Habitat tracking as a response of the planktic foraminifer Globorotalia truncatulinoides to environmental fluctuations during the last 140 kyr

Morphological variability of the planktic foraminifer Globorotalia truncatulinoides, estimated by size, shape, and coiling direction of the test, has been studied throughout the last 140 kyr in three cores in the South Atlantic. The biogeographic component of the morphological variation has been identified as difference between the three cores, located in the subantarctic frontal system, the equatorial upwelling zone, and the northern margin of the subtropical gyre. Temporal variability of morphology has been quantified and compared to biogeographic morphological variations, and paleoenvironmental proxies. The most important morphological differentiation is related to biogeography. Size and shape vary according to a temperature gradient across the different cores. This pattern is likely the result of differences between the four cryptic genetic species that have been previously identified within the taxon, and that are associated with different ecological preferences. Temporal variations can be recognized within each of the three cores, even in the most stable situation of the subtropical gyre. Significant correlations emerge between morphology and paleoenvironmental proxies, suggesting that the morphological variations are a response to environmental change. The same shape–temperature relationship emerges from both, biogeographic differences and local temporal variations. This suggests that the complex of species G. truncatulinoides mainly reacted to the glacial–interglacial climatic fluctuations of the last 140 kyr by a process of habitat tracking, i.e. the different species shifted their geographic distribution without major modifications of their ecological preferences. Yet, evolution may be involved as a response to environmental changes on a longer time scale.