The Herpetological Journal

Authors: Anh Van Pham, Truong Quang Nguyen, Cuong The Pham & Minh Duc Le

Abstract: The Lao sucker frog Amolops cremnobatus is known from Laos and Vietnam while the chloronate huia frog Odorrana chloronota has been recorded from Bangladesh, China, India, Laos, Myanmar, Thailand and Vietnam. However, the diet of the two species is still poorly understood. In this study, we investigate the diet composition and niche overlap in the two species living in sympatry at three streams in Vu Quang National Park, Ha Tinh Province, Vietnam. We use the stomach-flushing method to obtain the stomach contents of 83 individuals, including 51 of A. cremnobatus and 32 of O. chloronota. In total, 21 prey categories from 101 food items of invertebrates, and 18 prey categories from 103 food items of invertebrates are identified in the diet of A. cremnobatus and O. chloronota, respectively. Generally, A. cremnobatus consume more diverse prey types than those taken by O. chloronota, and beetles, cockroaches, grasshoppers and crickets represented the most important prey categories in both species. Our results also strongly corroborate the gape hypothesis by demonstrating that O. chloronata with a larger body size can ingest both larger prey items and greater food volumes. Furthermore, our findings show that body size and foraging behaviour play a significant role in selecting prey categories between the sympatric frog species.

Keywords: amphibian, gape hypothesis, niche overlap, prey types, stomach contents

Authors: Gumma Kubo & Akira Mori

Abstract: Several animals advertise their escape performance toward potential predators and convey their unprofitability as prey by exhibiting pursuit-deterrent displays. Foot shakes, which are exhibited by lizards in response to potential predators, are considered as a pursuit-deterrent signal. This pursuit-deterrent signal is thought to be either perception advertisement, indicating the detection of a predator, or quality advertisement, informing the individualʼs condition. However, it remains unclear what foot shakes advertise to predators. To address this, we conducted a field experiment using the Japanese grass lizard Takydromus tachydromoides, which is known to perform foot shakes. To simulate a predator, we approached the lizards, and measured our distance from the lizards when first spotted (starting distance) as well as the distance between the lizards and us when they fled (flight initiation distance). We also recorded the presence or absence of foot shakes and their distance from us when they initiated the display (display distance). Tested lizards were captured whenever possible and snout-vent length (SVL), sex and body temperature (Tb) were recorded. In 151 approaches, 43 lizards exhibited foot shakes. Approximately half of the lizards displayed foot shakes with display distance between 1 m and 2 m, but none at closer distance. These results align with those observed in foot shakes of other lizards, which are considered as a pursuit-deterrent signal, and are consistent with pursuit-deterrent theory. SVL and Tb had a positive correlation with the probability of foot shakes, and males performed foot shakes more frequently than females. Because SVL and Tb are well known to influence the escape performance of lizards, and sex potentially influences the performance, our results suggest that foot shakes of T. tachydromoides advertises the quality of the lizard rather than the perception of predators.

Keywords: predator-prey interaction, pursuit-deterrence, antipredator signal, visual display, Lacertidae

Authors: Gumma Kubo & Akira Mori