TEMPERATURE INDUCED BODY SIZE INCREASE IN A BENTHIC MARINE MOLLUSK FAUNA FROM SEYMOUR ISLAND, ANTARCTICA

The relationship between body size and temperature has long been the focus of evolutionary biologists. With climate change being a pressing issue in our modern world, it is crucial to understand the impact of temperature on organisms as well as communities. In the recent, thermal body size clines of ectotherms have widely been documented with smaller individuals occurring in the warmer low latitude and this so-called temperature-size rule has proven to be a widespread geographical phenomenon. Here we tested for the temporal expression of this spatial pattern of body size in the marine benthic mollusk fauna of Seymour Island, Antarctica. During the Eocene environmental conditions in the high latitudes changed from temperate to polar and we hypothesis that, due to the change of temperature over time, we should see an increase of body size in this community.

We measured body size of gastropod lineages including taxa from the nassariids, buccinids, and struthiolariids as well as one bivalve genus Eurhomalea sp. spanning this time period. Our samples included 1669 individuals from over 100 localities. Preliminary results indicate that body size in the gastropod lineages increased on average 26% when the climate cooled. This trend can also be observed in the size data of the bivalve taxon from the same layers (increase of 7%).

Reasons for this phenomenon are still widely discussed. Putative causes range from adaptive theories of cost-benefit of certain life-history traits connected to e.g., early maturity at small sizes in warm climate to non-adaptive models explaining the pattern with temperature dependent biochemical processes at cellular and molecular levels. Although causes are still debated, our data supports the notion that evidence for the temperature-size rule is not limited to spatial body size clines in the recent, but can also be observed temporally in the fossil record.