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Imperfect male mimicry in blue female Polyommatus icarus butterflies

Aliwi, Zainab (2021) BIOY01 20211
Degree Projects in Biology
Abstract
Natural selection and genetic drift are relentlessly removing variation in natural populations. Yet, many species show polymorphism, with multiple phenotypes coexisting in the same populations, and these species serve as important model systems for studies aimed at understanding what evolutionary forces that maintain variation in natural populations. For example, different morphs can be favored in different environments or stages in a life cycle. Alternatively, natural selection can act to maintain polymorphism through negative frequency-dependent selection, if rare morphs are favored over more common morphs. Females of the butterfly Polyommatus icarus are polymorphic, and vary from having completely brown dorsal wing surfaces to being... (More)
Natural selection and genetic drift are relentlessly removing variation in natural populations. Yet, many species show polymorphism, with multiple phenotypes coexisting in the same populations, and these species serve as important model systems for studies aimed at understanding what evolutionary forces that maintain variation in natural populations. For example, different morphs can be favored in different environments or stages in a life cycle. Alternatively, natural selection can act to maintain polymorphism through negative frequency-dependent selection, if rare morphs are favored over more common morphs. Females of the butterfly Polyommatus icarus are polymorphic, and vary from having completely brown dorsal wing surfaces to being almost fully blue and male-like in appearance. For this species, the underlying reason for the polymorphism, and its putatively adaptive value, is yet to be discovered. In this Bachelor’s thesis, I provide a first test of the hypothesis that the blue female morph is mimicking the appearance of males also in other traits than color, which would suggest that one hypothesis explaining the polymorphism could be that male-like females are benefitted by avoiding unwanted male attention under certain circumstances. I tested this hypothesis by photographing butterfly individuals of three different groups (blue females, brown females and males) from the Lund University’s Biological museum collection. Results show that blue females were significantly larger (body length/wing length) than brown females, but still smaller than males, and that the blue females showed intermediate wing shape to brown females and males. Thus, blue P. icarus females are not perfect male-mimics, but that they differ in size and shape from brown females in the predicted direction. However, it is not clear to what extent the optimal phenotype of a male-mimicking female should be to perfectly match the phenotype of a male, because the female and male life-histories are largely different. Hence, it is possible that a too male-like female would suffer other fitness costs involved in e.g. sexual selection or egg-laying. Therefore, I cannot reject the hypothesis that blue females are indeed an example of a male-mimicking morph. Further studies, focusing on observing behavior of blue females, along with population comparisons between the morphs and male mating choice in lab conditions are thus warranted. (Less)
Popular Abstract (Swedish)
Denna studie utforskar varför olika fjärilshonor av arten puktörneblåvinge (Polyommatus icarus) är bruna, medan andra har blå vingar. Hos P. icarus har hanarna blå vingar medan honorna i varierande grad är bruna eller blå på vingarna, och olika populationer i Sverige skiljer sig åt i om de domineras av bruna eller blå honor. Att ha blå vingar skulle kunna kan vara en egenskap som hjälper blå honor att undvika trakasserier från hanar, om det är så att dessa honor undgår ovälkommen uppvaktning genom att likna hanar. I mitt examensarbete testar jag om blåa fjärilshonor liknar hanar också i andra egenskaper, såsom kroppsstorlek, vingstorlek och vingform. Om så är fallet så stödjer det hypotesen att polymorfismen i P. icarus upprätthålla av... (More)
Denna studie utforskar varför olika fjärilshonor av arten puktörneblåvinge (Polyommatus icarus) är bruna, medan andra har blå vingar. Hos P. icarus har hanarna blå vingar medan honorna i varierande grad är bruna eller blå på vingarna, och olika populationer i Sverige skiljer sig åt i om de domineras av bruna eller blå honor. Att ha blå vingar skulle kunna kan vara en egenskap som hjälper blå honor att undvika trakasserier från hanar, om det är så att dessa honor undgår ovälkommen uppvaktning genom att likna hanar. I mitt examensarbete testar jag om blåa fjärilshonor liknar hanar också i andra egenskaper, såsom kroppsstorlek, vingstorlek och vingform. Om så är fallet så stödjer det hypotesen att polymorfismen i P. icarus upprätthålla av sexuell selektion. Jag använde fjärilar från samlingarna i det Biologiska museet på Lunds universitet där ett antal blå och bruna honor, samt hanar som matchade honorna i tidsperiod och insamlingslandskap, valdes ut och fotograferades. Därefter analyserade jag alla individer morfometriskt för att ta reda på deras vingform, och jag mätte även vinglängden, kroppslängden och kroppsvidden. Mina resultat visade att hanar hade större kroppar och längre och mer spetsiga vingar än honorna. Intressant nog, så var blå honor större jämfört med bruna honor även om de var mindre än hanfjärilar. Dessutom visade det sig att blå honor tenderar att också ha något spetsigare vingar än de bruna honorna. Resultatet visar att sexuell selektion skulle kunna bidra till färgvariationen bland puktörneblåvinge honor, men det kan, såklart också finnas andra processer som påverkar färgpolymorfismen i arten. Denna studie visar mycket intressanta resultat som öppnar upp flera frågor och potentiella framtida studier till att förstå färgvariationen hos puktörneblåvingarna.

Handledare: Magne Friberg (Less)
Please use this url to cite or link to this publication:
author
Aliwi, Zainab
supervisor
organization
course
BIOY01 20211
year
type
M2 - Bachelor Degree
subject
language
English
id
9077989
date added to LUP
2022-04-01 11:11:18
date last changed
2022-04-01 11:11:18
@misc{9077989,
  abstract     = {{Natural selection and genetic drift are relentlessly removing variation in natural populations. Yet, many species show polymorphism, with multiple phenotypes coexisting in the same populations, and these species serve as important model systems for studies aimed at understanding what evolutionary forces that maintain variation in natural populations. For example, different morphs can be favored in different environments or stages in a life cycle. Alternatively, natural selection can act to maintain polymorphism through negative frequency-dependent selection, if rare morphs are favored over more common morphs. Females of the butterfly Polyommatus icarus are polymorphic, and vary from having completely brown dorsal wing surfaces to being almost fully blue and male-like in appearance. For this species, the underlying reason for the polymorphism, and its putatively adaptive value, is yet to be discovered. In this Bachelor’s thesis, I provide a first test of the hypothesis that the blue female morph is mimicking the appearance of males also in other traits than color, which would suggest that one hypothesis explaining the polymorphism could be that male-like females are benefitted by avoiding unwanted male attention under certain circumstances. I tested this hypothesis by photographing butterfly individuals of three different groups (blue females, brown females and males) from the Lund University’s Biological museum collection. Results show that blue females were significantly larger (body length/wing length) than brown females, but still smaller than males, and that the blue females showed intermediate wing shape to brown females and males. Thus, blue P. icarus females are not perfect male-mimics, but that they differ in size and shape from brown females in the predicted direction. However, it is not clear to what extent the optimal phenotype of a male-mimicking female should be to perfectly match the phenotype of a male, because the female and male life-histories are largely different. Hence, it is possible that a too male-like female would suffer other fitness costs involved in e.g. sexual selection or egg-laying. Therefore, I cannot reject the hypothesis that blue females are indeed an example of a male-mimicking morph. Further studies, focusing on observing behavior of blue females, along with population comparisons between the morphs and male mating choice in lab conditions are thus warranted.}},
  author       = {{Aliwi, Zainab}},
  language     = {{eng}},
  note         = {{Student Paper}},
  title        = {{Imperfect male mimicry in blue female Polyommatus icarus butterflies}},
  year         = {{2021}},
}