''Colias eurytheme'', the orange sulphur, also known as the alfalfa butterfly and in its
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
The ...
l stage as the alfalfa caterpillar, is a
butterfly
Butterflies are insects in the macrolepidopteran clade Rhopalocera from the Order (biology), order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The ...
of the
family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Pieridae
The Pieridae are a large family of butterflies with about 76 genera containing about 1,100 species, mostly from tropical Africa and tropical Asia with some varieties in the more northern regions of North America and Eurasia.DeVries P. J. in Le ...
, where it belongs to the lowland group of "
clouded yellows and sulphurs"
subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...
Coliadinae
Coliadinae, the sulphurs or yellows, are a subfamily of butterflies with about 300 described species.
There are 36 species in North America, where they range from Mexico to northern Canada. In most species, males are easily distinguished from ...
. It is found throughout North America from southern Canada to Mexico.
Other members of this lineage including the common or clouded sulphur (''
C. philodice'') and ''C. eriphyle'' and ''C. vitabunda'', which are often included in ''C. philodice'' as
subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
.
Hybridization runs rampant between these, making
phylogenetic
In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analyses exclusively utilizing one type of data (especially
mtDNA
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial DNA ...
sequences
In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called t ...
) unreliable. Therefore, little more can be said about its relationships, except that it is perhaps closer to ''C. (p.) eriphyle'' than generally assumed, strengthening the view that the latter should be considered a valid species.
[Wheat, Christopher W. & Watt, Ward B. (2008). A mitochondrial-DNA-based phylogeny for some evolutionary-genetic model species of Colias butterflies (Lepidoptera, Pieridae). ''Mol. Phylogenet. Evol.'' 47(3):893-902. doi:10.1016/j.ympev.2008.03.013 (HTML abstract, supplement available to subscribers)]
The orange sulphur's
caterpillar
Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sym ...
s feed off various species in the pea family (
) and are usually only found feeding at night. Occasionally this species multiplies to high numbers, and can become a serious
pest to
alfalfa
Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, and silage, as w ...
(''Medicago sativa'') crops. The parasitoid wasp, ''
Cotesia medicaginis'' can be used as a
biocontrol
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...
agent against the caterpillars.
Distribution
''C. eurytheme'' butterflies can be found from southern Mexico to almost all throughout North America. Historically, they were distributed primarily in the western
Nearctic
The Nearctic realm is one of the eight biogeographic realms constituting the Earth's land surface.
The Nearctic realm covers most of North America, including Greenland, Central Florida, and the highlands of Mexico. The parts of North America t ...
, but were displaced to the east by logging and alfalfa field planting.
Appearance
Wing pattern
Male ''C. eurytheme'' hindwings demonstrate an
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
reflectance pattern while female ''C. eurytheme'' hindwings demonstrate ultraviolet absorbing patterns. According to studies, these ultraviolet reflecting wing scales found in males also contain
pterin
Pterin is a heterocyclic compound composed of a pteridine ring system, with a "keto group" (a lactam) and an amino group on positions 4 and 2 respectively. It is structurally related to the parent bicyclic heterocycle called pteridine. Pterins, a ...
pigments that absorb wavelengths below 550 nm. Although this may seem paradoxical, the pterin pigments have been found to decrease the amount of diffuse ultraviolet reflectance that comes from the wing scales. By suppressing the diffuse ultraviolet reflectance, the directionality and spectral purity of the iridescence is heightened. In addition, the presence of the pterin pigments increases the signal's
chromaticity
Chromaticity is an objective specification of the quality of a color regardless of its luminance. Chromaticity consists of two independent parameters, often specified as hue (h) and colorfulness (s), where the latter is alternatively called ...
and potential signal content, suggesting that these pigments are responsible for amplifying the contrast between ultraviolet reflectance and background colors as a male's wings move during flight.
Further studies have found that the ultraviolet reflectance signal is brightest within a wing beat cycle when viewed from directly above the male. This supports the idea that male wing color should be able to be readily distinguished from that of females and the visual background that consists mostly of UV-absorbing vegetation.
Genetic inheritance
Studies have suggested that most of the
genes
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
controlling male courtship signals are inherited as a co-adapted gene complex on the
X-chromosome
The X chromosome is one of the two sex-determining chromosomes (allosomes) in many organisms, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and XO sex- ...
