This 1957 study by Hawker, Hepden, and Perkins examined how low temperature affects sexual reproduction in the fungus Rhizopus sexualis and related species. When colonies grown on malt agar at 20°C were transferred to 5-10°C, low temperature prevented the initiation of conjugation (the first stage of sexual reproduction) and blocked development of early-stage zygospores unless gametangia were already fully delimited before transfer. However, fully delimited gametangia continued developing into mature zygospores at low temperatures, though at reduced rates. Interestingly, sporangia (asexual spores) were produced in greater numbers at low temperature. The inhibitory effect was independent of medium composition and pH. Similar temperature-dependent inhibition of early conjugation stages was observed in other Mucoraceae species (Mucor hiemalis, Zygorrhynchus species), though Phycomyces blakesleeanus showed minimal inhibition. The researchers concluded that low temperature likely blocks synthesis of essential substances rather than merely slowing diffusion, supported by evidence that mature zygospores could facilitate continued development of younger stages even at low temperature.

Key findings

• Low temperature (5-10°C) prevents initiation of new conjugation but allows continued development of zygospores that had reached the gametangial stage before cooling
• The inhibitory effect of low temperature is greatest at early stages of sexual reproduction, suggesting a temperature-sensitive synthesis step rather than simple metabolic slowing
• Medium composition and pH do not influence the temperature-dependent inhibition, indicating the effect operates through fundamental physiological mechanisms
• Presence of mature zygospores partially rescues development of young stages at low temperature, suggesting a diffusible substance promotes conjugation
• Asexual sporangial production increases at low temperature, opposite to the effect on sexual zygospore formation