Harrison, T. | Search bioRxiv

bioRxiv2017

Non-contact measurement of emotional and physiological changes in heart rate from a webcam

Heart rate, measured in beats per minute (BPM), can be used as an index of an individuals physiological state. Each time the heart beats, blood is expelled and travels through the body. This blood flow can be detected in the face using a standard webcam that is able to pick up subtle changes in color that cannot be seen by the naked eye. Due to the light absorption spectrum of blood, we are able to detect differences in the amount of light absorbed by the blood traveling just below the skin (i.e., photoplethysmography). By modulating emotional and physiological stress--i.e., viewing arousing images and sitting vs. standing, respectively--to elicit changes in heart rate, we explored the feasibility of using a webcam as a psychophysiological measurement of autonomic activity. We found a high level of agreement between established physiological measures, electrocardiogram (ECG), and blood pulse oximetry, and heart rate estimates obtained from the webcam. We thus suggest webcams can be used as a non-invasive and readily available method for measuring psychophysiological changes, easily integrated into existing stimulus presentation software and hardware setups.

physiology↗

bioRxiv2017

Geographically structured genetic variation in the Medicago lupulina-Ensifer mutualism

Mutualisms are interspecific interactions affecting the ecology and evolution of species. Patterns of geographic variation in interacting species may play an important role in understanding how variation is maintained in mutualisms, particularly in introduced ranges. One agriculturally and ecologically important mutualism is the partnership between legume plants and rhizobia. Through characterizing and comparing the population genomic structure of the legume Medicago lupulina and two rhizobial species (Ensifer medicae and E. meliloti), we explored the spatial scale of population differentiation between interacting partners in their introduced range in North America. We found high proportions of E. meliloti in southeastern populations and high proportions of E. medicae in northwestern populations. Medicago lupulina and the Ensifer genus showed similar patterns of spatial genetic structure (isolation by distance). However, we detected no evidence of isolation by distance or population structure within either species of bacteria. Genome-wide nucleotide diversity within each of the two Ensifer species was low, suggesting limited introduction of strains, founder events, or severe bottlenecks. Our results suggest that there is potential for geographically structured coevolution between M. lupulina and the Ensifer genus, but not between M. lupulina and either Ensifer species.

evolutionary biology↗