RESPONSE OF ANTARCTIC FISHES TO QUATERNARY CLIMATIC CHANGES

Karel Janko

Institute of Animal Physiology and Genetics CAS, Libechov, Czech Republic

Objective

The Antarctic and its surrounding ocean are mostly considered as a system isolated from the rest of world due to the existence of the Antarctic Polar Front (APF), which greatly reduces the exchange of surface waters and marine organisms (Kock 1992). Despite some interconnections of marine biota from the north and the south of the APF (Clarke et al. 2005, Antezana 1999, Hodgson et al. 1997), there is no doubt that evolution in isolation resulted in many cladogenetic events and the formation of endemic taxa (Bargelloni et al.

2000, Patarnello et al. 1996, Held 2000, Page and Linse 2002, Lorza and Held 2004). These organisms had to cope with freezing water temperatures

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and the potential eradication of their habitat by ice sheet advances and grounding, which affects the Antarctic ecosystem on a scale much greater than elsewhere on Earth. Especially when it is evident that during glacial maxima the Antarctic ice sheet extended to the continental shelf break and in places was grounded between there and the continent (Hambrey and Barrett 1993) and continental slope ecosystems were further subjected to intense flows of debris pushed by expanding grounded glaciers and ice shelves (Thatje et al. 2005). They suggest that benthic biota faced extensive reductions of suitable habitat and was either fragmented into geographically restricted glacial refuges, or escaped to greater depths (Eastman and Clarke 1998). On the other hand, some organisms, especially pelagic feeders, might have experienced population expansions in consequence of the northward expansion of polar habitats during cold climatic phases (Zane et al. 2006 and citations therein). Only few studies on demographic histories of Antarctic marine and coastal species have been performed to date, because of the difficulties in obtaining the samples from the areas of interest.

Work at sea

Samples of muscle or fin tissue have been taken from approximately 1700 specimens belonging to 40 species (Table 2.31). The material was stored in pure ethanol. For a subset of samples, I also preserved the whole body frozen for subsequent parasitological examination. The study shall be accomplished after the arrival of the samples into laboratory, when selected specimens shall be sequenced for their genetic variability in recently identified fast-mutating loci.

Preliminary results

We previously analysed (manuscript submitted) the variability within samples collected during previous cruises of Trematomus bernacchi, T. pennelli, T.

newnesi and Pagothenia borchgrevinki. We observed striking differences among the studied species. All demographic analyses suggested a recent population expansion in both benthic species (of T. bernacchi, T. pennelli) dated by the cyt b locus to the recent deglaciation of the Antarctic shelf, while the population structure of pelagic feeders (T. newnesi, P. borchgrevinki) either did not deviate from a constant-size model or suggested that the onset of major population expansion by far predated those of the benthic species.

Such a pattern was apparent even when comparing previously published data on other Southern Ocean organisms, but we observed considerable heterogeneities within both groups as to the onset of major demographic events and their rates.

We propose that available data do not contradict the hypothesis that Pleistocene ice-sheet expansions significantly reduced the suitable habitat for benthic species, whereas different and less disruptive processes affected pelagic feeders. However, given the asynchronicity of major demographic events observed in different species, more species have to be analysed in

CCAMLR and related topics

order to more precisely assess the role of life history in response to climatic changes. The considerable samples-sizes collected during this cruise of many species with different life histories will most probably allow us to accomplish this study.

Table 2.31 Samples taken during the cruise.

Species Locality

Elephant I. South Shetland Ils. Joinville I. Larsen B

Aethotaxis mitopteryx 49 0 0 0

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References

Antezana T 1999. Plankton of southern Chilean fjords: trends and linkages. Sci Mar 63: 69–

80

Bargelloni L, Marcato S, Zane L, Patarnello T 2000. Mitochondrial phylogeny of notothenioids:

a molecular approach to Antarctic fish evolution and biogeography. Syst Biol 49: 114–

129

Clarke A, Barnes DKA, Hodgson DA 2005. How isolated is Antarctica? Trends Ecol Evol 20:

1-3

Eastman JT, Clarke A 1998. Radiations of Antarctic and non-Antarctic fish. In: di Prisco G, Pisano E, Clarke A, (eds) Fishes of Antarctica: A Biological Overview, pp 3–26, Milan:

Springer-Verlag Italy

Hambrey MJ, Barrett P 1993. Cenozoic sedimentary and climatic record, Ross Sea region, Antarctica, 1993. In: Kennett JP, Warnke DA (eds.) The Antarctic paleoenvironment: a perspective on global change. Part two. Antarctic Research Series. 60. American Geophysical Union. Washington, pp 91-124

Held C. 2000. Phylogeny and biogeography of serolid isopods (Crustacea, Isopoda, Serolidae) and the use of ribosomal Expansion segments in molecular systematics. Mol Phyl Evol 15: 165–178

Hodgson DA, Vyverman W, Tyler PA 1997. Diatoms of meromictic lakes adjacent to the Gordon River, and of the Gordon River estuary in south-west Tasmania. Biblio Diatomol 35: 1–172

Kock K-H 1992: Antarctic Fish and Fisheries. Cambridge University Press, Cambridge, 359 pp

Lorza AN, Held C 2004. A preliminary molecular and morphological phylogeny of the Antarctic Epimeriidae and Iphimediidae (Crustacea, Amphipoda). Mol Phyl Evol 31: 4–15

Page TJ, Linse K 2002. More evidence of speciation and dispersal across the Antarctic Polar Front through molecular systematics of Southern Ocean Limatula (Bivalvia: Limidae).

Polar Biol 25: 818–826

Patarnello T, Bargelloni L, Varotto V, Battaglia B 1996. Krill evolution and the Antarctic Ocean currents: evidence of vicariant speciation as inferred by molecular data. Mar Biol 126:

603–608

Thatje S, Hillenbrand C-D, Larter R 2005. On the origin of Antarctic marine benthic community structure. Trends Ecol Evol 20: 534-540

Zane L, Marcato S, Bargelloni L, Bortolotto E, Papetti C, Simonato M, Varotto V, Patarnello T 2006. Demographic history and population structure of the Antarctic silverfish Pleuragramma antarcticum. Mol Ecol 15: 4499-4511