Diel variation in use of cover and feeding activity of a ...

Diel variation in use of cover and feeding activity of a benthic freshwater fish in response to olfactory cues of a diurnal predator Jeffrey P. Vanderpham, Shinichi Nakagawa & Gerard P. Closs

Environmental Biology of Fishes ISSN 0378-1909 Volume 93 Number 4 Environ Biol Fish (2012) 93:547-556 DOI 10.1007/s10641-011-9949-1

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Author's personal copy Environ Biol Fish (2012) 93:547–556 DOI 10.1007/s10641-011-9949-1

Diel variation in use of cover and feeding activity of a benthic freshwater fish in response to olfactory cues of a diurnal predator Jeffrey P. Vanderpham & Shinichi Nakagawa & Gerard P. Closs

Received: 1 November 2010 / Accepted: 24 October 2011 / Published online: 19 November 2011 # Springer Science+Business Media B.V. 2011

Abstract Some fish recognize the threat of predatory fish through chemical cues, which may result in variation in diel activity. However, there is little experimental evidence of diel shifts in activity of prey fish in response to the diel activity of a predator. We compared the total prey consumed and the use of cover by common bullies (Gobiomorphus cotidianus), a native benthic feeding eleotrid, when exposed to the odour of an exotic predator, European perch (Perca fluviatilis), over a 12-h period. Our results showed no significant effect of perch odour on feeding activity, but a significant increase in the use of cover at night and a decrease in the use of cover by day. While common bullies may recognize the presence of a predator through chemical cues, dark conditions may inhibit this and other sensory mechanisms, affecting their ability to recognize the proximity of a predator. For example, during the daytime they may rely on visual cues to initiate cover-seeking behavior, but in the dark, vision is impaired giving them less warning of predators, thus potentially making them more vulnerable.

Electronic supplementary material The online version of this article (doi:10.1007/s10641-011-9949-1) contains supplementary material, which is available to authorized users. J. P. Vanderpham (*) : S. Nakagawa : G. P. Closs Department of Zoology, University of Otago, PO Box 56, Dunedin, New Zealand e-mail: [email protected]

Keywords Chemical cues . Gobiomorphus cotidianus . Mysid . Perca fluviatilis . Predator cues . Sensory

Introduction The ability to avoid predators increases the survival and fitness of individuals (Mirza and Chivers 2000, 2001). In addition to visually detecting a predator, many organisms use olfactory cues to detect and avoid predators (e.g., Amo et al. 2008; Blumstein et al. 2008; Kullmann et al. 2008; Webb et al. 2010). In aquatic systems, prey fish can visually detect predators (e.g., Hartman and Abrahams 2000; Kelley and Magurran 2003), but the ability to use visual cues is limited under conditions of darkness, high turbidity or dense macrophytes (e.g., Abrahams and Kattenfeld 1997; Lehtiniemi et al. 2005). To supplement vision, fish may utilize olfactory cues for predator detection and avoidance (e.g., Brown et al. 2000; Hartman and Abrahams 2000). Recognition of predators through chemoreception and resulting behavioural responses are well documented (e.g., Kelley and Magurran 2003; Martin et al. 2010). Other cues used by fish include social, electrical and mechanosensory (Montgomery et al. 1995; Hanika and Kramer 2000; Brown and Laland 2003). Fish mechanosensory systems are a complex network of clustered receptor cells (i.e. neuromasts), connected by nerve tissue, which sense vibrations and movements in the surrounding

