Simulated chorus attracts conspecific and heterospecific Amazonian explosive breeding frogs

In tropical regions, some anuran species breed "explosively", reproducing in massive and highly diverse aggregations during a brief window of time. These aggregations can serve as acoustic beacons, attracting other anurans toward seasonal ponds. We hypothesize that conspecific and heterospecific calls play a role in navigation toward ponds and synchronization of reproduction among species. We simulated a chorus of two species (Trachycephalus coriaceus and Chiasmocleis shudikarensis) with contrasting call characteristics (low‐frequency vs. high‐frequency) and reproductive strategies (strict pond breeder vs. opportunistic) near known explosive breeding sites. We predicted that choruses of T. coriaceus are more attractive to heterospecifics than of C. shudikarensis because the first provides a more reliable indicator of a suitable breeding pond and a better long‐distance signal. We found that both choruses attracted conspecific frogs to the playback outside a natural breeding event. As predicted, heterospecifics were attracted only by low‐frequency calls of T. coriaceus that breeds exclusively in large ponds, but not by higher frequency calls of C. shudikarensis that also breeds in small pools not suitable for other species. Our study presents the first experimental evidence that tropical explosive breeding anurans are attracted to conspecific and heterospecific choruses. The contrasting effect of the playback of the two species on heterospecifics suggests that the attractive effect of a chorus depends on the reproductive strategy of both the sender and the receiver. Given the abundance and diversity of communities in tropical ecosystems, the use of heterospecific acoustic cues may prove widespread and requires further investigation. Abstract in Portuguese is available with online material.     

Thermal influences on the habitat preference and the diurnal activity in three European Rana species

The diurnal behaviour of frogs was recorded quantitatively in a habitatlike experimental environment by a new method of automatic registration via thermocouples. Three species with different habitat preferences during their summer activity period were chosen: the terrestrial common frog Rana temporaria LINNÈ and the semiaquatic water frog Rana lessonae CAMERANO and Rana ridibunda PALLAS. The activity, the location and the skin temperatures of these frogs were recorded continuously in four different temperature ranges (8.1° C–31.0° C) within the temperature span of the summer activity period. The thermal requirements and behavioural adaptations to the habitat of each species were analysed. The experimental results coincided with field observations and showed some details not yet known. The northern species R. temporaria exhibited a distinctive behavioural thermoregulation including cooling behaviour at high temperatures and warming behaviour at low temperatures during the day. In all temperatures tested these frogs remained on land changing their preferred location from the open area to the hiding places. The main activity period shifted from night to day with decreasing temperatures. The more southern species R. lessonae preferred higher temperatures than the other species showing basking behaviour during the day independent of the ambient temperature. With decreasing temperatures the preferred location changed from the shore to the water and the activity during the night almost disappeared. The closely related R. ridibunda tolerated high temperatures too, but only rarely basked. This species, however, reacted contrarily to decreasing temperatures: it changed its preference from the water to the land. This behavioural differenciation between the water frog species may be of importance for the actual habitat preference of these central european water frogs.     

Patterns of orientation behavior in marsh frogs (Rana ridibunda Pall.) of southern populations

The behavior of frogs from southern areas with an arid climate released during the reproductive period between their “home” pond and a less distant river is shown to be independent of weather conditions. The experiments were performed on frogs living near the village of Dosang, Astrakhan oblast. The frogs were released 60 to 150 m from their “home” breeding waterbody and 60 to 80 m from an “alien” waterbody. Four experiments were performed on 27 individuals. The movements of the frogs were traced by the method of “tracking by a thread.” The results revealed no preference in the frogs to return to their own breeding ponds, rather than to the nearby river. This behavior is peculiar to frogs of southern populations.     

