Dating the fungus-growing termites' mutualism shows a mixture between ancient codiversification and recent symbiont dispersal across divergent hosts.

The mutualistic symbiosis between fungus-growing termites and Termitomyces fungi originated in Africa and shows a moderate degree of interaction specificity. Here we estimate the age of the mutualism and test the hypothesis that the major splits have occurred simultaneously in the host and in the symbiont. We present a scenario where fungus-growing termites originated in the African rainforest just before the expansion of the savanna, about 31 Ma (19-49 Ma). Whereas rough age correspondence is observed for the four main clades of host and symbiont, the analysis reveals several recent events of host switching followed by dispersal of the symbiont throughout large areas and throughout different host genera. The most spectacular of these is a group of closely related fungi (the maximum age of which is estimated to be 2.4 Ma), shared between the divergent genera Microtermes, Ancistrotermes, Acanthotermes and Synacanthotermes (which diverged at least 16.7 Ma), and found throughout the African continent and on Madagascar. The lack of geographical differentiation of fungal symbionts shows that continuous exchange has occurred between regions and across host species.

The electric organ discharges of the Petrocephalus species (Teleostei: Mormyridae) of the Upper Volta system.

In this study, a first comparative investigation of all four species of Petrocephalus (P. bovei, P. bane, P. soudanensis and P. cf. pallidomaculatus) present in the Upper Volta system and their electric organ discharges (EOD) was conducted. It was found that P. bovei was the most widespread (in terms of habitat use), but in several places P. bovei, P. soudanensis and P. cf. pallidomaculatus occurred syntopically. All species emitted a triphasic signal, and with very few exceptions, the Petrocephalus species of the Upper Volta system could clearly be identified on the basis of their EOD waveforms. The most obvious differences between species in EOD waveforms were in amplitude of the last phase, total duration and fast Fourier transformation (FFT) peak frequency. No sexual dimorphism was present in the EOD of any species although external dimorphism, i.e. an indentation at the base of the anal fin of mature males, was common. The EOD waveform diversity in the Upper Volta principally resembled that found in four sympatric Petrocephalus species from the Ogooué system (Gabon) and might play a role in species recognition and speciation processes.

Improved recruitment of a lemur-dispersed tree in Malagasy dry forests after the demise of vertebrates in forest fragments.

The objective of this study was to examine how the processes of seed dispersal and seed predation were altered in forest fragments of the dry forest of Madagascar, where the usual seed dispersers and vertebrate seed predators were absent, using a lemur-dispersed tree species (Strychnos madagascariensis; Loganiaceae) as an example. We then assessed how the changes in vertebrate community composition alter the regeneration pattern and establishment of this tree species and thus, ultimately, the species composition of the forest fragments. By using size-selective exclosures, data from forest fragments were compared with results from continuous forest where vertebrate dispersers and predators were abundant. Visits to the exclosures by mammalian seed predators were monitored with hair traps. In the continuous forest up to 100% of the seeds were removed within the 7 days of the experiments. A substantial proportion of them was lost to seed predation by native rodents. In contrast, practically no predation took place in the forest fragments and almost all seeds removed were dispersed into the safety of ant nests by Aphaenogaster swammerdami, which improves chances of seedling establishment. In congruence with these findings, the abundance of S. madagascariensis in the forest fragments exceeded that of the continuous forest. Thus, the lack of vertebrate seed dispersers in these forest fragments did not lead to a decline in regeneration of this animal-dispersed tree species as would have been expected, but rather was counterbalanced by the concomitant demise of vertebrate seed predators and an increased activity of ants taking over the role of seed dispersers, and possibly even out-doing the original candidates. This study provides an example of a native vertebrate-dispersed species apparently profiting from fragmentation due to flexible animal-plant interactions in different facets, possibly resulting in an impoverished tree species community.

Trade-off between chemical and biotic antiherbivore defense in the South East Asian plant genus Macaranga.

