HERPETOLOGICAL JOURNAL, Vol. 13, pp. 121-124 {2003)

OVIPOSITION BEHAVIOUR AND VULNERABILITY OF EGGS TO PREDATION IN FOUR NEWT SPECIES (GENUS TR ITURUS)

GERMAN ORlZAOLA AND FLORENTINO BRANA

Departamento de Biologia de Organismos y Sistemas, Un iversidad de Oviedo, clCatedratico Rodrigo Uria sin , 33071 Oviedo, Sp ain

Most animals develop some kind of parental care in order to protect eggs or offspring from predation. Female newts (genus Triturus) protect eggs from predators by wrapping them individually in plant leaves. We studied oviposition characteristics of four newt species

inhabiting the northern Iberian Peninsula (marbled newt, Tr iturus marmoratus; alpine newt, T. alpestris; palmate newt, T. helveticus and Bosca's newt, T. boscai). All of these species are able to wrap their eggs in aquatic plants in laboratory experiments, but - whereas T. marmoratus, T.

alpestris and T. helveticus wrapped more than 90% of their eggs - T. boscai covered only half of the eggs completely with leaves. T. boscai is found in running waters more frequently than the other species, and lays larger eggs relative to femalesize, as is typical ofrunning water urodeles. A parallel experiment exposing newt eggs to predation by larvae ofthe dragonflyAeshna cyanea, demonstrated the protective value ofwrapping behaviour. About half of the unwrapped eggs were consumed, whereas protected eggs remained almost unattacked.

Keywords : Aeshnidae, egg-laying, Odonata, parental care, Urodela

INTRODUCTION cated that predatory larvae detect the eggs by tactile cues, so wrapping eggs in leaves could prevent dragon­ Amphibians show a great diversity of reproductive flies detecting their presence. A. cyanea has also been modes ranging fromthe deposition of masses of eggs in reported to alter the behaviour and development of newt ponds to viviparity (Duellman & Trueb, 1986). The de­ larvae (Van Buskirk & Schmidt, 2000; Schmidt & Van velopment of each reproductive mode is associated with Buskirk, 2001). different degrees of exposure of eggs and larvae to envi­

