Fiona M. Hunter

Extra-pair paternity and intraspecific brood parasitism in wild zebra finches Taeniopygia guttata, revealed by DNA fingerprinting

SummaryThe frequency of extra-pair parentage in a wild population of zebra finches Taeniopygia guttata was examined by DNA fingerprinting. A total of 25 families, comprising 16 pairs of parents and 92 offspring (in broods of 1 to 6) were examined. Ten cases of extra-pair parentage, presumed to constitute intraspecific brood parasitism, were detected (10.9% of offspring or 36% of broods), including one possible instance of ‘quasi-parasitism’ (parasitism by a female fertilized by the male nest owner). The average number of parasitic eggs per clutch detected by fingerprinting was 1.10±0.32 SD, very similar to the one egg difference in average clutch size between parasitised (6.0±0.82) and unparasitised nests (5.0±0.95). Two cases of extra-pair paternity (EPP) were detected among 82 offspring whose maternity was confirmed: 2.4% of offspring, or 8% of broods. In both cases EPP accounted for only a single offspring within a brood. Behavioural observations show that EPP occurs through extra-pair copulation rather than rapid mate switching. The results are discussed in the light of what is known about the fertile period and sperm precedence patterns in this species.

Sperm competition in the zebra finch, Taeniopygia guttata

Abstract Extra-pair copulation is known to occur in zebra finches in the wild and the aim of this study was to examine several aspects of sperm competition in domesticated zebra finches breeding in captivity. Female zebra finches are fertile between day −11 and +3 (where day 0=the day the first egg is laid). Pair copulation occurs about 12 times per clutch, peaking on day −1 and decreasing markedly after day 0. Copulation was most frequent in the first hour of the morning. Copulation behaviour of zebra finches breeding in groups in an aviary differed from that of single pairs in cages in that copulations were often disrupted in the aviary, and multiple pair copulations occurred in the aviary but not in cages. Extra-pair courtship was common in the aviary and extra-pair copulation was observed. All extra-pair copulations occurred within the females fertile period. Males guarded their partners by close following, defended them from extra-pair copulation attempts, and sometimes followed extra-pair copulations by forced pair copulations. The temporary removal of guarding males greatly increased the likelihood of the female being subject to extra-pair copulation attempts. Genetic plumage markers were used to determine paternity, and showed that in an aviary, naturally occurring extra-pair copulations resulted in extra-pair paternity. Sperm competition experiments showed that single extra-pair copulations could fertilize eggs and that sperm from the last male to mate had 70–80% precedence over previous matings.

Mechanisms of sperm competition

Sperm competition occurs when two (or more) males inseminate a single female during a reproductive cycle, but what determines which one of them will fertilize her eggs? Is it simply a lottery, or are there some more complex rules by which matings are translated into offspring? Several studies covering various animal groups have shown that mating order effects are often important in determining paternity patterns: in animals as different as insects and birds, the sperm from the last male to mate often has precedence over previously introduced sperm. Recently, behavioural ecologists and physiologists have started to examine the mechanisms by which sperm precedence is achieved. The study of sperm competition mechanisms complements the more behavioural studies, and a combination of the two approaches used on single species should prove to be particularly rewarding.

Oil pollution and climate have wide‐scale impacts on seabird demographics

Oil spills often spell disaster for marine birds caught in slicks. However, the impact of oil pollution on seabird population parameters is poorly known because oil spills usually occur in wintering areas remote from breeding colonies where birds may be distributed over a wide area, and because it is difficult to separate the effects of oil pollution from the effect of natural environmental variation on seabird populations. Using a long-term data set we show that over-winter survival of adult common guillemots (Uria aalge) is negatively affected by both the incidence of four major oil-spills in their wintering grounds and high values of the North Atlantic Oscillation (NAO) index. After controlling for the effect of the NAO index, we show that winter mortality of adult guillemots is doubled by major oil pollution incidents. Our results demonstrate that oil pollution can have wide-scale impacts on marine ecosystems that can be quantified using populations of marked individuals to estimate survival.

