Home ground advantage: selection against dispersers promotes local adaptation in wild Atlantic salmon Kenyon B. Mobley , Hanna Granroth-Wilding , Mikko Ellmen , Juha-Pekka Vähä , 1 4 5 5 1,6,7 Tutku Aykanat , Susan E. Johnston , Panu Orell , Jaakko Erkinaro , Craig R. Primmer 1*
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Overview A long held, but poorly tested, assumption that disperers are at a reproductive disadvantage compared to local individuals
Study system
We capitalize on naturally migrating Atlantic salmon on a spawning ground sampling over 4 consecutive cohort-years to test if reproductive success of locals is higher than in dispersers (strays) Local individuals had 3-9x higher reproductive success than naturally dispersing individuals straying from nearby populations
Kenyon Mobley
Email:
[email protected] twitter: @kenyon_mobley “I’m at the conference”
Selection against dispersal may drive local adaptation and population divergence even on small spatial scales and without phenotypic differences in size or age.
Approach
Parentage analysis
Adults (230 males, 34 females) and offspring (>5000) were collected on the lower Utsjoki spawning ground (Fig. 1) over four consecutive cohort-years Collected adults were determined to be local or disperers using mixed stock assessment simulations based on a massive baseline microsatellite dataset1 Offspring were assigned to local, disperser or uncollected parents using Bayesian parentage analysis of microsatellite loci (Fig. 2).
Hanna Granroth-Wilding Email:
[email protected] “I’m not at the conference”
Sea age of maturity (number of years spent at sea before returning to spawn) was determined from scale samples Reproductive success was quantified as the number of offspring assigned to an adult (Fig. 3)
Figure 2. Juveniles collected on the spawning ground were assigned to local, disperser or uncollected adults (unfilled).
Figure 1. Locations sampled for baseline populations (indicated with circles) in the Teno river basin1. Orange square = lower Utsjoki study site. Orange circles = locations in the Teno mainstem that were considered as ‘local’. Black circles = spawning adults were assigned as dispersers with the number of assigned individuals noted in parentheses. Open circles = baseline populations to where none of the breeding adults were assigned. Lower right inlay shows areas in green where adult and juveniles were sampled in the lower Utsjoki sampling location.
Key findings Local females had 9.6 times higher reproductive success than dispersers (Fig. 3)
Craig Primmer
Email:
[email protected] twitter: @FishConGen “I’m at the conference”
Local males had 2.9 times higher reproductive success than dispers (Fig. 3) Reproductive success increases with sea age at maturity in males (Fig. 3)
Other findings No differences in river age, age at maturity, body size, or body weight between locals and dispersers Selection against dispersal is also found in a second location (AJ, Fig. 1) sampled over one cohort-year
Teno River Atlantic salmon
Figure 3. The effect of origin (local or disperser) and sea age of maturity (sea winters) on reproductive success. Large circles with error bars indicate the mean and ± standard error of the mean, small circles show individual data points. For clarity, points are jittered on the x axis. Acknowledgements We thank Katja Salminen, Meri Lindqvist, Jenni Kuismin, Jani Aaltonen, Susanna Ukonaho and Jan Laine for laboratory assistance, Jorma Kuusela, Jari Haantie and Matti Kylmäaho for scale aging analyses, and Olavi Guttorm, Topi Pöyhönen, Timo Kanniainen, Arto Koskinen, Jorma Ollila, Mari Lajunen, Tuomo Karjalainen (deceased), Mikko Kytökorpi, Seda Karslioglu, Anna Ellmen and Hans Pieski for field assistance. Fishing permission for research purposes was granted by the Lapland Centre for Economic Development, Transport, and the Environment (permit numbers 1579/5713-2007 and 2370/5713-2012).
References 1. Vähä, J.-P., J. Erkinaro, M. Falkegård, P. Orell, and E. Niemelä. 2017. Genetic stock identification of Atlantic salmon and its evaluation in a large population complex. Can. J. of Fish. Aquat. Sci.74:327-338.
Funding Departmental Addresses 1 Organismal and Evolutionary Biology Research Program, PO Box 56, 00014 University of Helsinki, Finland 2 Department of Biology, University of Turku, Finland, Itäinen 10 Pitkäkatu 4, Turku FI-20520, Finland 3 Association for Water and Environment of Western Uusimaa, POB 51, FI-08101 Lohja, Finland 4 Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3FL, UK 5 Natural Resources Institute Finland (Luke), PO Box 413, FI-90014 Oulu, Finland 6 Insititute for Biotechnology, 00014 University of Helsinki, Finland 7 Helsinki Institute of Sustainability Science, 00014, University of Helsinki, Finland *KBM and HG-W contributed equally to this work.
A 25kg male collected in the Teno river. The Teno River supports one of the world’s largest and most phenotypically diverse Atlantic salmon stocks. Up to 50,000 individuals are harvested by local fishers and recreational fisheries annually, representing up to 20% of the riverine Atlantic salmon catches in Europe. For more information follow @TenoSalmon on twitter
Preprint available on bioRxiv 30/4/18 doi: https://doi.org/10.1101/311258
