DOI: 10.5061/dryad.j3tx95xrs
title: Predicting sex bias in mobility from functional traits in flying insects

description: Understanding the movement patterns of organisms is crucial for effective
 biodiversity conservation in the increasingly dynamic and fragmented
 landscapes. Since the colonization of habitat patches relies largely on
 females, sex differences in movement capability must also be considered.
 However, obtaining direct measurements of mobility and dispersal, and sex
 biases in these traits, is often challenging. This underscores the
 importance of predicting sex-specific estimates of mobility based on
 species’ functional traits. Our phylogenetic comparative study aims at
 identifying species traits that could serve as proxies for sex bias in
 mobility in flying insects. We rely on a comprehensive dataset on the sex
 ratios of 454 moth species (Lepidoptera: Macroheterocera), captured by
 light traps of the Finnish national moth monitoring scheme. We first
 demonstrate that, in the vast majority of species, males outnumber females
 among the captured individuals. Our phylogenetic regression models reveal
 that species-specific sex ratios correlate with traits typically predicted
 to be associated with sex differences in mobility. Female proportions
 decrease as sexual dimorphism in wingspan becomes more male-biased and
 female wing loading relative to males increases. Proportions of females
 are also lower in larger species. Females are particularly scarce in trap
 samples of species in which the reproductive output of females is
 primarily determined by larval-derived resources (i.e., capital breeders).
 These associations suggest that the observed variations in sex ratios do
 indeed mirror the variation in sex bias in mobility across species. Our
 findings highlight the potential of trait-based approaches to identify
 meaningful indicators of insect mobility, including sex biases in
 mobility. The availability of such proxies facilitates predictions about
 how different species might respond to contemporary challenges, such as
 light pollution and habitat loss and fragmentation. The detected
 associations also advance ordination schemes of insect life histories by
 integrating mobility measures into relevant analyses.
description: <strong>Sex ratio data</strong> We
 took advantage of a vast dataset generated by the Finnish Moth Monitoring
 Scheme 'Nocturna', which has been operating an extensive
 nationwide network of light traps for over three decades (Huikkonen et al.
 2024). The essence of using light trapping in moth monitoring lies in the
 well-known habit of these nocturnal insects to be attracted to artificial
 light sources. The light traps deployed by the monitoring scheme cover the
 entire flight period of moths in the region; they are installed in early
 spring (early April to early May, depending on latitude) and dismantled in
 autumn after moths cease flying (early October to early November). The
 traps are typically serviced and emptied once a week, with all captured
 macroheteroceran moths identified to the species level by voluntary
 lepidopterists, and the number of individuals per species is reported in
 an online database. Conveniently for our study, many
 contributors of the scheme systematically report the numbers of trapped
 individuals separately for males and females (53 % of the total number of
 individuals in the database), thus providing data on the relative
 proportions of the two sexes among the trapped individuals. Sex-identified
 catches from 34 light traps, each operated for at least ten years between
 1993 and 2012, provided a total of 358 trap-year samples, comprising
 1,383,297 moth individuals. Data used in our analyses were extracted from
 the moth monitoring database (Yöpeti) on 22 October 2014. In our analyses,
 we included only species with more than 20 individuals captured over the
 trapping years. This criterion was met by 483 out of the 635 species in
 the total dataset. We applied two further inclusion criteria. Firstly, we
 excluded nine species with short-winged or wingless females, as light
 traps capture only males from these species. Secondly, we did not consider
 twenty species known to exhibit significant day-flying activity. In such
 species, there are often sex-related differences in circadian rhythms,
 potentially introducing unpredictable effects on sex ratios derived from
 night-operated light traps. For instance, in the lasiocampid Macrothylacia
 rubi, males primarily fly in the afternoon, whereas females fly only at
 night, causing a strong female bias in light traps. Applying these
 additional criteria left us with sex ratio data on 454 moth species,
 representing ten moth families, forming the basis of our study. 
