NORTH-WESTERN JOURNAL OF ZOOLOGY 12 (2): 299-303 ©NwjZ, Oradea, Romania, 2016 Article No.: e161503 http://biozoojournals.ro/nwjz/index.html Food composition of alpine newt (Ichthyosaura alpestris) in the post-hibernation terrestrial life stage Oldřich KOPECKÝ1,*, Karel NOVÁK1, Jiří VOJAR2 and František ŠUSTA3 1. Department of Zoology and Fisheries, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Kamýcká 129, Praha 6 - Suchdol 165 21, Czech Republic. 2. Department of Ecology, Faculty of Environmental Sciences, Czech University of Life Sciences Prague, Kamýcká 129, Praha 6 - Suchdol 165 21, Czech Republic. 3. Prague Zoological Garden, U Trojského zámku 3/120, Praha 7 - Troja 171 00, Czech Republic. *Corresponding author, O. Kopecký, E-mail: [email protected] Received: 26. Juy 2015 / Accepted: 29. December 2015 / Available online: 09. January 2016 / Printed: December 2016 Abstract. Amphibians in the temperate climatic zone, including European newt species, annually migrate to water for reproduction. While prey consumption and the composition of their diet during the breeding season have been explored relatively well, the opposite is true for the spring period before reproduction. Therefore, the primary of aim our study was to determine whether newts consumed food in the post- hibernation terrestrial life stage. We studied one population of alpine newts from the Czech Republic. The majority of the newts examined (65.30%) contained some food item. Repletion level was not connected with the newts’ body condition and also did not differ between males and females. In addition, the number of items consumed and the diversity of prey were not connected with an individual’s body condition or sex. Most numerous and frequent in the stomachs of both sexes were Collembola followed by Isopoda. Exploitation of other groups of prey was also almost the same, which resulted in a high niche overlap in the prey of males and females (Ojk=0.888). Key words: prey, diet, foraging, intersexual difference, body condition, Urodela. Introduction (Roček et al. 2003). Alpine newts’ hibernation sites can be as much as 1,000 m distant from their Migration is an integral part of the life history breeding sites, and to overcome this distance can strategies of many animal taxa, including am- be time and energy consuming (Joly & Miaud phibians (Wells 2007). In the tropics, amphibians’ 1989). breeding migration to ponds is irregular and oc- In contrast to the explosive breeding of an- curs opportunistically after heavy rainfalls (Wat- urans, as in the cases of the common frog (Rana ling & Donnelly 2002). Conversely in the temper- temporaria) and common toad (Bufo bufo), which do ate zone, breeding is circannual. The life cycle of not eat while breeding, newts are prolonged most temperate amphibians thus consists of terres- breeders (Griffiths 1996, Arntzen 2002) with bi- trial hibernation, a spring stage which includes phasic seasonal plasticity in prey capture behav- migration to water for reproduction, followed by a iour (Heiss et al. 2013, Heiss et al. 2015). Prey con- summer and autumn terrestrial stage (Griffiths sumption and the composition of the diet during 1996, Wells 2007). Environmental changes are ac- their breeding period (i.e. when the newts are in companied by great phenotypic changes (Warburg water) has been examined relatively well, includ- & Rosenberg 1997) along with changes in prey- ing resource partitioning between morphs (Denoël capture mechanics, which recently have been & Andreone 2003, Denoël & Schabetsberger 2003, studied in newts (Heiss et al. 2013, Heiss et al. Denoël et al. 2004), interspecific competition with 2015). other newts (Fasola & Canova 1992, Joly & Gia- Newts of the former genus Triturus are poly- coma 1992, Jehle et al. 2000), and intersexual vari- phagous opportunistic predators in the middle of ance (Kopecký et al. 2012a). On the other hand, trophic pyramids, but some of them, such as al- newts’ diet during the terrestrial phase, including pine newts (Ichthyosaura alpestris) from high alti- the post-hibernation period, has not been suffi- tude lakes, can assume the role of top predators ciently examined (Kuzmin 1990, Denoël 2004). (Schabetsberger & Jersabek 1995). The alpine newt This is mainly because of newts’ well-concealed is a common species widely distributed across lifestyle during terrestrial phase (Verrell 1985, Europe, where it occupies various habitats while Schabetsberger et al. 2004). Inasmuch as gamete preferring woody, hilly, or mountainous regions production and behaviour associated with breed- 300 O. Kopecký et al. ing are energy-intensive processes (von Lindeiner repletion levels were compared using 2×2 contingency 2007), the level of energy reserves accumulated in tables. Differences between sexes in prey variables (num- the previous period (in our case, the post- ber of prey items, number of prey categories) were exam- ined