Peder Fiske

Spatial pattern of MHC class II variation in the great snipe (Gallinago media)

The genes of the major histocompatibility complex (MHC) code for proteins involved in antigen recognition and triggering of the adaptive immune response, and are therefore likely to be under selection from parasites. These selection regimes may vary in space and time. Here we report a strong geographical structure in MHC class II B genes of a migrating bird, the great snipe (Gallinago media). Genetic differentiation in the MHC between two ecologically distinct distributional regions (Scandinavian mountain populations vs. East European lowland populations) was still present after statistically controlling for the effect of selectively neutral variation (microsatellites) using partial Mantel tests. This suggests a role for selection in generating this spatial structure and that it represents local adaptation to different environments. Differentiation between populations within the two regions was negligible. Overall, we found a high number of MHC alleles (50, from 175 individuals). This, together with a tendency for a higher rate of nonsynonymous than synonymous substitutions in the peptide binding sites, and high Tajimas D in certain regions of the gene, suggests a history of balancing selection. MHC variation is often thought to be maintained by some form of balancing selection, but the nature of this selection remains unclear. Our results support the hypothesis that spatial variation in selection regimes contributes to the high polymorphism.

Major histocompatibility complex variation and mate choice in a lekking bird, the great snipe (Gallinago media)

Genes of the major histocompatibility complex (MHC) play a major part in the activation of the vertebrate immune system. In addition, they also appear to function as cues for mate choice. In mammals especially, several kinds of MHC‐dependent mate choice have been hypothesized and observed. These include choice of mates that share no or few alleles with the choosing individual, choice of mates with alleles that differ as much as possible from the choosing individual, choice of heterozygous mates, choice of certain genotypes and choice of rare alleles. We investigated these different aspects of mate choice in relation to MHC in a lekking bird species, the great snipe (Gallinago media). We found no evidence for MHC disassortative mating, no preference for males with many MHC alleles and no preference for rare alleles. However, we did find that some allelic lineages were more often found in males with mating success than in males without mating success. Females do not seem to use themselves as references for the MHC‐dependent mate choice, rather they seem to prefer males with certain allele types. We speculate that these alleles may be linked to resistance to common parasites.

Inferring local adaptation from QST–FST comparisons: neutral genetic and quantitative trait variation in European populations of great snipe

We applied a phenotypic QST (PST) vs. FST approach to study spatial variation in selection among great snipe (Gallinago media) populations in two regions of northern Europe. Morphological divergence between regions was high despite low differentiation in selectively neutral genetic markers, whereas populations within regions showed very little neutral divergence and trait differentiation. QSTu2003>u2003FST was robust against altering assumptions about the additive genetic proportions of variance components. The homogenizing effect of gene flow (or a short time available for neutral divergence) has apparently been effectively counterbalanced by differential natural selection, although one trait showed some evidence of being under uniform stabilizing selection. Neutral markers can hence be misleading for identifying evolutionary significant units, and adopting the PST–FST approach might therefore be valuable when common garden experiments is not an option. We discuss the statistical difficulties of documenting uniform selection as opposed to divergent selection, and the need for estimating measurement error. Instead of only comparing overall QST and FST values, we advocate the use of partial matrix permutation tests to analyse pairwise QST differences among populations, while statistically controlling for neutral differentiation.

Male mate choice, sexual conflict and strategic allocation of copulations in a lekking bird.

The males of lekking species are not expected to be choosy about mating because a reduced reproductive rate due to lost mating opportunities should outweigh any benefits of male choice. Females have traditionally not been expected to be competitive in this system since their reproduction has usually been assumed to be unconstrained by male availability. Here we show that, in contrast to these predictions, males are choosy and females may be competitive in the lekking great snipe Gallinago media. Males preferred by many females often refused to copulate with and even chased away females that the male had already copulated with, whereas females seemed to compete for repeated copulations. We conclude that choosiness may sometimes pay for popular males in those lekking species where females copulate repeatedly. Apparently, evolutionary conflicts of interest between individuals may cause a richer repertoire of behavioural adaptations than, to our knowledge, hitherto realized.

Mate sampling and copulation behaviour of great snipe females

Mate sampling by great snipe, Gallinago media, was studied by following individually marked females on their visits to two leks in five consecutive mating seasons. The main objectives were to determine whether the females used a sequential search or a best-of-N-males comparison when selecting a mating partner, and to evaluate the consequences of females engaging in copulations with more than one male and in repeated copulations with the same male. The minimum length of the period between the first observation of a female and her first observed copulation varied from 0 to 18 days (median 4). One to 10 males (median=2) were visited in the pre-mating period. Nineteen females (58%) mated on their first observed visit to the territory of a male, whereas 14 (42%) returned to a previously visited male to mate. Seven (21%) of the females were seen copulating on more than one night, and four of them changed copulation partner between nights. The fact that so many females were seen returning to a previously visited male to mate is best explained by a best-of-N-males comparison, but the results could also be explained by a sequential search strategy with a variable threshold. Females copulated more with successful males and they copulated more when other females were present on the territory of the male than when alone. Competition between females is most likely to account for these differences, but the mechanism is not known. The testes of great snipe males were large compared with those of other waders, indicating that sperm competition is important in this lekking species.

