Comparative morphology and trophic ecology in a population of the polymorphic lizard Sceloporus minor (Squamata: Phrynosomatidae) from central Mexico

Abstract

Polymorphism among individuals of the same population has generally been linked to alternative reproductive tactics, where different morphs can exhibit differences in their morphological, ecological, and behavioral attributes. These differences may result in a divergence in diet between morphs due to differential exploitation of habitat, morphological differences that influence prey selection, or differential energy expenditure that results in different nutritional needs. The present study analyzes the morphology (morphometry and body mass) and diet of red and yellow male morphs in a population (El Enzuelado) of the lizard Sceloporus minor from central Mexico. No differences between morphs were found for any of the morphometric variables analyzed (snout-vent length, tail length, jaw length, jaw width, head length, head width, head height, tibia length, femur length, forearm length and ventral patch length). In both morphs, allometric growth was observed in all body features analyzed, as well as in morphometric features of the head across seasons. Analysis of stomach contents showed that the diet of red males was composed of 12 categories of prey, while that of yellow males was composed of 10 categories; those categories of diet not shared between morphs (e.g., Isoptera, Psocoptera) were consumed by their respective morph in very low proportions. Categories of diet with the highest values of food importance for both groups were Coleoptera, Orthoptera, and leaves; a similar pattern was seen across seasons. This, in turn, is reflected in low niche breadth values for each morph and a very high niche overlap. There were no significant differences between morphs overall, or between morphs per season, in the weight and volume of stomach contents or in the number of prey items found in stomachs; however, differences in these variables across all males (independent of morph) were recorded between seasons. Likewise, no significant correlations were found between body size (snout-vent length) and the volume of stomach contents for either morph or between lizard mandibular dimensions and the volume of stomach contents for red morph males. For the yellow morph, prey volume unexpectedly decreased significantly with jaw size rather than increasing as expected. Overall, this study adds new information about the morphology and feeding of males in this species, and suggests that in this population, color morphs lack the morphological and ecological differences found in some other species of polymorphic lizard.

Female choice and male aggression in the polymorphic lizard Sceloporus minor

“…In contrast, the possible function of polymorphic male dorsal coloration in S. minor remains unresolved (García-Rosales et al, 2017;Stephenson, 2010). Previous studies have argued that maintenance of the color polymorphism in this population is probably not due to niche partitioning (García-Rosales, Ramírez-Bautista, & Stephenson, 2019;García-Rosales et al, 2021); furthermore, in this study, we found no effect of the polymorphism on female choice or degree of male aggressiveness. Therefore, fieldbased studies of reproductive physiology and behavior are needed to evaluate the proportion of morphs over a longer period of time, since the polymorphism in this population could be explained by at least two hypotheses: (1) the morphs are maintained by their different reproductive qualities, and each morph is evolutionarily stable, or (2) the maintenance of these morphs at this site is due to frequency-dependent selection, where the fitness of a morph depends on the frequencies of the other morphs with which it competes (Pryke et al, 2007;Sinervo & Lively, 1996).…”

“…For example, Bastiaans et al (2013) noted that in studies of lizards with discrete red or orange morphs, field experiments have found increased aggression in these color morphs as compared to others (Olsson et al, 2007;Sinervo & Lively, 1996), whereas studies conducted in the laboratory or semi-natural enclosures have found that individuals with orange coloration show a decrease in aggressiveness (Bastiaans et al, 2013). However, earlier work evaluating aggressive behavior of male S. minor in the field showed greater aggressiveness of the yellow morph as compared to the red morph (García-Rosales et al, 2021), in contrast to the pattern reported by Bastiaans et al (2013) in S. grammicus.…”

“…Tests were performed outdoors in a rectangular-shaped arena (0.8 m wide × 1.6 m long × 0.5 m high; Figure 2), placed directly on the natural soil of the study area. As before, given that there is no standard rule for arena size, we used an arena slightly larger than that used by Bastiaans et al (2013) with S. grammicus, given that adult male S. minor are somewhat larger than adult male S. grammicus (García-Rosales, Ramírez-Bautista, & Stephenson, 2019;Ramírez-Bautista et al, 2009). The sand was divided into two halves by a vertical wooden partition positioned at the midpoint; each trial began when this partition was removed.…”

“…In lizards, color polymorphism has been linked to variation in behavioral tactics in several species, with certain colors associated with more aggressive behavior of males as compared to the corresponding conspecific morph(s) (Sinervo & Lively, 1996;Thompson & Moore, 1991, 1992. Likewise, these morphs can differ in body size, life history traits, physiology, and size of territory and/or home range, among other characteristics (García-Rosales, Ramírez-Bautista & Stephenson, 2019;García-Rosales et al, 2021;Lattanzio & Miles, 2016;Sinervo & Lively, 1996;Thompson & Moore, 1991).…”

Caudal autotomy among populations of the lizard Sceloporus variabilis (Squamata: Phrynosomatidae) in contrasting environments

“…Regarding sexes, it has been observed that males generally show a higher frequency of tail loss compared to females, which has been related to the greater exposure of males during courtship and mating (García-de la Peña et al, 2004;García-Rosales & Martínez-Coronel, 2016;Leyte-Manrique et al, 2007). Furthermore, in some species of lizards, males are more colourful than females and are therefore more visible to predators (García-Rosales et al, 2021).…”