Two congeners with distinct genetic signatures

Predicting range shifts in the Arctic zooplankton: On the distribution and genetic connectivity of Themisto amphipods

Charlotte Havermans1,2, Wilhelm Hagen1, Christoph Held2, Holger Auel1

1Marine Zoology, Bremen Marine Ecology (BreMarE), Universität Bremen2Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven

Charlotte.Havermans@awi.de

« Arctic wanderers »

Zooplankton sampling during Polarsternexpedition PS107 to Fram Strait in 2017

References:1. Auel H, Werner I (2003) J Exp Mar Biol Ecol 296: 183-197 2. Dalpadado P (2002) Polar Biol 25: 656-666 3. Auel H, Harjes M, da Rocha R, Stübing D, Hagen W (2002) Polar Biol 25: 374-383 4. KohlbachD, Graeve M Lange BA, David C, Peeken I, Flores H (2016) Limn Ocean 61: 2027-2044 5. McNicholl DG, Walkusz W, Davoren GK, Majewski AR, Reist JD (2016) Polar Biol 39: 1099-1108 6. Lønne OJ,Gabrielsen GW (1992) Polar Biol 12: 685-692 7. Nilssen KT, Haug T, Potelov V, Timoshenko YK (1995) Polar Biol 15: 485-493 8. Marion A, Harvey M, Chabot D, Brêthes JC (2008) Mar Ecol Progr Ser 373:53-70 9. Volkov AF (2012) Russ J Mar Biol 38:7-15 10. OBIS (2018) Distribution records of Themisto libellula and T. abyssorum. Available: Ocean Biogeographic Information System. IntergovernementalOceanographic Commission of UNESCO. www.iobis.org. Accessed: 2018-01-03.

Funding: German Science Foundation (DFG)

Project HA 7627/1-1

Arctic macrozooplankton sampling

Towed bongo net

Multinet: few animals but depth stratification

Bongo net: shallow (ca. 40 m) and deep (ca. 150 – 310 m) tows

shallow tow: nets equipped with two GoPro® cameras

Polarstern expeditions PS100 (2016) and PS107 (2017)

Fram Strait and Greenland shelf

Tree & haplotype networksCytochrome c oxidase I gene (COI)

Sampling sites & regions

T. libellula

PS107TabC148

T. abyssorum

T. libellula

PS107TabC148

T. abyssorum

T. abyssorum

T. libellula

T. compressa

99

99

N=132

N=49

N=100 N=21

N=10

Top left: Sampling map with different stations sampled with plankton nets during PS100 and PS107 from which specimens were used for molecular analyses. Bottom left: Neighbour-Joining Tree based on pairwise distances (p) with bootstrap support (Nreps = 2000) for the three species sampled: T. libellula (132 specimens), T. abyssorum (49 specimens) and T.compressa (1 specimen). Right: Haplotype networks (parsimony, 95% probability threshold) with the colours representing sampling regions, referring to the coloured rectangles on themap. The areas of the circles are proportionate to the frequencies of the haplotypes in the sampling. Black nodes represent hypothetical or ‘missing’ haplotypes and each line a singlesubstitution.

Distributional patterns

045

002

038

007

034

032031

021

030

028

029

T. libellula

T. abyssorum

Map with Bongo net stations of PS107 and the different proportions of T. libellula and T. abyssorum caughtin both shallow and deep tows.

Themisto abyssorum

Abundances varying from0.003 ind.m-3 (St 031) – 0.506 ind.m-3 (St 002)

- Abundant in deeper waters within West SpitsbergenCurrent (WSC) or Return Atlantic Current.- Also present in shallow Bongo tow samples, indicatingpresence in colder waters.

Themisto libellula

Abundances varying from0.007 ind.m-3 (St 045) – 2.178 ind.m-3 (St 002)

- High abundances compared to literature(Fram Strait, Greenland shelf1)- Both in 40m and 300m tows- Highly abundant in stations influenced by the warmer WSC (e.g. St 002, St 034)- Less abundant in western Greenland shelf stations and in very low numbers on the Svalbard shelf.

Who is where & how are populations connected?

Occurrences, vertical distribution & abundances

Population structure: Length-frequency distributions

Connectivity: molecular analyses of different populations

Vertical distribution and population structure

Images of swimming T. libellula from the underwater recordings,

Recordings show that T. libellula does not formswarms in the water column

Outlook: what’s next?

How tightly are the two species linked to the different water masses?

Thermal acclimation and resilience of T. abyssorum vs. T. libellula

Whole-transcriptome profiling of amphipods exposed to thermal stress to assess their ecophysiology and predict the effects of warming waters

R/V Polarstern

Atlantic vs. Arctic species in a scenario of Atlantification: Themisto as case study

Themisto libellulaThemisto abyssorumBoth species

High biomassSwarming (?)

CarnivorousOpportunistic (?)

Overlappingdistributions

Some aspects of theirbiology understudied,

genetic structure unknown

Deeper layers

Boreal-Atlantic

1-2 year life-cycle1,2

smaller

Pelagic trophicpathway3,4

Arctic

Epipelagic layer

Important resource for Arcticmarine vertebrates5,6,7

Cryo-pelagic trophic pathway3,4

– ice-dependent

2-4? year life-cycle1,2

bigger

Less valuable resource for Arcticmarine vertebrates

OBISOBIS

Expected range expansion Expected range retractionbut recent new occurrences in Southern Bering Sea

and Gulf of St Lawrence8,9

Consequences for food web & biogeochemical cycles?

Likelihood of range shifts?the Multinet

Size structure within species varies according to site…

St 038N = 73

…and according to depth at the same site

St 007N = 592

N = 310

St 034, 0-40 m St 034, 0-300 mN = 116

Length distributions of T. libellula (blue bars) and T. abyssorum (red bars) at selected stations.

A closer look at the different findings will allowto identify fine-scale population structure - varying along a bathymetric and geographic

gradient, - influenced by local hydrography

Themisto abyssorum

Size from < 1 mm to 1.8 cm

Themisto libellulaSize from 2.5 mm to 3.3 cm

Newly hatched juveniles present for bothspecies

Mean sizes of Themisto species known to vary accordingto water masses2

Themisto abyssorum

High haplotype diversity

Genetic heterogeneity– even between specimens fromthe same station

Depth stratification, aggregation between sexes?

- Morphological investigations of specimens, - Comparison genetic structure with exact depth occurrences

Higher dispersal capacities linked to behaviour or hydrography?

Themisto libellula

Low haplotype diversity: 1 dominant one

Genetic homogeneity– between stations on the Greenland Shelf& Fram Strait

Distinct historical events?

Higher degree of local adaptation???

Identical haplotypes acrosslarge distances and

temperature range (-1°C – 5°C)

Higher plasticity???

Now on Youtube!

Admixture of divergent lineagesfrom different regions?

Fram Strait