Artificial light at night alters life history in a nocturnal orb-web spider

Abstract

The prevalence of artificial light at night (ALAN) is increasing rapidly around the world. The potential physiological costs of this night lighting are often evident in life history shifts. We investigated the effects of chronic night-time exposure to ecologically relevant levels of LED lighting on the life history traits of the nocturnal Australian garden orb-web spider (Eriophora biapicata). We reared spiders under a 12-hour day and either a 12-hour natural darkness (~0 lux) or a 12-hour dim light (~20 lux) night and assessed juvenile development, growth and mortality, and adult reproductive success and survival. We found that exposure to ALAN accelerated juvenile development, resulting in spiders progressing through fewer moults, and maturing earlier and at a smaller size. There was a significant increase in daily juvenile mortality for spiders reared under 20 lux, but the earlier maturation resulted in a comparable number of 0 lux and 20 lux spiders reaching maturity. Exposure to ALAN also considerably reduced the number of eggs produced by females, largely associated with ALAN-induced reductions in body size. Despite previous observations of increased fitness for some orb-weavers in urban areas and near night lighting, it appears that exposure to artificial night lighting may lead to considerable developmental costs. Future research will need to consider the detrimental effects of ALAN combined with foraging benefits when studying nocturnal insectivores that forage around artificial lights. (Bedrosian et al., 2011; Durrant et al., 2015), survival (Shah et al., 2011) and 38 fecundity (McLay et al., 2017), as well as shifts in reproductive behaviours (Firebaugh & 39 Haynes, 2016; McLay et al., 2017; van Geffen et al., 2014 van Geffen et al., , 2015. Indirectly, where exposure to 40 night lighting stimulates earlier maturation and smaller adult size, there may be reproductive 41 costs due to poorer male performance (Elgar & Jones, 2008; van Geffen et al., 2014) and reduced 42 female fecundity (Honěk & Honek, 1993; van Geffen et al., 2014). Adults that emerge earlier 43 may benefit if this extends their potential breeding period and thus increases offspring 44 production (Lowe et al., 2014; Schneider & Elgar, 2002). However, each sex may respond 45 differently to the presence of ALAN, and maturation time for males and females could 46 desynchronise (Dominoni et al., 2013; van Geffen et al., 2014).47 A potential underlying mechanism for these life history shifts is that the presence of ALAN may 48 simulate a longer day and/or mask daily and seasonal patterns of light. Changes in natural 49 lighting drive a multitude of daily and seasonal biological rhythms, including reproduction 50 (Nelson et al., 2010; Tauber et al., 1986), and thus ALAN may have serious consequences for 51 juvenile development and reproductive maturation (McLay et al., 2017; Shah et al., 2011; van 52 Geffen et al., 2014). For species that exhibit seasonal diapause or overwintering (Schaefer, 1987; 53 Shah et al., 2011; van Geffen et...

Guiding lights: Foraging responses of juvenile nocturnal orb‐web spiders to the presence of artificial light at night

“…Urban insect communities appear to be declining around the globe (Eisenbeis, Hänel, McDonnell, Hahs, & Breuste, ; Fox, ; Longcore & Rich, ), and the compounding costs of ALAN may accelerate these declines. Similarly, the physiological costs experienced by insects appear to be experienced by spiders: E. biapicata reared under ALAN mature earlier and at a smaller size (Willmott et al, ). These developmental shifts are likely to affect the ability of predators to capture prey and the predation pressure they consequently place on declining insect communities.…”

“…There was no difference in body size between light treatment groups for juveniles, although spiders exposed to ALAN mature at a smaller body size (Willmott et al, ), suggesting that consequences for foraging dynamics will depend on the age of the spiders. Given the strong physiological impact of the presence of ALAN on growth and reproduction in this species (Willmott et al, ), increased prey capture rates are likely to translate to increased growth and reproductive output (Higgins & Goodnight, ), potentially explaining field observations of larger spiders in illuminated areas (Heiling & Herberstein, ). However, long‐term declines in insect populations have been attributed to night lighting (Longcore & Rich, ).…”

“…Prey composition may also change, due to the effects of artificial light on web detection by prey depending on the variable visual systems of different prey types. Exposure to ALAN stimulates faster maturation but a smaller adult size in E. biapicata when diet is controlled (Willmott, Henneken, Selleck, & Jones, ). Maturation rate and eventual body size both depend on juvenile foraging success (Moya‐Laraño et al, ; Neumann et al, ), so a more complete understanding of the impacts of ALAN on these spiders requires a comparison of the prey capture rates of juvenile spiders in illuminated and naturally dark sites.…”