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Common Noctule Bats Are Sexually Dimorphic in Migratory Behaviour and Body Size but Not Wing Shape

View Article: PubMed Central - PubMed

ABSTRACT

Within the large order of bats, sexual size dimorphism measured by forearm length and body mass is often female-biased. Several studies have explained this through the effects on load carrying during pregnancy, intrasexual competition, as well as the fecundity and thermoregulation advantages of increased female body size. We hypothesized that wing shape should differ along with size and be under variable selection pressure in a species where there are large differences in flight behaviour. We tested whether load carrying, sex differential migration, or reproductive advantages of large females affect size and wing shape dimorphism in the common noctule (Nyctalus noctula), in which females are typically larger than males and only females migrate long distances each year. We tested for univariate and multivariate size and shape dimorphism using data sets derived from wing photos and biometric data collected during pre-migratory spring captures in Switzerland. Females had forearms that are on average 1% longer than males and are 1% heavier than males after emerging from hibernation, but we found no sex differences in other size, shape, or other functional characters in any wing parameters during this pre-migratory period. Female-biased size dimorphism without wing shape differences indicates that reproductive advantages of big mothers are most likely responsible for sexual dimorphism in this species, not load compensation or shape differences favouring aerodynamic efficiency during pregnancy or migration. Despite large behavioural and ecological sex differences, morphology associated with a specialized feeding niche may limit potential dimorphism in narrow-winged bats such as common noctules and the dramatic differences in migratory behaviour may then be accomplished through plasticity in wing kinematics.

No MeSH data available.


Principal component 1 vs 2 of Procrustes scaled coordinates in the geometric morphometric analysis.The first two principal components account for a cumulative 51.1% and 68.1% of the variation, respectively.
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pone.0167027.g004: Principal component 1 vs 2 of Procrustes scaled coordinates in the geometric morphometric analysis.The first two principal components account for a cumulative 51.1% and 68.1% of the variation, respectively.

Mentions: A further subset (82 female, 27 male) of the 135 wing photos above had all 13 anatomical points visible for analysis. A PCA on the covariance matrix generated from Procrustes-fitted landmark data revealed that there were no sex differences in the shape of noctule wings and showed nearly complete overlap in shape space, with PC1 and PC2 (Figs 3 & 4) accounting for 68.1% of the cumulative variation in the data set. There was no influence of centroid size, sex, or their interaction on wing shape in the first three principal components (PC1: F3, 105 = 1.684, p = 0.18, PC2: F3, 105 = 1.152, P = 0.33; PC3: F3, 105 = 0.898, P = 0.45). Furthermore a MANOVA of the Procrustes coordinates showed a trend towards sex differences in centroid size (F1, 107 = 3.68, P = 0.06), with slightly larger male centroids, and in the size-corrected shape space (F22, 2354 = 1.14, P = 0.08). We therefore ran a final discriminant function analysis using 1000 permutations in MorphoJ and found that we were not able to reliably classify sex by shape of the wing alone (P = 0.38).


Common Noctule Bats Are Sexually Dimorphic in Migratory Behaviour and Body Size but Not Wing Shape
Principal component 1 vs 2 of Procrustes scaled coordinates in the geometric morphometric analysis.The first two principal components account for a cumulative 51.1% and 68.1% of the variation, respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120837&req=5

pone.0167027.g004: Principal component 1 vs 2 of Procrustes scaled coordinates in the geometric morphometric analysis.The first two principal components account for a cumulative 51.1% and 68.1% of the variation, respectively.
Mentions: A further subset (82 female, 27 male) of the 135 wing photos above had all 13 anatomical points visible for analysis. A PCA on the covariance matrix generated from Procrustes-fitted landmark data revealed that there were no sex differences in the shape of noctule wings and showed nearly complete overlap in shape space, with PC1 and PC2 (Figs 3 & 4) accounting for 68.1% of the cumulative variation in the data set. There was no influence of centroid size, sex, or their interaction on wing shape in the first three principal components (PC1: F3, 105 = 1.684, p = 0.18, PC2: F3, 105 = 1.152, P = 0.33; PC3: F3, 105 = 0.898, P = 0.45). Furthermore a MANOVA of the Procrustes coordinates showed a trend towards sex differences in centroid size (F1, 107 = 3.68, P = 0.06), with slightly larger male centroids, and in the size-corrected shape space (F22, 2354 = 1.14, P = 0.08). We therefore ran a final discriminant function analysis using 1000 permutations in MorphoJ and found that we were not able to reliably classify sex by shape of the wing alone (P = 0.38).

View Article: PubMed Central - PubMed

ABSTRACT

Within the large order of bats, sexual size dimorphism measured by forearm length and body mass is often female-biased. Several studies have explained this through the effects on load carrying during pregnancy, intrasexual competition, as well as the fecundity and thermoregulation advantages of increased female body size. We hypothesized that wing shape should differ along with size and be under variable selection pressure in a species where there are large differences in flight behaviour. We tested whether load carrying, sex differential migration, or reproductive advantages of large females affect size and wing shape dimorphism in the common noctule (Nyctalus noctula), in which females are typically larger than males and only females migrate long distances each year. We tested for univariate and multivariate size and shape dimorphism using data sets derived from wing photos and biometric data collected during pre-migratory spring captures in Switzerland. Females had forearms that are on average 1% longer than males and are 1% heavier than males after emerging from hibernation, but we found no sex differences in other size, shape, or other functional characters in any wing parameters during this pre-migratory period. Female-biased size dimorphism without wing shape differences indicates that reproductive advantages of big mothers are most likely responsible for sexual dimorphism in this species, not load compensation or shape differences favouring aerodynamic efficiency during pregnancy or migration. Despite large behavioural and ecological sex differences, morphology associated with a specialized feeding niche may limit potential dimorphism in narrow-winged bats such as common noctules and the dramatic differences in migratory behaviour may then be accomplished through plasticity in wing kinematics.

No MeSH data available.