using non-parametric Mann–Whitney U tests due to hibernation terrestrial life stage) can significantly imbalance in the samples’ sizes. Residuals from linear re- affect an individual’s breeding success. gression between the newts’ SVL and weight were com- The main aims of this study, therefore, were puted separately for males and females. In subsequent to: i) determine the food composition of alpine linear regression analysis, residuals were used as a body newts’ diet during the post-hibernation terrestrial condition variable (Denoël et al. 2002). Statistical signifi- life stage and identify their main prey; ii) ascertain cance was determined at the level α = 0.05. All tests were whether there are intersexual differences in reple- computed using Statistica 12.0 (Statsoft 2012). tion level and diversity and number of prey con- sumed; iii) quantify the niche overlap between Results sexes; and iv) identify the effect of body condition on prey variables. During our study, a total of 144 adult newts (58 males, 86 females) were examined. Mean body Materials and Methods size of 52.3 mm (± SD: 5.0 mm, range: 34.3–60.9) was greater for females than it was for males at The study was conducted at a location known as “Trojka” 44.2 mm (± SD: 2.2 mm, range: 38.0–49.0 mm) (GPS: 50°30′89.0′′, 12°45′94.3′′), which lies in a spruce for- (Mann–Whitney U test, z=−8.64, p<0.001). The est at 750 m a.s.l. near the village of Kraslice in the west- sexual dimorphism (SDI) of our samples was de- ern Czech Republic. The location consists of three artifi- termined to be 0.185. Females were also heavier cial ponds lying close to each other. Their overall surface (mean: 4.00 g, ± SD: 1.14 g, range: 1.00–7.00 g,) area is about 30 m², and the distance between them does not exceed 0.3 m. Adult alpine newts were captured using than were males (mean: 2.08 g, ± SD: 0.37 g, range: drift fences and pitfall traps from 28 April to 6 May 1997. 1.25–3.25 g) (Mann–Whitney U test, z=−8.74, From an earlier observational study at this location (data p<0.001). not shown), we know that this date range takes in the Newts consumed Nematoda, Oligochaeta, peak of newt migration to the “Trojka” breeding site. The Gastropoda, Araneida, Acarina, Isopoda, Diplo- traps were controlled twice per day, in the morning and poda, Chilopoda, Collembola, Plecoptera, Psocop- in the evening. Each captured newt was sexed, measured tera, Heteroptera, Sternorrhyncha, Lepidoptera, (snout–vent length, SVL) to the nearest 0.1 mm and weighed using a Pesola scale to the nearest 0.05 g after Diptera, Hymenoptera, and Coleoptera. Females stomach flushing. Stomach contents were extracted using contained all prey categories except for Nematoda. the stomach flushing technique described by Opatrný Males’ food spectrum was less diverse than was (1980). The newts measured and flushed were not anaes- that of females. The stomachs of males did not thetized. They were released into the water immediately contain Plecoptera, Heteroptera, Sternorrhyncha, after these procedures. or Hymenoptera. The most numerous prey – and Stomach contents were stored individually in vials which also was consumed by the largest propor- and preserved in 4% formaldehyde. Prey items were then identified using a stereoscopic microscope and sorted into tion of newts of both sexes – consisted of the Col- 17 taxonomic categories plus a category of unidentified lembola, followed by Isopoda (Fig. 1). prey items. Two prey variables were determined for each Dominance according to the Berger & Parker individual: the number of prey items and the presence of index was higher in the diet of the males (d=0.292) particular prey categories in stomach. Because there were than it was in that of females (d=0.158). Collem- no other bodies of water in the vicinity of the location, we bola were found in higher frequencies in males could presume that the prey found in the newts’ stom- than in females, and so niche breadth was nar- achs was captured only in a terrestrial environment. The sex of the newts was determined according to rower in males (BA=0.465) than it was in females external sexual characteristics. Sexual size dimorphism (BA=0.577). Despite this difference, prey niche was determined using the sexual dimorphism index (SDI) overlap during the post-hibernation terrestrial life proposed by Lovich & Gibbons (1992). Niche overlap be- stage was high among the sexes (Ojk=0.888). tween sexes was evaluated by means of a modified ver- Not all newts contained prey. Of all the newts sion of Pianka’s niche overlap index (Christensen et al. examined, 39.65% of males and 31.39% of females 2005). Dominance of a particular prey category in the had empty stomachs, and there were no signifi- overall diet was computed using the Berger & Parker (1970) index. Niche breadth was determined via Levins’ cant differences in repletion level between sexes standardized niche breadth index (Levins 1968).