Climate change and commercial fishing practices codetermine survival of a long-lived seabird.

Understanding the environmental mechanisms that govern population change is a fundamental objective in ecology. Although the determination of how top-down and bottom-up drivers affect demography is important, it is often equally critical to understand the extent to which, environmental conditions that underpin these drivers fluctuate across time. For example, associations between climate and both food availability and predation risk may suggest the presence of trophic interactions that may influence inferences made from patterns in ecological data. Analytical tools have been developed to account for these correlations, while providing opportunities to ask novel questions regarding how populations change across space and time. Here, we combine two modeling disciplines-path analysis and mark-recapture-recovery models-to explore whether shifts in sea-surface temperatures (SSTs) influenced top-down (entanglement in fishing equipment) or bottom-up (forage fish production) population constraints over 60 years, and the extent to which these covarying processes shaped the survival of a long-lived seabird, the Royal tern. We found that hemispheric trends in SST were associated with variation in the amount of fish harvested along the Atlantic coast of North America and in the Caribbean, whereas reductions in forage fish production were mostly driven by shifts in the amount of fish harvested by commercial fisheries throughout the North Atlantic the year prior. Although the indirect (i.e., stock depletion) and direct (i.e., entanglement) impacts of commercial fishing on Royal tern mortality has declined over the last 60 years, increased SSTs during this time period has resulted in a comparable increase in mortality risk, which disproportionately impacted the survival of the youngest age-classes of Royal terns. Given climate projections for the North Atlantic, our results indicate that threats to Royal tern population persistence in the Mid-Atlantic will most likely be driven by failures to recruit juveniles into the breeding population.

Enzymatic Pyridine Aromatization during Thiopeptide Biosynthesis.

Thiazole-containing pyritides (thiopeptides) are ribosomally synthesized and post-translationally modified peptides (RiPPs) that have attracted interest owing to their potent biological activities and structural complexity. The class-defining feature of a thiopeptide is a six-membered, nitrogenous heterocycle formed by an enzymatic [4 + 2]-cycloaddition. In rare cases, piperidine or dehydropiperidine (DHP) is present; however, the aromatized pyridine is considerably more common. Despite significant effort, the mechanism by which the central pyridine is formed remains poorly understood. Building on our recent observation of the Bycroft-Gowland intermediate (i.e., the direct product of the [4 + 2]-cycloaddition), we interrogated thiopeptide pyridine synthases using a combination of targeted mutagenesis, kinetic assays, substrate analogs, enzyme-substrate cross-linking, and chemical rescue experiments. Collectively, our data delineate roles for several conserved residues in thiopeptide pyridine synthases. A critical tyrosine facilitates the final aromatization step of pyridine formation. This work provides a foundation for further exploration of the [4 + 2]-cycloaddition reaction and future customization of pyridine-containing macrocyclic peptides.

Structural basis for the hydrolytic dehalogenation of the fungicide chlorothalonil.

Cleavage of aromatic carbon-chlorine bonds is critical for the degradation of toxic industrial compounds. Here, we solved the X-ray crystal structure of chlorothalonil dehalogenase (Chd) from Pseudomonas sp. CTN-3, with 15 of its N-terminal residues truncated (ChdT), using single-wavelength anomalous dispersion refined to 1.96 Å resolution. Chd has low sequence identity (<15%) compared with all other proteins whose structures are currently available, and to the best of our knowledge, we present the first structure of a Zn(II)-dependent aromatic dehalogenase that does not require a coenzyme. ChdT forms a "head-to-tail" homodimer, formed between two α-helices from each monomer, with three Zn(II)-binding sites, two of which occupy the active sites, whereas the third anchors a structural site at the homodimer interface. The catalytic Zn(II) ions are solvent-accessible via a large hydrophobic (8.5 × 17.8 Å) opening to bulk solvent and two hydrophilic branched channels. Each active-site Zn(II) ion resides in a distorted trigonal bipyramid geometry with His117, His257, Asp116, Asn216, and a water/hydroxide as ligands. A conserved His residue, His114, is hydrogen-bonded to the Zn(II)-bound water/hydroxide and likely functions as the general acid-base. We examined substrate binding by docking chlorothalonil (2,4,5,6-tetrachloroisophtalonitrile, TPN) into the hydrophobic channel and observed that the most energetically favorable pose includes a TPN orientation that coordinates to the active-site Zn(II) ions via a CN and that maximizes a π-π interaction with Trp227 On the basis of these results, along with previously reported kinetics data, we propose a refined catalytic mechanism for Chd-mediated TPN dehalogenation.