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environment, independent of vision (Coombs et al. 1988). The use of lateral-line systems in rheotaxis (i.e. orientation in flowing water), and predator and prey detection is widely known in many fish species (e.g., Montgomery et al. 1995; Janssen 2004). Species with well-developed mechanosensory systems are able to actively feed and avoid predators even in the absence of light. Nocturnal activity may also help fish avoid predators. The use of olfactory cues enables a fish to detect predators from a safe distance, triggering evasive behaviour to minimize the risk of a direct encounter including shifts in feeding habitat and prey selection (e.g., Werner et al. 1983; Katano et al. 2003), or reduced feeding activity (e.g., Milinski 1993; Paszkowski et al. 1996). Many species of fish exhibit plasticity in diel activity (Reebs 2002), and studies have related this variation in diel activity to predator avoidance (e.g., Fraser et al. 1993; Roussel and Bardonnet 1999), in some cases in response to chemical cues from a predator (Pettersson et al. 2001). However, there is little experimental evidence demonstrating a switch to nocturnal feeding in the presence of a diurnal predator. If prey fish can detect the diel patterns of activity of potential predators, then they may alter their patterns of feeding and habitat use. Many studies have suggested that patterns of diel habitat use are a means of predator avoidance (e.g., Anderson et al. 2007; Kattel and Closs 2007), and numerous studies have also documented an increased use of structure, or cover, by freshwater fish when exposed to the risk of predation (e.g., Eklov and Persson 1995; Stuart-Smith et al. 2008). Martin et al. (2010) demonstrated the increased use of cover by fish following the detection of predators by olfactory cues, but there is little experimental evidence for diel habitat use changes in response to olfactory cues alone. The primary aim of this study was to test whether a fish that is capable of chemical recognition of predators will alter its pattern of diel feeding activity and microhabitat use in response to olfactory cues from a diurnal predator. We hypothesized that a prey species capable of feeding in both light and dark conditions would feed predominantly at night and show increased use of cover in light conditions, when exposed to the odour of a diurnal predator. In this study, we examined the predator–prey interaction between common bully (Gobiomorphus

Environ Biol Fish (2012) 93:547–556

cotidianus) and European perch (Perca fluviatilis), hereafter perch. Common bully are small (adult length range 30 to 120 mm), benthic, freshwater eleotrid fish widely distributed throughout New Zealand lowland rivers and lakes (McDowall 2000). Perch were introduced to New Zealand in 1868 (Thompson 1922) and now frequently co-occur and prey on common bullies (Griffiths 1976). Common bullies can coexist with perch, albeit at significantly reduced densities (Ludgate and Closs 2003). The mechanisms by which these two species co-exist are not well understood, but Kristensen and Closs (2004) demonstrated that common bully use chemoreception to detect the presence of perch. Further, common bullies also have well developed mechanosensory systems (McDowall 1990; Bassett et al. 2007) that they use for nocturnal feeding (Rowe 1999; Rowe et al. 2001). In contrast, perch are highly successful visual predators (Bergman 1988) that are primarily diurnal (Craig 1977; Schleuter and Eckmann 2006). Therefore, a switch to nocturnal feeding and increased use of cover could reduce the vulnerability of common bully to predation by perch.

Methods Collection and maintenance of fish and prey All of the bullies used in this experiment were collected by seine netting along the shore of Lake Waihola, a shallow lowland lake in Otago, New Zealand during late spring and summer 2007. One hundred twenty bullies ranging in size from 30 to 61 mm total length were used in the experiments (average total length 42.13 mm, standard error 0.77). Breeding males, identified by their dark coloration, were avoided as their behaviour may differ from that of females and non-breeding males (Smith 1973). Bullies were placed in a large (300 L) rectangular glass holding tank. The holding tank was kept in a 15°C temperature-controlled room with a 12 h light: 12 h dark photoperiod. White PVC tubes of various diameters (30 mm to 90 mm) and lengths (100 mm to 200 mm) were randomly scattered on the bottom of the tank to provide areas of refuge and cover, with no other substrate. Four air-driven activated carbon and polyester batting filters were continually run in the holding tank, and approximately 30% of the water in

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the tank was replaced twice weekly. The water (13 ppt salt) used in all holding tanks and experimental tanks was a solution of ‘Speight’s’ spring water and filtered Otago Harbor saltwater (from the University of Otago Marine Science’s Portobello Marine Laboratory filtered saltwater tanks). Salt water was used to reduce infections and reflect the slightly brackish environment of Lake Waihola. All fish were maintained in this holding tank for a minimum of 1 week prior to the start of experimental trials to ensure acclimatization to tank and photoperiod conditions. During this time, they were fed a combination of live mysid shrimp (Tenagomysis spp.) from Kaikorai Estuary, Dunedin, New Zealand, and thawed bloodworms. They were fed twice daily sufficient to ensure satiation at 09:00 and 21:00, the start times of the light and dark periods, respectively. Live mysid shrimp were kept in a holding tank in the same room with 13 ppt saltwater and Speight’s spring water mix. Two perch, (total lengths 170 mm and 210 mm) were collected with a seine net during spring 2007 in the same shore area of Lake Waihola where the common bullies were collected. The perch were maintained in a large glass holding tank (300 L) with Speight’s spring water, natural light, gravel substrate, large PVC tubes as cover, and air-driven activated carbon and polyester batting filters. They were fed a combination of commercial dry pellet fish food (also used in Kristensen and Closs 2004) and thawed bloodworms. The perch holding tank was kept in a separate room from the bullies. Preparation of perch odour Preparation of perch odour followed the procedures of Kristensen and Closs (2004). After 1 week in the holding tank and 1 hour after feeding, the two perch were placed together in a 50 L plastic barrel containing 20 L of Speight’s spring water. After 24 h they were removed and returned to the holding tank. The water from the barrel was then measured out into 50 mL containers. All containers were then immediately frozen and stored in a −20°C freezer. Experimental design Experiments were conducted in eight 38 L aquaria (40 cm length×30 cm height×30 cm width) with 18 L of the 13 ppt saltwater and Speight’s spring water

