Female preference for males with lower pattern contrast follows Weber's law of proportional processing in jumping spiders

Read the free Plain Language Summary for this article on Journal blog. Animals make decisions based recognition, discrimination and assessment of stimuli in various behavioural contexts, such as foraging (Farhadinia et al., 2020; Frank & Linsenmair, 2017; Ishii 2019; Kaczorowski 2012; Prat Yovel, Ravi 2016), female mate-choice (Bo-jian 2018; Kubec Stoffer Walker, 2012) parasitism (Roncalli Thiel, 2011). Optimal made by animals can be influenced how well their sensory systems perceive trait differences between alternative choices, which may limited perceptual processes. Among these processes is proportional processing, stimulus values (not absolute) difference magnitudes, following Weber's law (Akre Johnsen, 2014; Bateson Healy, 2005; LaBarbera 2020). According to law, two (I1 I2, where I2 > I1) depends magnitude (i.e. [I2 − I1]/I1 or ΔI/I) instead absolute – I1 ΔI; Akre Fechner, 1966; Weber, 1978). The smallest change detectable constant proportion stimulus, described fraction equation ΔIJND = k*I, just-noticeable [JND], increase that perceived receiver 2014)). response should therefore remain if (ΔI/I) remains fixed, independent (ΔI) (LaBarbera In other words, whether processing comes into play when we are able detect a differentiate original stimulus. For instance, it would easier notice one ball taken away from 10 balls. However, harder 100 balls, even though number balls same. This means our perception greater will needed noticeable higher magnitude. A wide variety taxa have been observed follow ecological contexts. Examples include pheromone concentrations Argentine ant Linepithema humile (Perna 2012), among food quantities coyote Canis latrans (Baker 2011), preference group sizes angelfish Pterophyllum scalare (Gómez-Laplaza Gerlai, 2011) mate calls túngara frog Physalaemus pustulosus has common deviations: near miss opposite (Dixit 2021; improves increases. true sound amplitude frequency humans birds mammals (Fay Wilber, 1989; Lauer 2007). humans, discriminating sounds follows pattern, performance with amplitudes (Buus Florentine, 1991; Carlyon Moore, 1984; Doble 2006; Florentine 1993; Mallery 2010; Yost, 1994). Cases pattern explained chase-away selection, evolution male exaggerated traits males favoured (Cohen, 1984). As females select evolve certain enhance attractiveness females, also develop form resistance decreased attraction) overly attractive hence developing mating-response threshold (Holland Rice, 1998; Ryan Cummings, 2013). result, more extreme sexual signalling overcome courtship (Ryan Therefore, become increasingly using value increases provide mechanism contributing traits. Hence, favouring via selection influence an miss, ability same slightly worsens increasing individual difficulty distinguishing at larger than under mate-choice, example, eventually tough discriminate (Bateson Cohen, Jennions Petrie, 1997; Sound level insects frogs known (Bee Wyttenbach Farris, 2004). longer decreases average pulses grey treefrogs (Hyla versicolor; Bee, 2008; Ward Eventually, unfavourable cost becomes benefit brings. then new 2011; Endler 2005). evolutionary consequences animal behaviour acting brake signal/trait elaboration through drive novel signals 2014). Proportional often used making decisions. previous theoretical models, assumed absolute, assesses independently assigns fixed encounter according trait(s) (Jennions Real, 1990). many animals, tend several potential mates simultaneously sequentially, allowing them assess comparatively (DuVal Kempenaers, Reaney, 2009; Zandberg cases, available informational cues obtained male's Previous studies primarily focused vertebrate auditory (Hemingway Nieder, frog-eating bats, Trachops cirrhosus, prefer chorus sizes, they varying choruses relative size but not Additionally, recent study showed green swordtail fish, Xiphophorus helleri, better predicted body (Caves Kelley, 2023). focuses visual signal preferences. Although colour patterns including invertebrates, decisions, (Cuthill 2017), there no empirical evidence use patterns. study, investigated explains jumping spider, Siler semiglaucus (Araneae: Salticidae). Salticid spiders ideal case investigating signals. Salticids most diverse spider family containing approximately 6500 species worldwide (World Spider Catalog, They unique repertoires highly complex systems, support spatial acuity vision (Harland Land Nilsson, Morehouse, Zurek 2015), permit different colours, both (Lim Li, Nakamura Yamashita, 2000; Taylor Many salticids bear remarkable, sexually dimorphic colours and/or Otto Hill, Zhou 2021). Some shown selected (Li Lim Tedore untested. commonly distributed across tropical Asia (Jackson World 2023), exhibit colourations conspicuous humans. Males abdominal patches gross (defined combination patches; possess areas red smaller blue abdomen (Zhou Sexual dimorphism contrast mate-choice: S. lower (referred feature abundance adjacent Rojas Endler, 2013) dorsal done al. (2021) (1) quantification (2) contests) contrast. present mechanisms males. More specifically, here focus law. We hypothesised rather difference. Juvenile subadult were collected field site Kranji MRT station Singapore (1°25′37.93″N 103°45′43.95″E) October 2019 