Remarkable and Unexpected Mechanism for (S)-3-Amino-4-(difluoromethylenyl)cyclohex-1-ene-1-carboxylic Acid as a Selective Inactivator of Human Ornithine Aminotransferase.

Human ornithine aminotransferase (hOAT) is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that was recently found to play an important role in the metabolic reprogramming of hepatocellular carcinoma (HCC) via the proline and glutamine metabolic pathways. The selective inhibition of hOAT by compound 10 exhibited potent in vivo antitumor activity. Inspired by the discovery of the aminotransferase inactivator (1S,3S)-3-amino-4-(difluoromethylene)cyclopentane-1-carboxylic acid (5), we rationally designed, synthesized, and evaluated a series of six-membered-ring analogs. Among them, 14 was identified as a new selective hOAT inactivator, which demonstrated a potency 22× greater than that of 10. Three different types of protein mass spectrometry approaches and two crystallographic approaches were employed to identify the structure of hOAT-14 and the formation of a remarkable final adduct (32') in the active site. These spectral studies reveal an enzyme complex heretofore not observed in a PLP-dependent enzyme, which has covalent bonds to two nearby residues. Crystal soaking experiments and molecular dynamics simulations were carried out to identify the structure of the active-site intermediate 27' and elucidate the order of the two covalent bonds that formed, leading to 32'. The initial covalent reaction of the activated warhead occurs with *Thr322 from the second subunit, followed by a subsequent nucleophilic attack by the catalytic residue Lys292. The turnover mechanism of 14 by hOAT was supported by a mass spectrometric analysis of metabolites and fluoride ion release experiments. This novel mechanism for hOAT with 14 will contribute to the further rational design of selective inactivators and an understanding of potential inactivation mechanisms by aminotransferases.

A Remarkable Difference That One Fluorine Atom Confers on the Mechanisms of Inactivation of Human Ornithine Aminotransferase by Two Cyclohexene Analogues of γ-Aminobutyric Acid.

Human ornithine aminotransferase (hOAT), a pyridoxal 5'-phosphate-dependent enzyme, plays a critical role in the progression of hepatocellular carcinoma (HCC). Pharmacological selective inhibition of hOAT has been shown to be a potential therapeutic approach for HCC. Inspired by the discovery of the nonselective aminotransferase inactivator (1R,3S,4S)-3-amino-4-fluoro cyclopentane-1-carboxylic acid (1), in this work, we rationally designed, synthesized, and evaluated a novel series of fluorine-substituted cyclohexene analogues, thereby identifying 8 and 9 as novel selective hOAT time-dependent inhibitors. Intact protein mass spectrometry and protein crystallography demonstrated 8 and 9 as covalent inhibitors of hOAT, which exhibit two distinct inactivation mechanisms resulting from the difference of a single fluorine atom. Interestingly, they share a similar turnover mechanism, according to the mass spectrometry-based analysis of metabolites and fluoride ion release experiments. Molecular dynamics (MD) simulations and electrostatic potential (ESP) charge calculations were conducted, which elucidated the significant influence of the one-fluorine difference on the corresponding intermediates, leading to two totally different inactivation pathways. The novel addition-aromatization inactivation mechanism for 9 contributes to its significantly enhanced potency, along with excellent selectivity over other aminotransferases.

Interception of the Bycroft-Gowland Intermediate in the Enzymatic Macrocyclization of Thiopeptides.

Thiopeptides are a broad class of macrocyclic, heavily modified peptide natural products that are unified by the presence of a substituted, nitrogen-containing heterocycle core. Early work indicated that this core might be fashioned from two dehydroalanines by an enzyme-catalyzed aza-[4 + 2] cycloaddition to give a cyclic-hemiaminal intermediate. This common intermediate could then follow a reductive path toward a dehydropiperidine, as in the thiopeptide thiostrepton, or an aromatization path to yield the pyridine groups observed in many other thiopeptides. Although several of the enzymes proposed to perform this cycloaddition have been reconstituted, only pyridine products have been isolated and any hemiaminal intermediates have yet to be observed. Here, we identify the conditions and substrates that decouple the cycloaddition from subsequent steps and allow interception and characterization of this long hypothesized intermediate. Transition state modeling indicates that the key amide-iminol tautomerization is the major hurdle in an otherwise energetically favorable cycloaddition. An anionic model suggests that deprotonation and polarization of this amide bond by TbtD removes this barrier and provides a sufficient driving force for facile (stepwise) cycloaddition. This work provides evidence for a mechanistic link between disparate cyclases in thiopeptide biosynthesis.

