Júlio Manuel Neto

Endangered subspecies of the Reed Bunting (Emberiza schoeniclus witherbyi and E. s. lusitanica) in Iberian Peninsula have different genetic structures

In the Iberian Peninsula, populations of two subspecies of the Reed Bunting Emberiza schoeniclus have become increasingly fragmented during the last decades when suitable habitats have been lost and/or the populations have gone extinct. Presently, both subspecies are endangered. We estimated the amount of genetic variation and population structure in order to define conservation units and management practices for these populations. We found that the subspecies lusitanica has clearly reduced genetic variation in nuclear and mitochondrial markers, has a drastically small effective population size and no genetic differentiation between populations. In contrast, the subspecies witherbyi is significantly structured, but the populations still hold large amounts of variation even though the effective population sizes are smaller than in the non-endangered subspecies schoeniclus. We suggest several management units for the Iberian populations. One unit includes subspecies lusitanica as a whole; the other three units are based on genetically differentiated populations of witherbyi. The most important genetic conservation measure in the case of lusitanica is to preserve the remaining habitats in order to at least maintain the present levels of gene flow. In the case of the three management units within witherbyi, the most urgent conservation measure is to improve the habitat quality to increase the population sizes.ZusammenfassungAuf der Iberischen Halbinsel wurden die Populationen von zwei Rohrammer-Unterarten Emberiza schoeniclus in den letzten Jahrzehnten, als geeignete Habitate verloren gingen und/oder Populationen ausstarben, zunehmend fragmentiert. Derzeitig sind beide Unterarten gefährdet. Wir schätzten die Höhe der genetischen Variation und die Populationsstruktur um daraus Einheiten für den Schutz und Managementpraktiken für diese Populationen zu bestimmen. Wir fanden heraus, dass die Unterart lusitanica eine deutlich reduzierte genetische Variation in nukleären wie mitochondrialen Markern, eine dramatisch geringe effektive Populationsgröße und keine genetische Differenzierung zwischen Populationen aufweist. Im Gegensatz dazu ist die Unterart witherbyi deutlich strukturiert, aber die einzelnen Populationen beinhalten immer noch große Anteile der Gesamtvariation, wenngleich die effektiven Populationsgrößen kleiner sind als die der nicht gefährdeten Unterart schoeniclus. Wir schlagen mehrere Management-Einheiten für die Iberischen Populationen vor. Eine Einheit beinhaltet die Unterart lusitanica als Ganzes; die anderen drei Einheiten basieren auf den genetisch differenzierten Populationen der Unterart witherbyi. Die allerwichtigste Schutzmaßnahme aus genetischer Sicht im Falle der Unterart lusitanica ist die Bewahrung der verbleibenden Habitate um zumindest das derzeitige Maß an Genfluss zu erhalten. Im Falle der drei Management-Einheiten der Unterart witherbyi ist die dringlichste Schutzmaßnahme die Verbesserung der Habitate um die Populationsgrößen zu erhöhen.

Phenotypic Divergence among West European Populations of Reed Bunting Emberiza schoeniclus : The Effects of Migratory and Foraging Behaviours

Divergent selection and local adaptation are responsible for many phenotypic differences between populations, potentially leading to speciation through the evolution of reproductive barriers. Here we evaluated the morphometric divergence among west European populations of Reed Bunting in order to determine the extent of local adaptation relative to two important selection pressures often associated with speciation in birds: migration and diet. We show that, as expected by theory, migratory E. s. schoeniclus had longer and more pointed wings and a slightly smaller body mass than the resident subspecies, with the exception of E. s. lusitanica, which despite having rounder wings was the smallest of all subspecies. Tail length, however, did not vary according to the expectation (shorter tails in migrants) probably because it is strongly correlated with wing length and might take longer to evolve. E. s. witherbyi, which feed on insects hiding inside reed stems during the winter, had a very thick, stubby bill. In contrast, northern populations, which feed on seeds, had thinner bills. Despite being much smaller, the southern E. s. lusitanica had a significantly thicker, longer bill than migratory E. s. schoeniclus, whereas birds from the UK population had significantly shorter, thinner bills. Geometric morphometric analyses revealed that the southern subspecies have a more convex culmen than E. s. schoeniclus, and E. s. lusitanica differs from the nominate subspecies in bill shape to a greater extent than in linear bill measurements, especially in males. Birds with a more convex culmen are thought to exert a greater strength at the bill tip, which is in agreement with their feeding technique. Overall, the three subspecies occurring in Western Europe differ in a variety of traits following the patterns predicted from their migratory and foraging behaviours, strongly suggesting that these birds have became locally adapted through natural selection.

