David T. Parkin

An Association between Fertility and Cuckoldry in the House Sparrow, Passer domesticus

DNA fingerprinting of 183 broods of house sparrows and their attendant adults revealed that 13.6% of nestlings were unrelated to the attendant male. The occurrence of cuckoldry was unaffected by male age and experience, pair bond duration or time within a breeding season. However, cuckoldry was significantly more frequent in broods that included some infertile eggs. This study suggests that sperm competition can be strongly influenced by the fertility of the cuckolded male, and that females may benefit from extra-pair copulation as an insurance against their mate’s infertility.

Single-locus DNA fingerprinting reveals that male reproductive success increases with age through extra-pair paternity in the house sparrow (Passer domesticus)

Single-locus profiles produced with four cloned minisatellites were used to investigate the paternity of 44 house sparrow nestlings sired through extra-pair copulations. Comparison of the paternal alleles with a profile database of 144 candidate males resulted in 33 paternity assignments to 13 males. Both age and proximity were related to success in cuckoldry. Males achieving extra-pair paternity were usually breeding near to the cuckolded pair. Those at least two years old sired significantly more young through extra-pair matings, resulting in an average reproductive output 36% higher than that of yearlings. Whereas older males gained extra-pair fertilizations during their own breeding attempts, yearlings only achieved extra-pair success outside their own breeding cycle and did not significantly increase their own reproductive success. In contrast to other species in which extra-pair males are apparently chosen for their high quality, male sparrows siring extra-pair young were cuckolded at the same rate as other males.

Sexual dimorphism in house sparrow eggs

Abstract Recent evidence has revealed an apparently high degree of control by female birds over the physiological aspects of their reproduction and offspring sex allocation, consistent with adaptive hypotheses of sex allocation and differential investment in their offspring. In the house sparrow, we investigated possible mechanisms that may be used by females to enhance the fitness returns from a reproductive effort. Using molecular techniques, we demonstrate that house sparrow eggs containing male embryos are significantly larger than those containing female embryos. We also found that male embryos were laid randomly with respect to laying order. We speculate that this sexual dimorphism of eggs is adaptive, because male house sparrows show greater variance in condition-dependent reproductive success than females. More important, the result provides further evidence of the ability of females to detect or control ovulation of either male or female ova and to differentially invest in one sex over the other.

The Effects of Habitat Fragmentation on Demography and on the Loss of Genetic Variation in the Red Squirrel

A major problem in conservation biology is the extent to which the loss of genetic variability in isolated populations reduces their chance of survival. We present data in which the loss of genetic diversity in small and isolated populations can be directly related to population dynamics. Genetic similarity in red squirrels is inversely correlated with population size. The loss of genetic variation and the lower population densities in isolated populations are both the result of reduced immigration. Our data suggest that population processes rather than genetic problems are the real threat to small squirrel populations.

Extra-pair fertilizations and paternity defence in house martins,Delichon urbica

Abstract DNA fingerprinting showed that 15% of 62 house martin nestlings at study colonies in central Scotland were not related to their putative fathers, and 32% of 19 broods contained at least one extra-pair chick. There was no evidence of intraspecific brood parasitism. Birds were never seen to mate outside nests in the vicinity of nesting colonies, and the single copulation that was observed during this study was a pair mating that took place inside a nestbox. Extra-pair birds were often seen to enter nests, with seven of eight identified intruders being males from other nests where laying had already taken place. Pair males mate guarded by ensuring that females spent very little time alone at the nest from about 7 days before the first egg of the clutch was laid, and by accompanying females on up to 70% of flights away from the nest during the 4-5 days before laying commenced. Mate guarding seemed to slacken after egg laying began, with a gradual transition to incubation behaviour taking place. Associated with this was a higher likelihood that the youngest nestling would be fathered by an extra-pair male. Male removal experiments indicated that extra-pair birds were more likely to enter the nest of a fertile female when the pair male was absent, but in three cases where DNA fingerprints were obtained male removal during the fertile period of the pair female had no apparent influence on paternity.

