Seasonal Reproductive Success Research Articles

Colonial breeding impacts potentially fitness-relevant cognitive processes in barn swallows

Many animals breed colonially, often in dense clusters, representing a complex social environment with cognitive demands that could ultimately impact individual fitness. However, the effects of social breeding on the evolution of cognitive processes remain largely unknown. We tested the hypothesis that facultative colonial breeding influences attention and decision-making. Barn swallows (Hirundo rustica) breed in solitary pairs or in a range of colony sizes, up to dozens of pairs. We tested for selective attention to social information with playbacks of conspecific alarm calls and for decision-making with simulated predator intrusions, across a range of colony sizes from 1 to 33 pairs. We also evaluated the adaptive value of both processes by measuring seasonal reproductive success. Swallows breeding in larger colonies were more selective in their attention to social information. Birds breeding in larger colonies were also less risk averse, deciding to return more quickly to their nests after a predator approach paradigm. Finally, birds that showed higher selective attention hatched more eggs and birds that returned to their nests more quickly after a predator intrusion had more nestlings. Although we cannot fully attribute these fitness outcomes to the cognitive measures considered in this study, our results suggest that social breeding plays a role in adaptively shaping both the acquisition of social information and decision-making.

Null Models for the Opportunity for Selection.

AbstractCrow's "opportunity for selection" ( in relative fitness) is an important albeit controversial eco-evolutionary concept, particularly regarding the most appropriate null model(s). Here, we treat this topic in a comprehensive way by considering opportunities for both fertility selection (If) and viability selection (Im) for discrete generations, both seasonal and lifetime reproductive success in age-structured species, and experimental designs that include either a full or partial life cycle, with complete enumeration or random subsampling. For each scenario, a null model that includes random demographic stochasticity can be constructed that follows Crow's initial formulation that . The two components of I are qualitatively different. Whereas an adjusted If () can be computed that accounts for random demographic stochasticity in offspring number, Im cannot be similarly adjusted in the absence of data on phenotypic traits under viability selection. Including as potential parents some individuals that die before reproductive age produces an overall zero-inflated Poisson null model. It is always important to remember that (1) Crow's I represents only the opportunity for selection and not selection itself and (2) the species' biology can lead to random stochasticity in offspring number that is either overdispersed or underdispersed compared with the Poisson (Wright-Fisher) expectation.

Barn Swallows in East Asia show strong tolerance against nest mites

Abstract Hosts defend against parasites through two main strategies: resistance and tolerance. These two strategies have different influences on the parasite load of the host and so have variable effects on the fitness of parasites. In this study, we investigated the strategy used by the Barn Swallow (Hirundo rustica) to defend against a hematophagous mite (Dermanyssus hirundinis) in East Asia. For the first time, we found Barn Swallows were parasitized by D. hirundinis in Asia and, in northeastern China, over 60% of broods were parasitized. We examined whether swallows with better body condition or the males with more extravagant sexually selected traits (longer tail streamers or redder ventral plumage) showed stronger resistance or tolerance to these parasites. The results showed that males with more extravagant sexual ornaments had weaker resistance (heavier brood mite load) than males with less extravagant traits; however, the heavier mite load was likely to be a byproduct of larger brood size. Moreover, the Barn Swallow population showed strong tolerance against the parasite (i.e. the brood mite load did not affect brood size or nestling body mass). It is worth noting that male swallows with redder breast plumage showed weaker tolerance (lower seasonal reproductive success) than other males. Further, we conducted experimental ectoparasite manipulations in 46 Barn Swallow nests to verify the potential effect of these parasites on the body condition of nestlings. Neither the body mass nor the hemoglobin concentration differed between the designed groups; however, the hemoglobin concentration of nestlings decreased with mite load. We concluded that the Barn Swallow population in East Asia used the tolerance strategy, rather than resistance to defend against nest mites, and the ectoparasitic mite did not appear to be a strong selective factor for reproductive success owing to the strong tolerance of the studied Barn Swallow population.

