The diet of the edible cockle Anadara antiquata L. (Bivalvia,Arcidae) in Dar es Salaam,Tanzania, during the northeast monsoons

The diet of the cockle Anadara antiquata L. was studied along Dar es Salaam coast during the N-E Monsoon season. No zooplankton were found in the 80 cockle guts examined. 27 phytoplankton genera were identified, an indication of wide phytophagy. Members of classes Bacillariophyceae, Chlorophyceae, Pyrophyceae and Prasnophyceae were very prevalent in the diet. Scenedesmus, Chlamydomonas, Palmeria, Exuviella, and Coscinodiscus showed the highest recurrence frequencies per gut.     

Rank and reproduction in cooperatively breeding African wild dogs: behavioral and endocrine correlates

African wild dogs (Lycaon pictus) live in cooperative packswith a clear-cut dominance hierarchy in each sex. Reproductionis largely monopolized by the dominant male and female. Alphafemales produced 76% of all litters in the Selous Game Reserveand 81% in Kruger National Park. Only 6-17% of subordinate femalesgave birth each year, compared to 82% of dominant females. Innonmating periods, subordinate females had higher estrogen levelsand higher estrogen/progestin ratios than alpha females, apparentlypreventing ovulation. During mating periods, subordinate femaleshad lower estrogen levels than dominants, mated less often,and were less aggressive. Subordinate males mated at low rates,wore less aggressive than dominants, and had lower testosteronelevels. Beta males were similar to alpha males behavioraDy andhormonaUy, suggesting that alpha males may share paternity withbeta males. If paternity is more evenly shared than maternity,then subordinate males have a larger incentive than subordinatefemales to remain in the pack. Following this expectation, dispersalin Selous was female biased (49% versus 24% dispersing annually).Perhaps as a result of mortality associated with dispersal,the adult sex ratio was male biased, although the pup sex ratiowas unbiased. In Kruger, neither dispersal nor the adult sex-ratiowas biased. Reproductive suppression is widely thought to becaused by social stress in subordinates, but basal cortkosteronelevels were higher in dominants than in subordinates     

DNA RFLPs at a highly polymorphic locus distinguish European and African subspecies of the honey bee Apis mellifera L. and suggest geographical origins of New World honey bees

A highly polymorphic locus in the honey bee, Apis mellifera L., was detected with genomic probe pB178. Eighty-five alleles, consisting of Msp I and Dde I RFLPs, were found among the Old and New World bees tested. Forty-one Msp I and 43 Dde I restriction fragment patterns, or variants, were identified. Variants and alleles were discontinuously distributed in Old World European and African subspecies. Principal coordinate analysis of the genetic distances between the alleles resulted in the identification of three distinct groups corresponding to three groups of honey bee races with historically different geographical distributions: east European A. m. ligustica and A. m. caucasica ; west European A. m. mellifera ; and South African A. m. scutellata . The clustering of alleles into these groups is consistent with previous honey bee phylogeographic studies, employing other nuclear and mitochondrial DNA markers, which in part support the evolutionary history of the honey bee hypothesized by Ruttner based on morphometric and allozyme data. The majority of alleles in bees from the USA grouped with those found in east European bees, while other alleles grouped with alleles found in A. m. mellifera . While the majority of the alleles in neotropical bees grouped with or were identical to African alleles, other alleles grouped with alleles found in A. m. mellifera, A. m. ligustica , and A. m. caucasica . Clues to the ancestry of neotropical bees may be found in the identification of alleles that were identical or more similar to alleles found in South African and west European bees; evidence for west European ancestry has been suggested using other taxonomic characters that were not unique to west European bees. Both west European and African alleles were found in individual neotropical colonies, which may indicate that honey bee subspecies which evolved allopatrically have hybridized in the human-assisted extension of their original geographical ranges.     

