Canadian Journal of Zoology
Worms Make Risky Choices Too: The effect of starvation on foraging in the common earthworm, Lumbricus terrestris
Journal: Canadian Journal of Zoology
Manuscript ID cjz-2018-0006.R1
Manuscript Type: Note
Date Submitted by the 10-Apr-2018 Author:
Complete List of Authors: Sandhu, Pawandeep; University of Toronto - Mississauga, Biology Shura, Oskar; University of Toronto - Mississauga, Biology Murray, Rosalind; University of Toronto - Mississauga, Biology; University of Toronto, Ecology and Evolutionary Biology Guy, Cylita; University of Toronto, Ecology and Evolutionary Biology; University of Toronto - Mississauga, Biology
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common earthworm, Lumbricus terrestris, risk-taking, Keyword: FORAGINGDraft< Discipline, life-history trade-offs, starvation
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1 Worms Make Risky Choices Too: The effect of starvation on foraging in the common
2 earthworm, Lumbricus terrestris
3 P. Sandhu1§, O. Shura1§, R.L. Murray1,2, and C. Guy1,2 *
4 § Authors contributed equally
5
6 1Biology Dept., University of Toronto at Mississauga, 3359 Mississauga Road
7 Mississauga, ON L5L 1C6, Canada
8 2Dept. of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks Street,
9 Toronto, ON, M5S 3B2, Canada
10
11 Pawandeep Sandhu1: [email protected]
12 Oskar Shura1: [email protected]
13 Rosalind L. Murray1,2: [email protected]
14
15 *Corresponding author:
16 Cylita Guy
17 Dept. of Ecology and Evolutionary Biology, University of Toronto, 25 Wilcocks Street, Toronto,
18 ON, M5S 3B2, Canada
19 Tel: 647 886 9524
20 Fax: 416 978 5878
21 Email: [email protected]
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22 Worms Make Risky Choices Too: The effect of starvation on foraging in the common
23 earthworm, Lumbricus terrestris
24 Pawandeep Sandhu, Oskar Shura, Rosalind L. Murray, and Cylita Guy
25 ABSTRACT
26 Species should avoid risks to protect accumulated fitness. However, when faced with
27 starvation, organisms may accept risks to enhance future reproductive opportunities. We
28 investigated the effect of starvation on risk taking behaviour in the common earthworm,
29 Lumbricus terrestris (Linnaeus, 1758). L. terrestris are negatively phototactic annelids that feed
30 on decaying plant matter at the soil surface. Feeding in high light conditions is a potentially
31 riskier choice, given the threats of visual predators and desiccation. We predicted that starvation
32 in earthworms would increase risk takingDraft behaviour and decrease time taken (latency) to make
33 choices. We manipulated the starvation level of L. terrestris individuals (non starved, half
34 starved, and full starved) and presented them with a binary foraging choice. Earthworms could
35 choose either a low food/dark condition (low risk) or a high food/light condition (high risk). We
36 found that starved individuals selected the high risk condition more often than non starved
37 individuals. Starved individuals also had a decreased latency to first choice. Risk taking did not
38 scale with level of starvation; there was no difference in foraging choice and latency between the
39 half and full starved individuals. Our results indicate that L. terrestris makes state dependent
40 foraging choices, providing insight into the importance of fundamental life history trade offs in
41 this understudied species.
42 KEYWORDS
43 earthworm, Lumbricus terrestris, risk taking, foraging, life history trade offs, starvation
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44
45 INTRODUCTION
46 Foraging presents a cost benefit trade off between growth and survival (Puvanendran and
47 Brown 2002). Although necessary for energy acquisition, foraging can put organisms at a greater
48 risk of predation (e.g. Kie 1999). Willingness of prey to take risks while foraging can be
49 influenced by a variety of factors including age (Macrı̀ et al. 2002), reproductive status
50 (Bunnefeld et al. 2006), food availability (Godin and Sproul 1988) and refuge location (van Oers
51 et al. 2005). In particular, changes in risk taking can be strongly influenced by hunger level;
52 when faced with starvation, a variety of taxa have been observed to take greater risks to obtain
53 food (e.g.Lima 1998; Lima and Bednekoff 1999). For example, green sea turtles (Chelonia
54 mydas Linnaeus, 1758) in poor body conditionDraft select higher risk, but more profitable,
55 microhabitats more frequently than turtles in good body condition (Heithaus et al. 2007). Piglets
56 (Sus domesticus Erxleben, 1777), who are subject to accidental crushing by their mothers while
57 feeding, also make risky choices to feed more often and for longer if in poorer body condition
58 (Weary et al. 1996). Several theoretical foraging models (e.g. McNamara and Houston 1986;
59 Brown 1988; Clark 1994) characterize the tradeoff between body condition and risk taking in the
60 context of protecting accumulated reproductive assets (i.e., ‘asset protection principal’ Clark
61 1994). While exposure to predators puts the entire reproductive asset at risk, starvation reduces
62 the value of this asset, compromising future opportunities for fitness increases (Clark 1994).