Oviposition Site Selection and Spatial Predictability of Female White-faced Dragonflies (Leucorrhinia intacta) (Odonata: Libellulidae)

Location of breeding or egg-laying sites may be an important factor underlying social behavior of many organisms. We studied oviposition sites used by a population of Leucorrhinia intacta dragonflies at a small pond near Syracuse, NY, USA. Females preferentially used shallow water as an oviposition habitat. Shallow water increases egg hatching rate through temperature effects on development time and reduces predation on the female. Use of shallow water areas was reduced by locally high densities of territorial males. The same oviposition sites probably maximized the fitness of the male, female, and offspring, meaning that site selection did not necessitate fitness tradeoffs among these classes of individuals. Pond sectors used by ovipositing females were significantly correlated within and between years, but not within days or between consecutive days. Use of pond sectors within and between days was not related to the relative availability of the shallow water habitat, while seasonal use of pond sectors was related positively to availability of shallow water. In spite of the preference by females for ovipositing in shallow water, short-term location of females was not predictable and males could not search predictably good areas during a day. However, across a season, areas with more shallow water available were used for oviposition more than areas with limited substrate.     

Seasonal changes in the migratory behaviour of the toad Bufo bufo: direction and magnitude of movements

Summary The migratory behaviour of the toad Bufo bufo was studied from February 1985 to April 1986 in the submontane region of Bavaria, West Germany. Toads were fitted with a mechanical tracking device to record individual paths of migration. Three aspects of migratory behaviour were quantified: orientation in relation to the breeding site, straightness of path, and locomotory activity. The annual activity period began with migration from the hibernation sites to the breeding pond in April. The paths went straight towards the breeding pond independent of the distance (70–420 m). During the period of oviposition the preference for the breeding site direction vanished and toads moved away from the breeding pond, but in less straight paths than before. In summer migratory activity decreased considerably and was restricted to small areas, the home ranges, at distances of 55–1600 m from the natal breeding pond. The straightness of path was rather low, because toads often returned to their starting points. During rainy nights toads occasionally left their home ranges for extensive excursions. In autumn most toads again migrated towards the breeding pond, but paths were significantly less straight and direct than in spring. However, toads stopped before reaching the breeding pond and hibernated in holes or under the leaf layer. The mortality rate of tracked toads was about 45%. The relative influence of 17 environmental variables on locomotory activity was evaluated by principal component analysis and stepwise multiple regression. Temperature at night and rainfall variables accounted for significant amounts of variance, whereas temperature by day, air humidity, and atmospheric pressure showed no correlation. Activity decreased if temperature approached 0° C or after long periods without rainfall. Within a certain range of tolerance, however, the locomotory activity of the toads was widely independent of environmental factors, indicating that endogeneous factors are more important sources of variation in the migratory behaviour of these toads than commonly assumed.     

Effects of Experimental Canopy Manipulation on Amphibian Egg Deposition

ABSTRACT Although effects of forest management on amphibians are relatively well studied, few studies have examined how these practices affect egg deposition by adults, which can impact population recruitment. We quantified the effects of 4 canopy tree-retention treatments on amphibian oviposition patterns in clusters of 60-L aquatic mesocosms located in each treatment. We also related aquatic and terrestrial biophysical parameters in treatment plots to oviposition patterns. Cope's gray treefrogs (Hyla chrysoscelis) deposited more egg masses in clear-cut and 25–50% tree-retention treatments than in controls. In contrast, mountain chorus frogs (Pseudacris brachyp***hona) deposited more egg masses in unharvested control and 75% retention treatments than in clear-cut or 25–50% retention treatments. Spotted salamanders (Ambystoma maculatum) only deposited eggs in 75% retention treatments and controls. The number of egg masses deposited by mountain chorus frogs was positively related to canopy cover and negatively related to water temperature, pH, and dissolved oxygen, whereas we noted the opposite relationships for Cope's gray treefrogs. We did not detect a relationship between the number of egg masses deposited by any species and the distance of mesocosms to either the nearest mature closed-canopy forest or to the nearest natural amphibian breeding pool. The impacts of the silvicultural treatments we studied were species-specific and depended on the amount of trees removed. In areas where protection of spotted salamander and mountain chorus frog breeding habitat is a priority, we recommend harvests retain at least 75% of the canopy. Our results also suggest that retention of 25–50% of canopy trees surrounding amphibian breeding pools has little conservation benefit.     

