The relationship between breeding coloration and ...

Environ Biol Fish DOI 10.1007/s10641-014-0260-9

The relationship between breeding coloration and mating success in male pygmy sculpin (Cottus paulus Williams) N. C. Kierl & C. E. Johnston

Received: 14 June 2013 / Accepted: 12 March 2014 # Springer Science+Business Media Dordrecht 2014

Abstract Carotenoid-based coloration is well studied in birds and fishes because carotenoid pigments must be acquired from the diet, and therefore it may be used as an honest signal of condition. Females may select males based on the color and intensity of the carotenoid pigments found in a high quality male. The orange patches on the pectoral fins and body of male Pygmy Sculpin (Cottus paulus) differ in aspects of coloration between successful and unsuccessful males (defined as nest holders who either obtain egg clutches or not); however, these males do not differ in length or condition. Within successful males, condition was correlated with mating success (average eggs gained and average egg clutches gained) but coloration was not. However, aspects of coloration were correlated with male condition. Female Pygmy Sculpin seem to prefer males with more intense coloration and that are in good condition, which may correlate with numerous benefits such as effective brood defense, decreased filial cannibalism and fungal infections. Keywords Mate choice . Cottidae . Imperiled species . Spawning

Introduction As females are the choosier sex in numerous species, many studies have focused on traits indicative of male N. C. Kierl : C. E. Johnston (*) Fish Biodiversity Lab, Department of Fisheries, Auburn University, Auburn, AL 36849, USA e-mail: [email protected]

quality that are used by females for mate choice (Kirkpatrick 1987; Jennions and Petrie 1997; Kokko et al. 2003). Zahavi’s handicap principle suggested that males of high quality can afford elaborate ornamental traits (i.e. frog mating calls, antlers of deer or moose, peacock feathers, and courtship displays of some fish) while males lesser quality cannot (Zahavi and Zahavi 1997). For example, longer swords (elongated caudal fin ray) on male green swordtails, Xiphophorus helleri, are preferred over males with shorter swords by females (Basolo 1990). Basolo (1990) suggested that the elongation of this ornamental trait could increase conspicuousness to predators, decrease mobility and have higher energetic costs of swimming. Ornamental traits have been shown to be condition-dependent signals of individual quality (Andersson 1994), and are considered “indicator” traits that can be used by females when choosing a high quality mate (Andersson 1994). Most notable studies of condition-dependent signals have focused on conspicuous, brilliant carotenoid based coloration seen in birds (see Hill and McGraw 2006a) and fishes (Kodric-Brown 1989; Houde and Torio 1992; Frishchknecht 1993; Nicoletto 1993; Barber et al. 2000; Grether 2000). Carotenoids are responsible for most of the red, yellow and orange coloration found in the integuments of animals (Goodwin 1984). These pigments have been shown to provide beneficial properties acting as free radical scavengers, immune system enhancers and stimulants, cancer inhibitors and antioxidants (Bendich 1989, 1993; Mayne 1996; Matsuno 2001). Animals cannot synthesize their own carotenoids and must obtain them by eating plants, algae or carotenoid sequestering animals (Goodwin 1984). Coloration may be an “honest” indicator of foraging ability,

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swimming ability, a male’s current health status, health history, or potential resistance to future infections (Endler 1980; Kodric-Brown and Brown 1984; Nicoletto 1991; Olson and Owens 1998; Braithwaite and Barber 2000; Møller et al. 2000). Different pigments and ratios of pigments can have an effect on the coloration of ornaments as well as differences in the absorption, metabolic and deposition rates (Hill 2002; Hill and McGraw 2006b). Due to these differences, ornaments on different parts of the body may respond differently than each other, thus producing multiple signals. The red body coloration of sticklebacks (Gasterosteus aculeatus L.) and blue eye coloration respond differently to change diet quantities (Frishchknecht 1993). The yellow coloration on feathers and the bill of American goldfinches (Carduelis tristis) respond differently to carotenoid access, food intake and parasite load (Hill et al. 2009). This suggests that coloration may signal differently depending on the hue or body location. Sculpin (Cottidae) are cryptically colored. Most sculpin match the surrounding substrate, similar to the trend in other scorpaeniform fishes (Jenkins and Burkhead 1993). Breeding males in some sculpin species have color on the margin of the first dorsal fin that can be reddish, orange, pale to white, which contrasts against the typical brown, olive, black overall coloration, but otherwise lack breeding colors (Jenkins and Burkhead 1993; Boschung and Mayden 2004; Rohde et al. 2009). Most sculpin are nocturnal and probably breed at night, making visual signals unlikely. Few studies have investigated color in sculpin, however, Whiteley et al. (2009) looked at color change plasticity and background matching in the Coastrange Sculpin, Cottus aleuticus Gilbert, and heritability of these traits (Bergstrom and Whiteley 2012). In addition, Sköld et al. (2010) found sculpin to have a lower ability for internal color change relative to other models. Unlike other sculpin, breeding male Pygmy Sculpin, Cottus paulus, exhibit bright orange and black coloration. The colorful margin on the first dorsal is still present, but less prominent in comparison to the bright orange patches on the pectoral fins and body (Fig. 1). This species differs from other sculpin by its diurnal behavior (Williams 1968; McCaleb 1973), which makes the use of visual signals, such as male breeding coloration, a possibility. Male Pygmy Sculpin establish nests and provide parental care such as predator protection and egg fanning. Males also exhibit allopaternal care

