Applying ecological models to communities of genetic elements: the case of neutral theory

A promising recent development in molecular biology involves viewing the genome as a mini‐ecosystem, where genetic elements are compared to organisms and the surrounding cellular and genomic structures are regarded as the local environment. Here, we critically evaluate the prospects of ecological neutral theory (ENT), a popular model in ecology, as it applies at the genomic level. This assessment requires an overview of the controversy surrounding neutral models in community ecology. In particular, we discuss the limitations of using ENT both as an explanation of community dynamics and as a null hypothesis. We then analyse a case study in which ENT has been applied to genomic data. Our central finding is that genetic elements do not conform to the requirements of ENT once its assumptions and limitations are made explicit. We further compare this genome‐level application of ENT to two other, more familiar approaches in genomics that rely on neutral mechanisms: Kimura's molecular neutral theory and Lynch's mutational‐hazard model. Interestingly, this comparison reveals that there are two distinct concepts of neutrality associated with these models, which we dub ‘fitness neutrality’ and ‘competitive neutrality’. This distinction helps to clarify the various roles for neutral models in genomics, for example in explaining the evolution of genome size.     

A multi-lake study of seasonal variation in lake surface evaporation using MODIS satellite-derived surface temperature

Knowledge of the evaporative loss from lakes and reservoirs is critical to water resources managers as well as to the overall understanding of the water balance in a given basin, geographical region, or continent. Existing methods for ascertaining evaporation from lakes and reservoirs include point measurements, water balance and mass transfer calculations, and proxy measurements using a pan. Point measurements using the eddy flux covariance method can be accurate, but are resource intensive and unsuited for determining spatial variation over a lake, or for obtaining measurements over many lakes. Mass balance methods cannot provide spatial variability and their accuracy depends on other portions of the water balance that can be challenging to obtain, such as leakage. Similarly, relatively recently deployed scintillation methods provide only an average for a strip across a lake and are also resource intensive and not suited for multi-lake studies. Evaporation pan measurements can also be used, though their accuracy is poor. Herein, we use a combination of Moderate Resolution Imaging Spectroradiometer (MODIS) satellite measurements of water surface temperature, measurements of wind speed, air temperature, and relative humidity from local NWS stations, and a mass transfer method, to demonstrate multi-lake evaporation measurements. Specifically, the seasonal variation in evaporation is obtained for the five major lakes in the Savannah River Basin (in South Carolina, USA): Lakes Jocassee, Keowee, Hartwell, Russell, and Thurmond. Since this approach requires only an existing satellite resource with global coverage and existing NWS stations, this method can potentially be ported to any lake where there is a nearby meteorology station. Hence, this method could be used by both water resource managers and limnologists alike. The possibility is discussed of extending this approach beyond a single basin to encompass an entire geographical region or continent.     

Discrimination of angiotensin II receptor subtype distribution in the rat brain using non-peptidic receptor antagonists

The non-peptidic angiotensin II receptor subtype selective antagonists, DuP 753 and PD123177, were used to characterize angiotensin II receptor binding sites in the rat brain. Competitive receptor autoradiography with 125I-Sar1-Ile8 angiotensin II defined a regional distribution of binding sites that were sensitive to either DuP 753 (designated AII alpha subtype) or PD123177 (designated AII beta subtype). Whereas most brain nuclei could be assigned to a category containing a predominant subtype, a multiple receptor subtype analysis indicated that some regions are homogeneous, while others contain a mixture of both AII alpha and AII beta subtypes.