63 Animals in better body condition have accumulated fitness to protect. However, hungry
64 individuals can be expected to accept predation risks to increase their reproductive value through
65 increased body condition and, ultimately, enhance future fitness (Clark 1994). Risk driven
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66 flexibility while foraging, especially in relation to body condition, has been demonstrated in a
67 variety of vertebrate taxa including: mammals (e.g. Hughes and Ward 1993; Berger Tal et al.
68 2010), fish (e.g. Biro et al. 2005; Thomson et al. 2012), amphibians (e.g. Whitham and Mathis
69 2000), and birds (e.g. Macleod et al. 2005).
70 Numerous invertebrate species exhibit predator avoidance strategies that involve a trade
71 off between foraging and protection ( e.g. Hernandez and Peckarsky 2014; Szokoli et al. 2015;
72 Blubaugh et al. 2017; also reviewed in Scharf 2016), however, there are relatively few examples
73 documenting state dependent changes in foraging behaviour. Behaviours in response to predator
74 stimuli, such as tube retreat in the polychaete worm Serpula vermicularis Linnaeus,1767 (Dill et
75 al. 1997) and increased dispersal in the backswimmer Notonecta undulata Say, 1832 (McCauley
76 and Rowe 2010), have been shown to limitDraft foraging opportunities. Predator avoidance
77 behaviours, and the potential food stress that may result as a consequence, creates a scenario in
78 which these organisms may also be willing to make risky choices to increase foraging success.
79 Schadegg and Herberholz (2017) demonstrated that in response to a visual danger cue, starved
80 juvenile crayfish (Procmbarus clarkii Girad, 1852) make the risky decision to freeze and remain
81 near a food source, rather than fleeing. Additionally, in response to starvation, negatively
82 phototactic arthropods (i.e., those that move away from light stimuli) display a decreased
83 sensitivity to light (e.g. Shields and Wyman 1984; Dromph 2003), while some beetles spend less
84 time engaging in anti predator death feigning behaviour (Acheampong and Mitchell 1997;
85 Miyatake 2001; Hozumi and Miyatake 2005). However, as indicated in a recent review
86 examining the effects of starvation on arthropods (Scharf 2016), there is room to expand on these
87 studies given the rarity of experiments combining hunger level and predation threat. This is
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88 likely true for other invertebrate taxa, considering the existing taxonomic bias towards
89 vertebrates and model organisms in animal behaviour research (Rosenthal et al. 2017).
90 We explore hunger dependent risk taking behaviour in the common earthworm,
91 Lumbricus terrestris (Linnaeus, 1758). Earthworms are negatively phototactic (Parker and Arkin
92 1901), a behaviour known to be a predator avoidance strategy in other species such as the
93 polyclad flatworm Maritigrella crozieri Hyman, 1939 (Johnson and Forward 2003) and the
94 nematode Caenorhabditis elegans Maupas 1900 (Ward et al. 2008). Earthworms are also a
95 primary food source for a diversity of predators including the red fox (Vulpes vulpes Linnaeus,
96 1758 MacDonald 1980), the New Zealand flatworm (Arthurdendyus triangulates Dendy, 1895
97 Boag and Yeates 2001), the European badger (Meles meles Linnaeus, 1758 Roper 1994), and
98 the carnivorous land snail (PowelliphantaDraft augusta Walker, Trewick & Barker, 2008 Boyer et
99 al. 2011). Although many of these predators use a combination of vision and olfaction to locate
100 or dig for L. terrestris at night (Macdonald 1983), when earthworms are most active (Michiels
101 2001), other predators such as birds may forage for earthworms at dawn (Macdonald 1983) or
102 during the day (Macdonald 1983; Onrust et al. 2017). Thus, negative phototaxis may decrease L.
103 terrestris’ risk of predation, especially from diurnal, opportunistic predators. Additionally, L.
