Rare Morph Research Articles

Exploring polymorphism in a palatable prey: predation risk and frequency dependence in relation to distinct levels of conspicuousness.

Camouflage and warning signals are different antipredator strategies, which offer an excellent opportunity to study the evolutionary forces acting on prey appearance. Edible prey often escape detection via camouflage, which usually leads to apostatic selection favoring rare morphs. By contrast, defended prey often display conspicuous coloration acting as warning signals to predators, which usually leads to positive frequency dependence and signal uniformity. However, when two morphs of the same species vary greatly in conspicuousness, the maintenance of both cryptic and conspicuous forms in profitable prey populations remains enigmatic. Using the white and melanic morphs of the invasive box tree moth (Cydalima perspectalis) presented at three different frequencies, we investigate (a) the palatability of caterpillars and adult moths to birds, (b) predation rates on the less conspicuous melanic morph, and (c) the role of frequency dependence in balancing morph frequencies. Our results show that caterpillars are distasteful for birds but not adult moths that are fully palatable. We found that the less conspicuous, melanic morph, benefits from reduced predation due to its lower detectability. The more conspicuous, white morph, instead, is more predated and is best off when common, suggesting positive frequency dependence. These results offer new insights into the evolution of color polymorphism and prey defenses in a polymorphic moth species. Further investigation is required to understand the role of different predation regimes on the maintenance of the polymorphism in this species and test whether additional selection pressures operate in natural populations.

THE FIRST RECORD OF CEPAEA NEMORALIS (LINNAEUS, 1758) (MOLLUSCA: GASTROPODA: HELICIDAE) IN THE DONBASS AND THE PHENETIC STRUCTURE OF THE FOUND COLONY

The phenetic composition of Cepaea nemoralis (Linnaeus, 1758) (Mollusca: Gastropoda: Helicidae) colony found in an area of continuous high-rise buildings in the center of Donetsk in 2022 is described. The area of the colony is 2.5 ha, the number reaches 15 ind./m2, the age is at least 10 years. Individuals with a pink ground colours (81.5%) and one central band in 64.7% of yellow-coloured and 76.8% of pink-coloured shells are clearly dominated. The absence of unbanded shells and shells with reduced 1, 2, 4 and 5 bands was a distinctive feature of the Donetsk colony. The trend of dominance of phenotypes with fused bands is traced for five-banded shells with the relative frequency of 69.7%. Morphs with fusion types of bands, namely F(45) - 13.2% and F(23) - 12.8% dominate. The colony is characterized by a relatively high degree of polymorphism (𝜇 = 4.78±0.039) and proportion of rare morphs (h±𝑆ℎ = 0.47±0.026) showing no similarities with the colonies in Eastern Europe available for meta-analysis. Cepaea nemoralis is likely to remain one of the elements in the urban fauna, not showing any tendency to expand into natural ecosystems.

Rare morph Lake Malawi mbuna cichlids benefit from reduced aggression from con- and hetero-specifics.

Balancing selection is important for the maintenance of polymorphism as it can prevent either fixation of one morph through directional selection or genetic drift, or speciation by disruptive selection. Polychromatism, the presence of multiple genetically determined colour phenotypes, can be maintained if the fitness of alternative morphs depends on the relative frequency in a population. In aggressive species, negative frequency-dependent antagonism can prevent an increase in the frequency of rare morphs as they would only benefit from increased fitness while they are rare. Heterospecific aggression is common in nature and has the potential to contribute to rare morph advantage. Here we carry out field observations and laboratory aggression experiments with mbuna cichlids from Lake Malawi, to investigate the role of con- and heterospecific aggression in the maintenance of polychromatism and identify benefits to rare morphs which are likely to result from reduced aggression. We hypothesize that rare morph individuals receive less aggression than common morph individuals and therefore have an ecological advantage. Within species we found that males and females bias aggression towards their own morph, adding to the evidence that inherent own-morph aggression biases can contribute to balancing selection. Over-representation of rare morph territory owners may be influenced by two factors; higher tolerance of different morph individuals as neighbours, and the ability of rare morphs to spend more time feeding. Reduced aggression to rare morph individuals by heterospecifics may also contribute to rare morph advantage.

