Hobbits from the Deep South: Historical Drivers of Dwarfism in Modern Antarctic bivalves

RIVADENEIRA, M., VILLAFAÑA, J.; GORDILLO, S., BAYER, M.S.; NIELSEN, S.N.

Antofagasta

Conferencia; XXXIII Congreso de ciencias del Mar, At Antofagasta. Chile; 2015

The modern Antarctic bivalve fauna has longbeen considered as unusually small-sized or ?dwarf?.However the validity of this pattern and the underlyingcauses remain little studied. We used a worldwidecompilation of body sizes of 5185 bivalve species across17 major biogeographic provinces to show that Antarcticspecies are statistically smaller than in any other province,a pattern not attributable to sampling artifacts. Theavailable fossil record shows that dwarfism may haveexisted since the Oligocene-Neogene, after the onset ofglaciation, highlighting the importance of historicalprocesses. Indeed, models show that dwarfism cannot belinked to present-day ecophysiological or ecologicalrestrictions, but rather to the unusual bathymetric patternsof species. Our numerical experiments support the ideathat the combined effect of the extinction of large-sizedshallow-water forms, and the subsequent invasion of smallsizeddeep-water species has shaped the dwarfism ofAntarctic bivalves at evolutionary timescales. Thismechanism may further provide an explanation for theextreme body sizes in Antarctic organisms in general.