104 terrestris belong to a group of earthworms known as the anecic earthworms, which feed on
105 decaying plant material at the soil’s surface, rather than in underground burrows (Scheu 2003).
106 This soil surface foraging behaviour may be risky for earthworms because it exposes them to
107 potential predators. Although we speculate that the negative phototactic behaviour of L. terrestris
108 relates to predator avoidance, it could also be adaptive for avoiding areas where high light causes
109 arid soil conditions, putting individuals at a greater risk of desiccation. Regardless, the trade off
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110 that may exist between predator avoidance and soil surface foraging in L. terrestris makes them
111 an ideal species to examine how starvation can influence risk taking behaviour.
112 In addition to assessing starvation driven risk taking behaviour in L. terrestris, we also
113 characterize the time to first choice, or latency. Predation risk may be expected to impact not
114 only the decision to forage, but other aspects of feeding behaviour as well, including food
115 handling time, acceptable size of prey items, and latency to foraging decisions (Cooper 2000). A
116 negative relationship between latency to attack prey and hunger has been observed in bluntnose
117 minnows (Morgan and Colgan 1987). Changes in latency to risk taking behaviours have also
118 been associated with changes in body condition (Martins et al. 2007) and stress hormones
119 (Mathot and Dingemanse 2015). For example, in salmon (Reinhardt and Healey 1999) food
120 stressed individuals are faster (decreasedDraft latency) to engage in risk taking foraging relative to
121 individuals that are not food stressed.
122 Beyond being a good system to examine hunger dependent risk taking behaviour, L.
123 terrestris, like many earthworms found in northern North American forests, are an invasive
124 species (Bohlen et al. 2004; Addison 2009; Craven et al. 2017). Considering that L. terrestris is
125 one of the most prominent earthworm invaders in North America (Addison 2009), studying their
126 behavioural ecology has implications for understanding their spread within ecosystems. Non
127 native earthworm species are ecologically destructive, driving changes in plant diversity and
128 community composition, which may have lasting effects on proper ecosystem functioning
129 (Bohlen et al. 2004; Craven et al. 2017). This highlights the need to manage the spread of these
130 invasive species. Future management efforts would benefit from a greater knowledge of basic
131 earthworm behavioural ecology, as understanding behavioural mechanisms can provide insight
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132 into ecological invasions (Holway and Suarez 1999; Sih et al. 2012) as well as potentially
133 enhance models predicting invader spread (McTavish et al. 2013).
134 Considering the apparent ubiquity of state dependent risk taking in the animal kingdom,
135 it is important to examine whether this behaviour applies broadly by testing it in non traditional
136 taxa. To our knowledge, no study has yet characterized starvation induced risk taking behaviour
137 in earthworms. Here, we performed a binary choice experiment to assess the effect of starvation
138 on risk taking behaviour in L. terrestris. We hypothesized that, as seen in a variety of other
139 organisms and in line with theoretical expectations of fitness asset protection models (e.g., Clark
140 1994), an increased level of starvation would increase the willingness of L. terrestris to take risks
141 to increase foraging success. Further, we predicted that latency to making risky foraging
142 decisions would decrease as starvation levelDraft increased.
143
144 MATERIALS AND METHODS
145 We obtained L. terrestris individuals from a local bait shop; 15 were used in initial pilot
146 studies and 54 were used in experimental trials (totaling 69 individuals). Worms were housed in
147 groups of no more than 20 in plastic cylindrical containers filled with compost and covered with
148 an opaque black cloth to prevent disturbance by external light. We created three experimental
149 food treatments: non starved, half starved, and full starved individuals. Non starved worms were
150 kept in high nutrient compost for seven days prior to the experiment. Full starved worms were
151 kept in containers filled with low nutrient potting soil for 7 days prior to the experimental trials.
152 The starvation period was chosen based on the methods of Warne et al. (2001). Half starved
153 worms were kept in high nutrient compost for four days and then transferred to low nutrient
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154 potting soil for three days prior to experimental trials (roughly half of the time specified by
155 Warne et al. (2001)). The half starved treatment was implemented to test for a threshold in the
156 level of food stress necessary to cause a state dependent reaction in L. terrestris individuals
157 (similar to Morgan and Colgan 1987 and Dromph 2003).