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solution in each. Each tank contained one air-stone to provide aeration. White plastic dividers between each tank visually isolated the individual aquaria, preventing fish in adjacent aquaria affecting each other. Daytime conditions were produced by in-set ceiling lights producing 1,200 lux in the experimental room. Two desk lamps with a 60-watt red light bulbs in each were used for night observations. The red bulbs produced a low intensity light, and in many species red light wavelengths have been shown to be less disruptive to night vision capabilities and/or less visible to animals (e.g. Finley 1959; Jury et al. 2001) and therefore less disturbing. The lights were approximately 2 m from the aquaria and pointed upwards and away from the aquaria to reduce the intensity of the light experienced by the fish and minimize disturbance. Common bully did not exhibit any obvious response (e.g. sudden movements, darting for cover, etc.) when the red lights were switched on for assessment of nocturnal habitat use in either preliminary trials or the experiments, although we cannot rule out the possibility that more subtle movements may have occurred in some fish. For observations of cover use, three 30 mm diameter by 100 mm length pieces of white PVC tubes were connected side by side with a plastic zip-tie and placed in the center and base of each of the eight aquaria. The tubes were oriented with the openings towards the front of the aquaria to allow for unobstructed observation. Preliminary observations confirmed the use of the PVC tubes by fish as a source of cover when seeking refuge in response to disturbances such as tank cleaning and the presence of a small fish net moving within the tank. To ensure removal of any chemicals remaining from previous replicates, tanks, PVC tubes, air-stones and associated tubing were thoroughly flushed with tap water and then rinsed with spring water following each experimental trial. A total of 30 replicates under each light treatment (light control, light – odour) and 26 replicates for each dark treatment (dark - control, dark - odour) were completed. The odour treatment consisted of the addition of 100 mL of the perch odour water to each aquarium and the control treatment consisted of the addition of 100 mL of Speight’s spring water to each aquarium. Spring water was used to ensure no fish related odours were present in the water.


Experimental protocol Observations of diel feeding behaviour and the use of cover by bullies were maintained across eight replicate aquaria. Eight bullies were randomly selected from the holding tank and one placed into each aquarium. They were fasted and allowed to acclimatize for approximately 24 h before beginning each replicate trial. One hour before starting each trial, containers of perch odour were removed from the freezer and thawed. Fifteen minutes prior to the start of each replicate, 100 mL of perch odour water was added to each of four randomly selected aquaria, and 100 mL of Speight’s spring water was added to the remaining four control aquaria. The surface of each was gently stirred as the water was added. The 100 mL volume (per 18 L of aquarium water) followed the methodology previously used by Kristensen and Closs (2004) (50 mL per 18.5 L of aquarium water). A 12:12 light: dark cycle was maintained throughout each trial. Live mysid shrimp were used as prey as they are readily eaten by bullies and are large enough to see easily with the naked eye. In order to observe feeding behaviour over an entire 12-h experimental period, prey must be available in the aquaria at all times. Trials prior to the experiment indicated that 30 mysid shrimp would be sufficient to satiate a single bully over a 12 h period. Hence, at the start of each experimental period, 30 randomly selected mysid shrimp ranging in size from 5 to 10 mm were placed into each of the eight aquaria. At the conclusion of each experimental period fish were quickly removed from the aquaria, measured (total length) and euthanized. To quantify the proportion of prey consumed by each bully, all mysid shrimp remaining in each aquarium were counted following removal of all bullies. To quantify the use of cover by bullies, observations of bullies within and under the sides of the PVC tubes were made throughout the 12-h experimental period on all aquaria sequentially. The initial observations were made immediately following placement of the mysid shrimp into the experimental aquaria. Subsequent observations were made at three randomly selected times over a 2-h period commencing 15 min after the start, as well as during the final 2.25 h of the experimental period, ending 15 min before the conclusion. One final observation was made at the end of each period. Observations were based on immediate spot identification of fish locations in each aquarium. Fish


