Marine Biology 102, 15-23 (1989) Marine .......... Biology | Springer-Verlag 1989 Morphological and DNA sequence variation in the kelp Costaria costata (Phaeophyta) D. Bhattacharya * and L. D. Druehl Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada Abstract Kelp species show substantial intraspecific morphological variation. The annual kelp, Costaria costata (C. Agardh) Saunders, is found in the lower intertidal and subtidal re- gions of shores which vary in exposure from strongly wave- exposed to sheltered. Phenotypic variation was studied in this monotypic genus. Individuals of C. costata were col- lected from two morphologically-distinct populations (one wave-exposed and the other wave-sheltered) at Cape Beale and Stanley Park, Vancouver, Canada, in May 1985. Analy- sis of morphological variation, using multivariate statistical techniques, indicated significant differentiation between plants from the two sites. Blade widths and thicknesses were the major discriminating variables. Restriction fragment length polymorphism (RFLP) analysis of nuclear DNA with 42 anonymous probes demonstrated one polymorphism. Most of the probes are hypothesized to encode highly re- peated, dispersed sequences. These repeat sequence probes comprised 80.9% of all cloned fragments. Primary sequence analysis of 1595 base pairs of small-subunit ribosomal DNA and 204 base pairs of upstream sequence (probe pCc 18) failed to show any divergence between plants from the two sites. Introduction Characterizing morphological variation has been a central theme in phycology. Regarding intraspecific variation in sporophytes of kelp species, the relative contribution of en- vironmental and genetic components has been discussed (Norton et al. 1982, Innes 1984) and experimentally investi- gated (Sundene 1958, Sundene 1962, Chapman 1973, Naka- * Present address and address for reprint requests: National Jewish Center for Immunology and Respiratory Medicine (MCB), 1400 Jackson Street, Denver, Colorado 80206, USA hara and Yamada 1974, Espinoza and Chapman 1983). Sta- tistical analyses of morphological variation has also been carried out (Widdowson 1971, Druehl and Kemp 1982). There are, however, few data concerning molecular biologi- cal analyses of intraspecific variation in kelp taxa, though many such studies have been carried out on higher plants and animals (Mitton 1978, Moran and Marshall 1978, Giles 1984, Nevo et al. 1986, Polaris et al. 1986, Riesenberg et al. 1988, St. Louis and Barlow 1988). We present here results of an analysis of both morphol- ogy and molecules (DNA) of sporophytes from two pheno- typically differentiated populations of the kelp Costaria cos- tata. One population (Cape Beale) is heavily wave-exposed and the other (Stanley Park) is sheltered from wave action. The morphology of C. costata consists of a holdfast, a corrugated stipe and a bullate, five-ribbed blade. As is found in many kelp species which have the ability to exist in sites of varying wave and current exposure (Sundene 1958, Norton 1969, Nakahara and Yamada 1974), C. costata may display marked phenotypic variation (Obrien 1972). Intertidally, plants originating from exposed sites are rela- tively narrower, thicker and more straplike than plants drawn from sheltered sites. Intermediate forms are associat- ed with intertidal sites having moderate exposure (Obrieu 1972). Multivariate methods are valuable in morphometric studies because they can reveal biologically meaningful pat- terns of covariation among interrelated variables (pheno- typic traits) which may not be discernible in raw data (Rice and Chapman 1985, Rice et al. 1985, Shea 1985). General theories underlying multivariate analysis of continuous morphometric data derived from seaweed genera have been reviewed (see Widdowson 1971, Marsden et al. 1983). In this study, cluster analysis (average distance) and stepwise dis- criminant analysis were used. Population divergence at the molecular level, of Costaria costata plants from Cape Beale and Stanley Park, was as- sessed with hybridization analysis. Randomly cloned DNA fragments were used to probe genomic DNA fixed on a solid