46 research outputs found
Phylogenetically Widespread Polyembryony in Cyclostome Bryozoans and the Protracted Asynchronous Release of Clonal Brood-Mates
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Differentiation of haploid and diploid fertilities in Gracilaria chilensis affect ploidy ratio
Background
Algal isomorphic biphasic life cycles alternate between free-living diploid (tetrasporophytes) and haploid (dioicious gametophytes) phases and the hypotheses explaining their maintenance are still debated. Classic models state that conditional differentiation between phases is required for the evolutionary stability of biphasic life cycles while other authors proposed that the uneven ploidy abundances observed in the field are explained by their cytological differences in spore production. Results
We monitored the state and fate of individuals of the red seaweed Gracilaria chilensis periodically for 3 years in five intertidal pools from two sites with distinct conditions. We tested for differentiation in fecundity and spore survival among the gametophyte males and females (haploids) and the tetrasporophytes (diploids). We tested for the influence of fecundity and spore survival on the observed uneven ploidy abundances in recruits. The probability of a frond becoming fecund was size-dependent, highest for the haploid males and lowest for the haploid females, with the diploids displaying intermediate probabilities. Fecund diploids released more tetraspores than carpospores released by the haploid females. Spore survival depended on ploidy and on the local density of co-habiting adult fronds. An advantage of diploid over haploid germlings was observed at very low and very high adult fronds densities.
Conclusions
Neither spore production nor spore survival determined the highly variable ploidy ratio within G. chilensis recruits. This result invalidates the hypothesis of natural cytological differences in spore production as the only driver of uneven field ploidy abundances in this species. Diploid spores (carpospores) survived better than haploid spores (tetraspores), especially in locations and time periods that were associated with the occurrence of strong biotic and abiotic stressors. We hypothesise that carpospore survival is higher due to support by their haploid female progenitors passing-on nutrients and chemical compounds improving survival under stressful conditions.AHE was supported by fellowships SFRH/BPD/63703/2009, SFRH/BPD/
107878/2015 and UID/Multi/04326/2016 of the National Science Foundation
FCT of Portugal.info:eu-repo/semantics/publishedVersio
CLADOPHORA-PSEUDOBAINESII NOV-SPEC (CHLOROPHYTA) - AN ADDITION TO THE NW ATLANTIC SPECIES OF CLADOPHORA
CdZnTe Radiation Detectors with HgTe/HgCdTe Superlattice Contacts for Leakage Current Reduction
CdZnTe-based heterojunctionp-i-n or M-π-n detectors using HgTe/CdTe superlattice contacts are modeled and designed to reduce leakage currents under high electric fields and thereby improve X-ray and γ-ray detector performance. The employment of an n-type HgTe/CdTe superlattice as a contact layer can theoretically result in significantly less leakage current compared to a contact layer using either bulk semiconductors or metal contacts. The benefits arise from the ability to design HgTe/CdTesuperlattices to have large carrier effective masses in the electric field direction, which results in low carrier velocities. Nevertheless the density of states is lower than that of a comparable bulk semiconductor, which results in low carrier concentrations