![]() ![]() ![]() The maximum distance between isolates from the 965-ha A. Armillaria ostoyae genet sizes were approximately 20, 95, 195, 260, and 965 ha cumulative colonization of the study area was at least 9.5%. ostoyae and one of NABS X were identified through the use of somatic incompatibility pairings among the putatively diploid isolates. Armillaria spe- cies identifications done by using a polymerase chain reaction based diagnostic and diploid-diploid pairings produced identical results: 108 of the isolates were Armillaria ostoyae (Romagn.) Herink and four were North American Biologi- cal Species X (NABS X). Sampling of recently dead or live, symptomatic conifers produced 112 isolates of Armillaria from six tree species. The coarse-scale population structure of pathogenic Armillaria (Fr.) Staude species was determined on ap- proximately 16 100 ha of relatively dry, mixed-conifer forest in the Blue Mountains of northeast Oregon. Cell turnover is hypothesized to be the main underlying mechanism producing sponge-derived detritus, a major trophic resource transferred through sponges in benthic ecosystems, such as coral reefs. We have demonstrated that under steady-state conditions, cell turnover through cell proliferation and cell shedding are common processes to maintain tissue homeostasis in a variety of sponge species from different ecosystems. Detritus production could not be directly linked to cell shedding due to the degraded nature of expelled cellular debris. The amount of shed cells observed in histological sections may be related to differences in residence time of detritus within canals. d-1) and cell shedding was observed in seven out of eight species.All species investigated produced significant amounts of detritus (2.5-18% detritus bodyweight-1 Apoptosis was negligible and not the primary mechanism of cell loss involved in cell turnover. Choanocyte proliferation in Haliclona vansoesti was variable (2.8-73.1%). Monanchora arbuscula showed lower choanocyte proliferation (8.1☓.7%), whereas the mangrove species Mycale microsigmatosa showed relatively higher levels of choanocyte proliferation (70.5☖.6%). reniformis, showed 16.6☓.2% after 10 h BrdU-labeling. ![]() The majority of coral reef species (five) showed between 16.1☑5.9% and 19.0☒.0% choanocyte proliferation (mean±SD) after 6 h and the Mediterranean species, C. All species investigated displayed substantial cell proliferation, predominantly in the choanoderm, but also in the mesohyl. Cell loss through shedding was studied quantitatively by collecting and weighing sponge-expelled detritus and qualitatively by light microscopy of sponge tissue and detritus. Apoptosis was identified using an antibody against active caspase-3. Cell proliferation was determined through the incorporation of 5-bromo-2'-deoxyuridine (BrdU) and measuring the percentage of BrdU-positive cells after 6 h of continuous labeling (10 h for Chondrosia reniformis). This study describes in vivo cell turnover (the balance between cell proliferation and cell loss) in eight marine sponge species from tropical coral reef, mangrove and temperate Mediterranean reef ecosystems. This theory is compatible with a prominent role for environmental selection but, as it implicates some degree of internal mediation and direction, it is not entirely compatible with the 'modern synthesis' view of natural selection. With regards to life history theory it functions as the key variable mediating the correlation between life history traits. With regards to morphological evolution the oscillator, through alterations to developmental timing, controls change in size and shape. In advanced metazoans, where senescent cells are not continually replaced, it controls lifespan. It coordinates the timing of all cell-cell signalling systems, hence controls the timing of development and aging/senescence. In multicellular metazoans the oscillator remains synchronised across all cells. Cells such as neurons could be sustained throughout life, enabling the evolution of brains, hence, complex behaviour and intelligence. With increasing cell longevity, continual replacement of all senescent cells was no longer necessary. As the longevity of these cells was still relatively short in more primitive metazoans, stem cells, capable of differentiating into all specialised cell types, were retained in order to replace senescent cells. Slower oscillatory frequencies directed metazoan evolution towards extended longevity of individual cells, enabling generation of many specialised types of terminally differentiated cells. This was achieved through an intracellular oscillator, dubbed 'Life's Timekeeper', which evolved in the hypothetical ancestor of all metazoans. It is proposed that a primary and fundamental aspect of metazoan evolution is an ability to control and extend the longevity of individual cells. ![]()
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