Life history and body size evolution in Holopedium gibberum Zaddach (Crustacea, Cladocera)

SUMMARY. 1. Body size, development, sheath size and relative egg size were examined in two populations of Holopedium gibberum Zaddach. The populations were chosen because of differences in juvenile versus adult mortality.
2. The population subject to food limitation and predation from icthyoplankton (high juvenile mortality) exhibited large size at birth and maturity, large sheath size, and eggs which were relatively large compared to the adult. In contrast, individuals in the population exposed to predation by golden shiner (high adult mortality) were smaller at birth and maturity, had a smaller sheath, and produced relatively small eggs.
3. I contrast body size and relative egg sizes of these H. gibberum populations with literature values for all Cladocera, and propose a general hypothesis for the evolution of relative egg size in Cladocera.     

Species and pseudospecies: the structure of crossbill populations

The holarctic crossbills Loxia have often been regarded as one of the classic examples of avian panmixia, despite a large number of named races, clines and other geographic variation. There are also reports of two or more 'subspecies' nesting sympatrically, without interbreeding. Crossbills feed almost exclusively on conifer seeds. Eruptions occur at times of cyclical cone crop failures; the birds involved may then breed in new areas for one or more years. Rather than being nomadic in their movements, to explain the clinal and/or area effects, it is suggested that erupting birds are reasonably faithful to core breeding areas, to which some subsequently return. Genetic continuity within a species is maintained through adjoining or overlapping core breeding areas. Although normally connected by intermediates, some populations apparently do not interbreed when they come together temporarily during irruptions. At such times, they behave as separate species, to which the term pseudospecies is applied. Mechanisms promoting rapid speciation and founder effects are discussed.     

Effects of fungivory by two specialist ciid beetles (Octotemnus glabriculus and Cis boleti) on the reproductive fitness of their host fungus, Coriolus versicolor

On the basis of the evidence that insect fungivory has the potential to affect fungal reproductive fitness, we investigated the effects of two specialist ciid beetles ( Octotemnus glabriculus and Cis boleti ) on the reproductive potential of their host fungus, Coriolus versicolor . We found, from field data, a negative correlation between the number of individuals of O. glabriculus inhabiting C. versicolor fruit bodies and the percentage of the fungal spore-producing surface (hymenium) that was functional. By contrast, the number of C. boleti inhabiting C. versicolor fruit bodies did not correlate with the percentage of functional hymenium. Experimentally, O. glabriculus and C. boleti reduced the reproductive potential of C. versicolor by 58% and 30%, respectively, whereas the combined trophic activity of both beetles caused a reduction of 64%. This latter effect was not significantly different from that caused by O. glabriculus alone. These findings disagree with previous assertions that insect fungivory on fruit bodies has only neutral effects on fungal fitness. We conclude that in the short-term, fungivory by ciids significantly decreases the area of functional hymenium of C. versicolor and is likely to reduce fungal reproductive fitness. Within this perspective the evolution of certain fungal characteristics (i.e. chemical composition, consistency and phenology) can be interpreted as being driven by fungivory.     

Archaeology under Dictatorship

Archaeology under Dictatorship . Michael L. Galaty and Charles Watkinson, eds. New York: Kluwer/Plenum, 2004. 218 pp.     

Comparison of carbon dioxide fluxes over three boreal black spruce forests in Canada

Although mature black spruce forests are a dominant cover type in the boreal forest of North America, it is not clear how their carbon (C) budgets vary across the continent. The installation of an eddy covariance flux tower on an Old Black Spruce (OBS) site in eastern Canada (EOBS, Québec) provided a first opportunity to compare and contrast its annual (2004) and seasonal C exchange with two other pre-existing OBS flux sites from different climatic regions located in Saskatchewan [Southern OBS (SOBS)] and Manitoba [Northern OBS (NOBS)]. Although there was a relatively uniform seasonal pattern of net ecosystem productivity (NEP) among sites, EOBS had a lower total annual NEP than the other two sites. This was primarily because warmer soil under a thicker snowpack at EOBS appeared to increase winter C losses and low light suppressed both NEP and gross ecosystem productivity (GEP) in June. Across sites, greater total annual GEP and ecosystem respiration ( R ) were associated with greater mean annual air temperatures and an earlier beginning of the growing season. Also, GEP at all three sites showed a stronger relationship with air temperature in spring and early summer compared with later in the growing season, highlighting the importance of springtime conditions to the C budget of these boreal ecosystems. The three sites had different parameter estimates describing the responses of R and GEP at the half hour time scale to near surface temperature and light, respectively. On the other hand, the responses of both R and GEP to temperature at the monthly scale did not differ among sites. These results suggest that a general parameterization could be sufficient at coarse time resolutions to model the response of C exchange to environmental factors of mature black spruce forests from different climatic regions.     

