene, with mimetic alleles (H) dominant to the non-mimetic allele (h), controls this polymorphism (Katoh et al. 2017). So mimicry in P. polytes is affected by a single gene, being the dsx, where the H locus is tracked to a sex determining gene (Mallet 2015). Functional tests of the mimetic allele of the dsx(H) locus have been carried out and imply that it plays a role in changing wing coloration from a non-mimetic to a mimetic pattern (Nishikawa et al. 2015).

An interesting factor to look at is what drives the evolution of this mimicry. As stated in my last post, Batesian mimicry occurs in two steps. First, a major mutation of large affect produces a rough resemblance to the model, then, fine tuning of the mimic’s appearance toward the model through fixation of “modifier” alleles. Mutations can arise spontaneously at low frequencies due to chemical instabilities and errors during DNA replication (Lodish et al. 2000). They can also occur in organisms through natural exposure to certain environmental factors (Lodish et al. 2000). Micro-evolution towards better mimicry in the P. polytes has been influenced by selection pressures such as the arrival of a new model species, predation pressures and exposure to ultraviolet (UV) light (Katoh et al. 2017; Katoh et al. 2018). UV irradiation has been found to damage exposed tissues and damaged wings can reduce reproductive success (Katoh et al. 2018). Melanin is what many organisms use to protect themselves against UV irradiation and in the P. polytes it is the black pigment in the wings (Katoh et al. 2018).  A negative correlation between UV irradiation and red spot size has been observed in the species suggesting a conflict between protecting against UV damage and avoiding predation (Katoh et al. 2018).

On top is a female swallowtail butterfly (Papilio polytes) with the red spot markings that mimic those of a (Pachliopta aristolochiae) and below is a male swallowtail butterfly with non-mimetic white spot markings. Photos taken by Thomas Neubauer. Retrieved from https://en.butterflycorner.net/Papilio-polytes-Common-Mormon-Kleiner-Mormon-Mormon-Commun.516.0.html Date: 29/03/2019.

References

Katoh, M., Tatsuta, H. and Tsuji, K., 2017. Rapid evolution of a Batesian mimicry trait in a butterfly responding to arrival of a new model. Scientific reports, 7(1), p.6369.

Katoh, M., Tatsuta, H. and Tsuji, K., 2018. Ultraviolet exposure has an epigenetic effect on a Batesian mimetic trait in the butterfly Papilio polytes. Scientific reports, 8(1), p.13416.

Lodish H, Berk A, Zipursky SL, et al. 2000. Section 8.1, Mutations: types and causes. Molecular Cell Biology 4th edition.

Mallet, J., 2015. New genomes clarify mimicry evolution. Nature genetics, 47(4), p.306.

Nishikawa, H., Iijima, T., Kajitani, R., Yamaguchi, J., Ando, T., Suzuki, Y., Sugano, S., Fujiyama, A., Kosugi, S., Hirakawa, H. and Tabata, S., 2015. A genetic mechanism for female-limited Batesian mimicry in Papilio butterfly. Nature genetics, 47(4), p.405.