|The Barn Swallow Project||
Well, I’m back in China. It feels like I just left China, but I guess it’s been almost a year since our epic trip last summer. In the intervening months we were busy analyzing data, and were particularly focused on variation in color and body size measurements from our 14 different Chinese barn swallow populations. Our intuitions from the field were soon confirmed with quantitative data (always a good feeling for a biologist): there are three distinct “phenotypic clusters” of swallows in China.
In the first phenotypic cluster of swallows, found in central and southern China, the birds are relatively small, with whitish to tan bellies and thin black “collars” separating the orange throat from the white belly. This matches the classic description of the gutturalis subspecies. The second cluster, from western China, has a larger body size, with white bellies, thick black collars, and long tail streamers- consistent with the rustica subspecies. Finally, there’s a cluster of swallows in northeastern China with a larger body size and darker brown belly than those to the south; birds from this region have sometimes been classified as a separate subspecies, “mandschurica,” but are currently grouped with gutturalis. The ranges of these different subspecies had never been thoroughly documented before, so just finding these different clusters was interesting. However, since we are scientists, we wanted to know more- specifically whether the different clusters are interbreeding with each other and, if they are, how long they’ve been in contact.
To do this, we needed denser sampling of the transition areas between phenotypic clusters. Our 2014 sampling points are far apart, since we were aiming for broad coverage of the entire country. The closest rustica and gutturalis samples we collected were still separated by 700km in western China, and our gutturalis and mandschurica samples were 1000km apart. China is a BIG country. The goal for this year is to map those transition areas in more detail: is the switch in phenotypes from one cluster to the next very steep, or is there a broad region of birds with intermediate phenotypes? Do we find both types (e.g. rustica and gutturalis) living in the same place, or is there only ever one or the other “parental” type in a particular spot? The answers to these questions give us clues about the ecological and genetic processes underlying the formation and maintenance of these different phenotypic clusters.
Returning to these potential hybrid zones isn’t part of the National Science Foundation grant funding this project, but I fortunately received a grant from National Geographic to go back to China and collect more samples. The goal is to map the hybrid areas more densely and examine whether historical human movement could have brought previously separated groups of barn swallows in to contact with each other, thus resulting in gene flow between the different clusters. Liu Yu and I, along with UGA vet student Rachel Lock, will be working our way between Dunhuang and Lanzhou (in the west) and Beijing and Harbin (in the northeast). These are still big distances to cover, but we’re going to try to sample at 100-200 mile intervals, answer those questions about contact zone structure, and hopefully catch a couple hundred more birds- a few more pieces in the ongoing puzzle of barn swallow speciation