TheWeight: A simple and flexible algorithm for simulating non‐ideal, age‐structured populations

Abstract The Wright–Fisher model, which directs how matings occur and how genes are transmitted across generations, has long been a lynchpin of evolutionary biology. This model is elegantly simple, analytically tractable and easy to implement, but it has one serious limitation: essentially no real species satisfies its many assumptions. With growing awareness of the importance of jointly considering both ecology and evolution in eco‐evolutionary models, this limitation has become more apparent, causing many researchers to search for more realistic simulation models. A recently described variation retains most of the Wright–Fisher simplicity but provides greater flexibility to accommodate departures from model assumptions. This generalized Wright–Fisher model relaxes the assumption that all individuals have identical expected reproductive success by introducing a vector of parental weights w that specifies relative probabilities different individuals have of producing offspring. With parental weights specified this way, expectations of key demographic parameters are simple functions of w. This allows researchers to quantitatively predict the consequences of non‐Wright–Fisher features incorporated into their models. An important limitation of the Wright–Fisher model is that it assumes discrete generations, whereas most real species are age structured. Here I show how an algorithm (TheWeight) that implements the generalized Wright–Fisher model can be used to model evolution in age‐structured populations with overlapping generations. Worked examples illustrate simulation of seasonal and lifetime reproductive success and show how the user can pick vectors of weights expected to produce a desired level of reproductive skew or a desired Ne/N ratio. Alternatively, weights can be associated with heritable traits to provide a simple, quantitative way to model natural selection. Using TheWeight, it is easy to generate positive or negative correlations of individual reproductive success over time, thus allowing explicit modelling of common biological processes like skip breeding and persistent individual differences. Code is provided to implement basic features of TheWeight and applications described here, including one scenario implemented in SLiM. However, required coding changes to the Wright–Fisher model are modest, so the real value of the new algorithm is to encourage users to adopt its features into their own or others' models.

Seasonal change of flower sex ratio and pollinator dynamics in three reproductive ecotypes of protandrous plant

AbstractCimicifuga simplex has three genetically and ecologically distinct pollination morphs with different flowering phenology, flower sex expressions, and selfing rates. A previous study showed that strong protandry in hermaphroditic flowers of C. simplex causes there to be seasonal minority sexes; for example, unisexual female ramets are advantageous in the first half of the flowering season and bloom then (minority sex hypothesis). That study, however, did not distinguish among the three pollination morphs of C. simplex. We investigated seasonal sex ratio changes and pollinator environments of the three morphs to verify and expand the minority sex hypothesis. We investigated flowering phenology, pollinator quantity and quality, seasonal population sex ratio dynamics, and stamen/ovule ratios in hermaphroditic flowers. We also examined the seasonal female reproductive success of hermaphroditic flowers, and the effect of male flower excision on fruit set by morph II hermaphroditic flowers. Morph I (mainly hermaphroditic and female ramets) had high pollinator quality and quantity. Fruit set of hermaphroditic ramets was high throughout the flowering season. Morph II (hermaphroditic and andromonoecious ramets) had low pollinator quality, and few pollinators visited near the beginning and end of the season. Removal of male flowers led to a pollen limitation. Morph III (hermaphroditic ramets and a high selfing rate) had very low pollinator abundance throughout the flowering season, and male and female phases largely overlapped. The scarcity of male flowers in morph I is likely a result of the high pollinator quantity and quality. The high fruit set suggests that no pollen limitation existed. The low pollinator quality and quantity of the morph II population caused it to suffer from pollen limitation and may explain the absence of unisexual female ramets in this morph. The high selfing rate of morph III may be due to the extremely low pollinator abundance. Theoretical studies have indicated that the optimal investment allocation to male and female functions depends on whether a pollen limitation exists. In C. simplex, the observed relationships between pollinator environment and reproductive systems are consistent with these theoretical models.

Impact of weather conditions on seasonal development, population structure and reproductive success on Dactylorhiza traunsteineri (Orchidaceae) in the Komi Republic (Russia)

Impact of weather conditions on seasonal development, population structure and reproductive success on Dactylorhiza traunsteineri (Orchidaceae) in the Komi Republic (Russia)

Larger body size and earlier run timing increase alewife reproductive success in a whole lake experiment

Environmental conditions can influence biological characteristics, such as phenology and body size, with important consequences for organismal fitness. Examining these fitness consequences under natural conditions through genetic pedigree reconstruction offers a lens into potential population responses to changing environments. Over 3 years (2013–2015), we introduced adult alewife (Alosa pseudoharengus), anadromous, iteroparous clupeids, into one Massachusetts (USA) lake to complete the first detailed examination of this species’ mating system and assess relationships among body size, reproductive timing, and seasonal reproductive success. We reconstructed pedigrees using 15 microsatellites and genotypes from all possible parents and samples of naturally produced offspring within 4 months of hatching. In each of the 3 study years, spawning adults had multiple mates and spawned multiple times. Larger females that arrived and were translocated earlier had higher reproductive success. Declining body size and altered migration timing, through an influence on reproductive success, can influence population vital rates and productivity over time.