Prey diversity and selectivity of the African fish eagle: data from a roost in northern Kenya

A total of 1872 bones from a fish eagle roost at Lake Turkana, Kenya was identified and analysed to provide data on fish eagle prey and diet. The approach of this study complements field observation studies in that it provides a long‐term analysis and quantification of the diet, rather than short qualitative observations. The study found that, at least where fish is relatively abundant, fish eagles are both selective and opportunistic: selective in taking preferred fish in much greater proportions than natural availability, and also in avoiding unwanted fish regardless of abundance, but opportunistic in taking certain other species in proportion to their availability. They also show considerable selection in size and habitat preferences of prey. Non‐fish prey forms a considerable proportion of the diet, and probably represents both opportunistic hunting, possibly when conditions for fishing are poor, and killing of other predators robbing fish eagle nests.
As well as describing and quantifying the fish eagle diet at Lake Turkana, data from this study suggest that further study is needed to quantify the impact of fish eagle predation on Clarias lazera , a rare, but valuable species to the Lake Turkana fishery. The study of bird roost prey remains also provides baseline data for studies of fossil microfaunal accumulations. Scatters of bones under fish eagle roosts are common in eastern Africa, and undoubtedly contribute to many of the fossil bone accumulations recovered. One of us (DM) has noted that the taxonomic and skeletal composition of the Koobi Fora roost bears a great resemblance to some of the clusters she is analysing from Olduvai Gorge. Further similar studies will provide additional data on bird roost accumulations.     

Sexual differences in the anterior dentition in African primates

A study was made of ranges of variation of the anterior dentition of various African nonhuman primates. Comparisons of the dentitions were made between different species and sex differences within each species were determined. Among the nonhuman primate groups studied were: Gorilla gorilla gorilla, Pan troglodytes, Pan paniscus, Cercopithecus nictitans, Cercocebus albigena and Colobus badius. In monkeys the canine teeth of the males are considerably larger than those of the females. There are also considerable differences in size in the rest of the anterior dentition. In apes, and specifically only gorillas, distinct sex differences are only found in the maxillary canines. In the chimpanzees, sex differences in the dentition are much smaller and there is considerable overlap in the ranges of variation. There are no fundamental differences in the size of the rest of the anterior dentition in the apes. The present study shows that differences due to sex in the anterior dentition, excluding the canine, are not as great as has been considered. If we consider the fossil record of man, whose morphological complex includes a much reduced canine, the probability will be that sex differences in the rest of the dentition will be negligible. Given the fragmentary nature of the fossil record, it is, therefore, highly unlikely that the determination of the sex of any fossil hominid specimen can be accurately made based solely on the evidence of its dentition.     

Natural and experimental simian cytomegalovirus infections at a primate center

Simian cytomegalovirus infections were studied in captive, naturally infected primates and in experimentally infected rhesus monkeys. Neutralizing antibody to simian cytomegalovirus was prevalent in selected species of Old World Monkeys. Naturally infected, rhesus monkeys shed virus in their urine during the entire two-year period of study. Similarly, experimentally infected rhesus monkeys showed neutralizing antibody and viruria for more than two years. The indirect fluorescent antibody procedure was found more sensitive than the neutralization antibody technique but appeared less specific for antibody to cytomegalovirus strains.     

Estimating African American admixture proportions by use of population-specific alleles.

We analyzed the European genetic contribution to 10 populations of African descent in the United States (Maywood, Illinois; Detroit; New York; Philadelphia; Pittsburgh; Baltimore; Charleston, South Carolina; New Orleans; and Houston) and in Jamaica, using nine autosomal DNA markers. These markers either are population-specific or show frequency differences >45% between the parental populations and are thus especially informative for admixture. European genetic ancestry ranged from 6.8% (Jamaica) to 22.5% (New Orleans). The unique utility of these markers is reflected in the low variance associated with these admixture estimates (SEM 1.3%-2.7%). We also estimated the male and female European contribution to African Americans, on the basis of informative mtDNA (haplogroups H and L) and Y Alu polymorphic markers. Results indicate a sex-biased gene flow from Europeans, the male contribution being substantially greater than the female contribution. mtDNA haplogroups analysis shows no evidence of a significant maternal Amerindian contribution to any of the 10 populations. We detected significant nonrandom association between two markers located 22 cM apart (FY-null and AT3), most likely due to admixture linkage disequilibrium created in the interbreeding of the two parental populations. The strength of this association and the substantial genetic distance between FY and AT3 emphasize the importance of admixed populations as a useful resource for mapping traits with different prevalence in two parental populations.     