Mechanism of Inactivation of Ornithine Aminotransferase by (1S,3S)-3-Amino-4-(hexafluoropropan-2-ylidenyl)cyclopentane-1-carboxylic Acid.

The inhibition of ornithine aminotransferase (OAT), a pyridoxal 5'-phosphate-dependent enzyme, has been implicated as a treatment for hepatocellular carcinoma (HCC), the most common form of liver cancer, for which there is no effective treatment. From a previous evaluation of our aminotransferase inhibitors, (1S,3S)-3-amino-4-(perfluoropropan-2-ylidene)cyclopentane-1-carboxylic acid hydrochloride (1) was found to be a selective and potent inactivator of human OAT (hOAT), which inhibited the growth of HCC in athymic mice implanted with human-derived HCC, even at a dose of 0.1 mg/kg. Currently, investigational new drug (IND)-enabling studies with 1 are underway. The inactivation mechanism of 1, however, has proved to be elusive. Here we propose three possible mechanisms, based on mechanisms of known aminotransferase inactivators: Michael addition, enamine addition, and fluoride ion elimination followed by conjugate addition. On the basis of crystallography and intact protein mass spectrometry, it was determined that 1 inactivates hOAT through fluoride ion elimination to an activated 1,1'-difluoroolefin, followed by conjugate addition and hydrolysis. This result was confirmed with additional studies, including the detection of the cofactor structure by mass spectrometry and through the identification of turnover metabolites. On the basis of this inactivation mechanism and to provide further evidence for the mechanism, analogues of 1 (19, 20) were designed, synthesized, and demonstrated to have the predicted selective inactivation mechanism. These analogues highlight the importance of the trifluoromethyl group and provide a basis for future inactivator design.

Epidemiology of sarcoptic mange in a geographically constrained insular red fox population.

BACKGROUND: Sarcoptic mange is a skin disease caused by the contagious ectoparasite Sarcoptes scabiei, capable of suppressing and extirpating wild canid populations. Starting in 2015, we observed a multi-year epizootic of sarcoptic mange affecting a red fox (Vulpes vulpes) population on Fire Island, NY, USA. We explored the ecological factors that contributed to the spread of sarcoptic mange and characterized the epizootic in a landscape where red foxes are geographically constrained. METHODS: We tested for the presence of S. scabiei DNA in skin samples collected from deceased red foxes with lesions visibly consistent with sarcoptic mange disease. We deployed 96-100 remote trail camera stations each year to capture red fox occurrences and used generalized linear mixed-effects models to assess the affects of red fox ecology, human and other wildlife activity, and island geography on the frequency of detecting diseased red foxes. We rated the extent of visual lesions in diseased individuals and mapped the severity and variability of the sarcoptic mange disease. RESULTS: Skin samples that we analyzed demonstrated 99.8% similarity to S. scabiei sequences in GenBank. Our top-ranked model (weight = 0.94) showed that diseased red foxes were detected more frequently close to roadways, close to territories of other diseased red foxes, away from human shelters, and in areas with more mammal activity. There was no evidence that detection rates in humans and their dogs or distance to the nearest red fox den explained the detection rates of diseased red foxes. Although detected infrequently, we observed the most severe signs of sarcoptic mange at the periphery of residential villages. The spread of visual signs of the disease was approximately 7.3 ha/week in 2015 and 12.1 ha/week in 2017. CONCLUSIONS: We quantified two separate outbreaks of sarcoptic mange disease that occurred > 40 km apart and were separated by a year. Sarcoptic mange revealed an unfettered spread across the red fox population. The transmission of S. scabiei mites in this system was likely driven by red fox behaviors and contact between individuals, in line with previous studies. Sarcoptic mange is likely an important contributor to red fox population dynamics within barrier island systems.

Factors that affect migratory Western Atlantic red knots (Calidris canutus rufa) and their prey during spring staging on Virginia's barrier islands.