Intrapopulation foraging niche variation between phenotypes and genotypes of Spirit bear populations.

Foraging niche variation within a species can contribute to the maintenance of phenotypic diversity. The multiniche model posits that phenotypes occupying different niches can contribute to the maintenance of balanced polymorphisms. Using coastal populations of black bears (Ursus americanus kermodei) from British Columbia, Canada, we examined potential foraging niche divergence between phenotypes (black and white “Spirit” coat color) and between genotypes (black‐coated homozygote and heterozygous). We applied the Bayesian multivariate models, with biotracers of diet (δ13C and δ15N) together comprising the response variable, to draw inference about foraging niche variation. Variance–covariance matrices from multivariate linear mixed‐effect models were visualized as the Bayesian standard ellipses in δ13C and δ15N isotopic space to assess potential seasonal and annual niche variation between phenotypes and genotypes. We did not detect a difference in annual isotopic foraging niche area in comparisons between genotypes or phenotypes. Consistent with previous field experimental and isotopic analyses, however, we found that white phenotype Spirit bears were modestly more enriched in δ15N during the fall foraging season, though with our modest sample sizes these results were not significant. Although also not statistically significant, variation in isotopic niches between genotypes revealed that heterozygotes were moderately more enriched in δ13C along hair segments grown during fall foraging compared with black‐coated homozygotes. To the extent to which the pattern of elevated δ15N and δ13C may signal the consumption of salmon (Oncorhynchus spp.), as well as the influence of salmon consumption on reproductive fitness, these results suggest that black‐coated heterozygotes could have a minor selective advantage in the fall compared with black‐coated homozygotes. More broadly, our multivariate approach, coupled with knowledge of genetic variation underlying a polymorphic trait, provides new insight into the potential role of a multiniche mechanism in maintaining this rare morph of conservation priority in Canada's Great Bear Rainforest and could offer new understanding into polymorphisms in other systems.

Observational evidence of herbivore-specific associational effects between neighboring conspecifics in natural, dimorphic populations of Datura wrightii.

Associational effects—in which the vulnerability of a plant to herbivores is influenced by its neighbors—have been widely implicated in mediating plant–herbivore interactions. Studies of associational effects typically focus on interspecific interactions or pest–crop dynamics. However, associational effects may also be important for species with intraspecific variation in defensive traits. In this study, we observed hundreds of Datura wrightii—which exhibits dimorphism in its trichome phenotype—from over 30 dimorphic populations across California. Our aim was to determine whether a relationship existed between the trichome phenotype of neighboring conspecifics and the likelihood of being damaged by four species of herbivorous insects. We visited plants at three timepoints to assess how these effects vary both within and between growing seasons. We hypothesized that the pattern of associational effects would provide rare morphs (i.e., focal plants that are a different morph than their neighbors) with an advantage in the form of reduced herbivory, thereby contributing to the negative frequency‐dependent selection previously documented in this system. We found the best predictor of herbivory/herbivore presence on focal plants was the phenotype of the focal plant. However, we also found some important neighborhood effects. The total number of plants near a focal individual predicted the likelihood and/or magnitude of herbivory by Tupiochoris notatus, Lema daturaphila, and Manduca sexta. We also found that velvety focal plants with primarily sticky neighbors are more susceptible to infestation by Tupiochoris notatus and Lema daturaphila. This does not align with the hypothesis that associational effects at the near‐neighbor scale contribute to a rare‐morph advantage in this system. Overall, the results of our study show that the number and trichome‐morph composition of neighboring conspecifics impact interactions between D. wrightii and insect herbivores.

