Variation In Coloration Research Articles

Plumage polymorphism and variation in the melanocortin-1 receptor gene in the Fuscous Flycatcher, Cnemotriccus fuscatus (Wied, 1831)

We investigated the possible mechanisms behind the variation plumage color of the Fuscous Flycatcher, Cnemotriccus fuscatus, by sequencing the melanocortin-1 receptor (MC1R) gene, which has been associated with the variation in plumage coloration in birds. C. fuscatus is widely distributed in South America and includes seven subspecies, which differ in their plumage coloration. Here we tested the hypothesis that the variation in the MC1R gene explains the plumage polymorphism found in C. fuscatus. We sequenced the MC1R gene in six subspecies, representing two groups: group 1 (yellow morph), with three subspecies, C. f. duidae, C. f. fumosus, and C. f. fuscatus, and group 2 (white morph), with the remaining subspecies, C. f. bimaculatus, C. f. beniensis, and C. f. fuscatior. The only variation we found among the C. fuscatus sequences were six non-synonymous substitutions from 22 variable sites, none of which were associated systematically with either plumage morph. The result of the neutrality test indicated that the polymorphism of the MC1R gene is not suggestive of significant selection pressure. We conclude that variation in plumage coloration in C. fuscatus does not appear to be determined by the MC1R gene, and that it may be related to other loci or under the influence of environmental factors.

Advertisement calls, intraspecific variation and species diagnosis of six Brazilian species of Elachistocleis (Anura: Microhylidae: Gastrophryninae)

We describe for the first time the advertisement calls of three Elachistocleis species (E. surumu, E. magna, E. carvalhoi) and provide additional data on the calls of three other species (E. matogrosso, E. helianneae, E. muiraquitan). Additionally, we evaluate intraspecific variation in morphology and color patterns, and comment on species diagnosis in the genus. The advertisement calls of the six species of Elachistocleis have a stereotyped temporal and spectral structure, which consists of a long sustained multipulsed note with an upsweep in frequency at its onset, followed by a constant frequency along the note. Newly collected Elachistocleis from northern and western Brazil showed intraspecific variation in morphology and coloration that had not been previously reported. Coloration was listed as a diagnostic feature in the original descriptions of the Elachistocleis species evaluated in this study, but color patterns were variable in some species and sometimes did not allow for species differentiation. Our results indicated that the three species with greater degrees of morphological similarity (E. helianneae, E. matogrosso, E. muiraquitan) differed in microtemporal and spectral traits of their calls. Moreover, pulse duration in E. helianneae was very distinct, lasting approximately twice the average pulse duration in calls of the other species studied. Therefore, pulse duration might be an informative trait when assigning specimens to E. helianneae, which is widely distributed across Amazonian lowland forests and in a region of Amazonian savanna. Our results bring novelties on species diagnosis and intraspecific variation in Elachistocleis based on acoustic evidence and morphological/color patterns, and accentuate the importance of taking into consideration multiple lines of evidence as a means for accurate species-level identification in this genus of Neotropical frogs.

Nuclear introns help unravel the diversification history of the Australo-Pacific Petroica robins

Australo-Pacific Petroica robins are known for their striking variability in sexual plumage coloration. Molecular studies in recent years have revised the taxonomy of species and subspecies boundaries across the southwest Pacific and New Guinea. However, these studies have not been able to resolve phylogenetic relationships within Petroica owing to limited sampling of the nuclear genome. Here, we sequence five nuclear introns across all species for which fresh tissue was available. Nuclear loci offer support for major geographic lineages that were first inferred from mtDNA. We find almost no shared nuclear alleles between currently recognized species within the New Zealand and Australian lineages, whereas the Pacific robin radiation has many shared alleles. Multilocus coalescent species trees based on nuclear loci support a sister relationship between the Australian lineage and the Pacific robin radiation—a node that is poorly supported by mtDNA. We also find discordance in support for a sister relationship between the similarly plumaged Rose Robin (P. rosea) and Pink Robin (P. rodinogaster). Our nuclear data complement previous mtDNA studies in suggesting that the phenotypically cryptic eastern and western populations of Australia’s Scarlet Robin (P. boodang) are genetically distinct lineages at the early stages of divergence and speciation.

Resolving two Haploembia (Embioptera: Oligotomidae) cryptic species: molecular data confirms parthenogenetic females can be distinguished by their antisocial behavior.

