Reed Frog Research Articles

Diversity and distribution of reed frogs (Hyperolius spp.) on Bioko Island, Equatorial Guinea

Reed frogs (Hyperolius spp.) are the most species-rich genus in the family Hyperoliidae, a group of frogs endemic to sub-Saharan Africa and the Gulf of Guinea islands. Three species are endemic to oceanic islands in the archipelago, but the diversity and distribution of reed frogs on Bioko – a land-bridge island in the archipelago – remains unclear. Two species, H. tuberculatus and H. ocellatus ocellatus, were formally documented on Bioko in the colonial era, however, two additional reed frog species have been detected in recent surveys. In addition, observations of heterospecific amplexus suggest one of the unidentified species and H. o. ocellatus may be hybridising on the island. In this study, we examined mitochondrial DNA (mtDNA), nuclear DNA (nuDNA), morphological and acoustic data to confirm the tentative identifications of the reed frogs and determine if there is any evidence of hybridisation. Our data confirm that the two unidentified species are H. endjami and H. fusciventris, and that Bioko H. endjami have unique genetic diversity not shared with the mainland population. Additionally, our mitochondrial (16S) and nuclear DNA (CMYC) haplotype networks suggest that H. o. ocellatus and H. endjami are not hybridising on Bioko. Finally, we report colour pattern variation in H. endjami and H. o. ocellatus that is unique from populations on the continent, and describe male advertisement calls of Bioko H. endjami and H. o. ocellatus. Our study provides a first look at the diversity and distribution of reed frogs on Bioko Island and sets the stage for future studies of the ecology, evolution, and conservation of this island community. KEYWORDS: hybridisation, polymorphism, mitochondrial and nuclear DNA, morphology, land-bridge island

Phenotypic and genetic divergence in reed frogs across a mosaic hybrid zone on São Tomé Island

AbstractAlthough naturally heterogeneous environments can lead to mosaic hybrid zones, human-induced habitat fragmentation can also lead to environmental heterogeneity and hybridization. Here we quantify phenotypic and molecular divergence across a reed frog mosaic hybrid zone on São Tomé Island as a first step towards understanding the consequences of hybridization across this heterogeneous landscape. The São Tomé giant reed frog (Hyperolius thomensis) is strongly tied to cool, wet, forest habitats whereas the distribution of Moller’s reed frog (H. molleri) spans cool, wet, forests to warm, dry, disturbed habitats. Correspondingly, hybridization is concentrated in the more forested, cool, wet sites relative to non-forested, warmer, drier habitats. Four of six sites with hybrid frogs are artificial water bodies near the forest edge, indicating that both breeding habitat and broader scale environmental variation are probably important for understanding interspecific interactions and the extent of hybridization in this system. Phenotypic variation (body size and ventral coloration) largely tracks genetic and environmental variation across the hybrid zone with larger and more pigmented frogs occurring in forested, cool, wet habitats. Understanding whether human-induced changes in habitat break down reproductive barriers will be essential for conservation management of the less abundant, forest-associated H. thomensis in the face of rampant hybridization.

Partitioning of morphospace in larval and adult reed frogs (Anura: Hyperoliidae: Hyperolius) of the Central African Albertine Rift

Reed frogs of the genus Hyperolius inhabit a wide range of habitats from open savannah to montane forests in Sub-Saharan Africa with sympatric species frequently exploiting the same localities at tadpole and adult stage. Niche partitioning with respect to morphological traits related to diet and locomotion is expected to shape local Hyperolius communities. In a case study on Albertine Rift Hyperolius in Rwanda and Burundi, we analysed the partitioning of larval and adult morphospace (three-dimensional volume describing size and shape variation) as affected by phylogenetic relationships and environmental constraints. Morphological features and molecular barcoding demonstrated that the Albertine Rift Hyperolius resolved into 12 terminal groups (=species), which represent five phylogenetic lineages. The major morphological source of variation among species was isometric size variation at tadpole and adult stage. Among-species variation of tadpole size (maximum size reached before metamorphosis) predicted the range of snout-vent length variation in adult males indicating a strong coupling between the two stages. The adaptive decoupling hypothesis is not supported at the taxonomic scale of the Hyperolius genus. Size-independent shape traits were assessed using a principal component analysis. The two traits which explained most of the morphological variance at the two ontogenetic stages were related to feeding (mouth architecture in tadpoles, head shape in adults) and to locomotion (body/tail height in tadpoles, leg morphology in adults). Partitioning of the shape axes indicated that savannah-dwelling and forest-dwelling species exploit different volumes of the available morphospace. Transition from open savannah habitats to closed-canopy forests seems to induce modifications of both tadpole and adult morphology.

