A crucial challenge that animals face is timing reproduction to maximize offspring survival. Most of our understanding of how animals time reproduction comes from studies of mid- to high latitude species. For these animals, changes in day length are the primary cue they use to predict seasons and thus time seasonal processes. However, the majority of animals inhabit tropical latitudes where seasonal changes in day length are minimal. Yet many tropical species still breed seasonally and it appears that many rely on more localized cues to time reproduction. This can lead to wide disparity in reproductive timing between populations in close proximity. Previous studies have described populations of rufous-collared sparrows (Zonotrichia capensis) near the equator in Ecuador, that are separated by only 25km, yet breed at very different times of years. Interestingly, these populations have also diverged genetically. This system, where day length does not change seasonally, provides an ideal opportunity to further investigate mechanisms of seasonal reproduction. The proposed studies will investigate seasonal reproduction in terms of environmental and social cues, endogenous rhythms, breeding synchrony, population genetic differentiation, and nutrition. There are two primary components of the education portion of this project. For the first part, Ecuadorian locals and students will be incorporated into the research program, primarily as research assistants in the field. For the second part, a foreign studies class will be initiated at Virginia Tech to expose students to the culture and nature of Ecuador. Through this program, twelve students per year will travel for a month to Ecuador, interact with locals at four field sites and experience one of the most bio-diverse places on earth. Some of these students may also stay in Ecuador and work on the research project. This award is co-funded by the NSF's Office of International Science and Engineering.
Research: Our general understanding of how tropical animals function is dramatically behind our understanding of temperate zone animals. The largest problem with this disparity in our understanding is that tropical animals are vastly more diverse than temperate zone animals and thus might be expected to be more diverse in their control mechanisms. In addition, tropical animals are often under even larger threat by factors such as environmental change thus necessitating a better understanding. This project took a step to rectify this disparity by broadly and comprehensively investigating reproduction in a tropical bird. We described breeding seasons that differ between populations in close proximity. This reproductive difference was also associated with cultural (song dialect) and genetic (DNA) differences between the populations. We followed this up by describing the relative roles of cultural divergence and distance in maintaining the genetic divergence. In addition, we have determined that daylength cues (previously thought to be unimportant for equatorial species) can play a strong role in determining reproductive timing and that this effect can occur independent of food availability. In fact, food availability seems to stimulate self-maintenance rather that reproduction, unlike higher latitude species. Overall, we have described a number of differences and similarities between tropical and temperate zone species that have increased our overall understanding of animal form and function. Education: Over the course of the grant, four study abroad classes visited Ecuador and two to the Dominican Republic. These courses have served as capstone experiences for undergraduate students as they conduct independent research projects as part of the experience. In one case a research project even resulted in a peer-reviewed publication with the student as lead author. In addition to the undergraduate education, two PhDs have been completed directly associated with this grant and a third is in the works. Both PhDs have moved on to significant postdoctoral positions. Further, three postdoctoral fellows have been part of the project. Two of those now have faculty positions and the third has moved onto a senior research position.
