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Biomedical subjects

K E Linsenmair

Publications and source records attributed to K E Linsenmair.

8 recordsLinked to original sources
PubMed2001

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.

Adaptation, Physiological↗
PubMed2001

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.

Adaptation, Physiological↗
PubMed1999

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.

Adenosine Triphosphatases↗
PubMed1997

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.

Amino Acids↗
PubMed1995

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.

Acclimatization↗
PubMed1992

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.

Acclimatization↗