Swallowtails, Papilionidae, are among the most conspicuous of
American Butterflies, due to their large size and conspicuous colouration. The
group has been extensively studied by taxonomists and evolutionary biologists,
revealing a complex biological history, with widespread mimicry leading to a large
number of cryptic species (species which resemble one-another closely, making
it hard for even specialists to tell them apart) and many species that have
apparently arisen through hybridization. However within the group the Tiger
Swallowtails, Pterourus spp., have
been the most extensively studied, with the related Giant Swallowtails, Heraclides spp., being relatively less
well known.
In a paper published in the journal ZooKeys on 23 December 2014, Kojiro Shiraiwa
of San Diego in California, Qian Cong of the Departments of Biophysics and
Biochemistry at the University of Texas Southwestern Medical Center and Nick Grishin
of the Howard Hughes Medical Institute and the Departments of Biophysics and
Biochemistry at the University of Texas Southwestern Medical Center, describe a
new species of Giant Swallowtail Butterfly from the southwest United States,
Mexico and Central America.
The new species is named Heraclides rumiko,
in honour of the wife of Kojiro Shiraiwa. The species is not described from any
newly discovered populations, but rather the realization that the widespread Heraclides cresphontes, which is known
from Canada to Panama, is in fact a complex of (at least) two closely related
cryptic species.
Heraclide srumiko type specimens: 7–8 holotype ♂ 9–10 paratype ♀.
Dorsal/ventral surfaces are in odd/even-numbered figures. Labels areshown
between the images of the same specimen, exuvia and head capsules in a gelatin
capsule are below,and 3-fold magnified segment of head, neck and thorax is on
the left. All images are to scale (includinglabels), except the magnified
insets. Shiraiwa et al. (2014).
The discovery came about following an examination of specimens from
California and Indiana, which revealed differences in the patterns between the
two populations. This was followed by an examination of DNA from specimens from
the northeastern United States and Costa Rica, which revealed a 3% difference
in genetic structure. This is not in itself enough to justify the erection of a
new species, particularly in widespread species where genetic patterns are
likely to vary over distance, however it did provoke a wider study in which 200
specimens from across the range of the species were examined, revealing two
distinct population groups, separated by a genetic distance of 3%, but with
very little difference within populations. Notably in parts of Texas both
species were found living alongside one-another, suggesting that these are true
species.
Facies differences between Heraclides rumiko (left, r) Heraclides cresphontes
(right, c) indicated by red trianglesand lines. These differences are as
follows. (1) Dark spot on forewing: (r) almost always large; (c) variable,but
often weak and sometimes absent (2) Forewing margin: (r) often straight with smaller
or absentmarginal spots; (c) strongly scalloped with yellow marginal spots at
dips between veins (3) Forewing submarginalyellow spots: (r) smaller rarely
more than three; (c) frequently larger, more than three (4) Thoraxwith: (r)
yellow line running from head through patagia to tegulae; (c) spots instead of
the line, or just fewyellow scales. (5) Abdomen: (r) usually with a fainter
dark band; (c) often with solid dark band (6) Inneredge of black discal band on
ventral hindwing: (r) mostly straight; (c) usually curved (7) Tail: (r)
mostlynarrow and relatively longer; (c) typically rounder and wide, shorter. Heraclides rumikois usually smaller than Heraclides cresphontes, despite being a
southern taxon. Due to significant seasonal and individual variation, noneof
these characters is fully reliable and exceptions exist. The head-neck-thorax
line vs. spots might be the strongest single character. A combination of
characters should be used for reliable identification. Many specimens in
central Texas exhibit intermediate characters, a typical character combinations,
and possible hybrids can be found. Shiraiwa et
al. (2014).
The original species Heraclides cresphontes
is now thought to be found in southeast Canada, and the north and west of the
United States, while the new species is found in Texas, New Mexico, Arizona,
California and Colorado, plus across Mexico and in El Salvador, Honduras, Costa
Rica and Panama, though it is possible that other cryptic species are hidden
within these distributions.
Localities of Heraclides cresphontes and
Heraclides rumiko specimens with available
DNA barcode information. Colour of circles corresponds to species: Heraclides cresphontes - blue (based on
112 DNA COI barcode sequences, 103 obtained in this work); Heraclides rumiko - red (based on 183 barcodes, 146 obtained in
this work), split red/blue circles mark localities where both Heraclides cresphontes and Heraclides rumiko were recorded.
Type localities for taxa with available names are indicated with a corresponding
name followed by “TL”. Papilio cresphontes
var. maxwelli & Papilio cresphontes pennsylvanicus are
treated as junior subjective synonyms of Heraclides cresphontes.
Countries and states (for USA andMexico) with records are labeled. Shiraiwa et al. (2014).
The eggs of Heraclides rumiko
were laid singularly on young leaves of trees and shrubs from the family Rutaceae
in California and Texas, the only places where the life-cycle has been observed
to date. Host plants included Zanthoxylum fagara,
Ptelea trifoliata, Amyris texana, Ruta graveolens, Citrus
spp. and Geijera parviflora, and the
species probably utilizes other plants that have not been observed. The species
is particularly numerous in urban areas where widespread ornamental citruses
are planted. The eggs are 1.1–1.6 mm in diameter, round and have a granular
surface. They are yellowish when laid, but turn orange as they mature.
Eggs of Heraclides rumiko. Shiraiwa et al. (2014).
The eggs hatch 7-10 days after being laid, the larva eating the egg
after hatching. The first instar (an instar is a stage in the life of an
Insect, separated from other instars by moults) is 3-5 mm long, hairy, glossy
and mottled brown, generally resembling a Bird dropping. The second instar is
5-11 mm long, the third 11-16 mm, the fourth 16-30 mm, the fifth instar 30-50
mm. The fifth instar is matt rather than glossy in appearance, and is followed
by pupation. Under ideal conditions the caterpillar can progress from hatching
to pupation in about nine days.
Fifth instar caterpillars of Heraclides rumiko. Shiraiwa et
al. (2014).
While the caterpillars of Heraclides rumiko
are primarily protected by camouflage, resembling a Bird dropping, they also
have a pair of eyespots on their meta-thoraxes, which can be revealed suddenly
by raising the head and inflating the thorax, a defensive strategy employed
when the caterpillar is startled.
Defensive posture of a caterpillar of Heraclides rumiko. Shiraiwa et al. (2014).
Towards the end of its fifth instar the caterpillar changes colour,
becoming paler and more uniform. This apparently improves the camoflage as it
leaves the leafy parts of the plant and travels on woody branches, looking for
a suitable place to pupate. The pupae are 26-36 mm in length, and mottled
greyish or dark brown, mimicking the colour of the branch on which they rest to
some extent (i.e. pupae on greenish branches are greener, on dark-coloured
branches are darker, etc.). Adults can emerge in one to two weeks, but the
pupae can also act as the overwintering stage, going into diapause
(hybernation) for several months.
Pupae of Heraclides rumiko
on different coloured stems. Shiraiwa et al.
(2014).
Adults of Heraclides rumiko
are present throughout most of the year, being absent only in the coldest
months. In southern Texas they are seen on the wing from April till September,
going through emergence peaks every 1.5 months, though this can be affected by
the severity of the winter or variations in rainfall. In southern California
the adults are present from February till mid November, being most abundant in
August and September.
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