Yeong-Choy Kam

A skeletochronological study on a subtropical, riparian ranid (Rana swinhoana) from different elevations in Taiwan.

Abstract We estimated the age, longevity, and growth patterns of a subtropical ranid, Rana swinhoana from high (Lishing) and low (Wulai) elevations using skeletochronology. In addition, we also measured body mass and length of frogs from five other localities. Results showed that both snout-vent length and body mass of frogs were significantly correlated with altitudes for both sexes. Frogs of Lishing were significantly larger and older than that of Wulai. We used LAGs to estimate the age and growth of frogs and found that the growth of Wulai frog of both sexes slowed down at an earlier age than that of Lishing frogs. Male and female frogs from Wulai did not exceed 6 and 7 years, respectively, while the maximum age of males and females of Lishing was 7 and 11 years, respectively. Results suggest that the LAGs observed in R. swinhoana correspond to low temperature and/or decreased food availability instead of desiccation during the harsh annual period (November to February). Skeletochronological data suggest that the variations of body size of R. swinhoana among elevations are likely associated with the growth, age at sexual maturity, and longevity.

Thermal Physiology and Reproductive Phenology of Buergeria japonica (Rhacophoridae) Breeding in a Stream and a Geothermal Hotspring in Taiwan

Abstract We compared the reproductive phenology and tadpole thermal physiology of two populations of Buergeria japonica in Taiwan. The population in Jentse breeds in a geothermal hot spring whose water is a warm, over 35°C year-round, whereas the population in Chukou breeds in a stream whose water temperature is closely correlated with fluctuations in air temperature and averages 23°C. The B. japonica population in Jentse breeds year-round, but the Chukou population breeds only from March to October. Tadpoles from Jentse that reared at 32°C attained larger sizes than tadpoles from Chukou that reared at 32°C, whereas tadpoles from both sites attained similar body size when reared at 22°C. Chukou tadpoles reared at 40°C died within 1–2 d, whereas Jentse tadpoles survived for 9 d at 40°C. All tadpoles tolerated heat well, but Jentse tadpoles had higher critical thermal maxima (CTMax) than Chukou tadpoles. Tadpoles from Jentse showed no metabolic compensation but those from Chukou showed an “inverse” metabolic compensation. Results suggest that B. japonica that breed in the geothermal hot spring has a prolonged breeding season, high growth rates and the reduction or absence of intra- and inter-specific competition. Evolution of a high level of heat tolerance and, possibly, behavioral temperature selection, enable tadpoles in the hotsprings to offset the thermal stress imposed by warm water.

Irreversibility of a bad start: early exposure to osmotic stress limits growth and adaptive developmental plasticity

Harsh environments experienced early in development have immediate effects and potentially long-lasting consequences throughout ontogeny. We examined how salinity fluctuations affected survival, growth and development of Fejervarya limnocharis tadpoles. Specifically, we tested whether initial salinity effects on growth and rates of development were reversible and whether they affected the tadpoles’ ability to adaptively accelerate development in response to deteriorating conditions later in development. Tadpoles were initially assigned to either low or high salinity, and then some were switched between salinity levels upon reaching either Gosner stage 30 (early switch) or 38 (late switch). All tadpoles initially experiencing low salinity survived whereas those initially experiencing high salinity had poor survival, even if switched to low salinity. Growth and developmental rates of tadpoles initially assigned to high salinity did not increase after osmotic stress release. Initial low salinity conditions allowed tadpoles to attain a fast pace of development even if exposed to high salinity afterwards. Tadpoles experiencing high salinity only late in development metamorphosed faster and at a smaller size, indicating an adaptive acceleration of development to avoid osmotic stress. Nonetheless, early exposure to high salinity precluded adaptive acceleration of development, always causing delayed metamorphosis relative to those in initially low salinity. Our results thus show that stressful environments experienced early in development can critically impact life history traits, having long-lasting or irreversible effects, and restricting their ability to produce adaptive plastic responses.

Effects of Salinity on the Survival, Growth, Development, and Metamorphosis of Fejervarya limnocharis Tadpoles Living in Brackish Water

We studied salinity tolerance and the effects of salinity on growth, development, and metamorphosis in Fejervarya limnocharis tadpoles living in brackish water. Specifically, we examined whether tadpoles exhibit adaptive plasticity in development when exposed to different salinities. Tadpoles collected on Green and Orchid Islands off Southeastern Taiwan were assigned to salinities of 0, 3, 5, 7, 9, 11, and 13 parts per thousand (ppt). The daily survival, weekly growth, and development of tadpoles were recorded until metamorphosis. More than 50% of tadpoles survived in 9 ppt for over a month, and a few individuals survived in 11 ppt for 20 days, suggesting that F. limnocharis tadpoles tolerate salinity better than the tadpoles of most species studied to date. Tadpoles at 9 ppt had lower survivorship, and retarded growth and development (from Gosner stage 26 to 35) compared to the other treatments. Tadpoles metamorphosed early at a smaller size as salinity increased, suggesting the existence of adaptive developmental plasticity in F. limnocharis in response to osmotic stress. Phenotypic plasticity in the age and size at metamorphosis in response to salinity may provide a means for tadpoles to adapt to the unpredictable salinity variation in coastal rock pools.

