Biosystematics, genetics and upper temperature tolerance ofGigartina teedii (Rhodophyta) from the Atlantic and Mediterranean

Abstract

Plants ofGigartina teedii from the mediterranean isolated into laboratory culture showedPolysiphonia-type life histories with consistent formation of dioecious gametangial plants, as previously reported for Atlantic isolates. Male and female plants from the Atlantic and Mediterranean were almost completely compatible in terms of cystocarp formation on female plants, and carpospores from positive crosses always formed plants that released viable tetraspores. Sex-linked inheritance of branching pattern was found in all strains, but showed varying degrees of expression. Female plants were more branched than male plants and it is suggested that this may be an adaptation for spermatial capture.G. teedii plants showed differences in morphology in culture that are considered to be genetically-based. Preliminary studies of tip elongation showed that Mediterranean strains may have up to three times the elongation rates of Atlantic strains at 15°C,$\bar 8$. Such genetic variation in fully-interbreeding strains suggests that populations of this species in the Atlantic and Mediterranean are genecodemic. All strains showed an upper temperature tolerance of 31°C when tested at 1°C intervals from 29—34°C. An upper temperature tolerance of 31–32°C was found for the related speciesG. intermedia from Korea and Japan, butG. johnstonii from the Gulf of California showed an upper tolerance of 32–33°C.