Parasemia plantaginis

A two-year study of populations of P. plantaginis throughout the Alpine regions of Italy, Austria and Switzerland indicated a single whole population. Pairwise Fst values, AMOVA and COl results showed little to no differentiation between populations during the two sampling years of 2009 and 2010. This overall high genetic diversity and low differentiation between populations suggests much gene flow and high population density in P. plantaginis populations. Though this extreme gene flow would be thought to lead to fixation of a single morphological phenotype, the differential selective pressures experienced by various populations of the species likely leads to the maintenance of its widespread polymorphism.[6]

Though it may benefit caterpillars to intake more plant compounds that can help produce defensive chemicals (depending on the plant), this process can be costly and energy intensive for caterpillars. As polyphagous larvae, this process of detoxification and toxin sequestration can be especially costly if their physiology has to support detoxification processes for different types of plants and compounds. Investing more in detoxification as larvae results in lower reproductive output as adults.[8]

Lupine, a common host plant for Parasemia plantaginis

P. plantaginis are capital breeders, which means that they do not feed as adults, and thus the larval diet is incredibly important component in adult fitness.[8]

Wood tiger adult

Aposematism is common in many Lepidoptera species; it is an adaptive mechanism in which prey produce conspicuous warning signals. In the wood tiger moth, conspicuous coloration patterns communicate a poisonous, toxic, or otherwise unpalatable or unprofitable effect to predators. Typically, aposematic species experience strong selection favoring monomorphic populations. As a specific warning signal phenotype becomes more common in an environment, more and more predators learn to avoid individuals bearing such signals. In P. plantaginis, a distinct hindwing pattern of bands and splotches of white or yellow on black warns predators of its chemical defenses. Populations of P. plantaginis, are, however, almost always polymorphic, with males exhibiting varying degrees of either yellow or white melanized banding patterns. Yellow morphs show stronger warning signals and experience lower predation rates and longer predator-hesitation. White morphs are preyed upon significantly more by birds than yellow morphs, but persist as a frequent phenotype in many populations, suggesting there are other selection pressures favoring white morphs.[1]

A possible explanation for the persistence of white morphs despite their higher predation rates is selection heterogeneity; in other words, due to the wide geographic distribution of the wood tiger moth, different populations experience vastly different selective pressures. One consideration is immune variation. A 2013 study demonstrated that male yellow and white larvae saw different survival rates when reared in aggregations; yellow male survived to pupate better in aggregations than white males did, which may reflect different immune investments. In aggregations, white males saw better ability to encapsulate pathogens, while yellow males had higher hemolymph (equivalent to insect 'blood') lytic activity (virus attacking). Thus the two types of wood tiger moth may be maintained in populations because they have different immune investments. This is advantageous in thriving in heterogeneous environments with differential risk factors for immune challenges.[14]

Though the aposematic signal of a wood tiger moth is highly conspicuous against vegetative scenery, its patterning is less easy to detect when it drops to the ground. Disruptive coloration is when a pattern creates an illusion that makes discerning the edges of an object difficult. It essentially destroys the appearance of any outline the object may have. Though the idea of disruptive coloration, which is clearly a camouflage technique, seems counterintuitive in aposematism, it has been demonstrated that the same coloration pattern on a moth can act as either a warning signal or a camouflage depending on the backdrop. Wood tiger moths exhibit a behavior where they essentially 'feign death' by dropping suddenly on to the ground in the presence of a predator and taking on a specific, rigid posture with folded legs. Once on the ground, the moths are much more difficult to detect. This suggests that the hindwing pattern of the wood tiger moth can switch instantly from conspicuous to camouflage, which has obvious adaptive advantages.[15]

A 2017 study highlighted the ability of P. plantaginis to secrete two different chemical fluids as defense mechanisms in response to two different types of predators. Along with its colorful, conspicuous hindwing color patterns, these moths secrete defense fluids from their abdomen and thoracic glands. The abdominal fluids deterred ants and not birds, while thoracic fluids deterred birds but not ants, suggesting that a single species is capable of producing target-specific chemical defense fluids in response to predation threats.[12]

• Parasemia plantaginis plantaginis
• Parasemia plantaginis araitensis Matsumura, 1929
• Parasemia plantaginis carbonelli de Freina, 1993
• Parasemia plantaginis caspica Daniel, 1939
• Parasemia plantaginis caucasica (Ménétriès, 1832)
• Parasemia plantaginis hesselbarthi de Freina, 1981
• Parasemia plantaginis interrupta Draudt, 1931
• Parasemia plantaginis kunashirica Bryk, 1942
• Parasemia plantaginis macromera (Butler, 1881)
• Parasemia plantaginis melanissima Inoue, 1976
• Parasemia plantaginis melanomera (Butler, 1881)
• Parasemia plantaginis nycticans (Ménétriès, 1859)
• Parasemia plantaginis petrosa (Walker, 1855)
• Parasemia plantaginis sachalinensis Matsumura, 1930
• Parasemia plantaginis sifanica (Grum-Grshimailo, 1891)

Warning signals show no phenotypic plasticity in adult wood tiger moths. The shapes and patterning of adult warning signals are entirely determined during resource allocation of the larval stage. Once an adult metamorphoses, their warning signal phenotype can no longer change.[16]

Flight behavior in populations of P. plantaginis vary between color morphs and are under frequency dependent selection. In outdoor cage experiments of populations with various frequencies of yellow and white male morphs, researches found that white morphs were significantly more active and had longer periods of sustained activity than yellow morphs across all treatment groups. In groups with higher frequencies of yellow morphs, overall flying activity for both morphs was considerably lower. The data suggest that white male morphs invest less in producing costly warning signals and thus have more energy to invest in flight for both avoiding predation and finding mates. Yellow males, which in previous studies have been shown to be less sexually favored by females than whites, tend to be most active at peak female-calling periods.[19]

Wood tiger moths have a limited amount of resources to allocate to different life history traits and adaptive strategies; thermoregulation is an important part of their physiology, especially in the cooler climates of North America and Eurasia. As latitude increases, populations of P. plantaginis show higher melanization (conversion of resources into melanin). This melanin confers thermoregulatory advantages by increasing a male moth's ability to absorb radiation. This increased melanization comes at a cost, however, as it is costly to produce, and thus male moths with more melanization suffer increased predation as their warning signals are weaker. Thus it is thought that due to the various climactic conditions of populations of wood tiger moth, there are different costs and benefits to produces more melanin, which serves to maintain the global diversity of warning signals that we see throughout the species. In both yellow and white male phenotypes, individuals with more melanin had a heightened ability to trap heat but an increased predation rate due to its weaker and less effective signal.[20]