The systematics, ecology and physiology of New Zealand landhoppers (Crustacea: Amphipoda: Talitridae).
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The terrestrial Talitridae (landhoppers) are dominant members of mesic cryptozoic habitats in Gondwana fragments and other Southern Hemisphere land masses. Their respiratory apparatus consists of simple external gills bathed in fluid (exosomatic water). Respiratory rates are moderately high and vary with species, sex, weight, surface area, temperature, disease status, stage in the moult cycle, breeding status, time of day and season. Season acclimatisation is marked in Makawe hurleyi and is largely accomplished by an increase in gill area. Continuous respirometry shows that landhoppers are highly disturbed for a period of hours following their introduction into respirometers. In consequence, they have anomalous rates for some time during an experiment. Transpiration rates are very high. The time course of water loss is complex, but can be modelled by a series of decaying exponentials. Transpiration rate varies with vapour pressure deficit, body area and wind speed. When immersed, landhoppers drown. They cannot swim. Some species can climb and they may possess specific adaptations for finding an escape route and breaking through a meniscus. Survival under water is prolonged if the media is oxygenated, therefore death under water is probably related to respiratory failure. Haemolymph and exosomatic fluid osmotic pressures are lower the more terrestrial the species. M.hurleyi, the most terrestrial species investigated, had a mean haemolymph osmotic pressure 45% that of seawater. Starvation did not affect the haemolymph osmotic pressure of M.hurleyi. The supralittoral species, Transorchestia chiliensis, could regulate in both hypo- and hyperosmotic conditions. If environmental water sources became limited it ceased regulating and became a tolerator. Landhoppers possess extremely effective humidity receptors. Different species and genera favour environments with different degrees of terrestrialism. They are generally not found in regions with less than about 550 mm precipitation per year. The ecology of two species (M.hurleyi and Talorchestia patersoni) living in waste grassland is described. The two species exhibit partitioning of their habitat with T.patersoni living in dry, flood-free microhabitats immediately around the base of tussocks, and the more abundant M.hurleyi living between tussocks. This latter species can escape from flooding by climbing up grass stems. Brood size varies with body size of mother and with species. Eggs are lost from the brood as brooding proceeds. Growth in the field is dependent on temperature but generally there are about 15 instars per year. Mortality is high for young, immature animals, considerably lower for young adults, and high for older adults. Biomass is related to litter thickness. A whitey disease caused by a strain of Bacillus subtilis is affecting indigenous landhoppers. It causes a decline in density, age structure and egg production. It was probably introduced by the adventive Talitroides topitotum and is spread around the country by human agencies. Landhoppers are nocturnally active with activity peaks after dusk and at dawn. Factors affecting general and climbing activity are discussed based on field and laboratory investigations. Breeding ceases in winter. The time-setting clue for both cessation and initiation of breeding is daylength. Ecdysis is described in one species. In many species males do not carry females during courtship and copulation. Copulation is described for M.hurleyi. Cuticular structures are described. A mucoid layer covers the body and serves to lubricate and defend the body. The layer has antimicrobial properties. Biotic interactions are important in determining landhopper densities because they vary in density from plant community to plant community even though physical conditions appear to be very similar. They occur in a number of adventive plant communities. They are largely absent from damaged native communities and it is hypothesised that this is due to a nutrient deficiency. The phylogenetic age of landhoppers is considered and it is concluded that they are a relatively ancient group.