. The X-chromosome carries most of the genes controlling production of 13-methyl heptacosane, the main component of
pheromones
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
involved in sexual selection, and the ultraviolet wing reflectance pattern. Expression of the ultraviolet wing reflectance pattern found in male ''C. eurytheme'' is controlled by a recessive allele on the X-chromosome. This trait is
sex limited and not expressed in females of the same species.
Reproduction
Reproductive behavior
Unlike that of many other butterfly species, the
courtship
Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...
of ''C. eurytheme'' is very brief and does not involve many elaborate displays. Mature female butterflies participate in
mate selection
Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...
by utilizing a specific refusal posture that prevents any undesired mating with both
conspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
and non-conspecific males.
[Silberglied, Robert E., and Orley R. Taylor. (1978). Ultraviolet Reflection and Its Behavioral Role in the Courtship of the Sulfur Butterflies ''Colias eurytheme'' and ''C. philodice'' (Lepidoptera, Pieridae). ''Behavioral Ecology and Sociobiology'' 3(3):203-43.]
These butterflies exhibit a
polyandrous
Polyandry (; ) is a form of polygamy in which a woman takes two or more husbands at the same time. Polyandry is contrasted with polygyny, involving one male and two or more females. If a marriage involves a plural number of "husbands and wives" ...
mating system. Upon mating, male ''C. eurytheme'' donate a nutritious
spermatophore
A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...
to the female, which will erode over time as nutrients are extracted for
egg production
Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
and
somatic maintenance. Females have a
refractory period during which time they do not mate, but after they have depleted their spermatophore, they will search for another one and thus look for a new mate. In this mating system, females re-mate once every 4 to 6 days in summer, and mate a lifetime total of up to four times.
Sexual selection
Male ''C. eurytheme'' have a
visual cue (
ultraviolet reflectance) and an
olfactory cue (
pheromones
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
), both of which are suggested to be important in
mate choice
Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...
. Studies have suggested that pheromones may be more important in mediating female choice within a species, while ultraviolet reflectance may be more important in mediating female choice between species, such as between the very similar butterflies ''C. eurytheme'' and ''C. philodice''.
[Papke, Randi S., Darell J. Kemp, and Ronald L. Rutowski. (2007). Multimodal Signalling: Structural Ultraviolet Reflectance Predicts Male Mating Success Better than Pheromones in the Butterfly ''Colias eurytheme'' L. (Pieridae). ''Animal Behavior'' 73:47-54.] The pheromone, located on the
dorsal
Dorsal (from Latin ''dorsum'' ‘back’) may refer to:
* Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism
* Dorsal, positioned on top of an aircraft's fuselage
* Dorsal c ...
surface of the hindwing, consists of cuticular hydrocarbons ''n''-heptacosane (C27), 13-methylheptacosane (13-MeC27), and possibly ''n''-noncosane (C29). In addition, wing scales located on the dorsal wing surfaces in male ''C. eurytheme'' contain ridges with
lamella
Lamella (plural lamellae) means a small plate or flake in Latin, and in English may refer to:
Biology
* Lamella (mycology), a papery rib beneath a mushroom cap
* Lamella (botany)
* Lamella (surface anatomy), a plate-like structure in an animal
...
e that produce iridescent ultraviolet reflectance via thin-film interference.
[Rutowski, R.l, J. Macedonia, N. Morehouse, and L. Taylor-Taft. (2005). Pterin Pigments Amplify Iridescent Ultraviolet Signal in Males of the Orange Sulphur Butterfly, Colias Eurytheme. ''Proceedings of the Royal Society B: Biological Sciences'' 272(1578):2329-35.]
''C. eurytheme'' males rely on visual cues to locate and identify females. Instead of using chemical stimuli to find mates, males are attracted to the ultraviolet absorbing color of female hindwings. Studies have shown that males respond to paper dummies of the appropriate color and even attempt to mate with them. On the contrary, the ultraviolet reflection found on males strongly inhibits approaches from other males. This suggests that ultraviolet reflectance is also used by males as an inhibitory signal directed towards other males.
Unlike sexual selection in males, visible color differences among males do not play an important role in mate selection by females. Females preferentially mate with males whose wings reflect ultraviolet light.
