Environmental constraints on the foraging behaviour of a dwarf antelope (Madoqua kirkii)

Dik-diks (Madoqua sp.) inhabit semi-arid regions and experience very different conditions of food availability and quality between wet and dry seasons. By comparing the behaviour of dik-diks between these two seasons, we identified environmental constraints affecting their feeding strategies. In both seasons foraging time was limited by high mid day temperatures. In the wet season a high intake rate compensates for the loss in foraging time, but in the dry season water and protein become limiting. To meet minimum daily water requirements in the dry season dik-diks fed on plant species that they avoided during the wet season. Analysis at the plant species level showed higher species selectivity in the wet season than in the dry season. In a multiple regression analysis food species preferences were best explained by relative abundance and water content in the dry season, and by dry matter content in the wet season. In the wet season the daily dry-matter intake of dik-diks in the field was only about 10% higher than the theoretically predicted minimum for a ruminant of this body weight, while protein and water intake were about 3 times as high. This suggests that the most limiting dietary component in the wet season is energy. In the dry season the daily intake of all dietary components is lower than the theoretical minimum required, and also lower than the values suggested by laboratory studies of dik-diks. This dry season deficit is presumably met from body reserves. Dry season water intake was approximately 30% of the intake observed in laboratory studies indicating that dikdiks are even better adapted to arid conditions than suggested by physiological experiments.     

Does habituation to humans influence predator discrimination in Gunther's dik-diks (Madoqua guentheri)?

Animals living around humans may habituate to us, but little is known about the consequences of this habituation. Some wildlife managers assume that habituation to humans makes individuals less likely to respond to natural predators, which is something to be avoided in captive breeding programmes where animals are destined for release. We conducted a playback experiment where we broadcast the sounds of a terrestrial predator and the song from a non-threatening bird to Gunther's dik-diks (Madoqua guentheri), a small ungulate that is vulnerable to many predators, in areas where dik-diks were and were not habituated to humans. Contrary to our expectation, habituated dik-diks discriminated the predator sounds from the birdsong, while unhabituated dik-diks failed to make this discrimination. Our results demonstrate that humans may influence predation hazard assessment, but we should not generally assume that human-habituated animals will be especially vulnerable to predators.     

Genetic and behavioural evidence of monogamy in a mammal,Kirk's dik-dik (Madoqua kirkii).

Little is known about the mating behaviour of monogamous mammals. Here, we present behavioural and genetic evidence of fidelity in a socially monogamous dwarf antelope, Kirk''s dik-dik. DNA microsatellite analysis revealed no evidence of extra-pair paternity (EPP) in dik-diks: mothers'' partners matched the paternal genotype in all 12 juveniles tested. One likely reason for the absence of EPP is that males guard their mates closely during oestrus and over-mark all female scent, thereby reducing the likelihood of other males attempting to mate. In addition, males may be limited in their ability to search for extra-pair populations (EPCs) by activities associated with pair-bond maintenance. Year-round, males maintained proximity within pairs, followed their females'' activity patterns, and spent approximately 64% of their time with their partners. However, males did attempt to obtain EPCs when the opportunity arose, and genetic monogamy in dik-diks is probably best explained by the behaviour of females: in contrast to many monogamous female birds, female dik-diks do not appear to seek EPC partners. We propose that females avoid extra-pair males because they are unable to mate with them without instigating a potentially dangerous conflict.     

The entrainment of breathing rhythm to stride frequency in the dik-dik antelope (Rhynchotragus kirki) with observations on the thermoregulatory consequences

1. Three adult dik-dik antelopes with an average weight of 4.5 kg were used to investigate the rate of oxygen consumption (VO2) during exercise and the entrainment of respiratory rate with stride frequencies at running velocities between 2-11 km/hr. 2. The results of VO2 and the metabolic cost of horizontal locomotion were found to agree with what would be expected of an animal of this size. 3. Respiratory frequencies recorded during the most strenuous exercise were approximately 50% below the value observed when dik-diks are exposed to an ambient temperature (Ta) of 42 degrees C. 4. Respiratory evaporative heat loss was estimated to account for only 4% of the total heat production during exercise. 5. Respiratory frequencies were found to be entrained quite strongly to stride frequencies. The thermoregulatory consequences of this entrainment is discussed.     

The social and spatial organisation of the beira antelope (<Emphasis Type="Italic">Dorcatragus megalotis</Emphasis>): a relic from the past?

