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The converse to Bergmann's rule in bumblebees, a phylogenetic approach

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ABSTRACT

Two patterns commonly emerge when animal body size is analyzed as a function of latitudinal distribution. First, body size increases with latitude, a temperature effect known as Bergmann's rule, and second, the converse to Bergmann's rule, a pattern in which body size decreases with latitude. However, other geographic patterns can emerge when the mechanisms that generate Bergmann's and the converse to Bergmann's clines operate together. Here, we use phylogenetic comparative analysis in order to control for phylogenetic inertia, and we show that bumblebees exhibit the converse to Bergmann's rule. Bumblebee taxa are distributed worldwide in temperate and tropical regions. The largest species are found in places with high water availability during the driest time of the year. Nonetheless, large body size is constrained by extreme temperatures. Bumblebees’ body size could be related to a higher extent to the size of food rewards to be harvested than to the energetic advantages of thermoregulation. Moreover, we found that the body size of eusocial and cuckoo species responded in the same way to environmental variables, suggesting that they have not diverged due to different selective pressures.

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Thorax Width as a function of latitude for 91 bumblebee species. Ordinary least squares regressions fitted are shown for illustrative purposes. Bumblebees exhibit the converse to Bergmann's rule: The largest species are found in lower latitudes.
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ece32321-fig-0003: Thorax Width as a function of latitude for 91 bumblebee species. Ordinary least squares regressions fitted are shown for illustrative purposes. Bumblebees exhibit the converse to Bergmann's rule: The largest species are found in lower latitudes.

Mentions: After controlling for phylogenetic nonindependence among bumblebee taxa, the results of the MCMCglmm analysis indicated significant differences in bumblebees’ body size (Dummy variable; Table 1, Fig. 2). Nonetheless, there were no differences between queens and cuckoo females (P MCMC = 0.488), between workers and cuckoo females (P MCMC = 0.083), and between eusocial and cuckoo males (P MCMC = 0.635). Moreover, according to the inverse Bergmann's rule, we found a negative and significant relationship between latitude and Thorax Width (Fig. 3). The interactions between the dummy variable and all other independent variables were not significant (data not shown in simplified models), indicating a similar body size response to latitude between females and males of eusocial and cuckoo bumblebees. The model showed high λ values (λ > 0.980), indicating a strong phylogenetic effect on the relationships between the latitude and body size.


The converse to Bergmann's rule in bumblebees, a phylogenetic approach
Thorax Width as a function of latitude for 91 bumblebee species. Ordinary least squares regressions fitted are shown for illustrative purposes. Bumblebees exhibit the converse to Bergmann's rule: The largest species are found in lower latitudes.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016639&req=5

ece32321-fig-0003: Thorax Width as a function of latitude for 91 bumblebee species. Ordinary least squares regressions fitted are shown for illustrative purposes. Bumblebees exhibit the converse to Bergmann's rule: The largest species are found in lower latitudes.
Mentions: After controlling for phylogenetic nonindependence among bumblebee taxa, the results of the MCMCglmm analysis indicated significant differences in bumblebees’ body size (Dummy variable; Table 1, Fig. 2). Nonetheless, there were no differences between queens and cuckoo females (P MCMC = 0.488), between workers and cuckoo females (P MCMC = 0.083), and between eusocial and cuckoo males (P MCMC = 0.635). Moreover, according to the inverse Bergmann's rule, we found a negative and significant relationship between latitude and Thorax Width (Fig. 3). The interactions between the dummy variable and all other independent variables were not significant (data not shown in simplified models), indicating a similar body size response to latitude between females and males of eusocial and cuckoo bumblebees. The model showed high λ values (λ > 0.980), indicating a strong phylogenetic effect on the relationships between the latitude and body size.

View Article: PubMed Central - PubMed

ABSTRACT

Two patterns commonly emerge when animal body size is analyzed as a function of latitudinal distribution. First, body size increases with latitude, a temperature effect known as Bergmann's rule, and second, the converse to Bergmann's rule, a pattern in which body size decreases with latitude. However, other geographic patterns can emerge when the mechanisms that generate Bergmann's and the converse to Bergmann's clines operate together. Here, we use phylogenetic comparative analysis in order to control for phylogenetic inertia, and we show that bumblebees exhibit the converse to Bergmann's rule. Bumblebee taxa are distributed worldwide in temperate and tropical regions. The largest species are found in places with high water availability during the driest time of the year. Nonetheless, large body size is constrained by extreme temperatures. Bumblebees’ body size could be related to a higher extent to the size of food rewards to be harvested than to the energetic advantages of thermoregulation. Moreover, we found that the body size of eusocial and cuckoo species responded in the same way to environmental variables, suggesting that they have not diverged due to different selective pressures.

No MeSH data available.


Related in: MedlinePlus