Eco-evolutionary dynamics may show an irreversible regime shift, illustrated by salmonids facing climate change

The enhanced or reduced growth of juvenile masu salmon (Oncorhynchus masou masou) may result from climate changes to their environment and thus impact on the eco-evolutionary dynamics of their life-history choices. Male juveniles with status, i.e., if their body size is larger than a threshold, stay in the stream and become resident males reproducing for multiple years, while those with smaller status, i.e., their body size is below the threshold, migrate to the ocean and return to the stream one year later to reproduce only once. Since juvenile growth is suppressed by the density of resident males, the fraction of resident males may stay in equilibrium or fluctuate wildly over a 2-year period. When the threshold value evolves, the convergence stable strategy may generate either an equilibrium or large fluctuations of male residents. If environmental changes occur faster than the rate of evolutionary adaptation, the eco-evolutionary dynamics exhibit a qualitative shift in the population dynamics. We also investigated the relative assessment models, in which individual life-history choices are made based on the individual’s relative status within the juvenile population. The eco-evolutionary dynamics are very different from the absolute assessment model, demonstrating the importance of understanding the mechanisms of life history choices when predicting the impacts of climate change.

Fingerprinting of hatchery haplotypes by whole-mitogenome sequencing improves genetic studies of masu salmon Oncorhynchus masou masou

Stocking hatchery fish can lead to disturbance and extinction of the local indigenous population. Stocking similar lineages to the indigenous population makes it difficult to conduct genetic studies to determine conservation units. We considered that, due to the length of the mitogenome, whole-mitogenome analysis might overcome this problem by enabling identification of hatchery haplotypes. Here, to provide basic information for conservation of indigenous masu salmon Oncorhynchus masou masou, a commonly stocked fish in the Kase River system, Japan, we used whole-mitogenome analysis of fish to identify hatchery haplotypes in the river and in several hatcheries that might be used for stocking. Whole-mitogenome sequencing clearly identified hatchery haplotypes like fingerprints, identifying the tributaries contaminated with hatchery haplotypes. The results suggest that informal stocking of O. m. masou has been performed widely across the Kase River system. Non-hatchery haplotypes mainly belonged to clade I, which was not found in northern Hokkaido Island. Sites without hatchery haplotypes were estimated three, suggesting that these sites are suitable for conservation of the indigenous fish. This study demonstrated that the resolution of the conventional analysis using partial mitogenome is insufficient to distinguish hatchery haplotype from similar lineages. The whole-mitogenome sequences provided accurate information that was not available in the partial sequences, enabling various inferences: e.g., estimation of the origin of stocked fish and circulation of the reared strains. We conclude that whole-mitogenome analysis is useful for the genetic study of this species. The whole-mitogenome data produced will contribute to the conservation, resource management, and further study of O. m. masou.