preference in Arctic charr Salvelinus alpinus, but

Biological Journal of the Linnean Society, 2011, 103, 602–611. With 3 figures No evidence for an indirect benefit from female mate preference in Arctic charr Salvelinus alpinus, but female ornamentation decreases offspring viability MATTI JANHUNEN1*, JUKKA KEKÄLÄINEN2,3, RAINE KORTET3, PEKKA HYVÄRINEN4 and JORMA PIIRONEN1 1 Finnish Game and Fisheries Research Institute, Joensuu Game and Fisheries Research, Yliopistonkatu 6, FI-80100 Joensuu, Finland 2 Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, FI-40014 Jyväskylä, Finland 3 Department of Biology, University of Eastern Finland, PO Box 111, FI-80101 Joensuu, Finland 4 Finnish Game and Fisheries Research Institute, Kainuu Fisheries Research, Manamansalontie 90, FI-88300 Paltamo, Finland Received 19 January 2011; revised 19 February 2011; accepted for publication 19 February 2011 bij_1659 602..611 Female mate choice is considered an important evolutionary agent, but there has been an ongoing debate over the fitness consequences it produces, especially in species that have a resource-free mating system. We examined a potential fitness benefit resulting from the pre-spawning mate preference in Arctic charr Salvelinus alpinus, a salmonid fish with no parental care. The females were first allowed to discriminate behaviourally between two males presented to them in a free choice test. We then tested with controlled fertilizations whether the females would accrue indirect genetic benefits for their offspring, as measured by embryonic viability, if they had mated with the male they preferred. Both parental identities influenced offspring survivorship, but the females did not consistently prefer the male which gave her the higher reproductive success. Neither was the degree of male red breeding coloration associated with female preference or the observable genetic quality. In contrast, there was a negative relationship between female coloration and her offspring survivorship, suggesting a significant trade-off in resource investment between sexual ornamentation and reproduction. To conclude, the potential indirect fitness consequences arising from females’ pre-spawning mate preference seem to be negligible in early stages of development of Arctic charr. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611. ADDITIONAL KEYWORDS: carotenoid coloration – genetic quality – mate choice – maternal effects – salmonids. INTRODUCTION In general, mate choice has been considered an important evolutionary agent, and has a major influence on individual fitness (Andersson, 1994; Puurtinen, Ketola & Kotiaho, 2009). Owing to the disparity of *Corresponding author. E-mail: matti.janhunen@rktl.fi 602 reproductive inputs between sexes, females are generally predicted to be more selective of their mates than are males (Andersson, 1994; Reynolds, 1996). When there are no direct, material benefits available to females from mate choice, females should theoretically obtain indirect genetic benefits for mate choice to evolve (Tregenza & Wedell, 2000; Kokko et al., 2003; Nordeide, 2007). In such resource-free mating systems, female preference may be based on male © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 ARCTIC CHARR MATE PREFERENCE traits that signal heritable quality (e.g. additive ‘good genes’ effects), or alternatively on genetic compatibility (i.e. non-additive genetic benefits) (Tregenza & Wedell, 2000; Mays & Hill, 2004; Neff & Pitcher, 2005; Puurtinen et al., 2009). As far as the mate choice is predominantly based on ‘good genes’, females are expected to show congruence in their preference for sexually selected ornamental traits, which reveal the differences in individuals’ quality. In other words, genes of certain high-quality (and highly ornamented) males are expected to be good for all females (Møller & Alatalo, 1999; Hunt et al., 2004). Instead, genetic compatibility differs from mate choice for ‘good genes’ in that the variation in offspring viability should be dependent on how well the alleles from two parents function together (Tregenza & Wedell, 2000; Mays & Hill, 2004; Reid, 2007; Kekäläinen et al., 2009). As males are able to produce a large number of microgametes (sperm), they are likely to maximize their reproductive effort by mating as many times as possible (Bateman, 1948). Females, by contrast, have to expend more energy to produce more expensive macrogametes (eggs), and thus females can be expected to favour mate quality over quantity (Trivers, 1972). This also appears to be the case in most salmonid species for which the operational sex ratio in breeding systems is usually male-biased, and the total energy investment in gamete production is considerably higher for females than for males (reviewed by Fleming & Reynolds, 2004). Given that in many species males provide virtually no resources other than sperm, they are likely to be chosen