Ecological studies on crater lakes in West Cameroon Zooplankton of Barombi Mbo, Mboandong, Lake Kotto and Lake Soden

The zooplankton of four crater lakes in North-west Cameroon has been studied by means of vertical hauls from the bottom to the surface. Two of the lakes are deep, with sparse phytoplankton, while the other two are shallow with dense blooms of blue-green algae. All the lakes are without planktonic Cladocera. In Lake Kotto, Mboandong and Barombi Mbo the dominant zooplankter is Mesocyclops (Thermocyclops) hyalinus , which is replaced in Lake Soden by Mesocyclops leuckarti. Larvae of Chaoborus are present in all the lakes. In the two deep lakes, Soden and Barombi Mbo, the dominant rotifer is Polyarthra dolichoptera , but in the two shallow lakes, Kotto and Mboandong, three species, Hexarthra mira, Brachionus fakatus and B. caudatus , make up the bulk of the rotifers.
In Barombi Mbo during the daytime most of the zooplankton was in the top 20 m, but most of the Chaoborus larvae were below 20m.
The standing crops of zooplankton in these lakes are low compared with those of lakes in the Kigezi District of Uganda.
The most remarkable feature of the zooplankton in these lakes is the occurrence of dwarfed forms. Both species of cyclopoid copepods and the eight identifiable species of Rotifera are smaller here than in most other localities. Factors which may be associated with this dwarfing are low latitude with constant high temperature, low phytoplankton availability, and the low ratio of drainage area to lake area.     

Ecological studies on crater lakes in West Cameroon Lakes Kotto and Mboandong

Lake Kotto is a shallow crater lake, sometimes weakly stratified, and with a dense phytoplankton dominated by blue-green algae. The ecology of Lake Kotto and the similar, smaller lake Mboandong is described in relation to the feeding biology of their fishes. Of the five species of cichlids in Lake Kotto only one is endemic. Two are phytoplankton-feeders, one takes invertebrates as well as phytoplankton, one feeds mainly on chironomid larvae, and one preys on vertebrates as well as on invertebrates. The three phytoplanktivores are the main species eaten by man. One species of Clarias and one of Barbus also occur in Lake Kotto; and in the associated streams are four species of cyprinodont fishes. The fish fauna of Mboandong consists of three species of cichlids and two cyprinodonts, all known from the Kotto system. We contrast Lake Kotto with the oligotrophic lake Barombi Mbo, and conclude that Lake Kotto would probably be less sensitive to human interference than would Barombi Mbo.     

Kleptoparasitism of freshwater crabs by cichlid fishes endemic to Lake Barombi Mbo,Cameroon, West Africa

Synopsis Although kleptoparasitism, or food-stealing, is common in birds and some carnivorous mammals, reported instances are exceedingly rare in fishes. We studied the behaviour and ecology of the 11 endemic tilapiine cichlids of Lake Barombi Mbo, Cameroon, West Africa. Here we report that six of the Barombi cichlids (Stomatepia mariae, S. pindu, Konia eisentrauti, Pungu maclareni, Sarotherodon lohbergeri, andS. linnellii) kleptoparasitize freshwater crabsPotamon africanus.     

Isoenzyme analysis of Schistosoma haematobium,S. intercalatum and their hybrids and occurrences of natural hybridization in Cameroon

