Cuckoo-host Co-evolution Research Articles

Multi-species Cuckoo Search Algorithm for Global Optimization

Many optimization problems in science and engineering are highly nonlinear, and thus require sophisticated optimization techniques to solve. Traditional techniques such as gradient-based algorithms are mostly local search methods, and often struggle to cope with such challenging optimization problems. Recent trends tend to use nature-inspired optimization algorithms. This work extends the standard cuckoo search (CS) by using the successful features of the cuckoo-host co-evolution with multiple interacting species, and the proposed multi-species cuckoo search (MSCS) intends to mimic the multiple species of cuckoos that compete for the survival of the fittest, and they co-evolve with host species with solution vectors being encoded as position vectors. The proposed algorithm is then validated by 15 benchmark functions as well as five nonlinear, multimodal design case studies in practical applications. Simulation results suggest that the proposed algorithm can be effective for finding optimal solutions and in this case all optimal solutions are achievable. The results for the test benchmarks are also compared with those obtained by other methods such as the standard cuckoo search and genetic algorithm, which demonstrated the efficiency of the present algorithm. Based on numerical experiments and case studies, we can conclude that the proposed algorithm can be more efficient in most cases, leading a potentially very effective tool for solving nonlinear optimization problems.

The common redstart as a suitable model to study cuckoo-host coevolution in a unique ecological context.

BackgroundCo-evolutionary arms-races result in spatio-temporally dynamic relationships between interacting species, e.g., brood parasites and their avian hosts. However, majority of avian co-evolutionary studies are limited to “snap-shots” of a single breeding season in an open-nesting host. In a long-term study (11 breeding seasons), we explored a unique system between the brood parasitic common cuckoo (Cuculus canorus) and its host, the common redstart (Phoenicurus phoenicurus) which is exceptional among all cuckoo hosts due to being a cavity nester. Conditions in cavities are different from open nests, e.g., lower risks of predation, more favourable microclimate, increased risks of unsuccessful eviction of host offspring by the cuckoo nestling. Different conditions in cavities thus can be expected to shape parasite-host coevolution differently from what is typically studied in open nesting hosts.ResultsIn our highly parasitised nest-box population (32.5%, n = 569 nests) only 35.7% of cuckoo eggs were laid into the nest cup and incubated by redstarts. Host nests shifted availability to later into the breeding season from 2006 to 2016 and cuckoos followed this trend by also shifting their timing of parasitism. Although previous studies revealed that redstarts selectively eject experimental non-mimetic eggs (desertion was not a specific response to foreign eggs), the hosts never ejected naturally-laid cuckoo eggs or cuckoo eggs cross-fostered into naturally non-parasitised nests. We solve the long-standing debate about the origin of cuckoo eggs found on the nest rim: we gained the first direct video-recording evidence that eggs found on the nest rim were mislaid by parasites and not ejected by hosts. Naturally-parasitised nests were deserted more often (18.6%) than control non-parasitized nests (5.6%) or nests artificially parasitised by us (1.4%). This suggests that the sight of the laying cuckoo female is the primary cue that triggers egg rejection (by desertion) in this host. Review of data from this and other study sites (10 populations, n = 853 experiments) demonstrates high variability in rejection rates and shows that populations facing higher parasitism rates reject parasitic eggs with higher frequencies. Surprisingly, cuckoo chicks either growing solitarily or with redstart chicks did not differ in their fledging success.ConclusionsWe suggest that the redstart is an ideal model system to study the flexibility and limits of brood parasite-host co-evolution in an extreme ecological setting.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0835-5) contains supplementary material, which is available to authorized users.

Ambient light in domed nests and discrimination of foreign egg colors

In cuckoo-host coevolution, rejection of parasite eggs based on visual discrimination is the key host-defensive mechanism reducing the costs of parasitism. Although host discriminatory tasks often occur in variable environmental conditions, the influence of nest light variation on the perceptual processes involved in egg discrimination has been seldom considered. Here, we combine visual modeling, experimental manipulation of nest ambient light, and egg recognition experiments with model eggs differing in background color (cream vs. blue) to explore the possibility that variation in ambient light in magpie (Pica pica) domed nests may affect the perceptual process involved in discrimination of foreign eggs. We found that the architecture of magpie nests affects the quality of ambient light for egg recognition and that changes in luminosity did not differently affect rejection of blue and cream models. However, we found that ejection of model eggs declined throughout the season in nests in which luminosity remained unmodified, but that magpies rejected eggs at a similar rate over the season in nests in which luminosity was increased. These results therefore suggest that variation in ambient light at the nests might potentially influence the perceptual processes involved in visual detection of parasite eggs by cuckoo hosts.

CUCKOO SEARCH VIA LÉVY FLIGHTS FOR OPTIMIZATION OF A PHYSICALLY-BASED RUNOFF-EROSION MODEL

This paper aims to calibrate a physically-based, event-oriented runoff-erosion model by means of a global optimization method known as cuckoo-host co-evolution (CHC) which has co-evolutionary changes incorporated into the traditional cuckoo search algorithm. The physically-based erosion model that was chosen to be optimized here is the watershed erosion simulation program (WESP), which was developed for small semiarid basins to simulate runoff and erosion processes. The optimization technique was tested with the field data collected in an experimental watershed located in a semiarid region of Brazil, and such technique showed to be effective in order to locate the optimal erosion parameter values. On the basis of these results, such values for a semiarid region are given, which could be recommended as an initial estimate for other similar areas.