mainly for indirect genetic benefits (e.g. Forsberg et al., 2007; Consuegra & Garcia de Leaniz, 2008). Nevertheless, it remains unclear to what extent female preference actually determines the outcome of reproduction in wild populations. In the brown trout Salmo trutta L., for example, females seem to choose their mates based on the male’s body size and/or on certain external structures (Petersson et al., 1999; Labonne et al., 2009), but this supposedly adaptive mating behaviour may be over-ridden in importance by male–male competition (Petersson et al., 1999; see also Petersson & Järvi, 2007). Furthermore, the sexual conflict theory suggests that the manipulative behaviour among males may rather be a hindrance than a help for inter-sexual mate choice (Moore et al., 2001; Wong & Candolin, 2005; Garner et al., 2010). Thus, the effects of female mate preference may often be manifested only when the confounding forms of reproductive competition are eliminated or controlled for (e.g. Bluhm & Gowaty, 2004; Anderson, Kim & Gowaty, 2007). In the lek-like breeding system of Arctic charr Salvelinus alpinus L., sexually mature individuals 603 aggregate at the spawning sites (Sigurjónsdóttir & Gunnarson, 1989; Figenschou, Folstad & Liljedal, 2004), and the most dominant (or largest) males tend to establish and defend territories frequently visited by females (Fabricius & Gustafson, 1954). The expression of mutual, yet sexually dichromatic carotenoidbased red breeding coloration is assumed to be a sexually selected attribute that may provide important information in mate choice (reviewed in Møller et al., 2000). Red intensity can, for example, be linked to immune function (Skarstein & Folstad, 1996) and milt characteristics (Måsvær, Liljedal & Folstad, 2004; Janhunen et al., 2009), but there is also somewhat controversial information on whether it is a useful indicator of individual condition and health state (Skarstein, Folstad & Rønning, 2005; Nordeide et al., 2008). To our knowledge, no one has tested the functional significance of breeding coloration in respect of assortative mating preference in this species. However, a recent crossing experiment demonstrated a positive relationship between paternal redness and offspring endogenous growth (Eilertsen et al., 2009), suggesting that red coloration may signal, at least in some males, the underlying genetic quality as well. In females, on the other hand, the allocation of carotenoid pigments occurs, in addition to their own body maintenance and skin coloration, also to their eggs (through the yolk) (Blount, Houston & Møller, 2000; Nordeide et al., 2008), which may further complicate the informative content and evolution of this ornament. Yolk carotenoids are known to be highly responsible for egg-quality maternal effects in fish (e.g. Torrissen, 1984; Ahmadi et al., 2006), and according to a recent study on Arctic charr, the carotenoid-mediated effects may have implications on phenotype for fitness in mothers and their offspring (Janhunen et al., 2010b). In this study, we present the results of two interrelated experiments. We first followed the prespawning behaviour of Arctic charr females in a simplified ‘free choice’ situation (a population-level preference test). Reproductively active females were provided an opportunity to choose between two nest sites, each of which was ‘guarded’ by a male in the cage. Use of a remote monitoring system and passive integrated transponder (PIT) tags enabled us to continuously track female visits in the vicinity of both prospective mates. First, our aim was to determine whether the females display a pre-spawning mate preference that is consistently associated with the male’s red spawning coloration when the potential social constraints, such as intra-sexual contests or male harassment of females, are eliminated. Second, we assessed with controlled fertilizations whether the observed, freely expressed mate preference is selectively advantageous to a female, i.e. yields genetic © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 604 M. JANHUNEN ET AL. benefits that are revealed via offspring’s enhanced viability during embryonic development. In other words, we were primarily interested in females that clearly preferred either of the two males, so that we could experimentally pair these females with preferred and non-preferred mates (maternal half-sibling broods) and test for offspring’s early survival differences between these individuals. The potential effects of parental coloration on offspring viability were also examined. MATERIAL AND METHODS STUDY FISH AND THEIR SAMPLING The studied Arctic charr originated from the Lake Inari population and represented a hatchery brood stock held at the nearby Sarmijärvi Aquaculture station (Finnish Game and Fisheries Research Institute; 68°47′N, 28°8′E), in north-eastern Finland. The experimental fish were 7 years old (year-class 