May 2022. All housed laboratory (relative humidity: 80 ± 5%; temperature: 25 1°C; light regime: 12:12 h; lights 08:00 h) standard protocols 2007; Zeng 2019). Each was kept container (diameter: 6.5 cm, height: 8 cm) separated opaque cardboard minimise communication (Zeng fed each five eight fruit flies (Drosophila melanogaster) times per week. reared until adulthood so mating status post-maturation age known. total, 120 virgin 90 27 46, respectively, had 2016 2017 earlier 2021), (for details definitions calculations, see 2.3 below). To determine contrasts created types manipulation coverage (%), (%) (Figure 1). prepare manipulation, applied acrylic paint alter patterns, procedures 2021); thus, only essential study. altered produce manipulated extents prepared paints (Deep Tomato Red, Folkart, Plaid, USA) (a mixture Pond, Martha Steward Crafts, USA, Aqua, USA Brown, Simply Acrylic, UK, ratio 10:10:1) paints. hue brightness measured UV–VIS spectrometer ensure closely similar spiders' 2021) unable distinguish painted unmanipulated visually behaviourally. anaesthetised carbon dioxide gas 2 min easy applied. Once mature painted, carapace widths. Using camera (Nikon D800), photographed surfaces conditions white paper background, ruler scale. analysed photographs ImageJ (v1.53t) total area, red-coloured (3) blue-coloured (nearest 0.001 mm2). calculated chromatic area (red + area), area/total area; %) %). part as: area) × (blue (2013). describe blue. Specifically, blues equally frequent, either rarer. way, calculations hue, chroma patch. Moreover, manipulations keep chroma) all consistent. width) participating trials nearest 0.01 mm. conducted January 2021 2022 11:00 h 16:00 h, highest activity during period. full spectral light, provided six tubes (Hitachi BL/B, 20W) dark room. least 1 day days after feeding control hunger levels. recorded Samsung Galaxy A7 phone setting 5.0 MP, 1080p @ 30 fps. investigate carried out series dichotomous pairing 1; Table S1). pair trial matched width post maturation reduce effects confounding factors. arena consisting chambers shape equilateral triangle (side length 5 chamber trapezium (length side short base: long base length: cm; details, figure S2 Two wall effect male–male competition mate-choice. spectrum glass, other's (Kwek Prior trial, introduced barrier prevent any contact acclimatisation min. began immediately upon removal positioned equidistant lasted (5.0 MP; fps). videos reviewed attention time seconds spent gaze her anterior median eyes direction particular displaying male, regardless female's position distance [Lim 2008]), considered proxy (Elias Hebets Maddison, trials, 52 performed vs. 3: n 10; 4: 5: 6; 13; 5; 3 8; [Zhou 2021]). Nine pairs reused, faced once reused female). allowed rest experience. exact binomial test evaluate choosing probability randomly 0.5:0.5). repeated (Table combination, ratio, red/blue (calculated divided male) data, ones R version 4.2.2 (R Core Team, 2022). Generalised linear mixed models error structure could binary paired (preference 0) variable. variable ultimately included identity (ID) random effect, logged continuous predictors. Pattern contrast, alone, consideration estimation generated four 1) lowest Akaike's information criterion (AIC) best-fitting model (Burnham Anderson, alone compared three ∆AIC. AIC comparison small sample (AICc) values, parameters (K) (n), exceeding n/K 40 Nakagawa's R2 package calculate variation (Lüdecke hierarchical partitioning hier.part (Nally Walsh, 2004) estimate predictor contained either, maximum likelihood chi-square tests forward stepwise process compare nested contains subset variables another model). (model.sel MuMIn) model. data deviated generalised structure, contrast), predictors, effect. proposed S2) tests. interaction term retained significantly different. maximise statistical power, excluded final without (χ2 0.503, df 1, p 0.478; S2). reduced low deviates If expect positive relationship By negative Otherwise, simply significant Overall, preferred (82 trials; test: < 0.001). Within seven combinations 2). ∆AIC value, (AIC 150.3, Z 2.21, 0.027, 0.061; Figure 3a) superior, 155.5, 0.32, 0.747, 0.001; 3b) null 153.6, 3.45, 0.001, 0). best model, 147.9, 0.109) alone. While 77% 23% indicates Furthermore, lack suggests distinctive preference. addition process. Including improved fit (deviance 144.3; χ2 5.29, 0.021; S3). produced 147.9; 4.396, 0.036; 3c; improve difference, coupled Model comparisons MuMIn yielded results: fit, largest weight 0.723), followed S4). steep 55% seen increased 20% smaller, 3c). discriminated increased. Finally, assessed Female coefficient positive, zero S5; 4). appears consistent predictions deviation. Our results confirm finding show strong abdomens demonstrate smaller. together stronger males) thus processing. hypothesis perform decision-making corroborate findings reference magnitudes influences further validating strongly supporting implies rarer, fewer transitions patches. less frequent patches, implying complexity (Rojas 2013; van den Berg Counterintuitively, simpler pattern). It activate receiver's retina adaptation (Sibeaux Nevertheless, stimulating neurons differently especially although few dimensions colouration (Céchetto addition, depending guppies (Poecilia reticulata) patch boundary lengths patches) combinat