Surveillance for microbes and range expansion in house sparrows

Abstract

Interactions between hosts and parasites influence the success of host introductions and range expansions post-introduction. However, the physiological mechanisms mediating these outcomes are little known. In some vertebrates, variation in the regulation of inflammation has been implicated, perhaps because inflammation imparts excessive costs, including high resource demands and collateral damage upon encounter with novel parasites. Here, we tested the hypothesis that variation in the regulation of inflammation contributed to the spread of house sparrows ( Passer domesticus ) across Kenya, one of the world's most recent invasions of this species. Specifically, we asked whether inflammatory gene expression declines with population age (i.e. distance from Mombasa (dfM), the site of introduction around 1950). We compared expression of two microbe surveillance molecules (Toll-like receptors, TLRs-2 and 4) and a proinflammatory cytokine (interleukin-6, IL-6) before and after an injection of an immunogenic component of Gram-negative bacteria (lipopolysaccharide, LPS) among six sparrow populations. We then used a best-subset model selection approach to determine whether population age (dfM) or other factors (e.g. malaria or coccidian infection, sparrow density or genetic group membership) best-explained gene expression. For baseline expression of TLR-2 and TLR-4 , population age tended to be the best predictor with expression decreasing with population age, although other factors were also important. Induced expression of TLRs was affected by LPS treatment alone. For induced IL-6 , only LPS treatment reliably predicted expression; baseline expression was not explained by any factor. These data suggest that changes in microbe surveillance, more so than downstream control of inflammation via cytokines, might have been important to the house sparrow invasion of Kenya.

Behavioral and Immunological Features Promoting the Invasive Performance of the Harlequin Ladybird Harmonia axyridis

“…Invasive populations of the sparrows display higher surveillance against pathogens and a better immune status compared to non-invasive populations (Martin et al, 2014(Martin et al, , 2017. A superior immune system may represent a general attribute of invasive species because it can confer resistance to both pathogens and parasites encountered in newly colonized habitats or carried and co-introduced as bioweapons against indigenous competitors.…”

Exploratory behaviour and stressor hyper-responsiveness facilitate range expansion of an introduced songbird

“…Distance from Mombasa and altitude were determined using a GPS device (Garmin 60 CSx); microhabitat, shown to affect corticosterone regulation in other studies [34][35][36], was assessed as urban or non-urban by the proportion of pavement surrounding the netting site (within approx. 50 m) and the amount of vehicular and human traffic through the area; and house sparrow density was determined at the time of data collection by averaging point count estimates (two observers, 5 min fixedradius (50 m) distributed throughout each city (8-15 per city, depending on city size [37]). Backwards model selection was conducted based on corrected Akaike information criteria (AIC c ) scores; each single factor was used as well as interactions between distance and microhabitat, distance and condition, distance and sex, condition and house sparrow density, and microhabitat and density; we chose these interactions because microhabitat, condition and sex may vary by distance (dependent on the dispersal mechanism) and density might influence individual condition or be influenced by microhabitat.…”

Introduced and Native Congeners Use Different Resource Allocation Strategies to Maintain Performance during Infection

“…The native species, on the other hand, appears to allocate critical nutrients differently among tissues depending on parasite exposure, perhaps in an effort to maintain burden at lower levels. We speculate that these differences may belie mechanisms whereby the HOSP can expand their range using parasites as weapons Martin et al 2014). However, as GHSP exhibited similarly effective coping ability, the success of the invasive HOSP as mediated by interactions with parasites may be limited in areas of sympatry with congeners.…”

“…HOSP are native to the Middle East and Europe but have established populations across the globe, including our study site in Nakuru, Kenya, in the 1990s (Lewis and Pomeroy 1989;Martin et al 2014). In general, HOSP have lost many of their specialist parasites during introductions (Manwell 1957;Brown and Wilson 1975;Marzal et al 2011) but appear to be highly competent reservoirs for many generalist parasites in their introduced territories (Komar et al 2003;Lee et al 2005;Reisen et al 2005).…”