2002) and derived from a rearing lot produced by tens of paired fertilizations (i.e. 22 wild-caught males and 26 first-generation hatchery females had been used as founding individuals). The fish were fed continuously (ad libitum) with carotenoid-rich salmonid food (Rehuraisio Emo-Vital; astaxanthin content 80 mg kg-1). The experiment was conducted following the principles of animal treatment and welfare for scientific experimentation according to permission given by the National Animal Experiment Board (Project licence: ESLH-2008-04178/Ym-23). Before the spawning period (14–15 September 2009), 32 females and 56 males were randomly selected among the maturing fish and anaesthetized with clove oil (10 mL L-1) for the measuring and tagging operations. The fish were measured for their total length (to the nearest 5 mm) and body mass (to the nearest 1 g) and were individually tagged with PITs (half duplex PIT-tags; Texas Instruments Inc., Dallas, TX, USA). The PIT-tags were surgically implanted through the belly skin into the body cavity of the fish. To improve the detection efficacy of females during the experiment, larger PITtags (32 ¥ 4 mm) were used for females than for males (23 ¥ 4 mm). Also, males were tagged for later identification. At this stage, the males were ranked by eye as ‘more colourful’ and ‘less colourful’ individuals, based on their abdominal red intensity, and accordingly they were also individually tagged with either yellow or beige Floy (T-bar anchor) tags (Hallprint Pty Ltd, Hindmarsh Valley, South Australia) mounted on the base of the dorsal fin. In order to have a quantitative measure of the abdominal coloration, the skin coloration of each male was quantified with a handheld Minolta CR-10 colorimeter (Konica Minolta Sensing Americas Inc., Ramsey, NJ, USA) on the left flank from two skin areas: behind the tip of the pectoral fin and above the anal fin. The instrument uses parameter values in the CIE 1976 L*a*b* colour system mode [CIE (International Commission on Illumination), 1986], where L* indicates the reciprocal difference between black and white, i.e. lightness (0–100), a* represents the difference between red (+a*) and green (–a*), and b* represents the difference between yellow (+b*) and blue (–a*). Furthermore, a calculatory definition of colour saturation (i.e. chroma) was obtained as follows: C* = (a*2 + b*2)0.5. The two values of this parameter were averaged to provide the assessment of colourfulness for each male. The C*-values (mean ± SD) of ‘more colourful’ and ‘less colourful’ males were 44.3 ± 4.8 and 30.3 ± 4.1, respectively, and this difference was also statistically significant (t-test, t = 11.76, P < 0.001, N = 56). C* was highly correlated with both a* and b* (Spearman’s rank correlation, r = 0.82 and 0.93, respectively, P < 0.001, N = 56, in both cases), and thus its value can be assumed to inform about the amount of carotenoid-based pigmentation in the skin (Hatlen, Jobling & Bjerkeng, 1998). The fish were allowed to recover from the markings for 1 day, after which they were transported to the Kainuu Fisheries Research station (Finnish Game and Fisheries Research Institute), Paltamo, central Finland (64°30′N, 27°10′E), where the experiments were performed. FEMALE PREFERENCE TRIALS The study was conducted in seven circular outdoor ponds made of concrete (bottom area 38.5 m2, water depth 60–80 cm; Fig. 1). There were two cages made of plastic-coated steel wire (160 ¥ 80 ¥ 70 cm, mesh size 13 ¥ 13 mm) in each pond, and an artificial spawning ground (hereafter referred to as a nest site) was placed in front of each cage. The nest sites were built of two shallow ‘bread boxes’, which were joined together (72 ¥ 55 ¥ 10 cm) and filled with spawnable substratum, i.e. gravel and cobbles. Earlier observations have clearly indicated that females find boxes and substratum suitable for spawning, i.e. dig nests in them (J. Piironen, pers. observ.). The cages and nest sites were positioned in each pond so that their reciprocal differences in terms of water flow conditions were minimal. A stationary PIT system detected females’ movements continuously between nests using one flat-bed antenna (a coil inductor loop) on each nest site. PVC-coated multistrand copper wire (4 mm2) was used for six loops for each antenna. The wire was strung through 32-mm PVC pipe. Each antenna was connected to a Texas Instruments tuning module which in turn was connected to a © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 ARCTIC CHARR MATE PREFERENCE Figure 1. Schematic picture of the experimental unit. (1) Water inlet, from which the water current was conducted to the experimental pond (2) along the exterior ring. (3) Water outlet. (4) A pair of spawning grounds (‘nest boxes’) equipped with circular PIT-antennae. (5) The cages for the males. reader with a twin-axial cable (105 W, length 10–50 m). The reader was constructed of reader and