Relaxed predation selection on rare morphs ofEnsatinasalamanders (Caudata: Plethodontidae) promotes a polymorphic population in a novel dune sand habitat

AbstractThe ring species Ensatina represents a classic example of locally adapted lineages. The Monterey ensatina (Ensatina eschscholtzii eschscholtzii) is a cryptic subspecies with brown coloration, although a recently discovered polymorphic population within a wind-blown sand region also contains leucistic (pink) and xanthistic (orange) morphs. In the present study, the frequency of leucism/xanthism was mapped across the subspecies’ range, revealing that these morphs are generally rare or absent except within regions containing light-coloured substrate. Attack rates were estimated using clay models of the three morphs, deployed only at the crepuscular period and during the night, on both light and dark substrates at a site within the dune sand region. Model selection found that the interaction between morph and substrate colour best predicted attack rates. Typical morphs had equal attack rates on both substrates while xanthistic and leucistic morphs incurred significantly fewer attacks on light vs. dark substrate, and there was no significant difference in attack rates among morphs on light substrates. These results support the idea that xanthistic and leucistic morphs are poorly adapted for dark substrates compared to typical morphs, but they are more or less equally adapted for light substrates. We suggest that this microgeographic island of relaxed selection on light-coloured morphs helps to explain the existence of this polymorphic population.

Changes in the Fluctuating Asymmetry of the Leaf and Reproductive Capacity of Betula pendula Roth Reflect Pessimization of Anthropogenically Transformed Environment

We have estimated the reproductive capacity of Betulapendula Roth and its relationship with an integrated measure of developmental stability, i.e., fluctuating asymmetry (FA) of the leaf. On the territory of a city with moderate anthropogenic pollution, a change has been detected in the integrated fluctuating asymmetry (IFA) of the morphology of the female reproductive sphere and reproductive capacity of Betula pendula. In conditions of anthropogenic stress, the birch is observed to produce a large yield of fruits annually, which is not subject to year-to-year fluctuations. Morphological variety of size and shape of fruit-producing organs increases along the gradient of industrial and transport pollution; part of morphotypes of infructescences and seeds is characterized by lowered or zero capacity for reproduction determined by seed quality (germination energy and germination capacity). The statistical data processing involved correlation, Shapiro–Wilk test, Levene’s test, factorial ANOVA, Scheffe test, Kruskal–Wallis ANOVA, Mann–Whitney test, χ2 method. Analysis of IFA has allowed us to reasonably well assess the state of the plant organism and to characterize environmental quality. A negative correlation between IFA and quantitative parameters of the functions of the reproductive sphere of B. pendula (infructescence diameter, seed quality) has been found, and positive correlation with qualitative parameters (the number of morphs of infructescences and seeds, the share of rare morphs of infructescences). Pessimization of urban environment creates the conditions for an increase in the share of defective infructescences and non-germinating seeds; a compensatory mechanism for this is an increase in reproductive effort of B. pendula. The consistency of responses in the vegetative and reproductive spheres reflects the disturbances in developmental stability of plants in urban communities.

Intrapopulation variation in shell morphological traits and banding polymorphism of the land snail Cepaea vindobonensis (Gastropoda; Pulmonata; Helicidae)

