Eight microsatellite loci characterised in the European blackbird, Turdus merula

Although the European blackbird, Turdus merula, is one of the most abundant and conspicuous songbirds of the Western Palaearctic and, as such, has been subject of numerous behavioural and ecological studies, there is to date no specific, PCR-based marker system for this species, and information on the applicability of genetic markers from other species or genera is scant. Here, we report the successful amplification of eight microsatellite loci in the European blackbird. We compared levels of polymorphism between groups of individuals sampled during the breeding season at different geographic localities (Heligoland Island, North Sea and Radolfzell, south-western Germany). We found high levels of polymorphisms, which enabled us to ascertain population membership of individuals. The properties of the tested microsatellite markers make them suitable for population genetic studies as well as for kinship analyses.     

Is urbanisation of European blackbirds (Turdus merula) associated with genetic differentiation?

Because of the extreme ecological and environmental changes along an urban–rural gradient, it has been proposed that urbanised and non-urbanised populations of the same species may be distinctly isolated. There is evidence that urban populations have become significantly different from the original forest populations in several aspects. However, little is known about the extent to which urban and non-urban populations are genetically isolated from each other. We tested the hypothesis of genetic differentiation by comparing the genomic DNA of an urban and a nearby forest-living European blackbird (Turdus merula) population. The present results suggest that, based on amplified fragment length polymorphism analysis, the urban population studied is very similar to a forest population at neutral genetic markers. Thus, despite indications of obvious functional genetic adaptation, the hypothesis of an overall genetic differentiation between our urban and forest populations could not be supported.Eberhard Gwinner died on 7 September 2004     

Modelling the recent and potential future spatial distribution of the Ring Ouzel (Turdus torquatus) and Blackbird (T. merula) in Switzerland

We present here a multiscale modelling approach to predict the current and future spatial distribution of Ring Ouzel (Turdus torquatus) and Blackbird (T. merula) in Switzerland. Species distribution models (SDMs) are applied on three different scales in order to analyse the scale-dependency of predictors that describe the species’ realised niche. While the models on the macro- and mesoscales (grid of 100 and 1 km², respectively) cover the entire country, our small-scale models are based on a small set of territories. Ring Ouzels occur at altitudes above 1000 m a.s.l. only, while Blackbirds occur from the lowlands up to the timberline. Although both species coexist on the macro- and mesoscales, a direct niche overlap on territory scale is rare. Small-scale differences in vegetation cover and structure seem to play a dominant role in habitat selection. On the macroscale, however, we observed a high dependency on bioclimatic variables that mainly represent the altitudinal range and the related forest structure preferred by both species. Applying the models to climate change scenarios, we predict a decline of suitable habitat for the Ring Ouzel with a simultaneous median altitudinal shift of 440 m until 2070. In contrast, the Blackbird is predicted to benefit from higher temperatures and expand its range to higher elevations. Based on the species distribution models we (1) demonstrate the scale-dependency of environmental predictors, (2) quantify the scale-dependent habitat requirements of Blackbird and Ring Ouzel and (3) predict the altitudinal range shift of both species as related to climate change scenarios.     

Radiotelemetrische Untersuchungen der Herzfrequenz singender Amseln (Turdus merula)

Zusammenfassung Die Herzfrequenz (HF) von 4 Amsel- wurde mit Hilfe radiotelemetrischer Techniken aufgezeichnet, während die Vögel Subsong oder Vollgesang äußerten. Die 3 Versuchsbedingungen waren: (1) Käfighaltung mit akustischem Kontakt zu anderen Amsel- und ; (2) Isolierte Käfighaltung in einem reflexionsarmen Raum, in dem Tonbandvorspielexperimente mit den Amseln durchgeführt wurden; (3) Haltung in einer Freivoliere. Die Äußerung von Subsong konnte von 3 verschiedenen HF-Verläufen begleitet sein: a) einer mit langfristigen Schwankungen einhergehenden deutlichen Akzeleration; b) einem gleichmäßig ruhigen und niedrigen HF-Verlauf; c) einer Dezeleration, die mit Beginn des Gesangsabschnittes abrupt einsetzte und mit Beendigung des Singens ebenso abrupt wieder endete. Vollgesang-Strophen konnten von 4 verschiedenen HF-Verläufen begleitet sein: a) einer reinen Akzeleration; b) einer abrupten Dezeleration; c) einer gleichmäßig ruhigen HF auf dem Niveau der Ruhewerte; d) einem biphasischen Verlauf. In den unterschiedlichen HF-Kurventypen drücken sich möglicherweise unterschiedliche Grade der physischen und/oder psychischen Belastung der Amseln während des Singens aus. Niedrigste Belastung, d. h. eine entspannte Situation, wird angenommen, wenn die HF niedrig und gleichmäßig ist. Erhöhte Anspannung scheint zu bestehen, wenn Dezelerationen auftreten. Bei noch höherer Belastung wird der Gesang von HF-Erhöhungen begleitet. Der Grad der physischen und/oder psychischen Belastung des singenden Vogels hängt wohl mit dem sozialen Kontext und den Umgebungsbedingungen zusammen. Abhängig von dieser Belastung ist möglicherweise die Funktion der Lautäußerungen auch jedesmal eine andere.

