Food availability as a major driver in the evolution of life‐history strategies of sibling species

Life‐history theory predicts trade‐offs between reproductive and survival traits such that different strategies or environmental constraints may yield comparable lifetime reproductive success among conspecifics. Food availability is one of the most important environmental factors shaping developmental processes. It notably affects key life‐history components such as reproduction and survival prospect. We investigated whether food resource availability could also operate as an ultimate driver of life‐history strategy variation between species. During 13 years, we marked and recaptured young and adult sibling mouse‐eared bats (Myotis myotis and Myotis blythii) at sympatric colonial sites. We tested whether distinct, species‐specific trophic niches and food availability patterns may drive interspecific differences in key life‐history components such as age at first reproduction and survival. We took advantage of a quasi‐experimental setting in which prey availability for the two species varies between years (pulse vs. nonpulse resource years), modeling mark‐recapture data for demographic comparisons. Prey availability dictated both adult survival and age at first reproduction. The bat species facing a more abundant and predictable food supply early in the season started its reproductive life earlier and showed a lower adult survival probability than the species subjected to more limited and less predictable food supply, while lifetime reproductive success was comparable in both species. The observed life‐history trade‐off indicates that temporal patterns in food availability can drive evolutionary divergence in life‐history strategies among sympatric sibling species.     

Asexual and sexual reproductive strategies in clonal plants

Most plants can reproduce both sexually and asexually (or vegetatively), and the balance between the two reproductive modes may vary widely between and within species. Extensive clonal growth may affect the evolution of life history traits in many ways. First, in some clonal species, sexual reproduction and sex ratio vary largely among populations. Variation in sexual reproduction may strongly affect plant’s adaptation to local environments and the evolution of the geographic range. Second, clonal growth can increase floral display, and thus pollinator attraction, while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal. Geitonogamous pollination can bring a cost to plant fitness through both female and male functions. Some co-evolutionary interactions, therefore, may exist between the spatial structure and the mating behavior of clonal plants. Finally, a trade-off may exist between sexual reproduction and clonal growth. Resource allocation to the two reproductive modes may depend on environmental conditions, competitive dominance, life span, and genetic factors. If different reproductive modes represent adaptive strategies for plants in different environments, we expect that most of the resources should be allocated to sexual reproduction in habitats with fluctuating environmental conditions and strong competition, while clonal growth should be dominant in stable habitats. Yet we know little about the consequence of natural selection on the two reproductive modes and factors which control the balance of the two reproductive modes. Future studies should investigate the reproductive strategies of clonal plants simultaneously from both sexual and asexual perspectives. Translated from Acta Phytoecologica Sinica, 2006, 20(1): 174–183 [译自: 植物生态学报]     

Asexual and sexual reproductive strategies in clonal plants

Most plants can reproduce both sexually and asexually (or vegetatively),and the balance between the two reproductive modes may vary widely between and within species.Extensive clonal growth may affect the evolution of life history traits in many ways.First,in some clonal species,sexual reproduction and sex ratio vary largely among populations.Variation in sexual reproduction may strongly affect plant's adaptation to local environments and the evolution of the geographic range.Second,clonal growth can increase floral display,and thus pollinator attraction,while it may impose serious constraints and evolutionary challenges on plants through geitonogamy that may strongly influence pollen dispersal.Geitonogamous pollination can bring a cost to plant fitness through both female and male functions.Some co-evolutionary interactions,therefore,may exist between the spatial structure and the mating behavior of clonal plants.Finally,a trade-off may exist between sexual reproduction and clonal growth.Resource allocation to the two reproductive modes may depend on environmental conditions,competitive dominance,life span,and genetic factors.If different reproductive modes represent adaptive strategies for plants in different environments,we expect that most of the resources should be allocated to sexual reproduction in habitats with fluctuating environmental conditions and strong competition,while clonal growth should be dominant in stable habitats.Yet we know little about the consequence of natural selection on the two reproductive modes and factors which control the balance of the two reproductive modes.Future studies should investigate the reproductive strategies of clonal plants simultaneously from both sexual and asexual perspectives.     

