Helene M. Lampe

Low frequency of extra-pair paternity in pied flycatchers revealed by DNA fingerprinting

SummaryGenetic parentage of 135 nestlings from 27 broods of polygynous and monogamous pied flycatchers Ficedula hypoleuca was analyzed by means of multilocus DNA fingerprinting. The minisatellite probe alpha-globin 3′HVR detected approximately 12 scorable bands per fingerprint, and the proportion of bands shared between presumably unrelated adults averaged 0.22+0.08 SD. The fingerprints of 125 of the 135 nestlings made a complete match to those of their putative parents. In 4 nestlings a single mismatched band occurred, but since band sharing with both putative parents was high, the single mismatches were assumed to be caused by mutation. The 6 remaining nestlings had 5 or more mismatched bands each, low band-sharing proportions with their putative father and high band-sharing proportions with their putative mother. We thus conclude that they were all sired through extra-pair copulations (EPCs). Hence, only 4% of nestlings were sired through EPCs, and none resulted from intraspecific brood parasitism. One of the cuckolding males was identified, explaining all 5 mismatched bands in the nestlings fingerprint. Three of the illegitimate nestlings were from primary nests of polygynous males; 3 were from nests of monogamous males. The fact that many males in this study started to advertise for a second female in a distant territory several days before their first mate began egglaying, and still managed to secure almost exclusive paternity in their first brood, suggests that male polyterritoriality is not costly in terms of lost paternity. Common anti-cuckoddry tactics performed by male birds, like high rate of within-pair copulation and continuous mate-guarding thoughout the females fertilizable period, do not seem to be important in pied flycatchers.

QUIET SONG IN SONG BIRDS: AN OVERLOOKED PHENOMENON

ABSTRACT The theory of communication networks offers functional arguments for the evolution of unobtrusive signals in birds. The vulnerability of interacting conspecifics to predation and to eavesdropping by neighbours during both territorial disputes and courtship would select for short range signals such as the quiet songs of birds. In addition to suggesting contexts in which quiet songs should be used, we use our knowledge of the physics of sound transmission to make predictions about the physical structure of such songs relative to the well studied full songs. We present support for these predictions in six species where quiet singing has been observed.

Flycatcher song in allopatry and sympatry – convergence, divergence and reinforcement

The theory of reinforcement predicts that natural selection against the production of unfit hybrids favours traits that increase assortative mating. Whether culturally inherited traits, such as bird song, can increase assortative mating by reinforcement is largely unknown. We compared songs of pied (Ficedula hypoleuca) and collared flycatchers (F. albicollis) from two hybrid zones of different ages with songs from allopatric populations. Previously, a character divergence in male plumage traits has been shown to reinforce premating isolation in sympatric flycatchers. In contrast, we find that the song of the pied flycatcher has converged towards that of the collared flycatcher (mixed singing). However, a corresponding divergence in the collared flycatcher shows that the species differences in song characters are maintained in sympatry. Genetic analyses suggest that mixed song is not caused by introgression from the collared flycatcher, but rather due to heterospecific copying. Circumstantial evidence suggests that mixed song may increase the rate of maladaptive hybridization. In the oldest hybrid zone where reinforcement on plumage traits is most pronounced, the frequency of mixed singing and hybridization is also lowest. Thus, we suggest that reinforcement has reduced the frequency of mixed singing in the pied flycatcher and caused a divergence in the song of the collared flycatcher. Whether a culturally inherited trait promotes or opposes speciation in sympatry may depend on its plasticity. The degree of plasticity may be genetically determined and accordingly under selection by reinforcement.

Female Pied Flycatchers Prefer Males with Larger Song Repertoires

The evolution of secondary sexual male characteristics such as large song repertoires and bright plumage colour in birds, has been explained by sexual selection. In male pied flycatchers, Ficedula hypoleuca, song complexity correlates with phenotypic qualities like body condition and plumage colour. Here we show experimentally that females prefer males with larger song figure repertoires and more versatile song when given the choice between a male with a smaller repertoire and less versatile song and another male with a larger repertoire and more versatile song. Other male characteristics, like plumage colour, were similar in the two males. In the aviaries, the females started nest building with the male with the more complex song. We discuss potential benefits to females of choosing males with complex song.

