Daesik Park

Discrimination of conspecific sex and reproductive condition using chemical cues in axolotls (Ambystoma mexicanum)

Chemosensory cues play an important role in the daily lives of salamanders, mediating foraging, conspecific recognition, and territorial advertising. We investigated the behavioral effects of conspecific whole-body odorants in axolotls, Ambystoma mexicanum, a salamander species that is fully aquatic. We found that males increased general activity when exposed to female odorants, but that activity levels in females were not affected by conspecific odorants. Although males showed no difference in courtship displays across testing conditions, females performed courtship displays only in response to male odorants. We also found that electro-olfactogram responses from the olfactory and vomeronasal epithelia were larger in response to whole-body odorants from the opposite sex than from the same sex. In males, odorants from gravid and recently spawned females evoked different electro-olfactogram responses at some locations in the olfactory and vomeronasal epithelia; in general, however, few consistent differences between the olfactory and vomeronasal epithelia were observed. Finally, post hoc analyses indicate that experience with opposite-sex conspecifics affects some behavioral and electrophysiological responses. Overall, our data indicate that chemical cues from conspecifics affect general activity and courtship behavior in axolotls, and that both the olfactory and vomeronasal systems may be involved in discriminating the sex and reproductive condition of conspecifics.

Pheromones from Female Mosquitofish at Different Stages of Reproduction Differentially Affect Male Sexual Activity

Abstract Through a series of odor preference and sexual activity tests, the response of male western mosquitofish, Gambusia affinis, to female odors was investigated. Male mosquitofish prefer female odors to male odors and plain water, indicating that female odors function as a sex attractant. In odor preference tests, males did not show preferences among odors from nongravid, gravid, and parturient females. However, odors from females in different stages of the reproductive cycle induced different sexual activities from males. Odors from gravid females increased copulation trials, whereas those from parturient females increased male-male interactions without changing copulatory activity. These results suggest that (1) female western mosquitofish may produce sex pheromones and (2) female pheromones from different stages of the reproductive cycle stimulate different male sexual activities, suggesting that males may discriminate parturient females from others based on pheromonal output. In populations where the operational sex ratio (OSR) is female-biased, the discrimination of reproductive stages of females by males could increase male reproductive success by allowing males to avoid spending mating efforts with females whose eggs they are unlikely to fertilize.

F-series prostaglandin function as sex pheromones in the Korean salamander, Hynobius leechii

In order to test whether prostaglandins (PGs) function as sex pheromones in Hynobius leechii, a salamander that externally fertilizes its eggs, we conducted electro-olfactogram (EOG) studies with 19 PGs, liquid chromatography tandem mass spectrometry (LC-MS/MS) analyses of female and male holding waters, and behavioral tests on selected PGs. Of the 19 PGs tested, only three induced strong EOG responses from both males and ovulated females: 15-epi-prostaglandin F2alpha (15(R)-PGF2alpha), 15-keto-prostaglandin F2alpha (15K-PGF2alpha), and 13,14-dihydro-15-keto-prostaglandin F2alpha (13,14-dh-15K-PGF2alpha). In the LC-MS/MS studies, samples of holding water from ovulated females contained higher concentrations of 15(R)-PGF2alpha, PGF2alpha, and 13,14-dh-15K-PGF2alpha than those from males or oviposited females. In the behavioral tests, only 15(R)-PGF2alpha and ovulated female holding water induced significant reproductive behavior from male salamanders. These results suggest that F-series prostaglandins function as sex pheromones in amphibians.

Daily temperature fluctuations unpredictably influence developmental rate and morphology at a critical early larval stage in a frog

