Feeding ecology and its influence on social organization in Brown hyenas (Hyaena brunnea, Thunberg) of the Central Kalahari Desert

(1) Observations are presented on the diet, feeding habits, hunting and foraging behaviour of Brown hyaenas of the Central Kalahari. (2) The remains of kills left by other predators are the single most important food item in the Brown hyaena's diet. The diet also consists of small scavenged items, small prey such as rodents which the hyaena itself kills, and wild fruits. (3) Brown hyaenas hunt and scavenge small items solitarily, but congregate for communal scavenging of the large kills left by other predators. (4) Individual hyaenas are not territorial and there is great overlap in home ranges. They use common pathways and frequently meet to socialize while foraging. (5) Resident adults form a group with a social hierarchy maintained through neck-biting, muzzle-wrestling, chasing, and other social interactions. Subadult hyaenas often leave the group when approximately 22 months old. (6) Brown hyaenas have a complex system of communication including visual displays, social interactions, vocalizations, and extensive pasting. These are described. (7) Since carrion is an important source of food, Brown hyaenas have developed distinct relationships with other predators and these are described. (8) In conclusion, the Brown hyaena exhibits a highly flexible social system, foraging and hunting small items solitarily and congregating for the common utilization of a large carcass. The social organization is therefore influenced by the feeding ecology.     

Timing and Regulation of Nuclear and Cortical Events in the Cell Cycle of Tetrahymena pyriformis*

SYNOPSIS. Using continuous flow cultures based on the chemostat principle, we varied the cell generation times of the ciliate Tetrahymena pyriformis strain GL, from 4.9 to 22.2 hr and studied various parameters of the cell cycle at 28 C. These included: the duration of the periods required for oral morphogenesis, macronuclear division, cell division, G₁ S, and G₂. The size of individual cells was also measured. Independent of the growth rate, the period of oral morphogenesis occurred during the last 90 min of the cell cycle. In all cases macronuclear and cell divisions took place during the last part of these 90 min, and the final macronuclear separation occurred just before final cell separation. The S-period increased slightly, while the G₁ and G₂ both increased in roughly the same relative proportion to the increasing generation times. Slowly growing cells (generation time 20.5 hr) were shorter but broader and somewhat larger in volume than quickly growing cells (generation time 4.9 hr).     

Winter Temperature as a Constraint to the Migration of Preindustrial Peoples

The dispersion of preindustrial peoples is strongly related to winter temperature in two surprising respects. Based on a classification of societies by language, we introduce a statistical model for their dispersion and show that (1) the 10°C (50°F) winter temperature isotherm has been an effective constraint to migration and expansion, and (2) the dispersion of language phyla has been remarkably homogeneous in a certain temperature scale, in contrast to the marked heterogeneity in terms of geographical dispersion , [climate, language, migration]     

Incubation in Mice Provides a Signal for the Differentiation of Trypanosoma cruzi Epimastigotes to Trypomastigotes1

The differentiation of Trypanosoma cruzi epimastigotes into trypomastigotes was studied in diffusion chambers sub-cutaneously implanted in mice. Using epimastigotes of the Tulahuén strain, transformation was first evident at 16 h after implantation and reached its maximum (92% trypomastigotes) by 24 h. Shortly before their differentiation into trypomastigotes, epimastigotes were found to develop resistance to lysis by the alternative pathway of complement. Furthermore, implantation of stationary-phase (as opposed to log-phase) parasites resulted in the accumulation of large numbers of complement-resistant epimastigotes in the chambers. These observations suggest that epimastigotes pass through a complement-resistant transitional stage before differentiating into trypomastigotes and that transformation may require cell division. In a further series of experiments, epimastigotes recovered 7 h after implantation in mice were found to differentiate into trypomastigotes when cultured in vitro for an additional 17 h at 37°C. This observation indicates that the events which trigger the morphologic transformation of epimastigotes into trypomastigotes can be dissociated operationally from the differentiation process itself.     

Natural convection from leaves at realistic Grashof numbers

Abstract. The boundary layer resistance of model leaves was measured in still air, at a range of leaf-to-air temperature differences. The results were compared to those calculated from standard formulae for natural convection. The agreement between observed and calculated was only satisfactory when Grashof numbers exceeded about 105. At the lower Grashof numbers, which often prevail in nature, the observed rates of heat transfer considerably exceeded those calculated.     

Comparative Studies of Reproductive Behavior in Mantis Shrimps and Fiddler Crabs

Comparative ethological studies of closely related species canplace into clear perspective the functions of behavioral traitsas species diverge and adapt to different environments. In thispaper we contrast the reproductive behavior of species withintwo crustacean groups: the mantis shrimps (stomatopods) andthe fiddler crabs (genus Uca). For the stomatopods, we identifyprobable selective relationships between features of species'ecology and their mating systems. Population density, the kindand availability of shelters in which these shrimps live, theintensity of predation and spawning cycles all play importantroles in molding reproductive behavior in this group. Associationsbetween the ecology and mating systems of fiddler crabs havebeen discussed recently elsewhere. Here we focus on a comparativeanalysis of sexual communication in these crabs. A study ofcompetitive courtship signaling and mate choice in the fiddlercrab Uca beebei has shown that certain male courtship signalsare highly attractive probably because they exploit female sensory-responsesystems that have been molded by selection for escape from predators.Interspecific comparison of male courtship displays and theresponses of females to these displays suggest that sensoryexploitation may play an important role in the evolution ofsexual signals in the genus. Comparative studies have advancedour understanding of how natural and sexual selection affectthe reproductive behavior of both stomatopods and fiddler crabs.     

Dimorphism in a Tethyan early Jurassic Juraphyllites

A lappeted microconch specimen of the phylloceratid ammonoid Juraphyllites from the Tethyan Jurassic of Anatolia (Turkey) indicates that sexual dimorphism in this group was established as early as in the early Lower Pliensbachian (Lower Jurassic) and that dimorphism in this genus of the Phylloceratina follows the same pattern as that proven [or many groups of the Ammonitina. This is the earliest record of well-developed lateral lappets in the Mesozoic Ammonoidea