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Is flying riskier for female katydids than for males?

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Abstract

Morphological and behavioural differences between the sexes often make one sex of a species more vulnerable to predation than the other. Onomarchus uninotatus, a canopy katydid, forms an important component of the diet of the insectivorous bat Megaderma spasma. Examination of culled prey remains in M. spasma roosts suggested that female O. uninotatus may be at higher risk of predation than males. As in many insects, the females of O. uninotatus are larger and heavier and might be easier for predators to detect and capture and/or preferred for their higher nutritive value. We tested these hypotheses by conducting behavioural experiments in an outdoor enclosure, examining the bat predator approach to free-flying O. uninotatus and their capture success. We found that the flying female and male katydids were equally likely to be approached, but males were captured more by M. spasma, with a weak effect. This indicates that females may have a better escape strategy after being approached. We then asked whether females were at higher risk of predation because they moved more often or for longer durations across trees than males, in search of mates and egg-laying sites. We investigated landscape-level movement patterns of O. uninotatus females and males using VHF radio-telemetry. Females had 1.6 times higher frequency of movement and 1.8 times greater displacement across trees than males. This difference may be ecologically important and cause higher bat predation risk on females.

Significance statement

Studying the factors affecting sex-specific levels of predation risk is crucial to better understand the natural selection and the hypothesised causes and consequences of sexual dimorphism. Katydid females, including Onomarchus uninotatus, are at a higher risk of bat predation than males, and flying is one of the most risky prey behaviours. Onomarchus uninotatus females are larger than males, which could make them easier to detect and capture. Our experiments involving free-flying bats and katydids showed, however, that bat approaches are similar for flying females and males. Females might be better at escaping bat captures after being approached. Katydid males typically broadcast acoustic signals, and females move towards these signals, potentially placing females at higher predation risk. Radio-telemetry studies revealed that on average, females were likely to move more often with greater displacements across trees, which may place them at higher risk of predation.

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Data Availability

The datasets generated and analysed during the current study, including datasets used in supplementary information, along with the R code used for data processing and statistical analyses are available on figshare [flight_risk_datasheets_and_code].

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Acknowledgements

We thank Kunjan Joshi and Ayaz Ahmed for their assistance during behavioural experiments and radio-telemetry, and Sudhakar Malekudiya Gowda, Balakrishna, and Guruprasad for maintaining and catching animals and building the enclosure for conducting experiments. We also acknowledge the local residents of Peradka in Mala village for allowing us to work on their properties at night. We are greatful to Dr. Kavita Isvaran for her valuable inputs regarding the analysis and Dr. Aswathy Nair for helping with the study design.

Funding

This project was funded by DST-SERB (Department of Science and Technology, Ministry of Science and Technology, Science & Engineering Research Board, India; grant numbers EMR/2016/002293, SPG/2020/000043) to RB. Some of the equipment were funded by DST-FIST [Fund for Improvement of S&T Infrastructure; sanction number SR/FST/LSII-025/2009(C)]. The expenses for fieldwork and consumables were covered by DBT-IISc Partnership Program (Phase II; Department of Biotechnology, Ministry of Science and Technology and Indian Institute of Science, India). KS was supported by a scholarship from the Ministry of Human Resource Development (MHRD), Ministry of Education, India.

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Authors

Contributions

Kasturi Saha: conceptualization, methodology, investigation, data curation, formal analysis, validation, writing—original draft, writing—review and editing, and visualisation. Harish Prakash: validation, formal analysis, and writing—review and editing. Prajna Paramita Mohapatra: investigation. Rohini Balakrishnan: conceptualization, methodology, resources, writing—review and editing, supervision, project administration, and funding acquisition.

Corresponding author

Correspondence to Kasturi Saha.

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Ethics approval

Ethical approval for animal handling was sanctioned by the Institutional Animal Ethics Committee, Indian Institute of Science, India for project number CAF/Ethics/563/2017.

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The authors declare no competing interests.

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Communicated by K. Shaw

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Supplementary information

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Saha, K., Prakash, H., Mohapatra, P.P. et al. Is flying riskier for female katydids than for males?. Behav Ecol Sociobiol 77, 27 (2023). https://doi.org/10.1007/s00265-023-03298-7

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  • DOI: https://doi.org/10.1007/s00265-023-03298-7

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