Danaus chrysippus

The plain tiger's larval host plants are from several families, most importantly Asclepiadoideae (Apocynaceae):[10]

• Asclepias – milkweeds (recorded on A. cancellata, A. coarctata, A. curassavica, A. fulva, A. kaessneri, A. lineolata, A. physocarpa, A. reflexa, A. scabrifolia, A. semilunata, A. stenophylla, A. swynnertonii, A.syriaca)
• Aspidoglossum interruptum
• Calotropis – mudar (recorded on C. gigantea, C. procera)
• Caralluma burchardii (recorded from Canary Islands/Spain)
• Ceropegia dichotoma (recorded from Canary Islands/Spain)
• Cryptolepis buchananii
• Cynanchum (recorded on C. abyssinicum, C. acutum, C. altiscandens, C. amplexicaule, C. carnosum, C. floribundum, C. sublanceolatum)
• Gomphocarpus fruticosus
• Kanahia laniflora
• Leichardtia australis
• Leptadenia hastata
• Marsdenia leichhardtiana
• Metaplexis japonica
• Orbea variegata (recorded from Canary Islands/Spain)
• Oxystelma pulchellum
• Pentatropis (recorded on P. atropurpurea, P. quinquepartita)
• Pergularia daemia
• Periploca linearifolia
• Pleurostelma cernuum
• Secamone (recorded on S. afzelii, S. parvifolia, S. platystigma
• Stapelia gigantea
• Stathmostelma (recorded on S. gigantiflorum, S. pedunculatum)
• Tylophora (recorded on T. stenoloba, T. sylvatica)

Host plants from other families include Dyerophytum indicum (Plumbaginaceae), Ficus (Moraceae; recorded on F. laevis, F. racemosa), Ipomoea (Convolvulaceae; recorded on I. alba, I. bona-nox), Lepisanthes rubiginosa (Sapindaceae) as well as some Euphorbiaceae, Malvaceae, Poaceae, Rosaceae and Scrophulariaceae.

Adult plain tiger butterflies obtain nectar from various flowering plants. The particular plants available vary depending on the geographic range of the butterfly population and the season, as certain plants do not flower throughout the entire year.[11][12]

• Catheranthus roseus
• Lantana camara
• Vernonia cinera
• Tridax procumbens
• Asystasia gangetica
• Antigonon leptopus, January through April and August through December
• Tecoma stans, May through December[11]

• Goodenia maidenian
• Eucalyptus conglobata
• E. oleosa
• Ptilotis obovata
• Asclepias
• Lantana
• Leucopogon
• Daviesia

In addition to nectar, adult plain tigers obtain pyrrolizidine alkaloids from the dead stems of different plant types. In Australia, the following plants have been identified as sources of pyrrolizidine alkaloids for D. chrysippus:[12]

• Parsonsia eucalyptophylla
• P. straminea
• Echium plantogineum
• Senecio pterophorus
• Heliotropium amplexicaule

Females lay eggs singly on the underside of the leaves of a larval food plant.[11] The eggs are most often laid close to the ground.

The egg of the plain tiger is about 1.7 mm (0.067 in) long and 0.5 mm (0.020 in) across. When first laid it is white, but gradually turns brown over time. The egg is ridged and dome-shaped. Depending on temperature, the egg is typically hatched in 3–5 days.[11]

• 
  Egg at Tamil Nadu, India
• 
  At Mananpur, Mumbai, Maharashtra

The larvae of D. chrysippus proceeds through five instar stages. The first instar is about 4 mm (0.16 in) long, and its body is white while the head is black. The second instar is about 8 mm (0.31 in) long, and its body is primarily gray with yellow and black horizontal stripes. This coloration remains for the final three instar stages. The third instar is about 14 mm (0.55 in) long, the fourth about 25 mm (0.98 in) long, and the fifth about 36 mm (1.4 in) long. Depending on temperature, the larval stage can last from 12–20 days.[11]

• 
  Larva eating its own eggshell
• 
  Caterpillar making "moat" to feed during the first instar
• 
  Second instar
• 
  Mature caterpillar
• 
  Older caterpillar

Before pupation, the caterpillar will become motionless and cease feeding. Its color shifts slightly from gray to brown, and it may lose a small amount of body mass. The prepupal stage lasts 1–3 days depending on temperature. The pupal stage lasts 9–15 days depending on temperature, and the pupa changes color over this period from a pale green to dark brown. Pupae are about 17 mm (0.67 in) tall and 8 mm (0.31 in) wide.[11]

• 
  Pupa
• 
  Fresh pupa at Bandra Kurla Complex, Mumbai
• 
  Pink pupa due to pupation among inanimate objects

Male and female D. chrysippus butterflies look very similar and are also similar in size. Adult butterflies typically have a wingspan of 75 mm (3.0 in). The bodies of adult plain tigers are about 23 mm (0.91 in) long, and their antennae are about 12 mm (0.47 in) long. Depending on temperature, males live about 10–15 days and females live about 7–12 days.[11]

• 
  A newly emerged plain tiger female in captivity
• 
  Male D. c. chrysippus, recently emerged from chrysalis
• 
  Form alcippoides in Mysore, Karnataka, India
• 
  Mud-puddling
• 
  Resting with its wings closed
• 
  Basking

Most predators of the early developmental stages of D. chrysippus are arthropods. Such potential predators include various kinds of spiders, assassin bugs, cockroaches, ladybugs, ants, and mantises. The caterpillars will even cannibalize each other. Egg and larval mortality is often high; as many as 84% of eggs may be lost to predation and up to 97% of larvae can be lost by the fifth instar, although most larval deaths occur during the third instar.[13]

