Comparative rates of lower jaw diversification in cichlid adaptive radiations

The lower jaw (LJ) provides an ideal trophic phenotype to compare rates and patterns of macroevolution among cichlid radiations. Using a novel phylogeny of four genes (ND2, dlx2, mitfb, and s7), we examined the evolutionary relationships among two of the most phylogenetically disparate cichlid radiations: (i) the Central America Heroines; and (ii) the East African Lake Malawi flock. To quantify jaw morphology, we measured two LJ lever systems in approximately 40 species from each lineage. Using geologic calibrations, we generated a chronogram for both groups and examined the rates of jaw evolution in the two radiations. The most rapidly evolving components of the LJ differed between the two radiations. However, the Lake Malawi flock exhibited a much faster rate of evolution in several components of the LJ. This rapid rate of divergence is consistent with natural selection, promoting unparalleled trophic diversification in Lake Malawi cichlids.     

There is no trade-off between speed and force in a dynamic lever system

Lever systems within a skeleton transmit force with a capacity determined by the mechanical advantage, A. A is the distance from input force to a joint, divided by the distance from the joint to the output force. A lever with a relatively high A in static equilibrium has a great capacity to generate force but moves a load over a small distance. Therefore, the geometry of a skeletal lever presents a trade-off between force and speed under quasi-static conditions. The present study considers skeletal dynamics that do not assume static equilibrium by modelling kicking by a locust leg, which is powered by stored elastic energy. This model predicts that the output force of this lever is proportional to A, but its maximum speed is independent of A. Therefore, no trade-off between force and velocity exists in a lever system with spring-mass dynamics. This demonstrates that the motion of a skeleton depends on the major forces that govern its dynamics and cannot be inferred from skeletal geometry alone.     

Aquatic insect emergence in two Great Lakes marshes

This study determined total number, biomass, taxa, and seasonal occurrence of adult aquatic insects emerging from four vegetation zones in one diked and one undiked freshwater coastal marsh on hypereutrophic lower Green Bay, Lake Michigan, USA during the summer of 1984. Floating box traps were placed in open water, sparse emergent, dense emergent, and wet meadow vegetation zones in each marsh. Insects were collected during 20 24-hour periods, each four days apart, from June 11 to August 26. Two-way ANOVA was used to test differences in number and biomass of insects between marshes and among vegetation zones. Polynomial regression was used to evaluate seasonal emergence patterns. More insects, insect biomass, and insect taxa were found in the diked marsh, especially during the first half of the sampling period. Damselflies were much more abundant in the diked marsh. Most insects and insect biomass were found in the sparse emergent vegetation zone of both marshes. The emerging insect community in the diked marsh appears enhanced by its separation from the hypereutrophic and turbid waters of lower Green Bay.     

The development of ecosystem objectives for the Laurentian Great Lakes

Historically management of human use of ecosystems has been based around engineering and chemical approaches and through the construction of treatment facilities, effluent controls and setting chemical concentrations, both at end of pipe and in the aquatic environment. However, the general continued degradation of many ecosystems shows these approaches alone are insufficient. In the Laurentian Great Lakes the Great Lakes Water Quality Agreement was first signed in 1972 and ratified in 1978 and in 1987 tacitly acknowledged the problems with a chemical only approach by requiring the development of ecosystem objectives in the 1978 agreement. Furthermore, the agreement specifically identified numerical ecosystem objectives in the 1987 agreement. The evolution of ecosystem objectives in the Great Lakes has expanded from the strictly numerical objectives such as production of lake trout and abundance of the amphipod Pontoporeia hoyi. More recent developments in ecosystem objectives have been the inclusion of indicators for wildlife, habitat, human health and stewardship.Prepared as a discussion paper presented to the United Nations Economic Commission for Europe's seminar on an Ecosystems Approach to Water Management (May 27–31, 1991).     

Is speciation of demersal fishes in Lake Tanganyika restrained by physical limnological conditions?

Both Lake Malawi and Lake Victoria have many species of offshore demersal cichlids, most of which are stenotopic. In Lake Tanganyika there are fewer, more eurytopic, demersal species. These differences may be the effect of the physical regimes of the lakes. In Lake Victoria there is no permanent anoxic layer. In both the other lakes, water below 250 m depth is permanently anoxic and the seasonal cycle is dominated by upwelling. In Lake Malawi this is mainly derived from intermediate water containing free oxygen. In Lake Tanganyika upwelling involves hypolimnetic water, which may rise to within 80 m of the surface, causing great short-term changes in oxygen concentration over the depth range 50–250 m. This has inhibited the development of deep water species restricted to narrow depth ranges.     