Acoustic Preference of Frog‐Biting Midges (Corethrella spp) Attacking Túngara Frogs in their Natural Habitat

In many animals, males aggregate to produce mating signals that attract conspecific females. These leks, however, also attract eavesdropping predators and parasites lured by the mating signal. This study investigates the acoustic preferences of eavesdroppers attracted to natural choruses in a Neotropical frog, the túngara frog (Engystomops pustulosus). In particular, we examined the responses of frog‐biting midges to natural variation in call properties and signaling rates of males in the chorus. These midges use the mating calls of the frogs to localize them and obtain a blood meal. Although it is known that the midges prefer complex over simple túngara frog calls, it is unclear how these eavesdroppers respond to natural call variation when confronted with multiple males in a chorus. We investigated the acoustic preference of the midges using calling frogs in their natural environment and thus accounted for natural variation in their call properties. We performed field recordings using a sound imaging system to quantify the temporal call properties of males in small choruses. During these recordings, we also collected frog‐biting midges attacking calling males. Our results revealed that, in a given chorus, male frogs calling at higher rates and with higher call complexity attracted a larger number of frog‐biting midges. Call rate was particularly important at increasing the number of midges attracted when males produced calls of lower complexity. Similarly, call complexity increased attractiveness to the midges especially when males produced calls at a low repetition rate. Given that female túngara frogs prefer calls produced at higher repetition rates and higher complexity, this study highlights the challenge faced by signalers when increasing attractiveness of the signal to their intended receivers.     

Phonotaxis to male’s calls embedded within a chorus by female gray treefrogs, Hyla versicolor

During the reproductive season, male Hyla versicolor produce advertisement calls to attract females. Females exhibit phonotaxis and approach the individual callers, resulting in amplexus. For frogs that call from dense choruses, the extent to which and the range from which a male’s advertisement call within a chorus can be heard by a receptive female leading to phonotaxis is unclear. We investigated females’ responses to natural choruses in the field and found that they were attracted and showed directed orientation to breeding choruses at distances up to 100 m. To assess the role of acoustic cues in the directed orientation, we conducted acoustic playback experiments in the laboratory using conspecific call and noise as stimuli, as well as chorus sounds (that contained calls from a focal male) recorded at various distances, all played at naturalistic intensities. Using two response metrics (females’ normalized response times and their phonotaxis trajectories) we found that, unlike the field experiments, females oriented and were attracted to chorus sounds from 1 to 32 m only, but not from >32 m, or to band-limited noise. Possible reasons for the observed difference in phonotaxis behavior in the two experimental conditions were discussed.     

Annual activity patterns of anurans in a seasonal neotropical environment

Summary At Panguana, a study in the upper Amazon basin, 7 different aquatic breeding sites of anurans were investigated from Nov. 1, 1981 to Oct. 31, 1982. Rainfall in this area is seasonal. Only 20% of the total annual precipitation was maesured during the dry period, which lasted from mid-March until mid-September 1982. The reproductive periods of the species were highly affected by the rainfall distribution. Calling males and/or gravid females of 46 species were found during the study period. 37.0% of the anuran species were exclusively, and 43.5% predominantly, active during the rainy season. Plots of 100 m² were established at 6 aquatic sites in primary rainforest. A total of 2126 frogs was counted; 93.2% of these were made during the rainy season. A maximum of 378 individuals were found during one check in the plot at the permanent pond. At this site high concentrations of individuals and large choruses were found at the beginning of the rainy season. As soon as favourable temporary aquatic sites were established, reproductive activities decreased at the permanent pond and increased at temporary breeding sites.     

