From quiet-night-in to party animal: sex ratio and density affect male/female aggregations in a ‘harem’ polygynous insect
Section snippets
Methods
The sex ratio of a wild population of H. thoracica was measured during nocturnal observations at Matuku Reserve (-36.86, 174.48) in the Waitakere ranges near Auckland, New Zealand in January–March 2017 and 2018. Two observers walked down the track and carefully scanned the foliage up to 10 m into the bush from the track. The sex, life stage (juvenile or adult), weight (assessed using Toltec portable field scales), head length and lengths of the hind tibia (using Mako digital callipers measuring
Results
The sex ratio of H. thoracica at Matuku reserve over the two seasons was female biased for both adults and juveniles (Table 2). The adult sex ratio was not significantly different from even in 2017 (1:1.29 males: females; binomial test: N = 39, P = 0.522) and significantly female biased in 2018 (1:1.60 males: females; binomial test: N = 104, P = 0.024).
In the laboratory trials, females and males did not distribute themselves randomly, and there were significant differences between the observed and
Discussion
The manipulation of sex ratio and density showed that as the number and proportion of male and female wētā changed from an even sex ratio to male or female biased so did their aggregation behaviour. In all treatments empty roosts were observed much more commonly than expected. This suggests that individuals chose to aggregate rather than spreading themselves among the available roosts. In high-density/even sex ratio (6M6F) treatments, there was a higher incidence of aggregations of multiple
Acknowledgments
We thank the Royal Forest & Bird Protection Society and John Staniland for access to Matuku Reserve administered by the Waitakere Branch. M.J.G. was supported by Deakin University Centre for Integrated Ecology funding and a Deakin University Postgraduate Research Scholarship and received funding from the New Zealand Entomological Society 21st Anniversary Fund and the Royal Society of New Zealand Hutton Fund. Thanks are due to those who helped with fieldwork for this project: Leilani Walker,
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