Rob Cross

Taxonomic and functional characterisation of fungi from the Sebacina vermifera complex from common and rare orchids in the genus Caladenia

The terrestrial orchid genus Caladenia contains many species which are threatened with extinction. They have highly specific associations with Sebacina vermifera and closely related fungi, and conservation of these terrestrial orchids, in part, relies on symbiotic propagation to produce plants for reintroduction and ex situ conservation collections. However, little is known of the diversity of mycorrhizal fungi associating with natural populations. Here, restriction fragment polymorphism analysis, internal transcribed spacer and nuclear large subunit sequencing and symbiotic seed germination were used to investigate the taxonomic and functional diversity of fungal isolates from single populations of six endangered Caladenia species and one common species across the same biogeographic range. Fifty-nine fungal isolates were collected for investigation including ten isolates from the six endangered species Caladenia audasii, Caladenia amoena, Caladenia sp. aff. fragrantissima (Central Victoria), Caladenia sp. aff. patersonii, Caladenia rosella and Caladenia orientalis and 49 isolates from six populations of the common species Caladenia tentaculata. While the common species associated with three distinct S. vermifera-like taxa, the six endangered species were restricted to one of these fungal taxa. No direct relationship between the taxonomic identity of the fungi and their ability to stimulate seed germination was observed; however, the majority of the fungi isolated from the Caladenia species were capable of germinating seed in vitro, indicating their mycorrhizal status and potential for symbiotic propagation in conservation programmes.

Propagation and reintroduction of Caladenia

Many Caladenia species have been reduced to extremely small and/or fragmented populations, and reintroduction/translocation into natural or rehabilitated habitats, by using ex situ propagated plants or via direct seeding, represents an important adjunct in conservation planning. However, Caladenia species are some of the most difficult terrestrial orchid taxa to propagate, in part because of the specificity of the mycorrhizal associations and the need to provide growing conditions that suit both the mycorrhizal fungi and Caladenia plants. The present paper reviews recent advances in Caladenia propagation and reintroduction methods, including in vitro seed germination, transferral from in vitro to nursery environments, ex vitro symbiotic germination (germination in inoculated nursery media), nursery cultivation, the use of nurse plants and reintroduction of Caladenia into natural habitats by using seed, dormant tubers or growing plants. Techniques discussed in the present paper increase the options for future Caladenia conservation programs, especially for those species currently on the brink of extinction.

Observer effects occur when estimating alert but not flight-initiation distances

Abstract Context. The estimation of alert (vigilance) and flight-initiation (escape) distances (AD and FID, respectively) has underpinned theoretical and applied studies of the escape behaviour and management of disturbance to wildlife. Many studies use multiple observers, and some conduct meta-analyses; these efforts assume no observer effects in the estimation of these distances. Aims and methods. We compared the estimates of FID and AD under ideal conditions (i.e. of black swans, Cygnus atratus, a large species with obvious behaviour, and at a location where swans allowed close approaches in open habitats), by one experienced and four inexperienced observers. Key results. FID did not differ among observers but AD differed between the experienced and all inexperienced observers, and among inexperienced observers. Thus, FID estimates appear more repeatable than those of AD. Experience apparently results in more conservative estimates of AD. Conclusions. FID represents a repeatable measure that is consistent across observers. This study supports its broad application in the study of wildlife escape behaviour. Implications. We recommend the use of FID rather than AD for comparative analyses that involve multiple observers, because FID is more reliably measured.

Effects of environmental conditions on the production of hypocotyl hairs in seedlings of Melaleuca ericifolia (swamp paperbark)

The production of hypocotyl hairs in the early stages of seedling development can strongly influence the success with which plants recruit sexually in harsh environments. Although wetlands are one type of environment in which seedlings might be expected to develop hypocotyl hairs, there have been few studies of these structures in the woody aquatic plants. We investigated the production of hypocotyl hairs in Melaleuca ericifolia Sm., a small wetland tree widely distributed across swampy coastal areas of south-eastern Australia, in relation to water availability, salinity, temperature and light regime. Hypocotyl hairs were ~20 mm long × 30 μm wide; in contrast, root hairs were generally less than 5 mm long and 15 μm wide. Hypocotyl hairs were produced only under a narrow range of environmental conditions—low salinity, low water availability, moderate temperature, and darkness—and seedlings that failed to produce hypocotyl hairs did not survive. Since the conditions under which hypocotyl hairs were produced were at least as, and possibly even more, restricted than those required for successful germination of seeds, it is likely that the successful sexual recruitment of M. ericifolia would be rare and episodic under conditions existing in most coastal wetlands in south-eastern Australia.