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The monsoons that drowned the rat

11 March 2015

Scientists from the School of Earth Sciences, University of Bristol, have found that variation of monsoon intensity has profound effects on species of Asian and African rats. The results from phylogenetic and biodiversity studies of the rodents suggest that weakenings in the South Asian monsoon have had a severe impact on the evolution of these animals.

The group studied the evolution of the Rhizomyinae (Asian bamboo rats and African mole rats) and found that there is a correlation between these animals’ diversity and monsoon variations.

The team, led by Raquel López-Antoñanzas from Bristol identified several periods when the evolution of the rats was hampered in some way. They concluded that these coincide with phases of monsoon weakening.

Dr López-Antoñanzas explains why they chose to use these rodents: “Rodents are ideal material for such studies given that they are the most common mammals in the fossil record, they evolved very rapidly, and are particularly sensitive to the modification of their habitat.”

The period studied spans the last 23 million years and uses a complex system of discovering and then understanding how the animals evolved from their ancestors. The methods applied, phylogenetic palaeobiogeography and biodiversity analyses calibrated against geological time, were paired with information about Monsoons. The phylogenetic corrections of palaeobiodiversity estimates bestow a huge potential on palaeontological data to understand the evolutionary impact of environmental alteration.

The scientists also observed how changes in the animals’ teeth as they evolved reflected their food source. They noted that the food source changes depended on the food available which is, in turn, was linked to the climate of the area.

Using all this available information, they were able to draw interpretations about when and why the rat species increased in numbers and diversity and then decreased or even went extinct. They found that there was increased extinction of some species and a reduction in the appearance of new species during monsoon weakening phases. It is likely that the rats’ evolutionary adaptations were not sufficient to allow all the species to survive in this new environment. The majority of the species that did survive were those that were able to adapt to become burrowing creatures allowing them to find shelter in an area with reduced and damaged vegetation.

The study, published in Scientific Reports, is the first of its kind to link past climate fluctuations with rodent biodiversity and the results are an important piece of the puzzle in deciphering the effects of climate modification on our changing planet. 

Further information

For further information please contact Keri McNamara from the Earth Sciences Press Gang

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