Donald Blomqvist

Genetic similarity between mates and extra-pair parentage in three species of shorebirds

Matings between close relatives often reduce the fitness of offspring, probably because homozygosity leads to the expression of recessive deleterious alleles. Studies of several animals have shown that reproductive success is lower when genetic similarity between parents is high, and that survival and other measures of fitness increase with individual levels of genetic diversity. These studies indicate that natural selection may favour the avoidance of matings with genetically similar individuals. But constraints on social mate choice, such as a lack of alternatives, can lead to pairing with genetically similar mates. In such cases, it has been suggested that females may seek extra-pair copulations with less related males, but the evidence is weak or lacking. Here we report a strong positive relationship between the genetic similarity of social pair members and the occurrence of extra-pair paternity and maternity (‘quasi-parasitism’) in three species of shorebirds. We propose that extra-pair parentage may represent adaptive behavioural strategies to avoid the negative effects of pairing with a genetically similar mate.

Nest site selection : a trade-off between concealment and view of the surroundings ?

For most birds, nest predation is the main cause of reproductive failure. Many species reduce predation by hiding their nests in vegetation. However, it is unclear whether they maximize cover around nests. Individuals may benefit also by keeping potential predators, food, and conspecifics in view, and selection of nest site may be a trade-off between concealment and visibility. We examined this idea in the Song Thrush Turdus philomelos, which builds cup-shaped nests in trees. For artificial nests, the risk of predation decreased when nests were more concealed within individual trees. However, Song Thrushes did not maximize concealment of nests within trees but selected intermediate concealment from the range of concealment available. The proportion of destroyed natural nests was not related to degree of nest concealment. Song Thrushes also selected patches of intermediate tree density, but tree density did not influence predation rate of artificial nests. These results are consistent with the trade-off hypothesis, which deserves more attention in future studies of nest site selection.

Do woodpecker finches acquire tool-use by social learning?

Tool–use is widespread among animals, but except in primates the development of this behaviour is poorly known. Here, we report on the first experimental study to our knowledge of the mechanisms underlying the acquisition of tool–use in a bird species. The woodpecker finch Cactospiza pallida, endemic to the Galápagos Islands, is a famous textbook example of tool–use in animals. This species uses modified twigs or cactus spines to pry arthropods out of tree holes. Using nestlings and adult birds from the field, we tested experimentally whether woodpecker finches learn tool–use socially. We show that social learning is not essential for the development of tool–use: all juveniles developed tool–use regardless of whether or not they had a tool–using model. However, we found that not all adult woodpecker finches used tools in our experiments. These non–tool–using individuals also did not learn this task by observing tool–using conspecifics. Our results suggest that tool–use behaviour depends on a very specific learning disposition that involves trial–and–error learning during a sensitive phase early in ontogeny.

Age-independent telomere length predicts fitness in two bird species

Telomeres are dynamic DNA‐protein structures that form protective caps at the ends of eukaryotic chromosomes. Although initial telomere length is partly genetically determined, subsequent accelerated telomere shortening has been linked to elevated levels of oxidative stress. Recent studies show that short telomere length alone is insufficient to induce cellular senescence; advanced attrition of these repetitive DNA sequences does, however, reflect ageing processes. Furthermore, telomeres vary widely in length between individuals of the same age, suggesting that individuals differ in their exposure or response to telomere‐shortening stress factors. Here, we show that residual telomere length predicts fitness components in two phylogenetically distant bird species: longevity in sand martins, Riparia riparia, and lifetime reproductive success in dunlins, Calidris alpina. Our results therefore imply that individuals with longer than expected telomeres for their age are of higher quality.

Parental quality and egg size affect chick survival in a precocial bird, the lapwing Vanellus vanellus

Abstract Effects of egg size and parental quality on lapwing Vanellus vanellus chick survival were studied in southwestern Sweden over 6 years. Chicks from large eggs were heavier at hatching and survived significantly better than those from small eggs. To control for the confounding effect of parental quality on egg size and chick survival, we performed a cross-fostering experiment during 2 years, exchanging clutches between nests with large and small eggs. In control clutches, chicks from large eggs survived better than those from small eggs, but we found no significant difference in chick survival between exchanged clutches. Thus, egg size did not affect chick survival independently of parental quality. Fledging success increased with parental age and/or experience, and with female body mass. Hence, both egg size and parental quality affect chick survival in the lapwing.

Sex differences in sand lizard telomere inheritance: paternal epigenetic effects increases telomere heritability and offspring survival

Background To date, the only estimate of the heritability of telomere length in wild populations comes from humans. Thus, there is a need for analysis of natural populations with respect to how telomeres evolve. Methodology/Principal Findings Here, we show that telomere length is heritable in free-ranging sand lizards, Lacerta agilis. More importantly, heritability estimates analysed within, and contrasted between, the sexes are markedly different; son-sire heritability is much higher relative to daughter-dam heritability. We assess the effect of paternal age on Telomere Length (TL) and show that in this species, paternal age at conception is the best predictor of TL in sons. Neither paternal age per se at blood sampling for telomere screening, nor corresponding age in sons impact TL in sons. Processes maintaining telomere length are also associated with negative fitness effects, most notably by increasing the risk of cancer and show variation across different categories of individuals (e.g. males vs. females). We therefore tested whether TL influences offspring survival in their first year of life. Indeed such effects were present and independent of sex-biased offspring mortality and offspring malformations. Conclusions/Significance TL show differences in sex-specific heritability with implications for differences between the sexes with respect to ongoing telomere selection. Paternal age influences the length of telomeres in sons and longer telomeres enhance offspring survival.

