Sjæklen

22.

Hvidt, C.B. & Christensen, I.G.: Træk af Nordsøsnæb-

lens (Coregonus oxyrhynchus L.) biologi i Vidå-systemet.

Zoologisk Laboratorium, Aarhus Universitet. Specialerap-

port, 1990.

23.

Renaut, S., Nolte, A.W. & Bernatchez, L.: Mining tran-

scriptome sequences towards identifying adaptive single

nucleotide polymorphisms in lake whitefish species pairs

(

Coregonus

spp. Salmonidae). Molecular

Ecology

: 19, 2010,

p. 115-131.

24.

Hansen, M.M., Fraser, D., Als, T. & Mensberg, K.-L.:

Reproductive isolation, evolutionary distinctiveness and

setting conservation priorities: The case of European lake

whitefish and the endangered North Sea houting (

Corego-

nus

spp.).

BMC Evolutionary Biology

: 8, 2008, p. 1-17.

25.

Waples, R.S.: Pacific Salmon,

Oncorhynchus

spp. & the

definition of ´species´ under the endangered species act.

Ma-

rine Fisheries Review

: 53, 1991, p. 11-22.; Crandall, K.A.,

Bininda-Emonds, O.R.P., Mace, G.M. &Wayne, R.K.: Con-

sidering evolutionary processes in conservation biology.

Trends in Ecology and Evolution

: 17, 2000, p. 390-395.

Summary

The importance of regulatory genetic variation in the pro-

cess of adaptive evolution has been emphasised by seve-

ral recent studies. Moreover, the development of powerful

DNA microarray technologies that allow simultaneous as-

sessments of gene expression profiles of thousands of genes

has greatly fuelled the expansion of ecological genomics in

non-model organisms. Thus, investigating patterns of gene

expression using high density microarrays in a conservation

genomics framework is a promising approach to better un-

derstand how endangered species are adapted to the local

environment.

The North Sea houting (

Coregonus oxyrinchus

) is an en-

dangered salmonid fish belonging to the

Coregonus lavare-

tus

species complex. As a species endemic to the Wadden

Sea and listed as vulnerable in the IUCN red list of endan-

gered species, the North Sea houting has high conservation

priority. While the North Sea houting was previously distrib-

uted throughout the Wadden Sea area, eradication of spawn-

ing and nursery areas, pollution and overfishing caused

extinction of local populations. As a consequence, the only

remaining indigenous population of North Sea houting is lo-

cated in the Danish River Vidaa. Based on brood stock from

this population, North Sea houting have been reintroduced

into several rivers, including the River Treene in northern

Germany. Being anadromous, the North Sea houting returns

from the Wadden Sea to the rivers to spawn during the au-

tumn and winter. While anadromy is well known among

coregonids, the ability to tolerate oceanic salinities of 35‰

makes the North Sea houting unique.

The objective of this study was to elucidate adaptive evo-

lution in the North Sea houting by analysing gene expression

patterns in North Sea houting and two populations of white-

fish from the Baltic Sea and Lake Kellersee in Germany. Fol-

lowing normalisation and filtering of the microarray data,

6,993 genes were included in the analysis. Using an FDR of

0.01, a total of 674 genes were found to be differentially ex-

pressed among populations. Contrasting pairs of populations

identified 212 genes differently expressed among North Sea

houting and whitefish from the Baltic Sea, and 76 differ-

ently expressed genes when contrasting North Sea houting

and whitefish from Lake Kellersee. Hierarchical clustering

consistently grouped individual samples into three separate

clusters representing North Sea houting, the Baltic Sea and

Lake Kellersee. Gene ontology analyses showed a general

over-representation of metabolic processes.

The functional divergence of the North Sea houting sug-

gests a potential for local adaptation in metabolic processes

as well as a potential for adapting to future environmental

changes. The indications of adaptive divergence of North

Sea houting are clearly central to conservation designation.

While the status of North Sea houting as a separate species

remains uncertain, our data could warrant designation as an

Evolutionarily Significant Unit (ESU). The finding of func-

tional divergence of North Sea houting from other whitefish

populations suggests that the North Sea houting harbours a

unique part of the evolutionary legacy within the

Coregonus

lavaretus

species complex.

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