Lack of phylogeographic structure in the endangered Pickersgill’s Reed Frog; Hyperolius pickersgilli (Raw, 1982)

ABSTRACTThe Endangered Pickersgill’s Reed Frog (Hyperolius pickersgilli) is endemic to South Africa and restricted to the KwaZulu-Natal (KZN) coast. The natural habitat of H. pickersgilli is limited to fragmented patches of coastal reed-bed wetland, the majority of which continues to undergo transformation and degradation caused by urbanisation, agriculture, mining and forestry. These changes have resulted in the steady reduction of suitable, quality habitat and severe fragmentation. In the current study we employed mitochondrial DNA and species-specific microsatellites markers (developed in the current study) to investigate the genetic structure and diversity of H. pickersgilli. Genetic markers revealed moderate to high levels of genetic diversity throughout the remnant groups and absence of specific phylogeographic structure among individuals sampled across twelve localities throughout the range of the species. Results from the current study indicate that gene flow between H. pickersgilli individuals is not restricted, whereby neighbouring groups may interact with each other through continued migration, thereby facilitating possible range expansion should habitat be available. However, the need for continued conservation of the H. pickersgilli population through the protection and management of its natural habitats should remain a top priority in order to conserve representative levels of genetic diversity.

A new distribution record of <i>Polypedates taeniatus</i> (Amphibia : Anura : Rhacophoridae) with notes on its Breeding Call and Post-Embryonic developmental stages

The Terai Reed frog, Polypedates taeniatus (Boulenger, 1906) was described on the basis of two specimens collected from Purneah, Bihar by W. Patridge. IUCN categorized the species as Least Concern due to its wide distribution all along the Himalayan foothills of Nepal and India at elevations below 500 meters a.s.l, supposedly large population and unlikeliness of declining fast enough to be considered in a threatened category. Although their breeding call was syllabilized (Ray, 1991) it was never recorded and analyzed. Nothing was known about the developmental stages of this Rhacophorid anuran which was known to inhabit tall grasslands. While conducting casual field-work in Behala Aerodrome area of south Kolkata, West Bengal, we observed the presence of the species calling from Typha angustifolia reeds. Three foam-nests were also collected and brought to the laboratory for study. The tadpoles were studied and photographed to determine their life stages (Gosner stages). It’s each post-embryonic stage was measured later for their body lengths and tail lengths. Collection of three adult frogs (Registration No: ZSI A 11457 - A 11459) constitutes the first record of the species from the State of West Bengal, India and is more than 600 km from the foothills of the Himalayas. The breeding call of the species was recorded and analyzed. One call was analyzed; the call width was 4.103 seconds with 46 pulses. The pulse rate was 11.21 pulses per second. The fundamental frequency was found to be 1156 Hertz and the peak frequency was 2832 Hertz.

Multimodal Signal Testing Reveals Gestural Tapping Behavior in Spotted Reed Frogs.

In the majority of anuran species, acoustic signals are the dominant mode of inter- and intrasexual communication. Male calls are always accompanied by the movement of a more or less conspicuous vocal sac-a potential visual cue. Reed frogs possess a striking vocal sac with a colorful patch of gland tissue clearly visible once the vocal sac is inflated during acoustic signaling. To investigate the visual signal function of vocal sac and gular gland, we presented male Spotted Reed Frogs (Hyperolius puncticulatus) with unimodal and multimodal signal playbacks of conspecific rivals in their natural habitat and recorded their behavioral responses. We found no difference in receiver response to unimodal advertisement call stimuli and to multimodal stimulus presentations of calls combined with visual signals of an artificial vocal sac with or without a gular patch, moving synchronously or asynchronously with the call playback. The inflations of a vocal sac with a colorful gular patch did not alter receiver response and neither increase nor decrease signal salience during male-male communication. Interestingly, males frequently displayed a novel hind and front foot-tapping behavior in response to all playbacks. Comparison of male responses to advertisement and aggressive call playbacks showed that Spotted Reed Frogs approached the sound source less during aggressive call presentations. Tapping behavior was not influenced by either call playback. We suggest that the gestural tapping behavior might act as vibrational signal and discuss its potential signal function in male contests and courtship for females.

Tropical anurans mature early and die young: Evidence from eight Afromontane Hyperolius species and a meta-analysis.

