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Variation in Reproductive Strategy Among Clones of the Bryozoan Celleporella Hyalina
Author(s) -
Hughes D. J.
Publication year - 1989
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/1943073
Subject(s) - biology , sex ratio , sex allocation , ecology , zoology , demography , genetics , offspring , population , pregnancy , sociology
To test alternative hypotheses concerning life history flexibility in variable environments I focused on the genotypic and environmental components of variation in Sex Ratio and Reproductive Allocation in clones of a benthic modular animal, the bryozoan Celleporella hyalina, grown in different flow regimes through all seasons. Clones of this bryozoan growing in autumn and winter varied significantly in growth rate, modular sex ratio, and relative investment in sexual reproduction. Experimental reduction of ambient water flow significantly reduced growth rate but did not affect Reproductive Allocation or Sex Ratio. Clonal differences in Reproductive Allocation were associated with a trade—off between somatic and sexual functions: clones investing more heavily in sex reached a smaller somatic size. In spring and summer, Celleporella clones showed an inconsistent and less pronounced growth response to flow regime. Significant genetically based variation was found for all measured characters except Reproductive Allocation. In both seasonal groups, clonal Sex Ratio was genetically canalized, and insensitive to the experimental treatments. The presence of clonal variability in Reproductive Allocation in autumn/winter but not in spring/summer may arise from seasonal differences in lifespan on natural substrata. These may select for maximal sexual investment in short—lived generations, but allow scope for alternative strategies if potential longevity is greater. The genetic constraint on clonal Sex Ratio may not conflict with models predicting flexible sex expression in variable environments, since the seasonal fluctuations experienced probably do not affect sex—specific reproductive success. The small Genotype × Treatment interactions and the positive correlations between clonal performance in differing treatments and seasons, suggest that the relative fitness of clones does not vary, a result at odds with assumptions underlying current hypotheses for the adaptive basis of sexual reproduction.