Potential and realized rates of vegetative reproduction in Spirodela polyrhiza, Lemna minor, and Wolffia borealis

The rate of vegetative propagule development was estimated in three duckwee d (Lemnaceae) species, Spirodela polyrhiza, Lemna minor, and Wolffia boreal is, by measuring the number of daughter fronds produced over the life span of mother fronds. Under the same constant environmental conditions, plants of L. minor lived the longest (31.3 days) and produced the most daughter fr onds (14.0), yet W. borealis had the highest reproduction rate (0.62 fronds per day). This trans lates to a higher rate of population growth for W. bo realis. Plants of S. polyrhiza had the shortest life span (12.1 days), prod uced the least number of daughter fronds (1.1), and thus bad the lowest fro nd production rate (0.08 fronds per day). When S. polyrhiza was experimenta lly induced to release daughter fronds at maturity, and not well past matur ity (which is usually the case), mother fronds produced three times more da ughter fronds with no effect on their longevity. Presumably different reten tion times are associated with different costs and benefits, however frond longevity appears unrelated to retention time, Vegetative propagule product ion in the Lemnaceae forms a continuum from Wolffia, which develops relativ ely small (0.5-1.5 mm) and numerous propagules that are released before mat urity to Spirodela, which develops fewer yet relatively large propagules (4 -12 mm) that are retained well past maturity. The different rates of propag ule production likely represent different reproduction strategies, from an opportunistic strategy (i.e. Wolffia), to a strategy of increased competiti ve ability (i.e. Spirodela). (C) 2001 Elsevier Science B.V. All rights rese rved.