Within-clutch patterns of egg viability and paternity in the House Sparrow

One of the potential benefits of extra-pair copulation is an enhanced likelihood of successful fertilization if the pair male is unable to produce sufficient viable sperm to ensure the fertility of an entire clutch. Low male fertility can be a transient phenomenon associated with higher rates of sperm usage than production, leading to a progressive depletion of sperm reserves. Evidence of a correlation between hatching success and the occurrence of extra-pair fertilizations has been reported in House Sparrows. In this study we have used single-locus minisatellite and microsatellite profiling to investigate the distribution of extra-pair fertilizations within House Sparrow broods to determine whether there are changes in the level of hatching failure or extra-pair paternity during the course of producing a clutch. Embryonic material was collected at mid-incubation to minimize loss of data through pre-sampling mortality and to ensure that laying order was known. A significant clustering of both infertile eggs and extra-pair young was noted in the earliest eggs in a clutch. Possible causes of this phenomenon are discussed.

No evidence for extrapair fertilizations in the merlin revealed by DNA fingerprinting

Broods of young merlins were compared with the adults in attendance at their nest by DNA fingerprinting. No offspring were found that mismatched genetically suggesting that intraspecific brood parasitism and extrapair fertilization are very rare in this population. The results are discussed in the light of the Paternity Assurance Hypothesis.

Genetic differentiation and rates of evolution in some introduced populations of the House Sparrow, Passer domesticus in Australia and New Zealand

Samples of House Sparrows have been taken from endemic populations in Britain and south-western Europe, and introduced populations in Australia and New Zealand.The genetic structure of the samples has been determined at a series of loci by electrophoresis.The differentiation between the British and European material is consistent with a rate of evolution of 10−7 electrophoretically detectable amino acid substitutions per locus per year over the two thousand years since the colonisation of the British Isles.The Australian and New Zealand populations show a higher rate of differentiation, but this can be explained by a similar rate of evolution combined with a succession of population bottlenecks during the years immediately following their introduction.

Fluctuating Asymmetry and Body Size as Indicators of Stress in Red Squirrel Populations in Woodland Fragments

1. In large parts of Europe, red squirrels (Sciurus vulgaris) live in fragmented woodlands, where populations are small, and dispersal rate and genetic diversity are reduced. These small populations are, therefore, likely to have been exposed to substantial environmental and/or genetic stress. Fluctuating asymmetry (FA) represents a measure of the sensitivity of development to stress. 2. We examined the expression of FA in the hind foot (a non-sexually selected trait) of live-caught squirrels from two large and six small populations, of which we had data on population density, reproductive rate and genetic variation. 3. Red squirrels in woodland fragments were smaller and had a slightly higher degree of FA than squirrels from large forests. In fragments, heavier squirrels tended to have lower degrees of FA and reproducing females were less asymmetric than non-reproducers. Both relationships indicate that, in small populations, FA increased in poor quality individuals. 4. Interpopulation variation in the mean level of FA, however, could not be correlated with genetic similarity or with woodland quality. We conclude that FA in the hind foot of red squirrels is too variable to be a useful indicator of stress differences between populations.

The variability of DNA fingerprints in three species of swan

The genetic variation in three species of swans was examined by DNA fingerprinting. Human minisatellite probes detected a number of highly variable fragments in the restriction digests of total nuclear DNA. Assuming bands to be independent, the average allele frequency for minisatellite loci was 0·154, 0·154 and 0·109 for Mute, Whooper and Bewicks Swans, respectively. The pattern of band-distribution showed a certain degree of species-specificity, so that the fingerprints may reflect taxonomic affinities of the species. Pedigree analysis of a single family of Mute Swans showed that most of the variable fragments were inherited in a simple Mendelian fashion, allowing the relatedness of the individuals to be determined. DNA fingerprinting potentially provides a large number of genetic markers for studying the behavioural ecology, population genetics and evolution of swans.