The names of two cryptic species of Haploembia found in California are resolved and methods for identification are summarized. Molecular data of the Histone III subunit was used to evaluate color and behavior as species identifiers, confirming that antisocial behavior is a good identifier for the parthenogenetic species (Haploembia tarsalis), whereas the more variable coloration patterns were helpful, but less so. A genome size ratio of 1.44 between the parthenogenetic H. tarsalis and the sexually reproducing H. solieri was observed, along with higher genetic variation within the asexual lineage. This, and the identification of what appears to be a putative hybrid, contributes to current work examining mutation rates and selective pressures on genome size in parthenogenetic populations.

Differential gene regulation underlies variation in melanic plumage coloration in the dark-eyed junco (Junco hyemalis).

Colour plays a prominent role in species recognition; therefore, understanding the proximate basis of pigmentation can provide insight into reproductive isolation and speciation. Colour differences between taxa may be the result of regulatory differences or be caused by mutations in coding regions of the expressed genes. To investigate these two alternatives, we studied the pigment composition and the genetic basis of coloration in two divergent dark-eyed junco (Junco hyemalis) subspecies, the slate-coloured and Oregon juncos, which have evolved marked differences in plumage coloration since the Last Glacial Maximum. We used HPLC and light microscopy to investigate pigment composition and deposition in feathers from four body areas. We then used RNA-seq to compare the relative roles of differential gene expression in developing feathers and sequence divergence in transcribed loci under common-garden conditions. Junco feathers differed in eumelanin and pheomelanin content and distribution. Within subspecies, in lighter feathers melanin synthesis genes were downregulated (including PMEL, TYR, TYRP1, OCA2 and MLANA), and ASIP was upregulated. Feathers from different body regions also showed differential expression of HOX and WNT genes. Feathers from the same body regions that differed in colour between the two subspecies showed differential expression of ASIP and three other genes (MFSD12, KCNJ13 and HAND2) associated with pigmentation in other taxa. Sequence variation in the expressed genes was not related to colour differences. Our findings support the hypothesis that differential regulation of a few genes can account for marked differences in coloration, a mechanism that may facilitate the rapid phenotypic diversification of juncos.

Expression of and choice for condition-dependent carotenoid-based color in an urbanizing context

Urban environments create a unique suite of conditions, leading to changes in animal behavior, morphology, phenology, and physiology. Condition-dependent traits such as the carotenoid-based coloration offer a unique opportunity to assess the impacts of urbanization on organisms because they reflect the nutrition, health, or other resource-based attributes of their bearers and they play an essential role in intra and intersex interactions. To determine if and how the carotenoid-based coloration of male house finches (Haemorhous mexicanus) varies along a gradient of urbanization, we quantified the plumage coloration of more than 1000 individuals in urban, suburban, rural, and desert habitats over the course of 17 months. We also examined for the first time the preference of females for male plumage coloration across the urban-rural gradient, to test if and how female preferences varied relative to the plumage coloration displayed by males in their local population. We found that carotenoid-based coloration decreased along the gradient of urbanization, suggesting that the enzyme-driven metabolic conversion of dietary carotenoids into red carotenoids used to color plumage is sensitive to urban stressors. The stronger negative effect of urbanization on carotenoid-based plumage coloration during breeding than during molt and winter suggests that urbanization affects color fading rate, maybe through modifications of feather-degrading bacterial load. Finally, we have shown that urbanization influences female mate-choice behavior, suggesting that female color preferences may track the variation in male coloration across the gradient of urbanization.

Experimental evidence of the role of heterochrony in evolution of the Mesoamerican cichlids pigment patterns.

The Mesoamerican cichlids display a spectacular diversity of pigment patterns, which serve a variety of functions and serve as a strong selective trait for this lineage. The development and variation of coloration in the Mesoamerican cichlids have been detailed by several groups. In particular, Říčan, Musilová, Muška, and Novák () and Říčan, Piálek, Dragová, and Novák () determined homology of pattern and revealed four alternative types of coloration and their ontogeny. In this work, this group posed an "ontogenetic timing hypothesis" proposing heterochronic shifts underlying major transitions in the evolution of the Mesoamerican cichlids. Here, we experimentally test this hypothesis by experimentally altering timing of pigment pattern formation in the convict cichlid Amatitlania nigrofasciata, a member of the Mesoamerican cichlids, via manipulations of thyroid hormone (TH) function. The response of different pigment cell lineages to TH-perturbations revealed that the transition from larval to juvenile coloration in the convict cichlid is under the control of TH-signaling. Importantly, hormonally induced changes in the timing of pigment cell lineages' development resulted in shifts of coloration ontogeny type observed between lineages and led to the appearance of phenotypes mimicking those in phylogenetically close and distant species. Thus, our findings support the hypothesis that simple changes in ontogenetic timing underlies species specific patterns in pigmentation and provide new perspectives for studying the role of endocrine signaling in the evolution of cichlids.

