A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera

Levels of mitochondrial DNA (mtDNA) sequence divergence between species within each of several avian (Anas, Aythya, Dendroica, Melospiza, and Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were compared. An analysis of digestion profiles generated by 13-18 restriction endonucleases indicates little overlap in magnitude of mtDNA divergence for the avian versus nonavian taxa examined. In 55 interspecific comparisons among the avian congeners, the fraction of identical fragment lengths (F) ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these translate into estimates of nucleotide sequence divergence (p) ranging from 0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater than 0.070. The small mtDNA distances among avian congeners are associated with protein-electrophoretic distances (D values) less than approximately 0.2, while the mtDNA distances among assayed fish and amphibian congeners are associated with D values usually greater than 0.4. Since the conservative pattern of protein differentiation previously reported for many avian versus nonavian taxa now appears to be paralleled by a conservative pattern of mtDNA divergence, it seems increasingly likely that many avian species have shared more recent common ancestors than have their nonavian taxonomic counterparts. However, estimates of avian divergence times derived from mtDNA- and protein-calibrated clocks cannot readily be reconciled with some published dates based on limited fossil remains. If the earlier paleontological interpretations are valid, then protein and mtDNA evolution must be somewhat decelerated in birds. The empirical and conceptual issues raised by these findings are highly analogous to those in the long-standing debate about rates of molecular evolution and times of separation of ancestral hominids from African apes.      

Genotypic succession in the cyclomorphosis of Bosmina longirostris (Cladocera)

SUMMARY. The pattern of cyclomorphosis of Bosmina longirostris was followed over a 21-month period in Lake Travis, Texas. Appreciable variation was observed in body size and in the lengths of antennules and mucrones. Electrophoresis of clonal isolates collected over the period of study showed a seasonal cycle in esterase phenotypes. A definite association was demonstrated between the esterase phenotypes and morphologies of these clonal isolates. Individuals of one esterase phenotype were usually large and long-featured, whereas individuals of the other esterase phenotypes were smaller, with short features. The association of morphology and esterase phenotypes from laboratory experiments corresponded to the association observed in field samples. These results support the hypothesis that the cyclomorphosis of Lake Travis Bosmina involves a succession of clones as well as phenotypic plasticity.     

Basisphenoid and basioccipital pits in microchiropteran bats

We examined 686 skulls of 420 species of microchiropteran bats in 16 families to assess variation in pits in the basisphenoid and basioccipital bones. A total of 26 measurements were used to describe variation in pits, and patterns in the distribution of pits were examined across the families. Pits were absent from 154 species and present in 266 species. While some species had as many as four basisphenoid pits, basioccipital pits, when present, always occurred as a single pair. No species had more than four pits (basisphenoid or basioccipital and basisphenoid) in total. In some families all species either had pits (e.g. Emballonuridae) or none had pits (e.g. Rhinolophidae), but the incidence of pits usually was variable within families. The results of a cluster analysis of families based on the incidence of pits and morphological features of pits bore little resemblance to a recent phylogeny of Microchiroptera. A discriminant function analysis of features of pits of Emballonuridae, Phyllostomidae, Vespertilionidae and Molossidae correctly classified 66% of species to family revealing some continuity in pit structure among related species. There was no evidence of significant sexual dimorphism in the incidence or features of pits. Basisphenoid and basioccipital pits tended to increase in size with skull size. Neither the incidence nor the morphology of basisphenoid nor basioccipital pits was consistently associated with echolocation, diet or foraging behaviour. Pits were present or absent from species using either high‐intensity or low‐intensity echolocation calls, and the same was true of bats using high or low duty cycle modes of echolocation. Furthermore, the presence or absence of pits did not correspond to the presence or absence of harmonics in echolocation calls. We propose that basisphenoid and basioccipital pits are oscillators in the vocal tract and contribute to the production of non‐linear phenomena in vocalizations made by bats. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 78 , 215–233.     

Changes in biotic communities developing from freshwater wetland sediments under experimental salinity and water regimes

1. Reduction in diversity of both freshwater aquatic and terrestrial ecosystems has been attributed to salinity increase and such increases are a symptom of changes to land use. Hydrological alteration to ground and surface water are likely to be associated with salinity increase and its influence on biodiversity. However the combined effects of salinity and hydrology on aquatic biodiversity have not been elucidated fully in either field or experimental situations. 2. The effect of salinity and water regime on the biota in sediments from seven wetlands from inland south‐eastern Australia was tested experimentally using germination of aquatic plant seeds (five salinity and two water levels) and emergence of zooplankton eggs (five salinity levels). Salinity levels were <300, 1000, 2000, 3000, 5000 mg L^?1 and water regimes were damp (waterlogged) and submerged. 3. Aquatic plant germination and zooplankton hatching was not consistent for all seven wetland sediments. Four of the wetland sediments, Narran Lakes, Gwydir Wetlands, Macquarie Marshes and Billybung Lagoon showed similar responses to salinity and water regime but the other three wetland sediments from Lake Cowal, Great Cumbung Swamp and Darling Anabranch did not. 4. As salinity increased above 1000 mg L^?1 there was a decrease in the species richness and the abundance of biota germinating or hatching from sediment from four of the wetlands. 5. Salinity had a particularly strong effect in reducing germination from sediments in damp conditions when compared to the flooded conditions. In parallel, salts accumulated in the sediment in damp conditions but did not in flooded conditions. 6. There is potential for increasing salinity in freshwater rivers and wetlands to decrease the species richness of aquatic communities and thus of the wetland community as a whole, resulting in loss of wetland biodiversity. This reduction in diversity varies between wetlands and is at least partly related to hydrology. For aquatic plants the reduction in diversity will be more marked for plants germinating from seed banks at the edges of wetlands where plants are not completely submerged than for the same seed bank germinating in submerged conditions.