Saturday, 20 April 2019

Evolution News - A Matter of Joined-Up Thinking

Buff-browed Foliage gleaner, Syndactyla rufosupercilita.

Photo credit: Ricardo O. de Oliveira
Source
The Cerrado once connected the Andes with the Atlantic Rainforest | AGÊNCIA FAPESP

Far from being, as creationists would have their duped believe, a theory in crisis, evolution is so well embedded as a fundamental science that no serious scientists even question it any more, that it can be used to settle debate about things like climate change and distribution of different biomes in the past.

An example of this is the paper in Molecular Phylogenetics and Evolution in which the distribution of a family of oven birds in the Amazon and Andean rain forests was used to show how and when these two rainforests were connected at times.

The Andean rainforest is today separated by about 1000 Km of drier habitat with open vegetation from the Amazon (Atlantic) rainforest yet they contain some 23 clearly related species of rainforest birds. The area between them consists of the Chaco, the Carrado and the Caatinga. Briefly, the Chaco spans southern Bolivia, northern Argentina and Paraguay; the Carrado, an area of savannah, spans part of Bolivia, Central-west Brazil and northern Paraguay, and the Caatinga is a semiarid area of Brazil.

These areas now effectively keep the forest species in both rainforests isolated and prevent gene flow between them, and yet the different species are clearly related and genetic evidence is that there have been periods when gene flow occurred, hence there were times when the two rainforest biomes were connected. The question was when and where.

An international team of scientists led by Gustavo Cabanne, an ornithologist with Argentina's Museum of Natural Sciences and Cristina Yumi Miyaki, a professor at Brazil's University of São Paulo’s Bioscience Institute, assisted by scientists from Brazil, Biolivia, USA and Canada, used a genetic analysis of the species, Syndactyla rufosupercilita and S. dimidiata to show that a connection between the two rainforests ran through the Carrado. This connection could have occurred several times during the Pleistocene, which lasted from about 2.5 million years ago until 11,700 years ago.


Graphical abstract
As the accompanying press release by Peter Moon from Agenêcia FAPESP explains:

Biogeography studies the relationships among living beings, latitude, elevation and climate over time. Paleobiogeography focuses on species distribution and relationships in remote epochs. An understanding of the paleobiogeography of the species that inhabit certain biomes in the present can help scientists infer the distribution of these same biomes in the past.

Sadly, the paper in Molecular Phylogenetics and Evolution is behind Elsevir's paywall. The authors conclude that during drier, colder periods, the two rainforest area act like refugia, linked during warmer, wetter periods by the Cerrado. They also recommend on the basis of current isolation that the two populations of S. rufosupercilita should be regarded as different species with the Andean population renamed S. cabanisi.

What this paper shows is how speciation can occur, not as an event, not by anything that can be observed to happen and not even with a 'transitional species' showing one species turning into another, but slowly over time simply by populations becoming isolated and evolving on their own trajectories determined by local environmental change and genetic drift. It also shows how during this process of divergence, there will be a period during which the two diverging populations can still interbreed if they should come back into contact.

It also shows how not only is there no suggestion in the relevant fields of research that there is a major problem with the scientific explanation for how species tend to diverge over time, but that this self-evidently true explanation can form the basis of conclusions about pas environmental changes and changes in climate, which, incidentally, mesh fully with evidence from other fields of science.

In contrast to what creationist frauds tell their dupes, there is no crisis in evolution theory which remains a basic science, fully-integrated with other bodies of science.





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