Susan Lawler

Phylogenetic relationships among the Australian and New Zealand genera of freshwater crayfishes (Decapoda : Parastacidae)

We sequenced approximately 500 base pairs of DNA from the 16S region of the mitochondrial genome to estimate relationships among the freshwater crayfish genera of Australia and New Zealand. In total, 35 sequences were obtained, representing 32 species and all 10 genera native to Australia and New Zealand. From these sequences, maximum likelihood, minimum evolution and parsimony estimates of phylogenetic relationships among the genera were obtained and compared with previous hypotheses concerning the relationships among the crayfish genera. Our results support the monophyly of each genus (except perhaps Euastacus) and the organisation of these genera into three major clades: the first clade contains the genera Engaeus, Tenuibranchiurus, Geocharax, Gramastacus, and Cherax; the second clade contains the genera Paranephrops, Parastacoides, Euastacus, and Astacopsis; and the third clade contains the genus Engaewa. We reject the ecological hypothesis of Riek for two major clades of crayfish species. Finally, we provide a checklist of the Australian and New Zealand species as they are currently recognised.

Population demography of Australian feral bees (Apis mellifera)

Abstract Honey-bees are widespread as feral animals in Australia. Their impact on Australian ecosystems is difficult to assess, but may include competition with native fauna for floral resources or nesting sites, or inadequate or inappropriate pollination of native flora. In this 3-year study we examined the demography of the feral bee population in the riparian woodland of Wyperfeld National Park in north-west Victoria. The population is very large but varied considerably in size (50–150 colonies/km2) during the study period (1992–1995). The expected colony lifespan for an established colony is 6.6 years, that for a founder colony (new swarm), 2.7 years. The population is expected to be stable if each colony produces 0.75 swarms per year, which is less than the number predicted on the basis of other studies (2–3 swarms/colony per year). Therefore, the population has considerable capacity for increase. Most colony deaths occurred in the summer, possibly due to high temperatures and lack of water. Colonies showed considerable spatial aggregation, agreeing with earlier findings. When all colonies were eradicated from two 5-ha sites, the average rate of re-occupation was 15 colonies/km2 per year. Ten swarms of commercial origin were released and were found to have similar survival rates to founder colonies. However, the feral population is self-sustaining, and does not require immigration from the domestic population.

Agonistic behavior of the crayfish Euastacus armatus and Cherax destructor

The intra- and interspecific agonistic behavior of Euastacus armatus and Cherax destructor from northeastern Victoria were examined. While the agonistic patterns of E. armatus appeared similar to those shown by most crayfish, individuals of C. destructor execute an unusual, highly stylized cheliped “punch” behavior during strong interactions, along with the other behaviors seen in many species. Juvenile C. destructor exhibited gregarious behavior, tending to co-occupy burrows and being physically near each other. Tests showed that the white chelipeds which are characteristic of mature E. armatus affect the outcome of aggressive interactions. When individuals had their chelipeds whitened, they won agonistic interactions more often. This result held for both intraspecific pairings and size-matched pairings with individuals of C. destructor. Individuals of C. destructor won the majority of size-matched pairings with non-whitened individuals of E. armatus.

The Ecological Genetics of Abnormal Abdomen in Drosophila mercatorum

Natural selection and adaptation are central to theories of organismal evolution. In order to study natural selection in the field, four basic problem areas must be investigated as part of an ecological genetics research program. The first problem is to document the genetic basis of the phenotypic variation observed in nature. Without genetic variation underlying the phenotypic variation, it is impossible to have an evolutionary response to selective forces. The second problem is to determine the phenotypic expression of this genetic variation under field conditions. Phenotypes are the result of genotype-by-environment interactions, and there is no guarantee that phenotypic expression in the laboratory corresponds to that found in nature. The third problem is to relate the phenotypic variation to variation in life history. Natural selection requires fitness differences, and the potential for selection cannot be evaluated in a predictive fashion unless differences in life history attributes can be inferred. The fourth problem is to estimate the structure of the natural population.

