Abstract
The challenges of seasonal environments are thought to contribute to brain evolution, but in which way is debated. According to the Cognitive Buffer Hypothesis (CBH) brain size should increase with seasonality, as the cognitive benefits of a larger brain should help overcoming periods of food scarcity via, for instance, increased behavioral flexibility. However, in line with the Expensive Brain Framework (EBF) brain size should decrease with seasonality because a smaller brain confers energetic benefits in periods of food scarcity. Empirical evidence is inconclusive and mostly limited to homoeothermic animals. Here we used phylogenetic comparative analyses to test the impact of seasonality on brain evolution across 30 species of anurans (frogs) experiencing a wide range of temperature and precipitation. Our results support the EBF because relative brain size and the size of the optic tectum were negatively correlated with variability in temperature. In contrast, we found no association between the variability in precipitation and the length of the dry season with either brain size or the sizes of other major brain regions. We suggest that seasonality-induced food scarcity resulting from higher variability in temperature constrains brain size evolution in anurans. Less seasonal environments may therefore facilitate the evolution of larger brains in poikilothermic animals.
Highlights
The challenges of seasonal environments are thought to contribute to brain evolution, but in which way is debated
The Cognitive Buffer Hypothesis (CBH)[15,16] states that a relatively larger brain allows for increased behavioral flexibility, which facilitates the behavioral buffering of unpredictable changes in the environment[17]
In the separate models in which we tested the relationships of relative brain size and the degree of environmental seasonality we found a negative correlation between relative brain size and coefficient of variation (CV) in mean temperature when controlling for the effects of phylogenetic relationships, snout-vent length (SVL) and body mass (Fig. 1; λ = 0.1260.670,
Summary
The challenges of seasonal environments are thought to contribute to brain evolution, but in which way is debated. If behavioral flexibility or other cognitive assets help to overcome such periods of food shortage we would expect a positive association between brain size and seasonality (CBH) If such periods of food shortage were met by saving energy on overly large brains we would expect a negative association between brain size and seasonality (EBF). We test these opposing predictions in 30 species of Chinese frogs using phylogenetically comparative methods (PGLS; see ‘Methods’) and relate aspects of brain anatomy to three measures of seasonality (Coefficient of variation in precipitation, length of the dry season ‘P2T’, coefficient of variation in temperature; see ‘Material and Methods’ for details)
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