Isoelectric focusing of glucose-6-phosphate dehydrogenase (G6PD) produced clearly identifiable profiles for S. haematobium and S. intercalatum and their hybrids. To provide a more detailed analysis of the interactions of S. haematobium and S. intercalatum in South West Cameroon over the last 12 years, G6PD analyses were carried out on individual schistosomes collected in Kumba in 1990, Loum in 1990, 1999 and 2000 and Barombi Mbo and Barombi Kotto in 1999. Studies were also carried out on the two parental species S. haematobium Barombi Mbo, S. intercalatum Edea and subsequent generations of hybrids resulting from laboratory crosses of the two parental species. The isoenzyme analysis demonstrated that the 1990 isolate from Kumba, was a recombinant of S. intercalatum x S. haematobium, and that 30% of individual schistosomes collected in 1990 in Loum were also recombinants. The remainder gave data indicative of S. haematobium. In 1999, 12.5% of individuals from Loum showed recombination and 10% in 2000. Results from the most recent parasitological survey in October 2000 showed the persistence of the recombinant population in addition to that of S. haematobium. There was also evidence of recombination having taken place in Barombi Kotto but not Barombi Mbo. This study demonstrates how the situation has changed over the last 12 years, and emphasizes the importance of assessing morphological, biological and molecular data together to gain a true picture of the rapidly evolving situation.     

Genetic signatures of a demographic collapse in a large-bodied forest dwelling primate (Mandrillus leucophaeus)

It is difficult to predict how current climate change will affect wildlife species adapted to a tropical rainforest environment. Understanding how population dynamics fluctuated in such species throughout periods of past climatic change can provide insight into this issue. The drill (Mandrillus leucophaeus) is a large-bodied rainforest adapted mammal found in West Central Africa. In the middle of this endangered monkey's geographic range is Lake Barombi Mbo, which has a well-documented palynological record of environmental change that dates to the Late Pleistocene. We used a Bayesian coalescent-based framework to analyze 2,076 base pairs of mitochondrial DNA across wild drill populations to infer past changes in female effective population size since the Late Pleistocene. Our results suggest that the drill underwent a nearly 15-fold demographic collapse in female effective population size that was most prominent during the Mid Holocene (approximately 3-5 Ka). This time period coincides with a period of increased dryness and seasonality across Africa and a dramatic reduction in forest coverage at Lake Barombi Mbo. We believe that these changes in climate and forest coverage were the driving forces behind the drill population decline. Furthermore, the warm temperatures and increased aridity of the Mid Holocene are potentially analogous to current and future conditions faced by many tropical rainforest communities. In order to prevent future declines in population size in rainforest-adapted species such as the drill, large tracts of forest should be protected to both preserve habitat and prevent forest loss through aridification.     

Observations on the biology of nymphs of Povilla Adusta Navas (Ephemeroptera: Polymitarchidae) in Lake Kainji,Nigeria

Observations onPovilla adusta Navas nymphs in Lake Kainji revealed that seasonal fluctuations in abundance were due to a shortage of food during the period of rising lake level rather than a depletion of oxygen in the water column; this shortage was caused by the increased turbidity of the flood waters restricting the growth of both planktonic and periphytic algae. Planktonic algae apparently formed the diet of nymphs <4–6 mm and also of larger nymphs if their preferred diet of periphytic algae was in short supply. Both depth distribution and individual size of the nymphs were closely related to the distribution of periphytic algae. Depth distribution patterns of the nymphs revealed a peak between 2–4 m below the surface.The dimensions of the nymphs and the duration of the aquatic stages (3–4 months) in Lake Kainji correspond closely with results obtained elsewhere as does the mean percentage of males in the population (28%±10%). Seasonal fluctuations in the sex ratio were apparently caused by variations in the intensity of predation.Department of Zoology, University of Reading     

Ecological studies on crater lakes in West Cameroon Fishes of Barombi Mbo

In the West Cameroonian crater lake, Barombi Mbo, and its inflowing stream there are 17 species of fishes, of which 12, including the 11 cichlids, appear to be endemic. We give a systematic account of the endemics, including four new species and two new genera, Konia and Myaka. The ecology of the lake is described in relation to the feeding biology of the fishes, studied by underwater observation in the lake and the examination of stomach contents. The cichlids in Barombi Mbo probably evolved there from two or three ancestral populations and now show clear ecological separation in their feeding and breeding. The problem of speciation within the lake is of particular interest because of the apparent absence of physical barriers to account for the genetic isolation of incipient species.     

