Relationship between rates of swimming and growth in veliger larvae: genetic variance and covariance

Many marine invertebrate species have larvae that depend upon the same orga n for both locomotion and feeding. This potentially creates a covariance su ch that genetic variance in larval growth may depend upon differences in la rval swimming activity. The hypothesis that variation in larval growth may depend upon variation in swimming performance leads to two predictions: (1) if swimming speed varies among families larval growth rate will also vary among families and vice versa, and (2) variation in mean rates of larval gr owth and swimming will positively genetically covary. We tested these predi ctions by measuring growth rates and swimming speeds of over 1300 and 2000 larvae, respectively, from over 100 full-sib families of the marine snail C repidula fornicata. Adult C. fornicata release veliger larvae that have an opposed band ciliary system that generates both feeding and locomotory curr ents. We detected significant variation among families in both larval growt h rate and swimming speed. Broad sense heritabilities were similar in both cases and indicate that about one-third of the variation in larval growth a nd swimming speed may be genetic in origin. There was, however, no signific ant covariation between larval growth rate and swimming speed, indicating t hat the two traits are independent. (C) 1999 Elsevier Science B.V. All righ ts reserved.