Understanding factors that influence a species' distribution and abundance across the annual cycle is required for range-wide conservation. Thousands of imperiled red knots (Calidris cantus rufa) stop on Virginia's barrier islands each year to replenish fat during spring migration. We investigated the variation in red knot presence and flock size, the effects of prey on this variation, and factors influencing prey abundance on Virginia's barrier islands. We counted red knots and collected potential prey samples at randomly selected sites from 2007-2018 during a two-week period during early and peak migration. Core samples contained crustaceans (Orders Amphipoda and Calanoida), blue mussels (Mytilus edulis), coquina clams (Donax variabilis), and miscellaneous prey (horseshoe crab eggs (Limulus polyphemus), angel wing clams (Cyrtopleura costata), and other organisms (e.g., insect larvae, snails, worms)). Estimated red knot peak counts in Virginia during 21-27 May were highest in 2012 (11,959) and lowest in 2014 (2,857; 12-year peak migration [Formula: see text] = 7,175, SD = 2,869). Red knot and prey numbers varied across sampling periods and substrates (i.e., peat and sand). Red knots generally used sites with more prey. Miscellaneous prey ([Formula: see text] = 2401.00/m2, SE = 169.16) influenced red knot presence at a site early in migration, when we only sampled on peat banks. Coquina clams ([Formula: see text] = 1383.54/m2, SE = 125.32) and blue mussels ([Formula: see text] = 777.91/m2, SE = 259.31) affected red knot presence at a site during peak migration, when we sampled both substrates. Few relationships between prey and red knot flock size existed, suggesting that other unmeasured factors determined red knot numbers at occupied sites. Tide and mean daily water temperature affected prey abundance. Maximizing the diversity, availability, and abundance of prey for red knots on barrier islands requires management that encourages the presence of both sand and peat bank intertidal habitats.

(S)-4-Amino-5-phenoxypentanoate designed as a potential selective agonist of the bacterial transcription factor GabR.

Addressing molecular recognition in the context of evolution requires pursuing new molecular targets to enable the development of agonists or antagonists with new mechanisms of action. Disruption of transcriptional regulation through targeting transcription factors that regulate the expression of key enzymes in bacterial metabolism may provide a promising method for controlling the bacterial metabolic pathways. To this end, we have selectively targeted a bacterial transcription regulator through the design and synthesis of a series of γ-aminobutyric acid (GABA) derivatives, including (S)-4-amino-5-phenoxypentanoate (4-phenoxymethyl-GABA), which are based on docking insights gained from a previously-solved crystal structure of GabR from Bacillus subtilis. This target was selected because GabR strictly controls GABA metabolism by regulating the transcription of the gabT/D operon. These GabR transcription modulators are selective for the bacterial transcription factor GabR and are unable to bind to structural homologs of GabR due to distinct steric constraints. We have obtained a crystal structure of 4-phenoxymethyl-GABA bound as an external aldimine with PLP in the effector binding site of GabR, which suggests that this compound is capable of binding and reacting in the same manner as the native effector ligand. Inhibition assays demonstrate high selectivity of 4-phenoxymethyl-GABA for bacterial GabR versus several selected eukaryotic enzymes. Single-molecule fluorescence resonance energy transfer (smFRET) experiments reveal a ligand-induced DNA distortion that is very similar to that of the native effector GABA, suggesting that the compound functions as a potential selective agonist of GabR.

Successful breeding predicts divorce in plovers.

When individuals breed more than once, parents are faced with the choice of whether to re-mate with their old partner or divorce and select a new mate. Evolutionary theory predicts that, following successful reproduction with a given partner, that partner should be retained for future reproduction. However, recent work in a polygamous bird, has instead indicated that successful parents divorced more often than failed breeders (Halimubieke et al. in Ecol Evol 9:10734-10745, 2019), because one parent can benefit by mating with a new partner and reproducing shortly after divorce. Here we investigate whether successful breeding predicts divorce using data from 14 well-monitored populations of plovers (Charadrius spp.). We show that successful nesting leads to divorce, whereas nest failure leads to retention of the mate for follow-up breeding. Plovers that divorced their partners and simultaneously deserted their broods produced more offspring within a season than parents that retained their mate. Our work provides a counterpoint to theoretical expectations that divorce is triggered by low reproductive success, and supports adaptive explanations of divorce as a strategy to improve individual reproductive success. In addition, we show that temperature may modulate these costs and benefits, and contribute to dynamic variation in patterns of divorce across plover breeding systems.

Habitat selection and potential fitness consequences of two early-successional species with differing life-history strategies.