Telomere length is reflected by plumage coloration and predicts seasonal reproductive success in the barn swallow.

Individuals differ in realized fitness but the genetic/phenotypic traits that underpin such variation are often unknown. Telomere dynamics may be a major source of variation in fitness traits because physiological telomere shortening depends on environmental and genetic factors and may impair individual performance. Here, we showed that, in a population of a socially monogamous, biparental passerine bird, the barn swallow (Hirundo rustica), breeding in northern Italy, telomere length (TL) of both adult males and females positively correlated with seasonal reproductive and fledging success, as expected because long telomeres are supposed to boost performance. Telomere length was correlated with sexually dimorphic coloration in both sexes, showing for the first time in any species that coloration reliably reflects TL and may mediate mutual mate choice, leading to the observed positive assortative mating for TL in the barn swallow. Thus, TL appears to be associated with variation in a major fitness trait and may be an ultimate target of mate choice, as individuals of both sexes can use coloration to adaptively choose high-quality mates that possess long telomeres.

Spatio-temporal variation in European starling reproductive success at multiple small spatial scales.

Understanding population dynamics requires spatio-temporal variation in demography to be measured across appropriate spatial and temporal scales. However, the most appropriate spatial scale(s) may not be obvious, few datasets cover sufficient time periods, and key demographic rates are often incompletely measured. Consequently, it is often assumed that demography will be spatially homogeneous within populations that lack obvious subdivision. Here, we quantify small-scale spatial and temporal variation in a key demographic rate, reproductive success (RS), within an apparently contiguous population of European starlings. We used hierarchical cluster analysis to define spatial clusters of nest sites at multiple small spatial scales and long-term data to test the hypothesis that small-scale spatio-temporal variation in RS occurred. RS was measured as the number of chicks alive ca. 12 days posthatch either per first brood or per nest site per breeding season (thereby incorporating multiple breeding attempts). First brood RS varied substantially among spatial clusters and years. Furthermore, the pattern of spatial variation was stable across years; some nest clusters consistently produced more chicks than others. Total seasonal RS also varied substantially among spatial clusters and years. However, the magnitude of variation was much larger and the pattern of spatial variation was no longer temporally consistent. Furthermore, the estimated magnitude of spatial variation in RS was greater at smaller spatial scales. We thereby demonstrate substantial spatial, temporal, and spatio-temporal variation in RS occurring at very small spatial scales. We show that the estimated magnitude of this variation depended on spatial scale and that spatio-temporal variation would not have been detected if season-long RS had not been measured. Such small-scale spatio-temporal variation should be incorporated into empirical and theoretical treatments of population dynamics.

Avian abundance and reproductive success in the intermountain west: Local‐scale response to the conservation reserve program

ABSTRACTConversion of extensive shrubsteppe communities to cropland has greatly reduced the habitat available to grassland‐ and sagebrush‐obligate birds in the Intermountain West of the United States. In Washington State, approximately 600,000 ha of converted farmland have been planted to perennial grasses, forbs, and shrubs under the Conservation Reserve Program (CRP), currently the largest‐scale effort creating perennial grassland habitat in this region. From 2003 to 2005 we sampled breeding birds and vegetation characteristics on 48 study sites in CRP and in native shrubsteppe. We used generalized linear models to examine characteristics associated with avian abundance and reproductive success. Abundance of shrubland and grassland birds was more closely associated with site vegetation than either management (planting of native vs. exotic grasses) or landscape factors, with cover of shrubs the dominant variable both for shrubland (positive effect) and for grassland (negative effect) birds. Daily survival rate of 1,377 nests in CRP was equal to or greater than that for nests in shrubsteppe and was similar for CRP planted with native versus exotic grasses. Seasonal reproductive success (young/breeding pair) of 2 focal species—Brewer's sparrow (Spizella breweri; n = 81pairs) and Savannah sparrow (Passerculus sandwichensis; n = 58)—also was similar between CRP and native shrubsteppe. The CRP has the potential to significantly increase habitat available to shrubland and grassland birds in the Intermountain West and to increase local populations. Because shrubs take significantly longer than herbaceous plants to achieve a size beneficial to birds, CRP grasslands with a well‐developed sagebrush (Artemisia spp.) component should be viewed as a long‐term investment. © 2015 The Wildlife Society.