Mutations in the melanocortin-1 receptor (MC1R) gene have no influence on the distinct patterns of melanic plumage found in the manakins of the genus Antilophia (Aves: Pipridae).

The melanocortin-1 receptor gene is the most widely-used marker for the investigation of the genetic determination of melanic plumage patterns. Studies of a number of wild bird species have shown an association between non-synonymous mutations of the MC1R gene and the presence of melanic variants. The genus Antilophia (Pipridae) includes only two manakin species (A. galeata and A. bokermanni), which are distinguished primarily by the differences in the pattern of melanic coloration of the plumage of the mantle in the adult males. In A. galeata, this plumage is black, while in A. bokermanni, it is predominantly white. This study investigates the possible association between mutations of the MC1R marker and the variation in plumage coloration observed in the two species. The MC1R sequences of the two species was analyzed, and the observed nucleotide variation was compared. Six polymorphic sites were identified, representing seven distinct genotypes. Five of these polymorphic mutations were non-synonymous, but were not related to the different phenotypes. Neutral evolution and the absence of any systematic association between the variants of the MC1R and plumage coloration in the Antilophia species indicate that alternative mechanisms regulate the expression of the coloration of the plumage in the adult males.

Local adaptation versus historical isolation as sources of melanin‐based coloration in the white‐throated thrush Turdus assimilis

Local adaptation seems to be one of the causes of variation in melanin‐based colors in bird plumages, related mainly to the heterogeneity of the environmental conditions along the distribution of a species. Based on comparisons of genetic (mtDNA sequences), ecological (niche models), and quantitative colorimetric data, we explored variation in plumage coloration of the white‐throated thrush Turdus assimilis, a Mesoamerican species whose dorsal color varies from brown (northern and central Mexico) to dark gray (southern Mexico and Central America). Our results suggest the existence of two major patterns of coloration in this bird, which are congruent with the genetic structure, and comparisons of ecological niche models showed that population's niches were more similar than expected by chance, suggesting that color variation in plumage of T. assimilis is not consequence of local adaptation to different environmental conditions. Our results also showed that a greater geographic distance between populations is correlated with greater colorimetric differences, suggesting that color variation in T. assimilis may be consequence of historical isolation.

Scary clowns: adaptive function of anemonefish coloration.

Clownfishes, with their showy coloration, are well known for their symbiosis with sea anemones and for their hierarchical reproductive system, but the function of their coloration is unclear. We used a phylogeny of 27 clownfish species to test whether fish coloration (i) serves a protective function that involves their anemone hosts, or (ii) signals species identity in species with overlapping host ranges that can potentially share the same host. We tested for an association between fish colour pattern traits, host morphology and host toxicity and examined coloration in relation to host sharing and geographic proximity. Fish with fewer stripes occupied fewer anemone species, and hosts with shorter tentacles, than fish with multiple stripes. There was a negative relationship between anemone toxicity and tentacle length and these protective traits together were correlated with the evolution of stripes. Host sharing or range overlap was not associated with coloration divergence. We propose that ancestral anemonefishes had multiple stripes that served for hiding/camouflage among the hosts' long tentacles, whereas increased specialization towards fewer and more toxic hosts (with shorter tentacles) led to the use of coloration as an aposematic signal. The intriguing notion that an aposematic signal could advertise the defence of another species may reflect the unique symbiotic relationship between anemonefishes and their hosts.

Latitudinal variation in biophysical characteristics of avian eggshells to cope with differential effects of solar radiation.

