Patterns of Testa-imposed Seed Dormancy in Native Australian Legumes

The testa-imposed seed dormancy of 34 native Australian speciesof Faboideae and Mimosoideae was examined immediately afterthe seeds matured and again after 3.5 years of dry storage inthe laboratory. Three groups of dormancy patterns are recognized:17 species (of the Mirbelieae and Acacieae) that have a relativelysmall nondormant fraction (0–10%) of their ripe seedsand that maintain this fraction through time; ten species (ofthe Mirbelieae) that have a relatively large non-dormant fraction(10–40%) of their ripe seeds and that maintain this fractionthrough time; and seven species (of the Bossiaeeae and Phaseoleae)that have a relatively small non-dormant fraction when the seedsripen, and have this fraction increase significantly throughtime. The species in the second group have smaller seeds thando those of the first and third groups, while the species inthe third group have a different testa construction from thosein the first and second groups. For all of the non-dormant seedstested, the water permeability is not localized only at thelens. Leguminosae, Fabaceae, Mimosoideae, Papilionoideae, Faboideae, legume seeds, seed dormancy, hard-seededness, dormancy loss, germination     

Petals may act as a reward: myrmecochory in shrubby Darwinia species of south‐eastern Australia

The removal rates of fruits (the diaspore) were assessed in exclusion experiments in three shrubby species of Darwinia, endemic to the Sydney Basin of south‐eastern Australia. There was a clear pattern of fruit removal in just a few days by small species of ants from the genera Iridomyrmex, Crematogaster and Pheidole. When only ants had access to fruits an average of 41% of fruits were removed, whereas when only vertebrates had access an average of 13% of fruits were removed. There was some variation in the number of fruits removed both between species and within species across study sites or annual seed crops. When ants had access to seeds this variation in removal amounted to 10–80% over 1–4 days. Uniquely in Darwinia, it is the old petals (which remain attached to the fruit) that are attractive to the ants, rather than a specific lipid body. This likely represents a case of successful ecological fitting by Darwinia to take advantage of the widespread presence of myrmecochory in the Australian flora.     

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Fire and the transition to seedlings

Fire, through soil heating effects, causes flushes of seed germination in Acacia suaveolens. Optimal temperatures for germination are between 60 and 80°C for any duration, or up to 100°C for durations less than 1 h. Exposure to temperatures less than 60°C leaves seeds dormant and viable, whilst seed death occurs in increasing proportions with increasing exposure to temperatures greater than 80°C. A field study of temperatures in the soil under simulated burns showed that the innate seed dormancy in A. suaveolens would only be broken for seeds up to a depth of 1 cm in ‘cool’ or 4 cm in ‘hot’ burns. In the hot burns some of the seeds in the top 1 cm of the soil were killed by excessive heating. These simulated burns most resemble cool and moderate/high intensity wildfires, respectively. Seeds can emerge from depths up to 8 cm and, for any seeds buried deeper than this, the probability of emergence is progressively reduced down to nil at 14 cm. Seeds buried between 5 and 10 cm will be heated sufficiently to break their dormancy only in a very high intensity wildfire. Seeds buried between 5 and 10 cm deep mostly occur in nests of an ant, Pheidole sp. Field observations of emergent seedlings confirm that post-fire emergence is concentrated over a small range of soil depths directly related to the intensity and duration of heating that occurs, whilst occasional seedlings may appear from greater or lesser depths largely dependent upon the spatial heterogeneity of soil heating in natural fires.     

A Molecular Study of Euglenoid Phylogeny using Small Subunit rDNA

The euglenoids are an ancient and extremely diverse lineage of eukaryotic flagellates with unclear relationships among taxa. Synapomorphies for the euglenoids include a surface pellicle and a closed mitosis with a series of separate sub-spindles. The taxonomy currently in use is inconsistent with the available data and needs revision. Most euglenoid phylogenies are largely intuitive reconstructions based on a limited number of morphological characters. Therefore, we have added molecular characters from the Small Subunit (SSU) rDNA to generate an overall phylogenetic framework for the euglenoids. SSU rDNA sequences from photosynthetic, osmotrophic, and phagotrophic euglenoids were aligned based on secondary structure. Phylogenetic analysis using the conserved areas of the sequence was performed using parsimony, maximum likelihood, and distance methods. Trees derived using different criteria are in agreement. The euglenoids form a distinct monophyletic clade with phagotrophic members diverging prior to the phototrophic and osmotrophic members. Among photosynthetic members, the biflagellate form diverged prior to the uniflagellate form. Additionally, the genus Euglena appears to be paraphyletic, with osmotrophic taxa, such as Astasia and Khawkinea, diverging independently within the clade containing the photosynthetic genus Euglena.     

Population dynamics of the shrub Acacia suaveolens (Sm.) Willd.: Seed production and predispersal seed predation

Seed production and predispersal seed predation in the shrub Acacia suaveolens were examined over 3 consecutive years in eight populations in south-eastern Australia. Seed-crop sizes varied both between and within populations of different ages. Seed production was maximal in the first one to four flowering seasons after establishment, and then declined with plant age. The size of the annual seed-crop was also influenced by rainfall for that year. Predispersal seed predation varies between populations over fruiting seasons with the initial large seed-crops resulting in predator satiation. Within one fruiting season, no significant variation in the extent of predispersal seed predation was found in any of three populations studied. There were two major forms of predispersal seed loss: toss of whole fruits to Melanterius corosus (Coleoptera: Curculionidae) and external insect seed grazers, and loss of individual seeds within fruits to M. corosus. Exclusion experiments showed that seeds lost to these predispersal seed predators would otherwise have been matured by the parent plant. The effects of predispersal seed predation cannot be directly related to seedling recruitment. Indirectly, such predation may influence the dispersion of seeds in the soil profile and hence, subsequent recruitment.     

Seed predation in native legumes of south-eastern Australia

Seed predation in 28 species of native legumes in the Sydney region was examined. While bruchids are significant seed predators in the Sydney region they are not the dominant seed predators group, as is the case in central America. Other important groups include weevils, anthribids and lepidopterans. In each group of seed predators studied, apart from the lepidoptera, a particular genus was closely associated with a single plant genus. The degree of seed predation varied from 85% to 3%, with only six of the 28 species of plants studied relatively free from seed predation (less than 10% seed-crop losses). Variation in the degree of seed predation both within and between plant genera could not be explained by taxonomic relationships, morphology, distribution, seed weight or seed dispersal agents. A larger data base is necessary to account for such variations.