BackgroundEnvironmental temperature has profound consequences for early amphibian development and many field and laboratory studies have examined this. Most laboratory studies that have characterized the influence of temperature on development in amphibians have failed to incorporate the realities of diel temperature fluctuations (DTF), which can be considerable for pond-breeding amphibians.ResultsWe evaluated the effects of different ecologically relevant ranges of DTF compared with effects of constant temperatures on development of embryos and larvae of the Korean fire-bellied toad (Bombina orientalis). We constructed thermal reaction norms for developmental stage, snout- vent length, and tail length by fitting a Gompertz-Gaussian function to measurements taken from embryos after 66u2009hours of development in 12 different constant temperature environments between 14°C and 36°C. We used these reaction norms as null models to test the hypothesis that developmental effects of DTF are more than the sum of average constant temperature effects over the distribution of temperatures experienced. We predicted from these models that growth and differentiation would be positively correlated with average temperature at low levels of DTF but not at higher levels of DTF. We tested our prediction in the laboratory by rearing B. orientalis embryos at three average temperatures (20°C, 24°C, and 28°C) and four levels of thermal variation (0°C, 6°C, 13°C, and 20°C). Several of the observed responses to DTF were significantly different from both predictions of the model and from responses in constant temperature treatments at the same average temperatures. At an average temperature of 24°C, only the highest level of DTF affected differentiation and growth rates, but at both cooler and warmer average temperatures, moderate DTF was enough to slow developmental and tail growth rates.ConclusionsThese results demonstrate that both the magnitude of DTF range and thermal averages need to be considered simultaneously when parsing the effects of changing thermal environments on complex developmental responses, particularly when they have potential functional and adaptive significance.

Physical characteristics and age structure of Mongolian racerunner (Eremias argus; Larcertidae; Reptilia)

In this study, we have evaluated the physical characteristics of neonate, female, and male Mongolian racerunners (Er- emias argus) and determined the age structure of a population of the species in a field located in Taean-gun, Chungnam, South Korea. The physical parameters of females and males, including snout-vent length (SVL), head length, head width, and body mass were found to be significantly interrelated. Male Mongolian racerunners exhibited significantly longer heads than the females, but other physical parameters, such as SVL, head width, and body mass did not differ between the female and male specimens. In the study population, the females ranged in age from two to eleven years old and the males ranged between two to eight years of age. The number of females and males, when separated into different age classes, did not differ within each age class. Male Mongolian racerunners evidenced greater SVL growth coefficients than the females, but asymptotic SVL did not differ between the females and males.

Habitat Use and Home Range of the Endangered Gold-Spotted Pond Frog (Rana chosenica)

Abstract Because of their complex life styles, amphibians and reptiles living in wetlands require both aquatic and terrestrial buffer zones in their protected conservation areas. Due to steep declines in wild populations, the gold-spotted pond frog (Rana chosenica) is listed as vulnerable by the IUCN. However, lack of data about its movements and use of habitat prevents effective conservation planning. To determine the habitat use and home range of this species, we radio-tracked 44 adult frogs for 37 days between 10 July and 4 Nov. 2007 to observe three different populations in the breeding season, non-breeding season, and late fall. The gold-spotted pond frog was very sedentary; its daily average movement was 9.8 m. Frogs stayed close to breeding ponds (within 6.6 m), and did not leave damp areas surrounding these ponds, except for dormancy migration to terrestrial sites such as dried crop fields. The average distance of dormancy migration of seven frogs from the edge of their breeding ponds was 32.0 m. The average size of an individual’s home range was 713.8 m2 (0.07 ha). The year-round population home range, which accounts for the home ranges of a population of frogs, was determined for two populations to be 8,765.0 m2 (0.88 ha) and 3,700.9 m2 (0.37 ha). Our results showed that to conserve this endangered species, appropriately sized wetlands and extended terrestrial buffer areas surrounding the wetlands (at least 1.33 ha, diameter 130 m) should be protected.

Male Salamanders Hynobius leechii Respond to Water Vibrations via the Mechanosensory Lateral Line System

Abstract To test the hypothesis that male Korean salamanders, Hynobius leechii, respond to water vibrations via the mechanosensory lateral line system, we conducted a series of experiments. First, we examined behavioral responses of males to 0, 0.5, 1.0, and 1.5 Hz water vibrations generated by a model salamander, and we measured the number of times the males (1) oriented their heads toward the vibrating model; (2) approached within a 15-cm–diameter circle centered on the cloaca of the model; and (3) touched the model, as well as (4) the length of time the male stayed within the circle. To determine whether the mechanosensory lateral line system mediated these responses, we measured the same behavioral responses to 1.0 Hz water vibrations (1) both with and without a transparent vibration blocker placed between the model and test males, and (2) after exposing the test males to 0, 0.1, 0.5, and 1.0 mM concentrations of cobalt chloride for 1 h to disrupt the mechanosensory lateral line system. Test males showed significant responses to water vibrations from the model regardless of the vibration frequencies. Males showed significantly lower responses when a vibration blocker was placed and after cobalt chloride treatments. These results indicate that H. leechii males respond to water vibrations via the mechanosensory lateral line system. In addition, we describe aspects of the body undulation of mating males. This is the first clear result in urodeles that the mechanosensory lateral line system plays a role in male-male mating competition.

