I'll do you one better: The Song of the Dodo: Island Biogeography in an Age of Extinction https://www.amazon.com/dp/0684827123/ref=cm_sw_r_cp_apan_glt_fabc_KC3NG2V99A39KX0XW5ZM?_encoding=UTF8&psc=1
Among other subjects, this book discusses the Wallace/Darwin credit issue.
You may find The Song of the Dodo by David Quammen interesting. (Full title: The Song of the Dodo: Island Biogeography in an Age of Extinction).
It's not specifically about Madagascar and the Dodo of course didn't live on Madagascar, but it's a great piece of investigative journalism into the question of how species evolve often unique characteristics on islands. There is in fact a fairly large section about Madagascar but even more importantly it offers good insight in the subject of island biogeography.
It's quite a read with over 700 pages but it's sublimely written (Quammen is a very gifted science writer). The book also deserves special attention because it has a rather long section on how Darwin's younger contemporary Alfred Russel Wallace came to the same conclusions about evolution and natural selection as Darwin. In Wallace's case, his observations on the distribution of species on remote island was a key factor for his insights.
Speciation is not a fast process. I doubt there are a any significant, if any, gene flow between the two continents. A good book on how speciation occurs is https://www.amazon.com/Song-Dodo-Island-Biogeography-Extinction/dp/0684827123
A good read on the subject: https://www.amazon.com/Song-Dodo-Island-Biogeography-Extinction/dp/0684827123
Ive really enjoyed David Quamman's Song of the DoDo and E.O. Wilson's The Diversity of Life They both follow similar themes of Island Biogeography, extinction, and biodiversity. They also explain a lot of fundamental concepts in Ecology really well. E.O. is obviously an Entomologist so most of the large concepts he goes over are explained using insect models.