Sexual size dimorphism and life history traits in an island-mainland system: an overview of the lizard genus Microlophus

Abstract

Opposing life history strategies are a common result of the different ecological settings experienced by insular and continental species. Here we present a comprehensive compilation of data on sexual size dimorphism (SSD) and life history traits of Microlophus, a genus of lizards distributed in western South America and the Galápagos Islands, and test for differences between insular and continental species under life history theory expectations. Contrary to our predictions, we found no differences in SSD between localities or evidence that Microlophus follows Rensch’s rule. However, as expected, head dimensions and maturity sizes were significantly larger in insular species while continental species had larger clutches. Our results show that Microlophus exhibits some of the patterns expected from an island-mainland system, but unexplained patterns will only be resolved through future ecological, morphological and behavioural studies integrating both faunas.

Bergmann’s rule inMicrolophuslizards: testing for latitudinal and climatic gradients of body size

“…This strong association was explained by a "reproductive selection hypothesis" which states that females lay more clutches throughout the year in aseasonal habitats, resulting in stronger sexual selection on males as the benefits of controlling territories are higher when reproduction is continuous (Machado et al, 2016). Our results showed that the body size-latitude relationships were not different between males and females, indicating that patterns of sexual size dimorphism in Microlophus are not being driven by different latitudinal gradients of male and female body size and support previous results indicating no evidence of Rensch's rule in Microlophus lizards (Toyama and Boccia, 2021). Additionally, our results suggest that the latitudinal gradients of body size in Microlophus probably do not depend on latitudinal gradients of sexual selection acting on males as expected based on the "reproductive selection hypothesis".…”

“…These dynamics can result in what is termed the "island rule", the tendency of small and large taxa to exhibit trends towards gigantism and dwarfism on islands, respectively (Meiri, 2007). A previous comparison between island and mainland Microlophus species showed no differences between the average body sizes of these two groups (Toyama and Boccia, 2021), contradicting the expectations of the island rule.…”

“…We used body size data recently compiled by Toyama and Boccia (2021). These data are based on maximum SVLs reported in the literature for males and females for each Microlophus species.…”

“…Microlophus is a genus of diurnal and omnivorous iguanian lizards that includes 13 continental species distributed along the western coast of South America (Figure 1) and a radiation of 10 species within the Galápagos archipelago. All species show male-biased sexual size dimorphism, with maximum snout-vent lengths (SVL) ranging from 80 to 155 mm in males and from 65 to 116 mm in females (Toyama and Boccia, 2021). On the mainland, Microlophus species span ~30 degrees of latitude and inhabit different ecosystems including dry forests, intertidal rocky shores and seasonal oases (Dixon and Wright, 1975;Quispitúpac and Pérez, 2008).…”

When Rensch meets Foster: insular gigantism may reduce sexual dimorphism in anurans

“…In turn, sexual dimorphism itself may also influence the outcome of the Island rule. To date, very few studies have formally tested for the validity of Rensch's rule within the context of body‐size evolution in insular settings, and those that did found diverging patterns (Anaya‐Meraz and Escobedo‐Galván 2020, Avramo et al 2021, Toyama and Boccia 2021).…”