control modules. Readers were connected to two laptop computers with RS-232 cable through 8 ¥ RS port adapter in each. The system was configured to run and save (TIRIS datalogger programme, Citius Solutions Oy, Helsinki, Finland) ASCII data to computers simultaneously from seven antennas to each. The system logged detected tag IDs and date and time (nine times per second from each antenna) of detection from each antenna. Prior to the trials, the system was tuned and the comparability of the reading distances (c. 20 cm) within each antenna was verified. The observational trials were carried out in four consecutive periods during the spawning period of Arctic charr (26 October–12 November 2009). The trials comprised seven experimental units (ponds), in each of which one female and two males were held for about 4 days (90–96 h). The last observational period was reserved for the reuse of those females, from which we had not previously obtained reliable results (due to technical problems or the passivity of individuals), and then different male pairs were presented to each female from the previous time. The males used in the experiments had a mean length of 58.0 ± 3.0 cm (SD) (range: 52.0–64.0 cm) and mass of 605 3536 ± 742 g (range: 2065–5362 g). The females had a mean length of 62.0 ± 4.0 cm (SD) (range: 51.5– 69.5 cm) and mass of 3910 ± 991 g (range: 1874– 6169 g). The males within each pair were sizematched (a maximum difference in body length was 5%), but they belonged to different coloration categories, i.e. were previously ranked as ‘more colourful’ and ‘less colourful’ individuals. A male was placed in each of the two cages, after which a randomly assigned, ovulated female was put into the pond. The female was allowed to swim freely and inspect both males in their cages as well as the nest sites close to them. There was no physical contact between the three individuals, and moreover the opposite ends of the cages were covered with black plastic to prevent the males from seeing each other. Each time a female was detected on either nest, the identification code was relayed to a computer in the observation room and saved on an antenna-specific file with date and time stamps. After each trial, the recorded PIT-tag data were filtered and then summarized using a special software package (PIT-Data, N. Vuokko, 2007–2010, http://users.ics.tkk.fi/ntvuok/ rktl/). For each female, the seconds per minute spent in the detection range of each antenna were summed up for the entire observation period. Female preference for either male was interpreted on the basis of the overall time they were on each nest site. Finally, following the criteria of Drickamer, Gowaty & Holmes (2000) and Drickamer, Gowaty & Wagner (2003), only those cases for which the time ratio between the two antennae was 60:40 or more (in percentages) were used for further analyses [the average total time spent on the two nest sites was 315 ± 117 min (SE), N = 12 females]. IN VITRO FERTILIZATIONS AND INCUBATION After the behavioural trials, we tested, using a halfsib breeding design, whether female preference or male/female coloration is linked to offspring viability during incubation. The fertilizations were conducted in four sequential stages after each experimental period. The eggs of each female were stripped and divided into two portions. One portion was then fertilized with milt from the preferred male and the other one with milt from the non-preferred male, resulting in 12 maternal half-sib family pairs. In addition, seven extra half-sib family pairs were produced from females for which the mate preference result had remained unavailable. These extra families were included in the data set when we examined the effect of parental coloration on progeny traits. Excess quantities of milt were used to secure maximal fertilizations. The abdominal coloration of each parental fish (both males and females) was measured again as described previously. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 606 M. JANHUNEN ET AL. Following fertilizations, the swollen eggs from each family were divided into four batches of 100 eggs (N = 400 per family). Each batch was placed into an individual floating cylinder (depth 20 cm, diameter 10 cm) with plastic grid bottom. The cylinders were introduced into four, independent, circular 3.5-m2 rearing tanks with a flow-through water supply (water inflow c. 24 L min-1). Each family was thereby replicated once in each of the four tanks, resulting in 38 containers per tank. The temperature of the inflow water varied between 1.6 and 3.4 °C and oxygen level varied between 6.3 and 11.2 mg L-1 during the incubation period (from November 2009 to early April 2010). The number of dead eggs (i.e. those turning partially or completely white) was counted for the first time after about 1 week after the fertilizations [grand mean across all families = 3.1 ± 0.7% (SE), N = 