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Reversed brain size sexual dimorphism accompanies loss of parental care in white sticklebacks.

Samuk K, Iritani D, Schluter D - Ecol Evol (2014)

Bottom Line: We found overall low differentiation among populations, although F ST was increased in between-type comparisons.We found that sexual dimorphism in brain size is reversed in white stickleback populations: males have smaller brains than females.Thus, while several alternatives need to be ruled out, the PBH appears to be a reasonable explanation for sexual dimorphism in brain size in threespine sticklebacks.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology and Biodiversity Research Centre, University of British Columbia Vancouver, British Columbia, Canada.

ABSTRACT
Uncovering factors that shape variation in brain morphology remains a major challenge in evolutionary biology. Recently, it has been shown that brain size is positively associated with level of parental care behavior in various taxa. One explanation for this pattern is that the cognitive demands of performing complex parental care may require increased brain size. This idea is known as the parental brain hypothesis (PBH). We set out to test the predictions of this hypothesis in wild populations of threespine stickleback (Gasterosteus aculeatus). These fish are commonly known to exhibit (1) uniparental male care and (2) sexual dimorphism in brain size (males>females). To test the PBH, we took advantage of the existence of closely related populations of stickleback that display variation in parental care behavior: common marine threespine sticklebacks (uniparental male care) and white threespine sticklebacks (no care). To begin, we quantified genetic differentiation among two common populations and three white populations from Nova Scotia. We found overall low differentiation among populations, although F ST was increased in between-type comparisons. We then measured the brain weights of males and females from all five populations along with two additional common populations from British Columbia. We found that sexual dimorphism in brain size is reversed in white stickleback populations: males have smaller brains than females. Thus, while several alternatives need to be ruled out, the PBH appears to be a reasonable explanation for sexual dimorphism in brain size in threespine sticklebacks.

No MeSH data available.


Related in: MedlinePlus

Body weight versus standard length for male and females sticklebacks of two types, white and common, from seven populations in Canada. For clarity, regression lines were determined via standard linear models (no population effect, see text for details on mixed model analysis).
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fig02: Body weight versus standard length for male and females sticklebacks of two types, white and common, from seven populations in Canada. For clarity, regression lines were determined via standard linear models (no population effect, see text for details on mixed model analysis).

Mentions: As predicted by the PBH, we found that sexual dimorphism in brain size was altered in white sticklebacks (Table 1, Sex:Type, F1,239=13.46, P = 0.0007). This appears to be driven by a decrease in the intercept of the brain-standard length regression line for male white sticklebacks, rather than a difference in slope (Fig. 2 Males; Table 1, Males: Type, F1,5=11.016, P = 0.021). In other words, male white sticklebacks have smaller brains than male common sticklebacks across all body sizes. This pattern appears consistent across all three populations of white sticklebacks we sampled (Figs. 1, 2).


Reversed brain size sexual dimorphism accompanies loss of parental care in white sticklebacks.

Samuk K, Iritani D, Schluter D - Ecol Evol (2014)

Body weight versus standard length for male and females sticklebacks of two types, white and common, from seven populations in Canada. For clarity, regression lines were determined via standard linear models (no population effect, see text for details on mixed model analysis).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4222210&req=5

fig02: Body weight versus standard length for male and females sticklebacks of two types, white and common, from seven populations in Canada. For clarity, regression lines were determined via standard linear models (no population effect, see text for details on mixed model analysis).
Mentions: As predicted by the PBH, we found that sexual dimorphism in brain size was altered in white sticklebacks (Table 1, Sex:Type, F1,239=13.46, P = 0.0007). This appears to be driven by a decrease in the intercept of the brain-standard length regression line for male white sticklebacks, rather than a difference in slope (Fig. 2 Males; Table 1, Males: Type, F1,5=11.016, P = 0.021). In other words, male white sticklebacks have smaller brains than male common sticklebacks across all body sizes. This pattern appears consistent across all three populations of white sticklebacks we sampled (Figs. 1, 2).

Bottom Line: We found overall low differentiation among populations, although F ST was increased in between-type comparisons.We found that sexual dimorphism in brain size is reversed in white stickleback populations: males have smaller brains than females.Thus, while several alternatives need to be ruled out, the PBH appears to be a reasonable explanation for sexual dimorphism in brain size in threespine sticklebacks.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology and Biodiversity Research Centre, University of British Columbia Vancouver, British Columbia, Canada.

ABSTRACT
Uncovering factors that shape variation in brain morphology remains a major challenge in evolutionary biology. Recently, it has been shown that brain size is positively associated with level of parental care behavior in various taxa. One explanation for this pattern is that the cognitive demands of performing complex parental care may require increased brain size. This idea is known as the parental brain hypothesis (PBH). We set out to test the predictions of this hypothesis in wild populations of threespine stickleback (Gasterosteus aculeatus). These fish are commonly known to exhibit (1) uniparental male care and (2) sexual dimorphism in brain size (males>females). To test the PBH, we took advantage of the existence of closely related populations of stickleback that display variation in parental care behavior: common marine threespine sticklebacks (uniparental male care) and white threespine sticklebacks (no care). To begin, we quantified genetic differentiation among two common populations and three white populations from Nova Scotia. We found overall low differentiation among populations, although F ST was increased in between-type comparisons. We then measured the brain weights of males and females from all five populations along with two additional common populations from British Columbia. We found that sexual dimorphism in brain size is reversed in white stickleback populations: males have smaller brains than females. Thus, while several alternatives need to be ruled out, the PBH appears to be a reasonable explanation for sexual dimorphism in brain size in threespine sticklebacks.

No MeSH data available.


Related in: MedlinePlus