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Intraclutch Variation (intraclutch + variation)

Distribution by Scientific Domains
Life Sciences100%

Selected Abstracts

Experimental Manipulation of Intraclutch Variation in the Great Reed Warbler Shows No Effect on Rejection of Parasitic Eggs

ETHOLOGY, Issue 1 2003
Zsolt Karcza
In the continuing arms race between hosts and brood parasites, hosts are expected to reduce variation in the appearance of their own eggs within clutches, as it facilitates recognition of parasitic eggs. At the same time, by increasing interclutch variation, hosts should make it more difficult for parasites to evolve perfectly mimetic eggs. In this study, we experimentally manipulated intraclutch variation in the great reed warbler, Acrocephalus arundinaceus, in Hungary, where this species is heavily (c. 64%) parasitized by the common cuckoo, Cuculus canorus. We placed artificial cuckoo eggs, which appeared moderately mimetic to humans, in two groups of nests; in one group we increased variability of egg appearance within clutches by exchanging host eggs among nests. These clutches showed a significantly higher intraclutch variability than natural clutches, which we used as a control group. Our results indicate that it has no effect on rejection behaviour in this species, neither when variation was increased experimentally, nor within the natural range of variation displayed by our population. We suggest that when parasitism is high, selection for reduced intraclutch variation may be less important than frequency-dependent selection for increased variation between individuals within a host population. [source]

Rejection of Conspecific Eggs in Chaffinches: The Effect of Age and Clutch Characteristics

ETHOLOGY, Issue 6 2004
Bård G. Stokke
Previous experimental studies have found that the majority of chaffinches, Fringilla coelebs, are able to reject both non-mimetic and mimetic cuckoo eggs and also non-mimetic conspecific eggs. However, interestingly the frequency of rejecters of moderately mimetic conspecific eggs has been found to be only approx. 50%. We examined the possibility that acceptors of moderately mimetic conspecific eggs are first time breeders, because these individuals may lack the experience needed to reject eggs that deviate only slightly from their own eggs. Older individuals, with good knowledge of their own egg appearance, should therefore reject such eggs. We also examined the possibility that acceptors of moderately mimetic eggs have a higher intraclutch variation in egg appearance, which makes it more difficult to recognize such eggs when compared with rejecters. We obtained no support for any age-specific pattern in rejection behaviour. Furthermore, there was no relationship between age and intraclutch variation, or intraclutch variation and rejection behaviour. As there is no evidence of intraspecific brood parasitism in this species, the rejection of any foreign eggs is most probably an adaptation to past cuckoo, Cuculus canorus, parasitism. Acceptance of good and moderately mimetic conspecific eggs is probably due to cognitive limitations, because evolution of a more fine-tuned recognition ability is unnecessary in the absence of intraspecific brood parasitism. [source]

Experimental Manipulation of Intraclutch Variation in the Great Reed Warbler Shows No Effect on Rejection of Parasitic Eggs

ETHOLOGY, Issue 1 2003
Zsolt Karcza
In the continuing arms race between hosts and brood parasites, hosts are expected to reduce variation in the appearance of their own eggs within clutches, as it facilitates recognition of parasitic eggs. At the same time, by increasing interclutch variation, hosts should make it more difficult for parasites to evolve perfectly mimetic eggs. In this study, we experimentally manipulated intraclutch variation in the great reed warbler, Acrocephalus arundinaceus, in Hungary, where this species is heavily (c. 64%) parasitized by the common cuckoo, Cuculus canorus. We placed artificial cuckoo eggs, which appeared moderately mimetic to humans, in two groups of nests; in one group we increased variability of egg appearance within clutches by exchanging host eggs among nests. These clutches showed a significantly higher intraclutch variability than natural clutches, which we used as a control group. Our results indicate that it has no effect on rejection behaviour in this species, neither when variation was increased experimentally, nor within the natural range of variation displayed by our population. We suggest that when parasitism is high, selection for reduced intraclutch variation may be less important than frequency-dependent selection for increased variation between individuals within a host population. [source]

Meadow pipit (Anthus pratensis) egg appearance in cuckoo (Cuculus canorus) sympatric and allopatric populations

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2003
JESUS M. AVILES
Host populations tend to show less ability to discriminate against parasites when living in their absence. However, comparison of rejection rates among sympatric and allopatric host populations does not allow determination of whether the greater tolerance in allopatric populations reflects a genetic change or phenotypic plasticity. Here we test the existence of changes in a host's adaptation to brood parasitism in the absence of parasitism by studying intraclutch variation in egg appearance, which is a genetically determined component of host defence favouring discrimination of parasitic eggs. We investigated egg phenotypes of a common host of the European cuckoo, Cuculus canorus, in the presence and in the absence of cuckoos. By using objective spectroradiometry techniques of colour assessment we compared intraclutch variation between populations of meadow pipit, Anthus pratensis, sympatric (England) and allopatric (Iceland and Faeroe Islands) with C. canorus. Allopatric populations of A. pratensis showed greater intraclutch variation in egg appearance in the ultraviolet part of the spectrum than did a population sympatric with C. canorus. Two possible alternative mechanisms explaining these findings are discussed. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 543,549. [source]