Wednesday, June 24, 2020

[Herpetology • 2020] Phylogenomics of Monitor Lizards and the Role of Competition in Dictating Body Size Disparity

Varanus spp.

in Brennan, Lemmon, Lemmon, Portik, et al., 2020. 

Organismal interactions drive the accumulation of diversity by influencing species ranges, morphology, and behavior. Interactions vary from agonistic to cooperative and should result in predictable patterns in trait and range evolution. However, despite a conceptual understanding of these processes, they have been difficult to model, particularly on macroevolutionary timescales and across broad geographic spaces. Here we investigate the influence of biotic interactions on trait evolution and community assembly in monitor lizards (Varanus). Monitors are an iconic radiation with a cosmopolitan distribution and the greatest size disparity of any living terrestrial vertebrate genus. Between the colossal Komodo dragon Varanus komodoensis and the smallest Australian dwarf goannas, Varanus length and mass vary by multiple orders of magnitude. To test the hypothesis that size variation in this genus was driven by character displacement, we extended existing phylogenetic comparative methods which consider lineage interactions to account for dynamic biogeographic history and apply these methods to Australian monitors and marsupial predators. Incorporating both exon-capture molecular and morphological datasets we use a combined evidence approach to estimate the relationships among living and extinct varaniform lizards. Our results suggest that communities of Australian Varanus show high functional diversity as a result of continent-wide interspecific competition among monitors but not with faunivorous marsupials. We demonstrate that patterns of trait evolution resulting from character displacement on continental scales are recoverable from comparative data and highlight that these macroevolutionary patterns may develop in parallel across widely distributed sympatric groups.

Keywords: comparative methods, phylogenetics, Varanus, trait evolution, character displacement

Figure 2. Body size among Varanus species varies across multiple orders of magnitude. Bar plots at tips of the tree show total length of sampled monitor lizards broken down into snout-vent length (SVL) and tail length. The smallest monitor species Varanus sparnus reaches just over 200 mm long from snout to tail tip and may weigh only 20 g, while the largest living species Varanus komodoensis can reach well over 2 meters long (2000+ mm) and top the scales at 100 kg (100,000 g). By all accounts, the recently extinct Varanus priscus was even larger than the Komodo dragon and may have reached over 4 m long (Wroe 2002; Conrad et al. 2012). Inset map shows a rough global distribution of monitor lizards and the extinct relative Saniwa ensidens. Colored circles at nodes indicate primary distribution of the major clades of Varanus and correspond to distributions on the map (blue–North America; green–Africa and the Middle East; light orange–Indian Subcontinent; dark orange–Indochina and China; red–Sundaland and Wallacea; purple–AustraloPapua).


Ian G. Brennan, Alan R. Lemmon, Emily Moriarty Lemmon, Daniel M. Portik, Valter Weijola, Luke Welton, Stephen C. Donnellan and J.Scott Keogh. 2020. Phylogenomics of Monitor Lizards and the Role of Competition in Dictating Body Size Disparity. Systematic Biology. syaa046. DOI: 10.1093/sysbio/syaa046