Temporal spacing of breeding activity in the natterjack toad,Bufo calamita

Summary The reproductive behaviour of the toad Bufo calamita was studied in a large population in the northern Rhineland, Germany. Toads bred at four spatially separated but neighbouring areas including 34 breeding ponds. Three methods were applied to monitor quantitatively the intensity of breeding and migratory activity: capture-mark-recapture, a mechanical tracking device, and radio-telemetry. In 1987 a twofold temporal spacing of breeding activity was observed: (1) division of the reproductive period into early, main, and late breeding periods; (2) subdivision of each breeding period into several short calling periods. Since weather conditions were favourable during most of the reproductive period, environmental factors contributed little (23.4%–41.0%) to the temporal variation in breeding intensity as shown by multivariate statistics. The period of vocalization (April to August) included the activity of three distinct male groups. The first group called from April to mid-May (2 calling periods), the second from May to early July (5 calling periods) and the third from mid-July to August (2 calling periods). Within a calling period most males stayed near their calling sites and migratory activity was low. Extensive movements were detected when a new group of males immigrated from the feeding regions to the breeding areas and males that had been calling previously emigrated, at least partly. However, exchange of males among the neighbouring breeding choruses were clearly audible. It is suggested that the energetic costs of vocalization impeded continuous calling activity in individuals and accounted for the periodical variations in chorus size. The short-time variations of breeding activity therefore probably reflect the physiological limits of toads in a situation where the weather permits continuous reproductive activity.     

Inter-male Spacing and Aggression in African Painted Reed Frogs,Hyperolius marmoratus

Inter-male spacing and the role of aggression in the maintenance of spatial organization was examined in choruses of Hyperolius marmoratus males housed in a semi-natural enclosure. The effects of chorus size on spacing patterns, nearest neighbour distances and male aggressive behaviour were examined. Males were found to reduce nearest neighbour distances as chorus size increased. This was accompanied by a shift in spacing pattern from even in small choruses (5–9 males) to random in choruses of 10 to 13 males. In choruses of 14, spacing patterns were once again even. The reason for these shifts is unclear but may reflect a sudden, rather than gradual increased tolerance by individuals to high neighbour call intensity as space to call from becomes more limited. The level of male aggression was influenced by chorus size and the time of night. In general, more aggressive interactions occurred in high density choruses. However, this did not translate into higher levels of individual male aggression as density increased. Individual male aggression was high in early evening choruses and declined to a minimum at peak chorusing time. High levels of aggression during early evening may reflect the establishment of calling sites by males, while the drop in aggression at peak chorusing time may occur in response to the presence of females in the chorus at this time or as a consequence of masking of neighbours calls.     

Sexual selection in Woodhouse's toad (Bufo woodhousei) I. Chorus organization

I studied the reproductive behaviour of a population of prolonged-breeding Bufo woodhousei in central Arizona. Choruses formed in discrete and consistent areas of ponds, and males actively defended calling sites within these aggregations. Call rate and calling site residency, but not size, were important factors determining the outcome of male-male disputes within choruses. Females visited choruses to select males, and oviposition occurred away from the calling site of selected males. Natural and experimental observations revealed that females prefer males with a high call rate. Preliminary results indicated that large males did not achieve greater reproductive success, nor was there any suggestion of assortative mating in size of mated pairs. It is concluded that B. woodhousei has a lek mating system, possible because of its prolonged breeding period. These results are discussed in relation to other anuran mating systems and sexual selection in general.     

Thermal response in adult codling moth

Abstract.  The thermoregulation behaviour of the adult codling moth, Cydia pomonella , is investigated in the laboratory using temperature gradient experiments. Unmated males and females are tested at dawn when moths typically move to resting sites. Mated females are tested during oviposition over a complete diurnal cycle. Temperature strongly affects microhabitat selection in adult moths. Unmated males and females prefer to rest at the low-temperature ends of temperature gradients between 15 and 32 °C. Relative humidity does not influence the thermal response in unmated females, whereas males show a less distinct temperature selection under high humidity. By contrast to unmated moths, ovipositing females prove to be highly thermophilous (i.e. they deposit the highest proportions of their eggs in the zones of highest temperatures of gradients between 15 and 36 °C). This striking discrepancy in thermal response of females between their premating and oviposition period is likely to reflect an adaptation to different selection pressures from the thermal environment. Unmated moths may benefit from low temperatures by a longer lifespan and crypsis within the tree canopy, whereas the choice of warmer oviposition sites by mated females will favour a faster development of eggs.     

