Acidity and species diversity in freshwater crustacean faunas

SUMMARY. On the basis of material from over seventy acidic water bodies in three different areas a relationship is revealed between pH and the species diversity of their crustacean faunas. With increasing acidity species diversity decreases. No such relationship is shown between calcium concentration and species diversity. The very low calcium levels of such waters may, however, play a part in the exclusion of certain species.     

Response of the photosynthetic apparatus in maize leaves grown at low temperature on transfer to normal growth temperature

Low temperatures are known to restrict chloroplast development and prevent the attainment of photosynthetic competence in maize leaves. The responses of the photosynthetic apparatus of mature maize leaves grown at 14°C on transfer of the plants to 25°C are examined. The synthesis of thylakoid proteins increased immediately on transfer of leaves from 14 to 25°C, with a dramatic accumulation of thylakoid proteins and chlorophylls occurring after 3 d at 25°C. Thylakoid structure and organization also became similar to those observed in leaves grown at 25°C over this period. However, no comparable development of photosynthetic competence in photosystems I and II or in the rate of CO₂ assimilation was observed on transfer of leaves from 14 to 25°C. Immunocytological analyses demonstrated heterogeneity in the distribution of a range of thylakoid proteins (cy tochrome f, the α and β subunits of the coupling factor, Dl of the photosytem II reaction centre, the 33kDa protein of the extrinsic oxygen-evolving complex of photosystem II, and subunit II of photosystem I between mesophyll cells in leaves grown at 14°C, and in the responses of individual proteins to transfer of the leaves to 25°C. Such heterogeneity between mcsophyll cells would account for the inability of the leaves to develop the expected degree of photosynthetic competence on transfer to 25°C. The effects of low growth temperatures on chloroplast biogenesis are complex, as are the changes induced by the transfer ofleaves grown at low temperatures to optimal growth temperature, and both these factors may limit the canopy development and photosynthetic productivity of crops in temperate regions.     

An ecological validation of a taxonomic distinction: the ecology of Acanthocyclops vernalis and A. robustus (Crustacea: Gopepoda)

Long-standing taxonomic problems involving the vernalis complex of freshwater cyclopoid copepods of the genus Acanthocyclops have now been largely resolved, at least in Europe. Two species, A. vernalis and A. robustus , are recognizable on unambiguous morphological criteria, but each shows variation of a simular kind. Ecological data confirm this distinction. Ecological preferences are themselves reflected by the distribution patterns displayed in a restricted, but not small, area encompassing a diversity of environments. A. vernalis is eurytopic but displays a preference for acidic, calcium-poor waters, low in total ions, and is exclusively benthic. By contrast A. robustus does not colonize strongly acidic waters (min. pH 6.42) and is restricted to alkaline, or weakly acidic, nutrient-rich habitats. In some situations it becomes pelagic. While A. vernalis extends throughout the area frequented by A. robustus , the latter fails to colonize large tracts of upland country for which A. vernalis shows a definite preference and where it is common and widespread.     

A daphniid ephippium (Branchiopoda: Anomopoda) of Cretaceous age

An anomopod ephippium from the Lower Cretaceous of Australia, remarkably similar to that of Simocephalus , shows that daphniids whose ephippia at least were very similar to those of extant species, existed about 120 million years ago. The family clearly originated in pre-Cretaceous times, and the Anomopoda considerably early than this.     

The demonstration of speciation in fossil molluscs and living fishes

Contrary to a recent assertion, freshwater (and marine) prosobranch gastropods and freshwater bivalves are subject to considerable variability. This, and the lack of a detailed understanding of the taxonomy of the forms involved, makes it difficult to accept that the changes documented by Williamson (1981) in a fossil sequence from Lake Turkana (Africa) represent speciation events. That 10 lineages, involving gastropods and bivalves, should change simultaneously, and the deviant forms should then simultaneously become extinct, can, we believe, be more plausibly attributed to ecophenotypic responses to environmental changes than to speciation. In revealing the pattern and process of evolution, both fossil and living forms are helpful, but in demonstrating the fine-scale events during and after speciation in living animals one can utilize techniques and observations that cannot be applied to fossil material. African cichlid fishes are particularly informative in this respect. Their current explosive radiation can be interpreted as a punctuational event in evolution.     

A new classification of the branchiopod Crustacea

The first satisfactory groupings of the components of the Branchiopoda (Crustacea) were those of G. O. Sars, whose successive refinements, as modified by Caiman in a much used work, received wide acceptance. These schemes, and the more important of the subsequently suggested changes, are listed and tabulated. The Branchiopoda is a morphologically heterogeneous group whose component subgroups share a constellation of primitive features. It is also ancient, with representatives known from as far back as the Devonian, and probably originated in pre-Devonian times, yet still has many extant, sometimes highly successful, representatives. Such a situation presents difficulties to the would-be classifier. A new scheme is proposed which involves the elevation of four lower categories among the so-called Cladocera to ordinal rank. Two conchostracan taxa are also given ordinal status. The ten constituent orders now recognized within the Branchiopoda are defined in more detail than hitherto as a working basis for future investigations.     

The brine shrimp's tale: a topsy turvy evolutionary fable

It has been suggested that: (1) the brine shrimp, Artemia (Branchiopoda: Anostraca), which habitually swims inverted, has 'only recently turned over'; (2) if this habit were to persist for tens of millions of years, original dorsal–ventral homologies would become obliterated; (3) it would become necessary to re-define the concept of dorsal and ventral because so many details would have changed over evolutionary time; and (4) if modern brine shrimps were to maintain the habit of swimming upside down for 100 Myr into the future, they might give rise to a whole new subkingdom whose descendants would be defined as having a dorsal nerve cord. However, brine shrimps and their allies have not recently turned over. All the nearly 300 extant anostracans swim inverted, and members of the order have clearly done so for more than 400 Myr, yet their anatomical arrangements are the same as in crustaceans that live dorsal side up. Nor do crustaceans that swim inverted and even hang from the surface film depart from the standard arrangement. The claim that inverted swimming became a genetically determined attribute of brine shrimps via the operation of the so-called Baldwin effect is rejected, as is the concept itself.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 377–382.