High sediment temperatures influence the emergence of dormant aquatic biota

Under the influence of increasing air temperatures, dormant seeds of wetland plants and eggs of microfauna may be subjected to increased sediment temperatures that adversely affect their capacity to germinate or hatch, while the wetland is in its ‘dry’ phase. We conducted a mesocosm experiment to investigate the influence of sediment temperature on the emergence capacity of dormant seeds and eggs. Dry wetland sediment was exposed to temperatures ranging from –180 to 150°C. After re-wetting, the taxon richness and abundance of communities that developed were assessed. Both aquatic plants and microfauna emerged from the seed bank at sediment temperatures lower than 50°C. However, the composition of the microfaunal community was altered once temperatures exceeded 40°C and germination of aquatic plants ceased once temperatures exceeded 50°C. These results suggest that changes to sediment temperature during the dry phase of wetlands may play an important role in influencing communities of wetland aquatic plants and microfauna. Modelled sediment temperature data indicated that minimum sediment temperature could exceed 40°C for extended periods of time under existing climate-change scenarios by 2070. An increase in the occurrence and duration of such temperatures may threaten the abundance and diversity of wetland microfauna and aquatic-plant communities.

Current issues involved with the identification and nutritional value of wood grubs consumed by Australian Aborigines.

The so called witchetty grub is a publicized food source for Australian Aborigines. Despite heavy use, the identities and number of species consumed is still not known because of the lack of identified voucher specimens. Taxonomy based on adults makes identification of larval forms difficult. Dwelling in the root, trunks, and stems of woody plants, grubs are a reliable and highly valued food source that may be in decline. Much information on edible insects may already be lost in parts of Australia heavily settled by Europeans. However, there are many parts of Australia where information on edible insects is still strong and needs to be recorded accurately for long‐term use. Recent identification of “witchetty grubs” from the witchetty bush at Barrow Creek has revealed that those there, based on their DNA, are not Endoxyla leucomochla. As grubs are collected and eaten before they mature and scientific taxonomy is based on adults, there are many unanswered questions on the grub identification and biology, host plants, and plant and grub distributions.

Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

Australian spiny mountain crayfish (Euastacus, Parastacidae) and their ecotosymbiotic temnocephalan flatworms (Temnocephalida, Platyhelminthes) may have co-occurred and interacted through deep time, during a period of major environmental change. Therefore, reconstructing the history of their association is of evolutionary, ecological, and conservation significance. Here, time-calibrated Bayesian phylogenies of Euastacus species and their temnocephalans (Temnohaswellia and Temnosewellia) indicate near-synchronous diversifications from the Cretaceous. Statistically significant cophylogeny correlations between associated clades suggest linked evolutionary histories. However, there is a stronger signal of codivergence and greater host specificity in Temnosewellia, which co-occurs with Euastacus across its range. Phylogeography and analyses of evolutionary distinctiveness (ED) suggest that regional differences in the impact of climate warming and drying had major effects both on crayfish and associated temnocephalans. In particular, Euastacus and Temnosewellia show strong latitudinal gradients in ED and, conversely, in geographical range size, with the most distinctive, northern lineages facing the greatest risk of extinction. Therefore, environmental change has, in some cases, strengthened ecological and evolutionary associations, leaving host-specific temnocephalans vulnerable to coextinction with endangered hosts. Consequently, the extinction of all Euastacus species currently endangered (75%) predicts coextinction of approximately 60% of the studied temnocephalans, with greatest loss of the most evolutionarily distinctive lineages.

Responses to conspecific and heterospecific disturbance odours in the Australian crayfish Euastacus armatus and Cherax destructor

The responses of individuals of Cherax destructor and Euastacus armatus to water containing stressed or unstressed crayfish were tested in the laboratory. Individuals of E. armatus showed only an increase in locomotion when stressed crayfish water was introduced. Individuals of C. destructor showed a decrease in the time spent in a lowered posture, an increase in the time spent in the raised posture and in grooming behaviour when stressed crayfish water was introduced. Individuals of C. destructor responded more strongly to heterospecific animals (Cherax rotundus and E. armatus) than to conspecifics. The levels of responses to the two heterospecific species were similar.