Variation in growth rate and reproductive output in British populations ofthe dorid nudibranch Adalaria proxima: consequences of restricted larval dispersal?

Growth and reproduction were compared among six geographically and genetica lly distinct intertidal populations of the annual, semelparous, dorid nudib ranch Adalaria proxima (Alder & Hancock) to evaluate Variation in fitness-r elated traits. The six populations spanned the geographic range in the nort hern British Isles: NE England (Cowling Scar), E Scotland (Kinkell Braes), NW Scotland (Loch Eriboll), W Scotland (Cuan Ferry), Northern Ireland (Port aferry), and N Wales (Menai Bridge). Nudibranchs from five sites were colle cted in July to August 1992 as post-metamorphic juveniles and were laborato ry-reared under the same conditions of ambient temperature and photoperiod for up to 10 months and the completion of spawning. Individuals from the si xth site were added to the experiment in December 1992. Growth was monitore d every 2 weeks, and reproductive performance was expressed as a weight-adj usted dimensionless index (Sigma RI) of each individual's spawnings summed over the reproductive period. In general, larger nudibranchs produced large r first spawn masses and more total spawn than did smaller nudibranchs, but these size-related trends were observed only in some populations. The patt erns of energy partitioning to spawnings varied significantly among populat ions, from allocations of a large number of eggs to few spawn masses (Loch Eriboll) to production of many small spawnings over a long spawning period (Portaferry). There was no relationship between maximum body size and the a mount of spawn produced after the first spawning, nor to the length of the spawning period or the number of spawn produced. Both Menai Bridge and Kink ell Braes had low mean population Sigma RI reflecting a very poor reproduct ive performance, given their large maximum (pre-spawning) body sizes. By co ntrast, the Loch Eriboll, Cuan Ferry, and Portaferry populations all displa yed high mean population Sigma RI. albeit as a result of differing combinat ions of numbers and sizes of spawn masses and duration of the spawning peri od. This high variance of reproductive allocation among populations, and pr evious evidence of relatively stable among-population differences in allozy me frequencies, adult color, and embryo characteristics suggest very restri cted larval transport of lecithotrophic larvae of A. proxima.