Zoological Studies 49(3): 304-310 (2010) Paternal Care and Egg Survivorship in a Low Nest-Attendance Rhacophorid Frog Wei-Chun Cheng and Yeong-Choy Kam* Department of Life Science, Tunghai University, Taichung 407, Taiwan (Accepted October 19, 2009) Wei-Chun Cheng and Yeong-Choy Kam (2010) Paternal care and egg survivorship in a low nest-attendance rhacophorid frog. Zoological Studies 49(3): 304-310. We conducted a field study in Mar.-June 2007 to evaluate the importance of egg attendance by male Kurixalus eiffingeri to egg survivorship. We found 38 egg clutches and visited them on a fixed scheme by checking all nests at night for 6 d, yielding 1368 visits of 10 min each. Egg attendance frequency was highly uneven among nests and was positively correlated with clutch size. On average, 6.8% ± 4.4% of eggs in an egg clutch died each day. Daily egg mortality was inversely correlated with the attendance frequency, suggesting that paternal care is important to egg survival even though this is a low nest-attendance species. Variances of egg mortality were low when paternal care effort was high, but opposite results were found when paternal care effort was low, suggesting the fate of eggs can also be affected by factors other than paternal care, such as stump conditions. Our results suggest that parental care effort varies via a cost-benefit relationship of investment in the present offspring vs. future reproductive chances. Male frogs spent more time attending eggs when the clutch sizes were large but sought additional mating opportunities if the egg clutches were small, which resulted in large variations in egg mortality among clutches. http://zoolstud.sinica.edu.tw/Journals/49.3/304.pdf Key words: Anuran, Nest attendance, Egg brooding, Paternal care, Rhacophoridae. P arental care is any form of parental The forms of parental care are diverse; and it was behavior that increases an offspring’s chance of found in about 10% of extant species, including 15 survival (Clutton-Brock 1991). To understand of 21 extant families (Crump 1995, Lehtinen and the evolution of parental care, it is important to Nussbaum 2003). In total, 7 modes of parental understand how reproductive success varies as care were found, including egg attendance, egg a function of parental care. Parental care effort transport, tadpole attendance, tadpole transport, varies as individuals trade off between investment tadpole feeding, internal gestation, and froglet in the present offspring and future reproductive transport (Wells 1981 2007, Crump 1995 1996, potential, with confidence in paternity (Werren et Bickford 2001 2002). al. 1980, Winkler 1987, Whittingham et al. 1992, One of the most common modes of parental Xia 1992, Westneat and Sherman 1993, Houston care is egg attendance, i.e., a parent remains with 1995, Mauck and Grubb 1995), and with different an egg mass at a fixed location (Wells 1981 2007, mating systems (Maynard Smith 1977). Crump 1995, Lehtinen 2003). Earlier studies The occurrence of parental care in anuran showed that many terrestrial and arboreal frogs amphibians is more common than originally exhibit an array of attending behaviors which thought (McDiarmid 1978, Duellman and Trueb include egg guarding, turning, brooding, and even 1986, Crump 1995, Lehtinen and Nussbaum 2003). oophagy to remove infected eggs (Simon 1983, *To whom correspondence and reprint requests should be addressed. Tel: 886-4-23550609. Fax: 886-4-23550609. E-mail:[email protected] 304 Cheng and Kam – Paternal Care and Egg Survivorship of a Treefrog 305 Townsend et al. 1984, Jacobson 1985, Hayes to egg survivorship given that it is a low nest- 1991, Crump 1995). attendance species, (2) correlate the attendance The degree of nest attendance varies among frequency with clutch size, (3) quantify egg species. For species with high nest attendance, mortality of egg clutches with low and high levels egg guardians stay with egg clutches for long of paternal care, and (4) elucidate the possible periods of time; e.g., male Eleuterodactylus coqui, mechanism(s) underlying the paternal care effort. an aerial breeder, stayed at the nest 97.4% and 75.8% of the day and night time, respectively (Townsend et al. 1984). Nests from which male MATERIALS AND METHODS frogs were removed showed significantly lower embryo hatching success (Woodruff 1977, Simon Study site 1983, Townsend et al. 1984, Junca 1996, Bickford 2004, Vockenhuber et al. 2009). In contrast, for We conducted field observations in 2 bamboo species with low nest attendance, egg guardians forests at Chitou (120°48'10"E, 23°39'20"N), spend a small portion of time with eggs; e.g., central Taiwan. Chitou, at an elevation of about Centrolenella fleischmanni, an aerial breeder, 1,016 m, receives approximately 3,000 mm of stayed at the nest 12%-20% of the night (Hayes