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Sexual selection in the zebra finch Taeniopygia guttata : condition, sex traits and immune capacity 总被引:5,自引:2,他引:3
The aim of this study was to test two hypotheses: (1) that condition-dependent secondary sexual traits reflect an individual's
immune capacity and (2) that immune capacity and secondary sexual traits covary with primary sex traits, specifically ejaculate
quality. We used the zebra finch Taeniopygia guttata as a study species, since the traits that females find attractive in males of this species, song rate and beak colour, are
well established. A paired experimental design comprising 31 pairs of brothers was used; for each pair, one male was assigned
to a control group provided with ad libitum food and no additional exercise, and the other male was assigned to an experimental
group which experienced additional exercise and a reduced rate of food intake. After 11 weeks, the experimental group differed
significantly from the control group in a range of variables, including body mass, haematocrit, granulocyte:lymphocyte (G:L)
ratio and several primary sex traits, indicating that condition in this group was reduced. Birds in the experimental group
showed a differential response to the treatment. We used the rank order in which birds could be captured by an experimenter
as an index of condition. Birds easily caught were assumed to be in poorer condition than those which were more difficult
to capture. Rank capture order was repeatable and was significantly correlated with the G:L ratio in the experimental group,
but not in the control group. In the experimental group, rank capture order was correlated significantly with both secondary
sex traits: birds in better condition had redder beaks and a higher song rate. However, beak colour and song rate did not
covary significantly, suggesting that these two traits provide different types of information. Secondary sex traits did not
covary with primary sex traits or any sperm features. Thus, there was no evidence for Trivers' sexual-competence hypothesis
or the phenotype-linked fertility hypothesis. We used four assays of immune capacity, two general (G:L ratio and spleen mass)
and two specific [antibody titres to sheep red blood cells (SRBCs) and Brucella abortus (BA)]. The G:L ratio was significantly higher in the experimental group, spleen mass (absolute and relative) did not differ
between the groups, anti-SRBC antibody titres were significantly higher in the control group (contrary to expectation), and
anti-BA antibody titres were close to being significantly lower in the experimental group. Within the experimental group,
there was no evidence that antibody titres covaried with secondary sex traits. Although we demonstrated that beak colour and
song rate were condition dependent, our experiment provided no evidence that either of these traits covaried with immune capacity
or sperm features.
Received: 9 February 1998 / Accepted after revision: 5 September 1998 相似文献
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