The effects of the formation of Lake Kainji (Nigeria) upon the indigenous fish population

The changes in the species composition and structure of the fish population resulting from the damming of the River Niger at Kainji are illustrated and discussed. The main changes are shown to be a decline in the numbers of bottom feeding insectivores, especially the Mormyridae and an increase in the numbers of omnivores, predators and planktivores. The detailed specific changes within all the major families are examined. A brief comparison is made between the changes in the fish population following Lake Kainji's formation and the effects of the formation of other African man-made lakes     

The food and feeding habits of Eutropius niloticus (Ruppell), family Schilbeidae (Osteichthyes: Siluriformes) in Lake Kainji,Nigeria

Studies on the food and feeding habits of Eutropius niloticus in Lake Kainji, Nigeria revealed that the fish is omnivorous but fed more on insects than on any other food. The most important insects were Povilla adusta Navas nymphs and imagos and adults of the common grasshoppers. Fish, particularly the clupeids Sierrathrissa leonensis Thys Van den Audernaerde and Pellonula afzeliusi Johnels, also formed an important part of the diet. There was seasonal variation of organisms selected for food and there were variations in the dietary items selected by different age groups. Accumulation of fat was found to correlate with seasonal feeding intensity. E. niloticus serves as food for other fishes.     

Age of cichlids: new dates for ancient lake fish radiations

Timing divergence events allow us to infer the conditions under which biodiversity has evolved and gain important insights into the mechanisms driving evolution. Cichlid fishes are a model system for studying speciation and adaptive radiation, yet, we have lacked reliable timescales for their evolution. Phylogenetic reconstructions are consistent with cichlid origins prior to Gondwanan landmass fragmentation 121-165 MYA, considerably earlier than the first known fossil cichlids (Eocene). We examined the timing of cichlid evolution using a relaxed molecular clock calibrated with geological estimates for the ages of 1) Gondwanan fragmentation and 2) cichlid fossils. Timescales of cichlid evolution derived from fossil-dated phylogenies of other bony fishes most closely matched those suggested by Gondwanan breakup calibrations, suggesting the Eocene origins and marine dispersal implied by the cichlid fossil record may be due to its incompleteness. Using Gondwanan calibrations, we found accumulation of genetic diversity within the radiating lineages of the African Lakes Malawi, Victoria and Barombi Mbo, and Palaeolake Makgadikgadi began around or after the time of lake basin formation. These calibrations also suggest Lake Tanganyika was colonized independently by the major radiating cichlid tribes that then began to accumulate genetic diversity thereafter. These results contrast with the widely accepted theory that diversification into major lineages took place within the Tanganyika basin. Together, this evidence suggests that ancient lake habitats have played a key role in generating and maintaining diversity within radiating lineages and also that lakes may have captured preexisting cichlid diversity from multiple sources from which adaptive radiations have evolved.     

Comparative characteristics of the ichthyoplankton of lagoon lakes of the south-eastern part of Sakhalin

Ichthyoplankton surveys are made in lagoon water bodies of the south-eastern part of Sakhalin (the Vavai-Chibisan system of lakes, Lake Tunaicha, Lake Izmenchivoe) from April until November 2002–2007. Comparative characteristics of ichthyoplankton complexes in the ice-free period is given. In the investigated lagoon lakes, differences in the species composition of the ichthyoplankton by the number and time of appearance of the maxima of abundance of eggs and larvae are noted, and also related to morphological structure and hydrological conditions of water bodies. In lagoon lake Izmenchivoe with a salinity not less than 26‰, the eggs and larvae of marine fishes only takes place while, in Vavai-Chibisan lakes, that of freshwater fishes only takes place. In brackish lake Tunaicha, the lowest number of fish species reproduce. In the Vavai-Chibisan system and in Lake Izmenchivoe, one maximum of abundance of ichthyoplankton in June is recorded and, in Lake Tunaicha, two maxima (the highest in June and less expressed in August) are recorded. Irrespective of the species composition, the ichthyoplankton complexes of lagoon lakes have general traits determined by hydrological conditions of water bodies and by their general origin and geographic situation: prevalence of eggs and larvae of low boreal fish species, the maximum species diversity in the late spring-early summer, and decrease of abundance in cooler years.     

