The Effects of Temperature and Herbicide on Development and Behaviour in Latrodectus katipo

Abstract

Latrodectus katipo are a species of spider endemic to New Zealand. Latrodectus katipo numbers have markedly declined over the last 40 years. A species once common throughout New Zealand sand dunes, is now confined to a few specific areas. The cause of decline is likely due to habitat destruction and the introduction of exotic spiders and plants. Exotic spider species are displacing L. katipo in areas throughout NZ, while introduced plant species do not provide the ideal habitat for web-building. The introduction of exotic weed species has lead to herbicides being used throughout L. katipo habitat. Little research has been undertaken surrounding the effects of herbicide on behaviour. Similarly, few studies have been published on development in L. katipo. With climate change likely to impact temperatures around NZ, it is important to understand how temperature will affect development of the species in the future. This thesis aimed to examine the effects that temperature has on the development of the species, as well the effects that a glyphosate based herbicide has on L. katipo behaviour. The effects of temperature on development were determined by comparing development between three different temperature regimes (18°C, 23°C and 28°C). It was found that emergence time (duration inside egg-sac) was significantly shorter at higher temperatures. Hatching time (duration inside the egg), similarly, was found to be significantly shorter at higher temperatures. An overall negative pattern was observed, as temperature increased, hatching/emergence time decreased. Instar duration (time between moults) was found to be shorter at higher temperatures. Shorter instar duration meant that spiders at the highest temperature developed faster. The effects of herbicide on behaviour was determined by exposing individuals to a glyphosate based substrate and recording behaviour. Glyphosate is the active ingredient in most commonly used herbicide in NZ, which if found to have an effect on L. katipo could be very detrimental. Ethovision was used to compare the distance moved, velocity and activeness between herbicide exposure and control trials. Glyphosate exposure was found not to have a significant impact on any of the measured behavioural traits. Repeatability of behaviours were also analysed to determine whether there were consistent behavioural differences, representative of personality. Males were found to have high levels of repeatability across measures; however, females and juveniles did not (juveniles could not be sexed). Overall, higher temperatures were found to decrease development time, with higher temperatures leading to significantly faster emergence and hatching. These results could be a useful indicator of the effects that climate change may have on the development of the species. Faster development times could mean that L. katipo may have a greater chance at competing with introduced spiders, like Steatoda capensis. Further research needs to be conducted to determine whether there are any other detrimental physiological effects from higher temperatures. Glyphosate was found not to affect the measured behavioural traits. This is a positive finding as it suggests that herbicide use is not having a signficant impact on activity related behaviours and can therefore still be used to remove exotic plant species from L. katipo habitat, though further studies are needed to ensure that there are no negative effects of glyphosate.