Marc Sztatecsny

Delineation of terrestrial reserves for amphibians: post-breeding migrations of Italian crested newts (Triturus c. carnifex) at high altitude

Little is known about the terrestrial phase of high-altitude populations of European amphibians, in spite of potentially important implications for conservation and management. We followed 51 adult Italian crested newts (Triturus carnifex) that emigrated from an ephemeral lake (Lake Ameisensee, 1282 m a.s.l., Northern Calcareous Alps, Austria) with radio-tracking. Transmitters were inserted into each newt’s stomach and we collected data until it did not relocate for more than 1 week or until the transmitter was regurgitated. Most newts migrated in a north-westerly direction towards an old growth spruce forest. Subterranean shelters, mostly 5–80 cm deep burrows of small mammals located 13–293 m from the lake, were reached in between 4 h and 7.8 days. Twenty percent of T. carnifex shared their refuges with other congeneric species. Females migrated significantly further (median distance 168 m) than males (median 53 m). We propose a terrestrial core reserve extending 100 m from the furthermost terrestrial refuges of newts found with radio-tracking linked with patches of old-growth forest. This terrestrial reserve is substantially larger than has been suggested as sufficient in the recent literature.

Multimodal Communication in a Noisy Environment: A Case Study of the Bornean Rock Frog Staurois parvus

High background noise is an impediment to signal detection and perception. We report the use of multiple solutions to improve signal perception in the acoustic and visual modality by the Bornean rock frog, Staurois parvus. We discovered that vocal communication was not impaired by continuous abiotic background noise characterised by fast-flowing water. Males modified amplitude, pitch, repetition rate and duration of notes within their advertisement call. The difference in sound pressure between advertisement calls and background noise at the call dominant frequency of 5578 Hz was 8 dB, a difference sufficient for receiver detection. In addition, males used several visual signals to communicate with conspecifics with foot flagging and foot flashing being the most common and conspicuous visual displays, followed by arm waving, upright posture, crouching, and an open-mouth display. We used acoustic playback experiments to test the efficacy-based alerting signal hypothesis of multimodal communication. In support of the alerting hypothesis, we found that acoustic signals and foot flagging are functionally linked with advertisement calling preceding foot flagging. We conclude that S. parvus has solved the problem of continuous broadband low-frequency noise by both modifying its advertisement call in multiple ways and by using numerous visual signals. This is the first example of a frog using multiple acoustic and visual solutions to communicate in an environment characterised by continuous noise.

Multimodal signaling in the Small Torrent Frog (Micrixalus saxicola) in a complex acoustic environment

Many animals use multimodal (both visual and acoustic) components in courtship signals. The acoustic communication of anuran amphibians can be masked by the presence of environmental background noise, and multimodal displays may enhance receiver detection in complex acoustic environments. In the present study, we measured sound pressure levels of concurrently calling males of the Small Torrent Frog (Micrixalus saxicola) and used acoustic playbacks and an inflatable balloon mimicking a vocal sac to investigate male responses to controlled unimodal (acoustic) and multimodal (acoustic and visual) dynamic stimuli in the frogs’ natural habitat. Our results suggest that abiotic noise of the stream does not constrain signal detection, but males are faced with acoustic interference and masking from conspecific chorus noise. Multimodal stimuli elicited greater response from males and triggered significantly more visual signal responses than unimodal stimuli. We suggest that the vocal sac acts as a visual cue and improves detection and discrimination of acoustic signals by making them more salient to receivers amidst complex biotic background noise.

Genetic dissimilarity predicts paternity in the smooth newt (Lissotriton vulgaris).

Under sperm competition, paternity is apportioned by polyandrous females according to the order of matings and the genetic quality of the inseminating males. In order to distinguish between these two effects, we sequentially paired 12 female smooth newts (Lissotriton vulgaris) with each of two males and, where possible, repeated the same procedure in reverse order of the identical males after assumed sperm depletion. For a total of 578 offspring, amplified fragment length polymorphisms genetic markers revealed multiple paternities in all matings, without significant first- or second-male sperm precedence. The paternity share of individual males was transitive across the two trials with male order switch, and successful males had a significantly higher genetic dissimilarity to the female than expected by chance. We argue that patterns of paternity in natural newt populations are determined through a combination of good genes and relatedness.

Chin up: are the bright throats of male common frogs a condition-independent visual cue?

Male mating success is generally governed by either female choice or male–male competition and multiple cues may influence both processes. Anuran amphibians are best known for acoustic communication but visual cues have also been found to play a role. Little is known, however, about visual cues in explosively breeding anurans in which sexual selection is based almost exclusively on male–male competition. During their search for mates, males may not distinguish between the sexes or species and mismating attempts are known to occur. Assuming that mismatings are costly for males, one would expect selection to favour a trait that facilitates sex recognition. We determined the colour of the explosively breeding common frog, Rana temporaria, during reproduction by spectrophotometry. While reflectance of all body parts in both sexes decreased from immigration to spawning, reflectance of male throats increased significantly. The mean luminance of male throats was more than twice that of female throats. Male throats contrasted most against male flanks with luminance contrast being significantly higher than chromatic contrast. In an experiment with individually marked frogs, throat luminance was not correlated with male size, body condition or the physical presence of females, whereas temperature showed a significantly positive effect. Our results give no hint that throats indicate male status or indicate male quality. Considering the high densities during breeding, our results suggest that bright male throats can act as a visual signal among males to facilitate gender recognition and avoid attacks by other males.