38]. Thereafter, dead eggs were counted and removed weekly to minimize the risk of fungal infections. Offspring survivorship was assessed after the eggs in each container had developed visible eye pigmentation (3–13 February; post-fertilization degree-days c. 235 °C). The egg batches were then poured out at least twice from the incubators into a plastic cup at a height of 20 cm. After this mechanical standard treatment, the eggs that contained non-viable embryos could be recorded. The exact family-specific survival rates to eyed stage were then determined as the number (proportion) of remaining live eggs per replicate. Inferring from the low mortality rates at the start of the incubation, perhaps only a minor proportion of the total variation in this viability measure is attributable to variation in fertilization success (see also Johnston, 2002; Janhunen et al., 2011). STATISTICAL ANALYSES Wilcoxon’s signed-rank test was used to identify whether females consistently preferred, or spent more time (in total amount of seconds) on, the nest site close to a male classified as the more colourful (redder). A linear mixed model (REML procedure) was used to assess whether female mate preference or male coloration (ranked within pairs) affect offspring early survivorship. Here, the number of embryos surviving to eyed stage per replicate was used as a response variable. Female preference (preferred vs. non-preferred) or male coloration status (‘more colourful’ vs. ‘less colourful’) was included in the model as a two-levelled fixed factor and female identity and male identity (nested within female identity) as random factors. Fixed effect was tested using F-tests and random effects using likelihood ratio test. Finally, linear regression was used to determine whether female coloration could explain variation in offspring viability. The survival data were incorporated into the regression model by entering the grand means of females (obtained from two half-sib family means per female) against the average log-transformed C*-values. The possible confounding effect of female length proved to be insignificant in explaining variation in progeny survivorship (P = 0.951), and it was therefore excluded from the final regression model. The repeatability of family replicates was tested using AV Bio-Statistics software (A. Vainikka, http:// personal.inet.fi/koti/ansvain/avbs/). All other statistical analyses were performed using SPSS version 15.0, for Windows (SPSS Inc., Chicago, IL, USA). RESULTS FEMALE PREFERENCE EXPERIMENT Twelve females presented with two males in our mate preference trials provided an interpretable selectivity result, i.e. the overall time ratio they spent on the two nest sites was 60:40 or larger (range 60:40–98:2). Further, the observed time ratio was larger than 70:30 in ten cases. In each of the 38 males used in the crossings the saturation of red abdominal coloration was lower after the trials, compared with that measured in connection with tagging (a probable consequence of altered environmental conditions). The mean withinindividual decrease in the average C*-value was 32% (range 14–49%). As a consequence, the relative colour difference narrowed within 17 male pairs, although the previous within-pair rankings into ‘more colourful’ and ‘less colourful’ individuals remained unchanged. The mean within-pair difference in the C*-values was 8.9 ± 0.9 (SE) after the matepreference trials. Females did not consistently show a preference for the more colourful individual in male pairs (Wilcoxon signed-rank test: Z = -0.55, P = 0.583; N = 12). OFFSPRING VIABILITY We found large variation in offspring survival rates from fertilization to eyed stage across all families, although there was virtually no difference in the proportions of survived offspring from females mated with preferred males compared with offspring from females mated with non-preferred males (0.39 ± 0.27 and 0.41 ± 0.30, respectively; F1,11 = 0.49, P = 0.498; Fig. 2). Both parental identities contributed to progeny viability [female: c21 = 26.12, P < 0.001; male (female): c21 = 20.95, P < 0.001], but the independent effect of females appeared to be considerably larger than that of males (Fig. 2). We did not find a statistically significant difference between the survival rates of half-sibships sired by ‘more colourful’ and © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 ARCTIC CHARR MATE PREFERENCE Figure 2. The proportions of embryos survived to eyeembryo stage. The egg batches of each female (N = 4) were fertilized with sperm from a preferred male (black bar) and a non-preferred male (grey bar). Error bars indicate one standard error. Figure 3. The relationship between female red coloration (chroma, C*) and offspring’s early survival rates in Arctic charr (adjusted r2 = 0.181, P = 0.039). Survival values represent the grand means obtained from two maternal halfsib families. ‘less colourful’ males (F1,18 = 0.95, P = 0.34). Instead, the regression analysis revealed a negative relationship between female abdominal colourfulness (C*) and offspring survivorship (adjusted r2 = 0.181; F1,17 = 4.99, P = 0.039; Fig. 3). The family-specific replicates were highly comparable (repeatability, r = 0.97, F37,112 = 110.24, P < 0.001). DISCUSSION We did not find evidence that the pre-spawning mate preference of female Arctic charr was consistently 607 associated with the strength of male carotenoid-based breeding coloration, when social constrains, such as male–male competition and coercive and manipulative interaction between the sexes, were experimentally eliminated. Hence, the present study indicates that in our study population, male abdominal colourfulness (redness) was not the single most important signal predicting female preference, but there may be other traits, or perhaps combinations of them (multiple cues; see Candolin, 2003), that mattered as well. Based on the results of our crossing experiment, females did not gain apparent genetic benefits in the form of offspring’s early viability when they were paired with males they preferred versus with males they did not prefer. The saturation of red coloration in females, instead, showed a negative relationship with embryo survival, suggesting a significant trade-off in resource allocation between offspring and ornamentation. Mate choice experiments are often difficult to carry out reliably due to many potential problems that could affect and disturb animals in such situations. Furthermore, the use of female association preference as a proxy for female pre-spawning preference has been criticized (Wagner, 1998; Gabor, 1999; Shackleton, Jennions & Hunt, 2005). However, it has been recently demonstrated in fish that female preference in a dichotomous choice experiment, where the sexes are separated by a partition, actually is a good predictor of ultimate mate choice (Cummings & Mollaghan, 2006; Lehtonen & Lindström, 2008; Walling et al., 2010). In such laboratory-based experimental set-ups, the ornamental characteristics of the male have also been shown to be important determinants of female preference (e.g. Milinski & Bakker, 1990; Walling et al., 2010; Kekäläinen et al., 2010b). As we assigned males to preference tests at random with respect to other phenotypic traits besides body size (similar) and breeding coloration (divergent), we cannot further comment on the cue basis of the observed female preference. Although the importance of carotenoid-based signals in directional mate choice has been recognized in several vertebrate species (Møller et al., 2000), individual differences in mate preferences are highly probable (e.g. Lehtonen & Lindström, 2008). Furthermore, a female’s mate preference may be a very plastic character, varying in response to how a male’s attractiveness is dependent on his genetic quality in a particular ecological context (Qvarnström, 2001). For example, female preference for carotenoid coloration may be, to a great extent, environmentally induced, varying in respect of carotenoid availability (Grether et al., 2005). Our study fish originated from a culture environment, where the supply of dietary carotenoids is abundant. In such conditions, the association between red col- © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 608 M. JANHUNEN ET AL. oration and some components of male quality (e.g. foraging ability and parasite resistance) may be weak, and this in turn could have reduced the responsiveness of females to the carotenoid coloration of potential mates. Thus, the fact that we did not find preference for more colourful males could simply be due to the fact that females living in high-carotenoid environments are likely to put less emphasis on carotenoid coloration when choosing mates, in comparison with females living in low-carotenoid environments (see Grether et al., 2005). Furthermore, one of the possible explanations for individual, non-uniform preferences is that females tend to choose genetically compatible mates (Tregenza & Wedell, 2000; Ryan & Altmann, 2001). Offspring viability as an integral component of overall developmental success obviously involves multiple genes and hence is per se a complex quantitative trait that largely relies on parents’ compatibility (i.e. nonadditive effects within the genotype of the individual; see Wedekind, Müller & Spicher, 2001; Nordeide, 2007; Patton et al., 2007; Pitcher & Neff, 2007; Wedekind et al., 2008; Janhunen, Piironen & Peuhkuri, 2010; Kekäläinen et al., 2010c). Two independent crossing experiments on Atlantic cod Gadus morhua L. (Rudolfsen et al., 2005), and Chinook salmon Oncorhynchus tshawytscha Walbaum (Pitcher & Neff, 2007), for example, have demonstrated large variation in offspring survivorship due to interaction between males and females: an optimal mate selection had the potential to increase early