Knysna dwarf chameleons: city vs. forest habitat

Knysna dwarf chameleons: city vs. forest habitat

by Alex Laube Science

How do chameleons change when their natural habitat has to make way for human settlements? International scientists recently got to the bottom of this question. They hypothesised that a chameleon living in a suburban area must differ from its forest-dwelling conspecifics in terms of injury frequency, external characteristics and bite force as an expression of changed living conditions.

Between 2020 and 2022, 276 Knysna dwarf chameleons (Bradypodion damaranum) were studied in South Africa. The locations chosen were George and Knysna, two towns located around 60 kilometres apart on the south coast of South Africa. George was founded in 1811 and now has over 220,000 inhabitants, while Knysna was founded in 1825 and currently has just under 76,000 inhabitants, although they live in much less space and are therefore much more densely populated. In both cities, Bradypodion damaranum were caught in urban environments (private gardens, public parks, roadsides), examined and then released. Chameleons were also studied 10 to 12 kilometres away in their natural habitat (temperate forest). The adult chameleons were measured and photographed. The data was analysed and compared using various methods. Wounds, scars and bone fractures visible to the naked eye were counted as injuries. To measure bite force, the animals were each encouraged to bite five times on a special piezoelectric measuring device.

The analysis showed that the dwarf chameleons in urban environments had significantly lower casques and shorter gulars. The males from the city, however, had larger and wider heads. The female dwarf chameleons from the forest had significantly larger casque spurs. The males in the city had significantly more injuries (88.1%) compared to the males in the forest (72.5%). In the city, the dwarf chameleons also bit harder than in the forest when casque height and parietal crest were included in the calculations. However, when snout-vent length was included instead, there was no difference in bite force.

Differences between urban and natural populations of dwarf chameleons (Bradypodion damaranum): a case of urban warfare?
Melissa A. Petford, Anthony Herrel, Graham J. Alexander, Krystal A. Tolley
Urban Ecosystems 2023
DOI: 0.1007/s11252-023-01474-1

The microbiome of dwarf chameleons

The microbiome of dwarf chameleons

by Alex Laube Tiermedizin Science

The term microbiome has been very popular for some years now. In humans and animals, it refers to the totality of all microorganisms that colonise a living being. Most of them colonise the gastrointestinal tract. In the case of chameleons, there is only very limited literature on this topic. A master’s thesis from South Africa now deals with the bacterial composition of the microbiome in South African dwarf chameleons of the genus Bradypodion.

60 cheek swabs were collected from wild chameleons in KwaZulu-Natal. Of these, 20 were cheek swabs from Bradypodion melanocephalum, 20 from Bradypodion thamnobates and 20 from Bradypodion setaroi. After sampling, the same 60 animals were transported in cloth bags to the research base, where the animals were kept in 3.3 l boxes for 24 hours to obtain faecal samples. Since not all of the original 60 chameleons defecated, faeces were collected from additional chameleons.

The samples were all genetically tested. 40.43% of the samples contained Firmicutes, a similarly large proportion of the samples contained Proteobacteria with 36.86%. Bacteroidota followed with some distance, which could be detected in just under 16% of the samples. Verrucomicrobiota, Fusobacteriota, Actinobateriota, Spirochetes, Desulfobacteroa, Cyanobacteria, Thermoplamatota, Deferribacterota, Synergistota, Campylobacterota, Deinococcota, Halobacterota, Euryarchaeota, Elusimicrobiota and Myxococcota were found in significantly smaller numbers (up to 2%).

The microbiome of dwarf chameleons of the species Bradypodion melanocephalum, Bradypodion thamnobates and Bradypodion setaroi is similar to that of other reptiles. It consists mainly of proteobacteria and firmicutes, which may contribute to digestion. One particular bacterial species also suggests that the diet of the studied dwarf chameleons may include beetles of the genus Dendrophagus. The microbiome of all three dwarf chameleon species was very similar in the cheek swabs – this is called phylosymbiosis – while there were differences in composition between the species in the faeces. In all three dwarf chameleon species, significantly more different bacteria were found in the faeces than in the cheek swabs. A comparison between males and females did not reveal any significant differences in the microbiome of all three chameleon species. The author assumes that the bacterial species depend on the different habitats of the respective species. It is still unclear to what extent the microbiome is related to bacteria that a chameleon may ingest with feeding insects or from the soil of its environment. A detailed list of the bacterial species found can be found in the appendix of the publication.

