title: Sex- and season-dependent behaviour in a flightless insect, the Auckland tree weta (Hemideina thoracica)

authors: Wehi, Priscilla M.

subjects: Aggregation

abstract: In a polygynous mating system, males frequently compete by locating and defending sites with resources essential to female survival and reproduction. We investigated seasonal changes in site occupancy in a sexually dimorphic, harem-forming insect, the Auckland tree weta (Hemideina thoracica). First we established artificial cavities as diurnal refuge cavities and potential harem guarding sites. We then examined cavity occupancy changes, and, based on our knowledge of prior occupants, determined sex-specific patterns of arrival, departure, and aggregation at a population level throughout the year. Both season and the sex of prior occupants influenced weta occupancy patterns. Most observations were of single females. However, both males and females moved into cavities previously occupied by a weta of the opposite sex more often than expected by chance alone. Females avoided cavities where other females were present, except during summer when most harems formed. In early summer, male and female tree weta previously living apart began co-habiting. Generally there was little relationship between the number and sex of the weta inside cavities and female departure rates from cavities. Males who were sharing with other males departed cavities more frequently than single males, as might be expected in a polygynous species with male-male combat. Males were less likely to depart if they were sharing a cavity with a harem of more than two females during the summer-autumn period. Analysis of departure rates from artificial cavities indicates males are more mobile than females only in winter and spring. Based on our arrival and departure data, and high occupancy of artificial cavities, we suggest that female weta at this site are mobile and may search for mates during the summer. The data are consistent with a polygynandrous mating system as inferred for other tree weta species (Hemideina spp.).

text: Sex- and season-dependent behaviour in a flightless insect, the Auckland tree weta (Hemideina thoracica) In a polygynous mating system, males frequently compete by locating and defending sites with resources essential to female survival and reproduction. We investigated seasonal changes in site occupancy in a sexually dimorphic, harem-forming insect, the Auckland tree weta (Hemideina thoracica). First we established artificial cavities as diurnal refuge cavities and potential harem guarding sites. We then examined cavity occupancy changes, and, based on our knowledge of prior occupants, determined sex-specific patterns of arrival, departure, and aggregation at a population level throughout the year. Both season and the sex of prior occupants influenced weta occupancy patterns. Most observations were of single females. However, both males and females moved into cavities previously occupied by a weta of the opposite sex more often than expected by chance alone. Females avoided cavities where other females were present, except during summer when most harems formed. In early summer, male and female tree weta previously living apart began co-habiting. Generally there was little relationship between the number and sex of the weta inside cavities and female departure rates from cavities. Males who were sharing with other males departed cavities more frequently than single males, as might be expected in a polygynous species with male-male combat. Males were less likely to depart if they were sharing a cavity with a harem of more than two females during the summer-autumn period. Analysis of departure rates from artificial cavities indicates males are more mobile than females only in winter and spring. Based on our arrival and departure data, and high occupancy of artificial cavities, we suggest that female weta at this site are mobile and may search for mates during the summer. The data are consistent with a polygynandrous mating system as inferred for other tree weta species (Hemideina spp.).

year: 2013

title: Oxidation of surface sediment: effects of disturbance depth and seawater flow speed

authors: Vopel, Kay

subjects: cohesive sediment

abstract: Periodic disturbance of surface sediment is a natural feature of marine environments. Following exposure to oxygenated seawater, the disturbed sediment oxidises leading to the recovery of its surface chemistry. Despite its importance for the ecology of the sediment–water interface, the dynamics of this recovery is not well known. We studied the effects of disturbance depth and seawater flow speed on the oxidation of estuarine cohesive sediment in a laboratory flume with microelectrodes. We removed surface sediment to 2 depths (5 and 50 mm) and then observed changes in sediment O₂ distribution and consumption over 1 h under conditions of slow and fast flow (3.5 and 7.5 cm s–1). Measurements were repeated 1 d later. The consumption of O₂ in the treated sediments reached a ‘quasi stable state’ within 7 h (50 mm depth) and 16 h (5 mm depth) characterised by very slow changes due to slow oxidation of reduced solids. Faster flow increased the rate at which sediment from 50 mm depth oxidised but not that of the sediment from 5 mm depth. After 20 to 24 h, sediments disturbed to 50 and 5 mm depths still differed in O₂ distribution and consumption, both from each other and from the pre-treatment sediment. Differences in the response of pore water O₂ distribution to an abrupt increase in flow speed (3.5 to 7.5 cm s–1) were also still evident at this time. Our measurements confirmed the results of previous theoretical analyses in that they indicate that the duration of the recovery of the surface sediment chemistry from disturbance and the chemical properties of the recovering sediment are controlled by the kinetics of solute and solid oxidation. Oxidation of reduced solids in disturbed sediment can result in a characteristic chemical signature at the sediment surface that lasts in the order of at least days.

