Development of sexual dimorphism in two sympatric skinks with different growth rates

Abstract

Sexual size dimorphism (SSD) is widespread in animals, especially in lizards (Reptilia: Squamata), and is driven by fecundity selection, male–male competition, or other adaptive hypotheses. However, these selective pressures may vary through different life history periods; thus, it is essential to assess the relationship between growth and SSD. In this study, we tracked SSD dynamics between a “fading‐tail color skink” (blue tail skink whose tail is only blue during its juvenile stage: Plestiodon elegans ) and a “nonfade color” tail skink (retains a blue tail throughout life: Plestiodon quadrilineatus ) under a controlled experimental environment. We fitted growth curves of morphological traits (body mass, SVL, and TL) using three growth models (Logistic, Gompertz, and von Bertalanffy). We found that both skinks have male‐biased SSD as adults. Body mass has a higher goodness of fit (as represented by very high R 2 values) using the von Bertalanffy model than the other two models. In contrast, SVL and TL for both skinks had higher goodness of fit when using the Gompertz model. Two lizards displayed divergent life history tactics: P. elegans grows faster, matures earlier (at 65 weeks), and presents an allometric growth rate, whereas P. quadrilineatus grows slower, matures later (at 106 weeks), and presents an isometric growth rate. Our findings imply that species‐ and sex‐specific trade‐offs in the allocation of energy to growth and reproduction may cause the growth patterns to diverge, ultimately resulting in the dissimilar patterns of SSD.

Reproductive traits and change in body shape of neonates in the Oak Forest Skink, Plestiodon lynxe

“…While active, they are constantly on the move in search of food, and many aspects of their ecology, such as habitat use, types of prey they consume, and predators and anti‐predatory strategies, are expected to differ markedly from those of adults (Morafka et al, 2000; Vitt, 2000). In particular, in many Plestiodon species, including P. lynxe , the tail of neonates or hatchlings is bright blue, while this colour is lost or less conspicuous in adults (Hawlena et al, 2006; Yang et al, 2019) and, at least in some species, this difference in colour has been shown to imply a difference in their anti‐predatory strategies (Cooper Jr. & Vitt, 1985; Vitt & Cooper Jr., 1986b). In neonates, which are constantly on the move, the striking blue colour deflects predatory attacks towards the tail, while adults, who tend to be more sedentary, often rely on camouflage to avoid predation.…”

DIMORFISMO SEXUAL EN TAMAÑO Y FORMA EN UNA POBLACIÓN DE ESCÍNCIDOS DE COLA AZUL DEL GÉNERO Plestiodon (SCINCIDAE)

“…Esta tendencia también ocurre en Plestiodon. En la mayoría de las especies de escíncidos de cola azul estudiadas hasta la fecha un sexo es más grande que el otro (Breckenridge, 1943;Vitt y Cooper, 1985;Vitt y Coper, 1986;Huang, 1996;Du y Ji, 2001;Hikida et al, 2001;Yang et al, 2019) y hasta donde sabemos solo se conocen dos especies de Plestiodon monomórficas con respecto al tamaño corporal, P. fasciatus (Vitt y Cooper, 1986) y P. sp (el presente estudio).…”

“…En las especies estadounidenses P. septentrionalis, P. inexpectatus y P. laticeps los machos son más grandes que las hembras, si bien P. fasciatus es monomórfica en este aspecto (Breckenridge, 1943;Vitt y Cooper, 1985;Vitt y Cooper, 1986). Asimismo, se ha encontrado DST, con machos más grandes que las hembras, en las especies asiáticas P. chinensis, P. quadrilineatus, P. elegans, P. latiscustatus y P. tamdaoensis (Lin y Ji, 2000;Huang, 1996;Du y Ji, 2001;Hikida et al, 2001;Yang et al, 2019). En todas las especies estadounidenses y asiáticas señaladas anteriormente los machos tienen cabezas más grandes que las hembras y en la mayoría de ellas se han registrado combates y encuentros agresivos entre los machos, lo que ha conducido a asumir que el dimorfismo sexual en el tamaño de la cabeza es consecuencia de la selección sexual (Vitt y Cooper, 1985;Vitt y Cooper, 1986;Huang, 1996;Du y Ji, 2001).…”

Ontogenetic color change in the tail of blue‐tailed skinks (Plestodion elegans)

“…These factors vary and are uncontrolled in the wild, and may influence ontogenetic color changes. Third, obvious differences exist in the growth rules between the sexes of skink (Yang et al, 2019 ); however, it is unclear how the tails of different sexes vary in terms of ontogenetic color change.…”

“…These factors vary and are uncontrolled in the wild, and may influence ontogenetic color changes. Third, obvious differences exist in the growth rules between the sexes of skink (Yang et al, 2019); however, it is unclear how the tails of different sexes vary in terms of ontogenetic color change. Therefore, we selected the small fade-tail skink (blue-tailed skink: Plestiodon elegans) to analyze the slow color change in its tail in the laboratory.…”