Singing activity and song pattern of the Redwing Turdus iliacus during the breeding season

During spring in 1982 and 1983, 28 male Redwings Turdus iliacus were observed at Songli in Central Norway, from the time of arrival until most had completed reproduction. Function of song was studied by recording changes in singing rate and song structure throughout the breeding season. The singing rate of breeding males decreased significantly when egg-laying started, indicating that song might function in mate attraction and mate retention. Singing rate of individual males correlated positively with the number of simultaneously singing males, which suggests that the song may also function in competition between males. The seasonal variation of the introductory section of the song was negligible, whereas the terminating section became shorter after egg-laying or was omitted altogether.

Female-female aggression explains polyterritoriality in male pied flycatchers

Abstract Many male pied flycatchers, Ficedula hypoleuca , try to attract a second mate in a distant territory around the time their initial mate lays her clutch. In this study their success at becoming polygynous increased with the distance between the two territories. Two hypotheses may explain this result: either females are prevented from settling close to the males initial nest because of aggression from the initial female (the female aggression hypothesis), or males can more easily hide their mating status and deceive females into polygyny the further apart the nests are (the deception hypothesis). These hypotheses were tested by presenting a female in a cage near a males secondary nestbox during 3-h trials. (1) Females (and males) were able to locate and identify their mates a long distance from their own nests. (2) The males initial mate often visited the males secondary territory and (3) she was aggressive towards the caged female. (4) The proportion of initial mates visiting the males secondary territory decreased with the distance from their own nests. (5) The initial mates spent less time in the males secondary territory during their incubation periods than they did earlier on. (6) The already-mated males were more often absent from their secondary territories the further they were from their initial nests; this occurred despite the presence of the caged female. These results are most, consistent with the female aggression hypothesis.

POPULATION DIVERGENCE IN SEXUAL ORNAMENTS : THE WHITE FOREHEAD PATCH OF NORWEGIAN PIED FLYCATCHERS IS SMALL AND UNSEXY

Models of sexual selection suggest that populations may easily diverge in male secondary sexual characters. Studies of a Spanish population of the pied flycatcher, Ficedula hypoleuca, and a Swedish population of the closely related collared flycatcher, F. albicollis, have indicated that the white forehead patch of males is a sexually selected trait. We studied the white forehead patch of male pied flycatchers (n = 487) in a Norwegian population over seven years. Males with large forehead patches were in general more brightly colored, but patch height was not correlated to body mass, body size, or parasite loads. Conditions during the nestling period did not seem to influence patch height as an adult. Patch height increased slightly from the first to the second year as adults, but then remained relatively constant at higher ages. Patch height was not related to survival. Year‐to‐year changes showed that males who increased in patch height also increased in body mass, suggesting that expression of the forehead patch may be partly condition dependent. However, changes in body mass explained only a small proportion of the variance in patch height between males. Thus, patch height would not be a good indicator of male quality. Furthermore, patch size was also not related to male ability to feed nestlings, indicating that females would not obtain direct benefits by choosing males with large patches. However, patch height could be a Fisher trait, but this requires heritability and there was no significant father‐son resemblance in patch height. Comparisons of the males visited by each female during the mate sampling period indicated that chosen males did not have larger forehead patches than rejected males. Experimental manipulation of patch height did not affect male mating success. These results indicate that females do not use patch size as a mate choice cue. Finally, patch height did not predict the outcome of male contests for nestboxes, suggesting that the forehead patch is not an intrasexually selected cue of status. Norwegian pied flycatchers have smaller forehead patches than both Spanish pied flycatchers and Swedish collared flycatchers. We suggest that this pattern may be explained by the lack of sexual selection on the forehead patch in the Norwegian population as compared to the other populations, where the patch is apparently sexually selected. We discuss possible reasons for these population divergences, such as female choice on an alternative secondary sexual character (general plumage color) and speciation among Ficedula flycatchers.

