Low frequency of extra-pair fertilizations in the Great Tit Parus major revealed by DNA fingerprinting

Multilocus DNA fingerprinting was used to estimate the frequency of extra-pair fertilizations in a low density, island population of Great Tits Parus major. A total of 69 pairs and 516 offspring from 82 breeding attempts were examined. Only 18 offspring (3.5%) in seven different nests were not fathered by the attending male. The sample included one brood in which all nine chicks were fathered by an extra-pair male. One chick from a nest of eight was the result of intra-specific brood parasitism. Three chicks from a brood of nine could be matched with the male but not with the female. Observations at this nestbox suggested that mate switching had occurred during the laying period. The percentage of extra-pair fertilizations did not differ between first clutches and (experimentally induced) replacement clutches. Females mated to small males were more likely to have extra-pair young in the nest. Because both extra-pair paternity and intraspecific brood parasitism are rare in this population, a reliable measure of reproductive success can be obtained by counting the number of offspring. [KEYWORDS: Intraspecific brood parasitism; mixed reproductive strategies; conspecific nest parasitism; eastern bluebirds; genetic similarity; female preference; sperm competition; hatching failure; sexual selection; tree swallows]

Sexing birds using random amplified polymorphic DNA (RAPD) markers

We used random amplified polymorphic DNA (RAPD) markers to sex birds from small tissue (usually blood) samples. Arbitrarily chosen 10-mer PCR primers were screened with DNA from known-sex individuals for the production of a bright female-specific band. Suitable primers were found for seven bird species after screening about 30 primers (range 2-63), and no primer was found for three other species after screening about 50 primers for each species. Investigations into the reliability of RAPD markers for sexing great tits Parus major and oystercatchers Haematopus ostralegus show that: (i) when PCR reaction conditions for great tit DNA are varied, either the presence of the female-specific band correctly predicts the individual's sex or no DNA amplification occurs; (ii) the female-specific band in great tits can be sequenced,and subsequently amplified using specific PCR primers; (iii) null alleles of the female- specific fragment occur at an estimated frequency of 0% (n = 241 females) in great tits and 0.6% (n > 290 females) in oystercatchers; (iv) the female-specific fragment in great tits occurs in individuals from a wide geographical range encompassing two subspecies; and (v) the relative intensity of bands in great tit RAPD banding profiles is consistent across individual birds and scorers. The RAPD primers that we have identified are generally species specific, and the consequent time cost of screening for primers is the chief disadvantage of using RAPD markers to sex birds. However, with large sample sizes this disadvantage is outweighed by the relative technical simplicity and low cost of the technique. [KEYWORDS: birds; DNA isolation; null alleles; PCR; RAPD markers; sex determination Arbitrary primers; genetic-markers; w-chromosome; identification; pcr; ratios]

Opposite differential allocation by males and females of the same species

Differential allocation (DA)—the adjustment of an individual’s parental investment in relation to its mate’s attractiveness—is increasingly recognized as an important component of sexual selection. However, although DA is expected by both sexes of parents in species with biparental care, DA by males has rarely been investigated. We have previously demonstrated a decrease in the feeding rates of female blue tits Cyanistes caeruleus when their mate’s UV coloration was experimentally reduced (i.e. positive DA). In this study, we used the same experimental protocol in the same population to investigate DA by male blue tits in relation to their female’s UV coloration. Males mated to UV-reduced females had higher feeding rates than those mated to control females (i.e. negative DA). Thus, male and female blue tits display opposite DA for the same component of parental effort (chick provisioning), the first time that this has been reported for any species.

Great tit hatchling sex ratios

The sex of Great Tit Parus major nestlings was determined using PCR RAPDs. Because this technique requires minute amounts of DNA, chicks could be sampled soon (0-2d) after hatching, before any nestling mortality occurred. The proportion of males among 752 chicks hatching in 102 broods (98.9% of those that hatched) increased with hatching date from 42.4% male in first broods (n=555 chicks) to 50.9% male in second broods (n=167). The proportion of males among hatchlings also decreased with increasing clutch size and increased with increasing hatching asynchrony. These three variables are intercorrelated and it was not possible to separate them statistically. Hatchling sex ratio was not correlated with the age, weight or wing-length of either of the parents, brood size at hatching or fledging, hatching or fledging success, mean chick weight, or position in the hatching sequence. The functional significance of the sex ratio variation found is unknown. [KEYWORDS: Red-winged blackbirds; lesser snow geese; egg sequence; parus-major; seasonal-variation; size; identification; consequences; mortality; dispersal]

Parental behaviour is unrelated to experimentally manipulated great tit brood sex ratio