 <strong>Species trait data</strong>
 Data on species' ecological traits (host plant
 specialization, habitat preference, presence/absence of adult feeding) and
 sex-specific data on body-size-related (wingspan, wing loading, body mass,
 abdomen mass, relative abdomen size of females) traits were obtained from
 previously published studies. Data on host plant specialization were
 retrieved from Teder (2020), where species were categorized as
 monophagous, oligophagous, or polyphagous. Habitat preference was rated on
 a scale from 1 (strictly open-habitat species) to 5 (strictly forest
 species) (see Ude et al. 2024 for details). Species classification by the
 presence or absence of adult feeding was based on data from regional
 taxonomic handbooks. Male and female wingspan
 measurements were obtained from Teder (2020), where wingspan was defined
 as the maximum distance between the forewing tips measured in collection
 specimens mounted in the traditional way. Sex-specific wingspan data were
 available for all species for which we had sex ratio data. For a subset of
 38 species within the Geometridae family, we could use additional
 sex-specific size-related traits, empirically recorded for a comparative
 study by Davis et al. (2016). These variables included sex-specific
 measurements of dry body mass and dry abdomen mass, as well as relative
 abdomen size in females (RAF), calculated as abdomen mass divided by body
 mass at adult eclosion. Finally, the wing loading index was computed for
 each sex by dividing body mass by the squared wingspan, with the squared
 wingspan serving as a proxy for wing area. Higher values of the wing
 loading index indicate a larger body mass relative to wing size,
 suggesting a higher energetic cost of flying and potentially reduced
 mobility. For each trait with sex-specific values
 available, we calculated an index of sexual dimorphism (hereafter
 SSDwingspan, SSDmass, SSDabdomen, SSDwingloading). Using the algorithm
 proposed by Lovich and Gibbons (1992), SSD was calculated as follows: SSD
 = [(trait value of the larger sex) / (trait value of the smaller sex)] –
 1. The resulting SSD values were assigned a positive sign if females were
 larger and a negative sign if males were larger. The SSD values calculated
 this way are symmetrically distributed around zero, where SSD = 0
 indicates no size difference between sexes, while SSD &gt; 0 and SSD
 &lt; 0 denote female- and male-biased dimorphism,
 respectively.  <strong>Phylogeny of the
 species</strong> We took advantage of the fully
 resolved phylogenetic relationships of northern European Geometridae
 (Õunap et al. 2024), which were based on 11 molecular markers commonly
 used for phylogeny reconstruction in this group. In total, the data matrix
 encompassed 458 species of geometrids and 37 outgroup taxa. The maximum
 likelihood (ML) tree was constructed using IQ-TREE v2.1.2 (Nguyen et al.
 2015), and subsequently pruned to include only species relevant to our
 study (see Holm et al. 2018 for further details). 
description: # Predicting sex bias in mobility from functional traits in flying insects
 ## Metadata Data set creators: Tiit Teder, Juha Pöyry, Ida-Maria
 Huikkonen, Anna Suuronen, Reima Leinonen, Robert Barry Davis Other
 contributors: Ants Kaasik, Toomas Tammaru Date created: 10 September 2024
 ## Data and scripts supporting: Teder, T., Davis, R.B., Pöyry, J.,
 Huikkonen, I.-M., Suuronen, A., Leinonen, R., Kaasik, A., Tammaru, T.