Fig. 1 Breeding coloration of a male Pygmy Sculpin, Cottus Paulus

(Johnston 2000). Egg fanning requires the male to remain halfway in the nest, leaving only his head and pectoral fins visible, and during courtship males wiggle the pectoral fins towards females (pers. obs.). This wiggling behavior makes the orange coloration on the pectoral fins quite conspicuous to females while the orange coloration on the body is only visible when a male exits the nest. Thus, slight differences between body and pectoral coloration may reflect different signals. The objective of this study was to investigate the potential role of orange coloration in male pygmy sculpin mating success by: (1) examining the variation between pectoral color and body color; (2) investigating the relationship between coloration and mating success in successful and unsuccessful males; (3) examining the correlation between coloration and body condition and between condition and number of eggs and clutches obtained; (4) Assessing the relationship between male coloration and the number of eggs and clutches obtained.

Methods In order to follow mating success of individual males, 38 artificial nesting tiles (11 cm×11 cm×1.5 high) were placed in the spring run of Coldwater Spring 2 weeks before breeding observations began in order to allow ample time for males to colonize them. Breeding male C. paulus were followed from April 21 to May 1 2009, observations occurring every other day. On observation days, all nests were checked for breeding males and eggs using a mask and snorkel. Males were captured at the tile using a small dip net, then weighed to the nearest 0.1 g and placed in a clear, plexiglass view box for photographs and length measurements to the nearest 0.001 mm. Photographs were taken of the male’s left and right sides by an Olympus stylus 720SW digital

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camera, with a orange and black color standard in view to adjust for differences in lighting. At male removal, the nest tile was moved into a tray of water to prevent egg predation. Photographs were also taken of the eggs attached to the underside of the nest tile. Nest location was recorded for each male measured in order to track movement. Any marks, such as tears or scars on the fins, were noted for identification purposes. Identification of males from day to day was also done by reviewing photographs for matching body patterns. Intensity of black body coloration varied; however, the underlying pattern did not. Only males observed consecutively for two or more times were used for analysis. Males were considered successful if they obtained at least one clutch of eggs, and unsuccessful if they defended a nest tile but did not obtain eggs. Male length (SL, mm) was measured from digital photographs using the measure tool in ‘Image J’ software (National Institutes of Health, Bethesda, MD, USA); measurements were standardized to a 1 cm ruler in each photograph. A condition factor for each male was calculated using male weight (W) and standard length (L) in Fulton’s condition factor equation (Murphy and Willis 1996): K¼

100; 000W L3

For fishes, condition is used as a measure of robustness and is generally thought to be correlated with state of nutrition (Murphy and Willis 1996). The number of eggs each male had was recorded for each observation. Egg counts were relatively easy due to the small number per clutch (mean=25, SD=5.5; Johnston 2001) and the habit of this species of often laying eggs in a single layer. Due to the presence of allopaternal care behavior in C. Paulus (Johnston 2000), all eggs present on the first observation of each male were excluded because they may be from a prior breeding male that was displaced by the current residing male. Clutches were identified by diagrams and photographs taken on each occasion where nest tiles were checked. Therefore, eggs gained or lost from the first observation were averaged for an overall egg score. The average number of clutches gained was also quantified. The color quality of orange spots on the pectoral fins and body of breeding male C. paulus were measured using digital images with a color standard. Images were taken within five min of capture because the stress of handling can influence coloration associated with a change in melanin distribution within chromatophores

