Rearing density as a driver of adaptation to captivity and traits under selection by domestication in hatchery reared steelhead (Oncorhynchus mykiss) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/44558h224

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  • Releasing hatchery reared salmon and steelhead to supplement threatened and endangered populations is a widely used conservation tool. One issue with this strategy is hatchery fish have lower reproductive fitness than wild fish when spawning in the wild. One of the drivers of fitness loss in steelhead is adaptation to captivity via domestication selection. Although a cause of fitness loss is known, the mechanism and traits which domestication selection is acting on remain unknown. In a series of experiments using steelhead, (Oncohynchus mykiss) I evaluated if: (1) high growth rate is being selected for in captivity; (2) if high levels of dominance correlate with fitness at release from the hatchery and (3) if reducing rearing density has an effect on the opportunity for domestication selection to act. I found that body size did not differ between first generation hatchery fish and wild fish reared in a common environment. Mother's body size and date of spawning was correlated with body size of offspring in the hatchery. Larger mothers and earlier spawn dates resulted in larger offspring. I hypothesize that early spawned families had lower metabolic rates during embryonic development due to a chilling treatment that hatchery staff use to synchronize development across all spawning events. By reducing metabolic rate during development more energy could have been used for somatic growth compared to later spawned families. Hatchery juveniles are more aggressive than wild fish, but dominance level did not influence fitness in the hatchery environment in my experiments. A potential explanation for this result is that physiological characters that are correlated with dominance are truly under selection and dominance is simply a correlated response. The correlation between physiological characteristics (e.g. metabolic rate) and dominance may not be as strong in a novel environment, influencing the negative result. Lastly, I found lowering rearing density did not have an effect on the opportunity for selection to act in captivity. Equal amounts of variance in performance among families existed in high and low density. Additionally, rank order performance across densities was highly correlated (0.82-0.95 Spearman rank correlation) demonstrating that families that perform best in captivity will do so regardless of rearing density. Results from these experiments led to developing a novel model of how increased density might exacerbate domestication selection. In salmonids, the relationship between body size at release and probability of return tends to be strongly logistic, approaching truncation selection. Under high rearing density only the best pre-adapted families to captivity (having maladaptive traits for the wild environment) are able to grow above the threshold for high survival and return in large numbers to spawn. Families that are poorly adapted to the hatchery (with traits that have higher fitness in the wild) do not attain the threshold body size and return in relatively small numbers to spawn. Because the main effect of increased density is to shift the body size of all families downward, high density could simply reduce the number of families that are above the minimum body size to return, resulting in strong among-family selection.
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  • description.provenance : Approved for entry into archive by Julie Kurtz(julie.kurtz@oregonstate.edu) on 2014-12-15T20:19:08Z (GMT) No. of bitstreams: 2 license_rdf: 1223 bytes, checksum: d127a3413712d6c6e962d5d436c463fc (MD5) ThompsonNeilF2014.pdf: 1174730 bytes, checksum: 44364aed0a51828f0766a9b25f23cb5e (MD5)
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  • description.provenance : Submitted by Neil Thompson (thompsne@onid.orst.edu) on 2014-12-12T20:29:25Z No. of bitstreams: 2 license_rdf: 1223 bytes, checksum: d127a3413712d6c6e962d5d436c463fc (MD5) ThompsonNeilF2014.pdf: 1174730 bytes, checksum: 44364aed0a51828f0766a9b25f23cb5e (MD5)
  • description.provenance : Made available in DSpace on 2014-12-15T23:38:52Z (GMT). No. of bitstreams: 2 license_rdf: 1223 bytes, checksum: d127a3413712d6c6e962d5d436c463fc (MD5) ThompsonNeilF2014.pdf: 1174730 bytes, checksum: 44364aed0a51828f0766a9b25f23cb5e (MD5) Previous issue date: 2014-12-04

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