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A larger brain confers a benefit in a spatial mate search learning task in male guppies.

Kotrschal A, Corral-Lopez A, Amcoff M, Kolm N - Behav. Ecol. (2014)

Bottom Line: However, experimental evidence for the link between relative brain size and cognitive ability is surprisingly scarce and to date stems from a single study on brain size selected guppies (Poecilia reticulata), where large-brained females were shown to outperform small-brained females in a numerical learning assay.Because the results were inconclusive for males in that study, we here use a more ecologically relevant test of male cognitive ability to investigate whether or not a relatively larger brain increases cognitive ability also in males.Our results support that relatively larger brains are better also for males in some contexts, which further substantiates that variation in vertebrate brain size is generated through the balance between energetic costs and cognitive benefits.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University , Norbyvägen 18D, SE-75236 Uppsala , Sweden and ; Department of Zoology/Ethology, Stockholm University , Svante Arrheniusväg 18 B, SE-10691 Stockholm , Sweden.

ABSTRACT

Brain size varies dramatically among vertebrates, and selection for increased cognitive abilities is thought to be the key force underlying the evolution of a large brain. Indeed, numerous comparative studies suggest positive relationships between cognitively demanding aspects of behavior and brain size controlled for body size. However, experimental evidence for the link between relative brain size and cognitive ability is surprisingly scarce and to date stems from a single study on brain size selected guppies (Poecilia reticulata), where large-brained females were shown to outperform small-brained females in a numerical learning assay. Because the results were inconclusive for males in that study, we here use a more ecologically relevant test of male cognitive ability to investigate whether or not a relatively larger brain increases cognitive ability also in males. We compared mate search ability of these artificially selected large- and small-brained males in a maze and found that large-brained males were faster at learning to find a female in a maze. Large-brained males decreased the time spent navigating the maze faster than small-brained males and were nearly twice as fast through the maze after 2 weeks of training. Our results support that relatively larger brains are better also for males in some contexts, which further substantiates that variation in vertebrate brain size is generated through the balance between energetic costs and cognitive benefits.

No MeSH data available.


Related in: MedlinePlus

Maze learning in male guppies (Poecilia reticulata) selected for large and small brain size. Large-brained males (red diamonds) are faster to learn the way through a maze than small-brained males (blue triangles). The dashed gray area indicates the days when all fish finished the maze without guidance; the dark gray area marks the days when large-brain animals were faster to find the female than small-brain males. Shown are the estimated marginal means of 14-day-specific GLMMs with search time as dependent variable, controlled for replicate (s ± SE). Note that depicted data are untransformed, whereas data used in the analyses were log10 transformed (see main text).
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Figure 3: Maze learning in male guppies (Poecilia reticulata) selected for large and small brain size. Large-brained males (red diamonds) are faster to learn the way through a maze than small-brained males (blue triangles). The dashed gray area indicates the days when all fish finished the maze without guidance; the dark gray area marks the days when large-brain animals were faster to find the female than small-brain males. Shown are the estimated marginal means of 14-day-specific GLMMs with search time as dependent variable, controlled for replicate (s ± SE). Note that depicted data are untransformed, whereas data used in the analyses were log10 transformed (see main text).

Mentions: During the 2 weeks of the experiment, both large- and small-brained fish significantly decreased the time through the maze to find the female (“search time,” GLMMday1–14: day of experiment: F1,34 = 16.5, P < 0.001; (day of experiment)2: F1,428 = 5.9, P = 0.016, Figure 3). The decrease in search time was significantly steeper in the large-brained fish (GLMMday1–14: day of experiment × brain size selection line: F1,34 = 5.9, P = 0.016, Figure 3). There was a nonsignificant tendency for the intercept of the learning curve of large-brained fish to be higher (GLMMday1–14: F1,259 = 3.1, P = 0.081, Figure 3). At the end of the experiment, when the animals had learnt their way through the maze, large-brained males were on average nearly twice as fast at finding the female than the small-brained males (mean search time: 86±14 vs. 47±14 s; GLMMday12–14: brain size selection line: F1,99 = 9.4, P = 0.003). We note that the interaction between day of experiment and brain size in the overall model was not merely driven by a potential difference in search time on day 1 because a model excluding day 1 showed qualitatively similar results (GLMMday2–14: brain size selection line: F1,34 = 1.4, P = 0.235; day of experiment: F1,34 = 16.5, P < 0.001; (day of experiment)2: F1,34 = 7.7, P = 0.006; day of experiment × brain size selection line: F1,34 = 3.6, P = 0.064). Moreover, and importantly, search time on day 1 did not differ between groups (GLMMday1: F1,22 = 2.0, P = 0.168). The faster decrease in search time in large-brained compared with small-brained animals should, therefore, be driven by differences in learning ability and not by any preexisting differences, such as a different response to a novel situation. In fact, in this context, males of different brain sizes did not differ in personality because on the first day of the experiment, they did not differ in their latency to leave the start compartment (large brains = 129±30 s, small brains = 141±28 s; GLMMday1: brain size selection line: F1,21 = 0.1, P = 0.800).


A larger brain confers a benefit in a spatial mate search learning task in male guppies.