Snakes allocate amino acids acquired during vitellogenesis to offspring: are capital and income breeding consequences of variable foraging success?

Reproductive allocation strategies have been historically described as lying on a continuum between capital and income breeding. Capital breeders have been defined as species that allocate stored reserves to reproduction, whereas income breeders have been defined as species that allocate relatively recently‐ingested food resources to reproduction. Snakes are considered capital breeders because they efficiently store large amounts of nutrients and energy, potentially enough to support an entire reproductive bout without feeding. We examined the abilities of five viviparous snake species to allocate income to follicles during vitellogenesis. We fed ¹⁵N‐labelled L‐leucine to experimental females of each species during vitellogenesis, whereas control females were fed unlabelled meals. After ovulation, we measured yolk ¹⁵N p.p.m. using mass spectrometry. Maternal scale samples taken before labelling were used to estimate endogenous ¹⁵N concentrations, which should represent ‘capital’. Scale samples taken at ovulation were used to determine whether snakes assimilated ¹⁵N‐labelled‐leucine from labelled diets. Yolks and post‐ovulatory scales of labelled females were significantly more enriched in ¹⁵N than those of unlabelled females in all species, indicating significant assimilation and allocation of income‐derived amino acids to the yolk during vitellogenesis. The lack of among‐species differences suggests that all species allocated income amino acids to vitellogenesis. The results obtained in the present study suggest that proportional utilization of income or capital depends on the frequency and timing of foraging success during reproductive events. Therefore, capital and income breeding may be consequences of both life‐history and environmental constraints on foraging success, rather than strategies of reproductive allocation. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 390–404.     

克隆植物的无性与有性繁殖对策

许多植物同时具有克隆生长与有性繁殖,两种繁殖方式间的平衡在不同物种间以及同一物种内不同种群间变化很大。旺盛的克隆生长可能会从多方面影响生活史进化。首先,许多克隆植物的有性繁殖与更新程度都很低,甚至有一些植物由于克隆生长而几乎完全放弃了有性过程,从而影响到克隆植物对局域环境的适应和地理范围进化。其次,克隆生长增大花展示进而增加了对传粉者的吸引,同时也增加了同株异花授粉的风险,而同株异花授粉往往会导致植物雄性和雌性适合度的下降。因此,克隆植物的空间结构与交配方式间可能存在着协同进化关系。最后,克隆生长与有性繁殖间可能存在着权衡关系:对克隆生长的资源投入将会减少对有性繁殖的资源投入。这种权衡关系可能是由环境条件、竞争力度、植物寿命和遗传等因素决定的。如果不同的繁殖方式是植物在不同环境下采取的适应性对策,那么我们可以预期:在波动和竞争力度大的生境中,植物应将大部分的繁殖资源分配给有性繁殖;而在相对稳定的环境中,克隆繁殖应该占据优势地位。但是自然选择对两种繁殖方式的选择结果是什么,以及控制这两种方式间平衡的生态和遗传因子究竟有哪些,到底是克隆生长单向地影响了植物的有性繁殖,还是与有性过程相伴随的选择压力同时塑造了植物的克隆习性?目前尚不清楚。同时从无性与有性繁殖两个方面综合考察克隆植物的繁殖对策是今后亟待加强的工作。     

The impacts of Wolbachia and the microbiome on mate choice in Drosophila melanogaster