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Radiotelemetric measurements of heart rate in singing Blackbirds (Turdus merula)

Summary The heart rate (HR) of 4 male Blackbirds was monitored by means of radiotelemetry in subsong and full song phases of singing birds. Results were obtained under 3 experimental conditions: (1) caged birds in the presence of conspecific and ; (2) isolated caged birds in an anachoic chamber where playback experiments were conducted; (3) birds in an outdoor aviary. The singing of subsong could be related to 3 different types of HR curves: a) a marked acceleration combined with oscillations in longer cycles; b) a low and steady heart rate; c) a deceleration beginning abruptly with the onset of singing and ending abruptly when singing terminated. Strophes of full song were related to 4 kinds of HR curves: a) an acceleration; b) an abrupt deceleration; c) a steady HR on the level of the resting HR values; d) a biphasic course. The rather heterogeneous pattern of HR curves during singing suggests a hypothetic hierarchy related to motivation and function of certain song types. The low and steady curves express the lowest level, the decelerations a medium level and the accelerations the highest level of physiological strain or psychical tension. Strain and tension probably depend on the social context and the conditions in the birds' environment. The functions of the sounds may also differ and find expression in different modes of HR alterations.

     

Habitatpr?ferenzen, Dynamik der Raumnutzung und Bestandsstruktur bei Dorfamseln (Turdus merula)

Zusammenfassung In fünf Montandörfern bei Innsbruck/Tirol und zwei Probeflächen der Stadt wurde der Bestand der Amsel in 2 Winterhalbjahren und 2 bis 6 Brutperioden 1982–1987 untersucht. Die Siedlungsdichte nahm von bäuerlichen Dörfern höherer Montanlagen bis in Stadtbereiche Innsbrucks stark zu und zeigte deutliche Beziehungen zur Länge der Strauchschichtgrenzlinie in den einzelnen Probeflächen. Die Reviere waren sowohl in den städtischen als auch dörflichen Untersuchungsarealen sehr inhomogen verteilt. In den Dörfern wurden ältere Gartensiedlungen deutlich präferiert; zentrale Bauerndorfkerne waren am dünnsten besiedelt. Die Brutbestandsfluktuationen waren in zwei über 6 Jahre kontrollierten Dörfern insgesamt gering (9–15% Variationskoeffizient). Hingegen verdreifachte sich die Zahl der Amselreviere im Teilbereich eines Dorfes im Zuge zunehmender Durchgrünung von 1982 bis 1987. In der Nachbrutzeit gab es grundsätzliche Unterschiede in der Dynamik dörflicher und städtischer Amselpopulationen. Mit zunehmend urbanem Siedlungscharakter nahm offensichtlich nicht nur die Amplitude der saisonalen Bestandsoszillationen ab, sondern auch der Anteil von Standvögeln und insbesondere überwinternder Weibchen zu. Innerhalb der Dorflandschaften wechselte die Nutzungsintensität nahe benachbarter Teilareale kurzfristig und kleinräumig. Vor allem vom Herbst zum Winter waren Präferenzwechsel zwischen randlichen Gartensiedlungen und Obstanlagen und zentraleren, bäuerlichen Dorfbereichen auffällig.