Estimating the complexity of bird song by using capture-recapture approaches from community ecology

Repertoire size, the number of unique song or syllable types in the repertoire, is a widely used measure of song complexity in birds, but it is difficult to calculate this exactly in species with large repertoires. A new method of repertoire size estimation applies species richness estimation procedures from community ecology, but such capture-recapture approaches have not been much tested. Here, we establish standardized sampling schemes and estimation procedures using capture-recapture models for syllable repertoires from 18 bird species, and suggest how these may be used to tackle problems of repertoire estimation. Different models, with different assumptions regarding the heterogeneity of the use of syllable types, performed best for different species with different song organizations. For most species, models assuming heterogeneous probability of occurrence of syllables (so-called detection probability) were selected due to the presence of both rare and frequent syllables. Capture-recapture estimates of syllable repertoire size from our small sample did not differ significantly from previous estimates using larger samples of count data. However, the enumeration of syllables in 15 songs yielded significantly lower estimates than previous reports. Hence, heterogeneity in detection probability of syllables should be addressed when estimating repertoire size. This is neglected using simple enumeration procedures, but is taken into account when repertoire size is estimated by appropriate capture-recapture models adjusted for species-specific song organization characteristics. We suggest that such approaches, in combination with standardized sampling, should be applied in species with potentially large repertoire size. On the other hand, in species with small repertoire size and homogenous syllable usage, enumerations may be satisfactory. Although researchers often use repertoire size as a measure of song complexity, listeners to songs are unlikely to count entire repertoires and they may rely on other cues, such as syllable detection probability.

Song conformity and continuity in song dialects of Redwings Turdus iliacus and some ecological correlates

This study is based on the assumption that song sharing in neighbouring Redwings is advantageous in terms of genetic fitness. By calculating dispersal and immigration rates we also wanted to gain information about the timing of song learning and the causal background for the maintenance of local song dialects in this species. We recorded and analysed the song patterns of 304 Redwing males during three or four consecutive years in six populations in central Norway and Sweden. Data on breeding success, dispersal and immigration were collected for three of the populations. Although some males had two song types, most had only one. The frequency of two-type singers in the different areas did not correlate with the density of singing or breeding birds, nor with the extent of song sharing between birds, which differed considerably between areas. Song sharing did not correlate with the density of singing or breeding birds, but was positively correlated with breeding success. To explain this relationship we suggest that differences in age structure, onset of breeding in spring and nest predation are important. Sparsely populated areas and areas with high breeding success had a more stable song pattern from one year to the next than areas with higher density and lower breeding success, respectively. Colour-banding indicated that on average 17% of adults returned to the area in which they nested previously, whereas less than 1% of nestlings returned to the natal area. Thus, we suggest that the local nestling population contributed very little to the same breeding population in the following year, and that the longterm maintenance of a local dialect may be explained by the young males copying the song of the older males of the area in which they settle to breed in their first spring.

Selection on sperm morphology under relaxed sperm competition in a wild passerine bird

Theories regarding the role of sexual selection on the evolution of sperm traits are based on an association between pre-copulatory (e.g. female preference) and post-copulatory (e.g. ejaculate quality) male reproductive traits. In tests of these hypotheses, sperm morphology has rarely been used, despite its high heritability and intra-individual consistency. We found evidence of selection for longer sperm through positive phenotypic associations between sperm size and the two major female preference traits in the pied flycatcher, Ficedula hypoleuca. Our results support the sexually selected sperm hypothesis in a species under low sperm competition and demonstrate that natural and pre-copulatory sexual selection forces should not be overlooked in studies of intraspecific sperm morphology evolution.