Symbionts and parasites can manipulate their hosts’ reproduction to their own benefit, profoundly influencing patterns of mate choice and evolution of the host population. Wolbachia is one of the most widespread symbionts among arthropods, and one that alters its hosts’ reproduction in diverse and dramatic ways. While we are beginning to appreciate how Wolbachia's extreme manipulations of host reproduction can influence species diversification and reproductive isolation, we understand little about how symbionts and Wolbachia, in particular, may affect intrapopulation processes of mate choice. We hypothesized that the maternally transmitted Wolbachia would increase the attractiveness of its female hosts to further its own spread. We therefore tested the effects of Wolbachia removal and microbiome disruption on female attractiveness and male mate choice among ten isofemale lines of Drosophila melanogaster. We found variable effects of general microbiome disruption on female attractiveness, with indications that bacteria interact with hosts in a line‐specific manner to affect female attractiveness. However, we found no evidence that Wolbachia influence female attractiveness or male mate choice among these lines. Although the endosymbiont Wolbachia can greatly alter the reproduction of their hosts in many species, there is no indication that they alter mate choice behaviours in D. melanogaster.     

Selection on apomictic lineages of Taraxacum at establishment in a mixed sexual–apomictic population

A species’ mode of reproduction, sexual or asexual, will affect its ecology and evolution. In many species, asexuality is related to polyploidy. In Taraxacum, apomicts are triploid, and sexuals are diploid. To disentangle the effects of ploidy level and reproductive mode on life‐history traits, we compared established apomictic Taraxacum genotypes with newly synthesized apomictic genotypes, obtained from diploid–triploid crosses. Diploid–triploid crossing is probably the way that most apomictic lineages originate. New genotypes had on average a much lower seed set than established genotypes. Established genotypes differed on average from new genotypes, in particular under shaded conditions: the established genotypes had longer leaves and flowered later. The differences between new and established triploids resembled the differences that have been found between sexual diploids and established apomictic triploids. We conclude that ploidy differences alone are not directly responsible for observed differences between sexual diploid and apomictic triploid dandelions.     

Effects of food supplementation on the physiological ecology of female Western diamond-backed rattlesnakes (<Emphasis Type="Italic">Crotalus atrox</Emphasis>)

Food availability is an important factor in the life histories of organisms because it is often limiting and thus can affect growth, mass change, reproduction, and behaviors such as thermoregulation, locomotion, and mating. Experimental studies in natural settings allow researchers to examine the effects of food on these parameters while animals are free to behave naturally. The wide variation among organisms in energy demands and among environmental food resources suggest that responses to changes in food availability may vary among organisms. Since most supplemental feeding field experiments have been conducted on species with high energy demands, we conducted a supplemental feeding study on free-ranging, female Western diamond-backed rattlesnakes (Crotalus atrox), a species with low energy demands and infrequent reproductive investment. Snakes were offered thawed rodents 1–4 times per week. Over two active seasons, we collected data on surface activity, home range size, growth, mass change, and reproduction of supplementally fed and control snakes. Fed and control snakes did not differ in surface activity levels (proportion of time encountered above versus below ground) or home range size. Fed snakes grew and gained mass faster, and had a dramatically higher occurrence of reproduction than control snakes. Also, fed snakes were in better body condition following reproduction than snakes that were not fed. However, litter characteristics such as offspring number and size were not increased by feeding, suggesting that these characteristics may be fixed. These data experimentally demonstrate that food availability can directly impact some life history traits (i.e., growth and reproduction for C. atrox), but not others (i.e., surface activity and home range size for C. atrox). The relationship between food availability and life history traits is affected in a complex way by ecological traits and physiological constraints, and thus interspecific variation in this relationship is likely to be high.     