The costs of secondary sexual characters in the lekking great snipe (Gallinago media)

SummaryRecent studies of the lekking great snipe (Gallinago media) have shown that male mating success increases with display rate and the amount of white on the tail. An obvious question then arises: what is setting the limits to male display rate and to the evolution of even whiter tails? In this study the costs of these two traits are considered. In the case of the white on the tail, almost no predation was observed during the display period. However, predation on the winter grounds and/or during migration cannot be ruled out. Males differed in the amount of white on the tail between years. It is suggested that increasing the amount of white is costly, though the reason for this is still unknown. In the case of display rate, it is shown that predation cannot be a considerable cost, again because of the near absence of predation on the leks. Instead, it is shown that male displays are energetically costly. The daily energy expenditure of displaying males was estimated to be on average 4 times the basal metabolic rate, which is close to the supposed maximum sustainable work load for birds. Furthermore, males lost on average 1.8 g per h (1.7% of the body mass) which is about 7.2 g (6.8%) during a night of display activity. Males do gain some weight during the day when no displays are performed but loose on average 9 g during an 11-day period in the early part of the breeding season. These results indicate that high energetic demands set the limits to male display performance and that males do not have to trade off the benefit of attracting females by their displays against a cost of attracting predators.

Pushy males and choosy females: courtship disruption and mate choice in the lekking great snipe

We studied the effects of male disruptive behaviour on female mate choice and male mating success in the great snipe, Gallinago media, a lekking bird. Harassment from neighbouring males, a widespread behaviour in lekking animals, was the most prevalent cause of females leaving a male territory. Several lines of evidence show that females did not prefer to mate with males able to protect them from harassment. Males that obtained mating success were no less likely to suffer disruptions and females were no less likely to be disrupted when with their preferred male. Females returned to the male they later mated with, despite being repeatedly chased away by neighbours. The probability that an individual female returned and solicited mating from a male was 15 times higher for the male she was chased away from compared to the neighbour that chased her away. Females returned as often or more to the territory owner after being disrupted, compared to after leaving the territory without being harassed. Our results suggest that female great snipes are extremely choosy, but also that females do not gain direct benefits (harassment avoidance) by mating with certain males. Females appear to have neither direct nor indirect preferences for dominance that could give them such benefits: females appeared choosy despite, not because of, harassment. If females gain indirect benefits (genetically superior offspring) by being choosy, this is also likely to be unrelated to any dominance among males.

Direct and indirect mate choice on leks

Indirect mate choice is any behavior that restricts the individual’s set of potential mates without discrimination of mate attributes directly, for example, by having preferences about where to mate. We analyzed a 14‐year data set from great snipe (Gallinago media) leks for evidence of indirect mate choice based on relative and absolute position of lek territories. We found little or no effect of the centrality of territories on mating and no between‐year consistency in the spatial distribution of matings within leks. Instead, the probability of matings occurring at a particular site increased if the current territory owner had mated the previous year. Furthermore, individual females returned in later seasons to mate with the same male as previously rather than at the same site. Previous work found that male interactions and dominance do not control matings and that females are very choosy about which territory they mate in. Here we show that this is because of the male occupying the territory rather than its position. We therefore conclude that direct female mate choice is the main behavioral process affecting variation in mating success among great snipe males, unlike in some lekking mammals where male competition and/or indirect mate choice appears more important.

Female bluethroats prefer males with symmetric colour bands

Fluctuating asymmetry in male ornaments may be related to male quality and therefore may be used by females as a guide in mate choice. Experiments on different species have shown female preferences for symmetry, but few previous studies have addressed preferences for symmetry in coloration. Using the bluethroat, Luscinia s. svecicaa passerine with a conspicuous blue and chestnut throat patch, as a model species, we devised an experiment in which the females could choose between males with either symmetric or asymmetric coloured leg bands. The females associated more with symmetric than asymmetric males, indicating a preference for symmetry.

The Effect of Mating Probability on Risk Taking: An Experimental Study in Lekking Great Snipe

We model the relationship between mating probability and risk taking for lekking animals disturbed by predators. Our dynamic model is based on different mating probabilities among the lekking males and a decline in both predation risk and mating probability with hiding time after a predator attack at the lek. The model predicts that a lekking male with low expected mating probability should hide for a longer period after a predator attack than a male with high mating probability. It also predicts that males should hide for a longer period when predation risk is high and that a high mating advantage of a rapid return after an attack reduces the differences in optimal hiding time among males with different mating probabilities. To test the first prediction from the model, we have flushed great snipe (Gallinago media) males from leks and compared their hiding times to their temporary expected mating probabilities. As predicted by our model, males with the highest expected probabilities of mating had the shortest hiding times. Empirical data also showed that individuals adjusted their hiding time to temporary changes in their probability of mating. Such plasticity in mating behavior may reduce differences among males in lifetime reproductive success and thus also reduce the intensity of sexual selection.