DOES EXPERIMENTALLY INDUCED CONSPICUOUS COLORATION INCREASE RISK OF PREDATION AND CONSPECIFIC AGGRESSION IN FIRST-YEAR COLLARED LIZARD MALES?

Herpetologica, 65(1), 2009, 31 38 E 2009 by The Herpetologists League, Inc. DOES EXPERIMENTALLY INDUCED CONSPICUOUS COLORATION INCREASE RISK OF PREDATION AND CONSPECIFIC AGGRESSION IN FIRST-YEAR COLLARED LIZARD MALES? TROY A. BAIRD 1,2 1 Department of Biology, University of Central Oklahoma, 100 N. University Drive, Edmond, OK 73034, USA ABSTRACT: I used paint to manipulate the coloration of first-year collared lizard males in the field to test whether conspicuous coloration increases risk of predation and/or aggression from dominant same-sex conspecifics, or resulted in decreased activity as a consequence of either or both increased attention from predators or socially dominant conspecifics. First-year collared lizard males are a good system for this study because their coloration is less developed than that of older males, they may suffer significant predation pressure, and instead of defending territories, they use stealthy tactics to avoid aggression from older sociallydominant males. To test these potential costs, I enhanced the coloration of first-year males in a conspicuous group by painting them similar to older territorial males, used brown paint similar to that of conspecific females to alter coloration in an inconspicuous group, and painted a control group with water. I then recorded census and focal observation data on these males for 40 d to examine survivorship, receipt of aggression by dominant males, and two indices of their activity; the number of censuses when first-year males were emergent, and their rates of travel. Both rates of predation and the frequency of aggressive acts received from territorial males were low overall and did not differ among the three treatment groups. Moreover, males in the three treatment groups did not differ in either the number of censuses when they were sighted or their rates of travel. These results are not consistent with the hypothesis that conspicuous coloration increases risk of predator attack or aggression from dominant conspecific males, suggesting that other costs may explain the observation that conspicuous coloration develops gradually in first-year collared lizard males. Key words: Aggression; Coloration; Costs; Crotaphytus collaris; Predation NATURAL selection may shape the coloration patterns of animals to enhance effective thermoregulation (Bittner et al., 2002; Christian, 1996; Garcia et al., 2003) and interactions with both predators (Endler, 1980, 1992) and prey (Baird, 2008; Grether and Grey, 1996), whereas sexual selection sometimes favors coloration patterns that function in social signaling (Cooper and Greenberg, 1992; Whiting et al., 2003). Cryptic coloration is usually hypothesized to be adaptive for predator avoidance or increased foraging efficiency (Grether and Grey, 1996; Huhta et al., 2003; Stuart-Fox et al., 2003, 2004). Sexual selection, however, usually favors conspicuous coloration that functions during intrasexual contests (Vitt and Cooper, 1985), courtship interactions with potential mates (Andersson, 1994; Andersson and Iwasa, 1996; Kwiatkowski and Sullivan, 2002; Whiting et al., 2003), or both types of interactions (Baird et al., 1997; Berglund et al., 1996). Although conspicuous male coloration may confer mating advantages, it also may impose 2 CORRESPONDENCE: e-mail, tbaird@uco.edu one or more fitness costs. Increased aggression from same-sex competitors is one possible cost (Kotiaho, 2001; Macedonia et al., 2004), particularly in species where males use visual signals to advertise resource-holding potential to rivals (Husak, 2004; Lappin et al., 2006). Conspicuous coloration may also reduce foraging effectiveness if it renders predators more visible to their prey (reduced aggressive crypsis: Baird, 2008; Grether and Grey, 1996; Macedonia et al., 2002; Ortolani, 1999) and/or if it increases risk of attack causing foragers to spend more time taking refuge (Martín and López, 2001. Increased visual conspicuousness may also increase predation risk. Inverse correlations between interpopulation variation in color intensity and predation pressure are consistent with the predation risk hypothesis (Barlow and Ballin, 1976; Huhta et al., 2003; McPhail, 1969). A predation cost of conspicuous coloration is also supported by higher rates of attack on brightly colored inanimate models (Husak et al., 2006; Stuart-Fox et al., 2003). However, model studies do not provide an unequivocal test of the hypothesis that conspicuous 31