The main goal of this paper was to analyze intrapopulation variation of both morphological traits and shell banding polymorphism using the example of a continuous population (a metapopulation) of the land snail Cepaea vindobonensis (Férussac, 1821). A total of 14 samples of the land snail C. vindobonensis from a population located in the “Dubki” Park (Ukraine, Mykolayiv) were collected in May-July 2007. The land snail collection sites are divided into three areas by buildings and asphalt roads, indicated by the Latin letters A, B and C. The major diameter of shell (MJD), the minor diameter of shell (MID) and the shell height (SH) were measured with a digital calliper to the nearest 0.05 mm. Two shell shape indices (SF1 and SF2) were also computed. A high level of the intrapopulation variation of the land snail C. vindobonensis was found in our study. Significant differences between sample means were found for all shell traits and indices used (except for SF1), however, maximum difference was noted for SH and SF2 (in both cases: P ≤ 0.001). About 80% of the total variation of the variance-covariance matrix was explained by the 1st and 2nd Principal Components (PC1 and PC2). The PC1 was characterized by high positive factor loadings of MJD, MID and SH and thus can be interpreted as “shell size dimension” and the PC2 had a high correlation with SF2 and thus it can be interpreted as “shell globularity”. The PC1 and PC2 determined a high level of spatial differentiation of intrapopulation morphological variation of the land snail C. vindobonensis. Samples with small (area A) and large (areas B and C) shells were separated from each other according to the PC1. Areas B and C were characterized by individuals with flatness and globularity shells, respectively. The areas A, B and C differed significantly in the total number of morphs, average number of morphs and frequency of rare morphs (Kruskal-Wallis H-test; in all cases P ≤ 0.010). At the same time, the highest value of phenetic diversity was noted for samples collected within A and C areas. In general all phenetic diversity estimators showed a positive correlation with sample size (Spearman's correlation coefficient; in all cases P ≤ 0.05). It was found that the type of biotope did not likely affect the frequency of individual morphs with respect to the shell banding polymorphism pattern. With regard to the most common morphs two patterns of the spatial arrangement of the intrapopulation variation were found – clinal pattern was for the frequency of pallescens morph and chaotic pattern was for frequency of “12345” morph.

Herbivore-mediated negative frequency-dependent selection underlies a trichome dimorphism in nature.

Negative frequency‐dependent selection (NFDS) has been shown to maintain polymorphism in a diverse array of traits. The action of NFDS has been confirmed through modeling, experimental approaches, and genetic analyses. In this study, we investigated NFDS in the wild using morph‐frequency changes spanning a 20‐year period from over 30 dimorphic populations of Datura wrightii. In these populations, plants either possess glandular (sticky) or non‐glandular (velvety) trichomes, and the ratio of these morphs varies substantially among populations. Our method provided evidence that NFDS, rather than drift or migration, is the primary force maintaining this dimorphism. Most populations that were initially dimorphic remained dimorphic, and the overall mean and variance in morph frequency did not change over time. Furthermore, morph‐frequency differences were not related to geographic distances. Together, these results indicate that neither directional selection, drift, or migration played a substantial role in determining morph frequencies. However, as predicted by negative frequency‐dependent selection, we found that the rare morph tended to increase in frequency, leading to a negative relationship between the change in the frequency of the sticky morph and its initial frequency. In addition, we found that morph‐frequency change over time was significantly correlated with the damage inflicted by two herbivores: Lema daturaphila and Tupiochoris notatus. The latter is a specialist on the sticky morph and damage by this herbivore was greatest when the sticky morph was common. The reverse was true for L. daturaphila, such that damage increased with the frequency of the velvety morph. These findings suggest that these herbivores contribute to balancing selection on the observed trichome dimorphism.

МІЖПОПУЛЯЦІЙНА МІНЛИВІСТЬ ЗАБАРВЛЕННЯ ЧЕРЕПАШКИ РАВЛИКА ВЕЛИКОГО ЗВИЧАЙНОГО HELIX ALBESCENS ROSSMÄSSLER, 1839 (PULMONATA, HELICADAE) У ПІВНІЧНОЗАХІДНОМУ ПРИАЗОВ’Ї

