Research relates speciation in the Atlantic Forest and Amazon Rainforest to the incidence of solar energy

Findings from a study conducted in France were presented at the Dimensions US-BIOTA São Paulo workshop.

By Noêmia Lopes

Agência FAPESP – In the Atlantic Forest and Amazon Rainforest, the speciation (formation of biological species) events that occurred throughout the Quaternary period (which began 2.7 million years ago) coincided with periods during which the variability of insolation (the incidence of solar energy) was low.

This conclusion was presented at the Dimensions US-BIOTA São Paulo workshop held recently at FAPESP headquarters (10 Feb 2014) and represents a finding from the study “Temporal scales of climatic changes and paleodiversity patterns in the Atlantic Rainforest” conducted at the Institut de Recherche pour le Développement (Montpellier, France) under the leadership of Marie-Pierre Ledru and performed under the scope of the Dimensions US-BIOTA São Paulo project.

Ledru told Agência FAPESP that molecular clocks – mathematical models that geneticists use to determine the rates of genetic mutations of a particular species – coincide with neither the precession cycles (pluviometric cycles that repeat every 23,000 years, the driving power behind climate in the Quaternary period) nor any other known cycle except the so-called eccentricity cycle.

“This is a 400,000-year cycle related to the amount of energy that hits the Earth’s surface. We noted that the majority of speciation and diversification events in the Atlantic Forest and Amazon Rainforest occurred within intervals of low insolation variability,” she said.

According to Ledru, the Institut de Recherche pour le Développement focused its studies on analyses of bird species conducted by teams from the University of São Paulo (USP). “However, we already know that the same principle can apply to species of plants and amphibians, among other living things,” she said.

The hypothesis has not yet been proven by fossil evidence because, according to Ledru, the oldest records to which her team has access date back only 130,000 years. In 2015, however, the researcher’s team plans to drill in the Colônia Crater, located in the extreme south of the city of São Paulo, to further investigate the paleo-ecological history of the Atlantic Forest based on evidence from sources such as fossil records of pollen and isotope analyses.

The relevance of studies such as these stems from questions about the evolution of the Atlantic Forest. Questions raised at least 30 years ago about the evolution of the Amazon Rainforest are still applicable to these regions: did the last great ice age contribute to speciation in these biomes? Furthermore, during the Quaternary period, what were the consequences of glacial and interglacial events for plants and animals?

“Studies conducted up to now indicate that the responses provided by the glacial and interglacial cycles do not answer these questions about speciation. Therefore, we are looking for other ideas and hypotheses that could explain species uniqueness and diversification,” she said.

To increase scientific understanding of energy, climate and speciation, the next step in the research proposed by Ledru includes studying longer-term and continuous fossil records, improving molecular clock chronologies and perhaps redefining the organization of forests in the Holocene (the period that dates from the last ice age, approximately 12,000 years ago, to the present) in the context of the changes due to insolation.