 2025. Predicting sex bias in mobility from functional traits in flying
 insects. Oikos. ## Licensing This data set is covered by CC0 1.0 Universal
 (CC0 1.0). Researchers interested in the re-use of this data set and
 corresponding R-code are expected to contact the authors for
 collaboration. ### Contact Information Name: Tiit Teder E-mail:
 [tiit.teder@ut.ee](mailto:tiit.teder@ut.ee) Affiliations: Department of
 Zoology, Institute of Ecology and Earth Sciences, University of Tartu;
 Department of Ecology, Faculty of Environmental Sciences, Czech University
 of Life Sciences Prague ORCID ID:
 [https://orcid.org/0000-0001-6587-9325](https://orcid.org/0000-0001-6587-9325) ### Funding sources * Estonian Research Council (grant no. PRG741) * Internal Grant Agency of the Faculty of Environmental Sciences, Czech University of Life Sciences Prague (grant no. 42900/1312/3141) ### Data Files Overview * File count: 2 * Total file size: 39 KB * File formats: .xlsx, .RData \#1 'sr.data.xlsx': Excel file containing data of measured and literature-derived variables to analyse the relationships between sex ratio and various functional traits; corresponding R script 'R_code_Teder_et_al.R'. \#2 'sr.tree.RData': RData file containing the original phylogeny used for this study before pruning. Code for pruning can be found in the corresponding R script 'R_code_Teder_et_al.R'. ### Variables (#1 'sr.data.RData') Treename - Name of species as in sr.tree.RData so species names match names found in the phylogeny ID - Species identificator Genus, Species, Superfamily, Family, Subfamily - taxonomic affiliation of the species HostSpec - Host specialization (M - monophagous, O - oligophagous, P - polyphagous) HostSpec2 - Host specialization (O - monophagous + oligophagous, P - polyphagous) WingSpan - Maximum distance between the forewing tips measured in collection specimens mounted in the traditional way Mwingspan - Wingspan of males Fwingspan - Wingspan of females SSDwingspan - Sexual size dimorphism in wingspan (see above, for calculations) Mmass - Body mass of males Fmass - Body mass of females SSDmass - Sexual size dimorphism in body mass (see above, for calculations) Mabdomen - Abdomen mass of males Fabdomen - Abdomen mass of females SSDabdomen - Sexual size dimorphism in abdomen mass (see above, for calculations) MaleNumber - Total number of males captured by light traps FemaleNumber - Total number of females captured by light traps TotalNumber - Total number of species individuals captured (= MaleNumber + FemaleNumber) SexRatio - Percentage of females among all captured individuals Mloading - Wing loading of males (see above, for calculations) Floading - Wing loading of females (see above, for calculations) SSDloading - Sexual size dimorphism in wing loading (see above, for calculations) AdultFeeding - Presence of adult feeding (Y - present, N - absent) ForestAffinity - Habitat preference rated on a scale from 1 (strictly open-habitat species) to 5 (strictly forest species) RAF - relative female abdomen size (RAF), calculated as abdomen mass divided by body mass at adult eclosion DayActivity - Species categorized by the degree of diurnal activity (0 - nocturnal species, 1-3 some to substantial diurnal activity). Only nocturnal species (=0) were considered in the analyses. Missing data code: 'n/a' (= not available). For a number of species traits, data were available for a limited set of species. ### References * Davis, R. B. et al. 2016. An ordination of life-histories using morphological proxies: capital vs income breeding in insects. – Ecology 97: 2112–2124. * Holm, S. et al. 2018. Reproductive behaviour indicates specificity in resource use: Phylogenetic examples from temperate and tropical insects. – Oikos 127: 1113–1124. * Huikkonen, I.-M., Pöyry, J., Korhonen, P., Leinonen, R. and Suuronen, A. 2024. Valtakunnallinen yöperhosseuranta 30 vuotta (1993-2022). Suomen ympäristökeskuksen raportteja 26/2024. [[http://hdl.handle.net/10138/577595](http://hdl.handle.net/10138/577595)] * Lovich, J. E. and Gibbons, J. W. 1992. A review of techniques for quantifying sexual size dimorphism. – Growth Develop. Aging 56: 269–281. * Nguyen, L.-T., Schmidt, H. A., von Haeseler, A. and Minh, B. Q. 2015. IQ-TREE: a fast and effective stochastic algorithm for estimating maximum likelihood phylogenies. – Mol. Biol. Evol. 32: 268–274. * Teder, T. 2020. Phenological responses to climate warming in temperate moths and butterflies: species traits predict future changes in voltinism. – Oikos 129: 1051–1060. * Ude, K. et al. 2024. Evolution of wing shape in geometrid moths: phylogenetic effects dominate over ecology. – J. Evol. Biol. 37: 526–537.