Pekka T. Rintamäki

Inbreeding depression and male fitness in black grouse

The male lifetime lekking performance was studied, and related to inbreeding‐outbreeding in a wild population of black grouse (Tetrao tetrix) in central Finland between 1989 and 1995. Inbreeding was measured as the mean heterozygosity and mean d2 of 15 microsatellite loci. We found a significantly positive relationship between mean d2 and lifetime copulation success (LCS), while the relationship between heterozygosity and LCS was close to significant. We also found that males that never obtained a lek territory had significantly lower mean heterozygosity than males that were observed on a territory at least during one mating season in their life. Furthermore, among males that were successful in obtaining a lek territory, LCS and mean d2 were highest for those males that held central territories. We suggest that inbred males have a disadvantage (or outbred males have an advantage) in the competition for territories that may explain the relationships with LCS and inbreeding. Furthermore, the fact that mean d2 was positively correlated with LCS whereas heterozygosity was not when we restricted the analysis to territorial males, suggests that mean d2 provides more information about levels of inbreeding‐outbreeding than heterozygosity alone, and potentially highlights the effects of heterosis. To our knowledge, this is the first time that measures of inbreeding and lifetime fitness have been linked in a non‐isolated population. This is important in establishing that the relationships found in previous studies are not artefacts of low gene flow created by limited dispersal but a general feature of wild vertebrate populations.

Microsatellite markers reveal the potential for kin selection on black grouse leks

The evolution of social behaviour has puzzled biologists since Darwin. Since Hamiltons theoretical work in the 1960s it has been realized that social behaviour may evolve through the effects of kinship. By helping relatives, an individual may pass on its genes despite negative effects on its own reproduction. Leks are groups of males that females visit primarily to mate. The selective advantage for males to join such social groups has been given much recent attention, but no clear picture has yet emerged. Here we show, using microsatellite analysis, that males but not females of a lekking bird (the black grouse, Tetrao tetrix) are genetically structured at the lek level. We interpret this structuring to be the effects of strong natal philopatry in males. This has the consequence that males on any specific lek should be more related than expected by chance as indicated by our genetic data. Our results thus suggest that kin selection is a factor that needs to be considered in the evolution and maintenance of the lek mating system in black grouse and sheds new light on models of lek evolution.

Female choice selects for lifetime lekking performance in black grouse males

‘Good genes’ models assume that females can use a signal such as mating effort to assess a males lifetime fitness. Inferring long–term performance from short–term behavioural observations can be unreliable, and repeated sampling may be needed for more accurate assessment of males. Additionally, if sexual advertisement is viewed as a life–history trait subject to trade–offs, reliable comparison of mates should yield information on all life–history components rather than on one trait value in one season. We show that in the lekking black grouse (Tetrao tetrix), a males success is best explained by assuming that females are informed of the past history of males up to the beginning of the study (eight years). Much of this extremely lasting ‘memory’ can be attributed to females observing long–term outcomes of male–male competition: current territory position is the only momentarily observable variable that has high power in predicting female choice, and it correlates to a males past lekking effort on a cumulative lifetime scale. We conclude that females can use territory position as a signal that conveys information of a males lifetime performance that combines lekking effort and longevity. Females may thus overcome the problem of male allocations varying in time, without the need to pay costs associated with repeated sampling.

Testosterone and Male Mating Success on the Black Grouse Leks

On black grouse (Tetrao tetrix) leks females prefer dominant, viable males that have managed to acquire relatively central territories. The immunocompetence hypothesis predicts that, because high levels of testosterone are costly to the immune system, male sexual traits that are controlled by testosterone are likely to serve as reliable indicators of male health. Indeed, testosterone concentrations of black grouse males were highly variable, and strongly correlated with male mating success. This is related to the fact that males with high testosterone levels had most central territories. However, the association of testostestorone level with male mating success was not solely related to centrality. Indeed, the particularly strong correlation suggests a possibility for an important role of the immunocompetence hypothesis in this lekking bird species.

Mate sampling behaviour of black grouse females (Tetrao tetrix)

We studied female mate sampling behaviour in lekking black grouse (Tetrao tetrix). Females mainly visited males occupying territories in the centre of the lek with relatively large territories. They were also more likely to visit males that had high attendance. The same factors were also correlated with male mating success. A multiple regression model including these factors explained more of the variance in female visits per male (53%) than in mating success (33%). The pattern of female sampling conformed with a pool comparison (best-of-n) tactic. Such a tactic is expected if the costs of sampling are low. Females of high body mass visited more males than lighter females, however, which indicates that females may vary in their search tactics and suggests that there may be search costs. The existence of costs is further suggested by the fact that if the mate from a previous year was still present, females always mated with the same male in the following year. Though search costs were not measured directly, our findings suggest that some costs are negligible (e.g. energetic exhaustion or predation) whereas others (timing of mating) may be more important.

