Biological interactions on the behavioral, genomic, and ecological scale: investigating patterns in Drosophila melanogaster of the southeast United States and Caribbean islands

2014-07-01Biological systems are complicated webs of interactions at many different levels. It is through the ebb and flow of these interactions do we get processes such as molecular pathways or social behavioral systems, which can rapidly change large populations of organisms over time. Speciation is the process by which new species are formed and underlying this process are these intricate interactions between cellular, behavioral, and ecological levels. To understand the fundamentals of speciation, we study these interactions on multiple levels and at different time points of the ‘speciation continuum’ where at one end we have freely mating organisms and the other end we have reproductively blocked separate species. ❧ We present here a study of Drosophila melanogaster populations from the southeast United States and Caribbean islands. These populations represent a hybrid zone of secondary contact between cosmopolitan flies from Europe and African‐like flies from West Africa, which diverged over 10,000 years ago. With the presence of previously established clines in premating reproductive barriers (i.e. male courtship behavior, cuticular hydrocarbons, etc.), it was proposed that these flies were undergoing incipient sexual isolation, which is the start of the speciation process. We investigated putative postmating reproductive barriers of remating rates, egg hatchability, and female longevity after mating to assess the extent and influence of these barriers. We found remating rates had no effect and female longevity after mating had varied and patchy effects on several different female lines from our study area. Interestingly enough, there existed a hatchability ‘dip’ where there was an area of lower hatchability around the border of the southern US and the Caribbean islands indicating possible presence of Dobzhansky‐Muller incompatibilities. In addition to these postmating barriers, we also investigated the circadian rhythms of the southeast US and Caribbean flies and found that these populations are consistent with an existing sleep cline on the east coast of the US with increasing sleep with decreasing latitude. The differences of sleep are small, but statistically significant and could potentially impact gene flow between the D. melanogaster in the US and Caribbean islands. ❧ To investigate African and European admixture, we sequenced the genomes of our 23 isofemale fly lines from 12 locations in the southeast US and Caribbean islands. We compared these genomes to previously sequenced genomes from Raleigh, NC and Winters, CA from North America as well as to sequenced genomes of D. melanogaster from Montpellier, France and Oku, Cameroon. The genome sequences revealed up to 25% African ancestry present in the Caribbean population and decreasing percentages of African ancestry with increasing latitudes into the southeast United States. Given our results, we also propose a westward expansion model of D. melanogaster in the United States. ❧ Finally, in the spirit of studying speciation on the other end of the continuum, we establish a new study system of many closely related interacting cactophilic Drosophila species on Santa Catalina Island off the coast of southern California. We report species found on the island as well as abundance and seasonality of species compositions