ronmental factors such as predation, competition and MATERIALS AND METHODS desiccation. Amphibian larvae are well known to de­ velop antipredator strategies (Sih, 1987; Alford, 1999), During the 2000 and 2001 reproductive seasons, but eggs are more vulnerable to predation and other po­ . adult females of four newt species (T. marmoratus, tential risks due to their immobility. In contrastto those n=32; T alpestris, n=13; T. helveticus, n=44; T. boscai, of other salamanders, newt eggs (genus Triturus) are not n=55) were collected in several pools and cattle-water­ known to contain unpalatable or toxic substances (Ward ing tanks in Asturias (northern Spain) and transferred to & Sexton, 1981 ), but female newts attach eggs individu­ the laboratory. Females were placed for five days at ally to aquatic plants, wrapping these eggs by means of l 7°C and LD 12: 12 photoperiod in individual plastic adhesive substances on the egg membranes, as reported containers ( 18 cm in diameter) that held one artificial by Diaz-Paniagua ( 1989) for Triturus (marmoratus) oviposition support consisting of nine cloth strips ( 1 O x 0.8 cm) suspended from a float of polystyrene foam pygmaeus, and Miaud ( 1994b) for T. alpestris and T. cm). Eggs were removed from thestrips helveticus. Wrapped eggs are inaccessible to the maj or­ plate (8 x 5 x 1 ity of predators, such as aquatic invertebrates or adult twice a day and placed for 24 hr in a drying chamber at newts, and therefore experience reduced predation rates 50°C until the mass remained constant. Dry egg mass (Miaud, 1993). was recorded to the nearest O.OOOlg (nwnber of eggs: T. The present study examines oviposition behaviour in marmoratus, n=1379; T alpestris, n=269; T. he/veticus, four newt species inhabiting the northernIberian Penin­ n=1961; T boscai, n=609). We recorded female wrap­ sula (marbled newt, Triturus marmoratus; alpine newt, ping behaviour by placing newts in the same type of T. alpestris; palmate newt, T. helveticus and Bosca 's plastic containers filled with tap water and Glyceria sp. newt, T. boscal), and also experimentally tests forthe leaves taken fromnearby ponds. This type of vegetation effect of wrapping behaviour on egg survival in the pres­ was present in the localities of capture and was fre­ ence of dragonfly larvae, Aeshna cyanea, one of quently used by newts (T.cri status, T alpestris and T the top predators found in ponds and other temporal marmoratus) in experiments developed by Miaud aquatic habitats in the study area. Previous studies with ( 1995) studying the selection of plants during newt ovi­ other dragonfly species (Richards & Bull, 1990) indi- position. Natural vegetation was used to develop the experiments in realistic conditions. Oviposition was Correspondence: G. Orizaola, Departamento de Biologia de controlled every two days for a total of ten days per fe ­ Organismos y Sistemas, Universidad de Oviedo, c/ ma le. Only females that laid at least 15 eggs were Catedratico Rodrigo Uria s/n, 33071 Oviedo, Spain. E-mail: considered in the experiment (numbers of females: T. [email protected] 122 G. ORIZAOLA AND F. BRANA marmoratus, n=l 8; T. alpestris, n=20; T. helveticus, cies. Differences in oviposition tactics (mean percent­ n=21; T. boscai, n=13). Eggs were classifiedas wrapped age of wrapped or unwrapped eggs per female) and if they were completelycovered by foldsof the leaves or unwrapped egg survival between species were analysed unwrapped if they were uncovered (number of eggs: T. using a Kruskal-Wallis test and Mann-Whitney tests for marmoratus, n=683; T. alpestris, n=897; T. helveticus, post-hoe paired comparisons. The effect of oviposition n=898; T. boscai, 11=260). The effect of wrapping be­ mode on egg predation by Aeshna was tested using a haviour on egg predation by dragonfly larvae was Mann-Whitney test. Differences in total egg mass con­ investigated in a 24 hr experiment conducted in plastic sumption were tested with a Kruskal-Wallis test. containers (18 cm in diameter) filled with0.4 litre of wa­ Deviation from normality was tested with a Shapiro­ ter. Half of the containers received ten eggs wrapped Wilk test and homogeneity of variance with a with naturally vegetation, whereas the other half re­ Bartlett-Box test. ceived ten unwrapped eggs. Wrapped eggs were RESULTS selected from large samplesof eggs so that the degree of wrapping was the same between species, i.e. only eggs There were significant differences in female SVL completely covered with leaves were used. Unwrapped among species (ANOVA: F 0=958.95, P<0.001; 3•14 eggs were obtained from naturally unwrapped eggs if Scheffe test: T. marmoratus > T. a/pestris > T. possible, and in the other cases by the careful removal of helveticus = T. boscai; Table l ). Dry egg mass differs the vegetation covering wrapped eggs. This egg ma­ significantly among species (F =176.71, P<0.001), 3•140 nipulation has been described by Miaud (l 994a) as not revealing Scheffe post-hoe test differences between all affecting the survival ofthe embryos. Late instar Aeshna the species except for T. alpestris and T. boscai (T. cyanea dragonfly larvae were collected fromlocal water marmoratus > T. boscai = T. alpestris > T. helveticus; bodies and allowed to acclimatize to laboratory condi­ Table I). Oviposition tactics differed between species tions for three days. Dragonflies used in the trials were (Kruskal-Wallis test: H3=32.153, P<0.001; Table 1), starved for three days before the experiments to mini­ with T. alpestris having a significantly higher percent­ mize the effect of satiation on predator performance. age of eggs wrapped with the vegetation than the other Each predator was used only once during the experi­ species {Mann-Whitney tests: T.mar- T.alp: U =89 18•20 , ments. Trials for both treatments were repeated 15 times P=0.007; T. alp- T.helv: U20.i1=73, P<0.001; T.alp­ for each species. Total egg-mass consumption by T.bosc: U20 13=17, P<0.001). No differences in Aeshna larvae in 'unwrapped' trials was calculated by percentage of wrapped eggs were found between T. mu ltiplying the number of eggs consumed in each trial marmoratus and T. helveticus ( U18 2 =l 58.5, P=0.389), • 1 by the dry egg mass for each species, obtained as stated whereas T. boscai differed from the other species and above. After the experiments all the dragonflies, newt had only a half of their eggs wrapped (T.mar-T.bosc: fe males and the remainder of the eggs were released in U =19.5, P<0.001; T.helv- T.bosc: U =25, 18•13 21•13 their original locations. P<0.001). When ne\\1 eggs were exposed to Aeshna lar­ One-way ANOVA 's and Scheffe post-hoe tests were vae predation, egg survival was positively influenced by used to test for differences in female size (snout-vent wrapping {U60 60=557.5, P<0.001; Fig. 1). Differences in , length) and in dry egg mass between the four newt spe- unwrapped eggs survival were found only between T.

TABLE I. Summary of female size and characteristics of the eggs laid by Triturus species. All values are presented as 100 mean ± SE, with range in parentheses.