Neighbor Call Amplitude Influences Aggressive Behavior and Intermale Spacing in Choruses of the Pacific Treefrog (Hyla regilla)

Male Pacific treefrogs (Hyla regilla) aggregate in choruses during the breeding season. Within these choruses frogs distribute themselves nonrandomly. This study tested the hypothesis that the amplitude of neighbors' calls serves as a proximate cue in regulating the spacing of males in choruses, and that this is mediated by the incidence of aggressive-encounter calls by resident males. The amplitude of neighbors' calls showed little interindividual variation. Advertisement calls were played to males at three amplitudes that spanned the range of neighbor-call amplitudes measured between pairs of frogs. At playback amplitudes corresponding to the minimum neighbor-call amplitudes observed in choruses, frogs gave predominantly advertisement calls and few aggressive-encounter calls in response. As the playback amplitude was increased, subjects progressively decreased the number of advertisement calls and increased the number of encounter calls that they produced in response. The total number of calls (advertisement + encounter) given in response did not vary with playback amplitude. Intruders were likely to move away when a resident male gave encounter calls. In this way neighbor-call amplitude regulates intermale spacing in choruses.     

Male vocalization and female choice in the hybridogenetic Rana lessonae/Rana esculenta complex

In many species, females can improve their fitness by preferring particular males over others. In Palaearctic water frogs of the Rana lessonae/R. esculenta complex the consequences of such mate choice are particularly pronounced. To produce viable offspring, the hybrid R. esculenta (genotype RL) must mate with the parental species R. lessonae (LL); but R. lessonae should avoid mating with R. esculenta, because the resulting hybrid offspring will eliminate the L genome from the germline (hybridogenesis). Hence, there exists a conflict between the sexual parasite (RL) and its sexual host (LL) over the best mating partner. Previous studies have shown a preference for LL males in LL and RL females; but they have also shown that females cannot usually realize their choice when in close proximity to males, because the males forcefully and indiscriminately amplex them. We tested whether females use male vocalizations as a long-distance signal to increase their chances of mating with the preferred LL males. We exposed female R. lessonae and R. esculenta to playbacks of single LL and RL mating calls (experiment 1) and to choruses with a 3:1 excess of LL and RL calls, respectively (experiment 2). In experiment 1, both female types were attracted more by the LL than by the RL calls. In experiment 2, no discrimination between LL- and RL-dominated choruses was observed. The results suggest that females do not use distant male vocalization to approach preferentially ponds or arenas within a pond that hold an excess of LL males. But once they have arrived in a chorus, mating calls from nearby males can direct them to the preferred LL mates. We discuss possible reasons for the failure to discriminate between choruses and the chances for successful choice between individuals within choruses. Copyright 2000 The Association for the Study of Animal Behaviour.     

The Sounds of Silence as an Alarm Cue in Túngara Frogs,Physalaemus pustulosus

In many species males vocally advertise for mates in choruses and these choruses serve as acoustic beacons to conspecific females as well as to eavesdropping predators and parasites. Chorusing will often cease in response to disturbances, such as the presence of predators. In some cases the cessation is so rapid and over such a large area that it seems improbable that males are all responding directly to the same local disturbance. Here, we demonstrate experimentally in Neotropical túngara frogs, Physalaemus pustulosus, that the cessation of calling by males spreads rapidly through the chorus. The cessation of chorusing in response to the cessation of playbacks of three calling males is more effective in inducing chorus cessation than is the cessation of one male calling. When three males are calling, the cessation of complex calls is more effective in inducing chorus cessation than simple calls. There is no main effect on whether the final call of the male is complete or is interrupted. We thus conclude that the sudden lack of signals—the ‘sounds of silence’—becomes an alarm cue that can explain the rapid cessation of choruses that are common in many chorusing species.     

