The geographical diversification in varanid lizards: the role of mainland versus island in driving species evolution

Abstract

Monitor lizards (Varanidae) inhabit both the mainland and islands of all geological types and have diversified into an exceptionally wide range of body sizes, thus providing an ideal model for examining the role of mainland versus island in driving species evolution. Here we use phylogenetic comparative methods to examine whether a link exists between body size-driven diversification and body size-frequency distributions in varanid lizards and to test the hypothesis that island lizards differ from mainland species in evolutionary processes, body size, and life-history traits (offspring number and size). We predict that: 1) since body size drives rapid diversification in groups, a link exists between body size-driven diversification and body size-frequency distributions; 2) because of various environments on island, island species will have higher speciation, extinction, and dispersal rates, compared with mainland species; 3) as a response to stronger intraspecific competition, island species will maximize individual ability associated with body size to outcompete closely-related species, and island species will produce smaller clutches of larger eggs to increase offspring quality. Our results confirm that the joint effect of differential macroevolutionary rates shapes the species richness pattern of varanid lizards. There is a link between body size-driven diversification and body size-frequency distributions, and the speciation rate is maximized at medium body sizes. Island species will have higher speciation, equal extinction, and higher dispersal rates compared with mainland species. Smaller clutch size and larger hatchling in the island than in mainland species indicate that offspring quality is more valuable than offspring quantity for island varanids.

Competition and geography underlie speciation and morphological evolution in Indo‐Australasian monitor lizards

“…2A, B), congruent with previous work showing increased speciation rates in insular varanids (Zhu et al. 2020). The unguided approach used to search for rate shifts detected a positive shift in the indicus group, which has colonized numerous islands in the Pacific (Weijola et al.…”

In “defense” of Podarcis latastei, an Italian insular endemic species (Squamata: Lacertidae)

“…Instead, we think that the insularity itself of P. latastei is very important in order to affirm its specific status. In fact, it is widely recognized that islands represent a set of particular conditions for which evolution is accelerated with a large number of studies focusing on lizards (e.g., Herrel et al, 2008;Raia et al, 2010;Senczuk et al, 2014;de Amorim et al, 2017;Anderson and Poe, 2019;Zhu et al, 2020). The time of isolation of P. latastei, has been estimated around 4 million years (Senczuk et al, 2019), in agreement with the genesis and geological evolution of these islands (Cadoux et al, 2005).…”

A simple island biodiversity model is robust to trait dependence in diversification and colonization rates

“…Oceanic islands are home to some of the most extraordinary radiations, such as Darwin’s finches (Losos and Ricklefs, 2009) and a key question is whether certain traits or trait states have played a role in the presence or absence of rapid radiations. While insular radiations are thought to be mostly driven by increased ecological opportunity on islands, it has long been hypothesized that some traits may trigger, facilitate or hinder diversification in an insular setting (García-Verdugo et al, 2014; Zhu et al, 2020). Some characteristics of species, such as seed size in plants and flight ability in birds, evidently affect the chances of species colonizing an island or an isolated habitat (Onstein et al, 2017).…”