Morphology of fossil salamanders reflects climate change

A fossil record of the Tiger Salamander (Ambystoma tigrinum) shows population-wide changes in body size and morphology in response to climate change over the last 3,000 years. The observed changes offer predictions about the response of the species to future climate change, and the impact on the ecosystem. The research is published in the open access journal, BMC Ecology.

Researchers analysed a late-Holocene fossil record to track morphological traits in the Tiger Salamander through the last 3,000 years. The team, led by Elizabeth Hadly from Stanford University, United States, analysed trends in the fossil record within the context of known climate change, to distinguish patterns of response correlating to specific climatic periods during this time.

The fossils were all collected from Lamar Cave in Yellowstone National Park in Wyoming, United States. The cave deposits were dated and divided into five time periods according to their estimated age. The researchers then grouped the fossils into four morphologically distinct groups: young larval, paedomorphic, young terrestrial or old terrestrial, and measured the body size index (BSI) of fossils in each group and time period.

The team found that paedomorphic individuals – sexually mature, yet still aquatic and retaining larval characteristics – were much smaller than terrestrial adult individuals, during the Medieval Warm Period (MWP). The authors claim that this is eveidence for a response to warm and dry climate conditions, which allowed a terrestrial ectotherm to flourish. They conclude that the fossil record of the Tiger Salamander reflects known climatic conditions during the MWP, a time period characterised by a warm and dry climate that occurred approximately 1150 to 650 years ago.

Based on these findings, the authors speculate that the future warmer and drier climate predicted for the Yellowstone region is likely to create less permanent aquatic environments and select against aquatic paedomorphic individuals. This scenario would decrease the vertebrate biomass and alter the food web structure in the aquatic system.