Moving beyond body condition indices as an estimate of fitness in ecological and evolutionary studies

Wilder, Shawn M.; Raubenheimer, David; Simpson, Stephen J.

doi:10.1111/1365-2435.12460

Cited by 125 publications

(128 citation statements)

References 80 publications

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“…The SMI can be associated with the amount of energy reserves and general health of the organism (Peig & Green, , ), and our results confirm that it can be a useful proxy for survival (and reproductive potential, see below) in bats, but see a critique of general use of body condition measures in Wilder et al. (). Although there is considerable variation in SMI during the year, it is intuitive to consider that animals with better average body condition have greater survival probability, as they are likely to be obtaining enough resources, regardless of season.…”

Section: Discussionsupporting

confidence: 79%

Individual asymmetry as a predictor of fitness in the batCarollia perspicillata

Monteiro

Mellado

Nogueira

et al. 2019

J of Evolutionary Biology

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The measurement of fitness in wild populations is a challenging task, and a number of proxies have been proposed with different degrees of success. Developmental instability/stability (DI) is an organismal property associated with variance in bilateral asymmetry (fluctuating asymmetry—FA) and a correlated effect on fitness. This study provides evidence to corroborate the hypothesis that asymmetry partly reflects DI and is correlated with a reduction in fitness measured by survival and reproduction in bats. We studied two colonies of the bat Carollia perspicillata in southeastern Brazil over 5 years, marking and recapturing individuals. Gaussian mixture models for signed Forearm Asymmetry (ForA) distribution indicated that ~20% of asymmetry variation was due to DI heterogeneity among individuals. ForA, body condition (Scaled Mass Index—SMI) and Forearm Length (ForL) were used as predictors of survival probability in Cormack‐Jolly‐Seber models. Asymmetry was negatively associated with survival, whereas SMI and ForL were positively associated. The male C. perspicillata defend sites within the roost that are favoured by female harems, but there are mating opportunities for bachelor males, leading to both territorial disputes and sperm competition. As predicted by sexual selection, ForA was negatively associated with relative Testicle Length, a measure of reproductive potential. In females, ForA was negatively associated with the probability of two pregnancies (as opposed to one) in a given breeding season. The effect magnitudes and directions of associations suggest that asymmetry, even though not perfectly reflecting DI variation, is a useful predictor for fitness components in C. perspicillata.

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Section: Discussionsupporting

confidence: 79%

Individual asymmetry as a predictor of fitness in the batCarollia perspicillata

Monteiro

Mellado

Nogueira

et al. 2019

J of Evolutionary Biology

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“…In some cases, condition index and mass can be related to body reserves with different intensities (e.g. Wilder, Raubenheimer & Simpson, ). The fact that the data were obtained from wild or captive conditions was recorded as a two‐level factor (Wild versus Captive). We considered a population as being captive when the individuals were kept in an enclosure and artificially fed.…”

Section: Methodsmentioning

confidence: 99%

Causes and consequences of variation in offspring body mass: meta‐analyses in birds and mammals

et al. 2017

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Early survival is highly variable and strongly influences observed population growth rates in most vertebrate populations. One of the major potential drivers of survival variation among juveniles is body mass. Heavy juveniles are better fed and have greater body reserves, and are thus assumed to survive better than light individuals. In spite of this, some studies have failed to detect an influence of body mass on offspring survival, questioning whether offspring body mass does indeed consistently influence juvenile survival, or whether this occurs in particular species/environments. Furthermore, the causes for variation in offspring mass are poorly understood, although maternal mass has often been reported to play a crucial role. To understand why offspring differ in body mass, and how this influences juvenile survival, we performed phylogenetically corrected meta-analyses of both the relationship between offspring body mass and offspring survival in birds and mammals and the relationship between maternal mass and offspring mass in mammals. We found strong support for an overall positive effect of offspring body mass on survival, with a more pronounced influence in mammals than in birds. An increase of one standard deviation of body mass increased the odds of offspring survival by 71% in mammals and by 44% in birds. A cost of being too fat in birds in terms of flight performance might explain why body mass is a less reliable predictor of offspring survival in birds. We then looked for moderators explaining the among-study differences reported in the intensity of this relationship. Surprisingly, sex did not influence the intensity of the offspring mass-survival relationship and phylogeny only accounted for a small proportion of observed variation in the intensity of that relationship. Among the potential factors that might affect the relationship between mass and survival in juveniles, only environmental conditions was influential in mammals. Offspring survival was most strongly influenced by body mass in captive populations and wild populations in the absence of predation. We also found support for the expected positive effect of maternal mass on offspring mass in mammals (r = 0.387). As body mass is a strong predictor of early survival, we expected heavier mothers to allocate more to their offspring, leading them to be heavier and so to have a higher survival. However, none of the potential factors we tested for variation in the maternal mass-offspring mass relationship had a detectable influence. Further studies should focus on linking these two relationships to determine whether a strong effect of offspring size on early survival is associated with a high correlation coefficient between maternal mass and offspring mass.

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“…Body mass and tarsus length were linearly related (linear regression: r 2 = 0.13, P = 0.001), so we used these parameters to calculate body condition following the scaled mass index approach (Peig and Green, 2009). Body condition is generally assumed to reflect the energy stores of an individual; however, this assumption may not hold in all cases and direct measures of energy stores may be a more accurate estimate of energetic status (Wilder et al, 2015). To that end, we also quantified fat stores by visually inspecting the amount of furcular fat and assigned a score of 0-5 (a score of 0 representing no fat, 5 representing bulging fat deposits).…”

Section: Morphometricsmentioning

confidence: 99%

Advanced seasonal reproductive development in a male urban bird is reflected in earlier plasma luteinizing hormone rise but not energetic status

Davies

Behbahaninia

Giraudeau

et al. 2015

General and Comparative Endocrinology

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Urban animals inhabit an environment considerably different than do their non-urban conspecifics, and to persist urban animals must adjust to these novel environments. The timing of seasonal reproductive development (i.e., growth of gonads and secondary sex organs) is a fundamental determinant of the breeding period and is frequently advanced in urban bird populations. However, the underlying mechanism(s) by which birds adjust the timing of reproductive development to urban areas remain(s) largely unknown. Here, we compared the timing of vernal reproductive development in free-ranging urban and non-urban male Abert's Towhees, Melozone aberti, in Phoenix, Arizona, USA, and tested the non-mutually exclusive hypotheses that earlier reproductive development is due to improved energetic status and/or earlier increase in endocrine activity of the reproductive system. We found that urban birds initiated testicular development earlier than non-urban birds, but this disparity was not associated with differences in body condition, fat stores, or innate immune performance. These results provide no support for the hypothesis that energetic constraints are responsible for delayed reproductive development of non-urban relative to urban male Abert's Towhees. Urban birds did, however, increase their plasma luteinizing hormone, but not plasma testosterone, earlier than non-urban birds. These findings suggest that adjustment to urban areas by Abert's Towhees involves increases in the endocrine activity of the anterior pituitary gland and/or hypothalamus earlier than non-urban towhees.

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Moving beyond body condition indices as an estimate of fitness in ecological and evolutionary studies

Cited by 125 publications

References 80 publications

Individual asymmetry as a predictor of fitness in the batCarollia perspicillata

Individual asymmetry as a predictor of fitness in the batCarollia perspicillata

Causes and consequences of variation in offspring body mass: meta‐analyses in birds and mammals

Advanced seasonal reproductive development in a male urban bird is reflected in earlier plasma luteinizing hormone rise but not energetic status

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