We studied the social and spatial organisation of the beira (Dorcatragus megalotis) in arid low mountains in the South of the Republic of Djibouti. Beira was found to live in socio-spatial units whose ranges were almost non-overlapping, with a surface area of about 0.7 km². Each unit included a single adult male, and from one to three adult females. On average, the members of a unit made up a single group during 76% of the observation time, 92% outside the periods when a neonate was in the “hider” stage and/or an adult female in oestrus. Collective sequences of linked urination–defecation were frequent. Members of neighbouring units rarely met and interacted, chasing behaviour occurring mainly between adult males. Overall, the social and spatial organisation of the beira appears to be intermediate between that of the dik-diks (Madoqua spp.), in which units exceptionally include more than one adult female, and that of the oribi (Ourebia ourebi), in which units can include several adult males. Moreover, it resembles those of the klipspringer (Oreotragus oreotragus) and rhebok (Pelea capreolus), two morphologically conservative species that do not belong to the tribe Antilopini. We suggest that the beira’s social and spatial organisation might be similar to that of the last common ancestor to the Antilopini, if not to most of the extant Antilopinae.     

Seasonal Patterns of Mixed Species Groups in Large East African Mammals

Mixed mammal species groups are common in East African savannah ecosystems. Yet, it is largely unknown if co-occurrences of large mammals result from random processes or social preferences and if interspecific associations are consistent across ecosystems and seasons. Because species may exchange important information and services, understanding patterns and drivers of heterospecific interactions is crucial for advancing animal and community ecology. We recorded 5403 single and multi-species clusters in the Serengeti-Ngorongoro and Tarangire-Manyara ecosystems during dry and wet seasons and used social network analyses to detect patterns of species associations. We found statistically significant associations between multiple species and association patterns differed spatially and seasonally. Consistently, wildebeest and zebras preferred being associated with other species, whereas carnivores, African elephants, Maasai giraffes and Kirk''s dik-diks avoided being in mixed groups. During the dry season, we found that the betweenness (a measure of importance in the flow of information or disease) of species did not differ from a random expectation based on species abundance. In contrast, in the wet season, we found that these patterns were not simply explained by variations in abundances, suggesting that heterospecific associations were actively formed. These seasonal differences in observed patterns suggest that interspecific associations may be driven by resource overlap when resources are limited and by resource partitioning or anti-predator advantages when resources are abundant. We discuss potential mechanisms that could drive seasonal variation in the cost-benefit tradeoffs that underpin the formation of mixed-species groups.     

Observations on the behaviour and ecology of a threatened and poorly known dwarf antelope: the beira (<Emphasis Type="Italic">Dorcatragus megalotis</Emphasis>)

Observations on the behaviour and ecology of the beira (Dorcatragus megalotis) were made during spring 2004 in a wild population discovered in 1993 in a low mountain range in the South of the Republic of Djibouti. Spring was found to be both a birthing and a mating season. Beiras fed in the first and last daylight hours, mainly on dicotyledons and in patches supporting trees and/or bushes. They spent the warmest hours of the day in the shade of trees, or in rock shelters when the temperature became too hot. Observed groups (n = 56) ranged in size from one to five individuals (mean ± SD = 2.70 ± 1.49). Most of these groups included a single adult male (62.5%) or no adult male at all (33.9%). The only encounter observed between two adult males resulted in the chasing of one by the other. Furthermore, the mixed-sex groups including a single adult male seemed rather stable, and their members used collective urination–defecation sites. From a behavioural point of view, the beira thus appears not very far from the dik-diks (Madoqua spp.), but differs from them by a greater sociability between adult females and its type of habitat.     

Matched Case Control Studies with Random Exposure Effects

A method for analysing matched case control data in presence of overdispersion or correlation between observations within matched sets is presented. A generalised linear mixed model approach is adapted to account for overdispersion by allowing random exposure effects. Expressions for the elements of the estimation equation are derived and a strategy for achieving efficiency in computing is discussed. Results from simulation studies and two applications are presented.     

Marginal models for correlated binary responses with multiple classes and multiple levels of nesting.

A model for correlated binary data is presented. Marginal probabilities and odds ratios are allowed to have general regression structures that include multiple classes and multiple levels of nesting. Estimation is done through the generalized estimating equations approach of Liang and Zeger (1986, Biometrika 73, 13-22). They are contrasted with conditional models and recommendations for choosing between the two are given. Examples from genetic epidemiology are presented.     

On estimating mortalities from osteological age data

A statistical method (based on the maximum likelihood principle) for estimating mortalities of skeletal populations is presented. The method can be applied both when osteological age groups are not overlapping as well as when they are. The results are presented as point estimates and as confidence intervals around these. The method is applied to two series from the Middle Ages: Westerhus and Helgeandsholmen.     

