Nina Overgaard Therkildsen
nthe //at// stanford.edu
Postdoctoral Scholar [CV]

Ph.D. in Population Genetics, Technical University of Denmark, 2012
M.Sc. in Biology, University of Copenhagen, Denmark, 2009
B.A. in Human Ecology, College of the Atlantic, ME, USA, 2005

 

Research interests:

My research aims to improve our understanding of how species adapt to their environment, and how quickly they can respond to altered conditions caused by climate change or other anthropogenic pressures. With a primary focus on marine fish, I study how spatial and temporal variation in selection pressures interact to shape patterns of genetic variation within species, and I’m particularly interested in how the genetic composition of populations changes over short time scales. More generally, I am also keenly interested in how genetic information can help improve conservation efforts and fisheries management.

 

Current Projects:

Elucidating the genomic signature of fisheries-induced evolution

It has become evident that fisheries can inflict evolutionary changes in the exploited populations, but the full extent of these changes and their impacts on future fisheries yields and sustainability remain an open question. Using high-throughput DNA sequencing methods, I will revisit a seminal study, which demonstrated that experimental size-selective harvesting of Atlantic silversides (a small marine fish) caused substantial changes in growth rates and a suite of other traits over less than four generations. Characterizing the genomic basis underlying these observed changes will improve our mechanistic understanding of how fisheries-induced evolution operates, and will illustrate which genomic impacts we may expect in wild commercial fish stocks if they have undergone similar evolution due to fishing pressure. Since the Atlantic silverside experiences parallel natural variation in size-selective mortality across its distribution range in the wild, we will also be able to evaluate how the genomic signature of rapid anthropogenic selection differs from patterns of accumulated long-term natural selection –insights that can prove important for predicting responses to rapid environmental shifts e.g. in relation to climate change.

Using genetic tools to improve fisheries management

Many fish species are made up of multiple populations, and at any given time, some populations may be doing well, while others are declining due to unfavorable environmental conditions or overexploitation. In such cases, managers may decide to cut back on all fishing effort to allow for stock rebuilding. However, if we can identify population boundaries, we can continue to fish sustainably in areas inhabited by thriving populations and only close fishing in areas with vulnerable populations, thereby maximizing long-term yields and ensuring continued employment for fishing industries. I am collaborating with the Greenland Institute of Natural Resources to refine a cost-effective genetic assay that can distinguish separate populations of Atlantic cod, one of the historically most important commercial fish species in Greenland. With a panel of diagnostic genetic markers, we can assign unknown individuals to their population of origin, and this tool can in the future be used for real-time monitoring of the geographical distribution of Greenland’s cod resources.

Retrospective genetic monitoring of Atlantic cod

My PhD research was based on historical DNA extracted from archived otoliths (“ear stones”) collected from Atlantic cod over the past century. By tracking how the genetic composition of different cod populations have changed over time, I could directly observe signatures of microevolution in retrospective “real time”, and found evidence of both cryptic distribution shifts and response to selection over decadal time scales. In ongoing collaboration with DTU Aqua (Denmark) and the Greenland Institute of Natural Resources, I am continuing this line of research to obtain a better understanding how cod populations have responded to fishing pressure and climate change in the past. This knowledge should help improve predictions of future response patterns.

 

Publications:

  • Heino, M., Baulier, L., Boukal, D. S., Ernande, B., Johnston, F. D., Mollet, M., […], N. O. Therkildsen et al. in press. Can fisheries-induced evolution shift reference points for fisheries management? ICES Journal of Marine Science
  • Laugen, A. T., Engelhard, G. H., Whitlock, R., Arlinghaus, R., Dankel, D. J., Dunlop, E. S., […], Therkildsen, N. O., et al. online early. Evolutionary impact assessment: accounting for evolutionary consequences of fishing in an ecosystem approach to fisheries management. Fish and Fisheries
  • Hemmer-Hansen. J., Nielsen, E. E., Therkildsen, N. O., Taylor, M. I., Ogden, R., Geffen, A., Bekkevold, D., Helyar, D., Pampoulie, C., Johansen, T., FishPopTrace Consortium, Carvalho, G. R. 2013. A genomic island linked to ecotype divergence in Atlantic cod. Molecular Ecology 22: 2653-2667.
  • Therkildsen, N. O., Hemmer-Hansen, J., Hedeholm, R. B., Wisz, M., Pampoulie, C., Meldrup, D., Bonanomi, S., Retzel, A., Olsen, M. A., Nielsen, E. E. 2013. Pronounced biocomplexity at the northern range margin of Atlantic cod Gadus morhua. Evolutionary Applications 6:690-705.
  • Therkildsen, N. O., Hemmer-Hansen, J, Als, T. D, Swain, D. P., Morgan, J., Trippel, E., Meldrup, D., Nielsen, E. E. 2013. Microevolution in time and space: SNP analysis of historical DNA reveals dynamic signatures of selection in Atlantic cod. Molecular Ecology 22:2424-2440.
  • Bothwell, H., Bisbing, S., Therkildsen, N. O., Crawford, L., Alvarez, N., Holderegger, R., and Manel, S. 2013. Identifying genetic signatures of selection in a non-model species, alpine gentian (Gentiana nivalis L.), using a landscape genetic approach. Conservation Genetics 14:467-481.
  • De Wit, P., Pespeni, M. H., Ladner, J. T., Barshis, D. J., Seneca, S., Jaris, H., Therkildsen, N. O., Morikawa, M., and Palumbi, S. R. 2012. The Simple Fool’s Guide to RNA-Seq: Gene expression and SNP data analysis in the age of high-throughput sequencing. Molecular Ecology Resources 12:1058-1067
  • Behrens, J. W., Gräns, A., Therkildsen, N. O., Neuenfeldt, S., and Axelsson, M. 2012. Correlations between hemoglobin type and temperature preference of juvenile Atlantic cod Gadus morhua. Journal of Experimental Marine Biology and Ecology 413: 71-77
  • Therkildsen, N. O., Nielsen, E. E., Swain, D. P, and Pedersen, J. S. 2010 Effective population size and temporal genetic stability in Atlantic cod (Gadus morhua) in the southern Gulf of St. Lawrence. Canadian Journal of Fisheries and Aquatic Sciences 67: 1585-1595
  • Therkildsen, N. O., Nielsen, E. E., Hüssy, K., Meldrup, M., and Geffen, A. J. 2010. Does DNA extraction affect the physical and chemical composition of historical cod (Gadus morhua) otoliths? ICES Journal of Marine Science 67:1251-1259
  • Therkildsen, N. O. 2007. Small versus large-scale fishing operations in New England, USA. Fisheries Research 83:285-296

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