Variation in body condition of breeding Savi’s Warblers Locustella luscinioides: the reproductive stress and flight adaptation hypothesis revisited

Current theory suggests that mass change in adult birds while breeding may be adaptive (to reduce wing-loading during nestling feeding) or result from physiological stress. To test which might be more important in determining mass loss in breeding Savi’s Warblers (Locustella luscinioides), we used a new approach in which the variation in four indices of body condition was described: weight, fat score, muscle score and lean weight (i.e. excluding fat and muscle). We expected weight variations to be adaptive if they involved changes in fat and lean weight, whereas physiological stress should influence the muscle score to a greater extent. As in other species, females showed a greater variation in weight, and carried more fat, than males during the breeding cycle. During incubation, females had greater weight and fat score than males. The weight remained constant and lean weight declined in both sexes, whereas females increased in muscle, which probably reflects the regression of the reproductive organs. During the nestling stage, both sexes declined significantly in all four indices of condition, showing evidence of physiological stress. However, the greater decline in weight in females than in males is consistent with the flight-adaptation hypothesis, as are the cyclic changes in lean weight associated with the various nesting attempts. The fact that both sexes declined significantly in weight, muscle and lean weight with an increasing number of nesting attempts, but not in fat, which was recovered after each nestling period, also indicates that both reproductive stress and adaptive changes occur during breeding. When the whole breeding season was considered, females showed a greater decline in muscle than males, which we interpret to be evidence for a greater reproductive stress in females. We suggest that the small breast muscle size and depleted protein reserves at the end of the breeding period might influence future survival through impaired flight ability and a compromised post-breeding moult.

Phylogeography of a Habitat Specialist with High Dispersal Capability: The Savi’s Warbler Locustella luscinioides

In order to describe the influence of Pleistocene glaciations on the genetic structure and demography of a highly mobile, but specialized, passerine, the Savi’s Warbler (Locustella luscinioides), mitochondrial DNA sequences (ND2) and microsatellites were analysed in c.330 individuals of 17 breeding and two wintering populations. Phylogenetic, population genetics and coalescent methods were used to describe the genetic structure, determine the timing of the major splits and model the demography of populations. Savi’s Warblers split from its sister species c.8 million years ago and have two major haplotype groups that diverged in the early/middle Pleistocene. One of these clades originated in the Balkans and is currently widespread, showing strong evidence for population expansion; whereas the other is restricted to Iberia and remained stable. Microsatellites agreed with a genetic break around the Pyrenees, but showed considerable introgression and a weaker genetic structure. Both genetic markers showed an isolation-by-distance pattern associated with the population expansion of the eastern clade. Breeding populations seem to be segregated at the wintering sites, but results on migratory connectivity are preliminary. Savi’s Warbler is the only known migratory bird species in which Iberian birds did not expand beyond the Pyrenees after the last glaciation. Despite the long period of independent evolution of western and eastern populations, complete introgression occurred when these groups met in Iberia. Mitochondrial sequences indicated the existence of refugia-within-refugia in the Iberian Peninsula during the last glacial period, which is surprising given the high dispersal capacity of this species. Plumage differences of eastern subspecies seemed to have evolved recently through natural selection, in agreement with the glacial expansion hypothesis. This study supports the great importance of the Iberian Peninsula and its role for the conservation of genetic variation.

Sex allocation in Savi's warblers Locustella luscinioides: multiple factors affect seasonal trends in brood sex ratios

Sex allocation theory predicts that whenever the relative fitness of sons and daughters differ, females should invest more in the sex with the greatest fitness return. In this study, we evaluated the influence of various ecological factors on the brood sex ratio (BSR) of Savi’s warblers (Locustella luscinioides) across several breeding seasons. There was a slight but significant female production bias at the population level, which is consistent with the ‘local resource competition’ hypothesis, as the breeding density is very high and females are more prone to disperse. We found that there was a significant decline in BSR during the breeding season, but no influence of male size, female size, social status nor extra-pair paternity were detected. The seasonal decline in BSR was further evaluated by assessing the within- and between-female effects, which indicated that multiple factors were operating simultaneously in our study population. First, there was a significant within-female decline in BSR, which was consistent with the decline in female condition due to the reproductive effort associated with multiple brooding (supporting the Trivers and Willard hypothesis). Second, a significant decline in BSR with the laying date of first clutches of different pairs indicated that male and/or female qualities are also associated with the seasonal variation in BSR. Finally, a comparison between the sex of the youngest nestling with the remaining ones did not suggest any bias, indicating that females do not compensate for the increased mortality of the last nestling (caused by asynchronous hatching) by producing a male from the last laid egg.

Autumn migration of Savi's Warblers Locustella luscinioides in Portugal: differences in timing, fuel deposition rate and non-stop flight range between the age classes

Capsule The autumn migration strategy of Portuguese Savis Warblers differs between age classes in timing, fuel deposition rate and flight range. Aims To describe the autumn migration strategy of Savis Warblers, and compare the age classes. Methods Data from 533 first captures and 149 retraps, held by the Portuguese Ringing Centre, were analysed, and potential non-stop flight ranges were estimated. Results Juveniles started migrating in early August whereas adults departed at the end of August and both vacated the breeding quarters in early October. In contrast to juveniles, adults showed a marked increase in mass and fat from the end of August and had a significantly greater fuel deposition rate. Accordingly, in adults, the average potential still-air flight range increased dramatically from 600 km in August to 1500 km in September, whereas in juveniles it remained approximately the same (about 150 km). The fattest adults had an average flight range of 2750 km, and so were able, theoretically, to reach the winter quarters without refuelling. Conclusions The autumn migration strategy of Portuguese Savis Warblers differs between age-classes in timing, fuel deposition rate and flight range. Adult Savis Warblers are time-selected migrants in autumn. The early departure of juveniles with smaller fuel stores is consistent with their lower fuel deposition rates, as expected under time-minimizing migration models, as is the fuel-overloading and by-passing of potential staging sites seen in adults. However, energy-selected migration cannot be excluded as a possible explanation for the juvenile migration pattern, as these birds left the breeding quarters with only enough fuel to reach the next staging site.