The scapulocoracoid of flightless birds: a primitive avian character similar to that of theropods

The scapula and coracoid of the first bird Archaeopteryx represents a highly specialized morphology approaching that of modern carinate birds, with the scapula meeting the coracoid at an angle of approximately 90^o. The primitive condition of the avian scapula and coracoid is exhibited by the flightless ratites, birds exhibiting many other primitive characters of the skeleton, either retained from primitive ancestors or derived through neoteny. The fact that the scapulocoracoid of ratites is the primitive condition is confirmed by its presence in the embryos of certain birds, and its presence through neoteny in other unrelated birds that have secondarily evolved Sightlessness. This morphology of the primitive avian scapulocoracoid closely approaches that of theropod dinosaurs, such as Deinonychits , and may well indicate relationship between the two groups.     

Patterns of ant community organization in mesic southeastern Australia

study of the ants of 11 sites at Wilson's Promontory, Victoria, found that patterns of ant community organization varied markedly between habitats, being controlled by climate and vegetation structure. Community organization showed continuous change from drier sites (especially woodlands) where broadly-adapted species of Rhytidoponera were particularly abundant, but many other taxa were also well-represented, to wet forests where cool-climate specialists (Prolasius and certain Chelaner) and cryptic species (mostly Solenopsis) cotnprised almost all ants. These patterns appear to be typical of those in mesic regions of Australia, and contrast with those in the arid zone where ant faunas are dominated by highly active and aggressive species of Iridomyrmex which apparently play a pivotal role in community organization. The results suggest that ant communities in mesic regions are less tightly structured than those in the arid zone, and that interspecific competition is a less important factor influencing community organization. The findings of this study are briefly discussed in relation to the potential use of ants as bio-indicators.     

Ventilation and Its Effect on "Infinite Pool" Exchangers

SYNOPSIS. Unlike internal exchange surfaces, the skin contactsan "infinite pool" of air or water with which exchange of gases,water, ions, and other solutes may occur. Even though the "infinitepool" may be well mixed, an unstirred diffusion boundary layeris always present about the skin and may constitute a significantresistance to exchange. The thickness of the diffusion boundarylayer (as approximated by the fluid dynamic boundary layer)is related to the flow of the respiratory medium, viscosityand density of the medium, and the morphology of the exchangesurface. Oxygen microelectrode studies suggest that, in mostcircumstances, the diffusion boundary layer in water is at leastas thick as the blood-respiratory medium distance in amphibianskin. Accordingly, the movement of water about the skin {i.e.,skin ventilation) should have pronounced effects on cutaneousexchange, especially at low "free stream" velocities. Mountingphysiological evidence suggests that: (1) skin ventilation canaugment cutaneous gas exchange; and (2) some vertebrates activelyventilate their skins, especially in aquatic hypoxia. The ubiquityand significance of diffusion boundary layers are central toa general understanding of cutaneous exchange and all surface-mediatedexchange processes.     

INDIVIDUALITY IN “YODEL” CALLS RECORDED FROM A BANDED POPULATION OF COMMON LOONS,GAVIA IMMER

ABSTRACT

Male common loons, Gavia immer, produce a territorial vocalization called the yodel. We quantitatively examined yodels using discriminant and cross correlation analysis. Both techniques correctly assigned the majority of the male's yodels to the proper group, however discriminant analysis was more accurate for making long term comparisons of a yodel's stability. Of four male loons in a color marked, breeding population at the Seney National Wildlife Refuge in Michigan, each male's yodel was different and these differences were maintained over the six years of this study. There is a suggestion that changes in the yodel may be related to territory and mate switching, indicating that individuality in the yodel may be linked to female choice.     

Seedling mortality of metal hyperaccumulator plants resulting from damping off by Pythium spp.

Seedling mortality of Alyssum serpyllifolium ssp. lusitanicum and A. murale , both nickel hyperaccumulators, was reduced by increasing concentrations of metal within plant tissues when inoculated with the fungi Pythium mamillatum or P. ultimum , both of which cause damping-off disease of seedlings. Pythium mamillatum , isolated from nickel-rich serpentine soil, was more tolerant of nickel than P. ultimum , isolated from low-metal control soil, and was more pathogenic than P. ultimum towards seedlings containing high concentrations of metal. These results support the hypothesis that metal hyperaccumulation by plants is closely linked to increased protection against disease.