The plant genus Macaranga is known for its manifold mutualistic associations with ants. The plants provide food for the ants and in turn get protection from herbivores. Depending on the strength of the plant-ant interaction, the plant's investment in ants and the biotic defense derived from them is more or less effective. We conducted a comparative study on tannin content in 12 Macaranga species that were selected based on their associations with ants (three nonmyrmecophytes and nine myrmecophytes, three of which start their ontogeny as nonmyrmecophytes). Different developmental stages were investigated in three Macaranga species. Extracts of every individual plant analyzed for tannins were also tested for their effects on larval growth employing larvae of the common cutworm (Spodoptera littoralis). The studied Macaranga species differed significantly in their tannin contents as well as in the effects of their leaf extracts on the growth of S. littoralis larvae. A correlation analysis shows a connection between tannin contents and larval growth. High tannin contents and, thus more effective chemical defense, were observed in nonmyrmecophytic Macaranga species associated only facultatively with ants as compared to obligate myrmecophytes. Our study supports the hypothesis of a trade-off between chemical and biotic defense in the genus Macaranga.

Adaptations to biotic and abiotic stress: Macaranga-ant plants optimize investment in biotic defence.

Obligate ant plants (myrmecophytes) in the genus Macaranga produce energy- and nutrient-rich food bodies (FBs) to nourish mutualistic ants which live inside the plants. These defend their host against biotic stress caused by herbivores and pathogens. Facultative, 'myrmecophilic' interactions are based on the provision of FBs and/or extrafloral nectar (EFN) to defending insects that are attracted from the vicinity. FB production by the myrmecophyte, M. triloba, was limited by soil nutrient content under field conditions and was regulated according to the presence or absence of an ant colony. However, increased FB production promoted growth of the ant colonies living in the plants. Ant colony size is an important defensive trait and is negatively correlated to a plant's leaf damage. Similar regulatory patterns occurred in the EFN production of the myrmecophilic M. tanarius. Nectar accumulation resulting from the absence of consumers strongly decreased nectar flow, which increased again when consumers had access to the plant. EFN flow could be induced via the octadecanoid pathway. Leaf damage increased levels of endogenous jasmonic acid (JA), and both leaf damage and exogenous JA application increased EFN flow. Higher numbers of nectary visiting insects and lower numbers of herbivores were present on JA-treated plants. In the long run, this decreased leaf damage significantly. Ant food production is controlled by different regulatory mechanisms which ensure that costs are only incurred when counterbalanced by defensive effects of mutualistic insects.

Do ant mosaics exist in pristine lowland rain forests?

Ant mosaics have been described as characteristic elements of arboreal ant communities from tropical plantations, and it is often assumed that they also exist in undisturbed lowland rain forests. Until now, however, there have been no studies from pristine rain forests to show this. Our investigations on the mechanisms structuring arboreal arthropod communities in a southeast-Asian lowland rain forest allowed us to compare our results with the predictions of the ant mosaic theory. According to this theory aggressive dominant ant species should maintain mutually exclusive territories. Furthermore, communities of associated nesting species dominated by the same dominant species should be more similar to each other than communities governed by other dominants. The ant communities of 19 individuals of three understorey tree species were collected with an improved method of canopy fogging that guaranteed selective tree sampling in a multilayered rain forest. Ten trees were re-fogged after 6 months and seven again after 3 years to investigate whether the reorganization of the ant communities occurred in a similar way. To test whether the pattern of an ant mosaic emerged when not only single trees but also somewhat larger areas containing several adjacent trees were sampled, we collected the nesting ant species from a group of Aporusa lagenocarpa with tuna baits. All ant communities were highly heterogeneous in their species composition and neither negative nor positive species associations were found. The lack of an ant mosaic in mature forests is also suggested by a Monte Carlo computer simulation, according to which ant community composition differed only slightly from random. The re-fogged communities showed the same structural heterogeneity as was found in the first fogged communities, without any observable convergence to the original species composition. No pioneer or climax species could be identified. All results combined indicate that the ant mosaic theory does not apply to the mature lowland rain forest investigated, where community organization seems to be the product of very complex dynamic processes.

Unusual cell ultrastructure in ventral epidermis of the African reed frog Hyperolius viridiflavus, (Anura; Hyperoliidae).