Global Optimization of Some Difficult Benchmark Functions by Cuckoo-Host Co-Evolution Meta-Heuristics

This paper proposes a novel method of global optimization based on cuckoo-host co-evaluation. It also develops a Fortran-77 code for the algorithm. The algorithm has been tested on 96 benchmark functions (of which the results of 30 relatively harder problems have been reported). The proposed method is comparable to the Differential Evolution method of global optimization.

Pattern mimicry of host eggs by the common cuckoo, as seen through a bird's eye

Cuckoo-host interactions provide classical examples of coevolution. Cuckoos place hosts under selection to detect and reject foreign eggs, while host defences result in the evolution of host-egg mimicry in cuckoos. Despite a long history of research, egg pattern mimicry has never been objectively quantified, and so its coevolution with host defences has not been properly assessed. Here, we use digital image analysis and modelling of avian vision to quantify the level of pattern mimicry in eight host species of the common cuckoo Cuculus canorus and their respective cuckoo host-races. We measure a range of pattern attributes, including marking size, diversity in size, contrast, coverage and dispersion. This new technique reveals hitherto unnoticed sophistication in egg pattern mimicry. We show that various features of host egg pattern are mimicked by the eggs of their respective cuckoo host-races, and that cuckoos have evolved better pattern mimicry for host species that exhibit stronger egg rejection. Pattern differs relatively more between eggs of different host species than between their respective cuckoo host-races. We suggest that cuckoos may have more 'average' markings in order to be able to use subsidiary hosts. Our study sheds new light on cuckoo-host coevolution and illustrates a new technique for quantifying animal markings with respect to the relevant animal visual system.

A comparative study of host selection in the European cuckoo Cuculus canorus.

Certain kinds of hosts are commonly regarded as being more suitable than other for rearing European cuckoos (Cuculus canorus) - insectivores that lay small eggs and have open, shallow nests - although empirical tests of cuckoo host selection are lacking. We analysed host use by the European cuckoo in 72 British passerines that are potential hosts and for which there was information available on life-history variables and variables related to cuckoo-host coevolution, such as rate of parasitism, rejection rate of non-mimetic model eggs and degree of cuckoo-egg mimicry of host eggs. The relative population size of the host species affected parasitism rate most strongly, followed by relatively short duration of the nestling period, and the kind of nest, with cuckoos selecting open-nesting hosts. However, the effect of the nestling period could be related to host body size and the kind of nest used, because hole-nesting species normally have longer nestling periods than open-nesters. We re-analysed the data excluding hole nesters and corvid species (species with larger body mass), but the results remained identical. The European cuckoo may benefit from selecting hosts with short nestling periods because such hosts provide food for their nestlings at a very high rate. When only those species known as cuckoo hosts were analysed, the variable that best accounted for the parasitism rate was duration of the breeding season. Therefore, availability of potential hosts in both time and space is important for cuckoos in selecting hosts.

Cuckoo-host coevolution: from snapshots of an arms race to the documentation of microevolution

Cuckoo-host coevolution: from snapshots of an arms race to the documentation of microevolution

Constraints on egg discrimination and cuckoo-host co-evolution

To understand the co-existence of rejection and acceptance of cuckoo eggs within a host population, the mechanism of egg discrimination and the cost-benefit balance of rejection behaviour were investigated. At a study site in central Japan, rejection rate of cuckoo,Cuculus canorus, eggs by great reed warblers,Acrocephalus arundinaceus, was 61·5%. An analysis of host response to natural and experimental parasitism with real cuckoo eggs, cuckoo egg models and painted host eggs indicated that: (1) hosts are more likely to reject eggs that look different from their own; (2) almost all individuals (94%) can reject highly non-mimetic eggs, suggesting that there are few, if any, true accepter genotypes in the host population; (3) hosts usually reject by egg ejection; (4) during the host-laying period, the day of parasitism does not affect host response; (5) egg types that were rejected at lower rates also took longer to be rejected; (6) acceptance was more likely to occur among mid-season breeders which consist of a higher proportion of younger females in the host population. Two experiments indicated that previous exposure of a host to its own eggs affects its rejection behaviour, suggesting that a learning mechanism (an imprinting-like process) is involved. Parasitized nests from which the cuckoo egg was experimentally removed, or ejected by hosts, fledged more host young than nests in which the cuckoo egg was accepted. Hosts that deserted parasitized nests were likely to re-nest, and the success of re-nests was high. Costs due to breakage of host eggs occurred in only 3·5% of successful cuckoo egg ejections. A cost-benefit model of egg rejection suggests that under some circumstances, the cost of recognition errors may exceed that of parasitism. Egg variability within a clutch was higher among younger females. Some hosts rejected painted eggs and conspecific eggs based on differences that may occur naturally within variable clutches of other individuals. It is suggested that host egg variability is a major constraint on the learning mechanism of egg recognition. Accordingly, the cost of mistakenly rejecting an odd egg from the nest selects for greater tolerance towards divergent eggs in young breeders, and justifies a prolonged learning mechanism in which a host can learn to recognize the variation range of its own eggs. The co-existence of rejection and acceptance within the host population can therefore be explained as a compromise between the cost of parasitism and the cost of recognition errors, rather than as an evolutionary lag. This explanation is particularly pertinent where the cuckoo has evolved mimetic eggs and where the parasitism rate is low.