Solar radiation is an important driver of animal coloration, not only because of the effects of coloration on body temperature but also because coloration may protect from the deleterious effects of UV radiation. Indeed, dark coloration may protect from UV, but may increase the risk of overheating. In addition, the effect of coloration on thermoregulation should change with egg size, as smaller eggs have higher surface‐volume ratios and greater convective coefficients than larger eggs, so that small eggs can dissipate heat quickly. We tested whether the reflectance of eggshells, egg spottiness, and egg size of the ground‐nesting Kentish plover Charadrius alexandrinus is affected by maximum ambient temperature and solar radiation at breeding sites. We measured reflectance, both in the UV and human visible spectrum, spottiness, and egg size in photographs from a museum collection of plover eggshells. Eggshells of lower reflectance (darker) were found at higher latitudes. However, in southern localities where solar radiation is very high, eggshells are also of dark coloration. Eggshell coloration had no significant relationship with ambient temperature. Spotiness was site‐specific. Small eggs tended to be light‐colored. Thermal constraints may drive the observed spatial variation in eggshell coloration, which may be lighter in lower latitudes to diminish the risk of overheating as a result of higher levels of solar radiation. However, in southern localities with very high levels of UV radiation, eggshells are of dark coloration likely to protect embryos from more intense UV radiation. Egg size exhibited variation in relation to coloration, likely through the effect of surface area‐to‐volume ratios on overheating and cooling rates of eggs. Therefore, differential effects of solar radiation on functions of coloration and size of eggshells may shape latitudinal variations in egg appearance in the Kentish plover.

Frequency dispersion reveals chromophore diversity and colour-tuning mechanism in parrotfeathers.

Variation in animal coloration is often viewed as the result of chemically distinct pigments conferring different hues. The role of molecular environment on hue tends to be overlooked as analyses are mostly performed on free pigments extracted from the integument. Here we analysed psittacofulvin pigments within parrot feathers to explore whether the in situ organization of pigments may have an effect on hue. Resonance Raman spectra from a red region of a yellow-naped amazon Amazona auropalliata tail feather show frequency dispersion, a phenomenon that is related to the presence of a range of molecular conformations (and multiple chromophores) in the pigment, whereas spectra from a yellow region on the same feather do not show the same evidence for multiple chromophores. Our findings are consistent with non-isomeric psittacofulvin pigments behaving as a single chromophore in yellow feather barbs, which implies that psittacofulvins are dispersed into a structurally disordered mixture in yellow feathers compared with red feathers. Frequency dispersion in red barbs may instead indicate that pigments are structurally organized through molecule–molecule interactions. Major differences in the hues of parrot feathers are thus associated with differences in the organization of pigments within feathers.

Flower colour within communities shifts from overdispersed to clustered along an alpine altitudinal gradient.

Altitudinal gradients are interesting models to test the effect of biotic and abiotic drivers of floral colour diversity, since an increase in UV irradiance, decrease of pollinator availability and shifts from bee- to fly-pollination in high relative to low altitudes are expected. We tested the effect of altitude and phylogeny, using several chromatic and achromatic colour properties, UV reflectance and pollinators' discrimination capacity (Apis mellifera, Bombus terrestris, Musca domestica and Eristalis tenax), to understand the floral colour diversity in an alpine altitudinal gradient. All colour properties were weakly related to phylogeny. We found a shift from overdispersed floral colours and high chromatic contrast with the background (for bees) in the low altitude, to clustered floral colours (UV and green range for bees and flies) and clustered chromatic and achromatic properties in the high altitude. Different from flies, bees could discriminate floral colours in all altitudinal ranges. Low altitudes are likely to exhibit suitable conditions for more plant species, increasing competition for pollinators and floral colour divergence. Conversely, the increase in UV irradiance in high altitudes may filter plants with specific floral UV-reflectance patterns. Overall, floral colour diversity suggests that both biotic (pollinator fauna) and abiotic (UV irradiance) drivers shape floral communities, but their importance changes with altitude.