Queen–worker ratio affects reproductive skew in a socially polymorphic ant

The partitioning of reproduction among individuals in communally breeding animals varies greatly among species, from the monopolization of reproduction (high reproductive skew) to similar contribution to the offspring in others (low skew). Reproductive skew models explain how relatedness or ecological constraints affect the magnitude of reproductive skew. They typically assume that individuals are capable of flexibly reacting to social and environmental changes. Most models predict a decrease of skew when benefits of staying in the group are reduced. In the ant Leptothorax acervorum, queens in colonies from marginal habitats form dominance hierarchies and only the top‐ranking queen lays eggs (“functional monogyny”). In contrast, queens in colonies from extended coniferous forests throughout the Palaearctic rarely interact aggressively and all lay eggs (“polygyny”). An experimental increase of queen:worker ratios in colonies from low‐skew populations elicits queen–queen aggression similar to that in functionally monogynous populations. Here, we show that this manipulation also results in increased reproductive inequalities among queens. Queens from natural overwintering colonies differed in the number of developing oocytes in their ovaries. These differences were greatly augmented in queens from colonies with increased queen:worker ratios relative to colonies with a low queen:worker ratio. As assumed by models of reproductive skew, L. acervorum colonies thus appear to be capable of flexibly adjusting reproductive skew to social conditions, yet in the opposite way than predicted by most models.     

Activity patterns of two syntopic and closely related aerial-hawking bat species during breeding season in Białowieża Primaeval Forest

Temporal and spatial activity of bats is species specific and shaped by many factors such as energy requirements, climate conditions and food distribution. Pregnancy and lactation are the most energy-demanding periods throughout the female life cycle. During these periods, females have to optimize their activity patterns to maximize foraging success; however, they simultaneously need to take care of their young. In addition, daily and seasonal fluctuations of insect availability strongly affect bat foraging activity. If females, which are under strong energy constraints, belong to closely related species, they may potentially suffer from competition. One of the mechanisms that allows them to avoid competition is temporal and spatial niche partitioning. Noctule and Leisler’s bats are closely related forest-dwelling species whose diet is similar and consists mainly of ephemeral insects. The aim of our study was to test if they exhibit similar patterns in relation to the time and duration of their nocturnal activity. In Bia?owie?a Forest, we demonstrated that female nocturnal activity of both noctule and Leisler’s bats was shaped mostly by reproductive period and ambient temperature. We did not observe significant differences in the activity patterns of the two noctule species, which suggests that physiological constraints connected with reproduction and environmental conditions affect these species in a similar way and outweigh the competition between species.     

Review: kisspeptin and reproduction in the pig

The activation of the hypothalamic–pituitary axis is critical for the initiation and maintenance of reproductive cycles in pigs and is influenced by a number of factors, such as nutrition, metabolism and gonadal steroids. Kisspeptin is a neuropeptide that is expressed in discrete regions of the porcine hypothalamus and is positioned to mediate the action of many of these factors. The expression of kisspeptin in the pig hypothalamus does not appear to be regulated by gonadal steroids in the same way as other species. It is unclear if kisspeptin is mediating nutritional or metabolic effects on gonadotropin secretion in pigs as it takes large deficits in feed intake or BW to affect hypothalamic expression of the KISS1 gene in the porcine hypothalamus. There appears to be little genetic diversity in kisspeptin or its receptor that is useful for improving reproduction in swine. Both peripheral and central injection of kisspeptin strongly stimulates the secretion of gonadotropin hormones, LH and FSH, in gilts. Similarly, synthetic analogues have been developed and showed potential promise as tools to manage reproductive cycles in gilts and sows. Review of the literature nonetheless reveals that research on kisspeptin and its function in controlling reproduction in pigs has lagged that of other livestock species.     

Pollination efficiency and reproductive patterns in relation to local plant density,population size,and floral display in the rewarding Listera ovata (Orchidaceae)

