Sexual and asexual production of planulae in reef corals

Electrophoresis was used to provide genetic evidence of the mode of production of brooded planulae in each of four species of scleractinian coral collected from the central region of the Great Barrier Reef during September, October and November 1984. Comparisons were made of the multi-locus genotypes of planulae and their broodparents for two ahermatypic (non zooxanthellate) species,Tubastraea diaphana andT. coccinea and two hermatypic (zooxanthellate) species,Acropora palifera andSeriatopora hystrix. For both ahermatypic species, all planulae were found to be genetically identical to their broodparents, including 91 planulae which were heterozygous for at least one locus. These results are consistent with asexual (ameiotic) reproduction. In contrast, non-parental genotypes were detected in the majority of hermatypic broods, which is consistent with expectations for sexual reproduction with at least some outcrossing. These data confirmed that brooded planulae may be produced both sexually and asexually and countered the suggestion that electrophoretic studies of hermatypic corals may be weakened by the contaminating effect of the enzymes of their symbiotic xooxanthellae.Contribution No. 306 of the Australian Institute of Marine Science     

Reproductive biology of a deep-sea brittle star Amphiura carchara (Echinodermata: Ophiuroidea)

 New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples indicated that there are seasonal trends in reproduction. Received: 14 February 2000 / Accepted: 3 July 2000     

Brood size manipulation affects frequency of second clutches in the blue tit

The reproductive trade-off hypothesis predicts that the investment made in current reproduction determines the breeders’ future fitness as a consequence of intra-or inter-generational reproductive costs. Long-lived species are expected to favour their own reproductive value at the expense of their offspring, hence incurring in inter-generational costs, whereas short-lived species are expected to invest in the current breeding attempt even at the expense of their own survival, thus incurring in intra-generational costs. We tested whether intensity of current reproductive effort has intra-or inter-generational costs in a short-lived bird, the blue tit Parus caeruleus, with a brood size manipulation experiment. We expected more intra-generational (parental reproduction and/or survival) than inter-generational (offspring quality and survival) reproductive costs. We found that parental effort, measured as the hourly rate of parental visits to nests, increased gradually with experimental manipulation. Brood size manipulation resulted in a gradual increase in the number of fledglings per nest from reduced to increased treatments. We found an effect of the manipulation on the probability of making a second clutch, with adults rearing enlarged broods being less likely to undertake such a second reproduction during the season compared to those rearing control or decreased broods. We found no evidence of other reproductive costs; neither as adult weight after manipulation, apparent parental local survival, apparent offspring local survival or local recruitment. Although the results seem to support the a priori expectations, alternative explanations are discussed.Communicated by M. Soler     

Reproduction, dispersal and settlement of the bathyal ophiuroid Ophiocten gracilis in the NE Atlantic Ocean

  Ophiocten gracilis is an ophiuroid found at bathyal depths in the North Atlantic Ocean. The adults show strong seasonal reproduction, with an ophiopluteus in the surface plankton. Settling postlarvae were collected in sediment traps moored at 1000 and 1400 m depth in the NE Atlantic during Julian Days 142 to 212 (May to July) in 1996. During this period, growth of postlarvae in the traps was linear and the diet consisted of phytodetritus and foraminifera. Experiments suggest that postlarvae sink at rates of up to 500 m d⁻¹, although this may well be slower in the natural environment. The high fecundity, seasonality and high population density resulted in high fertilization success, and many of the offspring were advected outside the normal adult range, where they were able to settle but did not survive to adulthood. Received: 8 October 1999 / Accepted: 8 May 2000     

Reproductive biology of a filter-feeding amphipod, Leptocheirus pinguis , with extended parental care

Leptocheirus pinguis (Stimpson, 1853) is a widely distributed, abundant, endobenthic amphipod that engages in extended parental care, i.e. females host their juveniles in their burrows for extended time periods. I examined reproduction and population biology of L. pinguis at mean low water (MLW) in muddy sediment in Lowes Cove, Maine, USA. Cores around individual burrows were taken monthly in 1994 and 1995, and four seasonal samples were taken at different tidal heights. During the major reproductive periods in spring/early summer and in the fall, females produced several consecutive broods and hosted growing offspring in their burrows. Juveniles remained in their mothers' burrows until they reached a length of 5 mm (approximately one-third adult size) or more. At the study site, the majority of amphipods in individual burrows were adult females. Following the main reproductive periods, subadult individuals were found in their own burrows, but densities did not increase following the reproductive period in spring/early summer 1994, probably because large numbers of L. pinguis emigrated via the water column between June and December. L. pinguis is an annual species. Many members of the cohort born in spring/early summer start reproducing in the fall, and survive until the following spring when they produce several broods. Members of the cohort born in the fall start reproducing the following spring and also produce several consecutive broods. Both the spring/early summer and fall cohorts die off after the major reproductive period in the following spring/early summer. High standing stocks of microphytobenthos occur in soft-bottoms at MLW, and I conclude that L. pinguis can engage in extended parental care there because its food is abundant year-round. The limited expandability and low stability of burrows in soft-bottoms at MLW do not permit long persistence of parent–offspring groups in L.␣pinguis. Received: 27 March 1997 / Accepted: 30 July 1997     