Studies have suggested that this trait was the strongest and most informative predictor of male courtship success. This may be because it has the potential to be an honest indicator of male condition,
viability, and/or age.
Due to the widespread cultivation of the
alfalfa
Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, and silage, as w ...
, the host plant for ''C. eurytheme'' and ''C. philodice'', the species was able to expand their ranges across most of North America. These two species of sulphur butterflies have retained a large degree of genetic compatibility that allows them the produce viable and fertile offspring.
[Grula, John W., and Orley R. Taylor. (1980). The Effect of X-Chromosome Inheritance on Mate-Selection Behavior in the Sulfur Butterflies, ''Colias eurytheme'' and ''C. Philodice''. ''Evolution'' 34(4):688-95.] As a result of the recent
sympatry
In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
and possible
hybridization between these two species of sulphur butterflies, numerous studies have been conducted on
intraspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
and
interspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organi ...
mating.
[Taylor, Orley R., Jr. (1970). Random vs. Non-Random Mating in the Sulfur Butterflies, ''Colias eurytheme'' and ''Colias philodice'' (Lepidoptera: Pieridae). ''Evolution'' 26(3):344-56.] In terms of mating under natural conditions, the males do not discriminate between the species, but females maintain nearly complete
reproductive isolation
The mechanisms of reproductive isolation are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring ...
. Studies suggest that the females do so by looking for the ultraviolet reflectance pattern on the dorsal wing surface of ''C. eurytheme'' males.
Therefore, it was suggested that ''C. eurytheme'' and ''C. philodice'' do not randomly mate with each other. Instead, mating was found to be positively
assortive and mostly
conspecific
Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species.
Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
.
Sexual selection theory
Previous studies have suggested that males make a nutrient investment during copulation. This idea agrees with the sexual selection theory, which predicts that females would act in ways to maximize the nutrient material they receive and predicts that males would act in ways to maximize the return on their investments. Studies support this theory by showing that younger males (males with less wing wear) are more successful in courtship than older males, males accepted by females are significantly less variable in size than males rejected by females, persistence increases a male's chance of
copulating
Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...
up to a point, and the size of females accepted by males is less variable than that of rejected females. The amount of protein in a male's
spermatophore
A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...
is negatively correlated with age because it is more likely for older males to have mated previously. Females therefore prefer younger mates perhaps to secure large ejaculates, as smaller males and males that have mated previously produce smaller ejaculates.
The brightness of ultraviolet reflectance and pheromone descriptors, both important factors in
mate selection
Mate choice is one of the primary mechanisms under which evolution can occur. It is characterized by a "selective response by animals to particular stimuli" which can be observed as behavior.Bateson, Paul Patrick Gordon. "Mate Choice." Mate Choic ...
, are also negatively correlated with age. However, variation between these two traits (
visual
The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the ...
and olfactory) is mostly uncorrelated. Since ultraviolet brightness emerges as the best predictor of male mating success, female preferences for brighter males may also indicate its relation to a material benefit.
In addition, studies have shown a
longevity
The word " longevity" is sometimes used as a synonym for "life expectancy" in demography. However, the term ''longevity'' is sometimes meant to refer only to especially long-lived members of a population, whereas ''life expectancy'' is always d ...
difference between virgin and mated females, suggesting a cost to mating. It is hypothesized that there is a toxic side effect of the male
ejaculate
Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential component ...
. However, it is still unclear how this longevity cost influences the evolution of lifetime mating schedules. The supposed cost also does not affect the number of eggs a female lays in its lifetime.
[Kemp, Darell J., and Ronald L. Rutowski. (2004). A Survival Cost to Mating in a Polyandrous Butterfly, ''Colias eurytheme''. ''Oikos'' 105(1):65-70.]
Gallery
Male Orange Sulphur Megan McCarty18.jpg, Upperside of male
Orangesulphur.jpg, Underside pattern
Clouded and orange sulphur.jpg, Cloudless sulphur male (left) and orange sulphur male (right)
Albino Female Orange Sulphur, Megan McCarty57.jpg, Albino female laying an egg
References
External links
Northern Prairie Wildlife Research CenterOrange sulphur Butterflies of Canada
{{Taxonbar, from=Q1944775
eurytheme
Butterflies of North America
Butterflies described in 1852
Agricultural pest insects