32 HERPETOLOGICA [Vol. 65, No. 1 coloration increases actual predation of live prey, and evidence from field studies of increased predation on conspicuously colored live prey is limited (Götmark and Olson, 1997; Kotiaho, 2001; Slagsvold et al., 1995). In a companion study, conspicuous coloration decreased foraging effectiveness and hence rate of growth in first-year collared lizard males (Baird, 2008). Evidence for of a reduced foraging cost does not preclude the possibility of other costs, Therefore, in the present study I use paint-manipulations of lizards in the field to test the extent to which conspicuous coloration increases predation and aggression from socially dominant rival males, and to test the hypothesis that conspicuous coloration imposes the indirect cost of decreased activity necessary to evade attempts by predators and/or chases by dominant males. I manipulated lizard color by enhancing the green and yellow of some first-year males (hereafter conspicuous males), obscuring these colors in other males by applying brown paint similar to the color of conspecific females (hereafter inconspicuous males), and painting a control group with water. First-year male collared lizards at Arcadia Lake (hereafter AL), Oklahoma, are a good model system for this study. Although males that are 2 y and older (hereafter 2y+ - males) display fully developed coloration, firstyear males are only in the process of developing these bright hues (McCoy et al., 1997). Spectrophotometric measurements of reflectance from 12 body surfaces of male and female collared lizards at AL showed that at least 90% of the reflectance was in visible wavelength spectra (Macedonia et al., 2004). This study also demonstrated that females are the most cryptically colored individuals in this population, whereas the bright coloration of 2y+ - territorial males gives them higher contrast against the substrate. Contrast between the rock background and lizard coloration was intermediate in first-year males (Macedonia et al., 2004). Therefore, the degree to which natural coloration can be altered by painting is higher in first-year males than in 2y+-males. First-year males in the AL study population may also suffer significant predation pressure. In thirteen previous study seasons at AL, 40 60% of first-year males died between the beginning of their first and second activity seasons (April August, T. A. Baird, unpublished data). Mortality during this period may be a consequence of causes other than predation when males are emergent during their first season, such as freezing or insufficient stored energy during the first winter. However, two species of snakes (Masticophis flagellum, Nerodia rhombifera), and two species of raptors (Buteo jamaicensis, Ictinia mississipiensis) that are known predators on C. collaris are abundant at AL (T. A. Baird, unpublished observations). Although snakes often use chemical cues to trail prey, M. flagellum hunt using visual cues (Husak et al., 2006; Secor and Nagy, 1994). At AL, coachwhips hunt C. collaris by elevating vertically and remaining motionless while scanning for perched lizards (T. A. Baird, unpublished observations). Increased bite marks on conspicuously painted clay model collared lizards in other Okahoma populations where these same predators occur (Husak et al., 2006) indicates that these predators detect colors in the visible spectra. Therefore, I expected that the rate of predation on first-year males in my treatment groups would be positively correlated with their color conspicuousness (Table 1, prediction 1). Increased aggression from socially dominant conspecifics is also potentially a significant cost to first-year males of developing conspicuous coloration. First-year males at AL live within territories defended by larger 2y+ - territorial males by adopting stealthy, socially subordinate behavior including low rates of travel and display (Baird and Timanus, 1998; Baird et al., 1996, 2003). Aggressive encounters between males are rare at AL (Baird et al., 2007). Male-male aggression that escalates to biting is even more rare, and when it does occur almost always involves two territorial males. Because they immediately flee and hide when approached by larger territorial males, first-year males almost never suffer injurious attacks. Therefore, if conspicuous coloration imposes a cost of increased conspecific aggression, I expected a positive relationship between the frequency that subject males were chased and hid and color conspicuousness of my three treatment groups (Table 1, prediction 2).