An adaptive annual rhythm in the sex of first pigeon eggs

When the reproductive value of male and female offspring varies differentially, parents are predicted to adjust the sex ratio of their offspring to maximize their fitness (Trivers and Willard, Science 179:90–92, 1973). Two factors have been repeatedly linked to skews in avian offspring sex ratio. First, laying date can affect offspring sex ratio when the sexes differ in age of first reproduction, such that the more slowly maturing sex is overproduced early in the season. Second, position of the egg in the laying sequence of a clutch may affect sex ratio bias since manipulating the sex of the first eggs may be least costly to the mother. We studied both factors in two non-domesticated pigeon species. Both the Wood pigeon (Columba palumbus) and the Rock pigeon (Columba livia) have long breeding seasons and lay two-egg clutches. In the field, we determined the sex of Wood pigeon nestlings. In Rock pigeons, housed in captivity outdoors, we determined embryo sex after 3 days of incubation. On the basis of their sex-specific age of first reproduction, we predicted that males, maturing at older age than females, should be produced in majority early and females later in the year. This was confirmed for both species. The bias was restricted to first eggs. Rock pigeons produced clutches throughout the year and show that the sex of the first egg followed an annual cycle. To our knowledge, this study presents the first evidence of a full annual rhythm in adaptive sex allocation in birds. We suggest that this reflects an endogenous seasonal program in primary sex ratio controlled by a preovulatory mechanism.     

The genetic mating system of a sex-role-reversed pipefish (Syngnathus typhle): a molecular inquiry

In the pipefish Syngnathus typhle as in other species of Syngnathidae, developing embryos are reared on the male's ventral surface. Although much laboratory research has been directed toward understanding sexual selection in this sex-role-reversed species, few studies have addressed the mating behavior of S. typhle in the wild, and none has capitalized upon the power of molecular genetic assays. Here we present the first direct assessment of the genetic mating system of S. typhle in nature. Novel microsatellite loci were cloned and characterized from this species, and employed to assay entire broods from 30 pregnant, field-captured males. Genetic analysis of 1340 embryos revealed that 1–6 females (mean = 3.1) contributed to each brooded clutch, the highest rate of multiple maternity yet documented in any pipefish. Evidence of multiple mating by females was also detected. Thus, this population of S. typhle displays a polygynandrous mating system, a finding consistent with previous field and laboratory observations. Our results, considered together with similar studies of other syngnathid species, provide preliminary support for the hypothesis that the genetic mating system is related to the evolution of sexual dimorphism in the fish family Syngnathidae. Received: 19 January 1999 / Received in revised form: 15 April 1999 / Accepted: 9 May 1999     

Reproductive dominance and differential ovicide in the communally breeding burying beetle Nicrophorus tomentosus

Communal breeding can be characterized by the division of reproduction among cooperating individuals and, if the distribution of reproduction is inequitable, by the mechanisms for achieving skewed reproductive success. The burying beetle (Nicrophorus tomentosus) is a facultative communal breeder. Unrelated adults, especially females, provide extensive parental care to broods of mixed parentage. The frequency and degree of reproductive skew between two females were examined experimentally. On medium-size carcasses, the proportion of eggs attributed to each female was not significantly different from random in 42% of the broods, skewed in 42% and not shared in 16%. Although reproduction was usually skewed in favor of the larger female, the relative sizes of the two females did not predict the degree of skew. On large carcasses, the proportion of eggs attributed to each female was not different from random in 87% of the broods and weakly skewed in 13%. Several mechanisms for biasing reproductive success were investigated. Females increase the proportion of their offspring in the brood by committing differential ovicide. Secondly, burying and preparing a carcass cooperatively stimulates ovarian development of the larger female and slows it for the smaller female, reducing or delaying oviposition by the subordinate. Thirdly, larger females are more likely to be dominant and are more fecund than smaller females. Received: 20 July 1996 / Accepted after revision: 30 November 1996     