(Donald 1998; Höglund et al. 2000, 2002; Parsons 2001). This species is federally protected, threatened, and the animals could not be killed for this study (USFWS, http://www.fws.gov/endangered/). The Adobe Photoshop color sampler tool (5 by 5 pixel average)(Adobe Photoshop CS4 extended, v.11.0.1, Adobe Systems Incorporated, San Jose, CA, USA) was used to quantify orange hue, saturation and brightness at four points on both pectoral fins, each side of the body and the orange color standard. Two photographs were measured for each observation, a right and left picture (i.e. a male followed for 3 days would have six photographs). The assistant who measured these points did not know how many eggs a male had and was instructed to sample the most intense areas of orange pigmentation within the pectoral fins and on the body, thereby eliminating the possibility of quantifying regions with glare or water spots as could have happened by choosing random points (modeled from Hill et al. 2009). All color measurements for a single male were averaged to get a single orange hue, saturation and brightness for the pectoral and body. Color standard scores from all photographs were averaged to get a single overall standard score, which was used to standardize all photographs based on the deviation of a photograph’s color standard score from the overall standard score. Because field lighting conditions (sunny vs cloudy) varied between observation days, photos in which the standardization adjustment was larger than average were excluded. In Photoshop, hue is a degree measure on a color wheel (0–360°); low values closer to red wavelengths and higher values closer to green wavelength. Chroma (saturation) is measured using a percentage scale with 0 % dull and 100 % fully saturated. Brightness is also uses a percentage scale with 0 % equaling black and 100 % equaling white (Adobe Photoshop CS4 extended, ver. 11.0 manual). Digital photographs only record human visible coloration, therefore no analysis of UV coloration was possible. All statistical analyses were conducted using the SPSS software package (SPSS ver. 11.0, SPSS Inc, Chicago, IL.). Color differences between body and pectoral patches were tested for using a paired t-test. All relationships between male coloration, body condition and mating success (number of eggs and clutches) were examined by linear and multiple regression analyses, and MANOVA was used to test for differences between characteristics of successful and unsuccessful males.

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Results Sixty-one individual males were identified at the artificial nesting tiles, 28 of the males were seen two consecutive observation periods or more. However, six males already had 3 or more clutches on the first observation periods and only lost eggs through all subsequent observations due to development. These males were presumed past the courtship stage and focusing on the parental care stage, therefore were excluded from the analyses. Twenty-two males obtained eggs during the observation periods, and are considered successful males. Twenty-nine males were found defending nest tiles but were unsuccessful at obtaining eggs; these males were classified as unsuccessful males for the purposes of analysis. The hue of the pectoral patches is significantly more orange than body patches (paired t-test, n=22: p=0.03). The mean hue of pectoral is 23.36±4.83 while the mean hue of body is 24.93±4.29. The chroma of the pectoral patches is significantly less saturated than body patches (paired t-test, n=22; p=0.00). The mean chroma of pectoral and body patches is 64.69±8.43 and 70.34± 6.96, respectively. The brightness of pectoral and body patches did not differ significantly (paired t-test, n=22; p=0.13). The mean brightness of pectoral and body patches is 55.35±10.40 and 56.91±12.84, respectively. Successful and unsuccessful males differed in every measurement of coloration; including darker, oranger and more saturated color patches (Table 1), but did not differ in length (F=0.41, p=0.521) or condition (F= 1.46, p=0.232). Mean length=78.5±2.8 mm for successful males (n=22); 75.4±3.4 mm unsuccessful males (n=29). Mean condition of successful males was 2.25± 0.32 and 2.14±0.36 for unsuccessful males.

Fig. 2 Relationship between body condition and average eggs gained for successful male Pygmy Sculpin (r=0.43, p=0.04), Y= a13.3+−19.3

The color of pectoral and body coloration and body condition of successful males was correlated (multiple regression, n=22, F=3.01, r=0.74, p=0.03). Coloration of pectoral or body patches of successful males was not correlated with the average number of eggs gained by a male (multiple regression, n=22, F=1.11, r=0.55, p= 0.40) or the average number of clutches gained by a male (multiple regression, n=22, F=1.10, r=0.15, p=0.51). Body condition of successful male Pygmy Sculpin was correlated with both measures of mating success. Body condition and average eggs gained were positively correlated (linear regression, n=22, F=4.60, r=0.43, p=0.04, Fig. 2). Body condition was also positively correlated with the average clutches gained (linear regression, n=22, F=5.71, r=0.47, p=0.02, Fig. 3).