Pollination efficiency and reproductive success vary strongly among populations of most animal‐pollinated plant species, depending on their size and local density, whereas individual plants within populations experience varying levels of reproductive output as a result of differences in floral display. Although most orchid species have been shown to be severely pollination limited, few studies have investigated the impact of the above‐mentioned factors on pollination success and reproduction, especially in rewarding species. In this study, the impact of population size, local density of flowering plants, and floral display on the rates of pollinia export and fruit production was investigated in 13 natural populations of the rewarding terrestrial orchid Listera ovata. In addition, an emasculation experiment was set up to examine how floral display and local density of flowering plants affected the relative importance of cross‐ vs. geitonogamous pollination in determining fruit set. In the studied populations, pollination efficiency, pollen removal, and fruit set increased with increasing population size until a threshold value of 30–40 flowering plants was reached, above which pollination efficiency and reproductive output decreased again. On average, plants with large floral displays showed higher proportional pollinia removal and fruit set compared with smaller plants. Fruit production was also significantly and positively related to local plant density, whereas emasculation did not affect the relationship between local plant density and fruit set, suggesting that geitonogamous pollination did not affect the outcome of female function. The results of this study are discussed in the light of the flowering mechanism of the species and its generalized pollination system. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 713–721.     

Correlation between numerical dynamics and reproductive behavior in Cypripedium lentiginosum

Isolation, molecular identification and phylogenetic analysis were carried out to investigate the biodiversity of manganese bacteria in sediments which were collected from the Arctic Ocean during the 2^nd Chinese Arctic Scientific Expedition. 21 and 19 species of cultivable strains were isolated from sediments at Stations P11 and S11, respectively, according to their distinct morphological character on the screening plate of manganese medium. Molecular identification and phylogenetic analysis showed that the cultivable manganese bacteria from Station P11 were basically composed of γ-Proteobacteria (γ subgroup of the Proteobacteria branch of the domain Bacteria) and Actinobacteria, which accounted for 86% and 14%, respectively. The isolates of γ-Proteobacteria mainly included Psychrobacter, Shewanella, Acinetobacter and Marinobacter, of which Psychrobacter was the major genus, which accounted for 67% of the γ-Proteobacteria. The cultivable manganese bacteria from Station S11 included α-Proteobacteria, γ-Proteobacteria and Flavobacteria of Bacteroides. The γ-Proteobacteria mainly included Shewanella, Marinomonas and Alteromonas. The majority of α-Proteobacteria was Sphingomonas. The phylogenetic analysis indicated that bacteria from sediments at Stations P11 and S11 had different cultivable manganese microbial communities. All tested strains had higher resistance to Mn²⁺, of which Marinomonas sp. S11-S-4 had the highest resistant ability.     

Widespread Presence of Human BOULE Homologs among Animals and Conservation of Their Ancient Reproductive Function

Sex-specific traits that lead to the production of dimorphic gametes, sperm in males and eggs in females, are fundamental for sexual reproduction and accordingly widespread among animals. Yet the sex-biased genes that underlie these sex-specific traits are under strong selective pressure, and as a result of adaptive evolution they often become divergent. Indeed out of hundreds of male or female fertility genes identified in diverse organisms, only a very small number of them are implicated specifically in reproduction in more than one lineage. Few genes have exhibited a sex-biased, reproductive-specific requirement beyond a given phylum, raising the question of whether any sex-specific gametogenesis factors could be conserved and whether gametogenesis might have evolved multiple times. Here we describe a metazoan origin of a conserved human reproductive protein, BOULE, and its prevalence from primitive basal metazoans to chordates. We found that BOULE homologs are present in the genomes of representative species of each of the major lineages of metazoans and exhibit reproductive-specific expression in all species examined, with a preponderance of male-biased expression. Examination of Boule evolution within insect and mammalian lineages revealed little evidence for accelerated evolution, unlike most reproductive genes. Instead, purifying selection was the major force behind Boule evolution. Furthermore, loss of function of mammalian Boule resulted in male-specific infertility and a global arrest of sperm development remarkably similar to the phenotype in an insect boule mutation. This work demonstrates the conservation of a reproductive protein throughout eumetazoa, its predominant testis-biased expression in diverse bilaterian species, and conservation of a male gametogenic requirement in mice. This shows an ancient gametogenesis requirement for Boule among Bilateria and supports a model of a common origin of spermatogenesis.     