Risk taking during parental care: a test of three hypotheses applied to the pied flycatcher

According to life-history theory, there will often be a conflict between investment in current versus future reproduction. If a predator appears during breeding, parents must make a compromise between ensuring the growth and survival of offspring (nest defence, feeding and brooding of young), and reducing the risk of predation to ensure their own survival. We model three hypotheses for the outcome of this conflict which are particularly relevant for altricial birds. They are not mutually exclusive, but focus on different costs and benefits. (1) Parental investment is determined by the parents’ own risk of predation. This hypothesis predicts that a lone parent should take smaller risks than a parent that has a mate. (2) Parental investment is related to the reproductive value of the offspring: Parents are predicted to take greater risks for larger broods, larger-sized or older offspring. (3) Finally, we present the new hypothesis that parental investment is related to the harm that offspring would suffer during a period of no parental care (incubation, brooding, feeding). This hypothesis predicts that parents should take greater risks for younger offspring, or for offspring in poorer condition, because the marginal benefit of parental care is largest in such cases. Hence, one may also expect that lone parents should take greater risks than two parents because their offspring are more in need of care. We tested these hypotheses on the pied flycatcher (Ficedula hypoleuca) by presenting a stuffed predator of the parents (a sparrowhawk, Accipiter nisus) close to the nest when parents were feeding the young. Risk taking was measured as the time that elapsed until the first visit to the nest. Most support was found for the ‘‘harm to offspring’’ hypothesis. Previous studies have usually measured the intensity of nest defence against typical nest predators, and have found evidence for the ‘‘reproductive value of offspring’’ hypothesis. However, our model predicts that the importance of the reproductive value of the offspring should decrease relative to the harm that offspring would suffer if they were not cared for when the predator type changes from a nest predator to a predator of adults, and when conditions for breeding turn from good to bad. Received: 13 April 1995/Accepted after revision: 11 March 1996     

Variation among populations of the sailfin molly in the rate of concurrent multiple paternity and its implications for mating-system evolution

We examined patterns of concurrent multiple mating in a live-bearing poeciliid fish, the sailfin molly (Poecilia latipinna). We tested whether the probability of multiple paternity was related to female body size or fertility and whether the rate of multiple paternity varied among four populations that differed in their distributions of female body size and fertility. We analyzed data on mother and offspring genotypes for three polymorphic allozymes by three techniques, including a maximum-likelihood estimator that accounts for sampling error in both parental and offspring allele frequencies. The estimated rate of multiple paternity varied between 0.09 and 0.85, and the rate in one population varied seasonally between 0.33 (spring) and 0.85 (autumn). The variation in these rates was not associated with variation in body-size distributions among populations but was closely associated with variation in size-specific fertility: populations with greater variation in female fertility had higher multiple-paternity rates. Within two populations, logistic regression revealed that individual females of larger body size and greater size-specific fertility were more likely to carry multiply sired broods. This result is consistent with observations made in one of the populations 5 years earlier. In general, the results strongly suggest that the mating system varies markedly among conspecific populations of sailfin mollies and that larger, more fertile females are the objects of intermale competition. Received: 6 May 1996 / Accepted in revised form: 5 December 1996     

Genetic evidence of self-fertilization in the sea anemone Epiactis prolifera

Biochemical genetic variation provided evidence for the mode of reproduction of brooded young in the sea anemone Epiactis prolifera Verrill, 1869. Individuals of E. prolifera are female when small but hermaphroditic when large (i.e., gynodioecious); juveniles are brooded externally on the column. Brooding individuals collected from 6 intertidal sites (5 in central California and 1 in Washington State, USA) in the spring and summer of 1980 were assayed for gene-enzyme variation by starch-gel electrophoresis. Three of 12 enzyme loci were polymorphic; phosphoglucose isomerase appeared to be encoded by two, closely linked loci. Genotypic frequencies deviated markedly from expected random mating proportions. Only three heterozygotes were found; two were heterozygous at all three polymorphic loci, and the other was polymorphic at the two PGI loci. All 158 juveniles from 25 brooding individuals were assayed (2–19 juveniles per parent). Juveniles on homozygous adults were always identical to their parent. However, brooded young of heterozygous individuals were not identical to their parent. but showed 1:2:1 phenotypic segregation ratios consistent with reproduction by self-fertilization. This genetic evidence together with findings of marked heterozygote deficiencies and genetic identity of homozygous adults and their brooded young supports the conclusion that E. prolifera usually reproduces by self-fertilization, and cross-fertilization is rate.     