Abundance and distribution of picoplankton in tropical, oligotrophic Lake Kivu, eastern Africa

1. We used flow cytometry to characterize freshwater photosynthetic picoplankton (PPP) and heterotrophic bacteria (HB) in Lake Kivu, one of the East‐African great lakes. Throughout three cruises run in different seasons, covering the four major basins, phycoerythrin‐rich cells dominated the PPP. Heterotrophic bacteria and PPP cell numbers were always high and spatial variations were modest. This represents an important difference from temperate and high latitude lakes that show high fluctuations in cell abundance over an annual cycle. 2. Three populations of picocyanobacteria were identified: one corresponded to single‐cells (identified as Synechococcus by epifluorescence microscopy, molecular methods and pigment content), and the two other that most probably correspond to two and four celled colonies of the same taxon. The proportion of these two subpopulations was greater under stratified conditions, with stronger nutrient limitation. 3. High PPP concentrations (c. 10⁵ cell mL^?1) relative to HB (c. 10⁶ cell mL^?1) were always found. Lake Kivu supports relatively less bacteria than phytoplankton biomass than temperate systems, probably as a consequence of factors such as temperature, oligotrophy, nutrient limitation and trophic structure. 4. A review of PPP concentration across aquatic systems suggests that the abundance of Synechococcus‐like cyanobacteria in large, oligotrophic, tropical lakes is very high. 5. Photosynthetic picoplankton cell abundances in the oligotrophic tropical lakes Kivu and Tanganyika are comparable to those of eutrophic temperate lakes. This apparently contradicts the view that PPP abundance increases with increasing eutrophy. More data on PPP in tropical lakes are needed to explore further this particular pattern.     

Situating stress: lessons from lay discourses on diabetes

In response to the serious toll diabetes takes on health and resources, researchers increasingly are examining physical and psychological pathways that affect and are affected by diabetes, including stress. Although biomedical researchers and practitioners are beginning to recognize the association between stress and diabetes onset and management, laypersons have long-standing and extensive insights into the multiple ways in which stress is associated with the diabetes disease process. In this article, we examine lay perspectives on stress and diabetes among a multiethnic sample of 80 adults. Participants suggest varying arenas in which stress intersects with diabetes, including stress as implicated in the origin of diabetes, as a threat to maintaining glycemic control, as a challenge to self-management, and as a precursor to and a consequence of diabetes complications. An improved understanding of such perspectives may enhance appropriate disease management and develop a more valid conceptualization of stress in research efforts.     

A QUARTER CENTURY OF GREAT LAKES RESEARCH IN AFRICA

SUMMARY

The African Great Lakes differ from shallower large African lakes by undergoing seasonal stratification and from large reservoirs in having long residence times, so that the ionic concentration of the lake water differs substantially from that of the inflows.

The African Great Lakes are so large that limnological events are usually local, causing regional differences. They can he regarded as models for oceanic systems, with local processes playing a major part in nutrient cycling, Production, on an area basis, may be high because of the considerable depth of the euphotic zones of many of the lakes, but the production cycle is poorly understood because of temporal and spatial limitations of sampling. Cyclonic upwelling may play an important part in offshore nutrient cycling.

Links between limnology and fisheries are becoming apparent. Catches of Oreochromis in Lake Malawi are correlated with falling lake levels three years previously, which is explained in climatological terms. Different transfer efficiencies between plankton and fish production may reflect differences in the depth of the euphotic zone. The history and seasonal changes in deep stratification appears to have had a large influences in the evolution of demersal fish faunas.

The lakes are so large and so complex that their complete investigation is beyond the resources of any single Government. There is a need for independently funded fundamental research to complement the applied research which must be the first priority of local Governments.     

Functional aspects of strepsirrhine lumbar vertebral bodies and spinous processes

The relationship between form and function in the lumbar vertebral column has been well documented among platyrrhines and especially catarrhines, while functional studies of postcranial morphology among strepsirrhines have concentrated predominantly on the limbs. This morphometric study investigates biomechanically relevant attributes of the lumbar vertebral morphology of 20 species of extant strepsirrhines. With this extensive sample, our goal is to address the influence of positional behavior on lumbar vertebral form while also assessing the effects of body size and phylogenetic history. The results reveal distinctions in lumbar vertebral morphology among strepsirrhines in functional association with their habitual postures and primary locomotor behaviors. In general, strepsirrhines that emphasize pronograde posture and quadrupedal locomotion combined with leaping (from a pronograde position) have the relatively longest lumbar regions and lumbar vertebral bodies, features promoting sagittal spinal flexibility. Indrids and galagonids that rely primarily on vertical clinging and leaping with orthograde posture share a relatively short (i.e., stable and resistant to bending) lumbar region, although the length of individual lumbar vertebral bodies varies phylogenetically and possibly allometrically. The other two vertical clingers and leapers, Hapalemur and Lepilemur, more closely resemble the pronograde, quadrupedal taxa. The specialized, suspensory lorids have relatively short lumbar regions as well, but the lengths of their lumbar regions are influenced by body size, and Arctocebus has dramatically longer vertebral bodies than do the other lorids. Lumbar morphology among galagonids appears to reflect a strong phylogenetic signal superimposed on a functional one. In general, relative length of the spinous processes follows a positively allometric trend, although lorids (especially the larger-bodied forms) have relatively short spinous processes for their body size, in accordance with their positional repertoire. The results of the study broaden our understanding of postcranial adaptation in primates, while providing an extensive comparative database for interpreting vertebral morphology in fossil primates.