Linked effects of dam-released floods and water temperature on spawning of the Clanwilliam yellowfish Barbus capensis

In South Africa, modified flow regimes designed to maintain ecosystem functioning at some pre-determined level are recommended for all rivers involved in major water-resource developments. One component of such flow regimes of special interest in the winter-rainfall region of the country is the small pulses of higher flow that occur in the dry season (November–April), here called freshes. Research was carried out in the Olifants River, in the winter-rainfall region of South Africa, on the link between freshes and spawning of an endemic, vulnerable cyprinid, the Clanwilliam yellowfish Barbus capensis. Experimental releases from Clanwilliam Dam on the Olifants River in a previous year showed that a greater than usual spawning success, assessed by larval recruitment levels, was correlated with hypolimnetic freshes released during the species' breeding season (October–January). In the study reported on here, a hypolimnetic fresh of the same size, duration and timing as those linked with successful spawning failed to induce spawning. Differences in the thermal regime of water releases appeared to be responsible. Two warm (19–21 °C), epilimnetic freshes of 15 hours duration were then released, and correlated with fish moving onto the spawn beds and exhibiting pre-spawning behaviour. However, the fish moved downstream away from the spawn beds when cold (16–18 °C) hypolimnetic baseflows were released for 15 hours between the two epilimnetic freshes and continually after the second one. The presence of free embryos and larval B. capensis indicated, from their developmental stages, that spawning had probably occurred before the experimental releases began, when warm (21–23 °C) epilimnetic water was spilling over the dam, and had halted once spillage stopped and hypolimnetic releases began. Indeed, the presence of dead and deformed young suggested that the cold water may have had a detrimental affect on those spawned during the earlier warmer spell. A summary table details the conditions, including the hydraulic characteristics of the spawn beds, believed to induce spawning and support early life stages of B. capensis. It is concluded that freshes released from Clanwilliam Dam at the appropriate time (October–January) should be able to increase spawning success of B. capensis, but only if the water temperature at the spawn site is at or above 19 °C and stable or rising. However, successful spawning will not necessarily lead to high recruitment if water temperatures are not then maintained at appropriate levels for some time for development of the embryos and larvae. This implies that additional epilimnetic releases will be required following critical trigger flows.     

The minimum effective spermatozoa : egg ratio for artificial insemination and the effects of mercury on sperm motility and fertilization ability in Clarias gariepinus

The optimal ratio of spermatozoa : egg (15 000 : 1) for artificial insemination of African catfish Clarias gariepinus gave fertilization and hatching rates of 80 and 67%, respectively. Below a sperm : ova of 3000 : 1 fertilization success decreased significantly. Excessive sperm (>15 000 : 1) partly inhibited fertilization success. Sperm motility was decreased significantly by 0·001 mg 1⁻¹ Hg²⁺ as HgCl₂, but its effect on fertilization was dependent on the sperm : ova ratio, since excess sperm masked the effect of the pollutant. The most sensitive sperm : ova ratio for monitoring pollutant effects on fertilization success was 1500 : 1, which corresponds to half the minimal amount that yields a high fertilization rate in artificial insemination. There was a good correlation between fertilization and hatching rates ( r =0·83; P<0·05). Although both fertilization and hatching rates provide equally good indicators of fertilization success, the more rapid fertilization rate test is recommended since it requires only 12 h.