Don’t get the blues: conspicuous nuptial colouration of male moor frogs (Rana arvalis) supports visual mate recognition during scramble competition in large breeding aggregations

Conspicuous male colouration is expected to have evolved primarily through selection by female choice. In what way conspicuous colours could be advantageous to males scrambling for mates remains largely unknown. The moor frog (Rana arvalis) belongs to the so-called explosive breeders in which spawning period is short; intrasexual competition is strong, and males actively search and scramble for females. During breeding, male body colouration changes from a dull brown (similar to females) to a conspicuous blue, and we wanted to test if male blueness influences mating success or facilitates male mate recognition. To do so, we first measured the colour of mated and non-mated males using a spectrophotometer. In an experiment, we then analysed interactions of actual male moor frogs in natural spawning aggregations with a brown (resembling a female or a non-breeding male) and a blue model frog. Mated and non-mated males did not differ in colouration, suggesting that female choice based on colour traits was unlikely. In our behavioural experiment, male moor frogs spent significantly more time in contact and in amplexus with the brown model than with the blue model. Our results suggest that the nuptial colouration in moor frogs can act as a new type of visual signal in anurans evolved to promote instantaneous mate recognition allowing males to quickly move between rivals while scrambling for females.

Divergent receiver responses to components of multimodal signals in two foot-flagging frog species.

Multimodal communication of acoustic and visual signals serves a vital role in the mating system of anuran amphibians. To understand signal evolution and function in multimodal signal design it is critical to test receiver responses to unimodal signal components versus multimodal composite signals. We investigated two anuran species displaying a conspicuous foot-flagging behavior in addition to or in combination with advertisement calls while announcing their signaling sites to conspecifics. To investigate the conspicuousness of the foot-flagging signals, we measured and compared spectral reflectance of foot webbings of Micrixalus saxicola and Staurois parvus using a spectrophotometer. We performed behavioral field experiments using a model frog including an extendable leg combined with acoustic playbacks to test receiver responses to acoustic, visual and combined audio-visual stimuli. Our results indicated that the foot webbings of S. parvus achieved a 13 times higher contrast against their visual background than feet of M. saxicola. The main response to all experimental stimuli in S. parvus was foot flagging, whereas M. saxicola responded primarily with calls but never foot flagged. Together these across-species differences suggest that in S. parvus foot-flagging behavior is applied as a salient and frequently used communicative signal during agonistic behavior, whereas we propose it constitutes an evolutionary nascent state in ritualization of the current fighting behavior in M. saxicola.

The Presence of Common Frogs (Rana temporaria) Increases the Body Condition of Syntopic Alpine Newts (Ichthyosaura alpestris) in Oligotrophic High-Altitude Ponds: Benefits of High-Energy Prey in a Low-Productivity Habitat

In low-productivity, high-altitude habitats food can become a limiting factor for the occurring amphibians. Common frog eggs deposited in ponds and the developing tadpoles represent energy-rich prey for syntopic Alpine newts that should be advantageous for storing sufficient amounts of energy to survive hibernation and breed the following spring. In our study population in the Zillertal Alps, Austria at 2100 m a.s.l., in two consecutive years we found the body mass of Alpine newts to be significantly higher in ponds containing tadpoles of the common frog than in ponds without tadpoles. As the frogs forage mostly on land, we regard their eggs as an allochtonous nutrient subsidy for ultra-oligotrophic high-altitude ponds that may have a profound effect on the fitness and distribution of Alpine newts and common frogs.

Male body size and parental relatedness but not nuptial colouration influence paternity success during scramble competition in Rana arvalis

Female mate choice promotes the development of male secondary sexual traits such as nuptial colouration, whereas scramble competition favours male traits which enhance their ability for access to females. In the explosively breeding moor frog (Rana arvalis), males express a conspicuous blue colouration during a short reproductive period characterised by scramble competition. In the present study we used controlled mating experiments and genetic markers to disentangle the effects of colouration, body size and pairwise genetic relatedness in determining paternity success. Males observed in amplexus with a female prior to spawning were larger than their competitors but did not differ from them in colouration. Polyandry occurred in 67% of the 18 analysed egg clutches, and amplecting males did not always achieve the highest siring success, most likely due to stray sperm. Successful mating pairs were characterised by higher genetic divergence between them than expected by chance. We confirm previous evidence that male nuptial colouration is not a trait selected by females, and provide evidence that male reproductive success is influenced by male size as well as genetic attributes.

AFLPs: genetic markers for paternity studies in newts (Triturus vulgaris)

DNA-based genetic markers can reveal paternity whenever the direct assignment of fathers to offspring is precluded by multiple matings and internal fertilisation. Microsatellites are the current marker of choice in many behavioural studies, and have revealed important insights into genetic mating systems of European amphibians. However, the number of amphibian species for which the time-consuming designing of locus-specific microsatellite primers was successful is still limited, and the cross-utilisation of existing markers to closely related taxa seems to have a particularly low success rate. Allozymes can infer parentage without a species-specific protocol, but, due to their low degree of polymorphism, in mate choice experiments require the a priori screening of individuals. Dominant markers such as RAPDs successfully identified closely-related amphibian species and their hybrids, but might be less suited to distinguish between closely related individuals with a putatively high frequency of shared bands.