DOI: 10.5061/dryad.2z34tmphw
title: Data from: Reproduction under light pollution: maladaptive response to spatial variation in artificial light in a glow-worm

description: The amount of artificial light at night is growing worldwide, impacting
 the behaviour of nocturnal organisms. Yet, we know little about the
 consequences of these behavioural responses for individual fitness and
 population viability. We investigated if females of the common glow-worm
 Lampyris noctiluca – which glow in the night to attract males – mitigate
 negative effects of artificial light on mate attraction by adjusting the
 timing and location of glowing to spatial variation in light conditions.
 We found females do not move away from light when exposed to a gradient of
 artificial light, but delay or even refrain from glowing. Further, we
 demonstrate that this response is maladaptive, as our field study showed
 that staying still when exposed to artificial light from a simulated
 streetlight decreases mate attraction success, while moving only a short
 distance from the light source can markedly improve mate attraction. These
 results indicate that glow-worms are unable to respond to spatial
 variation in artificial light, which may be a factor in their global
 decline. Consequently, our results support the hypothesis that animals
 often lack adaptive behavioural responses to anthropogenic environmental
 changes and underlines the importance of considering behavioural responses
 when investigating effects of human activities on wildlife.
description: <strong>Behavioural
 responses to light pollution</strong> We collected glow-worm females in
 June 2017 from the surroundings of Tvärminne Zoological Station (N
 59°51', E 23°14') in Southern Finland. We collected them by hand
 at night and transported them to the lab, where we placed them in
 individual vials (diameter: 8 cm) containing fresh moss and leaves. The
 vials were kept at room temperature, approx. 21°C, at a 20h: 4h light:
 dark cycle, as darkness is restricted to only 4 h during the height of the
 breeding season at the latitude. We investigated the responses of
 females to artificial light on the night after capture. We used a 100 cm x
 15 cm arena with a white light emitting diode, LED light (5 mm, cold
 white; peak intensity ~0.32 µW/nm (microwatts/nanometer)  at 660 nm (red)
 with a secondary peak intensity of ~0.26 µW/nm at 440 nm (blue), as
 measured with spectrophotometer and integrating sphere), at one of the
 short ends (Figure 1). Light intensity was 40 lx at the lit end, 1.5 lx in
 the middle, and 0.5 lx at the dark end of the arena, measured with an
 AIRAM UVM-B lx-meter. We covered the bottom of the arena with soil and
 placed a cardboard rectangle, 4 cm high, along the length of the arena (in
 the middle of it) for the female to perch on, as females usually climb up
 on suitable structures to enhance the visibility of the glow to flying
 males [28, 33]. A seashell was placed at each short end of the arena for
 the female to hide under. We alternated the position of the LED light
 between the two short ends among replicates. We had two treatments: a light
 treatment and a control. We started each replicate at 11 PM by placing a
 female on the cardboard in the middle of the arena and turning on the LED
 light in the light treatment while leaving the LED light unlit in the
 control. We recorded the position of the female every 20 min for 2 h and
 noted whether she had settled down and initiated glowing. The borders of
 the arena had markings 10 cm apart, which we used to determine the
 position of the female and calculate the distance moved during each 20 min
 period. We defined females as settled when they had kept the same position
 over at least two consecutive observations and recorded the location and
 time of settling. If a female settled multiple times, we used the last
 settling location and time in the analysis. We estimated distance moved by
 summing distances moved during each 20 min period. This could
 underestimate the distance moved, as females may not move in a straight
 line, however, this estimation was consistent across trials and
 treatments. To investigate whether glow intensity influences responses to
 artificial light, we measured the maximum width of the pronotum (the
 structure that covers the dorsal surface of the thorax) of the female, as
 this correlates with lantern size, which roughly correlates with glow
 intensity [29].  We tested 26 females in the light treatment and 63
 females in the control. To analyse the impact of the
 presence of artificial light and the pronotum width (glow intensity) of
 the female on behaviours that were binary, we used logistic regression,
 with separate models for each behaviour. The behaviours were: (i) whether
 a female started to glow, (ii) the direction of movement in relation to
 the light source (towards or away), (iii) whether a female hid under the
 shell or within the soil, and (iv) whether a female settled
