Project Title: Genomic analysis of a hybrid invasion with endangered tiger salamanders
Background: Sixty years ago, several tens of thousands of non-native barred tiger salamanders (Ambystoma tigrinum, BTS) were introduced into California’s Salinas Valley by the emerging fishing bait industry. These invasive tiger salamanders hybridized with native California tiger salamanders (Ambystoma californiense, CTS), producing a complex hybrid landscape that encompasses at least 25% of the range of CTS and was a critical element in the listing of the species under both federal and California Endangered Species Acts. We have continuous, range-wide sampling of CTS populations going back to the early 1980’s, totaling over 40,000 genetic samples from 700 unique sampling events, allowing us the unprecedented opportunity to track the movement of non-native genes in real time across California. Extensive work by our lab has demonstrated that hybrid salamanders often outperform pure native CTS, and that an estimated 4% of the genome (3/68 markers) is “superinvasive” and has moved more extensively across California than the “standard” hybrid swarm.
Approach: We propose two experiments. First, we will build on our current NSF-funded work to increase sampling by 33%, from three to four individuals per sampling event, for the 600 sampling events that we are analyzing with a 5200 gene target capture array. This increase will allow us to track the movement of rarer non-native alleles, which is particularly important in defining the edge of the genomic invasion. Second, we will conduct an RNAseq experiment on native and hybrid salamanders from our captive salamander colony to quantify differences in gene expression as a function of exposure to near-lethal temperatures. This experiment specifically targets the potential ability of hybrids to outcompete natives given California climate warming scenarios. Both are of great interest to state and federal regulatory agencies.
Resources: CTS has an estimated genome size of 32 Gb, making it a genomic challenge. We have developed, tested, and published a 5200 gene target capture array based on pre-existing EST resources. We are also mapping all of these markers in hybrid cross families. With current NSF support, we are analyzing three individuals per sampling event; here, we propose to increase this sampling to four individuals per site. We have maintained a living salamander colony for 20 years, and are using controlled crosses from that colony for our RNAseq experiment.