Brood sex ratio is dependent on female mating status in polygynous great reed warblers

Females capable of adjusting the sex ratio of their offspring should be more fit than females lacking such an ability. In polygynous birds where breeding success in males is more strongly influenced by body size and/or attractiveness than in females, females might produce more sons when predicting good conditions or when mating with attractive males. Polygynous great reed warbler, Acrocephalusarundinaceus, males direct most of their feeding effort to the primary (first-hatching) nest and in these nests increase their feeding effort in relation to the brood sex ratio (proportion of sons). Therefore, with the expectation of well-nourished sons, we would predict that females which start breeding first within harems might produce more sons than those which start breeding later, and in anticipation of sons with good genes, that females mated to polygynous males might produce more sons than females mated to monogamous males. I took blood samples from hatchlings and determined the sex using DNA markers. The sex ratio of primary (monogamous and polygynous primary) broods is more male-biased (mean 0.58 males, n = 50) than that of secondary (polygynous secondary and tertiary) broods (mean 0.46, n = 25). Moreover, in the secondary broods with the largest clutch (five eggs), in which offspring are most likely to suffer food shortage, the sex ratio was distinctively female biased (mean 0.33, n = 10). In the primary broods, sex ratio was correlated to harem size. The results suggest that great reed warbler females modify the brood sex ratio to produce both well-nourished sons and sons with good genes, but the former effect is probably stronger than the latter factor. Received: 11 March 1998 / Accepted after revision: 23 May 1998     

Paternity and paternal care in the polygynandrous Smith's longspur

In species where females copulate with more than one male during a single breeding attempt, males risk investing in offspring that are not their own. In the polygynandrous Smith's longspur (Calcarius pictus), females copulate sequentially with one to three males for each clutch of eggs and most of these males later assist in feeding the young. Using multilocus DNA profiling, we determined that there was mixed paternity in >75% of broods (n=31) but that few offspring (<1% of 114 nestlings) were sired by males outside the polygynandrous group. Male feeding rate increased significantly with the number of young sired, with males siring four nestlings feeding the brood at double the frequency of males siring only a single nestling. However, male Smith's longspurs appear to show a graded adjustment of paternal care in response to paternity only when other males are available to compensate for reduced care: feeding rate did not vary in relation to paternity when only one male provisioned young at the nest. There was no evidence that males could recognise their own offspring within a brood and feed them preferentially. The number of offspring sired by each male was significantly correlated with the number of days spent copulating with the attending female: on average, a male sired one offspring for every 2 days of copulatory access. If males use their access to females to estimate paternity (and thereby decide on their subsequent level of parental investment), a positive relationship is expected between the amount of female access and the subsequent feeding rate to the nestlings. Nonetheless, male feeding effort was only weakly correlated with female access and more study is needed to determine how males estimate their paternity in a brood. Received: 1 June 1997 / Accepted after revision: 1 April 1998     

Mode of reproduction,recruitment, and genetic subdivision in the brooding sponge<Emphasis Type="Italic"> Haliclona</Emphasis> sp.

Sponges display a variety of reproductive strategies that have the potential to influence population genetic structure. Histological examination of ten reproductive individuals of the Western Australian sponge Haliclona sp. showed that this species broods embryonic larvae that are potentially limited in dispersal capabilities. Because sponges have the potential to propagate in a number of modes, allozyme electrophoresis was used to assess the relative importance of asexual and sexual reproduction to recruitment, and to quantify genetic subdivision over different spatial scales. Tissue samples from 227 sponges were collected from reefs within two areas 400 km apart: Hamelin Bay and Rottnest Island. Contrary to expectations for highly clonal populations, genotypic diversity within sites was high, no linkage disequilibrium was found, and there was no evidence of genotypic clustering within reefs. There was no genetic evidence that asexual reproduction is important for the maintenance of populations. Genetic comparisons were consistent with mixing of sexually produced recruits within reefs, on a scale up to a few hundred metres, but significant genetic subdivision between reefs (F_ST=0.069 at Hamelin Bay, 0.130 at Rottnest Island) indicated that water gaps of several hundred metres are effective at preventing dispersal. Subdivision between the two areas, separated by 400 km, was moderately greater (F_ST=0.142) than within, but the same alleles were predominant in the two areas. These genetic patterns are consistent with limited dispersal capabilities of brooded larvae.Communicated by G.F. Humphrey, Sydney     

