Effect of Food and Density on Development of Typical and Cannibalistic Salamander Larvae in Ambystoma tigrinum nebulosum

Two subspecies of the tiger salamander, Ambystoma tigrinum,have a distinctive polymorphic life history that can includefour adult morphs as well as typical and cannibalistic larvalmorphs. We evaluated the effect of environment on developmentof larval morphology in two laboratory experiments. In ExperimentI, 180 larvae were raised in individual 3-liter containers andfed one of three food levels. Larvae in Experiment II receivedone of two levels of food, and were raised at three densities:one larva per 3 liters of water (50 containers), three larvaeper 22 liters of water (18 containers), or seven larvae per22 liters of water (18 containers). Cannibalistic morphs developedonly in nine containers at the highest density, and their occurrencewas independent of the two food levels. Our results suggestthe typical and cannibalistic larvae which occur in some populationsof Ambystoma tigrinum nebulosum is an environmentally induceddevelopmental polymorphism that results from some individualsresponding to the environment differently than others. Thisdifference in response may or may not be associated with geneticdifferences between these morphs. Based on our results we cannotdiscriminate between two models that differ in their assumptionsabout the genetic background of individual larvae.     

Honeyeater population changes in relation to food availability in the Jarrah forest of Western Australia

The numbers of honeyeaters present at particular sites in the Jarrah forest varied significantly from month to month, with peak abundance occurring between May and September. Numbers also varied from site to site, depending upon the major plant species present. Honeyeater abundance was not limited by arthropod availability, but in many instances was closely correlated with the availability of nectar, particularly that produced by Dryandra sessilis. Large honeyeaters, such as Anthochaera chrysoptera and Phylidonyris novaehollandiae, were generally most abundant at times and sites of greatest nectar production. Small honeyeaters, such as Acanthorhynchus superciliosis, were never abundant but were present for most of the year. The production of nectar between October and December was such that more honeyeaters could have been supported than were actually present. Low numbers at these times can be explained in terms of reduced foraging efficiency that would have resulted from more widely dispersed flowers, and the possible availability of more rewarding nectar resources at other sites.     

Interpretation of territorial behaviour in terms of a critical disability hypothesis

The hypothesis is that the great majority of behaviour relating to territorial defence presents difficult anomalies in terms of the normal explanatory mechanism of individual selection. Many, if not all, of the difficulties involved can be solved by using a critical disability hypothesis based upon the principle of group selection. Given this latter model, it is possible to predict the development of (1) highly variable territories, (2) microterritories and (3) macroterritories.     

The Relationship between Transport of Individual Elements and Dry Matter from the Cotyledons of Pisum sativum L.

The transport of dry matter, nitrogen, potassium, phosphorus,magnesium and sodium from the cotyledons of pea seedlings wasmeasured over a growth period of 4 weeks. A linear relationshipbetween the export of each element and dry matter was observedthroughout the experiment, and it was shown that when a certainproportion of the dry matter available for transport had beenexported the same proportion of the amount of each of the elementsavailable for transport had also moved out of the cotyledons.It is concluded that the movement of an individual solute fromthe cotyledons is controlled by a solute potential gradientexisting between the source and sink.     

The influence of microbial food sources and aeration on the growth of Ceriodaphnia quadrangula (O.F.Müller) (Crustacea: Cladocera) under experimental conditions

Casual observations had shown that, in laboratory cultures, populations of Ceriodaphnia quadrangula (O. F. Muller) rarely persisted for more than a month at most. It is shown here that populations of C. quadrangula can be maintained in static water on a diet of mixed algae (mainly Scenedesmus quadricauda (Turp.) Brev., but if the water is disturbed by a slow current of ascending air bubbles, the numbers of C. quadrangula decline. Death is not, however, immediate, and at high densities populations may persist in disturbed water for several weeks before numbers start to decline. Numbers of C. quadrangula did not decline in disturbed water when the food was changed from the alga Scenedesmus to the animal Artemia salina (L.). Individuals of C. quadrangula in the presence of decomposing naupliar larvae of A. salina grew as well in disturbed as in static water and in static water their numbers increased at a greater rate on this animal diet than on an algal diet of Scenedesmus. When the bacterial populations associated with Scenedesmus were greatly reduced, there was no increase in the numbers of C. quandrangula. Microbes associated with Scenedesmus, and not the alga per se, seem to be used as food by C. quandrangula.     

The shape of things to come: linking developmental plasticity to post‐metamorphic morphology in anurans

Development consists of growth and differentiation, which can be partially decoupled and can be affected by environmental factors to different extents. In amphibians, variation in the larval environment influences development and causes changes in post‐metamorphic shape. We examined post‐metamorphic consequences, both morphological and locomotory, of alterations in growth and development. We reared tadpoles of two phylogenetically and ecologically distant frog species (the red‐eyed treefrog Agalychnis callidryas and the African clawed frog Xenopus laevis) under different temperatures with ad libitum food supply and under different food levels at a constant temperature. Low temperature and low food levels both resulted in similarly extended larval periods. However, low temperature yielded relatively long‐legged frogs with a lower degree of ossification than warm temperature, whereas low food yielded relatively short‐legged frogs with a higher degree of ossification than high food levels. Such allometric differences had no effect on locomotor performance of juveniles. Our results provide a basis for understanding the relationship between growth, differentiation and post‐metamorphic shape in anurans and help explain many of the discrepancies reported in previous studies.