NICHAR GREGORY
Vector Ecologist
I am a Postgraduate Research Scientist at Columbia University, with a keen interest in issues that fall at the intersection of environmental, animal and human health. My research unites theory and empirical work to address applied questions in infectious disease dynamics, with a strong focus on the impacts of land use change on host and vector ecology.
MICROCLIMATE AND MOSQUITO ECOLOGY
Understanding how fine-scale variation in temperature affects mosquito life-history.
TROPICAL FOREST CONVERSION AND VECTORIAL CAPACITY
Understanding how tropical forest conversion to oil palm plantation affects the potential for mosquitoes to transmit disease
DUNG BEETLE AND FAECAL PARASITE TRANSMISSION
Understanding how dung beetles mediate the interactions between free-living parasite stages and their hosts that determine transmission.
EL NIÑO DROUGHT AND LAND-USE CHANGE SYNERGISTICALLY DETERMINE MOSQUITO DEVELOPMENT
Gregory et al. (2019) Environmental Research Letters
Extreme warming events can profoundly alter the transmission dynamics of mosquito-borne diseases by affecting mosquito life-history traits (e.g. survival, growth and reproduction). At local scales, temperatures are determined largely by vegetation structure and can be dramatically altered by drivers of land-use change (e.g. forest conversion). Disturbance activities can also hinder the buffering capacity of natural habitats, making them more susceptible to seasonal climate variation and extreme weather events (e.g. droughts). In experiments spanning three years, we investigated the interactive effects of tropical forest conversion and climate on fine-scale temperature, and the consequences for mosquito larval development. This study was conducted in the northern Malaysian Bornean state of Sabah using local Aedes albopictus mosquitoes; important vectors of dengue, chikungunya and Zika viruses. We demonstrate that variation in temperatures due to forest conversion dramatically increases development rates in Ae. albopictus mosquitoes. However, this effect was mediated by an El Niño Southern Oscillation (ENSO) drought event. In normal years, mean temperatures did not differ between land-use types, however mosquitoes reared in oil palm plantations typically emerged 2–3 days faster than in logged forests. During an ENSO drought, mean temperatures did differ between land-use types, but surprisingly this did not result in different mosquito development rates. Driving this idiosyncratic response may be the differences in daily temperature fluctuations between the land-use types that either push mosquito larvae towards optimal development, or over the thermal optimum, thereby reducing fitness. This work highlights the importance of considering the synergistic effects of land-use and seasonal climate variations for predicting the thermal response of a key mosquito life-history trait driving disease transmission dynamics.
TROPICAL FOREST CONVERSION TO OIL PALM PLANTATION INCREASES VECTORIAL CAPACITY OF AEDES ALBOPICTUS MOSQUITOES
Gregory et al. (2020) In prep
Land-use change is linked to the emergence and altered transmission dynamics of mosquito-borne diseases, however how the relationships between environment, mosquitoes and their
pathogens drive transmission remains poorly understood. Process-based epidemiological models have played a key role in elucidating the underlying mechanisms, but the environmental
data driving these models tends to be coarse in scale. Here, we used a combination of empirical and theoretical approaches derived at fine spatial scales to estimate the effects of tropical forest
conversion to oil palm plantation on mosquito transmission potential. We found that larval and adult mosquito survival was greater in oil palm plantations than in logged forests, and that this drove significantly higher vectorial capacity estimates in plantation sites. The prediction that oil palm plantations would support mosquito populations with higher vectorial capacity was robust to uncertainties in our adult survival estimates. We found that unless adult lifespan in logged forest habitats exceeded 1.5 times that in oil palm plantations, vectorial capacity was always
predicted to be greater in the latter. In addition, published thermal responses of key life history traits were inaccurate predictors of trait performance measured under field conditions, highlighting the need to better characterise variation in environment–mosquito interactions that determine transmission.
TRAIT-BASED CONSEQUENCES FOR...
Gregory et al. (2020) In prep
Land-use change is linked to the emergence and altered transmission dynamics of mosquito-borne diseases, however how the relationships between environment, mosquitoes and their
pathogens drive transmission remains poorly understood. Process-based epidemiological models have played a key role in elucidating the underlying mechanisms, but the environmental
data driving these models tends to be coarse in scale. Here, we used a combination of empirical and theoretical approaches derived at fine spatial scales to estimate the effects of tropical forest
conversion to oil palm plantation on mosquito transmission potential. We found that larval and adult mosquito survival was greater in oil palm plantations than in logged forests, and that this drove significantly higher vectorial capacity estimates in plantation sites. The prediction that oil palm plantations would support mosquito populations with higher vectorial capacity was robust to uncertainties in our adult survival estimates. We found that unless adult lifespan in logged forest habitats exceeded 1.5 times that in oil palm plantations, vectorial capacity was always
predicted to be greater in the latter. In addition, published thermal responses of key life history traits were inaccurate predictors of trait performance measured under field conditions, highlighting the need to better characterise variation in environment–mosquito interactions that determine transmission.