Molecular and morphological evidence of a single species, Boccardia proboscidea (Polychaeta: Spionidae), with multiple development modes

Most species of benthic marine invertebrates have a single mode of larval development. Poecilogonous species are those that produce more than one type of larval offspring. Reports of variable development within one species, especially in combination with widely differing ecological habitat, are frequently attributed to cryptic species. The spionid polychaete Boccardia proboscidea Hartman, 1940 exhibits development that varies both within a single brood and among broods produced by different females. Some females have planktotrophic development and produce many small larvae with a 2 week planktonic period before metamorphosis. Other females produce broods containing both planktotrophic larvae as well as nurse-egg-ingesting (adelphophagic) offspring that hatch as juveniles. Molecular analysis (RAPD-PCR) showed that a significant proportion of genetic variance is attributable to geographic origin, and not to developmental type. Adults of both developmental types showed no consistent differences in taxonomically important features (e.g. type and arrangement of chaetae, modified fifth setiger, caruncle, branchiae, pygidium) when examined with SEM. These data support the hypothesis that developmental variability in this species is a case of poecilogony, and is not attributable to cryptic species. Received: 21 April 1998 / Accepted: 20 April 1999     

Extra-pair paternity, offspring mortality and offspring sex ratio in the socially monogamous coal tit (Parus ater)

Females of many socially monogamous bird species commonly engage in extra-pair copulations. Assuming that extra-pair males are more attractive than the females’ social partners and that attractiveness has a heritable component, sex allocation theory predicts facultative overproduction of sons among extra-pair offspring (EPO) as sons benefit more than daughters from inheriting their father’s attractiveness traits. Here, we present a large-scale, three-year study on sex ratio variation in a passerine bird, the coal tit (Parus ater). Molecular sexing in combination with paternity analysis revealed no evidence for a male-bias in EPO sex ratios compared to their within-pair maternal half-siblings. Our main conclusion, therefore, is that facultative sex allocation to EPO is absent in the coal tit, in accordance with findings in several other species. Either there is no net selection for a deviation from random sex ratio variation (e.g. because extra-pair mating may serve goals different from striving for ‘attractiveness genes’) or evolutionary constraints preclude the evolution of precise maternal sex ratio adjustment. It is interesting to note that, however, we found broods without EPO as well as broods without mortality to be relatively female-biased compared to broods with EPO and mortality, respectively. We were unable to identify any environmental or parental variable to co-vary with brood sex ratios. There was no significant repeatability of sex ratios in consecutive broods of individual females that would hint at some idiosyncratic maternal sex ratio adjustment. Further research is needed to resolve the biological significance of the correlation between brood sex ratios and extra-pair paternity and mortality incidence, respectively.     

Offspring sex ratios reflect lack of repayment by auxiliary males in a cooperatively breeding passerine

The repayment hypothesis posits that primary sex ratios in cooperative species should be biased towards the helping sex because these offspring “repay” a portion of their cost through helping behavior and therefore are less expensive to produce. However, many cooperatively breeding birds and mammals do not show the predicted bias in the primary sex ratio. Recent theoretical work has suggested that the repayment hypothesis should only hold when females gain a large fitness advantage from the presence of auxiliary adults in the group. When auxiliaries provide little or no fitness advantage, competition between relatives should lead to sex ratios biased towards the dispersing (non-helping) sex. We examined the benefits auxiliaries provide to females and corresponding offspring sex ratios in the red-backed fairy-wren (Malurus melanocephalus), a cooperatively breeding Australian bird with male auxiliary helpers. We found that auxiliaries provide little or no benefit to female reproductive success or survival. As predicted, the population primary sex ratio was biased towards daughters, the dispersing sex, and females with auxiliaries produced female-biased broods whereas females without auxiliaries produced unbiased broods. Moreover, offspring sex ratios were more strongly biased toward females in years when auxiliaries were more common in the population. These results suggest that offspring sex ratios are associated with competition among the non-dispersing sex in this species, and also that females may use cues to assess local breeding opportunities for their offspring.     