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Habitat preferences and seasonal dynamics of space atilization in Blackbirds (Turdus merula) living in villages

Summary Between 1982 and 1987, habitat selection, seasonal changes in population densities and microspace use as well as fluctuations of breeding populations of the Blackbird were investigated in five mountain villages near Innsbruck, Tyrol. Results are compared with data from two city plots. The breeding density of Blackbirds increased dramatically (tenfold) from farmhouse dominated villages to suburbanlike village plots and to urban areas in the city of Innsbruck. There was a distinct relationship between the number of territories and the length of shrub layer boundaries. Remarkable differences in density existed between structurally different parts of the sample plots. These differences also correlated with the amount of vegetation cover available but were also related to other features of village subareas (e.g. density and character of buildings). The fluctuations of population levels within six years were surprisingly low in two villages (coefficients of variation 9 to 15%). In parts of one village, however, the number of blackbird territories tripled with an increase of the vegetation cover at the same time. In postbreeding season fundamental differences in the dynamics of village and suburban to urban populations were noticed. This is true for the amount of the population oszillations (lower with increasing urbanization) as well as for sex ratio in wintering populations (higher proportions of femals in suburban and city plots). Short-term shifts in habitat preferences were obvious within the village plots in the course of the year. Whereas orchards and older residential areas with rich shrub and tree layers at the village edges were heavily utilized by Blackbirds in autumn, the village centres were preferred in winter.

     

Sexual dimorphism of body size and shell shape in European tortoises

Adult body size and shape were examined in almost 1400 individuals of the tortoises Testudo graeca , T. hermanni and T. marginata from Greece. The size at maturity was greater in females than in males in all three species. Maximum and mean adult sizes were also greater in females than in males in T. graeca and T. hermanni . Males grew to a larger size than females in T. marginata , and mean adult size was similar in the sexes in this species. Sexual dimorphism of shape (adjusted for size covariate) was shown in most of the characters examined, and the degree of this dimorphism differed significantly among the three species. Differences were related to their contrasting courtship behaviours: horizontal head movements and severe biting in T. marginata , vertical head bobs and carapace butting in T. graeca , and mounting and tail thrusting in T. hermanni . There was no difference in the frequency of observations of courtship or fighting among the three species, but courtship was about 10 times more common than combat in males. All species showed greatest courtship activity in autumn; copulation was rarely observed in T. hermanni (only 0.36% of courting males) and not seen in the other species in the field. Observations made throughout the activity season indicated that feeding was equally common in males and females in all three species. Differences in shape were more likely to be the result of sexual selection than of natural selection for fecundity. Detailed predictions are made for sexual dimorphism of other characters in these species.     

Sexual size dimorphism in anurans

Several hypotheses have been proposed to explain the direction and extent of sexual size dimorphism in anurans (in which males are usually smaller than females) as a result of sexual selection. Here, we present an analysis to test the hypothesis that sexual dimorphism in anurans is largely a function of differences between the sexes in life-history strategies. Morphological and demographic data for anurans were collected from the literature, and the mean size and age in each sex were calculated for 51 populations, across 30 species and eight genera. Comparisons across 14 Rana species, eight Bufo species and across the genera showed a highly significant relationship between size dimorphism, measured using the female-male size ratio, and mean female-male age difference. A comparison of a subset of 17 of these species for which phylogenetic information was available, using the method of independent contrasts, yielded a similar result. These results indicate that most of the variation in size dimorphism in the anura can be explained in terms of differences in the age structure between the sexes in breeding populations. If sexual selection has an effect on size dimorphism in anurans, it is likely to be only a secondary one.     

Sexual size dimorphism and determination of sex in the Chough (Pyrrhocorax pyrrhocorax)

Summary 51 adult Choughs were sexed by their behaviour in NE Spain. The sexes clearly differ in body size. Two discriminant functions (DFA) allow sex determination with 100 % accuracy, irrespective of whether or not mass is used as a discriminant variable. These DFAs were applied to further 72 birds whose sex was assumed according to the size of the mate in each pair, this method reflecting a slight margin of error.

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Zusammenfassung Die Geschlechter von 51 adulten Alpenkrähen in NE-Spanien wurden nach ihrem Verhalten am Nest bestimmt. Ein deutlicher Größenunterschied zwischen Männchen und Weibchen ist erkennbar. Zwei Diskriminanzfunktionen erlauben eine Geschlechtsbestimmung mit einer Trefferquote von 100 %, unabhängig davon ob die Körpermasse als eine Variable eingeführt wird oder nicht. Die Diskriminanzfunktionen wurde auch für 72 Vögel angewendet, deren Geschlecht lediglich nach dem Größenunterschied der Partner eines Paares bestimmt worden waren. Hier gibt es einen kleinen Irrtumsbereich.