The Hitchhiker’s Guide to dwarf chameleons (Bradypodion): The composition and function of the microbiome
Matthew G. Adair
Master of Science dissertation at the university of Johannesburg, 2023
DOI: not available

Spines of tree- and ground-dwelling chameleons

Spines of tree- and ground-dwelling chameleons

by Alex Laube Tiermedizin Science

Various anatomical adaptations of the spine between ground and tree dwellers are known from mammals, especially primates. In some cases, the different vertebrae are even associated with certain movement patterns and bodily functions. In a comparative study, two scientists from New York (USA) have now investigated how the spine of ground- and tree-dwelling chameleons differs.

They measured the already existing CT scans on Morphosource.org of a total of 28 chameleons of different species. Brookesia perarmata, Brookesia superciliaris, Brookesia thieli, Palleon nasus, Rhampholeon platyceps, Rhampholeon spectrum, Rieppeleon brevicaudatus and Rieppeleon kerstenii were classified as ground dwellers. Archaius tigris, Bradypodion melanocephalum, Bradypodion pumilum, Bradypodion thamnobates, Calumma amber, Calumma brevicorne, Calumma parsonii, Chamaeleo calyptratus, Chamaeleo gracilis, hamaeleo zeylanicus, Furcifer lateralis, Furcifer pardalis, Furcifer verrucosus, Kinyongia carpenteri, Kinyongia tavetana, Kinyongia xenorhina, Nadzikambia mlanjensis, Trioceros feae, Trioceros jacksonii and Trioceros quadricornis were considered arboreal. The vertebrae were counted and the width of the lamina, length, width, height of the vertebral body, and the height of the spinous process and transverse processes on each vertebra were measured. In addition, the so-called prezygapophysial angle was determined. This is the angle of the intervertebral joint, i.e. the contact surfaces between the individual vertebrae. The measurements of ground and tree dwellers were compared and statistically evaluated. Only the vertebral column of the trunk was considered, the caudal vertebral column was left out.

First of all, the results showed that ground-dwelling chameleons generally have fewer trunk vertebrae (15 to 19) than tree-dwelling chameleons (18 to 23). The trunk spine of almost all species could be divided into the already known three areas: Cervical spine and anterior and posterior dorsal spine. A thoracic and lumbar spine as in mammals is generally not distinguished in chameleons because of the continuous ribs. Five chameleon species had four regions instead of three: they had an anterior and a posterior cervical spine, the anterior one consisting of only two vertebrae with rib processes. Six chameleon species had two additional lumbar vertebrae and one species had three transitional vertebrae in the region between the cervical and dorsal spine. In Kinyongia carpenteri, a total of five regions could be distinguished in the trunk spine: The chameleon had anterior and posterior cervical vertebrae as well as anterior and posterior dorsal vertebrae and two additional lumbar vertebrae. Brookesia perarmata was also a special case: the trunk spine of this chameleon consisted of only two regions and at the same time the smallest number of vertebrae of all species studied.

The greatest differences between ground and tree-dwelling chameleons were found in the prezygapophyseal angle (PZA) and the height of the spinous process. The intervertebral joint surfaces in the anterior dorsal vertebrae of tree-dwelling chameleons were clearly more dorsoventrally oriented and smaller than in ground-dwelling species. Several tree-dwellers showed a PZA of less than 90°. In tree-dwelling chameleons, the largest spinous processes were located at the transition from the cervical to the dorsal spine. Among the ground-dwelling species, the spinous processes were similar only in Palleon nasus. In ground-dwelling chameleons, the appearance of the spinous process varied greatly. Rieppeleon, for example, showed narrow, backward-sloping spinous processes, while the spinous processes in Brookesia were more like a kind of bone bridge than a process. Archaius tigris was an exception: The spinous processes in this chameleon hardly differed along the entire spine.

The authors conclude from the results that the anatomy of the different vertebrae is strongly related to the chameleons’ way of life and different locomotion. The intervertebral joint surfaces in tree-dwelling chameleons are probably important for climbing by supporting the function of the shoulder girdle. Reduced mobility in the mediolateral plane provides greater trunk stiffness, which facilitates climbing in arboreal dwellers. Stiffening of the axial skeleton (skull, trunk spine and thorax) is also known from tree-dwelling mammals. The larger spinous processes in larger chameleons could facilitate shoulder girdle rotation and muscle movement, resulting in increased stride length, better head support, and thus possibly easier feeding.