Bi- or multifunctional opioid peptide drugs

Strategies for the design of bi- or multifunctional drugs are reviewed. A distinction is made between bifunctional drugs interacting in a monovalent fashion with two targets and ligands containing two distinct pharmacophores binding in a bivalent mode to the two binding sites in a receptor heterodimer. Arguments are presented to indicate that some of the so-called “bivalent” ligands reported in the literature are unlikely to simultaneously interact with two binding sites. Aspects related to the development of bi- or multifunctional drugs are illustrated with examples from the field of opioid analgesics. The drug-like properties of the tetrapeptide Dmt¹[DALDA] with triple action as a µ opioid agonist, norepinephrine uptake inhibitor and releaser of endogenous opioid peptides to produce potent spinal analgesia are reviewed. Rationales for the development of opioid peptides with mixed agonist/antagonist profiles as analgesics with reduced side effects are presented. Progress in the development of mixed µ opioid agonist/δ opioid antagonists with low propensity to produce tolerance and physical dependence is reviewed. Efforts to develop bifunctional peptides containing a µ opioid agonist and a cholecystokinin antagonist or an NK1 receptor antagonist as analgesics expected to produce less tolerance and dependence are also reviewed. A strategy to improve the drug-like properties of bifunctional opioid peptide analgesics is presented.     

Hemispheric differences in visual recognition of two Kanji characters

The purpose of the present study was to examine hemispheric differences in visual recognition of two kanji letters. Kanji phrases and nonsense kanji letters were presented unilaterally to the left or right visual hemifield in thirty normal right-handed men by a tachistoscope. The experiments were separated into three conditions; the mixing tasks (ten phrases and ten sets of nonsense letters are presented by mixture), the phase task (twenty phrases are presented), and the nonsense letters task (twenty sets of nonsense letters are presented). Under all conditions, significant right visual hemifield superiorities for the accuracy of recognition of phrase and nonsense letters were observed.     

Simulation of the formation of accelerating structures and ion acceleration in the collision of magnetosonic shock waves

Results are presented from numerical calculations of the maximum energy of accelerated deuterons as a function of the magnetic field for two models of the formation of the accelerating field in the region where two magnetosonic shock waves collide. The numerical results are compared with the similar experimental dependence.     

Graphical rules for non-steady state enzyme kinetic

The exiting graphical methods in enzyme kinetics can be used only within the scope of steady state reactions. In this paper, two graphical rules are presented to deal with the non-steady state enzyme catalysed reaction systems. According to Rule 1 we can immediately write out the phase concentration of enzyme species. The calculation work such as setting up differential equations, making Laplace transformation, expanding determinants, which are both tedious and liable to error, are completely saved. By means of Rule 2 the secular equations for the consecutive first-order reactions can be written out directly without need of setting up differential equations, expanding determinants, etc., that would otherwise be laborious and prone to errors. In addition, two check formulae are also presented for these two graphical methods, respectively. They are useful in order for avoiding the omission of terms during calculations, especially, for complicated mechanisms.     

Efficient RMSD measures for the comparison of two molecular ensembles. Root-mean-square deviation

Quantitative measures are presented for comparing the conformations of two molecular ensembles. The measures are based on Kabsch's formula for the root-mean-square deviation (RMSD) and the covariance matrix of atomic positions of isotropically distributed ensembles (IDE). By using a Taylor series expansion, it is shown that the RMSD can be expressed solely in terms of the IDE matrices. A fast approximate method is introduced for the pairwise RMSD determination whose computational cost scales linearly with the number of structures. A similarity measure for two structural ensembles that is based on the trace metric of the differences of powers of the IDE matrices is presented. The measures are illustrated for conformational ensembles generated by a molecular dynamics computer simulation of a partially folded A-state analog of ubiquitin.     

Kinetic models for peptide-induced leakage from vesicles and cells

In this article analytical expressions for peptide-induced membrane leakage are presented. Two different models for time-dependent leakage have been developed. In the first, the leakage is assumed to be coupled by pores formed by the peptides. In the second model the peptide is assumed to induce a stress/perturbation in the membrane, and in order to reduce the stress, rearrangements in the membrane are induced. The leakage is coupled to these rearrangements, and when equilibrium is achieved no more leakage occurs. From the kinetic models simple fitting routines have been developed involving only two fitting parameters, and these have been used to fit experimental data for two prion protein-derived peptides as well as the honey bee toxin melittin in both vesicles and erythrocytes with good results. The fitted parameters provide both a quantitative and a qualitative basis for interpreting the experimental results. In addition a model for the peptide concentration-dependent leakage is presented, which was used to fit experimental data for leakage induced by the prion protein-derived peptides. The models presented in this article are compared with other models for peptide-induced membrane leakage.     

Two new mutations and a linkage map of Anopheles stephensi

Genetic analyses of two new mutations in Anopheles stephensi are presented. Spotless wings (sl) and 2nd-3rd costal spots fused (2-3f) have been mapped on chromosome 2, approximately 79.5 map units apart. A preliminary linkage map for this species also is presented.