GROWTH AND MATING OF GONZUM PECTORALE (VOLVOCALES) IN DEFINED MEDIA¹

Abstract

SUMMARY Growth in defined media of 32 populations of Gonium pectorale was studied to learn more about the sexual isolation reported for this species. The 23 populations containing both mating types (+ & ‐) were also studied for the ability to form zygotes in defined media. A preliminary study showed that some populations grew and reproduced sexually in a defined mineral medium, whereas others appeared to require exogenous organic materials for growth and/or zygote formation. The diverse reactions exhibited by the populations indicate physiological races which may explain, in part, the occurrence of sexual isolation.

2. Genome rearrangement and speciation in freshwater algae

“…Although about six morphospecies have been described in the isogamous colonial green algal genus Gonium (Nozaki et al, 1994), extensive biosystem-4 atic studies are focused on only G. pectorale, which is known to be distributed world-wide (Coleman et al, 1994;Sako et al, 1991;Stein, 1958Stein, , 1965Stein, , 1966aStein, , 1966bStein et al, 1976). At present, we have very limited biogeographic information of the other species (Nozaki, 1993;Pocock, 1955;Pringsheim, 1959;Watanabe, 1977).…”

“…Degrees of sexual isolation or compatibility were variable among the strains studied. As suggested from the great variety of original habitats of those isolates, degrees of sexual compatibility seemed to be largely affected by temperatures, nutrients, and pHs of the mating conditions (Stein, 1966a(Stein, , 1966b. Stein et al (1976), however, have studied sexual compatibility among 3 1 clonal cultures isolated from soil of a single pond at Lemon Cove, California and recognized two distinct groups of clones between which no zygote formation was observed.…”