Reproductive History and Nest Environment Are Correlated with Circulating Androgen and Glucocorticoid Concentrations in a Parental Care–Providing Teleost Fish

Using a long-term study population of wild smallmouth bass Micropterus dolomieu in a connected river-lake system, we investigated whether circulating glucocorticoid (cortisol) and androgen (testosterone) concentrations are influenced by reproductive investment and nesting environment in fish providing nest-guarding paternal care. For all individuals, we collected measures of reproductive history and the value of current parental care. We assessed nest environment and monitored individuals to quantify seasonal reproductive success. Finally, we measured circulating cortisol concentrations following a standardized stressor and circulating testosterone concentrations. Using general linear models, we found that poststress circulating cortisol concentrations were positively related to water temperature and were higher in fish nesting in the river than in the lake. Circulating testosterone concentrations were negatively related to water temperature and were higher in reproductively experienced fish. When considering the factors that influence reproductive success, we found that only parental size was positively related to current nest success. In summary, the results demonstrate that nesting environment is correlated with parental stress responses during parental care, while reproductive history and nesting environment are correlated with circulating androgen concentrations. Collectively, these results offer insight into the roles of both glucocorticoid and androgen steroid hormones during parental care in teleost fish.

Seasonal constraints and reproductive performance in female Common hamsters ( Cricetus cricetus)

Common hamsters ( Cricetus cricetus) are hibernators and therefore show a pronounced seasonal breeding behaviour. Previous studies suggest that an early onset of reproduction after vernal emergence can be crucial for reproductive success in the current year. In Vienna, the winter 2005/06 was exceptionally cold and snow cover lasted until late March. This enabled us to investigate the effects of harsh winter conditions on seasonal timing and reproductive success in female Common hamsters. We investigated differences in the timing of the active season, reproductive performance and physical condition before hibernation between 2006 and previous years (2003–05) to determine potential environmental effects. Hamsters were live-trapped throughout the active period, weighed, individually marked and reproductive status was determined. The number of litters per season and litter size were determined in individual females. Vernal emergence in 2006 was considerably delayed and females mated significantly later than in 2003–05. Reproductive output in 2006 was about half that of the preceding years. This was particularly pronounced in the size of the females’ first litters per season. The number of litters per female was similar in all periods. Almost 90% of the females in 2006 mated shortly after parturition and overlapped lactation of the first and gestation of the second litter. In 2003–05, only about one-third of the focal females successfully produced a litter after a postpartum oestrus. The time delay in spring 2006 led to a shorter active season compared to previous years reflecting the time constraints in this species. In conclusion, the results demonstrate that environmental factors can affect seasonal timing, reproductive output and preparation for hibernation in female Common hamsters.

Short-term demographic response of an old forest specialist to experimental selection harvesting

The brown creeper (Certhia americana) was recently identified as one of the forest bird species most sensitive to partial harvesting in North America. However, the processes underlying this sensitivity are poorly known. In this study, we quantified the immediate, post-treatment demographic response of this species to experimental selection harvesting in plots of northern hardwood forest in northwestern New Brunswick, Canada. We mapped individual detections and nest locations in 5 pairs (1 control and 1 treatment) of 25-ha plots in the first 2 y after single-tree selection harvesting. Linear mixed models with site and landscape context as random effects showed a significant negative effect of treatment on nest density and seasonal reproductive success. The density of large-diameter trees (≥ 30 cm dbh) was significantly lower in treated plots than in controls (mean: 77 versus 112 stems-ha−1), whereas the density of potential nesting substrates (snags with peeling bark) did not decrease significantly following treatment. Hence, the density of suitable foraging substrates may represent a limiting factor for both nest density and reproductive success, and partial harvesting may not be compatible with the persistence of breeding populations of brown creeper. Patches of untreated forest should be maintained in managed forest landscapes at all times for this and other taxa requiring old forest conditions.

