Melanism Flashcards
What is melanism?
A melanic variant is one in which significant amounts of black replace other colours
Common practice is to include variants in which chow a darkening of ground colour or pattern
Not always evolving to be darker, may evolve to be lighter (Homo sapiens for example)
What are the 3 major types of melanism?
Non-industrial melanism
Industrial melanism
Melanism in warningly coloured species
What are the types of non-industrial melanism?
thermal rural/background choice northern latitude western coastline pluvial fire-resistant tree assoication ancient conifer anti-search image
What are the types of industrial melanism?
Fully industrial polymorphism (only since industrial revolution)
Partial industrual melanic polymorphism (prior to IR but increased since)
Polygenic industrial melanism (average ground colour has darkened gradually in industrial areas)
What types of melanism are there in warningly coloured species?
Recessive
Mimetic
Sexual
What is thermal melanism? Give 3 examples
Black absorbs more heat, may be significant advantage at high northern and southern latitudes
Example - Polar bear (Ursus maritimus) (black skin)
Example 2 - Clouded yellow butterfly (Colias spp.) - Migratory species so show no local adaptation, have a melanic form though to help absorb heat (C. tyche N.Sweden)
Example 3 - Silver washed Fritillary (Argynnis paphia) - sex limited melanism, females less attractive to males but able to forage longer in cooler habitats and find violets to lay eggs upon
What is rural/background choice melanism? Give an example
Melanism assumed to evolve in response to heterogeneity (diversity) in background colour of resting sites
Example - Pine beauty moths (Panolis flammea) 3 variants - typical rests on pine trunks, heterozygous form rests on branches and foliate twigs homozygous (Melanic) form rests on foliate twigs and needles
Pine beauty melanism evolved due to vision using predators
What is Northern latitude melanism?
Melanism in Northern regions - multiple factors may play a part - thermal, background choice (peatlands etc) and the length of days/ angle of the sun
Darker forms may be more camouflaged in Northern regions
Example - Ingrained Clay Moth (Diarsia mendica) - lighter colour southern becomes gradually darker the further North it is found, not only 2 forms but a gradual melanism
What is Western Coastline Melanism?
Numerous moths show darkening near and along western coasts
Selective factor unclear - may be influenced by resting factors (wet rocks), greater tolerance to salt (unsupported), thermal in clouds, greater resistance to abrasion by wind-borne particles (evidenced in bird feathers desert beetles, in which melanin may increase toughness)
Example - Yellow Shell (Camptogramma bilineata)
What is pluvial melanism?
Melanisms associated with forests high in rainfall (South island, New Zealand) (Himalayas) etc.
May be camouflage may be thermal, unknown
What is melanism associated with fire resistant trees?
Resistant trees will be blackened by soot and so darker forms will have cryptic advantage
Associated with areas high in fires e.g Australia Eucalyptus trees
British example - Horse chestnut moth (Pachynemia hippocastarania)
What is ancient conifer melanism?
Appearance in flight may be important
Example - mottled beauty (Alcis repandata) has melanic form in Caledonian pine forests. At first appear more conspicuous but when in flight during daylight hours (disturbed by ants very often) are less visible in the darkness of the forest canopy
What is anti-search image melanism?
Predator avoidance through crypsis
Example - Peppered moth (Biston betularia)
Example 2 - Mottled Umber (Erannis defoliaria)
Give an example of industrial melanim
Peppered moth (Biston betularia) - Signel gene controls difference between natural and melanic morphs
- three morphs in Britain (white - typica, black - carbonaria, intermediate - insularia)
- Carbonaria morphs have better immunity to toxic chemicals put into environment by industrial pollution
- melanic forms shown decline with pollution controls (Majerus 1998)
Give an example of recessive melanism in warning colour species
5 spot burnet (Zygaena trifolii) - melanics appear as rare homozygous recessives but do not establish as polymorphisms in populations
- non-melanics brightly coloured aposematic
Additional Reading WCM - ladybirds
O’Donald and Majerus 1984
Adalia bipunctata - ladybird
- females prefer melanic variants
Example of mimetic melanism
Eastern Tiger Swallowtail - Papilio glaucus
- mimics pipevine swallowtail
Additional Reading Density - What insects exhibit DD melanism and why?
Cotter et al. 2004
- Locust, phasmids and lepidoptera
- May be down to increase immune resistance in melanic forms
- melanism may be secondary, increased phenoloxidase (key to melanism) also has important part in immune system
Additional Reading - locusts
Wilson et al., 2002
Schistocera gregaria - locusts
- melanic forms more resistant to entomopathogenic fungus than solitaria forms
Additional reading - African armyworm
Reeson et al., 1998
Spodoptera exempta - African armyworm
- Melanic forms more resistant than non-melanic
Additional Reading - Melanic IR crypsis
Kettlewell, 1955
Showed that dependent on habitat - polluted or non-polluted the subsequent morph would have a significant cryptic advantage when tested against bird predation
Additional Reading - ancient conifer
Kettlewell, 1958
Melanisms suited for camouflage in the air known as aerial crypsis
Additional Reading - Points on Ind. Mel
Kettlewell, 1961
- Industrial melanism is only found in cryptic species
- industrial melanism likely occurs in all industrial areas of the world with the exception of the tropics
- need for camouflage is outweighed by the disadvantage of melanic forms in great heat
- 780 spp. of Lepidoptera in Britain, 70-100 of which are undergoing melanism
Additional Reading - B.betularia (carboniferia) abundance
Kettlewell, 1961
- In 1848 the melanic form was first discovered in Manchester, although very rare
- 50 years later the melanic form comprised 95 percent of the population
Additional Reading - Industrial Melanism Immunity
Mikkola + Rantala 2009
- Industrial melanism may be due to increase in toxins, phenoloxidase build up during the larval stage results in a more melanic adult
