International Seagrass Biology Workshop, Wales, UK, October 16th-21st 2016 Alexander-Jueterbock@web.de

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Transcriptomic adaptation to warm temperaturesin Zostera marina

Jueterbock A.1,∗, Franssen S.U.2, Bergmann N.3, Gu, J.4, Coyer J.A.5, Reusch T.B.H. 6, Bornberg-Bauer E.4, Olsen J.L.7

1 Faculty of Biosciences and Aquaculture, University of Nordland, Bodø, Norway2 Institut fur Populationsgenetik, Vetmeduni Vienna, Austria

3 Integrated School of Ocean Sciences (ISOS), Kiel University, Germany4 Institute for Evolution and Biodiversity, University of Munster, Germany

5 Shoals Marine Laboratory, Cornell University, Portsmouth, USA6 GEOMAR Helmholtz-Centre for Ocean Research Kiel, Evolutionary Ecology of Marine Fishes, Germany

7 Marine Benthic Ecology and Evolution Group, Centre for Ecological and Evolutionary Studies, University of Groningen, The Netherlands

BACKGROUND

Heat waves are a major threat for Zostera marina, the most widely distributed sea-grass in the northern hemisphere. In previous studies, Z. marina was found tobe more heat tolerant at the southern edge of its European distribution (Mediter-ranean, [1]). We asked whether inherent heat resistance is a unique characteristicof Mediterranean seagrass or if Z. marina adapted to warm temperatures in par-allel along the American and European thermal clines.

METHODS

SAMPLING

NorthAtlanticCurrent

GulfStream

Northern and southern populations were sampled in Europe (NE, SE) and in thenortheastern USA (NU, SU). Thermally contrasting environments replicated on theNorth American and European coasts allowed to test for parallel adaptation towarm summer temperatures.

Weekly average summersea surface temperatures

>25◦C

<25◦C

HEAT STRESS LIBRARIESFollowing 20 days of acclimation, living seagrass samples were exposed for 20 daysto a simulated heatwave in a common-garden mesocosm, followed by a 20-day re-covery period. Samples for transcriptome sequencing (RNAseq) were taken at twotime points under heat stress and at three time points under recovery, resulting in 99RNAseq libraries with ca. 13,000 uniquely annotated, expressed genes.

2 3 5 7 9

26

19

Tem

pera

ture

(◦C

)

20 40 60 80Day of experiment

Sampling time points

RNAseq library per pop-ulation and temperaturetreatment

1 2 3

RNAseq (Illumina) + Quality control

Alignment (splice-aware)Zostera marina genome

Annotation

Filtering readsDuplicatesAmbiguous mappingsNon-annotated mappings

Expression profiles (rlog transformed)

Gene Library 1 Library 2 Library 3 ...

mRNA1 3.6 5.9 6.4 ...

mRNA2 1.5 0.2 4.0 ...

... ... ... ... ...

RESULTS AND DISCUSSION

HEAT RESPONSEHierarchical cluster on the firstfive principal components ofheat-responsive gene expressionshows stronger separationbetween Atlantic and Mediter-ranean samples than betweenNorthern and Southern samples.Faster recovery of gene expres-sion in both southern populationssuggests reduced sensitivity toglobal warming at the species’southern edge of distribution.

NEUTRAL DIFFERENTIATION

0.05

1.00

Neighbor-Joining tree based onNei’s genetic distances derivedfrom 139,321 biallelic neutralSNPs. Notably, the Mediter-ranean population (SE) was themost distant from the three At-lantic populations: a commonpattern associated with virtuallyall phylogeographic studies in-cluding seagrasses [2].

ADAPTIVE DIFFERENTIATIONDifferentially expressed genes(grey numbers) and adaptivelydifferentially expressed genes(black numbers). Black dotsindicate adaptive differentiation(upper dot: A vs. M, lower dot: Nvs. S) under control (C), stress(S) and/or recovery (R) condi-tions. Sixteeen of 21 genes thatwere likely involved in paralleladaptation to warm temper-atures showed also adaptiveexpression differences betweenMediterranean and Atlanticsamples. The strong adaptivedifferentiation between Atlanticand Mediterranean populationsat 128 genes suggests thatmuch of the previously observedNorth-South differentiation alongthe European coast [e.g. 1]might be better explained by ageneral Mediterranean-Atlanticdifferentiation.

CONCLUSION

Although adaptation to warm temperatures is expected to reduce sensitivity to heat-waves, the continued resistance of seagrass to further anthropogenic stressesmay be impaired by heat-induced downregulation of genes related to photosynthe-sis, pathogen defence and stress tolerance. Zostera marina has dominated theNorth Atlantic through several previous glacial-interglacial periods. Temperaturealone is not the driver, but rather numerous other anthropogenic stressors presstowards a tipping point.

REFERENCES

[1] Franssen SU, Gu J, Bergmann N, Winters G, Klostermeier UC, Rosenstiel P, Bornberg-Bauer E & Reusch, TBH (2011): Transcriptomicresilience to global warming in the seagrass Zostera marina, a marine foundation species. Proceedings of the National Academy of Sciences108(48):19276–19281

[2] Olsen JL, Stam WT, Coyer J, Reusch TBH, Billingham M, Bostrom C, Calvert E, Christie H, Granger S, la Lumiere R, Milchakova N, Oudot-Le Secq M-P, Procaccini G, Sanjabi B, Serrao E, Veldsink J, Widdicombe S, Wyllie-Echeverria S (2004): North Atlantic phylogeography andlarge-scale population differentiation of the seagrass Zostera marina L. Molecular Ecology 13(7):1923–1941