The parrot and the string: means-end understanding in twelve ...

2 downloads 0 Views 6MB Size Report
Does phylogeny predict parrots' performance in patterned-string tasks? INTRODUCTION. Quantifying ... Grey: broken-string task. Data for 12 species tested by ...
Anastasia Krasheninnikova, Ulrike Busse, Jutta M Schneider Zoological Institute and Museum, Biozentrum Grindel, University of Hamburg, Germany

Does phylogeny predict parrots’ performance in patterned-string tasks? INTRODUCTION Quantifying the degree to which closely related species share similar cognitive traits is a first step for testing evolutionary hypotheses in the field of comparative cognition. Here we capitalize on data about the ability in solving patterned-string problems from 23 parrot species and we map these data on a phylogenetic tree based on molecular and taxonomic data. The mean proportion of correct choices made by each species was used as the dependent measure for the phylogenetic analysis.

MATERIAL & METHODS Patterned-string problems is a broadly accepted paradigm for testing specific cognitive abilities in animals and it fulfils the methodological requirements for broad comparative studies as it 1) requires no training, 2) is easily applicable across species, and 3) requires few trials per subject. We used two basic configurations of patterned-string tasks: crossed-string task and broken-string task. We estimated the phylogenetic signal (using Pagel’ λ) in the cognitive traits tested.

RESULTS 1) The species tested differed significantly in the proportion of correctly solved trials in both task configurations (GLMM with individual as random factor, crossed strings: χ2 = 5.384, df = 22, p < 0.0001; broken-string configuration: χ2= 5.088, df = 20, p < 0.0001)

2) No statistically significant phylogenetic signal in crossed-strings or in broken-string configuration data  more closely related species do not show more similar cognitive trait values

Trait

λ

ln lik

ln lik (λ=0)

ln lik (λ=1)

Performance on crossed-string task

0.000068

9.247

9.247 n

11.501 *

Performance on broken-string task

0.000069

12.656

12.657 n

15.746 *

We estimated Pagel’s Lambda λ, the degree of phylogenetic dependence of the data, defined as the maximum likelihood estimate. The maximum likelihood estimate of λ is given together with its associated log likelihood. Also shown are the log-likelihood values for the model, with λ set to either 0 or 1 n Not

significant * P

Suggest Documents