Age- and size-related life-history traits of anuran amphibians are thought to vary systematically with latitude and altitude. Because the available data base is strongly biased towards temperate-zone species, we provide new estimates on eight afrotropical Reed Frog species. A meta-analysis of the demographic traits in 44 tropical anuran species aims to test for the predicted clinal variation and to contrast results with variation detected in temperate-zone species. The small-sized reed frogs reach sexual maturity during the first or second year of life, but longevity does not exceed three to four years. Latitudinal effects on demographic life-history traits are not detectable in tropical anurans, and altitudinal effects are limited to a slight size reduction at higher elevations. Common features of anuran life-history in the tropics are early sexual maturation at small size and low longevity resulting in low lifetime fecundity. This pattern contrasts with that found in temperate-zone anurans which mature later at larger size and grow considerably older yielding greater lifetime fecundity than in the tropics. Latitudinal and altitudinal contraction of the yearly activity period shape the evolution of life-history traits in the temperate region, while trait variation in the tropics seems to be driven by distinct, not yet identified selective forces.

The effect of airplane noise on frogs: a case study on the Critically Endangered Pickersgill's reed frog (Hyperolius pickersgilli)

AbstractSpecies communicating acoustically may develop behavioral responses that aid them to transmit information and overcome signal masking in habitats disturbed by anthropogenic noise. Although many studies have concentrated on road traffic noise, very few studies mentioned effects of low flying airplane flyby noise on the vocal behavior of frogs. We studied the Critically Endangered Pickersgill's Reed frog (Hyperolius pickersgilli) native to the eastern coastal regions of South Africa as a case study. In order to evaluate the call of H. pickersgilli, we compared a site with high levels of airplane flyby noise to a reference site without any airplane activity. Our results show that H. pickersgilli males made changes in both temporal and spectral properties of their call. Males call significantly more during and after an airplane flyby in relation to the call rate before the noise stimulus, but resumed normal call rhythms when measurements were taken 15 min after overflight. We found that males call at higher mean dominant frequencies (df difference = 161.4 Hz, P < 0.05) when exposed to high‐intensity airplane flyby noise. In comparison with call rate 5 min before the airplane flyby, males called 12 % more during and 18 % more after the airplane flyby. Although changes in the spectral and temporal properties of the call of H. pickersgilli were observed, this species was actively calling for much longer than any other local species. This is the first study from Africa to report effects of anthropogenic noise on anuran communication.

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.

Variations in anuran embryogenesis: yolk-rich embryos of Hyperolius puncticulatus (Hyperoliidae).

Anuran development is usually described using model species, most notably Xenopus laevis and Rana pipiens. We describe the development of the East African Reed Frog, Hyperolius puncticulatus, a species displaying development that is highly divergent from the "classic" anuran developmental pattern. Although having small eggs, the eggs of H. puncticulatus are characterized by a large amount of yolk, and embryonic development is reminiscent of species with large eggs. The eggs are teleolecithal and the cleavage is holoblastic, with a "pseudo-meroblastic" pattern. Gastrulation proceeds primarily at the dorsal lip and is characterized by reduced embryonic cavities. Gastrulation ends with a thickened "embryonic mantle" that sits upon a large yolk mass and forms most of the tissues of the embryo. The embryonic axis curves across the yolk mass, instead of the typical lengthening of anuran embryos. The tadpole hatches with a large ventral yolk mass which is gradually absorbed. We hypothesize about the developmental mechanisms that underlie this unusual development, based on comparisons with other anuran and fish species. We suggest that this type of development is not unique to this species, but can be found in many species of different anuran taxonomic groups. Comparing the development of H. puncticulatus and similar species to what is known about the development of model species, such as X. laevis, shows us the variation in early anuran embryogenesis. Knowing the existing diversity is a prerequisite to understanding the evolution of early anuran development and the changes in patterning mechanisms in different lineages.

Chorus Attendance by Male and Female Painted Reed Frogs (Hyperolius marmoratus): Environmental Factors and Selection Pressures

1. The numbers of male and female Painted Reed Frogs (Hyperolius marmoratus) were monitored over 28 consecutive nights at the height of the breeding season. Despite arguments that male and female numbers should be highly correlated we found that only 32% of the variance in female numbers was explained by the number of males present. 2. To assess our prediction that attendance was determined by considerations other than optimal access to mates we modelled attendance patterns using a wide range of environmental variables. 3. Male and female attendance patterns were best described by different models. For males, 76.6% of the variance in nightly attendance was accounted for by the following variables: a constant, evaporation, pond depth on the previous night, rainfall, atmospheric pressure at 1400 h. wind on the previous day and the number of days since rain. The nature of the inter-relationships suggest that males are primed to attend the chorus unless conditions are liable to lead to increased evaporative water loss. 4. The female model accounted for 87.8% of the nightly variation in attendance and incorporated the following variables: number of males present, number of hours of sunshine on the previous day, wind on the previous day, rainfall 2 days previously, humidity at 1900 h and minimum temperature. The data suggest that females are more selective about the timing of attendance than are males. Specifically, it appears that females attend when conditions favour the rapid development of larvae.

