A review of sexual dimorphism of eye size in Colubroidea snakes

Eye size is interesting in snakes because in most species body length differs between the sexes, while the eye’s performance depends on its absolute size. So, does the smaller sex see less well? We hypothesized that eye sexual mensural dimorphism (SMD) would be smaller than Body SMD. We found among 26 snake populations that body length SMD was female biased in 47.6% and male biased in 38.1% of samples. Often the larger sex’s head was further enlarged but the SMD of absolute eye size was mitigated or annulled by the smaller sex’s eye being enlarged within the head, and the head enlarged relative to the body. Overall generally the SMD of eye size was smaller than body SMD. This accords with a hypothesis that eye size affects the evolution of head size and its SMD, both reflecting and emphasizing that absolute eye size is functionally important. Although Colubridae exceed Viperidae in length, Viperidae have larger eyes in absolute terms. In Colubridae the females have larger eyes and in Viperidae the males have larger eyes. Additionally we examine to what extent SMD in different characters is correlated, and briefly review other aspects of SMD, including some aspects of Rensch’s rule

Lizards and snakes from southwestern Asia, collected by Henry Field

Volume: 138Start Page: 327End Page: 40

Bergmann's and Rensch's rules and the spur-thighed tortoise (Testudo graeca)

WOS: 000371527800010Body size is an ecologically important variable in animals. The geographical size variation of most snakes and some lizards counters Bergmann's rule in that, among related taxa, the larger ones live at warmer latitudes. However, exceptions notwithstanding, and despite being ectothermic, turtles as a group tend to obey Bergmann's rule. We examined this idea in Testudo graeca, ranging from Morocco to Romania and to Iran with disputed systematics, both at the global scale (using literature) and within the focal area of Israel (using museum specimens). Both globally and locally, carapace length correlated with latitude, in accordance with Bergmann's rule. The scant data on reproduction fully support the hypothesis that Bergmann's rule enables larger clutches where the climate would limit repeated clutches. The sexual size dimorphism (SSD) was approached using two methodologies: (1) conventional', using globally literature data and locally museum samples and (2) innovated', using photographs of copulating tortoises from Israel and Turkey. By each methodology, SSD emerged as being male biased in the larger-bodied populations and female biased in the smaller-bodied populations, obeying Rensch's rule. Some observations support the hypothesis that the evolution of large males serves intermale combating. Finally, Rensch's rule was found to apply separately within Anatolia and within the Levant, possibly indicating that these populations are separate

Figure 1 in The northward extension of reptiles in the Palearctic, with the Jordan Valley (Israel) as a model: snakes outrace lizards (Reptilia: Squamata)

Figure 1. The geographical distribution of all records of lizards in the study area, solid circles. Also indicated are the approximate locations of some key localities for orientation, open squares.Published as part of Shacham, Boaz, Federman, Roy, Lahav-Ginott, Shimrit & Werner, Yehudah L., 2015, The northward extension of reptiles in the Palearctic, with the Jordan Valley (Israel) as a model: snakes outrace lizards (Reptilia: Squamata), pp. 1017-1033 in Journal of Natural History 50 on page 1021, DOI: 10.1080/00222933.2015.1083057, http://zenodo.org/record/399011

Figure 3 in The northward extension of reptiles in the Palearctic, with the Jordan Valley (Israel) as a model: snakes outrace lizards (Reptilia: Squamata)

Figure 3. The geographical distribution of all records of snakes in the study area, solid circles. Some key localities for orientation are shown in Figure 1.Published as part of Shacham, Boaz, Federman, Roy, Lahav-Ginott, Shimrit & Werner, Yehudah L., 2015, The northward extension of reptiles in the Palearctic, with the Jordan Valley (Israel) as a model: snakes outrace lizards (Reptilia: Squamata), pp. 1017-1033 in Journal of Natural History 50 on page 1023, DOI: 10.1080/00222933.2015.1083057, http://zenodo.org/record/399011