基于人眼评估的灰喜鹊卵色的窝内变_省略_模拟寄生卵的拒绝行为无关_英文_Jes_

Introduction
Avian brood parasitism studies have provided us with some of the best examples of co-evolved adaptations (Rothstein, 1990; Davies, 2000). Obligate brood parasites receive parental care from unrelated individuals
Jesús M. AVILÉS , Deseada PAREJO
Estación Experimental de Zonas Áridas, CSIC, Departamento de Ecología Funcional y Evolutiva, Ctra. de Sacramento s/n, 04120, La Cañada de San Urbano, Almería, Spain Abstract The coevolutionary arms race between cuckoos and their hosts predicts that low variation in egg features within a host clutch would facilitate discrimination of mimetic parasite eggs. Here, we experimentally examine this prediction by using artificial and natural parasite eggs showing contrasting level of matching with host eggs. We quantified, based on human assessment, intra-clutch variation in egg appearance and egg discrimination in the Iberian Azure-winged Magpie (Cyanopica cyanus), a presumed former host of the Great Spotted Cuckoo (Clamator glandarius). Azure-winged Magpies rejected parasitic eggs in relation to their degree of dissimilarity with own eggs: Great Spotted Cuckoo model eggs were relatively more often rejected (73.7%) than real Great Spotted Cuckoo eggs (44.4%) and the less contrasting conspecific eggs (35.5%). Contrary to our predictions, we found that, irrespective of mimicry level of parasitic eggs, intra-clutch variation in host egg appearance did not differ significantly between rejecters and acceptors. We found, however, that individuals with higher variation in egg-size were almost significantly more prone to be rejecters than individuals showing lower variation in egg size. Our results do not support the hypothesis that the extent of intraclutch variation in egg discrimination varied with parasite egg mimicry in this particular system, and add to previous findings suggesting that perhaps an increase in intra-clutch variation in egg appearance, rather than a decrease, might be advantageous when discriminating against non-mimetic Great Spotted Cuckoo eggs. Keywords brood parasitism, Clamator glandarius, coevolutionary arms race, Cyanopica cyanus, egg appearance, intra-clutch variation, parasite egg discrimination
Chinese Birds 2012, 3(4):302–311 DOI 10.5122/cbirds.2012.0034
ORIGINAL ARTICLE
Intra-clutch variation in egg appearance assessed by human vision does not relate to rejection of parasite eggs in Iberian Azure-winged Magpies
Received 24 October 2012; accepted 07 December 2012

Author for correspondence (Jesús M. Avilés) E-mail: javiles@eeza.csic.es
(hosts) of other species. Successful parasitism often reduces host reproductive output, which favors the evolution of host defenses, leading to selection for more sophisticated trickeries by the parasite to overcome host defenses (Rothstein, 1990). This escalation of adaptations and counter-adaptations by both sides leads to a coevolutionary “arms race” between parasites and hosts (Davies, 2000). Discrimination and rejection of parasitic eggs are the most widespread and efficient host defensive mechanisms specifically evolved to counteract the costs imposed by brood parasitism (Rothstein, 1990; Payne, Nhomakorabea
Jesús M. Avilés and Deseada Parejo. Egg variation and discrimination in Azure-winged Magpie
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1997; Davies, 2000). Hosts can learn how their eggs look like and recognize and reject those with an appearance different from that of their own eggs (Victoria, 1972; Rothstein, 1975; Lotem et al., 1992). Experimental studies have shown that hosts of avian brood parasites are more likely to reject parasitic eggs that look different from their own eggs (e.g. Brooke and Davies, 1988; Davies and Brooke, 1988; Soler and Møller, 1990; Moksnes et al., 1993; Lotem et al., 1995; Marchetti, 2000; Moskát and Honza, 2002; Lathi and Lathi, 2002; Rutila et al, 2002; Cassey et al., 2008; Avilés, 2008; Avilés et al., 2010; Spottiswoode and Stevens, 2010; Stoddard and Stevens, 2010), which supports the view that mimetic cuckoo egg phenotypes have evolved due to host egg rejection. As matching between parasite and host eggs improves, hosts are expected to reduce variation in the appearance of their eggs within their clutches. A low variation in egg appearance within host clutches would facilitate host’s recognition of parasite eggs (e.g. Victoria, 1972; Davies and Brooke, 1989b). In addition, a high homogeneity in appearance within clutches would lead to a higher variation in egg appearance among clutches of different host individuals (i.e. inter-clutch variation). Hence, a higher inter-clutch variation in egg appearance will prevent the evolution of a good match for the parasite (Soler and Møller, 1996). Passerine species frequently parasitized by the Common Cuckoo (Cuculus canorus) have evolved a lower degree of intraclutch variation in egg appearance, and a higher degree of inter-clutch variation than those that have not experienced such interactions (e.g. Øien et al., 1995; Soler and Møller, 1996; Stokke et al., 2002; Avilés and Møller, 2003). Recent findings with three Australian hosts of the Pallid Cuckoo (Cuculus pallidus), however, cast doubts on the generality of these processes as intra-clutch variation did not vary between populations with different exposure to parasitism (Landstrom et al., 2011). Intra-specific evidence has so far focused on reporting a link between intra-clutch variation in host egg appearance and probability of rejection of artificial eggs, and, is even more controversial. While some studies have shown that low intra-clutch variation in host egg appearance may favor parasite egg discrimination (Stokke et al., 1999; Soler et al., 2000; Moskát et al., 2008), others did not find support for the parasite recognition function of such egg traits (Karcza et al., 2003; Avilés et al., 2004; Honza et al., 2004; Stokke et al., 2004; Lovászi and Moskát, 2004; Polacikova et al., 2007; Cherry et al.,