Diapause dynamics of two diaptomid copepod species in a large lake

Skistodiaptomus oregonensis and Leptodiaptomus minutus produce diapausing eggs in a large lake, Oneida Lake, in New York State. The timing of the switch from production of subitaneous (immediately hatching) eggs to diapausing eggs for both species is in October. This timing is consistent with a pattern, reviewed here, for other populations of diaptomid copepods: populations living in large lakes tend to begin production of diapausing eggs later in the season than those living in small lakes. Populations living in temporary ponds tend to switch still earlier in the season. All populations reviewed here live in the north temperate zone. The sediments of Oneida Lake contain densities of diaptomid diapausing eggs on the order of 10⁵ m^–2 per cm below the sediment surface down to 5 cm. Below this sediment depth, egg densities decline. The highest egg densities were found in sediments under the deepest water. Diapausing eggs of L. minutus survive in the sediments at least two years, as shown by the recovery of the population after a year in which no new diapausing eggs were produced, and probably for two or more decades. Long-term dormancy can have the effect of ensuring the continuation of a population through periods of poor recruitment, and can help create conditions for the coexistence of competing species. Other investigators have suggested that S. oregonensis and L. minutus are competitors in other lakes when they co-occur.     

The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

Variation in calanoid copepod resting egg abundance among lakes with different acidification histories

The maintenance of species and genetic diversity within zooplankton egg banks may be crucial to the re-establishment of zooplankton communities following historical disturbance, such as anthropogenic acidification which globally caused widespread damage to ecological communities. Despite this, no other study has described basic characteristics of zooplankton egg banks among lakes with different acidification histories, such as variation in resting egg concentration. Theoretically, habitats with frequent periods of harsh environmental conditions are expected to select for resting egg production or prolonged dormancy in zooplankton, which would increase the size of the resting egg bank in lake sediments. In this study, we compared abundances of viable and inviable calanoid copepod resting eggs among three freshwater lakes with different acidification histories. While Swan Lake underwent major chemical and biological changes from acid and metal deposition, Teardrop and Bat lakes were relatively unaffected by historical acidification and had comparatively constant, but different pH over time. We also tested the effect of age on the viability of resting eggs. As predicted, higher numbers of viable resting eggs were found in recent sediments from acid-recovering Swan Lake compared to study lakes with relatively temporally constant environments (Teardrop and Bat lakes) when the total number of eggs was held as a covariate. We detected this result in spite of similar pelagic abundances of Leptodiaptomus minutus, the dominant species in zooplankton communities of these lakes. This pattern did not necessarily hold for inviable egg concentrations since these eggs were more abundant in both Swan and Bat lakes compared to Teardrop Lake in older sediments (1939–1951, 1800s). Within study lakes, the abundance of viable resting eggs declined with increased egg age. Further study is required to test mechanisms underlying these patterns. Handling editor: S. I. Dodson     

The use of opercular bones in the study of age and growth in Labeo senegalensis from Lake Kainji, Nigeria

Check marks were found on the scales and opercular bones of Labeo senegalensis from Lake Kainji, Nigeria. The scale marks were often indistinct and difficult to interpret, but an attempt was made to determine age from the opercular bones.
At least two check marks per year were found on the opercular bones, one of these occurring during June-July, and the other during January. The relationship between opercular length and fish total length was plotted logarithmically and back-calculations of length made.
Problems of interpretation are discussed in relation to possible causes of ring formation.     