were considered to be using cover if ≥50% of their body was obscured from view from directly overhead. To minimize disturbance, personnel only entered the experiment room for observations and at the start and conclusion of experimental periods. During dark period observations, the red-bulb lamps were turned on immediately prior to making observations and turned off immediately upon conclusion. Mysid shrimp behaviour experiment An experimental trial was run to test for the behavioural responses of mysid shrimp to perch odour and light and dark conditions as this could influence the feeding success and behaviour of the common bullies. We detected no effects of light or dark, or perch odour on the location of mysid shrimp within the water column. For a detailed report see ESM 1. Analysis of data All statistical analyses were completed using R (version 2.10.1; R Development Core Team 2010). Generalized linear models (GLMs) were used to test for the effect of the treatments, control or perch odour, and light or dark, on the response variables (i.e. the proportion of eaten/uneaten prey and the use of cover) whilst controlling for the fish body length. The GLM with the proportion of eaten/uneaten prey was specified to have the logit-link with the quasibinomial family while the GLM with the use of cover was to have log-link with a quasi-Poisson family. We used a stepwise method to obtain all estimates of our predictors; that is, terms with P >0.1 were removed in stepwise fashion from successive models, beginning with the least significant second-order interactions and then to main effects, an α level of 0.05 being statistically significant. The values in the representative tables are those constructed in the model immediately prior to removal. Length was also centered in the GLMs to make the intercept biologically interpretable (Schielzeth 2010). For all GLMs, we confirmed the statistical assumptions of homogeneity of variance by visually inspecting the residuals of the models. An exploratory analysis for a relationship between the use of cover and the quantity of prey consumed was conducted.

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Results Feeding behaviour Successful feeding in light and dark conditions occurred across all replicates of both treatments (Fig. 1). A statistically significant difference in the number of prey consumed during light and dark replicates was observed with the GLM (t=−5.216, d.f.=111, P0.1000), were observed (Table 2). There was no observed relationship between the use of cover and feeding (proportion of eaten/uneaten prey) (Fig. 3; GLM analysis; t=−1.290, d.f.=119, P=0.1995).

Discussion This study demonstrated an effect of predator chemical cues (odour) alone on the diel behaviour of prey fish, with a shift in the diel use of cover in experimental aquaria. Common bullies in both control and odour treatments were observed using cover more in light than in the dark. However, in response to perch odour, bullies increased their use of cover by dark while decreasing their use of cover in light conditions, relative to the controls. A greater use of cover by day has been observed in other studies, most often related to predator avoidance (e.g.; MacKenzie and Greenberg 1998; Stuart-Smith et al. 2008). The increased use of cover by bullies in the dark in response to the presence of perch odour in our study suggests that bullies feel more threatened by the presence of perch in the dark, perhaps detecting a broad threat, but with an impaired ability to precisely locate the predator. At night, an odour may warn them of a predator’s presence, but they are unable to rely on visual cues to identify the position and activity of the perch, and therefore seek cover more often to reduce the risk of an attack (see also Hartman and Abrahams 2000; Lehtiniemi et al. 2005). Although Pettersson et al. (2001) did demonstrate short-term anti-predator responses in fish to chemical cues of a predator translating into longer-term adjustments in diel



Table 1 Results of GLM analysis on the proportion of eaten/not eaten prey by common bullies (Gobiomrophus cotidianus) exposed to perch (Perca fluviatilis) odour or Speight’s spring water (treatment) during light and dark periods (diel period) Response

Factor

Prey Consumed

Estimate

SE

d.f.

t

P

Intercept

0.4293

0.1315

111

3.264

0.0015

Treatment (odour)

0.2475

0.1542

111

1.605

0.1115

Diel Period (dark)

−0.8159

0.1564

111

−5.216