     

Sexual size dimorphism in parasitoid wasps

Sexual dimorphism in body length and proportion of overlap between the ranges of body length for males and females were estimated for 361 species of parasitoid wasps from 21 families. In most species, females are generally larger than males, though the range of male and female sizes overlap. Species in the family Ichneumonidae differ significantly from species in other families in three ways: (1) ichneumonids on average are larger, (2) in most species, females are generally smaller than males, and (3) on average, proportion overlap between the ranges of body length for males and females is greater. At present, there is a paucity of life history data on parasitoid wasp species for which size dimorphism is known. Thus it is not clear why ichneumonids differ from species in other families. Possible evolutionary explanations for variation in dimorphism among parasitoid wasp species are discussed.     

Sexual dimorphism of tooth size in anthropoids

We have examined the size of the canine and postcanine teeth of cebid and catarrhine primates in relation to each other, to jaw size and to body weight. We have found that the canine size of males is large enough to be limited by jaw shape and size. A large contribution of P4 to the postcanine row is associated with smaller canines in males. Neither factor seems to limit canine size in females. The females of a small number of species possess enlarged canines. Much of the variation of the postcanine row can be described by the ratio of the (nominal) crown areas of M1 to M3. This ratio is monomorphic which conforms with the general lack of dietary dimorphism in primates. A brief discussion of the evolution of canine size is offered with a new suggestion to account for canine reduction in male hominids.     

Sexual size dimorphism in the evolutionary context of facultative paedomorphosis: insights from European newts

Background  

Sexual size dimorphism (SSD) is a key evolutionary feature that has been studied in many organisms. In a wide range of species, this pattern is more complex because of polymorphism within each sex. However, it is not known whether the magnitude and direction of SSD could be affected by alternative developmental trajectories within sexes. Our aim was to test whether an intrasexual polymorphism, facultative paedomorphosis (a process in which the development of somatic and gonadal tissues differs in alternative morphs), could affect SSD variation patterns in European newts.     

Sexual size dimorphism in Asian colobines revisited

Asian colobines exhibit a wide range of sexual dimorphism in body mass. Some species are monomorphic, whereas others are strongly dimorphic. Strong sexual dimorphism is generally viewed as the consequence of intense male contest competition over access to mates, but this idea appears not to explain variation in sexual dimorphism in Asian colobines. Our results show that modular colobines, i.e. species in which social units aggregate into higher‐level bands or often associate, have significantly higher levels of sexual dimorphism in body mass than the nonmodular ones. This finding was corroborated by means of phylogenetically controlled methods and multiple regression analyses. The results suggest that living in a modular society intensifies the contest competition among males, which is further exacerbated by the continuous presence of all‐male units. Am. J. Primatol. 71:609–616, 2009. © 2009 Wiley‐Liss, Inc.     

Sexual size dimorphism in parasitic oxyurid nematodes

As in many invertebrates, female oxyurids are larger than male. Sexual size dimorphism (SSD) of oxyurid nematodes (the hosts of which are both invertebrate and vertebrate), is investigated regarding body size of both host and parasite. SSD of parasites appeared to be weakly, but not significandy, correlated with invertebrate and vertebrate host body size. However, this study reveals a different pattern for SSD with respect to either type of host. SSD does not increase in tandem with body size in vertebrate parasites either at the level of species or genus. SSD is much more pronounced in Syphaciidae than in Heteroxynematidae, two families of vertebrate parasites exhibiting different modes of transmission (members of the Syphaciidae are transmitted through perianal contamination). SSD is investigated in one monophyletic group of parasites of primates, for which a phylogeny is known. Independent comparisons method is used and we find that the body size of female parasite is strongly correlated with that of the male. The hypoallometry (slope<1) of the relationship suggests that the SSD is not linked to an increase of parasite body size. Moreover, there is no influence of host body size on parasite SSD. The pattern in parasites of invertebrates is different. First, SSD has been found to increase with parasite body size in two groups of invertebrate parasites: the oxyurids of Dictyoptera and Coleoptera. Second, female body size of invertebrate parasites is not correlated with male body size either at genus or species level. Finally, the evolution of SSD is discussed in relation to the demographic patterns of invertebrate parasites and the haplodiploid mode of reproduction of these parasitic nematodes.     