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment. VII. The heat budget of Hyperolius viridiflavus nitidulus and the evolution of an optimized body shape.

Estivating reed frogs of the superspecies Hyperolius viridiflavus are extraordinarily resistant to the highly adverse climatic conditions prevailing in their African savanna habitats during dry season (air temperature up to 45 degrees C, solar radiation load up to 1000 W.m-2, no water replenishment possible for up to 3 months). They are able to withstand such climatic stress at their exposed estivation sites on dry plants without evaporative cooling. We developed a heat budget model to understand the mechanisms of how an anuran can achieve this unique tolerance, and which allows us to predict the anuran's core and surface temperature for a given set of environmental parameters, to within 4% of the measured values. The model makes it possible to quantify some of the adaptive mechanisms for survival in semiarid habitats by comparing H. viridiflavus with anurans (H. tuberilinguis and Rana pipiens) of less stressful habitats. To minimize heat gain and maximize heat loss from the frog, the following points were important with regard to avoiding lethal heat stress during estivation: 1) solar heat load is reduced by an extraordinarily high skin reflectivity for solar radiation of up to 0.65 under laboratory and even higher in the field under dry season conditions. 2) The half-cylindrical body shape of H. viridiflavus seems to be optimized for estivation compared to the hemispheroidal shape usually found for anurans in moist habitats. A half-cylinder can be positioned relative to the sun so that large surface areas for conductive and convective heat loss are shielded by a small area exposed to direct solar radiation. 3) Another important contribution of body shape is a high body surface area to body mass ratio, as found in the estivating subadult H. viridiflavus (snout-vent lengths of 14-20 mm and body weights of 350-750 mg) compared to adult frogs (24-30 mm, 1000-2500 mg) which have never been observed to survive a dry season. 4) These mechanisms strongly couple core temperature to air temperature. The time constant of the core temperature is 29 +/- 10 s. Since air temperature can be 43-45 degrees C, H. viridiflavus must have a very unusual tolerance to transient core temperatures of 43-45 degrees C. 5) If air temperature rises above this lethal limit, the estivating frog would die despite all its optimizations, but moving from an unsuited to a more favorable site during estivation can be extremely costly in terms of unavoidably high evaporative water loss. Therefore, H. viridiflavus must have developed behavioral strategies for reliably choosing estivation sites with air temperature staying on average within the vital range during the whole dry season.

Graded Aggressive Calls in the African Painted Reed Frog Hyperolius marmoratus (Hyperoliidae)

AbstractThe African painted reed frog, Hyperolius marmoratus, has a potentially complex communication system. Advertisement calls and aggressive calls, although distinct from each other, are in fact two ends of a continuum of graded calls. Playback experiments using standard advertisement calls showed that males increased the proportion of aggressive calls as the stimulus intensity was increased. In addition, three characteristics of the aggressive calls changed in response to higher playback levels. Males increased the number of pulses/call, increased call duration, and decreased dominant frequency. Aggressive calling occurred primarily during the early hours of the night, with considerable overlap with times when females were searching for mates in the chorus. Females tested in two‐choice arena trials discriminated against aggressive calls in favor of advertisement calls. It is suggested that aggressive calls reduce a male's ability to attract a female and that a graded signalling system may enable males to escalate agonistic encounters with other males without rendering calls completely unattractive to females.

Chorus Size and Call Intensity: Female Choice in the Painted Reed Frog, Hyperolius Marmoratus

1. In two-choice phonotaxis experiments female painted reed frogs (Hyperolius marmoratus) preferentially chose the stimulus with the greater sound pressure level (SPL) at source when all other call parameters were identical. 2. However, this preference was not apparent when we increased the distance of the louder stimulus from the female such that the SPL of the two stimuli at the release point was equivalent. This suggests that females simply move up sound gradients ('passive attraction'). 3. Female choice of the loudest stimulus was also affected by the number of speakers. 4. There were significantly fewer responses to the loudest speaker in some four-choice compared to matched two-choice phonotaxis experiments. 5. Together these experimental results may partially account for the absence of a large male mating advantage in the field.

