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Microsatellites are DNA-fragments containing short repetitive motifs with 2-10 bp. They are highly variable in most species and distributed throughout the whole genome. It is broadly accepted that their high degree of variability is closely associated with mispairing of DNA-strands during the replication phase, termed slippage, although recombination is also observed. The aim of this study is to demonstrate evidence that non-reciprocal recombination processes changing the total genomic structure are common in microsatellites and flanking regions. We sequenced DNA fragments from birds in which microsatellites are located, and analyzed the structure of the microsatellites and their flanking regions. Additionally, other data and those from literature of three microsatellite regions of primates coding for the Ataxin-2, the Huntingtin and the TATA-box binding protein were analyzed. The structures of seven avian and three primate microsatellites support the hypothesis that non-reciprocal recombination is a common process that may also contribute considerably to the variation at microsatellite loci. We conclude that results of population genetic studies that are analyzed statistically with methods based on stepwise mutation models should be interpreted with caution if no detailed information on the allelic variation of microsatellites is available.

Genetic heterogeneity is considered an important parameter for individual fitness and reproductive success. In 1999 and 2000, we studied the population genetics of great tit (Parus major L., 1758) in southwestern Germany from two different forest types (deciduous and mixed-coniferous), which may significantly differ in prey diversity and/or food supply. Adults of 99 families were genotyped at four enzyme and eight microsatellite loci, in order to estimate individual heterozygosity. In the mixed-coniferous forest, a significant positive correlation between the genetic heterogeneity of females and early egg-laying date and clutch size was detected. Early egg-laying date and increased clutch size are conditions that positively affect the number of fledglings. This effect of individual heterozygosity was not observed in the deciduous woodland. Maternal genetic heterogeneity, however, did not correlate with fledgling condition, and individual heterozygosity of fathers had no impact on breeding success in either habitat. The positive effect of female genetic heterogeneity on brood size of great tits in mixed-coniferous forests is attributed to early egg-laying date, i.e. a maternal effect, rather than to a specific mating strategy that optimizes fitness through an increased brood size and the quality of offspring. Zusammenfassung Individuelle Fitness und reproduktiver Erfolg werden oftmals in einem engen Zusammenhang mit genetischer Heterogenitat gesehen. In den Jahren 1999 and 2000 untersuchten wir Kohlmeisenpopulationen (Parus major L., 1758) in suddeutschen Laub- und Nadelmischwaldern. Beide Waldformen konnen sich bzgl. der Futterdiversitat und Futterverfugbarkeit stark unterscheiden. Die Alttiere von 99 Familien wurden fur vier Enzym- und acht Mikrosatellitenloci genotypisiert, um die individuelle Heterozygotie abzuschatzen. Im Nadelmischwald fand sich eine signifikante positive Korrelation zwischen der individuellen Heterozygotie der Weibchen und Legedatum sowie Gelegegrose. Ein fruhes Legedatum und ein groseres Gelege haben einen positiven Effekt auf die Anzahl von Jungtieren. Ein solcher Effekt konnte im Laubwald allerdings nicht beobachtet werden. Weiterhin bestand kein Zusammenhang zwischen maternaler genetischen Heterogenitat und der Masse der Jungtiere, ebenso hatte die vaterliche genetische Heterogenitat in beiden Waldformen keinen signifikanten Einflus auf den Bruterfolg. Der positive Effekt mutterlicher genetischer Heterogenitat auf die Zahl der Nachkommen von Kohlmeisen im Nadelmischwald steht in engem Zusammenhang mit dem Legedatum, d.h. ein maternaler Effekt erklart eher die beobachteten Zusammenhange als eine spezifische Paarungsstrategie, die sich entwickelte und zur Fitnessoptimierung fuhrte.

Brood sex ratio was studied in 88 families of Parus caeruleus (blue tit) and 95 families of P. major (great tit) in deciduous and mixed forest habitats differing in food availability. As a food specialist, the blue tit is expected to be more sensitive to the nutritional differences between the habitats than a food generalist such as the great tit. A shift of brood sex ratio towards males was detected for great tits in the high quality habitat, but there was no significant impact of parental condition or the number of nestlings. In contrast, brood sex ratio of blue tits was not affected by habitat quality. In blue tits, male condition correlated positively with a male-biased sex ratio. Habitat quality, however, affected the body mass differences of male and female blue tit siblings, and nestlings developed differently. The low quality habitat had a negative effect on the sexual dimorphism of siblings in male-biased broods, and the condition of offspring was bad. Nevertheless, sexual dimorphism cannot explain the differences between great and blue tits with respect to the correlation of sex ratio and individual condition.