The variability of any organism is highly dependent on environmental conditions. Morphological parameters of living organisms are determined by the genetic constitution of the animal, as well as formed under the influence of the environment, where climatic factors play an important role. Thus, the shell features of land-based mollusks are reliable indicators of the environmental conditions in which animals develop. Malacology has accumulated a large amount of factual material from various species of gastropods, which confirms this position. The article deals with the polymorphism on the striped shell of Helixalbescens terrestrial mollusks in the northwest og the Azov region. In the course of the research, the frequency of each morph in the sample was estimated as well as the average number of morphs (μ), the frequency of rare morphs (h), and the similarity of the samples according to the phenotype (r) was calculated. All 11 morphs were found in all populations of H. albescens from urban habitats. Three main morphs (12345, 1(23)45, 12045) were present in all studied samplings. The occurrence of rare morphs was different in urbanized and unbuilt biotopes. For example, morph 123 (45) was found only in urban biotopes, morph 12 (345) – only in the city and at point 9. The dominant morphs are 12345, 1(23)45, to which 22.6% and 32.9% of 1058 specimens or hollow shells respectively belonged. The indicator of intra-population diversity μ varied within rather narrow limits both in urbanized (from 4,899 to 7,581) and in unburied biotopes (from 4,152 to 6,697). In total, among 1058 shells and 10 samplings, 11 morphs were registered. The coloring of the shells of H. albescens differs in a considerable variety both in natural and in urbanized biotopes.

Climate suggests environment‐dependent selection on lizard colour morphs

AbstractAimThe maintenance of polymorphisms is often explained by sexual selection. However, natural selection may also constrain morphs to particular locations, causing geographical variation in morph diversity. In many well‐known polymorphic organisms in which the relevance of sexual selection on the maintenance of polymorphisms is widely supported, the role of environmental factors has been poorly studied. Here, we adopted a population‐level approach to assess the extent to which geographical variation in climate explains morph composition in a colour polymorphic lizard. We predict that rare morphs are more environmentally constrained than common morphs.LocationEastern Pyrenees, Western Europe.TaxonPodarcis muralis (Lacertidae). The species shows up to five discrete colour morphs: white (W), orange (O), white‐orange (WO), yellow (Y) and yellow‐orange (YO). Populations strongly vary in morph composition.MethodsWe modelled the realised niche of each morph and the whole species with Maxent, Bioclim, and Domain, considering 110 localities over a relatively small but environmentally heterogeneous area. Morph ranges were compared to identify differences among their realised niches and local morph frequencies were interpolated to detect intra‐morph geographical variations beyond the mere presence of morphs.ResultsDifferences between morph distributions were mainly associated to temperature seasonality and annual precipitation. While W, O, and WO morphs were found along the whole environmental range of the species, Y and YO morphs were restricted to a subset of the environmental conditions suitable for the species, namely high temperature seasonality and relatively high precipitation. Local frequencies of common morphs also differ among localities, the W morph being more frequent at lower altitudes than the O and WO morphs, which are more locally abundant at higher altitudes.Main conclusionsWe found a remarkable geographical relationship between climate and local morph composition that suggests environmentally dependent selection acting in a different way on common and rare morphs, most likely in interaction with sexual selection.

The white neck-ring of the Eurasian Teal Anas crecca: rare mutation or stable morph? A first genetic and heuristic analysis

ABSTRACTCapsule: Individual Eurasian Teal Anas crecca with white neck-rings have been found in Italy and an extensive museum survey found this plumage character occurring with a low frequency, although no genetic difference was observed with respect to the normal phenotype.Aims: To estimate the relative frequency and distribution of this plumage variation and to provide a first genetic assessment to verify if this character could have a taxonomic basis or if it occurs by chance among populations.Methods: An extensive museum survey was conducted to check for the occurrence of white neck-ringed Eurasian Teals in preserved specimens from its distributional range. A genetic analysis was conducted at standard mitochondrial loci (D-loop and COI) of ten white neck-ringed Eurasian Teals from Venice lagoon, Italy. Haplotypes were compared with genetic data from Holarctic populations.Results: The museum survey uncovered additional cases of white neck-ringed Eurasian Teals in Italy and Europe. Moreover, this mutation has also been documented for the first time in the North American Green-winged Teal Anas carolinensis. The white neck-ring was found to be variable in size and occurred in both sexes and in different age classes in about 1.5% of examined individuals. The genetic analysis did not show any significant lineage differentiation between them and the normal phenotype, but the Italian samples showed high values of haplotype diversity indicating a key role of northeast Italy in attracting different migratory populations in winter.Conclusions: While the same variation occurs in many other species of the tribe Anatini, none of these cases clearly suggested the occurrence of hybridization, progressive greying, environmental causation or another kind of locally frequent mutation. It is most likely this plumage trait is a form of leucism or the expression of an ancestral phenotype, possibly occurring in different populations within the species’ range.

