Date of Award

Summer 2017

Document Type


Degree Name

Master of Science (MS) in Biology




Chapter 1. Invasive species pose a serious threat to native ecosystems. In eastern Washington brook stickleback (Culaea inconstans) is an important invasive species, especially at Turnbull National Wildlife Refuge, where they compete with waterfowl for food resources and are associated with declines in habitat quality. Understanding the invasion routes of this invasive species may help managers implement strategies to prevent further spread and mitigate damages caused by these fish. The objectives of this study were to identify the most likely point of brook stickleback invasion, to determine their most likely invasion routes, and to investigate landscape features and processes that may be impacting gene flow between populations. Genotypes at nine microsatellite loci from 560 brook stickleback from 20 putative populations were used determine the genetic variation within and among populations. Genetic diversity was highest in the headwaters of Pine Creek (HE = 0.753 in Kelley Creek, AR = 4.466 in Pine Creek) and on average water bodies in Pine Creek had greater genetic diversity than elsewhere (HE, p = 0.016; AR, p = 0.02). FIS values were globally high and Hardy-Weinberg expectations were violated due to an excess of homozygotes. A concrete dam at Cheever Lake and watershed boundaries act as barriers to gene flow as geographically proximate sites have on either side of these barriers higher than expected genetic distance. The data presented here along with the historically documented distribution of brook stickleback in eastern Washington indicate that the most likely point of invasion was in the headwaters of Pine Creek and that brook stickleback subsequently moved down Pine Creek to the confluence with Rock Creek and from there dispersed both upstream and downstream.

Chapter 2. The invasive fish brook stickleback (Culaea inconstans) was first detected in eastern Washington in 1999. They have subsequently expanded their range into water bodies of variable habitat stability. Successful colonization by an invasive species is often influenced by flexibility in life-history traits. One important life-history trait is the number and timing of reproductive events, which can be driven by the stability of spawning habitat. I hypothesized that brook stickleback living in unstable habitats may be functionally semelparous, due to unpredictable habitat conditions. Brook stickleback reach sexual maturity in one year; therefore functionally semelparous populations should be on average younger than age class I. Brook stickleback were collected from 18 water bodies and otoliths were extracted to determine age after which, standard length (SL) was measured to determine length-at-age. Average age of brook stickleback in permanent wetlands was significantly greater than that of fish in semi-permanent and ephemeral wetlands, but there was no significant difference in age structure between semi-permanent and ephemeral wetlands (permanent x̄ = 1.24, semi-permanent x̄ = 0.73, ephemeral x̄ = 0.76, p < 0.001). Average SL at age class 0+ was significantly less than age classes I, II, and III; however, there was no significant difference between age classes I, II, and III (0+: x̄ = 39.73; I: x̄= 46.42; II: x̄ = 45.14; III: x̄ = 49.10; p < 0.001). The results indicate that brook stickleback may be functionally semelparous and that the only accurate way to measure brook stickleback age

Chapter 3. Biological invasions are typically viewed as problematic because they are often associated with declines in habitat quality and negative impacts on native species; however, they also provide opportunities for conducting unique natural experiments. The enemy release hypothesis suggests that the success of invasive species may be due to the lack of coevolved predators, pathogens, and parasites in its introduced range. Under the enemy release hypothesis organisms can invest less energy in defensive morphology allowing them to invest more energy in growth and reproduction. The invasive fish brook stickleback (Culaea inconstans) was first detected in eastern Washington in 1999. Brook stickleback have dorsal, pelvic, and anal spines acting as defensive morphology, and there is a tradeoff between this defensive morphology and swimming ability. The waterways that brook stickleback inhabit in eastern Washington often lack piscine predators, the brook stickleback's most common natural predator. To determine if brook stickleback were spending less energy on developing defensive morphology, pelvic spine length (PL) to standard length (SL) ratios from brook stickleback collected in 2016 were compared to a dataset collected in 1999. The PL:SL of brook stickleback collected in 2016 was significantly smaller than those in 1999 (1999: x̄ = 0.079, SE = 0.001; 2016: x̄ = 0.061, SE 0.0005; p < 0.001). Linear regressions of PL with respect to SL were significantly positive in both 2016 brook stickleback and 1999 brook stickleback (1999: y = 0.0236x + 2.1901, r² = 0.2889, p < 0.0001; 2016: y = 0.0208x + 1.7138, r² = 0.1244, p < 0.001), and they had non-overlapping 95% confidence intervals. These results indicate that shorter pelvic spine length in brook stickleback in eastern Washington has been selected for since their introduction

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