Morphometric and genetic divergence in island and mainland populations ofAnolis nebulosus(Squamata: Polychrotidae) from Jalisco (Mexico): an instance of insular gigantism

Abstract

The clouded anole Anolis nebulosus (Squamata: Polychrotidae) is widespread on the Pacific coast of Mexico. The species also inhabits Don Panchito, a small islet located near the coast of the Chamela-Cuixmala Biosphere Reserve in the state of Jalisco. We studied the extent of intraspecific differences in morphology (absolute size and body proportions) and in mtDNA sequences (16S and NDH2) between the population living on the islet (N = 18 for morphometry; N = 12 for mtDNA) and the one on the facing mainland (N = 38 for morphometry; N = 16 for mtDNA). The individuals on the islet are larger than those on the mainland with little overlap in size for either males (islet: 52.79 ± 1.82 mm; mainland: 40.96 ± 2.99 mm) or females (islet: 46.18 ± 3.24 mm; mainland 37.14 ± 2.13 mm). The presence of insular gigantism, as here found in A. nebulosus, seems uncommon in the genus and could be explained as a combination of low predation pressure and higher intraspecific competition on the island. Moreover, we found that sexual dimorphism (SD) is higher in the island population than in the mainland one. The molecular analysis shows the absence of shared haplotypes between the island and mainland populations. Ten mtDNA haplotypes belonged to the mainland population and three to the island population. The shape of the minimum spanning network and of the mismatch distribution indicates a single colonization event. These molecular data indicate a certain degree of isolation of the island population notwithstanding its proximity to the coast. The morphological characteristics of the anoles on Don Panchito match with the expectation of the so-called "reversed island syndrome" theory, which predicts an increased body size and sexual dimorphism in lizards living on very small islands characterized by unpredictable environmental conditions.

Skin sheds as a useful DNA source for lizard conservation

“…Fitch dimorphism in A. nebulosus pooled across several populations in Mexico, and concluded that the species was the only mainland anole not However, Fitch and Hillis (1984) documented other mainland anoles that also lack sexual size dimorphism in SVL is also consistent with a previous study that found that male and female A. nebulosus growth rates in populations from Jalisco, Mexico (Siliceo-Cantero and García 2014). These results contrast with those of Senczuk et al (2014) who found that males in populations of A. nebulosus in Jalisco, Mexico were larger than females in SVL (especially in an island population), females had greater relative trunk length, and males had longer and wider heads, and there was no difference in femur length or tibia length. Jenssen (1970a) also found that male A. nebulosus were larger than females in a population from Nayarit, at least in the spring.…”

“…The growth, body size, and morphology from island and mainland populations in Jalisco, Mexico have been compared (Senczuk et al 2014, SiliceoCantero andGarcía 2014, Hernández-Salinas andRamírez-Bautista in press). Some previous work found no evidence of sexual size dimorphism in A. nebulosus (Fitch 1976), whereas others found that males are larger than females (Jenssen 1970a, Senczuk et al 2014. Ramírez-Bautista and Vitt (1997) and Hernández-Salinas and Ramírez-Bautista (in press) have described the reproduction of this species from Jalisco.…”

“…In particular, it appears that the island populations (see Senczuk et al 2014, Siliceo-Cantero andGarcía 2014, Hernández-Salinas and Ramírez-Bautista in press) differ from the mainland populations. Additional studies on both on island and mainland populations of A. nebulosus throughout its range are needed to determine the extent of variation in ecological and reproductive traits in the species, as well as to examine the underlying ecological and evolutionary causes of such variation.…”

Dimorphism and divergence in island and mainland Anoles

“…Senczuk et al . () also genetically analysed San Agustín and mainland Ch‐CBR A. nebulosus and found that the island population likewise exhibited reduced genetic variation relative to the mainland. That study, which utilized only mtDNA from a smaller sample of individuals, also failed to detect haplotype sharing between island and mainland populations.…”

“…Besides the research reported here, and related work by Senczuk et al . (), Siliceo‐Cantero & Garcia () and Hernandez‐Salinas, Ramirez‐Bautista & Pavon (), only two other studies have compared the adaptive divergence of an island Anolis population with an ancestral mainland population (Klutsch et al ., ; Logan et al ., ). Both of these latter studies focused on Anolis lemurinus in the Bay Islands of Honduras, and morphological comparisons were limited to dewlap and body size.…”