Correlates of color polymorphism in coconut crabs Birgus latro

Color polymorphisms are widespread in nature and can be maintained by several evolutionary processes. We used the coconut crab (Birgus latro) red/blue color polymorphism as a test case to explore the functional significance of intraspecific variation in crab coloration. Across our study sites on Pemba and Chumbe Islands, Tanzania, and Christmas Island, Australian Territory, red:blue morph ratios were 76.5%, 66.7% and 72.0% respectively, or approximately 3:1 in each case. To investigate whether coloration is sex or size dependent, signals strength or behavior, or is a physiological pleiotropic effect, we measured body weights, linear dimensions, pinch-force, behavioral dispositions and took crude environmental variables in the field. Except for a slight tendency for red crabs to be found in more open situations, we found no differences between color morphs for any of these variables. Other factors associated with color polymorphisms in other species, including frequency-dependent predation seems unlikely in such a large species with few natural predators, while niche separation in space seems improbable as morphs are typically found together. Assortative mating is plausible but mating is rapid, suggesting little choice is involved. Our findings suggest that neither morphological nor behavioral factors can explain color polymorphism in this species and that explanations must be found elsewhere.

Redescription of Trichomycterus striatus (Meek Hildebrand, 1913) (Siluriformes: Trichomycteridae), with notes on its geographic distribution.

Trichomycterus striatus is herein redescribed, based on examination of the types and recently collected specimens, and its geographic distribution is updated. This species can be diagnosed from all other northeastern South American congeners by its variable coloration pattern consisting of a yellowish to light brown background with a black lateral band and/or small dark brown spots on sides or uniformly light brown and by the following combination of characters: teeth conical arranged in three to four irregular rows in both jaws; anterior section of infraorbital canal (sensory pores i1 and i3) present; sensory pores s6 paired, 11-23 opercular odontodes; 27-44 interopercular odontodes; seven to eight pectoral-fin branched rays; 36-37 free vertebrae; 12-14 ribs; cleithrum pierced by several foramina; and caudal fin truncate to rounded. Trichomycterus striatus occurs from southern Costa Rica [from the Pirrís (herein reported for the first time), Térraba and Coto River basins] to eastern Panama (in most of the main river basins in both the Pacific and Atlantic versants), being the sole representative of the family in lower Central American waters.

Geographical variation in colour of female threespine stickleback (Gasterosteus aculeatus).

The ecological multifunctionality of colour often results in multiple selective pressures operating on a single trait. Most research on colour evolution focuses on males because they are the most conspicuous sex in most species. This bias can limit inferences about the ecological drivers of colour evolution. For example, little is known about population divergence in colour of female threespine stickleback (Gasterosteus aculeatus), which is among the most intensively-studied model vertebrates in evolution, ecology, and behaviour. In contrast, the evolution and ecology of colour in male stickleback has received considerable attention. One aspect of female colouration that is lacking previous research is non-ornamental body colour. Non-ornamental colour can play defensive and social roles, and indicate other aspects of female stickleback ecology. To remedy this knowledge gap, we measured the colour and brightness of one dorsal and one ventral lateral area on female stickleback from nine lake populations on Vancouver Island. We found that lake populations varied in overall colour brightness and dorso-ventral contrast. In addition, we found that female brightness increased with lake size, indicating potential ecological drivers of these colour differences. Our results demonstrate that there is substantial scope for future research on female colour diversification, which has been overlooked because past researchers focused on dramatic male nuptial colours.

Diversity and phylogenetic relationships of Drilus Olivier, 1790 (Elateridae: Agrypninae: Drilini) in Cyprus

The neotenic elaterid genus Drilus Olivier, 1790 (Elateridae: Agrypninae: Drilini) contains more than 40 species distributed primarily in the Mediterranean region. The precise number of species remains ambiguous due to the insufficient taxonomic investigation in several areas. Herein, we study Drilus diversity in Cyprus and we recognize the following species: D. humeralis Pic, 1931, D. rectus Schaufuss, 1867, and D. rufipes (Baudi di Selve, 1871). Drilus testaceipes Pic, 1933 syn. nov. is synonymized under D. rectus, and D. truquii (Baudi di Selve, 1871) syn. nov. is synonymized under D. rufipes. As consequence of these taxonomic changes, Drilus humeralis remains the only species endemic to Cyprus. Females of D. rectus and D. rufipes are described and figured for the first time, as well as the larvae of D. rufipes. A key to the males of Drilus species in Cyprus is given. Drilus rectus is recorded in Syria for the first time and D. rufipes is recorded in Rhodes. To examine the phylogenetic relationships of Drilus in Cyprus, we produced the cox1-3ʹ, cox1-5′ and rrnL mtDNA sequences for available specimens of D. rectus and D. rufipes and merged them with data from GenBank. Results of the maximum likelihood analysis and Bayesian inference suggest a close relationship between D. rectus and Drilus cf. mertliki from Turkey, and a sister position of D. rufipes to a clade formed by the species from the Ionian Islands, Peloponnese, and Crete. Using the multigene barcoding approach including the above mentioned mitochondrial markers and the nuclear arginine kinase, we have been able to associate the different larval stages from Cyprus with the adult males of D. rufipes, and confirm the intraspecific variability in male body size and antennal coloration. Moreover, the low genetic difference in the cox1-3′ fragments indicates the close relationship between D. rectus populations from Cyprus and southern Turkey.

