Latitudinal gradient in species richness of the New World Triatominae (Reduviidae)

Aim To quantify the latitudinal gradient in species richness in the New World Triatominae and to explore the species-energy and area hypotheses as possible causes. Location The gradient was studied for North and South America, between 43degrees N and 32degrees S. Methods A database was constructed containing the geographical distribution of the 118 New World Triatominae species based on data extracted from several published sources. Species richness was recorded as the number of species present within 5degrees latitudinal bands. We used univariate and multivariate models to analyse the relationship between area within each latitudinal belt, land surface temperature, and potential evapotranspiration as explanatory variables, and species richness. All variables were georeferenced and data were extracted using a GIS. Results Species richness of Triatominae increases significantly from the poles towards the Equator, peaking over the 5degrees-10 degrees S latitudinal band. It increases according to a linear model, both north and south of the Equator, although a quadratic model fits better to southern hemisphere data. Richness correlates with habitable geographical area, when it is analysed through a nonlinear multiple regression factoring out latitude, only in the southern hemisphere. Regarding the species-energy hypothesis, a multiple regression analysis controlling the effect of latitude shows a significant relationship between temperature and species richness. This effect is more pronounced in the southern hemisphere. Species richness shows a strong longitudinal trend south of the Equator (increasing to the east), but not north of the Equator. This differential pattern is reflected in significant interactions between longitude and both latitude and temperature in models of the species richness of the New World Triatominae. Main conclusions To our knowledge, this is the first time that a latitudinal gradient in species richness has been shown and analysed for obligate haematophagous organisms, and it shows that the species-energy hypothesis can account for this phenomenon. This relationship is stronger in the southern hemisphere.