158 Trials were conducted in a 25.4cm x 25.4cm x 5.08cm experimental arena divided into
159 two 12.7cm x 25.4cm x 5.08cm sections. One section (half the arena) was layered with 1.9cm of
160 low nutrient potting soil, while the other half was layered with 1.9cm of high nutrient compost
161 (see supplementary material Figure S1). The low nutrient section of the container was covered
162 with a black opaque cloth to decrease external light, at a height of 2.54cm above the soil. A
163 cardboard bridge, spanning the length of the container and covered with a layer of clear tape (3M
164 Scotch Magic Transparent Tape; to preventDraft the worms from consuming the cardboard), was
165 placed in the middle of the container to separate the low and high nutrient sections. A LED lamp
166 was set up 50.8cm above the container, shining directly on the high nutrient side. Light from
167 LED bulbs can be detected by L. terrestris (Ratner and Gardner 1968)), however LED lamps
168 give off less heat relative to incandescent bulbs (Petroski 2002). As such, we used an LED lamp
169 to decrease the potential effects of heat and soil moisture loss, and increase the likelihood that
170 earthworms were responding to the light cue, rather than a combination of light and heat. The
171 low food (potting soil), dark side of the container was considered the low risk choice, while the
172 high food (compost), light side was considered the high risk choice.
173 We performed a pilot trial to test for an effect of mass on risk taking behaviour in L.
174 terrestris. We also used the pilot trials to assess the time necessary for a worm to evaluate both
175 substrates and make a final choice (see supplementary material Table S2). Finally, we examined
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176 if worms had a preference for the high nutrient compost used here as the high food condition
177 (see supplementary material Table S3). Our pilot data showed that mass did not affect an
178 individual’s choice (see supplementary material Table S1) and was therefore not included in our
179 future trials. We also found that 12 minute trials allowed for ample time to sample and choose
180 one side/substrate (see supplementary material Table S2). Lastly, we confirmed that earthworm’s
181 had a preference for the high nutrient compost (see supplementary material Table S3).
182 We conducted 18 trials in each of our three starvation conditions (non starved, half
183 starved, and full starved), with each worm being used only once. For each trial, individuals were
184 placed in the center of the bridge and observed for a maximum of 12 minutes.. During the
185 observation period, we observed all animals sampling both substrates (high and low risk),
186 possibly assessing soil quality through useDraft of chemosensory organs. Earthworms are known to
187 have a variety of sensory cells in the integument (Knapp and Mill 1971), some of which are
188 involved in chemoreception (Syed et al. 2017). For each individual, we recorded final risk choice
189 (high or low) and time to make a final choice (latency). Worms were considered to have made a
190 final choice when their entire body was on one side of the experimental arena. We also recorded
191 the location of the worm (low or high risk section of arena) after the allotted 12 min trial length.
192 Between trials, potting soil and compost were replaced and the taped cardboard bridge was
193 wiped down with a wet towel.
194
195 Statistical Analyses
196 All statistical analyses were conducted in R (R Core Team 2014). We used the ‘car’ (Fox
197 and Weisberg 2011) and ‘lme4’ (Bates et al. 2014) packages to fit statistical models. To test for
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198 an effect of starvation treatment on an individual’s risk choice (high risk = high food and bright,
199 low risk = low food and dark), we fit a binomial generalized linear mixed model with risk choice
200 (high or low) as the response, starvation treatment (non starved, half starved, or full starved) as
201 the fixed effect and ‘day’ as a random effect. We also tested for an effect of starvation treatment
202 on an individual’s latency to make a choice regardless of the level of risk. We log transformed
203 the measure of latency (in seconds) to normalize the data and fit a linear model with latency as
204 the response variable, starvation treatment (non starved, half starved, or full starved) as the fixed
205 effect, and ‘day’ as a random effect.
206
207 RESULTS
208 We found that half and full starvedDraft individuals were more likely to choose the high risk
209 environment compared to non starved individuals (Figure 1, Table 1). When we tested for an
210 effect of starvation on latency to make a choice (either high risk or low risk) we found that non
211 starved individuals took longer to make a choice compared to the starved individuals (Figure 2,
212 Table 2). There was no difference between the starvation treatments (half vs. full) in their
213 latency to make a choice, but both starvation treatments were faster to choose than the non
214 starved individuals (Figure 2, Table 2).
215
216 DISCUSSION
217 State dependent changes in risk taking behvaiour have been documented in a number of
218 species. Here, we demonstrate that starvation alters risk taking behaviour in the common
219 earthworm L. terrestris. In line with our predictions, and the expectations of theoretical fitness
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220 models of foraging (e.g. McNamara and Houston 1986; Brown 1988; Clark 1994), starvation
221 resulted in L. terrestris individuals making riskier choices (Figure 1); starved earthworms were
222 more likely to select the high nutrient, bright light condition than non starved individuals (Figure
223 2). We also found that starved individuals, as predicted, had a decreased latency to their choice.