rainfall annually, approximately 90% of which 1991). Nests from which male frogs were removed occurs during the wet season from Feb. to Sept. showed no difference in embryonic survivorship when local thunderstorms and typhoons bring compared to a control group (Hayes 1991). This copious amounts of precipitation. The mean finding raises a question of whether paternal care annual temperature at the site is 18°C. The serves any function in enhancing the survivorship highest monthly temperature occurs in Aug. of eggs in low nest-attendance species. (20°C) and the lowest in Jan. (9°C). The bamboo, In this study, we used a Taiwanese frog Phyllostachys edulis, was the most abundant (Kurixalus eiffingeri, Anura, Rhacophoridae) that species in the study site. The bamboo is cut breeds in water-filled bamboo stumps as a model periodically for commercial purposes, and the animal to assess the function of paternal care to stumps remain for several years before collapsing. eggs. Kurixalus eiffingeri is a small-sized frog Bamboo stumps collect rain water and become endemic to Taiwan and 2 of the adjacent Japanese calling, oviposition, and tadpole development sites Ryukyu Is., Iriomote and Ishigaki (Kuramoto for K. eiffingeri (Kam et al. 1996). 1973, Lue 1990). This is a prolonged breeder, the breeding season of which extends from Feb. Field protocol and observations to Aug., and an amplectant pair deposits its fertilized eggs on the inner wall of a water-filled A field study was conducted in Mar.-June bamboo stump or tree hole above the water line 2007. We conducted weekly night surveys of (Kam et al. 1996). Male frogs exhibited paternal empty bamboo stumps with standing water to care during the embryonic period but spent about search for frogs and newly laid egg clutches. Once 27% of time attending eggs, and egg attendance a newly laid egg clutch was found, we recorded varied greatly among egg clutches at 0%-100% the clutch size and developmental stage (Gosner (Chen et al. 2007). Kurixalus eiffingeri eggs are 1960) of the embryos. Because the developmental subject to fungal infections, desiccation, predation, time for eggs to hatch is about 9-14 d, our weekly and flooding (Kam et al. 1996, Chen et al. 2007). survey allowed us to locate all newly laid egg Chen et al. (2007) reported egg brooding behavior clutches. in a field study where males lay on the clutches After an egg clutch was found, we visited when brooding and often changed positions. nests on a fixed scheme by checking all nests Males frequently descended into the water while at night for 6 d. First, we divided the embryonic brooding, stayed for several minutes, and then period into early and late phases according to climbed out of the water to lie on the clutch. whether any embryo in a clutch had reached Results from field observations clearly indicated Gosner stage 18 (Gosner 1960). For each phase, the presence of nest attendance behavior, but its we conducted behavioral observations of frogs and importance to embryonic survivorship has yet to be visited egg clutches for 3 consecutive nights. Each evaluated. night survey was conducted from 18:00 to 06:00 The aims of this study were to (1) evaluate the next morning at intervals of 2 h, and each the importance of egg attendance by K. eiffingeri observation session lasted 10 min. At the end of 306 Zoological Studies 49(3): 304-310 (2010) the study, each nest had been visited 6 times a (Kam et al. 1996, Chen et al. 2007). We recorded night for 6 nights for a total of 36 visits of 10 min the 2 most common causes of mortality if eggs in each. During each visit, we conducted behavioral a nest died of more than 1 cause. We considered observations of male frogs and recorded the that eggs had died of a fungal infection when duration of time male frogs were present in the we could clearly see hyphae covering the eggs, stumps or brooding eggs. We used a digital video flooding when the eggs were below the water line camera recorder with infrared night-shot mode and the embryos were dead, desiccation when (DCR-PC101, Sony, Tokyo Japan) to conduct the eggs had shrunk and become dehydrated, observations at night without using white light. and predation when the eggs had disappeared Chen et al. (2007) reported that attending males of between visits during embryonic development. K. eiffingeri spent 1/3 of their time brooding eggs. In this study, we scored egg attendance if a male Data and statistical analyses frog exhibited egg brooding behavior. If brooding behavior was not observed, we considered that a Attendance frequency was calculated by male frog attended eggs if it was always close to dividing the number of visits in which male frogs the egg mass (i.e., < 20 mm away) between and were attending eggs by the total number of visits during visits even when disturbed.