Title: Ecological and life-history traits and their relationship with West Nile virus and Saint Louis

18 Host life-history traits can influence host-vector encounter rates, and so differentially determine the 19 exposure risk of bird species. This modulation of host-virus encounters’ dynamics is especially 20 important when facing “generalist” arboviruses like West Nile virus (WNV) and Saint Louis 21 Encephalitis virus (SLEV). Using prevalence data collected by our laboratory since 2004, we tested 22 several hypothesis that included birds’ ecological and life-history traits to determine which traits were 23 better predictors of birds’ exposure risk to these arboviruses. By means of information-theoretic 24 procedures and generalized mixed linear models, we observed that body mass was an important trait 25 when predicting birds’ exposure risk to WNV and SLEV and migratory status significantly influenced 26 birds’ exposure risk only to WNV. Our study highlights important traits to consider when studying the 27 transmission system of these arboviruses, being useful to focus resources when characterizing viral 28 transmission networks and discuss the repercussions of these traits over birds’ immune function 29 throughout the pace of life syndrome and trade-offs theory. 30 Introduction 31 West Nile Virus (WNV) and Saint Louis Encephalitis Virus (SLEV) are two emerging arboviruses 32 belonging to the family Flaviviridae. Both are causative agent of encephalomyelitis and are 33 considered of global health concern (Guth et al. 2020), affecting not only humans but also wildlife 34 (LaDeau et al. 2007; Ong et al. 2021). Both, WNV and SLEV are maintained in a diverse ‘multi-vector 35 multi-host’ transmission network, with intrinsic spatial and seasonal fluctuation (Diaz et al. 2013b). 36 West Nile and SLE viruses share an ecological resemblance in their maintenance network being 37 predominantly maintained by members of the Culex genera and a wide range of avian hosts’ species 38 (mainly Passeriformes and Columbiformes) (Reisen 2003, 2013; Diaz et al. 2013a; Ciota 2017; 39 Rochlin et al. 2019; Giayetto et al. 2021). However, there are differences in their hosts’ species range 40 and in the consequences that these viruses might have on the health status of their hosts. For 41 example, WNV tends to have an increased mortality in a higher range of bird species (Lanciotti et al. 42 1999; Lord & Day 2001; Maharaj et al. 2018). 43 44 To be maintained in nature, both WNV and SLEV need a competent vector to feed on a competent 45 host. Consequently, mosquitoes feeding patterns take an important role in viral dynamics (Kilpatrick 46 et al. 2006a), affecting host-vector encounter rates and favouring certain host species to be chosen 47 by competent vectors. Despite certain evolutionary and environmental conditions that affect 48 mosquitos feeding patternsi.e. , host availability, hosts defensive behaviours and blood nutritive 49 valuethere are interspecific differences in host life-history traits that can influence host-vector 50 encounter rates, and so differentially determine the exposure risk of bird species and modulate the 51 host-viral encounters dynamics (Lyimo & Ferguson 2009; Kernbach et al. 2021). 52 53 Some of the life history traits that can have repercussions in modelling exposure risk in host species 54 are nest characteristics, body mass, clutch size, migratory behaviour, and diet type, among others. 55 Particularly, it has been described nest height and type were able to predict the infection probability 56 to heamosporadian parasites transmitted by Culex species in central and southern African birds (Lutz 57 et al. 2015; Ganser et al. 2020). Body mass and clutch size affect vector-hosts interactions since 58 larger and bigger bodies as well as bigger clutches releases more olfactory cues to vectors, as 59 observed by Figuerola et al. where a greater seroprevalence of WNV was observed in larger hosts 60 (Figuerola et al. 2008; Takken & Verhulst 2013). Migratory behaviour and seasonality also influence 61 vector-host encounters by affecting mosquito host availability (Rappole et al. 2000; Peterson et al. 62 2004). Finally, differences in hosts’ diet type have previously been associated with the infection risk 63 to other arboviruses, potentially due to the relationship between the type of diet and the foraging time 64 during which an individual may be exposed to a mosquito bite (González et al. 2014; Walsh 2019; 65 Skinner et al. 2021). 66 In the previously described frame, we hypothesize ecological and life history traits can modulate 67 vector-host encounters and consequently predict birds’ exposure risk to vector-borne pathogens, we 68 expect differences among traits when trying to predict exposure risk to WNV and SLEV in birds, with 69 some of such traits being better predictors than others. In evaluating whether the selected ecological 70 and life history traits are able to predict birds’ exposure risk to WNV and SLEV, we were able to 71 establish that certain hypothesis (and consequentially, certain traits) are better when predicting birds’ 72 exposure risk to WNV and SLEV. 73 74