survivorship by 74 and 19%, respectively. Neither of these studies could, however, associate offspring survivorship with male secondary sexual traits. Our present results also indicate that both female and male identity contribute to embryos’ chances of survival, even though the female effect was stronger than the male effect. Thus, a larger part of the observed variation among progenies was probably a result of maternal effects rather than direct genetic effects (see also Heath, Fox & Heath, 1999; Nagler, Parsons & Cloud, 2000; Kortet et al., 2004; Perry et al., 2004; Jacob et al., 2007). There were no differences between the half-sib families related to female mate preference or male coloration, suggesting that the potential fitness consequences (additive or non-additive genetic benefits) resulting from mate preference are perhaps less pronounced in the early stages of development in Arctic charr. However, our results are based on relatively small sample sizes and the experimental design was somewhat conservative, as we allowed the females to discriminate between only two males. If the number of available males per female had been larger, we might have increased a priori the probability of observing some differences, at least between the most preferred and least preferred ones. Interestingly, the variation in carotenoid coloration seems to be informative among females rather than males when predicting the reproductive success by the number of live offspring produced (see also Janhunen et al., 2011). The observed negative relationship between a female’s colourfulness and her offspring viability suggests that colourful females should be avoided as mating partners due to their lower fertility. A possible physiological basis for this is the pre-existing trade-off between ornamentation and eggs: the development of bright breeding coloration may reduce the availability of valuable carotenoid pigments (antioxidants) to developing embryos (Nordeide, Rudolfsen & Egeland, 2006; Nordeide et al., 2008), leading to a lower incubation success per brood. Egg carotenoids reduce the susceptibility of embryonic tissues to oxidative stress (Blount et al., 2000), and their positive effects on fertilization rate, early survival, and growth rates have been well documented in fishes (e.g. Torrissen, 1984; Salze et al., 2005; Ahmadi et al., 2006; Tyndale et al., 2008). In addition, a similar finding to our present results has also been made on another Arctic charr population (Janhunen et al., 2011), which strongly suggests that the female carotenoid-based ornamentation in this species may not have evolved independently (i.e. in accordance with the mutual sexual selection hypothesis; Kraaijeveld, KraaijeveldSmit & Komdeur, 2007), but it rather represents a maladaptive genetic correlation arising from sexual selection on male coloration (Lande, 1980; see also Nordeide et al., 2008; Janhunen et al., 2011). In summary, we applied an automatic PIT-tag detection system as a tool to observe the pre-spawning mate preference behaviour of female Arctic charr under captive conditions. Females’ freely expressed mate preference was not biased towards male carotenoidbased breeding coloration, which is perhaps not surprising given that directional preferences can often differ among individuals, be context-dependent (e.g. within-individual changes in preference may occur in response to changes in environmental or internal conditions; Wagner, 1998; Qvarnström, 2001; Lehtonen, Wong & Lindström, 2010), and act on more than only one phenotypic trait. Irrespective of the actual criteria used by individual females to express their preference, however, the corresponding matings did not involve an apparent fitness benefit. Although the early viability of offspring was largely attributable to the female parent (also involving the aspect of female ornamental coloration), we can expect a gradual strengthening in male-mediated effects (see Perry et al., 2004). Hence, depending on the magnitude of the maternal control through egg deposit, the indirect net fitness consequences connected with female mate preference and/or paternal sexual ornamentation might © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 602–611 ARCTIC CHARR MATE PREFERENCE appear only in later performance measures (e.g. Kekäläinen et al., 2010a) or under pathogen or parasite infections (Wedekind et al., 2001; Kekäläinen et al., 2009; Jacob et al., 2010). Further studies on the potential mechanisms and adaptability of female mate preference in the current and other Arctic charr populations are therefore needed. ACKNOWLEDGEMENTS This work was carried out with financial support from Jenny and Antti Wihuri Foundation (M.J.), the Finnish Game and Fisheries Research Institute (P.H., J.P., project no. 202501), and Academy of Finland (J.K., project no.121694; R.K., project no. 127398). 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