80 Female SVL Egg dry mass % wrapped {mm) {mg) eggs � ;;; 60 T. marmoratus > ·� :J 82.95±1 .07 2.1±0.05 92.47±1.53 VJ Cl { 68.28-96.31) {l.5 - 2.7) {78.57-100) Cl 40 w T. alpestris 56.40±0.68 1.6±0.04 96.81±0.72 20 {53.03-62.02) { 1 .4-2.0) (88.88-1 00)

T. helveticus 0 42.91±0.37 0.9±0.02 91.25±1.37 T. marmoratus T. alpestris T. helveticus T. boscai

(38.01-47.98) (0.6-1.2) (75.47-1 00) DWrapped •Unwrapped T. boscai FIG. I. Effect of oviposition mode (wrapped or unwrapped 42.81±0.38 1.7±0.03 45.81±7.55 egg) on the percentage of surviving eggs (mean + SE) after24 hrs of exposition to larval dragonfly, {38.00-5 1.01) (1.2-2.4) {5.26-1 00) Aeshna cyanea, predation. OVIPOSITION AND PREDATION INNEWTS 123

marmoratus and T. alpestris ( U15 15=43, P=0.003).Total (six arthropods, one gastropod and threeamphibian spe­ , egg mass consumptionby Aeshna presented marginally cies) did not affect egg survival. Furthermore, after one significant differences between species (H3=7.62, week in natural habitats no unwrapped eggs survived, P=0.054), being higher for T. alpestris (11.62±1.37 whereas 20-54% of the wrapped eggs were still alive mg). Differences using Mann-Whitney tests were ob­ (Miaud, 1994a) . Inthis study, predatory larvae wereob­ tained only between T. alpestris and the two species served moving along theleaves where eggs are attached, with lower egg mass (T. marmoratus V15•15=64, P=0.04 l searching for and identifying eggs using their antennae and T. helveticus U15•15=35, P=0.001). before eating them. So, wrapped eggs seem to be undetectable by the tactile sensory capacities of A. DISCUSSION cyan ea. The results of this study revealed that wrapping be­ ACKNOWLEDGEMENTS haviour is common in all the species considered. To our knowledge, this study provides the first data on wrap­ We are indebted to Carlos Rodriguez del Valle and ping behaviour in T. boscai, which - contrary to other Guillermo Bengoechea for theirgreat assistance infield species - wraps only a half of eggs in leaves. This spe­ and laboratory work. All the animals in this study were cies also lays eggs that are twice the size of those laid by used by permission of the regional authorities a similar-sized species (T.he lveticus), and is the only (Direcci6n General de Recursos Naturales y Proteccion species frequently foundin streams during the reproduc­ Ambiental, Principado de Asturias). A SpanishMinistry tive season. This reflects the pattern found in 74 of Science and Technology research project salamander species by Kaplan & Salthe (1979), who (BOOS2000-0452) supported this research. A Spanish observed that egg size was smaller in relation to female Ministry of Education and Culture doctoral fellowship size in pond breeders than in those species breeding in and a University of Oviedo grantprovided financialsup­ running waters. A relatively large egg size could present port to G. Orizaola. difficulties in terms of egg manipulation in T. boscai fe­ males, affecting the wrapping sequence of eggs with REFERENCES plant leaves and consequently the percentage of eggs Alford, R. A. (1999). Ecology: resource use, competition, protected. T. boscai eggs can be found in natural habi­ and predation. In Tadpoles: the bfology of anuran tats unwrapped or adhering to the underside of rocks, larvae, 240-278. McDiarmid, R. W. and Altig, R. behaviour rarely observed in the other three species. (Eds). Chicago: The University of Chicago Press. Percentages of wrapped eggs observed for T. alpestris Axelsson, E., Nystrom, P., Sidenmark, J. & Bronmark, C. and T. helveticus are higher than those reported by ( 1997). Crayfish predation on amphibian eggs and Miaud ( 1994a) in previous experiments in which only larvae. Amphibia-Reptilia 18, 217-228. 75% of the eggs were wrapped with the leaves. Diaz-Paniagua, C. ( 1989). Oviposition behavior of Wrapping behaviour reduces algal infection and DV­ Triturus marmoratus pygmaeus. Jo urnal of B-damaging effects in Triturus eggs (Marco et al., Herpetology 23, 159-1 63. 2001 ), but the most frequentlyreported functionwas re­ Duellman, W. E. & Trueb, L. (1986). Biology of lated to protecting eggs from predators (Miaud, 1993, amphibians. New York: McGraw-Hill Book Company. 1994a). Both vertebrate and invertebrate predators have Henrikson, B. I. (1990). Predation on amphibian eggs and been reported to attack and consume amphibian eggs tadpoles by common predators in acidified lakes. causing a significant reduction in reproductive success Holartic Ecology 13, 201-206. (Henrikson, 1990; Miaud, 1993; Axelsson et al., 1997; Kaplan, R. H. & Salthe, S. N. (1979). The allometry of Richter, 2000; Monello & Wright, 2001). Our results reproduction: an empirical view in salamanders. showed that the wrapping behaviour developed by fe­ American Naturalist 113, 671-689. male newts is highly effective in protecting eggs from Marco, A., Lizana, M., Alvarez, A. & Blaustein, A. R.

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