Ambient temperature effects on photo induced gonadal cycles and hormonal secretion patterns in Great Tits from three different breeding latitudes.

The present study determines how populations of Great Tits (Parus major) breeding in southern, mid and northern European latitudes have adjusted their reproductive endocrinology to differences in the ambient temperature during the gonadal cycle. A study based on long-term breeding data, using the Colwell predictability model, showed that the start of the breeding season has a high predictability ( approximately 0.8-0.9) at all latitudes, and that the environmental information factor (I(e)) progressively decreased from mid Italy (I(e)>4) to northern Finland (I(e)<1). The results indicate that integration of supplementary information, such as ambient temperature, with photoperiodic initial predictive information (day length), becomes progressively more important in maintaining the predictability of the breeding season with decreasing latitude. This hypothesis was verified by exposing photosensitive Great Tits from northern Norway, southern Sweden and northern Italy to sub-maximal photo-stimulatory day lengths (13L:11D) under two different ambient temperature regimes (+4 degrees C and +20 degrees C). Changes in testicular size, plasma levels of LH and testosterone were measured. The main results were: (1) Initial testicular growth rate, as well as LH secretion, was affected by temperature in the Italian, but not in birds from the two Scandinavian populations. (2) Maximum testicular size, maximum LH and testosterone levels were maintained for a progressively shorter period of time with increasing latitude, regardless of whether the birds were kept on a low or a high ambient temperature. (3) In birds from all latitudes, the development of photorefractoriness, as indicated by testicular regression and a decrease in plasma levels of LH and testosterone, started much earlier (with the exception for LH Great Tits from northern Scandinavia) when kept on +20 degrees C than when kept on +4 degrees C. The prolonging effects of a low temperature was more pronounced in Mediterranean birds, than in birds from Scandinavia, and more pronounced in Great Tits from southern Scandinavia than in Great Tits from northern Scandinavia. Ecological implications of the results are discussed, as well as possible impact of global warming on the breeding success of European Great Tits from different breeding latitudes.

Male aerial display and reversed sexual size dimorphism in the dunlin

Reversed sexual size dimorphism, with males smaller than females, is common in waders. The aerial display hypothesis suggests that sexual selection in males favours aerial agility, and hence small size, in species with male display flights. We tested this hypothesis in the dunlin, Calidris alpinaDisplay flights were uncommon in the early breeding season but increased markedly when females began laying. Male display areas were largely overlapping, and display flight seemed to be mainly an advertising signal to potential mates. Display rate, as well as proportion of time spent in aerial display, increased with decreasing male size. During aerial display, small males also performed costly hovering flights more often and for relatively longer than large males. These results support the aerial display hypothesis.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour

Trapped in the extinction vortex? Strong genetic effects in a declining vertebrate population

BackgroundInbreeding and loss of genetic diversity are expected to increase the extinction risk of small populations, but detailed tests in natural populations are scarce. We combine long-term population and fitness data with those from two types of molecular markers to examine the role of genetic effects in a declining metapopulation of southern dunlins Calidris alpina schinzii, an endangered shorebird.ResultsThe decline is associated with increased pairings between related individuals, including close inbreeding (as revealed by both field observations of parentage and molecular markers). Furthermore, reduced genetic diversity seems to affect individual fitness at several life stages. Higher genetic similarity between mates correlates negatively with the pairs hatching success. Moreover, offspring produced by related parents are more homozygous and suffer from increased mortality during embryonic development and possibly also after hatching.ConclusionsOur results demonstrate strong genetic effects in a rapidly declining population, emphasizing the importance of genetic factors for the persistence of small populations.

Habitat Selection and Diet of Lapwing Vanellus vanellus Chicks on Coastal Farmland in S. W. Sweden

1. Habitat use by colour-marked lapwing Vanellus vanellus broods was studied at three coastal farmland sites in S.W. Sweden from 1987 to 1990. 2. Initial brood movements between nest sites and home ranges used for chick-rearing varied between 7 and 332 m. At all sites, the proportions of habitats within lapwing home ranges differed from availability. Sea shore pasture was relatively the most used habitat. Lapwings selected home ranges with lower proportions of arable fields and moist pasture relative to sea shore pasture, and at two sites also to the shore, than expected if choice was due to availability. 3. Lapwing broods did not select feeding habitats in relation to availability. Feeding on sea shore pasture, and at one site also on the shore, occurred more frequently than expected relative to the use of arable fields and moist pasture. Foraging on the shore was constrained by variation in sea water level. Broods from nests on arable fields left the nest site habitat, and used the same feeding habitats as broods hatched on pastures. 4. Chicks fed on a wide variety of prey organisms, representing terrestrial, marine and freshwater invertebrates. Sampling of potential food supply suggested that numbers and biomass of invertebrates included in the chick diet were greater on a sea shore pasture than on an adjacent moist pasture. 5. Loss of important chick foraging habitats and isolation of nest sites and chick-rearing habitats, caused by changes in agricultural land use, have probably contributed to the decline of lapwings breeding on farmland in Europe. The results are related to conservation of this and other waders breeding on farmland.