Species diversification in chameleons

Species diversification in chameleons

Science

From earlier studies, we know that the first chameleons evolved in the late Cretaceous, about 90 million years ago, on mainland of Africa. Around the border between the Cretaceous and Tertiary periods, about 65 million years ago, different species began to evolve. It is still unclear today which factors contributed to the diversity of species. Two researchers from Swansea University in Wales have now used various computational models of phylogenetics to investigate what might have influenced diversification (the splitting of chameleons into many different species).

First, they studied the diversification of chameleon species in Madagascar. In terms of evolutionary history, there are two points in time when chameleons apparently spread across the sea from mainland Africa to Madagascar. One is about 65 million years in the past, the other 45 million years. You could now think that the climatically extremely different habitats in Madagascar could have driven the evolution of the species very quickly after the spread across the sea. To the surprise of the researchers, however, no evidence of this was found. The species richness of chameleons on Madagascar must therefore come from the fact that chameleons spread there very early and thus simply had much more time to develop into different species than elsewhere.

Furthermore, the researchers investigated whether switching between two ecomorphs – from ground-dwelling stub-tailed chameleons to tree-dwelling chameleons with longer tails – had an impact on species diversity. Rather surprisingly, this did not seem to be the case. The evolution to tree-dwellers with longer tails occurred relatively early on one or two occasions. No evidence could be found that different ecomorphs accelerated diversification. Instead, speciation rates were found to slow down progressively over the last 60 million years. Only a very early dispersal event of the genus Bradypodion in South Africa around 10 million years ago was accompanied by a two- to fourfold diversification rate.

As a third focus of the study, the researchers examined the genus Bradypodion. During the climate change in the Miocene around 10 million years ago, South Africa changed a lot. Forests disappeared, leaving behind isolated forest habitats and, in between, savannahs, some of which are now so-called hot spots of biodiversity. Two of them, the Cape Floristic Region at the southwestern tip of South Africa and Maputuland-Pondoland-Albany on the east coast of South Africa, are home to a particularly large number of Bradypodion species. Each species is limited to a geographically very clearly defined area. The researchers, therefore, suspect that Bradypodion species have actually evolved faster under the influence of habitat change. It should be noted that the diversification rate of the genus Bradypodion is probably rather underestimated, as there are still many hidden species to be assumed.

Diversification dynamics of chameleons (Chamaeleonidae)
Stephen Giles, Kevin Arbuckle
Journal of Zoology, 2022
DOI: 10.1111/jzo.13019

Unexpected genetic diversity in leaf chameleons in western Madagascar

Unexpected genetic diversity in leaf chameleons in western Madagascar

Science

Until now, it was thought that the earth chameleon Brookesia bonsi occurs exclusively in the Tsingy of Namoroka in western Madagascar. German and Malagasy researchers have now discovered that very close relatives of the species live a good 150 km further north, not far from the coastal town of Mahajanga. The earth chameleons from a forest near Antsanitia look more like Brookesia decaryi on the outside, but genetically they are more closely related to Brookesia bonsi. In contrast, the true Brookesia decaryi from Ankarafantsika, 80 km east of Mahajanga, seems to be exclusively restricted to this occurrence and not more widespread, as originally assumed. In the same studies, the scientists found that another population of leaf chameleons from the UNESCO World Heritage Site Tsingy de Bemaraha is also closely related to Brookesia bonsi. The leaf chameleons of the population found there had previously been assigned to Brookesia brygooi on a purely visual basis.

Further work is now necessary to clarify the exact genetic identity of Brookesia aff. bonsi. Are they separate species or merely locally isolated populations of Brookesia bonsi? One thing, however, is already certain: the habitat near Mahajanga should urgently be placed under protection. The leaf chameleons must be protected so that they can be studied further. According to current data, they could already be critically endangered (IUCN). And further research could still be very exciting!

New records of threatened leaf chameleons highlight unexpected genetic diversity of the Brookesia decaryi / B. bonsi species complex in western Madagascar
Frank Glaw, Njaratiana A. Raharinoro, Rojo N. Ravelojaona, David Prötzel und Miguel Vences
Der Zoologische Garten 90, 2022 (1)
DOI 10.53188/zg003