March 2009] HERPETOLOGICA 33 TABLE 1. Hypothetical costs of conspicuous coloration in first-year male collared lizards and the predicted outcomes of paint manipulation experiments. C 5 conspicuously-painted, I 5 Inconspicuously - painted, W 5 water-painted. Hypothetical cost Predictions for first-year males Vulnerability to predators 1. Frequency of predation: C. W. I Intrasexual aggression 2. Frequency of aggression received: C. W. I Indirect effects on activity 3a. Sighting frequency: C, W, I 3b. Rate of travel: C, W, I Potential costs of developing conspicuous coloration may also be indirect if frequent attacks cause first-year males to adopt riskadversive behavior (Lima and Bednekoff, 1999; Kavaliers and Choleris, 2001). Indirect costs can be assessed in collared lizards by quantifying common activities that would likely be influenced by the extent to which first-year males are threatened by either predators or aggressive same-sex conspecifics. First-year collared lizards take refuge from both by hiding in rock crevices. Movement by first-year males provides visual cues that likely elicit responses from both potential predators and conspecific competitors. Therefore, the amount of time that lizards are emergent and the rate of travel can be used to estimate the extent to which first-year male collared lizards in the three treatment groups are at risk. If color manipulation increases the frequency of stalking and unsuccessful attacks by predators and/or threats from conspecifics, then firstyear males are expected to minimize risk by increased hiding and decreased travel (Kavaliers and Choleris, 2001; Lima and Bednekoff, 1999). I tested this prediction by recording the percentage of censuses that first-year males in the three treatment groups were emergent, and their rates of travel during focal observations (Table 1, predictions 3a and b). METHODS Study Subjects and General Methods I conducted this study from 30 April 30 June 2002 04 at Arcadia Lake (AL) Dam 9.6 km east of Edmond, Oklahoma on State Hwy 66. At AL, C. collaris occupies three topographically homogeneous patches (1505 19,850 m 2 ) of boulders imported to construct flood-control spillways. This site is optimal for behavioral studies because human access is restricted, lizards are undisturbed and readily observed, and the age of all males is known from mark-recapture studies conducted since 1990 (Baird et al., 1996, 2003). The AL study site is mapped to scale using GPS accurate to the nearest m (Baird and Timanus, 1998; Baird et al., 2001). Beginning when they were hatchlings, all lizards in this study were noosed, the terminal phalanges of three digits were clipped for permanent identification, and unique combinations of nontoxic acrylic paint spots were applied to the dorsum for identification from a distance. Gender in hatchling collared lizards is readily determined by the presence (males) and absence (females) of enlarged post-anal scales, and later by development of dimorphic coloration (Baird et al., 2003; McCoy et al., 1997). This research was conducted with the permission of the Department of Fisheries and Wildlife of the State of Oklahoma, and the United States Army Corps of Engineers at the Arcadia Lake Dam. All procedures involving live lizards in this study were approved by the Institutional Animal Use Committee at the University of Central Oklahoma. Painting-Experiment Protocol For painting experiments, I used males (n 5 42) that were in their first activity season (April July). These males ranged from 73 93 in snout-to-vent length (SVL) at the beginning of the experiments. From 1 20 May, subject males were captured by noose, measured (SVL to the nearest mm, mass to the nearest g), and randomly assigned to one of three paint treatment groups (see below), and painted. Males in the conspicuous and inconspicuous treatment groups were painted on the dorsal and lateral surfaces of the torso, limbs, tail, head, and dewlap with nontoxic water-based acrylic paint. Control males were painted with water. Care was taken to keep

34 HERPETOLOGICA [Vol. 65, No. 1 paint (or water) away from the mouth, eyes, and external auditory meatus. To identify subject lizards from a distance, I painted a white number (3 4 mm high) on the dorsum of subjects in all treatment groups. All paint was lost when lizards molted. Worn paint was re-touched as necessary during routine recaptures (mean intercapture interval in d 6 1.0 SE 5 8.8 6 0.45), and recapture interval for the three treatment groups did not differ (F 2,41 5 0.67, P 5 0.51). Combined observations during quantitative censuses, focal observations, recaptures, and other sightings when I simply noted whether or not males were painted revealed that subject males in paint treatment groups were without paint for no longer than 2 d during the study period (1 May 30 June). The AL lizards that are most conspicuously colored against the background are 2 y+-males (Macedonia et al., 2004). Therefore, I used Munsell Color Charts (Munsell, 1969) to measure the coloration of unmanipulated 2y+ territorial males on the dorsal surface of the torso, limbs, and tail (hue 5 7.5 Green Yellow, value 5 4 6, chroma 5 5 7), and the dewlap (hue 5 2.5 Yellow, value 5 7, chroma 5 10) of these males. I then mixed paint to mimic this natural coloration, and in the conspicuous treatment group of first-year males (n 5 14) painted the dorsal surfaces of the torso, limbs, and tail green (hue 5 7.5 Green Yellow, value 5 5, chroma 5 6), and painted the dewlap, top and sides of the head yellow-orange (hue 5 2.5 Yellow, value 5 7, chroma 5 10). Females at AL are less conspicuous against their background than are adult males using spectral data (Macedonia