Paternity, copulation disturbance and female choice in lekking black grouse

Female copulation behaviour in the black grouse, Tetrao tetrix, was studied by detailed observations of individually marked birds together with DNA fingerprinting analyses for paternity assessment. For each breeding occasion females typically mated only once with one male, and did not mate outside the lek arena. They re-mated with the same or another male usually only if the initial copulation was disturbed and was probably unsuccessful in sperm transfer. The willingness of females to copulate only once with one male suggests that multiple mating with several males incurs a cost that more than outweighs any possible fertility or sperm competition benefits. Attempts by neighbouring males to disturb copulations were frequent, but only a small fraction of these were successful in terms of causing the female to re-mate. There was no tendency for females to redirect matings to the males that had disturbed them which also suggests that disturbance risk is not limiting female choice. However, risk of disturbance does increase the cost of female choice, and in that sense it will have some impact on mating decisions, in particular if the benefits of increasing choosiness are not great. ? 1996 The Association for the Study of Animal Behaviour

Lek Centre Attracts Black Grouse Females

In several lek mating systems, centrally located males enjoy higher mating success than peripheral males. The mechanism behind this pattern, however, has been controversial and a rigorous test of the different alternatives is missing. Here we report that in black grouse Tetrao tetrix, a lekking bird species, central males achieved many more copulations than males in the periphery. Generally, central territories were smaller than peripheral ones, and males were thus more clumped in the centre. A choice experiment in an aviary provided experimental support for females being attracted to densely clustered males, so that males in larger clusters have higher expected average mating success. Thus this mechanism, which was once the common belief for the lekking system but lately has been disregarded, is likely to provide the main explanation for the evolution of lekking in this species.

Assortative mating and female clutch investment in black grouse

Variation in female behaviour has only recently received attention in studies of sexual selection. It has been suggested that females may invest differentially in their offspring in relation to the quality of their mate. This may lead to females that mate with high-quality and/or attractive males laying larger clutches. Females may also differ in their ability to choose between males. For example, females in good physical condition may make better choices. If physical condition and clutch size are positively correlated, this hypothesis could also produce a relationship between male attractiveness and female clutch size. We found, in lekking black grouse, Tetrao tetrix, that females mated to the highest ranked males laid the largest clutches. Furthermore we found, regardless of female age, a positive relationship between a measure of female condition and male rank but not between female condition and her clutch size. In addition, females in good condition visited a larger number of different male territories, and old females produced the largest clutches. Our results suggest two mechanisms to explain our findings. First, females in good physical condition tend to mate with the top males, suggesting an assortative mating pattern. Second, females mating with the highest ranked males lay larger clutches as a consequence of their choice. In general, our result calls for caution in evaluating studies that look at the consequences of mate choice. It may be that differences in female quality produce effects that may be wrongly interpreted as male quality effects. (c) 1998 The Association for the Study of Animal Behaviour.

Why do Black Grouse males perform on lek sites outside the breeding season

Studies of sexual selection have focused mainly on explanations of how male characteristics influence mating success during the breeding season. By contrast, few studies have investigated how behaviours prior to the breeding season influence mate choice d

Female-female aggression and female mate choice on black grouse leks.

We studied female-female aggression in relation to female mate choice in black grouse, Tetrao tetrix, in central Finland, in 1994-1998. Aggression occurred on average every other minute when there was more than one female on a territory, and aggressive behaviour was most prominent when several females attended the lek. Interactions tended to be proportionally most frequent on the territories of the highest-ranking males, although not significantly so. Females that were chased by other females did not mate with lower-ranking males than their aggressors did. Furthermore, chased females were only rarely (6% of cases) forced to move off the territory by agonistic interactions and copulations were disrupted by other females even less often (3% of cases). The choice of a mating territory did not depend on the outcome of aggression even though the aggressors were more likely to mate on the territory where aggression occurred than elsewhere. There was a marginally significant tendency for aggressors to mate earlier in the season. Females placed themselves further away from other females on the territory when soliciting a copulation than just before aggression. Our results suggest that aggression between females does not effectively constrain female choice in black grouse. Its function may be to aid females to secure undisturbed mating opportunities for themselves rather than to prevent others from mating with a particular male. Copyright 2000 The Association for the Study of Animal Behaviour.