Song divergence between subspecies of reed bunting is more pronounced in singing styles under sexual selection

Song divergence between populations of a species can lead to reproductive isolation and speciation. However, birds may have different singing styles used in distinct social contexts, and songs of each style may change at different rates over time and space. Here, we tested whether song divergence between subspecies of reed bunting, Emberiza schoeniclus, differs with singing style, by comparing song traits of its three singing styles among three subspecies breeding in northern and western Europe. We show that the two singing styles under sexual selection (dawn and fast songs, related to obtaining extrapair and social mates, respectively) diverged significantly more than the slow songs (used as an all-clear signal to nest- attending social females). Multiple song traits differed significantly between the subspecies in all singing styles, with E. s. lusitanica generally being intermediate between E. s. schoeniclus and E. s. witherbyi, and the pattern of song complexity opposing the expected latitudinal gradient (of increasing complexity with increasing latitude). Cluster analyses of populations indicate that sexually selected singing styles are better for discriminating subspecies, describing a scenario of a major split in song features between the migratory, northern E. s. schoeniclus and the two resident, southern subspecies, rather than a clinal variation. The greater song divergence in fast and dawn singing styles suggests that sexual selection may be playing an important role in the incipient speciation of reed buntings. (Less)

Nest-site selection and predation in Savi’s Warblers, Locustella luscinioides.

Capsule Savis Warblers preferred sites dominated by high and dense Juncus and Rubus with thick litter, and avoided pure reeds; predation was higher in sites with less litter. Aim To describe nest-site selection and identify which habitat and nest features influence predation risk. Methods Comparisons were made between habitat characteristics measured at nest-sites and random points, and between predated and successful nests. Results Total vegetation cover, litter thickness, habitat type, undergrowth height and undergrowth cover, which were higher or denser at nest-sites, were the most important variables influencing the distribution of Savis Warbler nests. Nests were most often predated in sites with low litter thickness. Conclusion Savis Warblers are dependent on the presence of dense low vegetation and litter for nesting, which should be maintained close to or within reed-beds for their benefit.

Connectivity in Reed Warblers Acrocephalus scirpaceus Between Breeding Grounds in Europe and Autumn Stopover Sites in Iberia

We determined the degree of connectivity in the Eurasian Reed Warbler Acrocephalus scirpaceus between breeding regions in central and northern Europe and stopover sites in Iberia, during the autumn migration. We used both recovery data and wing length analyses to achieve this. Biometric data were obtained during 2009 at 11 sampling localities in Iberia, which we amalgamated into four major migratory areas within the region (Central, Western, Eastern and Southwestern Iberia, hereafter CI, WI, EI, SW). From the EURING database, we selected birds captured at their breeding sites in Europe and recaptured in Iberia during the autumn migration. Reed Warblers passing through WI had shorter wings than those in CI, EI and SW, suggesting that birds in WI migrated shorter distances, a fact also supported by recovery data. Although Reed Warblers showed some population overlap when passing through Iberia, we found that birds passing through EI and CI came from areas further to the east (continental Europe) than those passing through WI (mainly British Isles), thus supporting parallel migration. Reed Warblers tended to converge in southwestern Iberia, suggesting an effect of nearby geographical barriers.

Low frequency of extra-pair paternity in Savi's Warblers (Locustella luscinioides)

Although the frequency of extra-pair paternity (EPP) has been described for many species, the relative importance of the various contemporary and historical factors explaining EPP variation is still the subject of debate. In this study, we found 11 polymorphic microsatellite loci in the Savis Warbler (Locustella luscinioides), and used eight loci to analyze the paternity of 392 nestlings belonging to 102 broods of this little-known species. The frequency of EPP was 4.1% of nestlings and 5.9% of broods, which is surprisingly low given what is known about Savis Warblers life history and ecology, and among the lowest found of any socially-monogamous passerine bird. Comparisons with similar species indicate that this low frequency is unlikely to have been determined by the ancient evolution of life history strategies. Our observations suggest that the costs of engaging in extra-pair copulations might be high for the females. Larger males, particularly those with longer bill and tarsus, are more likely to be cuckolded; and the few possible comparisons between cuckolded males and extra-pair sires reveal a similar pattern. We further show that bill and tarsus lengths correlate with arrival date, which is associated with individual quality in many migratory bird species.