Salinity acclimation enhances salinity tolerance in tadpoles living in brackish water through increased Na+, K+-ATPase expression

Amphibians are highly susceptible to osmotic stress but, nonetheless, some species can adapt locally to withstand moderately high levels of salinity. Maintaining the homeostasis of body fluids by efficient osmoregulation is thus critical for larval survival in saline environments. We studied the role of acclimation in increased physiological tolerance to elevated water salinity in the Indian rice frog (Fejervarya limnocharis) tadpoles exposed to brackish water. We quantified the effects of salinity acclimation on tadpole survival, osmolality, water content, and gill Na⁺ , K⁺ -ATPase (NKA) expression. Tadpoles did not survive over 12 hr if directly transferred to 11 ppt (parts per thousand) whereas tadpoles previously acclimated for 48 hr in 7  ppt survived at least 48 hr. We reared tadpoles in 3 ppt and then we transferred them to one of (a) 3 ppt, (b) 11  ppt, and (c) 7  ppt for 48 hr and then 11 ppt. In the first 6 hr after transfer to 11 ppt, tadpole osmolality sharply increased and tadpole water content decreased. Tadpoles pre-acclimated for 48 hr in 7 ppt were able to maintain lower and more stable osmolality within the first 3 hr after transfer. These tadpoles initially lost water content, but over the next 6 hr gradually regained water and stabilized. In addition, they had a higher relative abundance of NKA proteins than tadpoles in other treatments. Pre-acclimation to 7 ppt for 48 hr was hence sufficient to activate NKA expression, resulting in increased survivorship and reduced dehydration upon later transfer to 11 ppt. J

Time- and Context-Dependent Oviposition Site Selection of a Phytotelm-Breeding Frog in Relation to Habitat Characteristics and Conspecific Cues

Abstract Time- and context-dependent nest site selection of a phytotelm-breeding frog (Kurixalus eiffingeri) was evaluated in a natural bamboo habitat in subtropical Taiwan from 2004 to 2005. At the beginning of the breeding season (mid-March), frogs preferred bamboo stumps with large water holding capacity, which may be considered high-quality stumps since water availability is critical to the survival of tadpoles. Prior to 21 May, no tadpole-occupied stumps were re-used even though they represented 10–40% of total stumps at the study site; however, tadpole-occupied stumps were consistently re-used afterwards. Stumps with fewer tadpoles were used proportionally more than those with more tadpoles. By choosing the stumps with fewer tadpoles, the negative competitive effect of the late-clutch tadpoles on the early-clutch tadpoles would be somewhat alleviated. Male frogs did not breed in the same bamboo stump for consecutive breeding events, which may relate to the male reproductive strategy. We propose that it would often be a better strategy for a male frog to breed in different stumps than to stay in the same stump, even if the stump was of high quality. Breeding in multiple stumps would increase the number of breeding opportunities by reducing the interval between successive mating attempts, minimize the inter-clutch competition between tadpoles, and avoid competition between two cohorts of its own genetically-related tadpoles. Our results suggest that stump quality is indicated by water holding capacity and the number of the tadpoles in the stump during early and late breeding seasons. Thus, oviposition site choice in this species is dependent on stump quality, but stump quality is both context- and time-dependent.

The fatty acid composition of oophagous tadpoles (Chirixalus eiffingeri) fed conspecific or chicken egg yolk.

We compared the lipid content and fatty acid composition of (1) the egg yolk of three anuran species (Chirixalus eiffingeri, Rhacophorus moltrechti and Buergeria robustus) and chicken eggs; and (2) C. eiffingeri tadpoles fed conspecific eggs or chicken egg yolk. Anuran and chicken egg yolk contained more non-polar than polar lipids but the proportions varied among species. Chicken egg yolk contained low amounts of 22:5n-3 in the polar lipid fraction, and B. robustus eggs did not contain any n-3 or n-6 non-polar lipids. The specific variation of lipid contents and fatty acid composition may relate to the maternal diet and/or breeding biology. In C. eiffingeri tadpoles that fed chicken yolk or frog egg yolk, the dominant components of polar and non-polar lipids were 16:0, 18:0, 18:1, and 18:2n-6, or 20:4n-6 fatty acids. C. eiffingeri eggs contained more n-3 fatty acids (e.g. 18:3n-3 and 20:5n-3) than chicken egg yolk, and tadpoles fed conspecific eggs contained more of these fatty acids than tadpoles fed chicken egg yolk. The compositional differences in the fatty acids between C. eiffingeri tadpoles that fed frog egg or chicken egg yolk are the reflection of the variation in the dietary sources. Our results suggest a direct incorporation of fatty acids into the body without or minimal modification, which provide an important insight into the physiological aspects of cannibalism.