The stratum corneum of the epidermis of Hyperolius viridiflavus contains several replacement layers. The outer layer is covered by mucopolysaccharide secretion. H. viridiflavus in their dry phase do not moult the sloughed off layers; these remain attached to the stratum corneum. Long and slender pillar-like cells situated under the stratum corneum extend through the stratum granulosum, stratum germinativum, and the basement membrane into the dermis. These cells abound in tonofilaments. Flask-shaped cells rich in mitochondria, reaching under the stratum corneum, extend into the stratum granulosum. They show delicate, membranous infoldings in their neck-like apical part. Granule-cells, arranged in 2 or 3 layers are situated in the stratum granulosum between the stratum corneum and germinativum. The germinative cells are large and separated from each other by wide intercellular spaces. ATPase activity was localized cytochemically in the baso-lateral cell membranes bordering with the intercellular spaces under the stratum corneum.

Choice of optimal oviposition sites by Hoplobatrachus occipitalis (Anura: Ranidae) in an unpredictable and patchy environment.

The rock pools on the river bank of the Comoé National Park (West Africa) provide a very diverse and unpredictable environment for anuran larval development. Because rock pools differ considerably in biotic and abiotic parameters, it should be adaptive for reproducing anurans to choose the most suitable oviposition sites. During the beginning of each rainy season (March to May), from 1991 to 1995, we investigated the allocation of breeding sites by Hoplobatrachus occipitalis, counted the number of eggs, and measured several biotic and abiotic factors that might influence the choice of a spawning site. The probability of predation by conspecific cannibalistic tadpoles and the water-holding capacity (WHC) of pools were the best predictor of number of eggs laid. We experimentally investigated the influence of these two parameters on egg-laying and showed that adults potentially can assess the presence, density, and size of tadpoles in pools by chemical cues. Likewise, manipulation of the water-holding capacity caused a rapid change in egg-laying behavior. To assess the risk of desiccation, frogs have to visit familiar pools repeatedly to monitor the decrease in volume over time and thus gain information about the pools' water-holding capacity.

Regulation of body water balance in reedfrogs (superspecies Hyperolius viridiflavus and Hyperolius marmoratus: Amphibia, Anura, Hyperoliidae) living in unpredictably varying savannah environments.

The regulation of body water balance was examined in the reedfrogs Hyperolius marmoratus taeniatus and Hyperolius viridiflavus ommatostictus. Temperature and stage of post-metamorphic development significantly affected the rate of water uptake. Hydrated reedfrogs prevented hyperhydration by voiding diluted urine when obtaining water. Within 48 hr after rehydration, body fluid osmolality remained at low levels, which may be supportive to counter excessive cutaneous water influx in hydrated frogs. Once evaporative water loss exceeded 10-12% total body mass, reedfrogs became anuric. The rate of water uptake strongly increased with increasing body water deficit. Both the anuric response and the increased rate of water uptake are assumed to strongly enhance the efficacy of using very briefly available water sources during dry-period conditions. Dry-adapted and estivating reedfrogs survived evaporative water losses between 40 and 55% total body mass. Bladder fluid stores contributed substantially to this desiccation tolerance. During a 16-day period of desiccation, H. v. ommatostictus could replace approximately 25% of evaporative water loss from the bladder fluid store. During desiccation, the level of free amino acids selectively increased in the gastrocnemius muscle tissue, which may support cell volume regulation and/or protect cellular structures from osmotic stresses. Even strongly dehydrated reedfrogs rehydrated quickly with no obvious osmoregulatory problem. Rehydration was associated with a higher than expected decrease of free amino acids in the gastrocnemius muscle tissue, a response that may help to protect cells from bursting during fast rehydration.

On sex determination in the Turkish desert woodlouse Hemilepistus elongatus (Crustacea, Isopoda, Oniscidea): searching for sex chromosomes and for sex-specific differences in simple DNA repeats.

