Meeting Abstract
Invasive species face several challenges when colonizing new areas, one of which is responding to novel pathogens. Toll-like receptors (TLR) are active in the innate immune response and might influence the spread of host species to new areas. Previously we showed that expression of two TLRs, TLR-2 and TLR-4, were related to range expansion in the house sparrow (Passer domesticus) colonizing Kenya. In the present study, we asked whether DNA sequence evolution was also related to range expansion in this species. We collected DNA sequence from a functional portion of the TLR-4 (exon 3) from 10 geographic locations across the global range. We divided locations into 3 categories: native, introduced/established, and recently introduced. Preliminary analyses identified 46 variable sites, including 27 single nucleotide polymorphisms, within 596 base pairs of TLR-4 sequence. There was a slight decrease in TLR-4 sequence diversity in more recently introduced populations, notably so in Kenya. Further, phylogenetic analysis detected two main clusters of individuals. The first cluster had the highest support and grouped all individuals from Kenya and two South Africa sequences. The second grouped individuals from Brazil; the remaining individuals formed a poorly supported collection of sequences. As these results and results from previous research suggest, variation in TLR-4 (sequence and expression) appear important to the success of the house sparrow as an invasive species. However, house sparrows from one of the most recent invasions, Kenya, are exceptional, as they still show the characteristics of ongoing range expansion. To capitalize on these findings, we recently have begun a next-generation sequencing based investigation of TLR-4 sequence variation among Kenyan house sparrow populations.
