Drivers and Fitness Consequences of Dispersal and Structure in Wild Sockeye Salmon Populations (Oncorhynchus Nerka) PDF Download

Author: Samuel Alexander May
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Languages : en
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Book Description
The life histories of migratory species such as salmonids, sea turtles, and birds often involve return migrations between feeding and natal habitats. These natal homing behaviors are known to produce structured metapopulations, where geographic and demographic barriers result in non-random mating among many locally adapted subpopulations. The resulting spatial and temporal diversity across heterogeneous landscapes can buffer metapopulations against disruptive events that influence any one subunit. Dispersal and gene flow within and between subpopulations can reduce fitness losses due to inbreeding depression, influence rates of adaptation, and facilitate colonization or recolonization of newly available habitat. However, an understudied aspect of metapopulation biology is the influence of biotic and abiotic factors that lead to genetic structure within and between subpopulations, and the effects of this structure on fitness. Therefore, the overall goal of this thesis was to investigate how environmental, behavioral, and life-history variation might influence dispersal, population structure, and fitness within and between subpopulations. To accomplish this goal, dispersal within and between two proximate stream-spawning populations of Sockeye salmon (Oncorhynchus nerka): A and C Creeks on the Wood River System, Bristol Bay, AK was studied over two complete generations of returning adults. First, a panel of 172 SNP loci was developed (genotyping-in-thousands by sequencing; Chapter One) and used to reconstruct a pedigree from fish returning over a 14-year period, and to identify dispersers between the two populations. Second, we investigated the drivers and fitness consequences of dispersal between A and C Creeks and found that return timing to spawning grounds and within-season variation in predation and population density influenced dispersal between the two populations (Chapter Two). Fitness consequences of dispersal depended on the direction dispersers moved; moving from A to C increased absolute fitness of dispersers (compared to individuals in their natal population) but decreased their relative fitness (compared to individuals in their new spawning population), while moving from C to A decreased absolute fitness but increased relative fitness. From these results, we concluded that dispersal was an active process in response to environmental cues and that gene flow was affected by habitat differences and within-season variation in ecological processes. Third, we aimed to examine the extent, drivers, and fitness consequences of population structure within the two streams. To achieve this aim, we quantified the scale of structure, the effect of natal homing on structure, and the fitness outcomes of homing to, and dispersing from natal sites (Chapter Three). Both spatial and temporal genetic structure was evident within both streams, and this structure was partly explained by adults returning to the same place and at the same time as they were fertilized as eggs. In addition, phenotypes of body size and return timing were spatially segregated within the creeks. In one of the two creeks, adults returning to spawn near natal sites had greater fitness. Taken together, we concluded that these findings provided empirical evidence for how natal homing and heterogeneous habitat may lead to assortative mating systems and possible microgeographic adaptation on very small spatial and temporal scales. In other words, natal homing and dispersal within populations may result in genetic or phenotypic neighborhoods and affect fitness. Finally, we discuss the utility of these findings for predicting responses of natural populations to future environmental and anthropogenic changes such as harvest, climate change, and supportive breeding.