The karyotype of male and female Hemilepistus elongatus was investigated by means of C-banding. The diploid chromosome number in both sexes is 2n = 50. By scrutinizing general morphology and localization of the constitutive heterochromatin, no heteromorphic sex chromosomes were found. All chromosome pairs in males are well paired during diakinesis. Hybridization of genomic DNA with (GACA)4 and (GATA)4 oligonucleotides revealed no sex-specific patterns. Key words : karyotype, C-banding, sex determination, simple DNA-repeats, Isopoda.

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.

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia: Anura: Hyperoliidae) to its arid environment. VI. The iridophores in the skin as radiation reflectors.

Hyperolius viridiflavus possesses one complete layer of iridophores in the stratum spongiosum of its skin at about 8 days after metamorphosis. The high reflectance of this thin layer is almost certainly the result of multilayer interference reflection. In order to reflect a mean of about 35% of the incident radiation across a spectrum of 300-2900 nm only 30 layers of well-arranged crystals are required, resulting in a layer 10.5 microns thick. These theoretical values are in good agreement with the actual mean diameter of single iridophores (15.0 +/- 3.0 microns), the number of stacked platelets (40-100) and the measured reflectance of one complete layer of these cells (32.2 +/- 2.3%). Iridescence colours typical of multilayer interference reflectors were seen after severe dehydration. The skin colour turned from white (0-10% weight loss) through a copper-like iridescence (10-25% weight loss) to green iridescence (25-42%). In dry season state, H. viridiflavus needs a much higher reflectance to cope with the problems of high solar radiation load during long periods with severe dehydration stress. Dry-adapted skin contains about 4-6 layers of iridophores. The measured reflectance (up to 60% across the solar spectrum) of this thick layer (over 60 microns) is not in keeping with the results obtained by applying the multilayer interference theory. Light, scattered independently of wavelength from disordered crystals, superimposes on the multilayer-induced spectral reflectance. The initial parallel shift of the multilayer curves with increasing thickness and the almost constant ("white") reflectance of layers exceeding 60 microns clearly point to a changing physical basis with increasing layer thickness.

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment : IV. Ecological significance of water economy with comments on thermoregulation and energy allocation.

After breeding African savanna dwelling reed-frogs of the "superspecies" Hyperolius viridiflavus face a severe dry season. The frogs withstand the adverse abiotic conditions in exposed positions, clinging to dry vegetation. Only juveniles (300-700 mg) are able to adjust water economy and metabolism to a prolonged dry season. Wet season frogs attain low levels of evaporative water loss (EWL) within 6-8 days after incipient water shortage. This time course is mainly determined by the animal's ability to lower metabolism and activity level to the minimum demands of a dry season. Barriers against diffusion of water which most probably are built up by the stratum corneum and/or the overlying film of dried mucus seem not to be essentially modified during adjustment to dry season conditions. Changeover to dry season physiology is greatly accelerated through preconditioning frogs to water shortage. AdultHyperoliusare unable to reduce activity and metabolism as fast and effectively as juveniles. Most probably these are the main reasons for their very restricted survival capability under dry season conditions; the generally poor energy reserves after the breeding period may further shorten their survival time. At the critical thermal maximum (CTM) Hyperolius uses skin gland secretions for evaporative cooling. Acclimation effects and regulation of evaporative cooling within some 1/10° C help to employ limited water reserves very economically. Dry adapted, dehydrated frogs take up water, whenever available, via specialized skin areas. Rate of uptake is high and is mainly determined by the actual stage of dehydration. The onset of the water-balance-response is also affected by preconditioning. Survival time of small (<500 mg) estivating Hyperolius is limited by their water reserves.Due to their unfavourable surface to volume ratio they loserelatively more water by evaporation than larger conspecifics. Therefore, smaller specimens should allocate energy preferably to growth, until reducing EWL so far to survive the average periods between the rare precipitations. In larger frogs (>500 mg) the amount of stored energy determines maximal survival time. When a critical size is reached in postmetamorphic growth, a change in energy allocation from body growth to energy storage would improve prospects of survival and should therefore be expected. Species specific differences in regard to EWL and CTM indicate a strong correlation between physiological properties and ecological demands.