Genetic relationship between offspring and guardian adults of a rhacophorid frog and its care effort in response to paternal share

The rhacophorid frog, Kurixalus eiffingeri, is one of only a few frog species that exhibits polyandry and paternal care of eggs. Previous studies predicted that multiple paternity within an egg clutch could influence the degree of paternal care and reproductive strategies. We used microsatellite DNA markers to assess the prevalence of multiple paternity within egg clutches and the relationship between male paternal care and the percent of male’s genetic contribution to the clutch, i.e., paternal share. We conducted field observations of paternal care and collected tissues from both male frogs and tadpoles for parentage analyses. Our results showed that at least five out of 31 egg clutches had multiple paternity. Attending males were always the genetic fathers of some, if not all of the eggs in the clutch they guarded. All egg clutches except one were attended by one male frog but the attending male did not necessarily sire the majority of offspring. Multiple paternity in all cases consisted of two fathers and one mother and most likely resulted from synchronous polyandry. Paternal care effort correlated significantly with the male’s genetic contribution to the clutch, suggesting that male frogs adjust the effort expended in care in response to paternal share. In addition, our results suggest that externally fertilizing species with parental care and multiple paternity may develop novel reproductive and behavioral strategies to safeguard their parental investment and overcome sperm competition.

The Ecology of Male Egg Attendance in an Arboreal Breeding Frog, Chirixalus eiffingeri (Anura: Rhacophoridae), from Taiwan

Abstract Field observations were conducted on egg attendance in Chirixalus eiffingeri from April to August 2003. Parental attendance during embryonic development was performed exclusively by males. The frequency of egg attendance was low (27%), but it had a distinct diel pattern in which males were observed to attend eggs more frequently at night than during the day. Attendance frequency significantly decreased with increasing developmental stage of the embryos, but it was not statistically significantly related to clutch size. Field observations confirmed that male frogs actively moisten egg clutches using their ventral surfaces, presumably to prevent desiccation of egg clutches. The non-significant relationship between hatching success and frequency of egg attendance suggests that embryonic survival of C. eiffingeri is more than a function of egg attendance, and ecological and environmental factors, such as climate and characteristics of microhabitats, may also influence the survivorship of the embryos.

Salinity Acclimation Affects Survival and Metamorphosis of Crab-eating Frog Tadpoles

Abstract Previous studies showed that Fejervarya cancrivora tadpoles were salt-tolerant (up to 24 parts per thousand [ppt] in the field and 35 ppt in the laboratory) but metamorphosed only at or below 6.6 ppt. We hypothesized that the discrepancy in salt tolerance of tadpoles is due to a mixture of results drawn from short- and long-term experiments and different acclimation procedures, which needed to be re-examined. We compared the salinity tolerance of acclimated and nonacclimated tadpoles and assessed salinity effects on growth, development, and metamorphosis among tadpoles of F. cancrivora throughout larval period. In Experiment 1, we determined 48-h tadpole survivorship by assigning 40 tadpoles to one of the 24 treatments ranging from 3-ppt to 30-ppt salinity. In Experiment 2, we assigned tadpoles to 3–15-ppt salinity at intervals of 3 ppt and monitored tadpole growth and development through metamorphosis. In Experiment 3, we exposed 15 tadpoles to a stepwise increase of salinity (i.e., 2 ppt every 3 d) and monitored the tadpole survivorship and metamorphic success. From Experiment 1 we estimated an LC50 (defined as the salt concentration that kills 50% of tadpoles within 48 h) of 13.7 ppt and tadpoles survived for 48 h at salinities as high as 16 ppt, suggesting that saline tolerance of F. cancrivora tadpoles is greater than all anuran species studied to date. Results of Experiment 2 showed that only tadpoles in 3, 6, and 9 ppt survived and reached metamorphosis. Tadpoles at 9 ppt grew and developed slower than in lower salinities during the first 7 wk, but the time to and size at metamorphosis were similar among treatments, suggesting that tadpoles were stressed at 9 ppt early, but they probably were able to maintain physiological homeostasis and to catch up growth after a period of adjustments. Results of Experiment 3 showed that all tadpoles survived through 18 d as the salinity was increased stepwise from 3 ppt to 15 ppt, and 6 out of 15 tadpoles were able to metamorphose at high salinities (17–21 ppt). This finding contradicts earlier results suggesting tadpoles could metamorphose only at salinities ≤6.6 ppt. Overall, our results showed that F. cancrivora tadpoles not only tolerate salt well, but also are capable of acclimation to higher salinities. This ability to acclimate could free tadpoles from dependence on the occurrence of rain to facilitate metamorphosis and thus, represents an adaptation to the unpredictable nature of salinity variation in brackish habitats.