Chemical signals and vomeronasal system function in axolotls (Ambystoma mexicanum)

We are studying the anatomy and physiology of the olfactory and vomeronasal systems in axolotls with the goal of determining the behavioral functions of these two chemosensory systems in aquatic amphibians. Our anatomical studies demonstrate that the vomeronasal epithelium of axolotls is much like that of other tetrapods. Other studies indicate that the projections from the olfactory and vomeronasal epithelia into the central nervous system are separate through several synapses, suggesting that these chemosensory systems serve different functions. Our electrophysiological experiments have not revealed striking differences in odorant responsivity between the olfactory and vomeronasal epithelia, but we are just beginning to work in this area and cannot draw yet strong conclusions about the relative quality or strength of odorant responses in these sensory epithelia. We have begun to show that odorant cues play a role in both foraging and in social behavior in axolotls; we hope that by combining neurobiological and behavior studies, we will be able to fully understand the ways in which chemosensory stimuli are processed to mediate behavior in axolotls. Given that separate olfactory and vomeronasal systems are present in amphibians and in amniotes, the vomeronasal system must have been present in the last common ancestor of these two groups, and this animal is now thought to have been fully aquatic (Panchen, 1991; Lebedev and Coates, 1995). An understanding of the function of the vomeronasal system in aquatic amphibians may help shed light on the factors that led to the evolutionary origin of the vomeronasal system.

Habitat use and Movement Patterns of the Viviparous Aquatic Snake, Oocatochus rufodorsatus, from Northeast Asia

To determine the habitat usage and movement patterns of the viviparous aquatic snake Oocatochus rufodorsatus (formerly Elaphe rufodorsata), we radio-tracked 21 snakes on agricultural lands during two active seasons in 2007 and 2008. Male and female snakes stayed close to aquatic habitats such as paddy fields and agricultural ponds during both breeding and non-breeding periods, except when the snakes moved to dry terrestrial areas to hibernate in late fall. The use of different structural features in the habitat, such as ground, tree, underground, and water, varied depending on the air and water temperatures, females reproductive conditions, and the time of day. Male and female snakes moved about 17 m daily and postpartum females moved farther than antepartum females. The home ranges of males and females were 0.45 ha and 0.47 ha, respectively, and the year-round home range of this species was approximately 1.54 ha (95% fixed kernel). Thus, to conserve a population of O. rufodorsatus in our study area, areas including both aquatic and terrestrial habitats within a radius of 150 m from a core pond habitat must be preserved.

Skeletochronological Age Determination and Comparative Demographic Analysis of Two Populations of the Gold-spotted Pond Frog (Rana chosenica)

To obtain demographic information on threatened gold-spotted pond frog (Rana chosenica Okada, 1931) populations, we determined the ages of 45 male and 13 female frogs (20 males and 9 females from Cheongwon and 25 males and 4 females from Tae-an) and compared the age structures and growth patterns of the two populations in 2006. The snout-vent length (SVL) and body weight of female frogs were greater than those of male frogs in both populations. Male frogs` ages ranged 2 to 7 years old and females` ages ranged 3 to 6 years old. In both populations, 4 years old male frogs were the most abundant age-sex class. The age structures of the two populations were significantly different and the growth coefficients of male frogs from the Cheongwon population were greater than those from the Tae-an population. The mean age of males from the Tae-an population was higher than that from the Cheongwon population. However, the SVL and body weights of male frogs were not different between two populations and there was no difference between the two populations in the mean male SVL at any age. The results could increase our understanding of the life-history of this threatened frog and may be useful in conservation planning.