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Welcome to the Weir Lab at the University of Toronto. Our lab uses comparative methods to investigate the pace of evolution in the tropics versus high latitudes. The tropics have exceptional levels of biodiversity, and understanding the drivers of that diversity is an underlying theme in our lab’s research. Using birds as our model group, we employ a variety of genetic, field and computational approaches to estimate evolutionary rates across latitudinal gradients. Most of our research falls under the following general categories:

Phylogenetic estimates of speciation and extinction rates

Are speciation rates fastest in the tropics, and can they explain the high species richness there? Using phylogenetic data we showed that rates of speciation have been much faster at high latitudes, and slower in the tropics over the past few million years. In contrast, extinction rates were very slow in the tropics, and might explain how the tropics have been able to accumulate such high levels of species richness (read here). Recent research by Ph.D. student Paola Pulido-Santacruz extended this work across the entire bird phylogeny. Her work suggests that extinction rates are consistently lower in geographic regions with low species richness across many replicate orders of birds, while speciation rates showed no consistent pattern with latitude across replicate clades (read here). Together, these studies suggest that low tropical extinction could be the key historical driver behind the latituidnal diversity gradient.

Latitudinal gradients in trait evolution

We investigate whether rates of evolution vary across latitudinal gradients in traits important for speciation or ecological differentiation. A key focus has been on rates of evolution in the courtship songs used by birds to attract mates. Our results demonstrate faster evolution of bird song at high latitudes and suggest that the process of species formation (bird song is a key component of reproductive isolation in birds) also occurs more rapidly outside of the tropics (read here and here).

More recently, lab member Adam Lawson (who defended his MSc in January 2014) has demonstrated a much faster rate of climatic niche evolution at high latitudes, suggesting that divergent selection pressures are stronger towards the poles (read Adam’s Ecology Letters paper here).

Hybrid zones and the genomics of speciation

A recent focus of the lab is on the genomics of speciation, and how the genetic architecture of reproductive isolation varies between birds living in the rainforests of the Amazon versus the boreal forests of Canada. Our past work has shown that closely related bird species in the tropics continue to form hybrid zones for up to four million years following divergence (see figure on left), while the oldest hybrid zones at boreal latitudes are less than 1.5 million years old (read.here). The older age of hybridizing species in the tropics suggests that tropical species are accumulating reproductive isolation more slowly there, and thus taking a longer time to complete

the process of speciation. Our research also demonstrates that many species pairs believed to be separated by major Amazonian rivers, come into geographic contact in headwater regions where they invariably form hybrid zones (read.here). To investigate further, several lab members (Ph.D. students Maya Faccio, Alfredo Barrera-Guzman, Paola Pulido-Santacruz, Ashley Bramwell) are now utilizing genome-wide genetic datasets to investigate the genetic architecture of reproductive isolation in tropical and temperate regions. Stay tuned!

Comparative Phylogeography and Biogeography

An ongoing focus of the lab is to utilize comparative approaches across many species to address key biogeographic questions such as the role of ice sheets in driving allopatric speciation in boreal birds (read.here) and New Zealand kiwi (PNAS in press), the role of climate change in driving diversification of lowland and highland birds of the Neotropics (read here), and the role of landbridge completion in driving the Great American Biotic Interchange between North and South American birds (read here). We are now using genome-wide, next generation sequencing datasets to study phylogeographic questions in antbirds (Ph.D. student Maya Faccio), manakins (Ph.D. students Diogo de Lavareda Medeiros and Alfredo Barrera-Guzman), warblers (Ph.D. student Maya Faccio), thrushes (with collaborators Alyssa FitzGerald and Jeremy Kirchmam), titmice (with collaborator Claire Curry) and a variety of Amazonian species (with collaborator Alexandre Aleixo).

The Weir Lab is currently accepting graduate students and post docs (details here)