Sexual size dimorphism and sexual selection in primates

1. In most animals, females are larger than males. Paradoxically, sexual size dimorphism is biased towards males in most mammalian species. An accepted explanation is that sexual dimorphism in mammals evolved by intramale sexual selection. I tested this hypothesis in primates, by relating sexual size dimorphism to seven proxies of sexual selection intensity: operational sex ratio, mating system, intermale competition, group sex ratio, group size, maximum mating percentage (percentage of observed copulations involving the most successful male), and total paternity (a genetic estimate of the percentage of young sired by the most successful male).
2. I fitted phylogenetic generalised least squares models using sexual size dimorphism as the dependent variable and each of the seven measures of intensity of sexual selection as independent variables. I conducted this comparative analysis with data from 50 extant species of primates, including Homo sapiens, Pan troglodytes, and Gorilla spp.
3. Sexual dimorphism was positively related to the four measures of female monopolisation (operational sex ratio, mating system, intermale competition, and group sex ratio) and in some cases to group size, but was not associated with maximum mating percentage or total paternity. Additional regression analyses indicated that maximum mating percentage and total paternity were negatively associated with group size.
4. These results are predicted by reproductive skew theory: in large groups, males can lose control of the sexual behaviour of the other members of the group or can concede reproductive opportunities to others. The results are also consistent with the evolution of sexual size dimorphism before polygyny, due to the effects of natural, rather than sexual, selection. In birds, the study of molecular paternity showed that variance in male reproductive success is much higher than expected by behaviour. In mammals, recent studies have begun to show the opposite trend, i.e. that intensity of sexual selection is lower than expected by polygyny.
5. Results of this comparative analysis of sexual size dimorphism and sexual selection intensity in primates suggest that the use of intramale sexual selection theory to explain the evolution of polygyny and sexual dimorphism in mammals should be reviewed, and that natural selection should be considered alongside sexual selection as an evolutionary driver of sexual size dimorphism and polygyny in mammals.

     

Sexual size dimorphism and Rensch's rule in Canidae

The size variation between males and females of a species is a phenomenon known as sexual size dimorphism (SSD). The observed patterns of variation in SSD among species has led to the formulation of Rensch's rule, which establishes that, in species showing a male size bias, SSD increases with an increase in the body size of the species. However, for species in which there is a female size bias, the SSD would decrease when the body size of the species increases. In the present study, we examined the variation in body size and SSD of 33 species of canids from estimates of body mass and body length. We studied its relationship with life‐history characteristics and tested Rensch's rule using phylogenetic generalized least squares and phylogenetic reduced major axis regressions, respectively. We observed the existence of correlation between body mass and body length, although the SSDs from these estimators are uncorrelated. SSD did not show the pattern predicted by Rensch's rule. SSD also did not show any correlation with life‐history traits. It is likely that the low SSD observed in canids is related to the monogamy observed in the family, which is a rare situation in mammals.     

Sexual size dimorphism in three North Sea gadoids

Existing biological data on whiting Merlangius merlangus, cod Gadus morhua and haddock Melanogrammus aeglefinus from a long‐term international survey were analysed to address sexual size dimorphism (SSD) and its effect on their ecology and management. Results show that SSD, with larger females of the same age as males, is a result of higher growth rates in females. A direct consequence of SSD is the pronounced length‐dependent female ratio that was found in all three gadoids in the North Sea. Female ratios of the three species changed from equality to female dominance at specific dominance transition lengths of c. 30, 35 and 60 cm for M. merlangus, G. morhua and M. aeglefinus, respectively. An analysis by area for M. merlangus also revealed length dependence of female ratios. SSD and length‐dependent female ratios under most circumstances are inseparable. Higher overall energy demand as well as a higher energy uptake rate must result from the observed SSD and dimorphism in growth rates. Potential processes related to feeding, locomotion and physiology are proposed that could balance the increased energy investment of females. Potential consequences of SSD and length dependency of female ratios are the reduction of the reproductive potential of a stock due to size‐selective fishing and biased assessment of the true size of the female spawning stock that could distort decisions in fisheries management.     

Sexual size dimorphism and male combat in snakes

Summary This paper reviews published literature on snakes to test the hypothesis that large male size, relative to female size, evolves because of the advantage it confers in male combat. Analysis of the data reveals a high correlation between the occurrence of male combat, and sexual dimorphism in which the male is the larger sex. This correlation holds (i) within the total sample of snake species (n=224), (ii) within the family Colubridae (n=134), and (iii) in a comparison between the eight families of snakes for which data are available. These results strongly support the hypothesis that large male size is an adaptation to intrasexual competition. The analysis also shows that females are larger than males in about 66% of snake species, that male combat is known in only about 15% of species, and that both sexual size dimorphism and the incidence of male combat tend to be distributed along taxonomic lines.