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.

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment : I. The skin of Hyperolius viridiflavus nitidulus in wet and dry season conditions.

Hyperolius viridiflavus nitidulus inhabits parts of the seasonally very hot and dry West African savanna. During the long lasting dry season, the small frog is sitting unhidden on mostly dry plants and has to deal with high solar radiation load (SRL), evaporative water loss (EWL) and small energy reserves. It seems to be very badly equipped to survive such harsh climatic conditions (unfavorable surface to volume ratio, very limited capacity to store energy and water). Therefore, it must have developed extraordinary efficient mechanisms to solve the mentioned problems. Some of these mechanisms are to be looked for within the skin of the animal (e.g. protection against fast desiccation, deleterious effects of UV radiation and overheating). The morphology of the wet season skin is, in most aspects, that of a "normal" anuran skin. It differs in the organization of the processes of the melanophores and in the arrangement of the chromatophores in the stratum spongiosum, forming no "Dermal Chromatophore Unit". During the adaptation to dry season conditions the number of iridophores in dorsal and ventral skin is increased 4-6 times compared to wet season skin. This increase is accompanied by a very conspicuous change of the wet season color pattern. Now, at air temperatures below 35° C the color becomes brownish white or grey and changes to a brilliant white at air temperatures near and over 40° C. Thus, in dry season state the frog retains its ability for rapid color change. In wet season state the platelets of the iridophores are irregularly distributed. In dry season state many platelets become arranged almost parallel to the surface. These purine crystals probably act as quarter-wave-length interference reflectors, reducing SRL by reflecting a considerable amount of the radiated energy input.EWL is as low as that of much larger xeric reptilians. The impermeability of the skin seems to be the result of several mechanisms (ground substance, iridophores, lipids, mucus) supplementing each other.The light red skin at the pelvic region and inner sides of the limbs is specialized for rapid uptake of water allowing the frog to replenish the unavoidable EWL by using single drops of dew or rain, available for only very short periods.

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment : II. Some aspects of the water economy of Hyperolius viridiflavus nitidulus under wet and dry season conditions.

Adaptations to aridity of the reedfrog Hyperolius viridiflavus nitidulus, living in different parts of the season-ally very dry and hot West African savanna, are investigated. 1. During the dry season mainly juveniles (weighing 200-600 mg) were found in the field. A very low rate of evaporative water loss (EWL; about 1.2% of the body weight/day under laboratory dry season conditions) enables the frogs to estivate unshaded on dry plants. There they are exposed to temperatures occasionally reaching 45° C and are to sustain high radiation loads. The EWL of wet season frogs (WSF) was on average 30 times higher. 2. In dry season frogs (DSF) a thin layer of desiccated mucus seals the body surface reducing water loss and securing tight attachment to the substrate. The DSF are not in a state of torpor but are able to become active at any moment. The highest tolerable water loss of DSF amounts to 50% of their initial body weight. Since uptake of water or food often is impossible for more than two months, the small DSF have to survive these harsh conditions with very limited reserves of energy and water. 3. The low EWL of DSF does not engender any cooling effects. Only above a certain high temperature limit, defined as the critical thermal maximum (CTM; 43-44°C) we found a steep increase of EWL-probably indicating evaporative cooling. The CTM is affected by the temperature during acclimatization. 4. In contrast to WSF cutaneous respiration is not found in DSF. All CO2 is delivered via the lungs by discontinuous ventilation. The simultaneous water loss via the respiratory tract makes up to 14.9+/-8.9% of the entire water loss. 5. A very fast water uptake (69.3+/-19.4%/h) via thin and vascular skin areas at the ventral flanks and the inner sides of the legs enables the frogs to use small quantities of water available for very short times only. This highly permeable skin is protected against desiccation by the typical squat resting position of the frogs. 6. DSF usually to neither urinate nor defecate; they are not proved to be uricotelic. Probably they store the nitrogenuous wastes as urea in the body fluids and as purines in the iridophores and connective tissues. It is suggested that there is no selective advantage for uricotelism in the small H. v. nitidulus.