An analysis of the spacing of aggregation centers in Polysphondylium pallidum☆

[摘要] TheprimarypurposeofthisinvestigationwastodeterminewhetherornotanonrandomdistributionofsorocarpsoccursinPolysphondyliumpallidum,andtodeterminethefactorsthatareinstrumentalindeterminingdistribution.Whileanonrandomdistributionofcentersdoesoccur,thedeterminingfactorisprobablynotasubstancepresentinthegaseousphaseoftheenvironment.Thereisacorrelationbetweenthedensityofsorocarpsonthesubstrateandtheirspatialdistribution.Theclusteredcondition(sorocarpsclosertogetherthanexpectedonthebasisofchance)isassociatedwithahighdensityoffruitingbodies,whileaspaceddistribution(sorocarpsfurtherapartthanexpected)isoftenfoundatlowdensities.Randomdistributionapparentlycanoccuratalmostanydensity.Centerdensitydependsupontherateofcenterformation.Thisrateismarkedlyenhancedifthecellsareinthestationaryphaseatthetimeofharvestanddeposition,andareexposedtocharcoal,mineraloil,orlight.Thelatterfactorsarethoughttoremoveoractuponacentersuppressingsubstanceintheenvironment.Cellstakenfromthelogarithmicphase,incubatedinthedark,andintheabsenceofcharcoalandmineraloilshowareducedrateofcenterformationandalowcenterdensity.Threehypothesesarepresentedtoaccountfortheapparentrelationshipbetweentherateofcenterformationandcenterdensity,andthespatialdistributionofcenters:(1)Aspacingsubstancesurroundingthecentermayprohibitothercentersfromformingintheimmediatearea;(2)spacingmayresultfromtheremovalofcellsthroughaggregationintheareaimmediatelysurroundingthecenter;(3)spatialdistributionmaybedeterminedbytheactionofacrasin.Inallcases,thelongertheintervalbetweentheappearanceofonecenterandanother,thegreatertheareacontrolledbythefirstcenterandthemorespacedthedistribution.The“acrasin”and“cell-depletion”hypothesesarefavoredfortheirequalacceptabilityasanexplanationandbecausethepostulationofanadditional,unknownfactorisnotrequired.Thedependenceofsorocarpdensityanddistributionuponcellpoolsizeisconsidered.Itissuggestedthathighcellnumberfavorsbothrandomization,byleavingenoughcellsafterthefirstburstofaggregationtoformsecondarycenters,andclustering,becauseaggregatesthatcontainalargenumberofcellsoftensplitintocloselyassociatedsecondarycenters.Lowcellnumberresultsinareasvirtuallyfreeofmyxamoebaesurroundingnewlyformedcenters,aconditionwhichstronglyfavorsaspaceddistribution.Thepossiblerelationshipbetweenspacingincellularslimeaggregationandspacinginotherdeveloping,biologicalsystemsisconsidered.

[学科分类] 生物科学（综合）