Detective story in Antarctica

Continental drift explains the formation of continents using the mechanism of plate tectonics and the mantle convention. Because of them, continents such as Africa and South America were once connected. Species distribution over the sea was a lot easier when continents were closer to each other millions of years ago. Over-water dispersal of small animals, such as insects, occurred primarily on rafts of biological material, for example, a dead tree. Where the raft floated was primarily affected by the direction of ocean currents.

Researchers looked at two possible dispersal scenarios of austral clades of Elmidae in the Tertiary Period in the Southern Hemisphere. In one scenario the clade occurred in Antarctica and in the second scenario, it didn’t. In the modeling of these two possible dispersal routes, they included the distances between Antarctica and other land masses in the Southern Hemisphere where this clade can be found nowadays. These include Australia, South America, Africa, and New Zealand.

Scientists have explored two scenarios - the spread of the species across and around Antarctica. However, in the case of spread across Antarctica, important factors such as the direction of the waves need to be taken into account. Source: the original article.

And what did they discover? This clade probably dispersed from Africa to Antarctica which then served as a source of colonizers to Australia and South America. These two continents were close to Antarctica in the studied era. New Zealand was colonized later from South America.

Antarctica can be included in the biogeographical analysis under priory assumptions. Firstly, the models have to be distance-constrained, because the dispersal success of species is higher with shorter distances between landmasses. Another constraint of the models is the maximal number of areas inhabited by a species. It’s almost impossible for one species to live on multiple continents at the same time. The spread of species between continents was separated by long periods of time during which they specialized. As a result, all modern Elmidae species inhabit only one continent. The last constraint of the model is an assumption that the direction of the currents hasn’t changed during the studied period.

The use of rafts may be widespread. The biological one, unlike the human one, is a free-floating object on which animal or plant species can overcome even such a challenging obstacle as the sea. Source: Jeremy Stewardson, unsplash.com

The specific assumptions required to include Antarctica in biogeographical analysis should be investigated in other taxa as well – they may be justified for some groups and geological settings but not for others.

As in a detective story, when studying the historical spread of species, it is always necessary to start from the very beginning. What applies to beetles might not apply to other groups.

Eliška Leštinová

Sýkora, V., Herrera‐Alsina, L., Maier, C., Martínez-Román, N. R., Archangelsky, M., Bilton, D. T., Seidel,

M., Leschen, R. a. B., & Fikáček, M. (2023). Reconstructing ancient dispersal through Antarctica: A

case study of stream‐inhabiting beetles. Journal of Biogeography, 50(11), 1939–1954.

https://doi.org/10.1111/jbi.14702