Frequent copulation as a method of paternity assurance in the northern fulmar

Abstract Male fulmars, Fulmarus glacialis , employ a mixed reproductive strategy, copulating frequently with their mates while also taking opportunities to inseminate other females by extra-pair copulation. This study combines a complete record of copulation behaviour with paternity determined by DNA finger-printing in order to establish whether extra-pair copulations result in extra-pair paternity and to investigate how the fertilizing male achieves paternity. Despite the regular occurrence of extra-pair copulation (2·4% of all copulations involved an extra-pair male), no extra-pair paternity was detected in the study population. The upper 95% confidence limit for the population as a whole was 4·6% extra-pair paternity. The fertilizing male in all cases achieved both the greatest number of copulations relative to any other male and the last copulation before egg laying. The possible mechanism of paternity attainment in this species is discussed.

MALE-FEMALE DIFFERENCES IN PARENTAL CARE IN MONOGAMOUS CRESTED AUKLETS

Abstract We studied patterns of parental care in Crested Auklets (Aethia cristatella), a monogamous seabird, for three breeding seasons (1996–1998) in the Aleutian Islands, Alaska, using radio-telemetry. In 1996, we found no sexual differences in parental care, low breeding site attendance rates, and reduced occurrences of copepods in food samples delivered to chicks, suggesting that food availability may have been low. In 1997 and 1998, we found significant differences in parental care between males and females, particularly early in the chick-rearing period: males attended and brooded their single chick 75% and 90% longer than females, while females provisioned 33% and 36% more often than males, respectively. We also found significant differences between prey types delivered to chicks by males and females for these two years. Males brought in 30% more euphausiids, a relatively large pelagic crustacean, than females, whereas females brought in 36% more copepods, a smaller crustacean, than males; however, prey mass per load did not differ. In 1998, we experimentally measured how vulnerable unattended young chicks were using models placed in unoccupied crevices. Eighty-three percent of the models showed signs of attack, presumably by conspecific adults. We concluded that unattended Crested Auklet chicks are highly vulnerable to attack. We suggest that males took on a greater role in chick brooding than their mates because they have a larger and more strongly hooked bill and are more aggressive than females, and thus better equipped than females to guard young chicks or the crevice breeding site. Diferencias en el Cuidado Parental entre Machos y Hembras en la Especie Monógama Aethia cristatella Resumen. Utilizando radiotelemetría para estudiar los patrones de cuidado parental en Aethia cristatella, un ave marina monógama, durante tres períodos reproductivos (1996–1998) en las Islas Aleutianas, Alaska. En 1996 no encontramos diferencias sexuales en el cuidado parental, encontramos bajas tasas de presencia en el lugar de nidificación, y baja ocurrencia de copépodos en las muestras de alimento entregadas a los polluelos, lo cual sugiere que la disponibilidad de alimento podría haber sido baja. En 1997 y 1998 encontramos diferencias significativas en el cuidado parental entre hembras y machos, particularmente en el período temprano de cría de los polluelos. Los machos asistieron y empollaron su único polluelo por un período un 75% y 90% más largo que las hembras, mientras que las hembras aprovisionaron con una frecuencia un 33% y 36% mayor que los machos, respectivamente. También encontramos diferencias significativas entre el tipo de presa entregado por las hembras y por los machos durante los dos años. Los machos entregaron un 30% más de eufáusidos (crustáceos pelágico relativamente grandes) que las hembras, mientras que éstas entregaron un 36% más de copépodos (crustáceos más pequeños) que los machos. Sin embargo, el peso de la carga de alimento no varió. En 1998 medimos experimentalmente la vulnerabilidad de los polluelos no cuidados utilizando modelos situados en grietas desocupadas. El 83% de los modelos presentaron signos de ataques presumiblemente producidos por adultos coespecíficos. Concluimos que los polluelos no cuidados de A. cristatella son altamente vulnerables a ataques. Sugerimos que los machos tomaron un rol más importante en la crianza de los polluelos que sus parejas debido a que ellos presentan un pico más grande y fuertemente arqueado y son más agresivos que las hembras. Por lo tanto están mejor equipados que las hembras para proteger a los polluelos o proteger el sitio de nidificación.

