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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.


Predictions of the number of young produced that survive to independence by scaled mass.Predictions are model-averaged and reflect the number of young in one breeding season. Scaled mass was centered to have a mean of zero such that the scale of the x-axis is the difference in grams from the mean. Predictions are presented for the 4-year analysis (A) which corresponds to the 2006−2007, 2007−2008, 2008−2009 and 2009−2010 breeding seasons, and for the 2-year analysis (B) which corresponds to the 2008−2009 and 2009−2010 breeding seasons. Individuals of any age are shown with unfilled circles; after-first year breeders in black; and those in their first breeding season in grey. Note that the scale of the y-axis differs between the 4-year (A) and 2-year (B) panels.
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pone.0136582.g002: Predictions of the number of young produced that survive to independence by scaled mass.Predictions are model-averaged and reflect the number of young in one breeding season. Scaled mass was centered to have a mean of zero such that the scale of the x-axis is the difference in grams from the mean. Predictions are presented for the 4-year analysis (A) which corresponds to the 2006−2007, 2007−2008, 2008−2009 and 2009−2010 breeding seasons, and for the 2-year analysis (B) which corresponds to the 2008−2009 and 2009−2010 breeding seasons. Individuals of any age are shown with unfilled circles; after-first year breeders in black; and those in their first breeding season in grey. Note that the scale of the y-axis differs between the 4-year (A) and 2-year (B) panels.

Mentions: Scaled mass had a positive effect on the number of young that survived to independence from low to above average mass, but this effect then plateaued at the highest values of scaled mass (Fig 2). The effect of scaled mass on reproductive success from the 4-year analysis (Fig 2A) is qualitatively similar to that from the 2-year analysis (Fig 2B), but is weaker, exhibits less variation and is not evident in all years. From the 2-year analysis, birds with optimal scaled mass are predicted to have an approximately three-fold increase in reproductive success over birds with low scaled mass: during an average year for reproductive success (2009−2010), an individual at an optimal scaled mass in at least their second-breeding season is predicted to produce 1.5 ± 0.7 young that survive to independence compared to 0.5 ± 0.4 young for an individual with a relatively low scaled mass (Fig 2B). During the year with high population-wide reproductive success (2008−2009), individuals of optimal scaled mass are predicted to produce 3.4 ± 1.2 young compared to 1.2 ± 1.1 young for individuals with low scaled mass (Fig 2B).


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)

Predictions of the number of young produced that survive to independence by scaled mass.Predictions are model-averaged and reflect the number of young in one breeding season. Scaled mass was centered to have a mean of zero such that the scale of the x-axis is the difference in grams from the mean. Predictions are presented for the 4-year analysis (A) which corresponds to the 2006−2007, 2007−2008, 2008−2009 and 2009−2010 breeding seasons, and for the 2-year analysis (B) which corresponds to the 2008−2009 and 2009−2010 breeding seasons. Individuals of any age are shown with unfilled circles; after-first year breeders in black; and those in their first breeding season in grey. Note that the scale of the y-axis differs between the 4-year (A) and 2-year (B) panels.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0136582.g002: Predictions of the number of young produced that survive to independence by scaled mass.Predictions are model-averaged and reflect the number of young in one breeding season. Scaled mass was centered to have a mean of zero such that the scale of the x-axis is the difference in grams from the mean. Predictions are presented for the 4-year analysis (A) which corresponds to the 2006−2007, 2007−2008, 2008−2009 and 2009−2010 breeding seasons, and for the 2-year analysis (B) which corresponds to the 2008−2009 and 2009−2010 breeding seasons. Individuals of any age are shown with unfilled circles; after-first year breeders in black; and those in their first breeding season in grey. Note that the scale of the y-axis differs between the 4-year (A) and 2-year (B) panels.
Mentions: Scaled mass had a positive effect on the number of young that survived to independence from low to above average mass, but this effect then plateaued at the highest values of scaled mass (Fig 2). The effect of scaled mass on reproductive success from the 4-year analysis (Fig 2A) is qualitatively similar to that from the 2-year analysis (Fig 2B), but is weaker, exhibits less variation and is not evident in all years. From the 2-year analysis, birds with optimal scaled mass are predicted to have an approximately three-fold increase in reproductive success over birds with low scaled mass: during an average year for reproductive success (2009−2010), an individual at an optimal scaled mass in at least their second-breeding season is predicted to produce 1.5 ± 0.7 young that survive to independence compared to 0.5 ± 0.4 young for an individual with a relatively low scaled mass (Fig 2B). During the year with high population-wide reproductive success (2008−2009), individuals of optimal scaled mass are predicted to produce 3.4 ± 1.2 young compared to 1.2 ± 1.1 young for individuals with low scaled mass (Fig 2B).

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.