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(b)
Sylvia nisoria
Locustella naevia
Locustella luscinioides
(a)
Locustella naevia
8
4
0
Locustella fluviatilis
Acrocephalus arundinaceus
0
1
Acrocephalus palustris
Acrocephalus palustris
8
4
0
Acrocephalus scirpaceus
Acrocephalus schoenobaenus
0
1
time / s
Acrocephalus melanopogon
(c)
0.6
2
0.4
1
0.2
3
6
8
0
7
4
5
-0.2
-0.2
-0.1
0
0.1
0.2
0.3
Contrasts in residual HVC volume
Fig. 2.9
Song complexity and brain anatomy in European warblers (family Sylviidae) from the genus
Acrocephalus
and
Locustella
. (a) Some species, like the grasshopper warbler
L. naevia
, have very simple songs
(in this species, one syllable is repeated). Others, like the marsh warbler
A. palustris
, have a complex song with
up to a hundred different syllable types in their repertoire. (b) Phylogeny of the
Acrocephalus
and
Locustella
warblers. The numbers refer to the eight independent contrasts used in the analysis. (c) Correlation between
contrasts in syllable repertoire size and contrasts in volume of the higher vocal centre (HVC) of the brain
(corrected for body size). The eight independent contrasts are labelled. From Szekely
et al
. (1996).
are intermediate between those of two descendant species (e.g. B is the mean of D and E).
Fig. 2.9 is an example using this method, which shows that during evolution an increase
in song complexity in warblers is correlated with an increase in the volume of a brain
nucleus (the higher vocal centre) involved in song learning. This relationship is evident,
too, in a wider comparison across 45 species of passerine birds (De Voogd
et al
., 1993).
This phylogenetic method encouraged a re-analysis of the data on primate testis size
(Fig. 2.7). A phylogeny of 58 primate species revealed seven independent pairwise
comparisons between multimale and single-male taxa. In all seven cases, the multimale