A life table study on three genetic strains of Ophryotrocha diadema (Polychaeta,Dorvilleidae)

A life-table study was performed on three strains of Ophryotrocha diadema. The wild type strain, YY (yellow eggs), was compared with a recessive mutant strain, ww (white eggs), and the F₁, hybrid, Yw.

The viability of the YY strain was greater than that of the ww strain. The hybrids were intermediate. Expectation of life. e., of zygotes were: YY 27.9, Yw 19.1, and ww 15.1 wk, respectively. The total outcome of reproduction followed the same pattern; the net reproductive rates, R ₀, were related as 1:0.62:0.47 for YY: Yw: ww.

Reproduction began in the fourth week. A maximum reproductive output during the next 4 wk was followed by a fast decline. The intrinsic rate of natural increase, r, was 0.880 per week for the YY strain, 0.903 for the Yw strain and 0.872 for the ww strain. For all strains, the first 7 wk of reproduction contributed more than 99% of the Lotka equation σ e ^?rx l _x m _x = l, i.e., l _x m _x values at older ages would not substantially affect population growth. In this 7–wk period (and the previous nonreproductive weeks), mortality differences were small among strains. During the period of maximum reproduction the average size of egg masses was approximately the same in all strains. The heterozygote superiority was due to shorter intervals between successive spawnings.

It is suggested that in the opportunistic species O. diadema deviations from an r–selected reproductive pattern are due to small adult size and to its ancestry from a mainly K–selected, very old polychaete group.

O. diadema has proven to be a useful test animal for marine pollution research. Observed effects on survival and reproduction have been summarized in a model to demonstrate population consequences of sublethal pollutant levels.     

Water conditions influence nestling survival in a Hooded Crow Corvus cornix wetland population

This paper examines how flooded river valley conditions affect reproductive success of Hooded Crows Corvus cornix nesting in the biotope considered as primary for this species. The main goals of the present study were to determine the nesting period that most influences the breeding output and to investigate the factors influencing reproductive efficiency of the studied population. Mean survival rate of the whole nesting period (53 days––from egg laying to fledgling) was 0.371 (95% CL: 0.338–0.403), while mean survival for the incubation period (to day 21) was 0.850 (0.827–0.875) and mean survival rate for the nestling period was 0.499 (0.460–0.538). The study has shown that the most critical period in the breeding cycle is the first half of the nestling stage, especially from hatching to day 5. Furthermore, the study demonstrated how water conditions affect reproduction in untypical wetland species. Similarly to many other waterbirds, in the studied population of the Hooded Crow, water level positively influences its reproduction.     

Cost of reproduction as reduced growth in genotypes of two congeneric species with contrasting life histories

Summary We examined the effect of reproduction on growth in 33 genotypes of Plantago major and 14 genotypes of P. rugelii. These two herbaceous perennials have contrasting life histories; P. major reproduces at a smaller size, and allocates a larger proportion of its biomass to reproduction, than P. rugelii. The effect of reproduction on frowth was determined experimentally using photoperiod manipulations to control level of reproduction. The difference in growth between reproductive treatments was divided by the difference in capsule weight to produce a measure of reproductive cost per g of capsule for genotypes of the two species. In both species there was substantial variation among genotypes in the effect of reproduction on growth. Much of this variation could be correlated with differences among genotypes in the extent of reproductive investment and plant size. Cost in terms of reduction in growth per g of capsule increased with reproductive investment in P. rugelii, and with plant size in P. major. We suggest the differences between species in timing and extent of reproduction are related to the differences between species in effect of reproduction on growth. Plantago rugelii may reproduce to a lesser extent than P. major because cost per g of capsule in terms of reduced vegetative biomass, increases with reproductive output in the former species, but not in the latter. Similarly, P. major may reproduce earlier than P. rugelii because cost per g of capsule increases with plant size in P. major, but not in P. rugelii.     