224 Interestingly, although starved individuals made risker and faster choices than non starved
225 individuals, we find no evidence for a difference in risk taking or latency between our two
226 starvation conditions (half and full starved). Our results provide strong support for the notion that
227 starvation can mediate life history trade offs, leading to increased risk taking behaviour in the
228 common earthworm L. terrestris.
229 There has been a vast amount of literature concerning risk taking behaviour in animals,
230 with numerous studies looking at the trade offDraft between feeding and predation risk (Lima and Dill
231 1990). The dependence of this trade off on body condition has been demonstrated in a variety of
232 vertebrate taxa (e.g. Hughes and Ward 1993; Biro et al. 2005; Mathot et al. 2015) and is in line
233 with theoretical fitness models of foraging and asset protection (e.g. Clark 1994). Studies
234 examining risk driven flexibility in foraging of invertebrates, although less common, also exist.
235 For example, scorpions in poor body condition, despite the higher predation risk from nocturnal
236 predatory birds, are more likely to forage on full moon nights compared to high body condition
237 scorpions (Skutelsky 1996). This trade off has also been demonstrated in a variety of other
238 invertebrate species including crayfish (Schadegg and Herberholz 2017), spiders (Walker and
239 Rypstra 2003), mollusks (Zhao et al. 2011), and mayfly larvae (Kohler and McPeek 1989). The
240 results of our study are consistent with the larger field: when challenged with starvation, L.
241 terrestris are more likely to take risks to acquire necessary resources.
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242 Here, we assume that the choice to feed in a high light environment is riskier for L.
243 terrestris as it may increase detection by potential predators. We felt that this was a reasonable
244 assumption given that L. terrestris is a negatively phototactic species and that negative
245 phototaxis is a known anti predator strategy in other groups (e.g. Johnson and Forward 2003;
246 Ward et al. 2008). Further, in pilot studies for this experiment we found that well fed earthworms
247 have a preference for dark conditions when soil quality is the same (see supplementary material
248 Table S4). Our results indicate that, as seen in other photophobic species (e.g. Shields and
249 Wyman 1984; Dromph 2003), earthworms will tolerate light conditions when under food stress.
250 Although we assumed that foraging in the light represented an increased risk of predation, it
251 could also represent an increased risk of desiccation (we do though control for and minimize heat
252 effects through use of an LED lamp). FutureDraft work should look to characterize risk taking in
253 earthworms in response to a direct predatory cue (e.g. bird calls or feces of a known predator, see
254 Walker and Rypstra 2003), and further examine the ecological conditions under which negative
255 phototaxis may provide an adaptive benefit to L. terrestris.
256 Other factors associated with life history trade offs could also be important for mediating
257 risk taking behaviour and resource acquisition in L. terrestris. For example, temperature is
258 associated with increased food intake in juvenile earthworms (Otto 1990), while litter type and
259 conspecific population density have been shown to modify habitat selection in L. terrestris
260 (McTavish et al. 2013). Although we tested for an effect of mass on risk taking in our pilot data,
261 it is also possible that size (assessed with a metric other than mass, such as body length) and age
262 may influence earthworm risk taking behaviour. Previous work in fish suggests that smaller
263 individuals are more willing to take risks than their larger counterparts (Reinhardt and Healey
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264 1999; Dowling and Godin 2002). This size mediated risk taking behaviour has implications for
265 both individual fitness and population composition (Pettersson and Bronmark 1993; Lima 1998),
266 and could be important for understanding L. terrestris ecology. In addition to considering how
267 size influences risk taking, future work could also examine individual variation in behaviour (i.e.
268 personality) in response to stress (e.g. as in Drent et al. 2003; Houslay et al. 2017). Interspecific
269 variation in behavioural responses to stressors, such as food stress, can impact an individual’s
270 fitness and by extension their success in a given environment (Sih et al. 2012). Considering that
271 L. terrestris is a hugely successful invasive species (Addison 2009), studies such as these would
272 expand on what little we know of the behavioural ecology of this species and could contribute to
273 future management.
