Browsing by Author "Spottiswoode, Claire N"
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- ItemOpen AccessCoevolutionary causes and consequences of high-fidelity mimicry by a specialist brood parasite(2021) Lund, Jess; Spottiswoode, Claire N; Jamie, Gabriel AMimicry is often invoked as a classic demonstration of the power of natural selection. However, mimicry systems are diverse and the accuracy of mimicry, or mimetic fidelity, varies from crude to near-perfect. There is growing evidence that low-fidelity mimicry is the norm, with cases of high-fidelity mimicry being rarer. This is particularly evident in avian interspecific brood parasites, which are birds that lay their eggs in the nests of other species, or ‘hosts'. A possible rare example of a “perfect mimic” is the African cuckoo Cuculus gularis (a specialist parasite of fork-tailed drongos Dicrurus adsimilis) which, to the human eye, exhibits some of the most sophisticated mimicry seen in a brood parasite-host system. In this work, I quantify the degree of mimetic fidelity in this system and investigate its consequences on the two antagonists, using experimental, observational and genetic data I collected in the field in Zambia. In Chapter 1 I first define perfect mimicry, and explore how mimetic fidelity can be quantified. I then review the factors responsible for the variability in mimetic fidelity among different mimicry systems. In Chapter 2 I use quantitative measures of egg colour and pattern, from models that approximate avian vision, to show that mimicry of drongo eggs by African cuckoos is near-perfect. I subsequently use field experiments and simulations to show that a high degree of interclutch variation (egg ‘signatures') means that drongos still have the upper hand in the arms race against this near-perfect mimic. In Chapter 3 I investigate the genetic architecture of perfect mimicry by comparing cuckoo egg phenotypes to their mitochondrial DNA haplotypes, providing evidence that the African cuckoo likely shows bi-parental inheritance of egg phenotype. Together these results highlight the effectiveness of egg signatures as a defence against brood parasites, even when mimicry shows high accuracy and precision, and underline the role of mechanistic factors in enabling high-fidelity mimicry to evolve.
- ItemOpen AccessSeasonal rainfall at long-term migratory staging sites is associated with altered carry-over effects in a Palearctic-African migratory bird(2016) Sorensen, Marjorie C; Fairhurst, Graham D; Jenni-Eiermann, Susanne; Newton, Jason; Yohannes, Elizabeth; Spottiswoode, Claire NAbstract Background An understanding of year-round habitat use is essential for determining how carry-over effects shape population dynamics in long-distance migratory songbirds. The recent discovery of long-term migratory staging sites in many species, prior to arrival at final wintering sites, adds complexity to efforts to decipher non-breeding habitat use and connections between sites. We investigated whether habitat conditions during migratory staging carry over to influence great reed warbler (Acrocephalus arundinaceus) body condition at final wintering sites in Zambia. We asked whether the presence/absence and strength of such carry-over effects were modified by contrasting rainfall conditions during 2 years. Results First, we found that individuals staging in a dry year had higher corticosterone (CORT f ) and stable nitrogen isotope values (suggesting higher aridity) than birds staging in a wet year, indicating that regional weather affected staging conditions. Second, we found that carry-over effects from staging habitat conditions (measured via carbon and nitrogen isotopes) to final winter site body condition (measured via scaled mass index and β-hydroxybutyrate) were only present in a dry year, suggesting that environmental factors have consequences for the strength of carry-over effects. Our results also suggest that wet conditions at final winter sites may buffer the effects of poor staging conditions, at least in the short term, since individuals that staged in a dry year had higher scaled mass indices in Zambia than individuals that staged in a wet year. Conclusions This study provides a first insight into the connections between long-term migratory staging sites and final wintering sites, and suggests that local environmental factors can modify the strength of carry-over effects for long-distance migratory birds.