Discussion Successful male Pygmy Sculpin have significantly darker, oranger and more saturated pectoral and body patches than males that did not obtain eggs, even though the size and body condition of males in these two groups did not differ. Once chosen, body condition, which is

Table 1 Mean value, standard deviation and MANOVA comparison in coloration of successful (n=22) and unsuccessful (n=29) male Pygmy Sculpin Color variable

Mean + S.D. Successful Unsuccessful p

Pectoral hue

23.9±4.8

29.1±6.9

Pectoral chroma

64.8±8.4

57.6±12.8

0.041 4.29

Pectoral brightness 55.9±10.4

61.9±11.7

0.031 4.90

Body hue

32.6±8.2

0.000 14.35

25.5±4.3

F

0.017 6.09

Body chroma

70.5±6.9

62.5±13.4

0.015 6.33

Body brightness

57.5±12.8

67.5±13.8

0.003 10.02

Fig. 3 Relationship betweeen male body condition and average clutches gained for successful male Pygmy Sculpin (r=0.47, p= 0.02), Y=a0.66+−0.9

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correlated with coloration in successful males, translated into more eggs and clutches for these males. The relationship between condition and carotenoid color in animals has been well documented (Hill 2002). Carotenoids have been shown to responsible for the orange and red coloration in fishes (Evans 1996; Wedekind et al. 1998; Barber et al. 2000; Grether et al. 2001). Since these pigments come from the diet, they are typically indicators of condition and are often used by females to choose a mate (Hill 2002; McGraw and Ardia 2003). Male body condition may translate into better paternal care for a number of reasons, including reduced filial cannibalism, better nest defense and better brood care. Filial cannibalism is less likely to occur when the male is in good condition (Manica 2002). Egg fanning is a common part of egg care in fishes that helps prevent fungus from growing on the eggs (Côté and Gross 1993). Males in bad condition may be less successful in keeping fungus off eggs. Male C. gobio fan eggs almost constantly for 4 weeks coupled with limited feeding opportunities, leads to body condition deterioration (Marconato and Bisazza 1988; Marconato et al. 1993). Brood defense is also very important for male reproductive success in C. gobio. Larger males are more effective at preventing conspecifics cannibalism (Marconato and Bisazza 1988). In pygmy sculpin, male size is less variable therefore male body condition may be the determining factor in effective brood defense. Therefore, females gain many benefits from choosing a male in good condition. Differences were also found in color characteristics of body vs pectoral fin patches. It is possible, given the courtship behavior of this species, that these color patches are used to signal different types of information. During courtship, male Pygmy Sculpin display to females by fin wiggling, and the pectoral patches are very evident during these displays. Therefore, these patches may be better indicators than the color patches on the body, which are only visible when the male is outside of the nest cavity, primarily during aggressive displays. The red color in the jaw and throat of male three-spined sticklebacks (Gasterosteus aculeatus) has been hypothesized to signal recent changes in condition factor while the blue irises in the eyes signal absolute condition or condition history (Frishchknecht 1993). It was also hypothesized that the two colors could act as indicators for different parasite resistances (Frishchknecht 1993). The coloration of feathers and bill in American goldfinches, Carduelis tristis, has been shown respond differently to carotenoid

access, food intake and parasite load (Hill et al. 2009). This supports the idea that feather and bill coloration are significantly different traits in songbirds, even though carotenoids are responsible for both pigmentations (Hill et al. 2009). Therefore, it is possible that pectoral and body patches of orange coloration may signal different traits linked to condition as well. There is no doubt that potential for visual signaling and female choice for male coloration has risen for Pygmy Sculpin. Unlike most other species of Cottidae, this species is diurnal and lives in crystal clear water. These factors may have led to the use of visual signaling as a form of mate choice in Pygmy Sculpin, in conjunction with other traits. It appears that once a male is chosen, females may use body condition as an indicator of a potentially successful parent. Other cues, such as acoustic signals, may also play a role in determining how many eggs a female lays with a given male, as well as how many clutches a successful male obtains. Acknowledgments The authors would like to thank the staff at the Paul B. Krebs Treatment Plant and Anniston Water Works and Sewer Board for their support and for allowing access. The authors would also like to thank D. Holt and P. Speares for helping create the acoustic set-up as well as two reviewers for valuable comments to this manuscript. This work was funded in part by a Section 6 grant from the Alabama Department of Conservation and Natural Resources, and covered by Auburn University animal welfare protocol number 2011–2016.

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