Mate replacement in experimentally widowed collared flycatchers (Ficedula albicollis): determinants and outcomes

There is increasing evidence that sexual selection may be intense even in socially monogamous birds, resulting from both mate choice and sperm competition. We studied these two modes of sexual selection experimentally by removing paired male collared flycatchers, Ficedula albicollis, from their mates for 2 days and investigating the factors that influenced the likelihood of a replacement male appearing and how the removals influenced paternity. Replacement males (usually neighbouring males) appeared at 81% (n = 37) of nests where males were removed. The likelihood of this appearance was unaffected by the probable reproductive value of the female's clutch to the replacing male. A replacement was, however, less likely when the original male had a large forehead patch, a trait previously shown to be subject to sexual selection in this population. Experimental removal of males increased the level of sperm competition: 74% of experimental broods were multiply sired, compared to 29% of unmanipulated broods in a previous study. Only two factors predicted how paternity was shared between males: removed males fathered more young if removed closer to laying, and if they had larger forehead patches. The former result is consistent with last-male sperm precedence determining paternity, whereas the latter adds to other evidence that forehead patch size is the target of female preference in this species. Our results suggest that females exert some control over male replacement, and also that they may influence the fertilisation success of males by behavioural means. Received: 15 July 1998 / Received in revised form: 16 March 1999 / Accepted: 28 March 1999     

Melanin-based colorations signal strategies to cope with poor and rich environments

One hypothesis for the maintenance of genetic variation states that alternative genotypes are adapted to different environmental conditions (i.e., genotype-by-environment interaction G×E) that vary in space and time. Although G×E has been demonstrated for morphological traits, little evidence has been given whether these G×E are associated with traits used as signal in mate choice. In three wild bird species, we investigated whether the degree of melanin-based coloration, a heritable trait, covaries with nestling growth rate in rich and poor environments. Variation in the degree of reddish-brown phaeomelanism is pronounced in the barn owl (Tyto alba) and tawny owl (Strix aluco), and variation in black eumelanism in the barn owl and Alpine swift (Apus melba). Melanin-based coloration has been shown to be a criterion in mate choice in the barn owl. We cross-fostered hatchlings to test whether nestlings sired by parents displaying melanin-based colorations to different extent exhibit alternative growth trajectories when raised by foster parents in poor (experimentally enlarged broods) and rich (experimentally reduced broods) environments. With respect to phaeomelanism, barn owl and tawny owl offspring sired by redder parents grew more rapidly in body mass only in experimentally reduced broods. With respect to eumelanism, Alpine swift offspring of darker fathers grew their wings more rapidly only in experimentally enlarged broods, a difference that was not detected in reduced broods. These interactions between parental melanism and offspring growth rate indicate that individuals display substantial plasticity in response to the rearing environment which is associated with the degree of melanism: at least with respect to nestling growth, phaeomelanic and eumelanic individuals are best adapted to rich and poor environments, respectively. It now remains to be investigated why eumelanism and phaeomelanism have a different signaling function and what the lifelong consequences of these melanism-dependent allocation strategies are. This is important to fully appraise the role played by environmental heterogeneity in maintaining variation in the degree of melanin-based coloration.     

Extra-pair paternity and tail ornamentation in the barn swallow Hirundo rustica

Females of socially monogamous species may copulate with attractive non-mates to obtain access to the genes of such males, and a preference for attractive copulation partners may result in sexual selection. Extra-pair copulations are common in the socially monogamous barn swallow Hirundorustica, and a 2-year study of paternity using multi-locus DNA fingerprinting demonstrated that 33% of 63 broods and 28% of 261 offspring were sired by extra-pair males. The frequency of extra-pair offspring within broods was highly skewed with the majority of all broods having either no extra-pair offspring or only extra-pair offspring. Individual pairs were consistent in their frequency of extra-pair paternity among broods, and the repeatability of extra-pair paternity of multiple broods of the same female was statistically significant. The proportion of extra-pair offspring was negatively related to the tail length of the male attending the nest. Behavioural observations showed that extra-pair fertilizations were more likely in broods raised by females that had been observed to engage in extra-pair copulations. The frequency of extra-pair offspring was unrelated to the intensity of two male paternity guards, mate guarding and the rate of intra-pair copulations. In an analysis of extra-pair paternity and male parental care in different broods of the same male, male barn swallows fed their offspring relatively less frequently if the brood contained more extra-pair offspring. Therefore, female barn swallows pursue extra-pair copulations with attractive males, which may result in sexual selection, even though extra-pair paternity is costly for females due to the reduction of paternal care by their social mates. Received: 24 January 1997 / Accepted after revision: 2 August 1997