GENIC CAPTURE AND THE GENETIC BASIS OF SEXUALLY SELECTED TRAITS IN THE ZEBRA FINCH

Abstract The lek paradox, in which female choice erodes genetic variation in male sexually selected traits, is a fundamental issue in sexual selection. If females gain only genetic benefits from preferentially having their ova fertilized by males with particular traits, what maintains variation in these traits? Under strong directional selection mediated through mate choice, the alleles for beneficial male traits are expected to go to fixation and exhibit little variation. A theoretical solution to the lek paradox is the genic capture hypothesis which states that: costly male traits subject to female choice are condition dependent, that male condition is dependent on genes at many loci and exhibits additive genetic variance, and that positive genetic correlations exist between sexually selected traits and condition. Using a captive population of the zebra finch Taeniopygia guttata, we tested two key predictions from this model: (1) that genetic variance exists in beak color which is a sexually selected trait, but also in condition and immune function, and (2) that positive genetic correlations exist between condition and beak color, and between beak color, condition, and immune function. Genetic parameters were estimated from a large breeding experiment involving 81 sires, 972 offspring, a pedigree of 1526 individuals, using the animal model. We employed the following index of body condition: residuals from a log-log plot of body mass on tarsus length following a standardized and extended period of exercise, in which residual mass is known to reflect fat and protein reserves. Our results were broadly consistent with the genic capture hypothesis because we found (1) additive genetic variation in beak color and immune function and condition, and (2) positive genetic correlations between condition and beak color, and between condition, beak color, and several assays of immune responsiveness. However, both of these results need qualification. In the first case we identified an important general problem in estimating the coefficient of additive genetic variance (CVA) in body condition. In the second case, although most of the genetic correlations were positive as predicted, only some were statistically significant, possibly due to our relatively small sample sizes, because genetic correlations typically have large standard errors and therefore require very large samples to be statistically significant. The statistically significant, positive genetic correlations included those between beak color and immune function (response to tetanus), and between immune function (response to tetanus) and condition, both of which indicate that females gain good genes from mating with males in good condition and/or with a redder beak color. We discuss the implications of our results for devising more rigorous but pragmatic tests of the genic capture hypothesis.

BREEDING BIOLOGY OF CRESTED AUKLETS AT BULDIR AND KASATOCHI ISLANDS, ALASKA

We quantified breeding parameters of Crested Auklets (Aethia cristatella) at Buldir and Kasatochi islands in the Aleutian Islands, Alaska, in 1996 and 1997. Crested Auk- lets incubated their eggs for about 36 days and chicks weighed about 35 g within the first three days of hatching (14% of adult mass; Buldir, n = 58). Growth rates averaged about 9.9 g per day during the linear phase (Buldir, n = 58; Kasatochi, n = 17), and chicks fledged at an average mass of 248 g (95% of adult mass; Buldir, n = 63) and a wing length of 123 mm (88% of adult wing length; Buldir, n = 37) at 34 days after hatching. We found no differences in intraisland and intrayear chick growth for Buldir and Kasatochi. Productivity (the product of hatching success and fledging success) averaged more than 60% for the two years at Ka- satochi and for eight years (1990 to 1997) at Buldir. Intercolony comparisons of productivity parameters revealed differences in hatching date, age of chicks at fledging, and hatching and fledging success. Adult mass differed significantly between the sexes (267 g for males, 253 g for females) and among years. At Buldir, we observed no effect of various levels of inves- tigator disturbance on hatching and fledging success or on other breeding parameters. We found no negative relationships between hatching date and fledging age, hatching date and fledging mass, or fledging mass and fledging age, contrary to the predictions of Ydenbergs (1989) model of intraspecific variation in timing of fledging of alcid chicks. Crested Auklet chicks, like those of other diurnally active species of auklets, grow relatively fast and depart at a younger age compared with chicks of two nocturnal species of auklets. Received 24 April