 down. To analyse
 the impact of artificial light on continuous measures, we used ANOVA, with
 separate models for each measure. The measures were: (i) total distance
 moved during the 2 h of observation, and (ii) the settling location (for
 those that settled). Pronotum width (glow intensity) was included as a
 covariate in the initial models, but as the interaction terms and the main
 effects were non-significant, and the removal did not influence the
 significance of the other variables, it was removed in the final model. To
 analyse the influence of artificial light on the latency to glowing, we
 used a time-to-event analysis, Cox proportional hazards model [34]. The
 times were “right-censored” for females that failed to glow by the end of
 the experiment. We checked that the data fulfilled the requirements of the
 analyses. All analyses were performed using SPSS 25. Significance was
 designated as P &lt; 0.05.   <strong>Impact on mate
 attraction</strong> We conducted the experiment from
 June 6th to July 7th in 2017 in the surroundings of Tvärminne Zoological
 station. We selected six sites that lacked shadowing trees or bushes, and
 where we had detected glow-worms during earlier years. We manipulated the
 presence of artificial light by erecting a pole and attaching a white LED
 light (ANSI FL1 Standard: 35 lumen, beam distance 24 m) at the height of
 1.7 m (Figure 2). The angle between the ground and the direction of the
 centre of the light was 55 degrees. We placed two dummy females (LED
 lures, see construction in [29]) at two different distances, in a straight
 line from the pole (Figure 2). One dummy was placed in the inner position
 (within the cone of light from the pole when lit), at 1.1 m from the pole,
 at 15–20 lx (peak intensity ~0.08 µW/cm2/nm at 455 nm, measured with
 spectrophotometer and cosine corrector), which corresponds to light levels
 under common streetlights [2, 35]. The other dummy was placed in the outer
 position, at 2.3 m from the pole, at 1–1.5 lx (peak intensity ~0.004
 µW/cm2/nm at 455 nm), which is slightly brighter than natural light levels
 at night in the area in the summer (0.1–0.6 lx, peak intensity
 0.0003–0.0016 µW/cm2/nm at 460 nm, measured on May 31th and June 1st 2020
 at 12.30 AM in an open area on both an overcast and a moonlit night). The
 dummies were designed to trap males within a plastic bottle [29]. The
 wavelength of the LED lures was 562 nm, similar to female glow-worms
 (550–570 nm) [33, 36]. To investigate the effect of glow intensity on mate
 attraction, we varied the glow intensity of the two dummies among
 replicates; peak glow intensity ~0.03, 0.06, and 0.13 µW/nm  (measured
 with spectrophotometer and integrating sphere). The paired dummies within
 a replicate had the same glow intensity. The differences in glow intensity
 reflected natural variation in the wild (AM Borshagovski, unpublished data
 on spectrophotometer measurements). We started each trial when dusk
 began to fall (approximately 10 PM), by turning on the glow of the two
 dummy females, as well as the light from the pole in the artificial light
 treatment, while leaving poles unlit in the control. We checked the dummy
 females 3–4 h later (at 1–2 AM) for the presence of males and turned off
 all lights. Males are unlikely to escape from the traps (Elgert, personal
 observation). We
 conducted 38 replicates of the artificial light treatment, with three
 dummy glow intensities (low: n = 13; medium: n = 14; high: n = 11, with
 two dummy females in each replicate) and 19 replicates of the control,
 with three dummy glow intensities (low: n = 6; medium: n = 5; high: n = 8,
 with two dummy females in each replicate). We distributed the treatments
 (presence of artificial light and glow intensities) equally among the six
 sites. In the
 analyses, we used the presence or absence of males in each dummy female
 trap as the response variable, rather than the number of males caught, to
 rule out the possibility that the presence of one male had attracted
 additional males. We analysed the data using a GLMM with binomial error
 distribution and logit link function, with presence or absence of male(s)
 in each dummy trap as the binary response variable. We used light
 treatment (light on or light off), position with respect to the light
 fixture (inner position or outer position), and glow intensity as fixed
 factors, and date and site as random factors, with site nested within
 date. We started with a full model and deleted non-significant interaction
 terms and fixed terms when this was supported by the Akaike Information
 Criterion (AIC) and did not reduce the significance of other terms [37].
 All analyses were performed using SPSS 25. Significance was designated as
 P &lt; 0.05.
description: The data, legends and captions for both the laboratory and field
 experiment are provided in the same document, on separate tabs. Female
 F159 is missing size data.