An integrative and citizen science based approach to the rediscovery and redescription of the only known high-altitude endemic Pill Millipede, Glomeris aurita Koch (Diplopoda, Glomerida)

The pill millipede species Glomeris aurita Koch, 1847 remained of relative unknown origin and appearance until its recent rediscovery in samples from the Bergamasque Alps, northern Italy. In order to provide an integrative redescription and accurate identification of the high-altitude microendemic G. aurita, COI barcode sequences from three individuals coming from two different localities were obtained. These sequences are compared with those of the syntopic endemic G. oblongoguttata Verhoeff, 1894, the widespread black morph of G. romana Verhoeff, 1900, as well as several widespread species including G. marginata Villers, 1789, G. connexa Koch, 1847, and G. klugii Brandt, 1833, which have rare colour morphs that exhibit some similarity to G. aurita. To rule-out any identity confusion of G. aurita with other high-altitude or little-known Italian Glomeris, specimens of G. transalpina Koch, 1836, G. oropensis Verhoeff, 1934, and G. primordialis Verhoeff, 1932 were also added to the dataset. Altogether, 24 sequences were compared. Morphologically, the specimens of G. aurita were studied utilizing scanning electron microscopy as well as non-invasive micro-CT technology. The distribution of both Bergamasque endemics, G. aurita and G. oblongoguttata, could be mapped and compared utilizing samples from the Museo civico di Scienze Naturali di Bergamo, as well as photographic evidence from an Italian naturalist forum. G. aurita has a very short active period and is the first known pill millipede species restricted to mountain tops and cold places, possibly representing a Nunatak survivor.

Modeling the impact of climate change on a rare color morph in fish

Species are typically comprised of a large number of genotypes, some of which are rare. Rare genotypes that are temperature-sensitive will predictably be impacted by climate change more profoundly than common genotypes for which gene expression does not depend on temperature. Computer simulations were used in this study to analyze the impact of changing temperatures on a very rare melanic morph that expresses a temperature-sensitive phenotype and is found in an abundant fish species (Gambusia holbrooki). This numerical model assesses the frequency of the two natural color morphs, silver and black-spotted, over time and iterates in each generation, incorporating survival estimates for different life stages based upon data collected during empirical experiments. Using the current projections for mean surface temperature increase, which are 2.5° F to 10.4° F by the year 2100, the impact of warming environment on the mosquitofish population was analyzed. Three different climate warming scenarios were used to address annual temperature fluctuations and incorporate predicted temperature rise at correspondingly minimal, mid, and maximum levels. Our results indicate that increasing temperatures will seriously affect the rare color morph and in some cases will result in extinction. The minimal climate-warming scenario produced lower extinction risks for the rare morph; however, it still decreased the frequency of the rare genotype to minimal values. The mid-range warming scenario produced a higher risk of extinction, while the maximum warming scenario resulted in the extinction of the rare color morph. The results of this study shed light on the possibility that the effects of climate change may have important ramifications for rare genotypes in nature and will likely drive some rare species genotypes to extinction.

A rare dark morph in the Canadian Arctic raises questions about molting and polymorphism in Long-tailed Jaeger (Stercorarius longicaudus)

ABSTRACT The existence of a dark morph in adult Long-tailed Jaeger (Stercorarius longicaudus) is still unclear and debated. For this species, dark plumages occur in juveniles and immatures, but no dark morph adults have yet been unequivocally confirmed. Ambiguous reports of presumed dark morph adults and lack of information on molt progression of immatures generate confusion regarding this issue. Here we describe observations conducted in the Canadian Arctic (Bylot Island) and show that Long-tailed Jaegers can apparently exhibit dark morph adult-like plumage (i.e., individuals showing some obvious criteria associated with definitive alternate ‘adult breeding' plumage). Careful examination of those sightings, however, also revealed immature characteristics, indicating the high variability of the first prealternate molt in this species. Well-documented observations of rare plumages like the one reported in this study are needed to elucidate molting strategies and polymorphism in Long-tailed Jaeger. Received...