IS MOM IN CHARGE? IMPLICATIONS OF RESOURCE PROVISIONING ON THE EVOLUTION OF THE PLACENTA

The Trexler–DeAngelis model shows that placentas are most likely to evolve in environments with consistent, high levels of resource availability. An assumption imperative to the model is that placental species abort embryos in low food conditions. However, a previous experimental test of this assumption using the northern clade of Poeciliopsis showed no evidence for abortion. To distinguish between the alternatives that placental species either sacrifice body condition to maintain reproduction when resources are restricted, or that the previously documented pattern of resource allocation is a function of other life‐history correlates of placentation rather than placentation alone, we perform a similar experiment on the southern clade of Poeciliopsis. The southern clade has the opposite relationship between life‐history traits and placentation as seen in the northern clade. Our results mirror those from the northern clade, indicating that reproductive mode, rather than life history, dictates the pattern of resource allocation. These results add to the difficulties of explaining placental evolution within the constraints of the Trexler–DeAngelis model by restricting the range of resource conditions in which placental species can outcompete nonplacental species. They also lend support to hypotheses that suggest parent–offspring conflict in utero drives the evolution of the placenta.     

Variation in reproductive investment among and within populations of the scorpion Centruroides vittatus

Although information concerning variation among and within populations is essential to understanding an organism's life history, little is known of such variation in any species of scorpion. We show that reproductive investment by the scorpion Centruroides vittatus varied among three Texas populations during one reproductive season. Females from the Kickapoo population produced smaller offspring and larger litters than females from the Independence Creek or Decatur populations; this pattern remained when adjusting for among population variation in either female mass or total litter mass. Relative clutch mass (RCM) and within-litter variability in offspring mass (V*) did not differ among populations. Among-population variation may result from genetic differences or from phenotypically plastic responses to differing environments. Within populations, the interrelationships among reproductive variables were similar for Decatur and Independence Creek: females investing more in reproduction (measured by total litter mass, TLM) produced larger litters and larger offspring, and V* decreased with increased mean offspring mass (and with decreased litter size at Decatur). At Kickapoo, larger females produced larger litters and had larger TLM; females investing more in reproduction produced larger litters but not larger offspring. Within litter variability in offspring mass was not correlated with any reproductive variables in this latter population. These patterns may be explained by the fractional clutch hypothesis, the inability of females precisely to control investment among offspring or morphological constraints on reproduction.     

The influence of climate and habitat on stable isotope signatures and the isotopic niche of nestling White‐headed Woodpeckers (Dryobates albolarvatus)

The majority of landbird species feed their nestlings arthropods and variation in arthropod populations can impact reproductive outcomes in these species. Arthropod populations in turn are influenced by climate because temperature affects survival and reproduction, and larval development. Thus, climate factors have the potential to influence many bird species during their reproductive phases. In this study, we assessed climate factors that impact the diet of nestling White‐headed Woodpecker (Dryobates albolarvatus), an at‐risk keystone species in much of its range in western North America. To do this, we measured stable isotope signatures (δ¹³C and δ¹⁵N) in 152 nestlings across six years and linked variation in isotopic values to winter (December–February) and spring (June) precipitation and temperature using mixed effects models. We also explored habitat factors that may impact δ¹³C and δ¹⁵N and the relationship between δ¹⁵N and nest productivity. Last, we estimated isotopic niche width for nestlings in different watersheds and years using Bayesian standard ellipses, which allowed us to compare dietary niche width and overlap. We found that colder winter temperatures were associated with an increase in δ¹⁵N and δ¹⁵N levels had a weak positive relationship with nest productivity. We also found that sites with a more diverse tree community were associated with a broader isotopic niche width in nestlings. Our findings suggest that nestling diet is affected by climate, and under future warming climate scenarios, White‐headed Woodpecker nestling diet may shift in favor of lower trophic level prey (prey with lower δ¹⁵N levels). The impact of such changes on woodpecker populations merits further study.