Freshwater crustaceans in Antarctic and sub-Antarctic lakes

Study Extent

The Antarctic continent can be divided into 3 biogeographic provinces which differ considerably in climatic conditions: the continental Antarctic, which is the largest and coldest region with temperature rarely above freezing, comprising the continent landmass south of 72ºS and the Balleny Islands; the maritime Antarctic, which includes the western side of the Antarctic Peninsula north of 72°S and experiences seasonal snowmelt; and the sub-Antarctic, which comprises a series of islands and small archipelagos in the Southern Ocean proximate to the zone of Antarctic Polar Front (APF), with temperatures that on average are above freezing point year-round. Besides, we considered a fourth biogeographic province, north of the APF and influenced by low temperatures: the southern cool temperate province, which is formed by several islands from New Zealand and South America, with cool to cold temperate climate.

Sampling

We elaborated a presence/absence matrix of all freshwater crustacean species reported for Antarctic and Subantarctic lakes, based on two major literature reviews, which contained all the available information to date. We divided each biogeographic province into regions following the above two reviews: continental Antarctica comprised the En (30ºE–90ºE), Wi (90ºE–150ºE) and Sc (150ºE–150ºW) sectors; maritime Antarctica included the Antarctic Peninsula, South Shetland Islands and South Orkeny Islands; sun-Antarctic islands included South Georgia, Prince Edward, Macquarie, Heard, Crozet and Kerguelen Islands; and Southern Cool Temperate included Campebell and Auckland Islands from New Zealand and Falkland from South Atlantic ocean.

Quality Control

We excluded suspect records from the dataset, ruled out possible synonymies, and updated scientific names. We assumed that sampling effort of different taxa was similar across sites, although potential differences may have some influence on our results.

Method steps

1. We explored the influence of biogeography on regional species composition using hierarchical cluster analysis integrated with similarity profile analysis in SIMPROF and metric multidimensional scaling, MDS based on a similarity matrix using the Jaccard index. We tested for significance of the different groups of regions generated by cluster analysis using one-way ANOSIM, with biogeographic province as factor, followed by pairwise tests. Further, we identified the main species associated with each group through SIMPER based on the presence/absence matrix of crustacean species. These analyses were done using Primer v.6 software. We explored the separate and joint influence of spatial autocorrelation among regions and climate using pRDA. The amount of variation explained by each factor and by their shared contribution was calculated by variance partitioning analysis, which is based on adjusted R2 (R2adj), and their statistical significance tested through permutation tests (999 randomizations). Species composition data was Hellinger-transformed prior to analysis to provide an unbiased estimate of variance partitioning based on RDA. Spatial autocorrelation was obtained with the eigenfunction analysis known as Principal Coordinates of Neighbor Matrix PCNM, which created 10 spatial variables (PCNM vectors) based on a matrix of Euclidean distances between regions calculated using the geographic coordinates. These vectors allow the representation of different spatial relationships among regions at different spatial scales and can be treated as independent variables. As we were not able to obtain consistent climatic data for all the study regions – there are relatively few meteorological stations in Antarctica and any gross estimate based on different data sources could be misleading –, we used decimal latitude as surrogate for climate. To eliminate any effect caused by different elevations, we used the residuals of a linear regression with latitude (as a response variable) against elevation (as a predictor) in the analysis. Elevation was obtained from www.gps-coordinates.net based on latitude and longitude. These analyses were performed on R v. 3.5.1, using the functions rda, varpart, anova.cca and pcnm from vegan package.

All crustaceans were identified at the genus or species level in the original publications (Pugh et al. 2002 and Dartnall 2017) and belong to the following classes: Branchiopoda, Hexanauplia, Malacostraca and Ostracoda.

1. Branchinecta gaini
   rank: species
2. Alona guttata
   rank: species
3. Alona quadrangularis
   rank: species
4. Camptocercus aloniceps
   rank: species
5. Camptocercus rectirostris
   rank: species
6. Chydorus patagonicus
   rank: species
7. Chydorus sphaericus
   rank: species
8. Daphnia gelida
   rank: species
9. Daphnia pulex
   rank: species
10. Daphniopsis studeri
    rank: species
11. Ceriodaphnia silvestrii
    rank: species
12. Ilyocryptus brevidentatus
    rank: species
13. Macrothrix boergeni
    rank: species
14. Macrothrix flagellata
    rank: species
15. Macrothrix laticornis
    rank: species
16. Macrothrix ruehei
    rank: species
17. Macrothrix oviformis
    rank: species
18. Macrothrix sp.
    rank: species
19. Ovalona weinecki
    rank: species
20. Pleuroxus macquariensis
    rank: species
21. Pleuroxus wittsteini
    rank: species
22. Eubosmina coregoni
    rank: species
23. Candona sp.
    rank: species
24. Chlamydotheca pestai
    rank: species
25. Chlamydotheca symmetrica
    rank: species
26. Cypretta sp.
    rank: species
27. Eucypris corpulenta
    rank: species
28. Eucypris fontana
    rank: species
29. Eucypris virens
    rank: species
30. Ilyodromus kerguelensis
    rank: species
31. Neocypridopsis frigogena
    rank: species
32. Tanycypris sp.
    rank: species
33. Candonopsis falklandica
    rank: species
34. Newnhamia patagonica
    rank: species
35. Boeckella poppei
    rank: species
36. Boeckella michaelseni
    rank: species
37. Boeckella brevicaudata
    rank: species
38. Boeckella vallentini
    rank: species
39. Boeckella sp.
    rank: species
40. Gladioferens antarcticus
    rank: species
41. Parabroteas sarsi
    rank: species
42. Acanthocyclops michaelseni
    rank: species
43. Acanthocyclops robustus
    rank: species
44. Acanthocyclops vernalis
    rank: species
45. Diacyclops mirnyi
    rank: species
46. Diacyclops joycei
    rank: species
47. Diacyclops kaupi
    rank: species
48. Diacyclops walkeri
    rank: species
49. Mixocyclops crozetensis
    rank: species
50. Paracyclops chiltoni
    rank: species
51. Tropocyclops prasinus prasinus
    rank: subspecies
52. Antarctobiotus koenigi
    rank: species
53. Epactophanes richardi
    rank: species
54. Marionobiotus jeanneli
    rank: species
55. Marionobiotus sp.
    rank: species
56. Tigriopus angulatus
    rank: species
57. Attheyella (D.) trigonura
    rank: species
58. Antarctobiotus robustus
    rank: species
59. Kergueleniola macra
    rank: species
60. Pseudingolfiella possessionis
    rank: species
61. Chiltonia mihiwaka
    rank: species
62. Hyalella curvispina
    rank: species
63. Hyalella neonoma
    rank: species
64. Falklandella obtusa
    rank: species
65. Praefalklandella cuspidatus
    rank: species
66. Iais sp.
    rank: species

We include the Antarctic continent which was divided into 3 biogeographic provinces: the continental Antarctic (CA), comprising the continent landmass south of 72ºS and the Balleny Islands; the maritime Antarctic (MA), which includes the western side of the Antarctic Peninsula north of 72°S; and the sub-Antarctic (SA), which comprises a series of islands and small archipelagos in the Southern Ocean proximate to the zone of Antarctic Polar Front (APF). Besides, we considered a fourth biogeographic province, north of the APF: the Southern Cool Temperate (SCT) province, which is formed by several islands from New Zealand and South America.