Natural rarity places clownfish colour morphs at risk of targeted and opportunistic exploitation in a marine aquarium fishery

As fish stocks become depleted, exploitation eventually fails to be cost-efficient. However, species or morphs of species can suffer from continual exploitation if their rarity results in increased value, justifying the cost-efficiency of targeted or opportunistic exploitation. The trade in coral reef fishes for public and private aquaria is an industry in which naturally rare species and rare morphs of species command high prices. Here we investigate the relationship between price and the natural prevalence of colour morphs of two highly demanded clownfish species using a localised case study. The export prices for colour morphs increased with decreasing prevalence of occurrence (y = 4.60x−0.51, R2 = 0.43), but price increase was inversely less than the observed reduction in prevalence. This renders rare colour morphs (i.e., those at relatively low prevalence) at risk of opportunistic exploitation. Using ecological data, we also demonstrate how this increased value can subject rare colour morphs with aggregated distributions to targeted exploitation. These findings are discussed in relation to the broader marine aquarium trade, identifying taxa potentially at risk from exploitation motivated by rarity and addressing potential management strategies.

The role of rare morph advantage and conspicuousness in the stable gold-dark colour polymorphism of a crater lake Midas cichlid fish.

Genetically based stable colour polymorphisms provide a unique opportunity to study the evolutionary processes that preserve genetic variability in the wild. Different mechanisms are proposed to promote the stability of polymorphisms, but only few empirical examples have been documented, resulting in an incomplete understanding of these mechanisms. A remarkable genetically determined stable colour polymorphism is found in the Nicaraguan Midas cichlid species complex (Amphilophus cf. citrinellus). All Midas cichlids start their life with a dark-grey coloration (dark morph), but individuals carrying the dominant "gold" allele (c. 10%) lose their melanophores later in life, revealing the underlying orange coloration (gold morph). How this polymorphism is maintained remains unclear. Two main hypotheses have been proposed, both suggesting differential predation upon colour morphs as the proximate mechanism. One predicts that the conspicuous gold morph is more likely to be preyed upon, but this disadvantage is balanced by their competitive dominance over the dark morph. The second hypothesis suggests a rare morph advantage where the rarer gold morph experiences less predation. Empirical evidence for either of these mechanisms is still circumstantial and inconclusive. We conducted two field experiments in a Nicaraguan crater lake using wax models simulating both morphs to determine predation pressure upon Midas cichlid colour morphs. First, we tested the interaction of coloration and depth on attack rate. Second, we tested the interaction of fish size and coloration. We contrasted the pattern of attacks from these experiments to the predicted predation patterns from the hypotheses proposed to explain the colour polymorphism's stability. Large models imitating colour morphs were attacked at similar rates irrespectively of their position in the water column. Yet, attacks upon small models resembling juveniles were directed mainly towards dark models. This resulted in a significant size-by-colour interaction. We suggest that gold Midas cichlids experience a rare morph advantage as juveniles when individuals of this morph are extremely uncommon. But this effect is reduced or disappears among adults, where gold individuals are relatively more common. Thus, the interaction of rare morph advantage and conspicuousness, rather than either of those factors alone, is a likely mechanism resulting in the stability of the colour polymorphism in Midas cichlids.