Kotrschal A, Corral-Lopez A, Amcoff M, Kolm N - Behav. Ecol. (2014)

Maze learning in male guppies (Poecilia reticulata) selected for large and small brain size. Large-brained males (red diamonds) are faster to learn the way through a maze than small-brained males (blue triangles). The dashed gray area indicates the days when all fish finished the maze without guidance; the dark gray area marks the days when large-brain animals were faster to find the female than small-brain males. Shown are the estimated marginal means of 14-day-specific GLMMs with search time as dependent variable, controlled for replicate (s ± SE). Note that depicted data are untransformed, whereas data used in the analyses were log10 transformed (see main text).
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Related In: Results  -  Collection

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Figure 3: Maze learning in male guppies (Poecilia reticulata) selected for large and small brain size. Large-brained males (red diamonds) are faster to learn the way through a maze than small-brained males (blue triangles). The dashed gray area indicates the days when all fish finished the maze without guidance; the dark gray area marks the days when large-brain animals were faster to find the female than small-brain males. Shown are the estimated marginal means of 14-day-specific GLMMs with search time as dependent variable, controlled for replicate (s ± SE). Note that depicted data are untransformed, whereas data used in the analyses were log10 transformed (see main text).
Mentions: During the 2 weeks of the experiment, both large- and small-brained fish significantly decreased the time through the maze to find the female (“search time,” GLMMday1–14: day of experiment: F1,34 = 16.5, P < 0.001; (day of experiment)2: F1,428 = 5.9, P = 0.016, Figure 3). The decrease in search time was significantly steeper in the large-brained fish (GLMMday1–14: day of experiment × brain size selection line: F1,34 = 5.9, P = 0.016, Figure 3). There was a nonsignificant tendency for the intercept of the learning curve of large-brained fish to be higher (GLMMday1–14: F1,259 = 3.1, P = 0.081, Figure 3). At the end of the experiment, when the animals had learnt their way through the maze, large-brained males were on average nearly twice as fast at finding the female than the small-brained males (mean search time: 86±14 vs. 47±14 s; GLMMday12–14: brain size selection line: F1,99 = 9.4, P = 0.003). We note that the interaction between day of experiment and brain size in the overall model was not merely driven by a potential difference in search time on day 1 because a model excluding day 1 showed qualitatively similar results (GLMMday2–14: brain size selection line: F1,34 = 1.4, P = 0.235; day of experiment: F1,34 = 16.5, P < 0.001; (day of experiment)2: F1,34 = 7.7, P = 0.006; day of experiment × brain size selection line: F1,34 = 3.6, P = 0.064). Moreover, and importantly, search time on day 1 did not differ between groups (GLMMday1: F1,22 = 2.0, P = 0.168). The faster decrease in search time in large-brained compared with small-brained animals should, therefore, be driven by differences in learning ability and not by any preexisting differences, such as a different response to a novel situation. In fact, in this context, males of different brain sizes did not differ in personality because on the first day of the experiment, they did not differ in their latency to leave the start compartment (large brains = 129±30 s, small brains = 141±28 s; GLMMday1: brain size selection line: F1,21 = 0.1, P = 0.800).

Bottom Line: However, experimental evidence for the link between relative brain size and cognitive ability is surprisingly scarce and to date stems from a single study on brain size selected guppies (Poecilia reticulata), where large-brained females were shown to outperform small-brained females in a numerical learning assay.Because the results were inconclusive for males in that study, we here use a more ecologically relevant test of male cognitive ability to investigate whether or not a relatively larger brain increases cognitive ability also in males.Our results support that relatively larger brains are better also for males in some contexts, which further substantiates that variation in vertebrate brain size is generated through the balance between energetic costs and cognitive benefits.

View Article: PubMed Central - PubMed

Affiliation: Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University , Norbyvägen 18D, SE-75236 Uppsala , Sweden and ; Department of Zoology/Ethology, Stockholm University , Svante Arrheniusväg 18 B, SE-10691 Stockholm , Sweden.

ABSTRACT

Brain size varies dramatically among vertebrates, and selection for increased cognitive abilities is thought to be the key force underlying the evolution of a large brain. Indeed, numerous comparative studies suggest positive relationships between cognitively demanding aspects of behavior and brain size controlled for body size. However, experimental evidence for the link between relative brain size and cognitive ability is surprisingly scarce and to date stems from a single study on brain size selected guppies (Poecilia reticulata), where large-brained females were shown to outperform small-brained females in a numerical learning assay. Because the results were inconclusive for males in that study, we here use a more ecologically relevant test of male cognitive ability to investigate whether or not a relatively larger brain increases cognitive ability also in males. We compared mate search ability of these artificially selected large- and small-brained males in a maze and found that large-brained males were faster at learning to find a female in a maze. Large-brained males decreased the time spent navigating the maze faster than small-brained males and were nearly twice as fast through the maze after 2 weeks of training. Our results support that relatively larger brains are better also for males in some contexts, which further substantiates that variation in vertebrate brain size is generated through the balance between energetic costs and cognitive benefits.

No MeSH data available.


Related in: MedlinePlus