Owl dusk chorus is related to the quality of individuals and nest‐sites

Dawn and dusk choruses represent one of the most investigated topics in avian vocal behaviour, but their underlying basis remains unclear. As with the dawn chorus in passerines, dusk chorus in owls seems to support the mate and rival assessment hypothesis and happens during the most constraining period, as individuals have not yet fed and, under the handicap principle, dusk chorus is likely to reveal inter‐individual differences in competitive ability, body condition and/or habitat quality. Here, a study of vocal displays at dusk of 14 Eurasian Eagle Owls Bubo bubo revealed a temporal succession in the order in which males began their vocalizations. The vocalization order appeared to be related to both the quality of the nesting territory (based upon mean number of fledged young and proportion of rats in the diet) and the male's individual quality, as revealed by haematocrit values and the brightness of the white throat patch.     

Moving south: effects of water temperatures on the larval development of invasive cane toads (Rhinella marina) in cool‐temperate Australia

The distributional limits of many ectothermic species are set by thermal tolerances of early‐developmental stages in the life history; embryos and larvae often are less able to buffer environmental variation than are conspecific adults. In pond‐breeding amphibians, for example, cold water may constrain viability of eggs and larvae, even if adults can find suitable thermal conditions in terrestrial niches. Invasive species provide robust model systems for exploring these questions, because we can quantify thermal challenges at the expanding range edge (from field surveys) and larval responses to thermal conditions (in the laboratory). Our studies on invasive cane toads (Rhinella marina) at the southern (cool‐climate) edge of their expanding range in Australia show that available ponds often average around 20°C during the breeding period, 10°C lower than in many areas of the toads’ native range, or in the Australian tropics. Our laboratory experiments showed that cane toad eggs and larvae cannot develop successfully at 16°C, but hatching success and larval survival rates were higher at 20°C than in warmer conditions. Lower temperatures slowed growth rates, increasing the duration of tadpole life, but also increased metamorph body mass. Water temperature also influenced metamorph body shape (high temperatures reduced relative limb length, head width, and body mass) and locomotor performance (increased speed from intermediate temperatures, longer hops from high temperatures). In combination with previous studies, our data suggest that lower water temperatures may enhance rather than reduce recruitment of cane toads, at least in areas where pond temperatures reach or exceed 20°C. That condition is fulfilled over a wide area of southern Australia, suggesting that the continuing expansion of this invasive species is unlikely to be curtailed by the impacts of relatively low water temperatures on the viability of early life‐history stages.     

MATE CHOICE OCCURS ONLY IN SMALL CHORUSES OF PAINTED REED FROGS HYPEROLIUS MARMORATUS

ABSTRACT

In two-choice discrimination experiments, females of Hyperolius marmoratus preferred the calls of lower frequency of the pair of stimuli. This preference was not shown in mating patterns observed in natural choruses, but is when females are phonotactically orienting in small choruses in an experimental enclosure. With an increase in chorus size, the mating pattern shifts from size-based, non-random (with some evidence of size-assortative) mating to random mating. This is the first time that frequency-based mate-choice by female anurans has been associated with chorus size, and hence with the sonic complexity of the acoustic environment.     

Calling Behaviour Influences Mating Success in Male Painted Reed Frogs,Hyperolius marmoratus

A detailed study was made of the natural calling behaviour of male painted reed frogs in the wild. Comprehensive minute by minute records of the vocal activity of males calling simultaneously in the breeding chorus were generated over a 19-night period using a multi-channel event recorder. With few exceptions, the period over which males called either spanned or extended beyond the time window when females sought mates in the chorus. Males varied little in calling persistence and the majority produced advertisement calls during each minute of the calling period. Aggressive interactions between males curtailed advertisement call production but fights were short-lived, seldom repeated and limited to a small proportion (12.6%) of males. Call rate was independent of body size and varied widely among males active in the chorus at the same time and under the same environmental conditions. The relative call rate ranks of individuals were sustained over time. The call rates of mated males were high in relation to the rates of other males monitored in the chorus at, and prior to, the time of mating. Females usually preferred the higher of two call rate alternatives presented in a range of two-choice phonotaxis experiments.