Flower Colour Polymorphism inGeranium nepalense(Geraniaceae): Adaptation to Non-Pollinator Agents

Flower colour polymorphism is attributed to pollinator or non-pollinator mediated selection. Geranium nepalense has common white morph and very rare pink morph. We compared pollinator visitation frequencies, temperature and soil moisture between two morphs in the mixed morph population. We also compared morph ratio and reproductive success between white and pink flower individuals. Our results indicated that no visitor groups were different between two colour morphs. But visitor groups differed in visits between two years. Halictidae preferred pink morph in the year of 2012 but showed no discrimination in 2014, whereas Syrphidae preferred white morph in 2014 but no discrimination in 2012. Overall, pink morph produced more seeds than white morph, but exhibited variation between two years. However, visitor discrimination was not the main cause of the difference in female fitness. Soil moisture was not different between two colour morphs. Temperature of white morph was lower than pink in evening but not different in morning and noon. The results indicated that non-pollinator factors may exert the selective pressure to maintain the flower colour polymorphism in this species. Although pollinators did not exert selection on the flower colour polymorphism, we suggest that they provided potential pollination environment of fluctuating selection to drive flower colour evolution if visitors were limited.

Experimental evidence for an antipredatory function of egg rejection behaviour in a common host of the brood-parasitic shiny cowbird

The rejection of foreign eggs is the most effective adaptation against brood parasitism in birds. Many hosts, however, show suboptimal responses towards parasitic eggs, which could reflect a compromise between the benefits and costs of egg rejection. Some large-sized hosts of the shiny cowbird (Molothrus bonariensis) accept any spotted parasite egg but reject a rarer pure white egg morph that occurs only in some parts of the parasite’s distribution. This behaviour is intriguing because it is not an effective defence against parasitism and recent evidences suggest that large-sized hosts could benefit from accepting cowbird eggs as this may dilute the risk of host egg losses at multiply parasitized nests. We studied whether rejection of pure white cowbird eggs can be driven by the increased predation risk of host nests parasitized with this conspicuous egg morph. We conducted a nest predation experiment using artificial clutches placed in natural, inactive nests of a large-sized host, the chalk-browed mockingbird (Mimus saturninus). Clutches consisted of two eggs resembling either one host plus one pure white cowbird egg, one host plus one spotted cowbird egg or two host eggs. Clutches with pure white eggs were more likely to be predated than those having either two host eggs or one host and one spotted cowbird egg, supporting an antipredatory function of egg rejection behaviour in mockingbirds. These results suggest that nest predation could operate as part of larger fitness trade-offs shaping host responses towards foreign eggs. Considering the role of nest predation in the studies of host rejection decisions would help to better understand the evolution and expression of antiparasite defences, especially when the hosts seem to behave suboptimally against costly brood parasitism. One major goal in avian brood parasitism research is to explain the evolution of host defences against parasite eggs and young. Some large-sized hosts of the shiny cowbird (Molothrus bonariensis) show an intriguing behaviour: they accept spotted cowbird eggs but reject a rare pure white egg morph that occurs only in some parts of the parasite’s distribution. Such behaviour provides little protection against parasitism, but it may serve as an antipredatory defence if conspicuous pure white eggs facilitate the detection of host nests to potential predators. Our study supports this idea by showing that pure white eggs increase the risk of nest predation compared to spotted host and cowbird eggs in a common large-sized host, the chalk-browed mockingbird (Mimus saturninus). These findings highlight the importance of considering the role of nest predation in the expression of hosts’ strategies against parasitism.

Silver-white Variants of the Eastern Red-backed Salamander, <i>Plethodon cinereus</i>, from Eastern Canada

The Eastern Red-backed Salamander (Plethodon cinereus) is well known for its colour polymorphism, which includes 8 colour phenotypes: the red-backed (striped), lead-backed (unstriped), and erythristic morphs, as well as the iridistic, albino, leucistic, amelanistic, and melanistic anomalies. Among these, the prevalence and geographic distribution of rare morphs have received little attention. In this article, we report 2 occurrences of silver-white variants of the red-backed morph of P. cinereus from Québec, Canada. To our knowledge, these variations in stripe colour on the red-backed phenotype represent the first 2 documented mentions for eastern Canada.