A physicochemical model of odor sampling

We present a general physicochemical sampling model for olfaction, based on established pharmacological laws, in which arbitrary combinations of odorant ligands and receptors can be generated and their individual and collective effects on odor representations and olfactory performance measured. Individual odor ligands exhibit receptor-specific affinities and efficacies; that is, they may bind strongly or weakly to a given receptor, and can act as strong agonists, weak agonists, partial agonists, or antagonists. Ligands interacting with common receptors compete with one another for dwell time; these competitive interactions appropriately simulate the degeneracy that fundamentally defines the capacities and limitations of odorant sampling. The outcome of these competing ligand-receptor interactions yields a pattern of receptor activation levels, thereafter mapped to glomerular presynaptic activation levels based on the convergence of sensory neuron axons. The metric of greatest interest is the mean discrimination sensitivity, a measure of how effectively the olfactory system at this level is able to recognize a small change in the physicochemical quality of a stimulus.This model presents several significant outcomes, both expected and surprising. First, adding additional receptors reliably improves the system’s discrimination sensitivity. Second, in contrast, adding additional ligands to an odor scene initially can improve discrimination sensitivity, but eventually will reduce it as the number of ligands increases. Third, the presence of antagonistic ligand-receptor interactions produced clear benefits for sensory system performance, generating higher absolute discrimination sensitivities and increasing the numbers of competing ligands that could be present before discrimination sensitivity began to be impaired. Finally, the model correctly reflects and explains the modest reduction in odor discrimination sensitivity exhibited by transgenic mice in which the specificity of glomerular targeting by primary olfactory neurons is disrupted.Author SummaryWe understand most sensory systems by comparing the responses of the system against objective external physical measurements. For example, we know that our ability to distinguish small changes in color is greater for some colors than for others, and that we can distinguish sounds more acutely when they are within the range of pitches used for speech. Similar principles presumably apply to the sense of smell, but odorous chemicals are harder to physically quantify than light or sound because they cannot be organized in terms of a straightforward physical variable like wavelength or frequency. That said, the physical properties of interactions between chemicals and cellular receptors (such as those in the olfactory system) are well understood. What we lack is a systematic framework in which these pharmacological principles can be organized to study odor sampling in the way that we have long studied visual and auditory sampling. We here propose and describe such a framework for odor sampling, and show that it successfully duplicates some established but unexplained experimental results.

Distribution survey of Kloss’s Gibbons (Hylobates klosii) in Mentawai Islands, Indonesia

Setiawan A, Simanjuntak C, Saumanuk I, Tateburuk D, Dinata Y, Liswanto D, Rafiastanto A. 2020. Distribution survey of Kloss’s Gibbons (Hylobates klosii) in Mentawai Islands, Indonesia. Biodiversitas 21: 2224-2232. The aim of this study was to assess the population density, distribution, habitats, and threats of Kloss’s gibbon (Hylobates klossii) in the Mentawai Islands, Indonesia. In 2011-2012 we conducted a survey on Siberut Island, outside of the National Park, as well as a short visit to Sipora, North Pagai, and South Pagai. From March to September 2017, we surveyed once again some previous localities on the Siberut and Sipora islands to keep up to date with recent developments on the ground. On Siberut we used an auditory sampling method through fixed point counts, combined with line transects, to estimate the gibbon densities. In total, 113-morning calls were recorded from 13 Listening Points; 75 of these were used for density calculations. We recorded 35 individuals based on direct sightings during 66.4 km of transect distance walked. We found 13 localities outside of Siberut National Park that still have Kloss's gibbons; densities varied between 1.04group/km2 to 4.16 group/km2. No gibbons were found and heard during the short survey in Sipora and South Pagai, though we found a group of gibbons in North Pagai. Our 2017 survey revealed massive habitat changes in South Siberut. Previously existing forest localities in South Siberut were gone due to road construction, agriculture expansion, and logging.

Identifying priority areas for the conservation of the Critically Endangered northern white-cheeked gibbon Nomascus leucogenys in northern Lao

All gibbon species are declining throughout South and South-east Asia because of habitat loss and human activities such as hunting. Lao still contains a relatively large area of forest habitat suitable for gibbons, but their status in the country remains poorly known. Here we present the first density estimate of the Critically Endangered northern white-cheeked gibbon Nomascus leucogenys in Nam Et-Phou Louey National Protected Area, northern Lao. We conducted gibbon surveys using an auditory sampling technique during May–August 2014 and May 2015, at 40 sites, covering 125.6 km2. We applied N-mixture models to analyse group counts, investigating which landscape and human disturbance covariates influenced the spatial variation of gibbon abundance across the study area. We estimated the average gibbon density to be 0.4 groups/km2. Gibbon density was higher in mixed deciduous forest (0.74 groups/km2) than in evergreen forest (0.09 groups/km2), which could be a result of long-term hunting in evergreen forest areas. Thus, future gibbon protection plans should consider not only evergreen forest as priority habitat, but also deciduous forest, which tends to receive less attention in conservation planning. We also highlight key areas containing gibbons where law enforcement patrols should be focussed, to limit threats such as poaching. Future forest management plans should aim to maximize the size and connectivity of suitable gibbon habitat, to enable exchange between subpopulations.