Effect of Intermale Spacing on Female Frequency Preferences in the Painted Reed Frog

Effect of Intermale Spacing on Female Frequency Preferences in the Painted Reed Frog

The combined effect of intensity and the temporal relationship of stimuli on phonotaxis in female painted reed frogs Hyperolius marmoratus

The combined effect of intensity and the temporal relationship of stimuli on phonotaxis in female painted reed frogs Hyperolius marmoratus

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment : III. Aspects of nitrogen metabolism and osmoregulation in the reed frog, Hyperolius viridiflavus taeniatus, with special reference to the role of iridophores.

Reed frogs of the superspecies Hyperolius viridiflavus occur throughout the seasonally very dry and hot African savannas. Despite their small size (300-700 mg), estivating reed frogs do not avoid stressful conditions above ground by burrowing into the soil, but endure the inhospitable climate relatively unprotected, clinging to mostly dry grass stems. They must have efficient mechanisms to enable them to survive e.g. very high temperatures, low relative humidities, and high solar radiation loads. Mechanisms must also have developed to prevent poisoning by the nitrogenous wastes that inevitably result from protein and nucleotide turnover. In contrast to fossorial amphibians, estivating reed frogs do not become torpid. Reduction in metabolism is therefore rather limited so that nitrogenous wastes accumulate faster in these frogs than in fossorial amphibians. This severely aggravates the osmotic problems caused by dehydration. During dry periods total plasma osmolarity greatly increases, mainly due to urea accumulation. Of the total urea accumulated over 42 days of experimental water deprivation, 30% was produced during the first 7 days. In the next 7 days rise in plasma urea content was negligible. This strong initial increase of urea is seen as a byproduct of elevated amino acid catabolism following the onset of dry conditions. The rise in total plasma osmolarity due to urea accumulation, however, is not totally disadvantageous, but enables fast rehydration when water is available for very short periods only. Voiding of urine and feces ceases once evaporative water loss exceeds 10% of body weight. Therefore, during continuous water deprivation, nitrogenous end products are not excreted. After 42 days of water deprivation, bladder fluid was substantially depleted, and urea concentration in the remaining urine (up to 447 mM) was never greater than in plasma fluid. Feces voided at the end of the dry period after water uptake contained only small amounts of nitrogenous end products. DSF (dry season frogs) seemed no to be uricotelic. Instead, up to 35% of the total nitrogenous wastes produced over 42 days of water deprivation were deposited in an osmotically inert and nontoxic form in iridophore crystals. The increase in skin purine content averaged 150 μg/mg dry weight. If urea had been the only nitrogenous waste product during an estimation period of 42 days, lethal limits of total osmolarity (about 700 mOsm) would have been reached 10-14 days earlier. Thus iridophores are not only involved in colour change and in reducing heat load by radiation remission, but are also important in osmoregulation during dry periods. The selective advantages of deposition of guanine rather than uric acid are discussed.

Some Determinants of the Mating System in a Population of Painted Reed Frogs (Hyperolius Marmoratus)

AbstractHyperolius marmoratus shares its breeding site with 12 synchronously breeding species. Males call from elevated perches to attract females. Observations of captive populations suggest that males may adopt alternative mating strategies when chorus densities are high. Similar strategies were not observed in natural choruses. The operational sex ratio (OSR) was always male-biased and also highly variable. Mating was polygynous, only 25% of the male population actually mated. Females mated either once or twice. Variance in mating success was much greater among males, an obvious consequence of a skewed OSR. Female choice was probably not a causal factor because male mating success was correlated with neither size nor age. Size-based variation in the male advertisement call does exist, but females cannot exploit this potential vocal cue because of their impaired discriminatory ability in a complex sonic environment and the potential risk of mismating. Although the mating system may best be described as lek-like, with males forming organised choruses through competitive interactions, the variance in male mating success is probably a consequence of stochastic factors.

The effect of chorus organization on mate localization in the Painted Reed frog (Hyperolius marmoratus)

Experiments with female Painted Reed frog (Hyperolius marmoratus) indicate that temporal separation of the calls of neighbouring males does not enhance their locatability. The ability of females to locate a sound source is not impaired when identical calls are broadcast simultaneously through two spatially separated loudspeakers (n=8). We suggest that call alternation may be important in the spatial distribution of males rather than in the ability of females to locate mates.

A New Species of Reed Frog, Hyperolius cystocandicans, from Montane Kenya

A new species of montane Hyperolius, H. cystocandicans, the silverbladdered reed frog, is described from Tigoni, Kenya. Although it is sympatric with and morphologically similar to H. montanus, it is readily distinguished by the presence of a silvery-white opaque bladder visible through the semi-transparent ventral skin and by the presence of pectoral, brachial and digital glands in males; these glands are absent in H. montanus. Hybrids between the two do not develop. Collections from Meru and Maua are tentatively assigned to H. cystocandicans.