Habitat selection and its relationship to fitness is a fundamental concept in ecology, but the mechanisms driving this connection are complex and difficult to detect. Despite the difficulties in understanding such intricate relationships, it is imperative that we study habitat selection and its relationship with fitness. We compared habitat selection of least terns (Sternula antillarum) and piping plovers (Charadrius melodus) on the Missouri River (2012-2014) to examine the consequences of those choices on nest and chick survival. We hypothesized that plovers and terns would select habitat that minimized the chance of flooding and predation of eggs, chicks, and adults, but that plovers would also select habitat that would provide foraging habitat for their chicks. We developed an integrated habitat selection model that assessed selection across multiple scales (sandbar and nest scales) and directly modeled the effect of selection on nest and chick survival. In general, the species selected habitat in keeping with our hypotheses, such that predation and flooding, in particular, may have been reduced. Sandbar selection had either a negative or no appreciable effect on nest survival for both species across years. Nest-site selection in 2012 had a generally positive effect on nest survival and chick survival for both terns and plovers, and this trended toward a negative effect by 2014. This result suggested that early selection decisions appeared to be adaptive, but we speculate that relatively high site fidelity and habitat degradation led to reduced benefit over time. Our results highlight the complex nature of habitat selection and its relationship to fitness.

Using a Bayesian network to understand the importance of coastal storms and undeveloped landscapes for the creation and maintenance of early successional habitat.

Coastal storms have consequences for human lives and infrastructure but also create important early successional habitats for myriad species. For example, storm-induced overwash creates nesting habitat for shorebirds like piping plovers (Charadrius melodus). We examined how piping plover habitat extent and location changed on barrier islands in New York, New Jersey, and Virginia after Hurricane Sandy made landfall following the 2012 breeding season. We modeled nesting habitat using a nest presence/absence dataset that included characterizations of coastal morphology and vegetation. Using a Bayesian network, we predicted nesting habitat for each study site for the years 2010/2011, 2012, and 2014/2015 based on remotely sensed spatial datasets (e.g., lidar, orthophotos). We found that Hurricane Sandy increased piping plover habitat by 9 to 300% at 4 of 5 study sites but that one site saw a decrease in habitat by 27%. The amount, location, and longevity of new habitat appeared to be influenced by the level of human development at each site. At three of the five sites, the amount of habitat created and the time new habitat persisted were inversely related to the amount of development. Furthermore, the proportion of new habitat created in high-quality overwash was inversely related to the level of development on study areas, from 17% of all new habitat in overwash at one of the most densely developed sites to 80% of all new habitat at an undeveloped site. We also show that piping plovers exploited new habitat after the storm, with 14-57% of all nests located in newly created habitat in the 2013 breeding season. Our results quantify the importance of storms in creating and maintaining coastal habitats for beach-nesting species like piping plovers, and these results suggest a negative correlation between human development and beneficial ecological impacts of these natural disturbances.

Comment on "Global pattern of nest predation is disrupted by climate change in shorebirds".

Kubelka et al (Reports, 9 November 2018, p. 680) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.

Senescence and carryover effects of reproductive performance influence migration, condition, and breeding propensity in a small shorebird.

Breeding propensity, the probability that an animal will attempt to breed each year, is perhaps the least understood demographic process influencing annual fecundity. Breeding propensity is ecologically complex, as associations among a variety of intrinsic and extrinsic factors may interact to affect an animal's breeding decisions. Individuals that opt not to breed can be more difficult to detect than breeders, which can (1) lead to difficulty in estimation of breeding propensity, and (2) bias other demographic parameters. We studied the effects of sex, age, and population reproductive success on the survival and breeding propensity of a migratory shorebird, the piping plover (Charadrius melodus), nesting on the Missouri River. We used a robust design Barker model to estimate true survival and breeding propensity and found survival decreased as birds aged and did so more quickly for males than females. Monthly survival during the breeding season was lower than during migration or the nonbreeding season. Males were less likely to skip breeding (range: 1-17%) than females (range: 3-26%; ßsex = -0.21, 95% CI: -0.38 to -0.21), and both sexes were less likely to return to the breeding grounds following a year of high reproductive success. Birds that returned in a year following relatively high population-wide reproductive output were in poorer condition than following a year with lower reproductive output. Younger adult birds and females were more likely to migrate from the breeding area earlier than older birds and males; however, all birds stayed on the breeding grounds longer when nest survival was low, presumably because of renesting attempts. Piping plovers used a variety of environmental and demographic cues to inform their reproduction, employing strategies that could maximize fitness on average. Our results support the "disposable soma" theory of aging and follow with predictions from life history theory, exhibiting the intimate connections among the core ecological concepts of senescence, carryover effects, and life history.

Substrate Trapping in the Siderophore Tailoring Enzyme PvdQ.

