Limits...
Exaggerated trait allometry, compensation and trade-offs in the New Zealand giraffe weevil (Lasiorhynchus barbicornis).

Painting CJ, Holwell GI - PLoS ONE (2013)

Bottom Line: Here we characterise the scaling relationship between rostrum and body size and show that males have a steep positive allometry, but that the slope is non-linear due to a relative reduction in rostrum length for the largest males, suggesting a limitation in resource allocation or a diminishing requirement for large males to invest increasingly into larger rostra.Increased investment in wing and leg length is therefore likely to compensate for the costs of flying with, and wielding the exaggerated rostrum of larger male giraffe weevils.These results provide a first step in identifying the potential for trait compensation and trades-offs, but are phenotypic correlations only and should be interpreted with care in the absence of breeding experiments.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Auckland, Auckland, New Zealand.

ABSTRACT
Sexual selection has driven the evolution of exaggerated traits among diverse animal taxa. The production of exaggerated traits can come at a cost to other traits through trade-offs when resources allocated to trait development are limited. Alternatively some traits can be selected for in parallel to support or compensate for the cost of bearing the exaggerated trait. Male giraffe weevils (Lasiorhynchus barbicornis) display an extremely elongated rostrum used as a weapon during contests for mates. Here we characterise the scaling relationship between rostrum and body size and show that males have a steep positive allometry, but that the slope is non-linear due to a relative reduction in rostrum length for the largest males, suggesting a limitation in resource allocation or a diminishing requirement for large males to invest increasingly into larger rostra. We also measured testes, wings, antennae, fore- and hind-tibia size and found no evidence of a trade-off between these traits and rostrum length when comparing phenotypic correlations. However, the relative length of wings, antennae, fore- and hind-tibia all increased with relative rostrum length suggesting these traits may be under correlational selection. Increased investment in wing and leg length is therefore likely to compensate for the costs of flying with, and wielding the exaggerated rostrum of larger male giraffe weevils. These results provide a first step in identifying the potential for trait compensation and trades-offs, but are phenotypic correlations only and should be interpreted with care in the absence of breeding experiments.

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Related in: MedlinePlus

The allometry of rostrum length for male and female Lasiorhynchus barbicornis.The line of best fit for each sex is fitted on the data, showing a Weibull growth curve for males (closed circles), and a simple linear regression line for females (open circles). The grey shaded area around each set of points is the 95% confidence intervals for each model (seen as a grey line for females due to CI’s being very tight). Inset drawings show the sexual dimorphism in rostrum morphology (drawings by Vivian Ward).
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pone-0082467-g002: The allometry of rostrum length for male and female Lasiorhynchus barbicornis.The line of best fit for each sex is fitted on the data, showing a Weibull growth curve for males (closed circles), and a simple linear regression line for females (open circles). The grey shaded area around each set of points is the 95% confidence intervals for each model (seen as a grey line for females due to CI’s being very tight). Inset drawings show the sexual dimorphism in rostrum morphology (drawings by Vivian Ward).

Mentions: To analyse the scaling relationship of female L. barbicornis a scatterplot of rostrum length against pronotum width was made to visually inspect the relationship (Figure 2). There was a clear linear relationship between these two traits, with no obvious deviation from a straight line. As expected, a simple linear regression model showed a very strong correlation between female rostrum length and body size (R2 = 0.96, rostrum length = 0.69 + 3.24x pronotum width, p <0.001). Following the parsimonious approach of Knell [5] we decided that it was not necessary to go further with this analysis, and it was concluded that the shape of the female scaling relationship is best described by a continuous, straight line. This conclusion is also supported by the extremely tight 95% confidence intervals for the slope estimate (Figure 2, 95% CI = 3.19 - 3.3).


Exaggerated trait allometry, compensation and trade-offs in the New Zealand giraffe weevil (Lasiorhynchus barbicornis).

Painting CJ, Holwell GI - PLoS ONE (2013)

The allometry of rostrum length for male and female Lasiorhynchus barbicornis.The line of best fit for each sex is fitted on the data, showing a Weibull growth curve for males (closed circles), and a simple linear regression line for females (open circles). The grey shaded area around each set of points is the 95% confidence intervals for each model (seen as a grey line for females due to CI’s being very tight). Inset drawings show the sexual dimorphism in rostrum morphology (drawings by Vivian Ward).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842246&req=5

pone-0082467-g002: The allometry of rostrum length for male and female Lasiorhynchus barbicornis.The line of best fit for each sex is fitted on the data, showing a Weibull growth curve for males (closed circles), and a simple linear regression line for females (open circles). The grey shaded area around each set of points is the 95% confidence intervals for each model (seen as a grey line for females due to CI’s being very tight). Inset drawings show the sexual dimorphism in rostrum morphology (drawings by Vivian Ward).
Mentions: To analyse the scaling relationship of female L. barbicornis a scatterplot of rostrum length against pronotum width was made to visually inspect the relationship (Figure 2). There was a clear linear relationship between these two traits, with no obvious deviation from a straight line. As expected, a simple linear regression model showed a very strong correlation between female rostrum length and body size (R2 = 0.96, rostrum length = 0.69 + 3.24x pronotum width, p <0.001). Following the parsimonious approach of Knell [5] we decided that it was not necessary to go further with this analysis, and it was concluded that the shape of the female scaling relationship is best described by a continuous, straight line. This conclusion is also supported by the extremely tight 95% confidence intervals for the slope estimate (Figure 2, 95% CI = 3.19 - 3.3).

Bottom Line: Here we characterise the scaling relationship between rostrum and body size and show that males have a steep positive allometry, but that the slope is non-linear due to a relative reduction in rostrum length for the largest males, suggesting a limitation in resource allocation or a diminishing requirement for large males to invest increasingly into larger rostra.Increased investment in wing and leg length is therefore likely to compensate for the costs of flying with, and wielding the exaggerated rostrum of larger male giraffe weevils.These results provide a first step in identifying the potential for trait compensation and trades-offs, but are phenotypic correlations only and should be interpreted with care in the absence of breeding experiments.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Auckland, Auckland, New Zealand.

ABSTRACT
Sexual selection has driven the evolution of exaggerated traits among diverse animal taxa. The production of exaggerated traits can come at a cost to other traits through trade-offs when resources allocated to trait development are limited. Alternatively some traits can be selected for in parallel to support or compensate for the cost of bearing the exaggerated trait. Male giraffe weevils (Lasiorhynchus barbicornis) display an extremely elongated rostrum used as a weapon during contests for mates. Here we characterise the scaling relationship between rostrum and body size and show that males have a steep positive allometry, but that the slope is non-linear due to a relative reduction in rostrum length for the largest males, suggesting a limitation in resource allocation or a diminishing requirement for large males to invest increasingly into larger rostra. We also measured testes, wings, antennae, fore- and hind-tibia size and found no evidence of a trade-off between these traits and rostrum length when comparing phenotypic correlations. However, the relative length of wings, antennae, fore- and hind-tibia all increased with relative rostrum length suggesting these traits may be under correlational selection. Increased investment in wing and leg length is therefore likely to compensate for the costs of flying with, and wielding the exaggerated rostrum of larger male giraffe weevils. These results provide a first step in identifying the potential for trait compensation and trades-offs, but are phenotypic correlations only and should be interpreted with care in the absence of breeding experiments.

Show MeSH
Related in: MedlinePlus