UC Riverside

For decades there has been considerable interest in understanding how variation in dispersal arises in nature. However, studying the dispersal of natural populations in an evolutionary framework is logistically challenging, thus, much of what we know about dispersal evolution comes from studies performed in artificial environments or in species with simplified dispersal morphologies. The objective of this dissertation is to examine how divergent natural populations vary in their tendency to disperse. To do so, I examined dispersal in guppies (Poecilia reticulata) across the Northern Range Mountains of Trinidad. In Chapter 1, I used spatially-explicit, mark-release-recapture experiments to identify differences in dispersal patterns among natural populations adapted to high- and low-levels of predation. I found that across all comparisons, the high-predation (HP) individuals were more likely to disperse and dispersed further than their low-predation (LP) counterparts. In Chapter 2, I collected HP and LP guppy populations and tested for movement differences in multi-patch stream mesocosms. I found that HP guppies are more inclined to move and make more movements within the mesocosms. In Chapter 3, I collected and reared wild HP and LP populations to a F2 generation and used multi-patch stream mesocosms to compare their movements with wild populations. The results revealed that the movement differences are retained even after being reared in a common environment, which suggests that dispersal has a strong genetic component. In Chapter 4, I experimentally displaced fish and examined whether there is intraspecific variation in homing success that is related to predation regime or dispersal status. I found no association between homing success and dispersal at the individual level, but I found a strong effect of phenotype. HP individuals exhibited greater homing success compared to LP fish. Across all 4 chapters I have documented consistent and predictable differences in dispersal traits between HP and LP populations. These studies include 6 evolutionarily independent replicates, two of which were experimental introductions. Overall, this work highlights the ecological and evolutionary relevance of intraspecific, genotypic variation in dispersal tendency and demonstrates that dispersal evolves under selective regimes that also drive the rapid evolution of life history traits.