et al., 2004). Therefore, I used Munsell charts to measure the brown dorsal coloration of mature females (hue 5 7.5 Yellow Red, value 5 5, chroma 5 2), mixed paint to match, and painted the inconspicuous group (n 5 13) on the dorsal surface of the torso, limbs, tail, dewlap, and sides and top of the head. Control males (n 5 15) were painted on these surfaces with water. Once the paint (or water) dried (#10 min), males were released at their precise capture locations. Males were first painted from 1 20 May which is the beginning of the reproductive season at AL. Date of first painting in the three treatment groups (mean date 6 1.0 SE in d; conspicuous 5 7 May 6 1.4, inconspicuous 5 8 May 6 1.5, water 5 7 May 6 1.3) did not differ among treatment groups (F 2,41 5 0.31, P 5 0.74). Excepting the few lizards that were taken by predators (see Results), all experimental subjects behaved normally, lost their paint when they molted, and survived through to the end of at least the current activity season (October), and in most cases into the following season, indicating that painting had no adverse affects on lizard health. Risk of Predation and Conspecific Aggression To test the influence of coloration on predation risk, I monitored male survival by conducting censuses of the study site at least every 2 d during which the location of subject males was recorded on maps (Baird et al., 2001, 2003). Several years of studies on the AL population confirmed that abrupt disappearance from home ranges indicated that first-year males had died, almost certainly from predation. Emigration is unlikely because C. collaris is restricted to rock substrata, our mapped study site includes all of the available rock habitat, the rock patches are surrounded by large expanses of mowed grass, and lizard movements among rock patches are rare (Hranitz and Baird, 2000). Hence, it is very likely that abruptly disappearing lizards were the subjects of predation, especially since ophidian and avian predators of collared lizards are both abundant at AL (T. A. Baird, unpublished observations). In addition, it is common for collared lizards at AL to acquire wounds like those expected from attacks by predators (Baird et al., 1997). Because males were painted on different dates, it was necessary to standardize the period over which I monitored survival. This was accomplished by monitoring all males for 40 d following painting, and recording the number of days between the date that lizards were painted and the last date that they were censused (maximum of 40 d). Because these data did not meet the assumptions for parametric statistics, I compared the number of days survived for the three treatment groups using Kruskal-Wallis ANOVA. To test whether males in the three treatment groups differentially altered their activ-

March 2009] HERPETOLOGICA 35 TABLE 2. Comparison of survival and behavioral variables (mean 6 1.0 SE) in conspicuous, inconspicuous, and waterpainted first-year C. collaris males. Male paint treatment Variable Conspicuous Inconspicuous Water Days survived out of 40 39.4 (0.58) 33.5 (3.52) 37.4 (1.47) Aggression received (encounters/h) 0.11 (0.07) 0.15 (0.08) 0.14 (0.08) Percent of censuses sighted 50.5 (4.3) 44.4 (4.1) 48.5 (4.5) Rate of travel (m/h) 29.4 (9.9) 27.5 (4.4) 31.3 (5.4) ity in response to attacks/stalking by either predators or aggressive conspecifics, I censused the entire study site at least every 2 d from 1 May 30 June (at least 30 censuses/ site), and calculated the percentage of sightings that males in the three treatment groups were emergent. I quantified the frequency with which first-year males received aggression from 2 y+-males, and their rates of travel by recording five, 20-min focal observations (Baird et al., 2003) on each first-year subject male. Focal observations were recorded on separate days distributed throughout May to 30 June, which is the period during which 2y+-males of this species aggressively defend breeding territories (Baird et al., 1996, 2001, 2003). Aggression received from dominant 2y+- conspecific males involved their chasing, and more rarely attacking first-year males. Therefore, I quantified the frequency of aggression from territorial males in the three paint treatment groups as the total number of aggressive encounters received divided by the total observation time for each subject male (Baird et al., 1996, 2001). I evaluated travel by first-year males by measuring the length of cumulative lizard travel paths using a digital planimeter (Planix 2000), and calculating the hourly rate of travel (m/h) by dividing the cumulative distance traveled during all focal observations by the total observation time on each subject male (Baird et al., 1996, 2001). I used separate one-way ANOVA s to examine the influence of treatment group on the frequency of aggression received, and the rate of travel, and the percentage of censuses that males were emergent. RESULTS Only 7 of 42 (16.7%) males disappeared abruptly during the 40 d study period, and were not sighted again during the remainder (ends in Oct) of those or subsequent activity seasons. Of these likely predation victims, three were in the inconspicuous treatment group, three were in the water-painted group, and only one was in the conspicuous group. The number of days survived (out of 40) was similar (H 2,41 5 1.57, P 5 0.30) in the three treatment groups (Table 2). The frequency with which first-year males in different treatment groups received aggression from territorial males was low, and did not differ (F 2,41 5 0.47, P 5 0.63) in the three treatment groups (Table 2). Neither the percentage of censuses that lizards were emergent (F 2,41 5 0.53, P 5 0.59), nor