text: Oxidation of surface sediment: effects of disturbance depth and seawater flow speed Periodic disturbance of surface sediment is a natural feature of marine environments. Following exposure to oxygenated seawater, the disturbed sediment oxidises leading to the recovery of its surface chemistry. Despite its importance for the ecology of the sediment–water interface, the dynamics of this recovery is not well known. We studied the effects of disturbance depth and seawater flow speed on the oxidation of estuarine cohesive sediment in a laboratory flume with microelectrodes. We removed surface sediment to 2 depths (5 and 50 mm) and then observed changes in sediment O₂ distribution and consumption over 1 h under conditions of slow and fast flow (3.5 and 7.5 cm s–1). Measurements were repeated 1 d later. The consumption of O₂ in the treated sediments reached a ‘quasi stable state’ within 7 h (50 mm depth) and 16 h (5 mm depth) characterised by very slow changes due to slow oxidation of reduced solids. Faster flow increased the rate at which sediment from 50 mm depth oxidised but not that of the sediment from 5 mm depth. After 20 to 24 h, sediments disturbed to 50 and 5 mm depths still differed in O₂ distribution and consumption, both from each other and from the pre-treatment sediment. Differences in the response of pore water O₂ distribution to an abrupt increase in flow speed (3.5 to 7.5 cm s–1) were also still evident at this time. Our measurements confirmed the results of previous theoretical analyses in that they indicate that the duration of the recovery of the surface sediment chemistry from disturbance and the chemical properties of the recovering sediment are controlled by the kinetics of solute and solid oxidation. Oxidation of reduced solids in disturbed sediment can result in a characteristic chemical signature at the sediment surface that lasts in the order of at least days.

year: 2010

title: /u/ fronting and /t/ aspiration in Māori and New Zealand English

authors: Maclagan, Margaret

subjects: Maori

abstract: This article examines the relationship between the frontness of /u/ and the aspiration of /t/ in both Māori and New Zealand English (NZE). In both languages, these processes can be observed since the earliest recordings dating from the latter part of the nineteenth century. We report analyses of these developments for three groups of male speakers of Māori spanning the twentieth century. We compare the Māori analyses with analyses of related features of the speakers' English and of the English of monolingual contemporaries. The occurrence of these processes in Māori cannot be seen simply as interference from NZE as the Māori-speaking population became increasingly bilingual. We conclude that it was the arrival of English with its contrast between aspirated and unaspirated plosives, rather than direct borrowing, that was the trigger for the fronting of the hitherto stable back Māori /u/ vowel together with increased aspiration of /t/ before both /i/ and /u/.

text: /u/ fronting and /t/ aspiration in Māori and New Zealand English This article examines the relationship between the frontness of /u/ and the aspiration of /t/ in both Māori and New Zealand English (NZE). In both languages, these processes can be observed since the earliest recordings dating from the latter part of the nineteenth century. We report analyses of these developments for three groups of male speakers of Māori spanning the twentieth century. We compare the Māori analyses with analyses of related features of the speakers' English and of the English of monolingual contemporaries. The occurrence of these processes in Māori cannot be seen simply as interference from NZE as the Māori-speaking population became increasingly bilingual. We conclude that it was the arrival of English with its contrast between aspirated and unaspirated plosives, rather than direct borrowing, that was the trigger for the fronting of the hitherto stable back Māori /u/ vowel together with increased aspiration of /t/ before both /i/ and /u/.

year: 2009