Hamm, C. A. | Search bioRxiv

bioRxiv2017

Chromosome Number of the Monarch Butterfly, Danaus plexippus (Linnaeus 1758) and the Danainae

The monarch butterfly, Danaus plexippus (Linnaeus 1758) is a charismatic butterfly known for its multi-generational migration in Eastern North America, and is emerging as an important system in the study of evolutionary genetics. Assigning genes or genetic elements to chromosomes is an important step when considering how genomes evolved. The monarch butterfly has a reported haploid chromosome number of 30. The specimens that this count is based on are from Madras, India where D. plexippus does not occur. As a consequence the reported haplotype for the D. plexippus is incorrect. A literature review revealed that the specimens this count was based on were most likely Danaus genutia (Cramer 1779), which Linnaeus and others conflated with D. plexippus. In a 1954 Opinion (#282) the International Code of Zoological Nomenclature decided that the name D. genutia refers to specimens originating from the Orient and D. plexippus to those from North America. To clarify the haplotype number of D. plexippus from North America I conducted chromosome squashes of male 5th instar larvae. All specimens examined had a haploid chromosome count of n = 28. Following these new data, I then reconstructed the evolution of haplotypes throughout the Danainae subfamily to provide a testable hypothesis on the evolution of chromosome number for this group.

evolutionary biology↗

bioRxiv2017

A hierarchical Bayesian approach to estimate endosymbiont infection rates

Endosymbionts may play an important role in the evolution of the Insecta. Bacteria such as Wolbachia, Cardinium, and Rickettsia are known to manipulate host reproduction to facilitate their own. Indeed, there are many documented cases where Wolbachia (Alphaproteobacteria: Rickettsiaceae) induces one of four manipulative phenotypes (cytoplasmic incompatibility, male killing, feminization, and parthenogenesis). The scale of infection among species has been a major subject of investigation, but quantification has been difficult because various approaches have yielded different estimates. One under-appreciated aspect of this problem arises when multiple--yet independent--samples are taken within a taxon. When independent samples within a taxon are treated as levels of a hierarchy, the problem is greatly simplified because data are partially pooled according to taxon. Here, we present a hierarchical Bayesian approach to estimate infection frequency where multiple independent samples were collected across several taxonomic levels. We apply this model to estimate the rates of infection for Wolbachia in the Lepidoptera, and then extend the model to account for phylogenetic non-independence. In addition, we highlight the current knowledge regarding Wolbachia and its effects within Lepidoptera. Our model estimates that the rate of endosymbiont infection for the Lepidoptera is approximately 12%. Given our limited knowledge regarding the phenotypes induced by these endosymbionts and the low infection rate, we urge caution when extrapolating the results of positive assays.

evolutionary biology↗