the rate of travel (F 2,41 5 0.17, P 5 0.85) by these first-year males were statistically different in the three treatment groups (Table 2). DISCUSSION The distribution of predation victims in the present study was not influenced by experimental manipulation of color, which does not support the hypothesis that conspicuous coloration increases vulnerability to predators in first-year male collared lizards. Less than 17% of first-year males were preyed upon during my 40-d experiment compared with 40 60% that died over much longer periods that included the first activity season (April August), the subsequent period when lizards are much less active but intermittently emergent (Sept. mid Oct.), plus the first winter (T. A. Baird, unpublished data). These results suggest that fewer males in the AL population are preyed upon during their first activity season than die during their first winter. The statistical power of my experiment to detect differences in actual predation is low because very few first-year males were preyed upon during my 40-d study period. Therefore, conclusions about the possible influence of

36 HERPETOLOGICA [Vol. 65, No. 1 coloration on predation risk based on these data must be viewed cautiously. However, these data are valuable because few studies have monitored survival of free-ranging colormanipulated individuals as long as in my study, and because color manipulations spanned the natural range observed between the sexes and among males of different ages (Baird, 2008; Macedonia et al., 2004). Even though successful predation was rare during the study, increased conspicuousness might have prompted more unsuccessful attempts by predators. If this had been the case, then males in the three treatment groups should differ in their risk-taking/refuging behavior (Lima and Dill, 1990; Martín and López, 2001). Inconsistent with this hypothesis, neither of the behavioral variables (travel, sighting frequency) used to evaluate this possibility differed among the three treatment groups, which also does not support the hypothesis that increased conspicuousness increases predation risk in first-year males in this population. Results of the present study are contrary to findings of studies on collared lizards (Husak et al., 2006) and rock dragons (Stuart-Fox et al., 2003) that employed painted inanimate models, both of which showed increased predator attacks on models painted conspicuously. The use of models to test the potential cost of predation is limited to measuring the extent to which predators detect prey (Olsson, 1993). Whether or not increased conspicuousness actually results in increased predation is also dependent upon the evasive abilities of prey. Husak and Fox (2006) reported that first-year collared lizard males used a higher proportion of their total capacity for sprinting when threatened by predators than both females and 2y+-males. It is possible, therefore, that heightened performance when evading attacks allowed even conspicuouslypainted first-year males in my study to escape predators. Conspicuousness to predators in my study may be relatively independent of coloration because first-year males at AL behave secretively rather than advertising ownership of territories (Baird and Timanus, 1998; Baird et al., 1996, 2003). The combination of bright coloration together with the conspicuous display and travel behavior that collared lizard males use to advertise their breeding territories (Baird et al., 2007) may indeed increase actual rates of predation. This hypothesis remains to be tested in collared lizards, however, by monitoring survival and behavior in free-ranging territorial males that are color manipulated. My results also do not support the hypothesis that conspicuous coloration prompts increased aggression from socially dominant males. Perhaps it is not surprising that conspicuously-colored first-year males did not receive more aggression because territorial males in the AL population appear to minimize direct aggression with same-sex competitors, and instead rely on display from a distance to advertise territory ownership (Baird et al., 1996, 2001, 2003; Baird et al., 2007; Schwartz et al., 2007). I did not quantify the display rates of territorial males that overlapped the home ranges of the first-year males that were painted conspicuously versus those of territorial males overlapping inconspicuous or water-painted first-year males. However, the observation that painting firstyear males conspicuously did not increase their receipt of overt aggression and did not alter their activities as would be expected if they had received more aggression that I did not witness suggests that increased attacks by dominant males are not necessary for territory defense in this population, even when coloration is enhanced. Conspicuous coloration as well as large size are probably both sexually selected traits that promote the ability of 2 y+-males to acquire territories that allow their access to female mates (Baird et al., 1996, 1997, 2003; Husak et al., 2006; McCoy et al., 1994, 2003). The lack of evidence in this study supporting either a cost of increased predation or conspecific aggression suggests an alternate explanation for the gradual development of conspicuous coloration during the first year in male collared lizards. One possible explanation is that developing conspicuous coloration reduces foraging efficiency because it renders sitand-wait collared lizard predators less cryptic to their arthropod prey (Baird, 2008). Collared lizard males grow at accelerated rates during their first year (Baird, 2008; Baird and Hews, 2007; Baird et al., 2003) because

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