Siderophore biosynthesis by Pseudomonas aeruginosa enhances virulence and represents an attractive drug target. PvdQ functions in the type-1 pyoverdine biosynthetic pathway by removing a myristoyl anchor from a pyoverdine precursor, allowing eventual release from the periplasm. A circularly permuted version of PvdQ bypasses the self-processing step of this Ntn-hydrolase and retains the activity, selectivity, and structure of wild-type PvdQ, as revealed by a 1.8 Å resolution X-ray crystal structure. A 2.55 Å resolution structure of the inactive S1A/N269D-cpPvdQ mutant in complex with the pyoverdine precursor PVDIq reveals a specific binding pocket for the d-Tyr of this modified peptide substrate. To our knowledge, this structure is the first of a pyoverdine precursor peptide bound to a biosynthetic enzyme. Details of the observed binding interactions have implications for control of pyoverdine biosynthesis and inform future drug design efforts.

Metapopulation viability of an endangered shorebird depends on dispersal and human-created habitats: piping plovers (Charadrius melodus) and prairie rivers.

BACKGROUND: Many species are distributed as metapopulations in dynamic landscapes, where habitats change through space and time. Individuals locate habitat through dispersal, and the relationship between a species and landscape characteristics can have profound effects on population persistence. Despite the importance of connectivity in dynamic environments, few empirical studies have examined temporal variability in dispersal or its effect on metapopulation dynamics. In response to this knowledge gap, we studied the dispersal, demography, and viability of a metapopulation of an endangered, disturbance-dependent shorebird. We examined three subpopulations of piping plovers (Charadrius melodus) on the lower Platte and Missouri rivers from 2008-2013. High flow events from an upstream dam on the Missouri River in 2010 and 2011 allowed us to assess the effect of total habitat loss and the subsequent creation of new habitat associated with a large disturbance at one 'natural' study location. The other two sites within the metapopulation, which were maintained by anthropogenic activities (e.g., mining, development, habitat restoration), were largely unaffected by this disturbance, resulting in a controlled natural experiment. RESULTS: High flow events were associated with increased emigration, decreased immigration, and decreased survival in the subpopulation that experienced high flows. Following the high flow event, immigration into that subpopulation increased. Dispersal rates among subpopulations were negatively correlated with distance. The metapopulation had a low probability of extinction over 100 years (0 %) under the current disturbance interval and associated dispersal and survival rates. However, persistence depended on relatively stable, human-created habitats, not the dynamic, natural habitat (47.7 % extinction probability for this subpopulation). CONCLUSIONS: We found that functional connectivity, as measured by the rate of dispersal among subpopulations, increased as a result of the high flow event in our study metapopulation. Plovers also increased reproductive output following this event. Although the study metapopulation had a low overall probability of extinction, metapopulation persistence depended on anthropogenically created habitats that provided a small but stable source of nesting habitat and dispersers through time. However, all subpopulations remained small, even if persistent, making them individually vulnerable to extinction through stochastic events. Given the highly dynamic nature of habitat availability in this system, maintaining several subpopulations within the metapopulation and stable sources of habitat will be critical, and this species will likely remain conservation-reliant.

Body Condition Indices Predict Reproductive Success but Not Survival in a Sedentary, Tropical Bird.

Body condition may predict individual fitness because those in better condition have more resources to allocate towards improving their fitness. However, the hypothesis that condition indices are meaningful proxies for fitness has been questioned. Here, we ask if intraspecific variation in condition indices predicts annual reproductive success and survival. We monitored a population of Neochmia phaeton (crimson finch), a sedentary, tropical passerine, for reproductive success and survival over four breeding seasons, and sampled them for commonly used condition indices: mass adjusted for body size, muscle and fat scores, packed cell volume, hemoglobin concentration, total plasma protein, and heterophil to lymphocyte ratio. Our study population is well suited for this research because individuals forage in common areas and do not hold territories such that variation in condition between individuals is not confounded by differences in habitat quality. Furthermore, we controlled for factors that are known to impact condition indices in our study population (e.g., breeding stage) such that we assessed individual condition relative to others in the same context. Condition indices that reflect energy reserves predicted both the probability of an individual fledging young and the number of young produced that survived to independence, but only during some years. Those that were relatively heavy for their body size produced about three times more independent young compared to light individuals. That energy reserves are a meaningful predictor of reproductive success in a sedentary passerine supports the idea that energy reserves are at least sometimes predictors of fitness. However, hematological indices failed to predict reproductive success and none of the indices predicted survival. Therefore, some but not all condition indices may be informative, but because we found that most indices did not predict any component of fitness, we question the ubiquitous interpretation of condition indices as surrogates for individual quality and fitness.