We choose the European Nuthatch (Sitta europaea), an extremely socially monogamous passerine species, to investigate the breeding biology and frequency of extra-pair activities of females. Breeding individuals live in strong pair bonds for their total life and defend their territory all year round. As a consequence of these narrow social bonds, nuthatches have to date been considered extremely sexually monogamous. Our genetic study, however, reveals a minimum of 10% of extra-pair young in 188 chicks from 32 broods in populations of southwestern Germany. Independently of the habitat type (high via low quality), most of extra-pair sires are identified as neighbouring territory holders.

Life-history theory predicts that parental effort in nestling provisioning is optimised in relation to the quality of individuals and/or their habitat. We studied the investment of breeding pairs of blue tits Parus caeruleus for their reproduction during three breeding seasons in deciduous (high quality) vs. mixed (low quality) habitats in order to quantify to what extent habitat quality affects parental effort. Parental effort (costs) was related to their feeding rates and flight distances during foraging. In the deciduous habitat flight distances between nest and foraging patch were shorter than in the mixed habitat (22 m and 40 m, respectively), but the feeding rates did not differ between the habitats. The total flight distance per breeding pair from the first day after hatching until the 17th day of the nestling period was about half of the distance observed in the mixed habitat (375 km and 674 km, respectively). As the quality of fledglings did not differ between habitats, the higher number of fledglings per brood reflects better rewards per foraging trip in the deciduous than in the mixed habitat. Considering the parental foraging effort (costs) and, the quality and number of offspring (benefits), the benefit-cost-ratio was 2–3 times higher in the deciduous than in the mixed woodland.

Huxley's rule predicts lower recombination rates in the heterogametic sex than in the homogametic one. The genotyping of Parus major and P. caeruleus families at 8 microsatellite and 4 enzyme loci yielded contradicting data. Significant genotypic disequilibrium was observed between esterase-1, esterase-2 and esterase-3 in adults of P. major and between esterase-2/esterase-3 and esterase-2/microsatellite PK-12 in P. caeruleus. Support comes from linkage analyses of nuclear families. In P. major, the recombination rate of esterase-2/esterase -3 in males is significantly lower than in females . The opposite is found for the recombination rates of esterase-1/esterase-2 and esterase-2/esterase-3 in P. caeruleus (EST-1/EST-2: , , EST-2/EST-3: , ). We conclude that the basis of differences in recombination rates cannot be heterogamety, per se, but must have multiple genetic causes including chromosomal rearrangments that have evolved after the cladogenesis of the two species.

Observations over a 14 year study revealed that Nuthatches had significantly higher breeding densities in a deciduous woodland than in coniferous-mixed woodland. However, the variability in breeding densities between years correlated in the two woodlands. In selecting a breeding site, birds may have to decide on different spatial scales. Possibly, these scales are reflected in a hierarchical series of decisions that might differ according to habitat quality. We correlated the frequency of nest box occupation by Nuthatches over 14 years with habitat parameters and PCA scores of different spatial scales (roughly 0.1 ha and 1 ha). In the coniferous-mixed woodland Nuthatches preferred similar habitat parameters at the small and the large scale like oaks, open areas and forest edge. In the deciduous woodland, however, a marked difference in habitat preference between small and large scale was shown: on the small scale parameters directly associated with nest box characteristics were significantly preferred. On the large scale only structural and floristic parameters associated with the general quality of the woodland were important for breeding site selection. Here tree stands with a superabundance of pine trees were avoided and the abundant oak trees were not important for the selection of a nest box. By further subdividing the very heterogeneous deciduous woodland into two parts, a stand of young trees and the rest of the woodland, opposing habitat choices could be shown. Thus scale effects of habitat choice are dependent upon habitat quality and heterogeneity.

Huxley's rule predicts lower recombination rates in the heterogametic sex than in the homogametic one. The genotyping of Parus major and P. caeruleus families at 8 microsatellite and 4 enzyme loci yielded contradicting data. Significant genotypic disequilibrium was observed between esterase-1, esterase-2 and esterase-3 in adults of P. major and between esterase-2/esterase-3 and esterase-2/microsatellite PK-12 in P. caeruleus. Support comes from linkage analyses of nuclear families. In P. major, the recombination rate of esterase-2/esterase -3 in males is significantly lower than in females (theta(male) = 0.076, theta(female) = 0.145). The opposite is found for the recombination rates of esterase-1/esterase-2 and esterase-2/esterase-3 in P. caeruleus (EST-1/EST-2: theta(female) = 0.218, theta(male) = 0.5, EST-2/EST-3: theta(female) = 0.109, theta(male) = 0.194). We conclude that the basis of differences in recombination rates cannot be heterogamety, per se, but must have multiple genetic causes including chromosomal rearrangments that have evolved after the cladogenesis of the two species.