Synopsis and taxonomic revision of three genera in the snake tribe Sonorini

ABSTRACTDelimiting species is a crucial goal of integrative biology, and yet can be misled by homoplasy and high levels of morphological variation. The snake tribe Sonorini contains three genera that have long confounded taxonomists: Chilomeniscus, Chionactis and Sonora. Dynamic colour evolution in this group, including rampant geographic variation in colour and colour polymorphism, has led to a chaotic taxonomy. We used mitochondrial and high-throughput nuclear data (ddRADseq) and complete taxonomic sampling of each genus to reconstruct phylogenetic relationships and systematically revise the genus. Our research revealed that Sonora is paraphyletic with regards to Chilomeniscus and Chionactis and that at least one species (S. semiannulata) is paraphyletic with respect to at least one other recognized species. Additionally, we found substantial undescribed genetic diversity within multiple species which is incongruent with morphological variation in coloration. Accordingly, we proposed synonymizing Chionactis and Chilomeniscus with Sonora, which has taxonomic priority over both genera. As we found genetic evidence that supported some of the historically delimited diversity within multiple taxa, we revised species-level taxonomy accordingly. This new taxonomy recognizes a revised genus of Sonora that contains 15 species of diminutive and often brightly coloured snakes that are distributed from central Mexico to north-western USA.http://www.zoobank.org/urn:lsid:zoobank.org:pub:45A553D8-6435-4E0A-84ED-DF31E2CCD872

Age variation in the body coloration of the orb-weaver spider Alpaida tuonabo and its implications on foraging

Spiders show a repertoire of strategies to increase their foraging success. In particular, some orb-weaver spiders use attractive body colorations to lure prey. Interestingly, coloration varies with age in many species, which may result in ontogenetic variation of foraging success. By using field observations, laboratory experiments and spectrophotometric analysis, we investigated whether pale juveniles and bright adults of the orb-weaver Alpaida tuonabo use different foraging strategies due to ontogenetic variation in coloration. Field observations revealed that foraging success of juveniles and adults was influenced by web properties. However, foraging success increased with body size only in adults, supporting the idea that larger individuals produce a stronger visual signal for prey. The attractiveness of the adult coloration for prey was confirmed in the laboratory with frame-web-choice experiments, in which webs bearing a spider intercepted more bees than empty webs. Our spectrophotometric analysis suggests that the yellow coloration may produce the deceiving signal for prey. Moreover, we identified potential alternative foraging strategies: cryptic juveniles at higher heights and ‘attractive’ adults at lower heights. This study reveals how ontogenetic colour variation may favour the use of alternative foraging strategies in orb-weaver spiders and reduces intraspecific competition.

Phenotypic divergence despite low genetic differentiation in house sparrow populations

Studying patterns of phenotypic variation among populations can shed light on the drivers of evolutionary processes. The house sparrow (Passer domesticus) is one of the world’s most ubiquitous bird species, as well as a successful invader. We investigated phenotypic variation in house sparrow populations across a climatic gradient and in relation to a possible scenario of an invasion. We measured variation in morphological, coloration, and behavioral traits (exploratory behavior and neophobia) and compared it to the neutral genetic variation. We found that sparrows were larger and darker in northern latitudes, in accordance with Bergmann’s and Gloger’s biogeographic rules. Morphology and behavior mostly differed between the southernmost populations and the other regions, supporting the possibility of an invasion. Genetic differentiation was low and diversity levels were similar across populations, indicating high gene flow. Nevertheless, the southernmost and northern populations differed genetically to some extent. Furthermore, genetic differentiation (FST) was lower in comparison to phenotypic variation (PST), indicating that the phenotypic variation is shaped by directional selection or by phenotypic plasticity. This study expands our knowledge on evolutionary mechanisms and biological invasions.