Linking big: the continuing promise of evolutionary synthesis.

Synthetic science promises an unparalleled ability to find new meaning in old data, extant results, or previously unconnected methods and concepts, but pursuing synthesis can be a difficult and risky endeavor. Our experience as biologists, informaticians, and educators at the National Evolutionary Synthesis Center has affirmed that synthesis can yield major insights, but also revealed that technological hurdles, prevailing academic culture, and general confusion about the nature of synthesis can hamper its progress. By presenting our view of what synthesis is, why it will continue to drive progress in evolutionary biology, and how to remove barriers to its progress, we provide a map to a future in which all scientists can engage productively in synthetic research.

Niche conservatism above the species level.

Traits that enable species to persist in ecological environments are often maintained over time, a phenomenon known as niche conservatism. Here we argue that ecological niches function at levels above species, notably at the level of genus for mammals, and that niche conservatism is also evident above the species level. Using the proxy of geographic range size, we explore changes in the realized niche of North American mammalian genera and families across the major climatic transition represented by the last glacial-interglacial transition. We calculate the mean and variance of range size for extant mammalian genera and families, rank them by range size, and estimate the change in range size and rank during the late Pleistocene and late Holocene. We demonstrate that range size at the genus and family levels was surprisingly constant over this period despite range shifts and extinctions of species within the clades. We suggest that underlying controls on niche conservatism may be different at these higher taxonomic levels than at the species level. Niche conservatism at higher levels seems primarily controlled by intrinsic life history traits, whereas niche conservatism at the species level may reflect underlying environmental controls. These results highlight the critical importance of conserving the biodiversity of mammals at the genus level and of maintaining an adequate species pool within genera.

Genetic response to climatic change: insights from ancient DNA and phylochronology.

Understanding how climatic change impacts biological diversity is critical to conservation. Yet despite demonstrated effects of climatic perturbation on geographic ranges and population persistence, surprisingly little is known of the genetic response of species. Even less is known over ecologically long time scales pertinent to understanding the interplay between microevolution and environmental change. Here, we present a study of population variation by directly tracking genetic change and population size in two geographically widespread mammal species (Microtus montanus and Thomomys talpoides) during late-Holocene climatic change. We use ancient DNA to compare two independent estimates of population size (ecological and genetic) and corroborate our results with gene diversity and serial coalescent simulations. Our data and analyses indicate that, with population size decreasing at times of climatic change, some species will exhibit declining gene diversity as expected from simple population genetic models, whereas others will not. While our results could be consistent with selection, independent lines of evidence implicate differences in gene flow, which depends on the life history strategy of species.