Parental investment may be biased with respect to parental sex or offspring sex or there may be an interaction between parental and offspring sex. We investigated whether any of these types of bias occurred in great tits, Parus major. By sexing chicks using random amplified polymorphic DNA (RAPD) markers and subsequently moving chicks between broods, we were able to manipulate broods early in the nestling period to give all-male, mixed-sex and all-female broods. Provisioning behaviour (total feeding rate, proportion of feeding visits by the male, prey size, visit duration and proportion of visits in which a faecal sac was removed) was measured for broods aged 8- 9 and 11-12 days. Nest defence behaviour was measured for 15- day-old broods. Parental weight, the occurrence of second broods and overwinter survival of the parents were also analysed, There were some differences in parental care between the parents: males made the majority of feeding visits and were more vigorous in nest defence. However, there was no evidence that parental care varied in relation to brood sex ratio. or that there was an interaction in parental tare between parental sex and brood sex ratio. (C) 1998 The Association for the Study of Animal Behaviour. [KEYWORDS: Red-winged blackbirds; parus-major; statistical power; zebra finches; offspring sex; selection; consequences; competition; allocation; dispersal]

Parental care and UV coloration in blue tits: opposite correlations in males and females between provisioning rate and mate’s coloration

Parental investment and sexually-selected signals can be intimately related, either because the signals indicate the amount of investment that an individual is prepared to make, and hence its value as a mate (the ‘good parent process’), or because individuals are selected to vary their own investment in relation to their mate’s signals (‘differential allocation’ or ‘reproductive compensation’). Correlations between parental investment and the sexually selected signals of both an individual and its mate are therefore of central interest in sexual selection. Blue tits Cyanistes caeruleus are an ideal study species to investigate such correlations because they provide substantial amounts of biparental care and possess sexually-selected structural UV coloration that seems to signal attractiveness in both sexes. We investigated whether feeding rates of male and female blue tits were correlated with either their own or their mate’s UV coloration, and whether any such correlation was affected by the sex ratio of the brood. We also investigated whether any such correlations were reflected in offspring phenotype. Feeding rates were not correlated with either sex of parent’s own UV coloration. However, they were correlated with the mate’s UV coloration, but in opposite directions in males and females: females had higher feeding rates when mated to bright UV males, implying differential allocation, while males had lower feeding rates when mated to bright UV females, implying reproductive compensation. These relationships were unaffected by the sex ratio of the brood. In addition, fledgling tarsus length, but not mass, was related to male UV coloration, and to female UV coloration in interaction with male age. These results suggest that both male and female attractiveness influence parental investment of the mate, and that this in turn affects offspring phenotype. We found no evidence for differential sex allocation.

Microsatellite loci in the European bee-eater, Merops apiaster

Twelve polymorphic microsatellite markers have been developed for the European bee-eater, Merops apiaster (Coraciiformes: Meropidae). Screening of eight individuals at these loci showed that the average allelic diversity was 5.8, with a range of two to 11 alleles per locus. The loci reported here will provide insight into the levels of extra-pair parentage, kin selection and dispersal in this species, which has co-operative breeding and nests in large colonies. [KEYWORDS: bee-eater Coraciiformes Meropidae Merops apiaster microsatellite]

Parental correlates of offspring sex ratio in Eurasian Oystercatchers

We investigated hatchling and fledgling sex ratios in Eurasian Oystercatchers (Haematopus ostralegus) using random amplified polymorphic DNA markers. The overall hatchling (53% males, n = 374 hatchlings from 177 broods) and fledgling (49% males, n = 51) sex ratio did not differ significantly from unity. Hatchling and fledgling sex ratios were not correlated with laying date, clutch size, brood size, egg-laying sequence, territory quality male age, or male breeding experience, but hatchling sex ratio was positively correlated with age and breeding experience of females (0.05 < P < 0.075, n = 71). Older females produced more sons irrespective of the position of the offspring in the egg-laying sequence. Fledging mass was not correlated with female age, so the Trivers and Willard (1973) hypothesis is unlikely to explain our results. Sons dispersed less than daughters, so the local resource competition hypothesis of Clark (1978) might apply. The adaptive significance of a male-biased sex ratio in clutches produced by older females is speculative because the costs and benefits of dispersing versus philopatric offspring to parents and offspring are largely unknown. [KEYWORDS: Local resource competition; haematopus-ostralegus; monogamous oystercatcher; reproductive success; territory quality; paternal age; birds; selection; population; helpers]

Sexual size dimorphism in the critically endangered Seychelles Scops Owl Otus insularis

The Seychelles Scops Owl Otus insularis is a critically endangered species restricted to the forests of Mahé in the Republic of Seychelles, Western Indian Ocean. This study presents the first biometric data collected from live individuals and investigates the occurence of sexual size dimorphism. Thirty-one birds were measured, and 30 of these were sexed by molecular analysis of their DNA: 6 females and 24 males. Females were generally heavier and larger than males. There was some variation in plumage colouration, which was unrelated to sex, but no evidence of distinct colour morphs as has been documented in other Western Indian Ocean Otus species.