Morphological and genetic predictors of parental care in the North American barn swallow Hirundo rustica erythrogaster

Sexually dimorphic traits often signal the fitness benefits an individual can provide to potential mates. In species with altricial young, these signals may also predict the level of parental care an individual is expected to provide to shared offspring. In this study, we tested three hypotheses that traditionally relate sexually dimorphic traits to parental care in two populations of North American barn swallows Hirundo rustica erythrogaster. The good parent hypothesis predicts a positive relationship between an individual's ornamentation and his or her care whereas the differential allocation (more care given by individuals when paired to high quality mates) and reproductive compensation (more care given by individuals when paired to low quality mates) hypotheses predict that an individual's level of parental investment is relative to the quality of their mate. Male and female North American barn swallows have colorful ventral feathers and elongated tail streamers, but there is evidence that ventral color, not tail streamer length, predicts measures of seasonal reproductive success. Accounting for the positive correlation between within‐pair feeding rates and other potentially confounding variables in all of our models, we found no support for the good parent hypothesis because in both males and females, traits shown to be under sexual selection did not predict feeding rates in either sex. However, our data reveal that male coloration, and not streamer length, predicted a female's provisioning rate to shared offspring (females fed more when paired with darker individuals) in two separate populations, supporting the differential allocation, but not the reproductive compensation hypothesis. Because genetic traits have also been shown to affect parental investment, we evaluated this variable as well and found that a male's paternity did not have significant effects on either male or female feeding rates. Overall, our results suggest that females do not pair with darker males in order to gain direct benefits in terms of his expected levels of parental care to shared offspring, but do themselves invest greater levels of care when paired to darker males. Further, our results are consistent with previous studies which suggest that ventral feather color, not streamer length, is a target of sexual selection in North American populations of barn swallow because females invested more in their offspring when paired to darker mates.

Seasonal and interannual correlations between right-whale distribution and calving success and chlorophyll concentrations in the Gulf of Maine, USA

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 394:289-302 (2009) - DOI: https://doi.org/10.3354/meps08267 Seasonal and interannual correlations between right-whale distribution and calving success and chlorophyll concentrations in the Gulf of Maine, USA Brittan L. Hlista1, Heidi M. Sosik1,*, Linda V. Martin Traykovski1, Robert D. Kenney2, Michael J. Moore1 1Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA 2Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882-1197, USA *Corresponding author. Email: hsosik@whoi.edu ABSTRACT: The North Atlantic right whale Eubalaena glacialis is one of the most endangered species of large whales. Although human-caused mortality is the primary factor contributing to poor recovery of E. glacialis, variability in reproductive success may also play a role. The present study evaluates the idea that seasonal distributions and reproductive success in E. glacialis are linked to food availability or related environmental conditions that can be assessed by treating satellite-derived sea-surface chlorophyll (chl) concentration as a proxy. Sea-surface chl time series in the major high-use feeding habitats and whale-sightings data were compared. Whale transition between habitats reflects a pattern in the seasonal distribution of peak concentration in satellite-derived chl. A regionally and seasonally weighted chl index was calculated to reflect aspects of average potential food condition. We found a significant correlation between the number of whale calves born and the weighted chl averaged over the prior 2 yr. These findings are consistent with the view that food availability during and just before the gestation period may be a critical factor regulating reproductive success, with low food years contributing to delays in conception. Longer time series are necessary to examine the predictive relationship between weighted chl concentration and calf production. Although ecological interactions and whale reproductive biology are certainly more complex than can be encompassed by emphasizing only food availability, analysis of satellite-derived surface chl concentrations provides a practical means to monitor a level of ecosystem variability that affects right-whale distributions and productivity. KEY WORDS: Right whale · Eubalaena glacialis · Calving · Seasonal patterns · Ocean color · SeaWiFS · Chlorophyll · Remote sensing Full text in pdf format PreviousCite this article as: Hlista BL, Sosik HM, Martin Traykovski LV, Kenney RD, Moore MJ (2009) Seasonal and interannual correlations between right-whale distribution and calving success and chlorophyll concentrations in the Gulf of Maine, USA. Mar Ecol Prog Ser 394:289-302. https://doi.org/10.3354/meps08267 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 394. Online publication date: November 18, 2009 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2009 Inter-Research.

Breeding in high‐elevation habitat results in shift to slower life‐history strategy within a single species