Morphological and functional regionalization of trunk vertebrae as an adaption for arboreal locomotion in chameleons
Julia Molnar, Akinobu Watanabe
Royal Society Open Science 10, 2023: 221509
DOI: 10.1098/rsos.221509

Illustration: Spines of different chameleon species

Species diversification in chameleons

Species diversification in chameleons

by Alex Laube 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

Preferred perches in Bradypodion pumilum

Preferred perches in Bradypodion pumilum

by Alex Laube Science

It has long been known that most chameleon species move around on branches. However, research into how and which branches they prefer to use has so far been based mainly on nocturnal observations. At night, chameleons are easier to find in bushes and trees because they usually sleep on the ends of branches and are easy to spot with a torch. However, less is known about the use of perches during the chameleons’ active time, namely during the day. The herpetologist Kristal A. Tolley from the Kirstenbosch Research Centre in Cape Town, South Africa, has now conducted a study to find out which perch sizes Bradypodion pumilum prefers at night and during the day.

It is known from other tree-dwelling reptiles that they tend to seek out thinner perches at night, but use different perch sizes during the day. The result of the study was all the more surprising: the branches used by Bradypodion pumilum did not differ in diameter or variety during the day and night. An astonishingly high range of branches was used overall. The only correlation found was with body size, which seems logical in principle: The larger the chameleon, the thicker the perches used.


Is it like night and day? Nocturnal versus diurnal perch use by dwarf chameleons (Bradypodion pumilum)
Krystal A. Tolley
African Journal of Herpetology
DOI: 10.1080/21564574.2022.2098392

Factors in the geographical dispersal of chameleons

Factors in the geographical dispersal of chameleons

by Alex Laube Science

For a long time, people have been trying to find out how and why chameleons have spread across the African continent, to islands and as far as Europe and Asia. French scientists, in collaboration with international colleagues, have now used phylogenetics and various computational models to investigate how the factors of body size, coastal habitat and extreme lifestyles may have affected the distribution of different chameleon species. The study examined 181 species divided into nine main biogeographical regions: North Africa and Arabia, Central Africa, Southeast Africa, Southwest Africa, India, Socotra, Madagascar, Comoros and Seychelles.

Chameleon species that occurred more than 10 km from the sea historically spread significantly less than the 74 coastal chameleon species. A similar phenomenon is known from skinks and crocodiles. Dispersal probably took place mainly along the coasts, mostly on the same continent and only rarely across the water to other continents or islands.

The size of the different chameleons also seems to have influenced their dispersal throughout history: Large chameleons spread further and more frequently than small chameleons. This could be related to the fact that larger chameleons have a lower metabolic rate – so they need less energy overall relative to smaller competitors. In addition, larger chameleons lay clutches with significantly more eggs, which simply gives them an advantage in numbers.

A somewhat unexpected result came from the study of different life cycles. One would initially assume that short life cycles are associated with faster dispersal. In fact, the calculations showed that especially chameleon species with extreme life cycles spread further. Thus, those that reproduced particularly slowly or particularly quickly were historically more successful among chameleons than the species “in the middle”. In this regard, the authors consider whether particularly slow life cycles with late sexual maturity and long gestation might be more successful on the same continent, while faster reproductive strategies with large clutches are more favourable for dispersal across the sea to islands and other continents. In line with this, Furcifer polleni and Furcifer cephalolepis in Comoros and Chamaeleo zeylanicus in India, all three examples of aquatic dispersal, have a very fast life cycle.

The 34 chameleon species with the combination of living close to the coast, large size and extreme life cycle had a 98% higher dispersal rate than species without these characteristics.  All in all, this is certainly a very theoretical study, but it nevertheless provides exciting insights into the historical distribution and dispersal of chameleons.

Chameleon biogeographic dispersal is associated with extreme life history strategies
Sarah-Sophie Weil, Laurie Gallien, Sébastien Lavergne, Luca Börger, Gabriel W. Hassler, Michaël P.J. Nicolaï & William L. Allen
Ecography
DOI: 10.1111/ecog.06323

Bradypodion: 2 Änderungen

by admin General topics

Die Gattung Bradypodion hat eine neue Art:  Colin Tilbury und Krystal Tolley beschrieben das im KwaZulu Forest lebende Tier als “Bradypodion ngomeense”. Im selben Paper synonymisieren sie Bradypodion nkandlae (Raw, 2008) mit B. nemorale (Raw, 1978)

Zootaxa 2226: 43–57 (2009) – A new species of dwarf chameleon (Sauria; Chamaeleonidae, Bradypodion
Fitzinger) from KwaZulu Natal South Africa with notes on recent climatic shifts
and their influence on speciation in the genus – ISSN 1175-5326 / ISSN 1175-5334