274 Our study demonstrates that starvationDraft alters risk taking behaviour in the common
275 earthworm L. terrestris. Relative to non starved individuals, starved earthworms select risker
276 environments for foraging and have a decreased latency to their foraging decisions. State
277 dependent trade offs, made to maximize long term fitness, have been observed in a variety of
278 organisms (e.g. Hughes and Ward 1993; Berger Tal et al. 2010; Thomson et al. 2012; Schadegg
279 and Herberholz 2017). However, to the best of our knowledge we present the first evidence of
280 state dependent trade offs in earthworms and one of the few examples in Annelida. The lack of
281 studies concerning the effects of starvation on annelid foraging speaks to the taxonomic bias in
282 animal behaviour research. A recent study by Rosenthall et al. (2017) quantifies the skew of this
283 bias, indicating that the field has largely focused on higher order taxa leaving other groups,
284 which account for proportionally more of the earth’s biodiversity, relatively understudied. While
285 it remains unclear why such a strong bias exists (e.g. tractability of study systems, innate human
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286 bias, easy study/capture), the authors call for a greater consideration of neglected taxa to help
287 understand the scope and pervasiveness of commonly studied behaviours such as mate selection,
288 predator avoidance, and foraging (Rosenthal et al. 2017). By characterizing an often assumed
289 common trade off in an understudied species, our study helps to fill this gap by expanding our
290 knowledge about the situations in which state mediated trade offs between foraging and
291 predation may exist. As outlined above though, there are a variety of ways in which future work
292 extending this study could enhance our understanding of earthworm behavioural ecology. Given
293 the invasive nature of L. terrestris in North America, this could greatly contribute to their future
294 management.
295
296 ACKNOWLEDGEMENTS Draft
297 We would like to thank D. T. Gwynne and K. Williams for advice and mentorship during
298 the development of this study and the University of Toronto Mississauga’s BIO318 class of 2017
299 for helpful feedback. We would also like to thank Susan Dixon for assistance managing lab
300 space and resources.
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504 TABLES
505
506 Table 1. Results from a binomial generalized linear model investigating the effect of starvation
507 treatment on risk taking behaviour in L. terrestris. Half and full starved individuals were more
508 likely to choose the high risk, high food environment compared to fed individuals. p <0.05 was
509 considered significant.
510
Starvation Estimate z p Treatment ± std error Intercept(Full 0.45±0.48 0.94 0.35 Starved) Half Starved 0.50±0.71 0.71 0.48
1.41±0.71 1.97 0.04 Non Starved Draft 511
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523
524 Table 2. Results from a linear model investigating the effect of starvation on latency to make a
525 decision (either high risk, high food or low risk, low food) in L. terrestris. Full and half starved
526 individuals were faster to make a choice (low latency measure) compared to non starved
527 individuals. Latency (in seconds) was log transformed prior to inclusion in the model. p <0.05
528 was considered significant.
529
Food stress Estimate t p treatment ± std error Intercept (Full Starved) 5.04±0.21 23.85 <0.001
Half Starved 0.37±0.29 1.25 0.22 Draft 0.83±0.35 2.43 0.02 Non Starved 530
531
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532 FIGURE CAPTIONS
533
534
535 Figure 1. The proportion of Lumbricus terrestris individuals that chose the high risk, high food
536 environment (rather than the low risk, low food environment) across three starvation treatments.
537 Non starved individuals were significantly less likely than half and full starved individuals to
538 choose the high risk environment (p=0.04). n=18 for each treatment group. Error bars represent
539 0.95 binomial confidence intervals.
540
541 Figure 2. Mean latency for Lumbricus terrestris to make a choice between a high risk, high food
542 or low risk, low food environment acrossDraft three starvation treatments: non starved, half starved
543 and full starved. Fed individuals took significantly longer than half and full starved individuals to
544 make a choice (p=0.02). n=18 for each treatment group. Error bars represent standard error.
545
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Draft
Figure 1. The proportion of Lumbricus terrestris individuals that chose the high risk, high food environment (rather than the low risk, low food environment) across three starvation treatments. Non-starved individuals were significantly less likely than half and full starved individuals to choose the high risk environment (p=0.04). n=18 for each treatment group. Error bars represent 0.95 binomial confidence intervals.
215x166mm (300 x 300 DPI)
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Draft
Figure 2. Mean latency for Lumbricus terrestris to make a choice between a high risk, high food or low risk, low food environment across three starvation treatments: non-starved, half starved and full starved. Fed individuals took significantly longer than half and full starved individuals to make a choice (p=0.02). n=18 for each treatment group. Error bars represent standard error.
215x166mm (300 x 300 DPI)
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