1. Elevational gradients create environmental variation that is hypothesized to promote variation in life-history strategies. We tested whether differences in life-history strategies were associated with elevation in a songbird, the dark-eyed junco (Junco hyemalis; Aves; A.O.U. 1998). 2. We monitored birds in four replicated sites per elevation, at 2000 m a.s.l. (high elevation) and 1000 m a.s.l. (low elevation), in the Rocky Mountains of Canada. 3. Over 5 years, we measured the following traits and vital rates: egg-laying schedules, morphological indicators of reproductive stage, seasonal reproductive success, indicators of competitive class (age, size, arrival time), and survival rates. 4. We found two main patterns: with an increase in breeding elevation, dark-eyed juncos delayed the development of structures necessary for reproduction (e.g. cloacal protuberance in males) and reduced the duration of their reproductive period to less than half of the time used by low-elevation birds; and 5. Juncos at high-elevation sites had 55-61% lower annual reproductive success and 15 to 20% higher survival rates. While adult juncos at high elevations produced fewer offspring, those offspring were in better condition. Proportions of age and size classes in high- compared to low-elevation populations were similar, suggesting that a life-history trade-off is present, rather than competition forcing inferior competitors to breed in a peripheral habitat. The apparent trade-off between reproduction and survival corresponded to a shorter period of favourable weather and available food in high- compared to low-elevation habitats. 6. Thus, elevation had a strong influence on life-history characteristics of a single species over a short spatial distance, suggesting a shift in life history from a high reproductive strategy at lower elevations to a high survivor strategy at high elevations. 7. This is the first paper to show a shift in avian life-history strategies along an elevational gradient (in both genders, of multiple age classes) when region (latitude) and phylogenetic histories are controlled for.

OCCURRENCE AND IMPLICATIONS OF DOUBLE BROODING IN A SOUTHERN POPULATION OF TREE SWALLOWS

Abstract Double brooding is the initiation of a second clutch of eggs after successfully raising young from the first clutch. Migratory birds that nest in temperate North America are often single-brooded, but there is widespread intra- and interspecific variation. Tree Swallows (Tachycineta bicolor), which are becoming a model species in biology, are typically classified as a single-brooded species. We documented 18 cases of double brooding in a population of Tree Swallows recently established in the Shenandoah Valley, Virginia. Double brooding may be underreported in this species or may be increasing as a result of climate change or range expansion. If double brooding is as common elsewhere as it was in our study population, it could significantly alter estimates of seasonal or lifetime reproductive success in this widely studied bird.

Polygyny and female breeding failure reduce effective population size in the lekking Gunnison sage-grouse

Populations with small effective sizes are at risk for inbreeding depression and loss of adaptive potential. Variance in reproductive success is one of several factors reducing effective population size ( N e) below the actual population size ( N). Here, we investigate the effects of polygynous (skewed) mating and variation in female breeding success on the effective size of a small population of the Gunnison sage-grouse ( Centrocercus minimus), a ground nesting bird with a lek mating system. During a two-year field study, we recorded attendance of marked birds at leks, male mating success, the reproductive success of radio-tagged females, and annual survival. We developed simulations to estimate the distribution of male reproductive success. Using these data, we estimated population size ( N ˆ ) and effective population size N e for the study population. We also simulated the effects of population size, skewed vs. random mating, and female breeding failure on N e. In our study population, the standardized variance in seasonal reproductive success was almost as high in females as in males, primarily due to a high rate of nest failure (73%). Estimated N e (42) was 19% of N ˆ in our population, below the level at which inbreeding depression is observed in captive breeding studies. A high hatching failure rate (28%) was also consistent with ongoing inbreeding depression. In the simulations, N e was reduced by skewed male mating success, especially at larger population sizes, and by female breeding failure. Extrapolation of our results suggests that six of the seven extant populations of this species may have effective sizes low enough to induce inbreeding depression and hence that translocations may be needed to supplement genetic diversity.

Plumage color and reproduction in the red-backed fairy-wren: Why be a dull breeder?

Males of many species can breed in distinct alternative phenotypes; for example, in many birds some males breed in dull plumage while others breed in bright plumage. Because females often appear to prefer brighter males, it is unclear why some males breed in dull plumage. Males in dull plumage might enjoy enhanced within-pair reproductive success if they can gain access to better breeding territories, or they might have relatively high extrapair reproductive success if they are better able to intrude on the territories of other males. To test these possibilities, we examined the reproductive consequences of plumage color in the red-backed fairy-wren (Malurus melanocephalus), a species in which males can breed in either bright plumage or dull plumage or serve as nonbreeding auxiliaries. Male plumage color was distributed bimodally and was loosely associated with age, such that some males molted into bright plumage a year or more earlier than others. Both male phenotypes were cuckolded at similar rates, but bright males sired significantly more extrapair young than did dull males, and this effect was independent of age. Thus, 1-year-old males who bred in dull plumage had low seasonal reproductive success compared with same-aged males who bred in bright plumage. These results suggest that males may not reap any fitness benefits by breeding in dull coloration, compared with breeding in bright plumage, but rather may be constrained to breed in suboptimal plumage by the timing of plumage acquisition.

A more informative method for analyzing reproductive success

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