The evolution of invasiveness in poeciliid fishes
Troendle, Nicholas Joseph
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Understanding how a species becomes invasive and knowing the traits that promote invasiveness are vital for developing effective management strategies. With respect to invasion biology, life history traits are understudied in vertebrate taxa. In this dissertation, I used museum collections to investigate the connection between life history traits and invasiveness in live-bearing fishes from the family Poeciliidae. Since one Poeciliid fish, Gambusia affinis, (the Western Mosquitofish) is an important model species for invasion, I completed a draft genome of this species as a community resource. I used this genetic information to reconstruct the historical invasion route of Gambusia affinis from the southeastern United States into east Asia. In Chapter 2, I compared 11 invasive species from the family Poeciliidae to 11 closely related, non-invasive species. An investigation of life history traits showed that invasive species have significantly more offspring but that those offspring are smaller than in non-invasive species. This tradeoff could lead to rapid rates of increase in invasive species allowing them to quickly get a foothold and expand when introduced to a new location. In Chapter 3, I examined life history traits of eleven invasive Poeciliid species comparing their native and invasive ranges in order to determine if life history traits shifted as a result of becoming invasive. My investigation showed that in their invasive range invasive species displayed life history strategies that increased their population growth rate. Body size, fecundity, and reproductive allotment all increased in the invasive range without sacrificing offspring size. This suggests that when a species colonizes a new environment there are shifts in life history that help them to become established more quickly. In Chapter 4, I assembled a reference genome for Gambusia affinis using Illumina short read sequencing of traditional paired end libraries in conjunction with the new Chicago Libraries. The reference genome has high contiguity and coverage, with N50 contig and N50 scaffold lengths of 17.6Kb and 6.65Mb, respectively, and total estimated coverage of 55X. I then annotated the genome and compared its quality to three other fish genomes to ensure that the assembly was of high quality. In Chapter 5, I used RadSeq data to produce a suite of 4405 SNPs, mapped to the Gambusia affinis genome, for 12 populations of the invasive Western Mosquitofish G. affinis along its presumed invasion route from the southeastern United States to east Asia. I then used these markers to perform statistical and phylogenetic analysis in order to assess the genetic diversity in the invasive range and to determine the likelihood of multiple introductions. I found higher levels of genetic diversity in parts of the invasive range than would be expected from serial introductions over such a short time period. This is likely due to multiple introductions, possibly of large numbers of individuals.