Sex- and performance-based escape behaviour in an Asian agamid lizard, Phrynocephalus vlangalii

Comparative metabolomics analysis reveals high-altitude adaptations in a toad-headed viviparous lizard, Phrynocephalus vlangalii

Extreme environmental conditions at high altitude, such as hypobaric hypoxia, low temperature, and strong UV radiation, pose a great challenge to the survival of animals. Although the mechanisms of adaptation to high-altitude environments have attracted much attention for native plateau species, the underlying metabolic regulation remains unclear. Here, we used a multi-platform metabolomic analysis to compare metabolic profiles of liver between high- and low-altitude populations of toad-headed lizards, Phrynocephalus vlangalii, from the Qinghai-Tibet Plateau. A total of 191 differential metabolites were identified, consisting of 108 up-regulated and 83 down-regulated metabolites in high-altitude lizards as compared with values for low-altitude lizards. Pathway analysis revealed that the significantly different metabolites were associated with carbohydrate metabolism, amino acid metabolism, purine metabolism, and glycerolipid metabolism. Most intermediary metabolites of glycolysis and the tricarboxylic acid cycle were not significantly altered between the two altitudes, but most free fatty acids as well as β-hydroxybutyric acid were significantly lower in the high-altitude population. This may suggest that high-altitude lizards rely more on carbohydrates as their main energy fuel rather than lipids. Higher levels of phospholipids occurred in the liver of high-altitude populations, suggesting that membrane lipids may undergo adaptive remodeling in response to low-temperature stress at high altitude. In summary, this study demonstrates that metabolic profiles differ substantially between high- and low-altitude lizard populations, and that these differential metabolites and metabolic pathways can provide new insights to reveal mechanisms of adaptation to extreme environments at high altitude.

Age structure and growth pattern of a high-altitude lizard population based on age determination by skeletochronology

Age determination provides crucial data regarding the life history of a species. Skeletochronology is considered to be a reliable method for age determination but is seldom applied to the genus Phrynocephalus (Agamidae) as it requires careful bone histological analysis to determine the formation of the lines of arrested growth (LAGs). We analyzed LAGs in different bones of Phrynocephalus vlangalii, a small, high-altitude lizard, and demonstrated that the phalanges are the best materials for skeletochronology in this species. We also found that the proximal half of the phalangeal diaphysis exhibits the most complete LAGs because of the unidirectional longitudinal growth of the phalange. Histologically, as the embryo bone that developed during the embryonic period was preserved even in very old individuals, no LAGs were eroded by endosteal resorption in the phalanges. The maximum age was 4 years for males and 5 years for females. It was determined that the age at maturity was 3 years for males and 2 or 3 years for females. On the basis of age determination, the age structures of both sexes were compared, and age-specific growth differences between the sexes were also analyzed. No differences in the snout-vent length were observed between sexes in any age group. However, the tail length of males aged 3 and above was significantly longer than that of females. Thus, the use of phalanges in the age determination of P. vlangalii is effective and can be widely applied to the ecological studies of this species as well as other small lizards.

Covariations between personality behaviors and metabolic/performance traits in an Asian agamid lizard (Phrynocephalus vlangalii)

Ecological factors related to predation risks and foraging play major roles in determining which behavioral traits may mediate life history trade-offs and, therefore, the pace-of-life syndrome (POLS) structure among behavioral, physiological, and life-history traits. It has been proposed that activity/exploration or risk-taking behaviors are more likely to impact resource acquisition for organisms (individuals, populations, and species) foraging on clumped and ephemeral food sources than for organisms foraging on abundant and evenly distributed resources. In contrast, vigilance or freezing behavior would be expected to covary with the pace of life when organisms rely on food items requiring long bouts of handling. Nevertheless, it remains unclear how general this pattern is. We tested this hypothesis by examining the associations between exploration/risk-taking behaviors and metabolic/performance traits for the viviparous agamid lizard, Phrynocephalus vlangalii. This species forages on sparse and patchy food sources. The results showed positive correlations between exploration and endurance capacity, and between bite force and risk-taking willingness. Our current findings, in conjunction with our previous work showed no correlations between freezing behavior and performance in this species, support the idea that behaviors in life-history trade-offs are natural history-dependent in P. vlangalii, and provide evidence that behavioral types play functional roles in life history trade-offs to supporting POLS hypothesis.

Comparability and repeatability of three commonly used methods for measuring endurance capacity

Measures of endurance (time to exhaustion) have been used to address a wide range of questions in ecomorphological and physiological research, as well as being used as a proxy for survival and fitness. Swimming, stationary (circular) track running, and treadmill running are all commonly used methods for measuring endurance. Despite the use of these methods across a broad range of taxa, how comparable these methods are to one another, and whether they are biologically relevant, is rarely examined. We used Australian water dragons (Intellagama lesueurii), a species that is morphologically adept at climbing, swimming, and running, to compare these three methods of endurance and examined if there is repeatability within and between trial methods. We found that time to exhaustion was not highly repeatable within a method, suggesting that single measures or a mean time to exhaustion across trials are not appropriate. Furthermore, we compared mean maximal endurance times among the three methods, and found that the two running methods (i.e., stationary track and treadmill) were similar, but swimming was distinctly different, resulting in lower mean maximal endurance times. Finally, an individual's endurance rank was not repeatable across methods, suggesting that the three endurance trial methods are not providing similar information about an individual's performance capacity. Overall, these results highlight the need to carefully match a measure of performance capacity with the study species and the research questions being asked so that the methods being used are behaviorally, ecologically, and physiologically relevant.

Escape strategy of Schreiber’s green lizards (Lacerta schreiberi) is determined by environment but not season or sex

Antipredator escape behaviour varies with several well-established sources of variation ranging from the physical environment to reproductive status. However, the relative roles of these sources are rarely assessed together. We measured (i) the distance to the nearest refuge that Schreiber’s green lizards, Lacerta schreiberi, maintained before an attack (refuge distance) and (ii) the distance lizards allowed a simulated predator to approach before fleeing (flight initiation distance, FID). Refuge distance was unaffected by studied variables. However, FID was positively related to refuge distance on grassy, but not on rocky substrates. Furthermore, refuge distance and escape angle interacted in a substrate-independent manner: lizards allowed predators close when refuges were close or when lizards had to flee towards the predator. In contrast, neither mating season nor sex affected FID. We suggest that the escape strategy of L. schreiberi is determined more by the physical environment than by sex or reproductive condition.