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

Milenkaya O, Catlin DH, Legge S, Walters JR - PLoS ONE (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.

ABSTRACT
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.

No MeSH data available.


Relationship between PC2 and the probability of an adult fledging at least one young.PC2 is an axis of variation in individual condition indices (packed cell volume, hemoglobin, scaled mass, muscle score, fat score) with those having high energy reserves and high oxygen carrying capacity on the positive end of the axis, and those having low energy reserves and low oxygen carrying capacity on the negative end of the axis. Breeding stages refer to the stage of the adult when he/she was sampled for condition indices (pre-breeding, egg-laying, incubating, and nestling stages).
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pone.0136582.g001: Relationship between PC2 and the probability of an adult fledging at least one young.PC2 is an axis of variation in individual condition indices (packed cell volume, hemoglobin, scaled mass, muscle score, fat score) with those having high energy reserves and high oxygen carrying capacity on the positive end of the axis, and those having low energy reserves and low oxygen carrying capacity on the negative end of the axis. Breeding stages refer to the stage of the adult when he/she was sampled for condition indices (pre-breeding, egg-laying, incubating, and nestling stages).

Mentions: We performed post-hoc tests to explore possible explanations for an unexpected result in the relationship between PC2 and the probability of fledging young (see Results, Fig 1). We asked if individuals in the upper and lower quartiles of PC2 scores differ in age (first year versus after-first year); reproductive effort during the current breeding season including the number of nesting attempts, clutches laid, and broods hatched; reproductive effort and success in the previous breeding season including the number of nesting attempts, clutches laid, broods hatched, young fledged, and young produced that survive to independence; and survival of the bird to the following breeding season through band re-sighting. We used R version 3.0.0 [21] to conduct chi-square tests without continuity correction for age and survival data, and the Mann-Whitney-Wilcoxon test for the other variables. We set statistical significance at α = 0.05.


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

Milenkaya O, Catlin DH, Legge S, Walters JR - PLoS ONE (2015)

Relationship between PC2 and the probability of an adult fledging at least one young.PC2 is an axis of variation in individual condition indices (packed cell volume, hemoglobin, scaled mass, muscle score, fat score) with those having high energy reserves and high oxygen carrying capacity on the positive end of the axis, and those having low energy reserves and low oxygen carrying capacity on the negative end of the axis. Breeding stages refer to the stage of the adult when he/she was sampled for condition indices (pre-breeding, egg-laying, incubating, and nestling stages).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4549336&req=5

pone.0136582.g001: Relationship between PC2 and the probability of an adult fledging at least one young.PC2 is an axis of variation in individual condition indices (packed cell volume, hemoglobin, scaled mass, muscle score, fat score) with those having high energy reserves and high oxygen carrying capacity on the positive end of the axis, and those having low energy reserves and low oxygen carrying capacity on the negative end of the axis. Breeding stages refer to the stage of the adult when he/she was sampled for condition indices (pre-breeding, egg-laying, incubating, and nestling stages).
Mentions: We performed post-hoc tests to explore possible explanations for an unexpected result in the relationship between PC2 and the probability of fledging young (see Results, Fig 1). We asked if individuals in the upper and lower quartiles of PC2 scores differ in age (first year versus after-first year); reproductive effort during the current breeding season including the number of nesting attempts, clutches laid, and broods hatched; reproductive effort and success in the previous breeding season including the number of nesting attempts, clutches laid, broods hatched, young fledged, and young produced that survive to independence; and survival of the bird to the following breeding season through band re-sighting. We used R version 3.0.0 [21] to conduct chi-square tests without continuity correction for age and survival data, and the Mann-Whitney-Wilcoxon test for the other variables. We set statistical significance at α = 0.05.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.

ABSTRACT
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.

No MeSH data available.