Frosted glass-whiskers (Sclerophora peronella) COSEWIC assessment and status report: chapter 6

Biology

General

This species is found exclusively on the wood and bark of older trees. The Canadian occurrences of S. peronella have all been with apothecia bearing mature spores. Based on the available habitat descriptions, the species seems to have a preference for old-growth forests with stable humidity and small temperature fluctuations.

Reproduction

The thallus of S. peronella is imbedded in the substrate, and has not been observed to produce vegetative propagules. All thalli of S. peronella at Canadian sites have apothecia containing mature spores. As a result, it is the sexual spores housed in the capitulum of the stalked apothecia that must be distributed to new locations. This is thought to take place via wind, rain and, to a lesser degree, by invertebrates. These sexual spores must land and germinate in close proximity to a compatible green algal partner before lichenization can occur. The world’s leading authority on the calicioid lichens and fungi, Leif Tibell, has indicated (pers. comm.) that longevity of thalli, age at sexual maturity, and generation time, remain unanswered questions within this group of species. According to Canters et al. (1991), the distribution of lichens "is governed by microclimatic factors that influence higher plants in different ways or not at all." Therefore microclimatic factors of the wood substrate such as pH, water holding capacity, or chemistry, may influence longevity of thalli, age at sexual maturity, and generation time.

Survival

It is generally assumed that the establishment of this and other lichen species is determined by such factors as age, texture, pH, moisture-holding capacity and nutrient status of the substrate, as well as degree of illumination and humidity of the microenvironment, inclination of surfaces, aspect, air pollution and stand continuity (e.g., Barkman 1958, Brodo 1973, James, Hawksworth and Rose 1977). However, specific microclimatic and physiological requirements for S. peronella have yet to be determined. According to Mattson and Middelborg (2000), microclimatic humidity is, perhaps, the most important ecological factor for explaining the distribution of calicioid species: the microclimatic humidity is primarily a product of topography and vegetation, not of precipitation.

Movements/dispersal

It is difficult to know whether the populations in British Columbia, Nova Scotia, and at isolated locations in the United States, Europe and Russia, are remnant populations from a previously continuous range, or if each is the consequence of a long distance dispersal event. Although the thalli at each of the disparate sites are of very limited size, they are healthy and capable of reproducing. However, given the species’ apparent preference for old forest habitat, the destruction and/or unavailability of such habitat is a reason for concern. Dispersal by sexual spores means that the fungal spore must land close to a compatible alga and on the appropriate substrate before another lichen can grow. If vegetative propagules were produced, the propagule containing both fungal and algal partners would only have to land on suitable substrate since both partners are already present. However, the lack of vegetative propagules, and the production of sexual spores only, presents an additional challenge for survival of the lichen.

Nutrition and interspecific interactions

Sclerophora peronella, as a lichenized fungus, satisfies its need for carbon by growing symbiotically with a photosynthetic algal partner. It receives water and other nutrients from the atmosphere. Because of the efficient adaptation for absorption from the atmosphere (as in most lichens and bryophytes), any pollutants soluble in the atmospheric moisture will also be efficiently absorbed by the lichen. The species does not seem to be impacted by interactions with other organisms based on the Selva’s field observations and literature searches.

Behaviour/adaptability

As perhaps our most sensitive biomonitors of forest ecosystem health, the calicioid lichens and fungi, including S. peronella, remain one of the forest’s most elusive and poorly known inhabitants. The habitat data suggests that this species prefers the stable environment of established forests--particularly those associated with older stands. Like other calicioid lichens, it appears to be intolerant of disturbance and, considering the limited number of records available, its global range is perhaps directly linked to the worldwide decline of suitable old-forest habitat. 

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