Effect of temperature on the respiration of an Antarctic freshwater anostracan, <Emphasis Type="Italic">Branchinecta gaini</Emphasis> Daday 1910, in field experiments

The Antarctic crustacean Branchinecta gaini (Branchiopoda, Anostraca) occurs in nine fresh water lakes near the Polish H. Arctowski Station. In one of the largest, Lake Wujka (Lake Uncle in English), we determined how temperatures affect its respiration and whether this is sex dependent. Experiments were carried out on males and females bearing eggs over a range of temperatures from 0.5 to 10°C. An ANOVA showed that while the amount of oxygen consumed increased with temperature (P < 0.001) males consumed more oxygen than similarly-sized females bearing eggs (P < 0.001).     

Notes and Records

Variation in activities of Senegal kob (Kobus kob kob Erxleben 1777) during daylight period in an enclosure at Kainji Lake Research Institute range farm, New Busa, Nigeria     

Notes and Records

Gastro intestinal helminths and food of the African hedgehog Atelexia albiventris (Wagna) in the Kainji Lake area of Nigeria     

Vertical structure of archaeal communities and the distribution of ammonia monooxygenase A gene variants in two meromictic High Arctic lakes

The distribution of archaeal amoA and 16S rRNA genes was evaluated in two marine-derived, meromictic lakes in the Canadian High Arctic: Lake A and Lake C1 on the northern coast of Ellesmere Island. The amoA gene was recorded in both lakes, with highest copy numbers in the oxycline. Sequence analysis showed that amoA from the two lakes shared 94% similarity, indicating at least two phylogenetically distinct clusters. Clone libraries of archaeal 16S rRNA genes from Lake A revealed strong vertical differences in archaeal community diversity and composition down the water column. The oxic layer was dominated by one group of Euryarchaeota affiliated to the Lake Dagow Sediment (LDS) cluster. This group was absent from the oxycline, which had an extremely low archaeal diversity of two phylotypes. Both belonged to the Crenarchaeota Marine Group I (MGI), the marine group that has been linked to archaeal amoA ; however, there was a low ratio of amoA to MGI copy numbers, suggesting that many MGI Archaea did not carry the amoA gene. The anoxic zone contained representatives of the RC-V (Rice Cluster-V) and LDS clusters of Euryarchaeota. These results show the strong vertical differentiation of archaeal communities in polar meromictic lakes, and they suggest archaeal nitrification within the oxycline of these highly stratified waters.     

Abundance and age of viable resting eggs of the calanoid copepod Boeckella poppei Mrázek in sediments: evidence of egg banks in two Antarctic maritime lakes

The existence of egg banks not only ensures the survival of zooplankton through harsh periods, but could also affect microevolutionary dynamics. Whether zooplankton at high latitudes can build up an egg bank in sediments, as occurs at lower latitudes, is still unknown. The distribution and age of viable resting eggs of the calanoid copepod Boeckella poppei Mrázek in sediments of two small freshwater lakes on King George Island were determined by slicing sediment cores at 1-cm intervals. Most viable resting eggs were found near the sediment surface, with abundance sharply declining to very low values at the depth of 5?cm, although eggs were present as deep as 9?cm in the sediments of Yanouhu Lake. The egg abundances in Xihu Lake and Yanouhu Lake were estimated to be 9.2?×?10⁴ and 7.2?×?10⁴?eggs?m^?2, respectively. ²¹⁰Pb dating indicated a relatively constant sedimentation rate (0.023?cm?year^?1) in Xihu Lake, which was used to estimate the mean age (46.8?year), the maximum age (195.7?year), and the mortality rate (1.64?% year^?1) of resting eggs of B. poppei in Xihu Lake. The accumulation of resting eggs with long-term viability in sediments provided the first evidence for the existence of egg banks in two Antarctic maritime lakes. An egg bank may serve as an overwintering strategy for B. poppei in Antarctica, enhance their ability to cope with random extreme changes, and contribute to their broad distribution.