The most common predator of adult plain tigers are birds. In eastern Africa, the most common predator is the fiscal shrike L. c. humeralis.[14]

There are several organisms which parasitize the larvae of D. chrysippus. The fly S. flavohalterata of the Family Tachinidae is responsible for small amounts of parasitization in D. chrysippus populations. It is unclear whether the fly oviposits on the eggs of D. chrysippus or whether the fly oviposits on leaves which are then consumed by D. chrysippus larvae. S. flavohalterata does not kill the larvae, and development is normal until the pupal stage, when larvae dies and the parasite emerges from the pupa instead. A. chrysippi, a parasitic wasp of the family Braconidae, oviposits on larvae early in their development and then kills them in the later stages. As many as fifty wasps may emerge from one large caterpillar, and they then pupate on the deceased host. Parasitic wasps of the genus Charops also infest plain tiger populations, likely during the egg or first instar stage, and then kill the larvae in a later instar stage.[15]

Sturmia convergens is also a parasitoid of D. chrysippus.[16]

The plain tiger is infected by a male-killing bacterium called Spiroplasma. Male-killing bacteria are transmitted vertically, from mother to offspring. Female plain tigers infected with Spiroplasma will produce all-female broods, because the bacteria kills infected male offspring during either their embryonic or first larval instar stage. Although male-killing bacteria are uncommon in species which lay eggs singly, experimentally treating infected females with antibiotics restored an even sex ratio to their subsequent broods, thus indicating that it is indeed Spiroplasma which is responsible for all-female broods in D. chrysippus. However, the prevalence of this bacteria in the plain tiger seems to be restricted to east African populations.[17]

Batesian mimics are palatable species which mimic unpalatable species, and D. chrysippus is a model for several Batesian mimics, including H. misippus, P. poggei, M. marshalli, and P. dardanus in east Africa. Batesian mimicry is only effective so long as the mimic is less common than the model, or predators will learn that the mimics are in fact edible and then attempt to eat the similar-looking unpalatable butterflies.[19]

Müllerian mimicry occurs when multiple species which are all unpalatable evolve to resemble one another. In this case, the relative abundance of each species does not have a deleterious effect on any others, because a predator which eats any one of them will be deterred from eating any similar-looking butterflies. In Uganda, D. chrysippus has several Müllerian mimics, including A. encedon and A. encedana.[19]

Despite the external similarity, the common tiger (D. genutia) is not closely related to the plain tiger. Three subspecies were considered valid in a 2005 review:[20]

• Danaus chrysippus chrysippus

Asia, Mediterranean region, northern tropical Africa

• Danaus chrysippus alcippus (Cramer, 1777) - formerly D. c. aegyptius

From the Cape Verde Islands through tropical Africa to Yemen and Oman. Browner with broader white forewing spots.

• Danaus chrysippus orientis (Aurivillius, 1909) - formerly D. c. liboria

Saint Helena, southern tropical Africa to South Africa, Madagascar, Comoros, Seychelles and Mascarenes. Small white forewing spots.

D. c. alcippus is well on the way of becoming a distinct species.[20]

On the other hand, the former subspecies petilia is nowadays recognized as a good species, the lesser wanderer (D. petilia). More enigmatic[20] is the status of the former subspecies (or forms) dorippus and bataviana. These are tentatively also regarded as a distinct species, the dorippus tiger (D. dorippus).

However, it appears (from analysis of mtDNA sequences, which are only inherited from the mother) that the dorippus tiger is the product of an ancient lineage of Danaus hybridizing with plain tiger females.[20] As the plain tiger is known to be parasitized at least occasionally by Spiroplasma bacteria which selectively kill off male hosts,[21] a subsequent scarcity of plain tiger males might have led to this hybridization and the evolution of the dorippus tiger. From the colour pattern of this species, it can be assumed that the ancient lineage had no black apex on the forewings, as this characteristic is still absent in D. dorippus.

The presumed subspecies cratippus most likely belongs to either the lesser wanderer or the dorippus tiger, but confirmation of its taxonomic status requires more research. In any case, these three species are closely related; their closest relatives, in turn, might be the soldier (D. eresimus) and queen (D. gilippus) butterflies.[20]

Several local forms have been described from Asia:

• Danaus chrysippus chrysippus f. alcippoides

The upper hindwing is more or less very white; about half of the individuals have a second submarginal spot in the forewing. Occasionally found in South-East Asia, very rarely in India.

• Danaus chrysippus chrysippus f. gelderi

The upper hindwing has white markings. Occasionally found on Sulawesi.

• Danaus chrysippus chrysippus f. bowringi

The upper hindwing has a subapical band composed of somewhat larger spots, and an additional forewing spot as in f. alcippoides is always present. Found throughout the eastern parts of this subspecies' range.

On the other hand, the plethora of named taxa from Africa are apparently F₁ or F₂ hybrids between the plain tiger subspecies (the contact zone of which is in the general area of Uganda) and/or D. dorippus:

• Danaus chrysippus × alcippoides

is D. c. chrysippus × D. c. alcippus

• Danaus × transiens, Danaus × klugii, Danaus × albinus and Danaus × semialbinus

are D. c. alcippus × D. dorippus

When D. chrysippus was analyzed via a sample from Kampala, Uganda, it was found that the population was undergoing a significant level of evolutionary change. Three loci were examined, and genotypic frequency differences found at two of the three suggested that opposing selective forces, likely pertaining to Mullerian and Batesian mimicry, acting on males and females is contributing to a balanced polymorphism.[19]