The fascinating complexities of Monarch butterfly mimicry and bacteria that only kills males.

Maajabu ya vipepeo vinavyofanana na aina ya kipepeo ‘African Monarch’ na bakteria inayoua dume tu.

The African Monarch butterfly is a famous example of a butterfly whose colors show up across a variety of other butterflies. The African Monarch caterpillars feed on milkweed and instead of the milk-weed’s chemicals killing the caterpillars, they accumulate the toxins and taste bad to their predators. There are some species of butterfly that look like the African Monarch, like the  females of the Mocker Swallow Tail and Common Diadem who don’t taste bad, but there are also other butterflies that also taste bad especially two Acrea species (Acrea encedon & A. encedana). The way we explain this from an evolutionary point of view is that individuals that look like a species that tastes bad have a greater chance of surviving if they come across a predator that has had a bad experience with a bad tasting individual. As a result, their chance of reproducing successfully increases. The more bad tasting individuals are out there, the quicker predators will be educated. Each of the three toxic species has different forms which to an extent defeats the purpose of looking like each other especially in areas where there is hybridization. But this is where it gets fascinating and I need to introduce you to some bacteria.

Let me introduce you to a species of bacteria called Spiroplasm. Spiroplasma is a parasite that lives inside butterfly blood and gets passed on to the Monarch butterfly’s offspring through the female’s oocyte (egg). It can live in males but cannot get passed to the male’s offspring in the male’s sperm so if the bacteria get into males it is a dead-end because they die with the male. To avoid this waste, Spiroplasma infecting a subspecies of the African Monarch in East Africa kill males. During the initial stages of development after the butterfly’s eggs are fertilized, the Spiroplasma produces a protein that kills all male eggs. When the female caterpillars hatch, they then eat the dead male eggs and get a protein boost.

As you can imagine this is potentially a huge problem for the African Monarch subspecies at some point over time there will not be enough males to mate and the population will die out.

So how does this explain the color variation? A mutation in the gene that gives the subspecies of African Monarch the different color is found on the female sex-chromosome so it is passed on from female to female. The gene for local color version comes from the male. This is where the bacteria come into play again. The bacteria take out the males so it effectively takes the effect that the local male’s genes on color play in the offspring. The gene that comes from an immigrant male gets passed on and provides us with the variation.

A. The map shows the approximate ranges of the different subspecies of Monarch.
B. The cartoon shows how the local ‘color gene’ that would have come from the local males gets lost because it is passed on to the males who are killed by bacteria. If you want to read the full scientific paper link here.

Are you’re worried about the African Monarch in East Africa? Fortunately, the Spiroplasma hasn’t infected all females so there are non-infected females that are still breeding. Males can also arrive from an uninfected area so for the time being they are not going to go extinct. However, the bacteria is essentially isolating the two different sub-species of butterfly and reducing the amount of gene flow between them. When this happens we have the potential for the different sub-species to change enough that they eventually become different species.

A similar bacteria called Wolbachia infected a population of butterfly called the Blue Moon on a small island in the South Pacific. The population of males dropped to 1%, but then a mutation occurred. The mutation produced a suppressor that doesn’t allow the bacteria to kill the males. In only 10 generations the percentage of males in the population increased to 39%.

This is all very exciting to scientists. We normally think of evolution and the process of natural selection taking a very long time to act and being mostly because of environmental factors, but this shows how significant the effect of an invisible parasite can be. It also has some very real applications in terms of pest and disease control.

I hesitate to write this because we don’t know what the unintended consequences of eliminating any species is, but for example, imagine if we can infect malaria carrying mosquitos with Walbachia or Spiroplasma, could effectively create local extinctions? You can read more about it here.

Kuna spishi ya kipepeo inayoitwa ‘African Monarch’ ambaye ni mfano wa vipepeo wenye rangi ambazo spishi nyingi za vipepeo zinafanana nayo. Kiwavi cha ‘African Monarch’ anakula aina za mimea zenye sumu, lakini badala ya hiyo sumu kuwadhuru, wanaikusanya mwilini na inawapa ladha mbaya wakiliwa na maadui yao. Kuna spishi zingine ambazo majike hufanana na ‘African Monarch’, kwa mfano ‘Mocker Swallow Tail’ na ‘Common Diadem’ lakini hawa hawana ladha mbaya. Lakini pia, kuna vipepeo vingine wenye ladha mbaya haswa spishi mbili ya jamii ya ‘Acrea’. Kuielezea kwa mtazamo wa uchaguzi asilia (evolution) ni kwamba kila mmoja anayefanana zaidi na spishi yenye ladha mbaya hupata nafasi zaidi ya kukwepa kuliwa akikutana na adui aliyejifunza ladha mbaya ya mwenzio. Hii basi husababisha kuongeza uwezekano wa kufanikiwa kuzalisha. Vipepeo vyenye ladha mbaya huongezeka, na elimu ya adui huongezeka. Kila mmoja ya hawa spishi tatu wenye sumu huwa wanatofautiana wenyewe kwa wenyewe ndani ya spishi, kitu ambacho kinapunguza manufaa ya kuigana haswa kwenye maeneo yenye makutano ya subspishi mbili.  Hapa ndipo pana sisimua na inabidi nikutambulishe kuhusu aina za bakteria.

Kuna spishi ya bacteria inachoitwa ‘Spiroplasm’. ‘Spiroplasm’ ni kimelea ambayo inaishi ndani ya damu ya kipepeo na inasambazwa kwa kizazi cha ‘African Monarch’ kwa kupitia mayai ya jike. Inaweza kuishi kwa dume lakini huwa haiwezi kusambazwa kwa mbegu za kiume na kwa hivyo hiyo bakteria itafifia ikiingia kwenye umbo la dume. Kupunguza huo hasara, ‘Spiroplasma’ inayolemea subspishi (jamii fulani) ya ‘African Monarch’ hapa Afrika Mashariki inaua dume. Wakati wa hatua za kwanza ya ukuaji baada ya utungisho, Spiroplasma inatengeneza protein ya kuuwa madume ndani ya mayai. Viwavi jike vinapoanguliwa vinakula mayai yenye madume waliokufa na kupata msaada wa protini.

Unaweza kufikiria kwamba hii inaweza kuwa tatizo kubwa kwa subspishi ya ‘African Monarch’ na baada ya muda fulani kuna uwezekano mkubwa wa kukosa madume wa kutosha, hadi idadi yao kuisha kabisa.

Sasa, hii bakteria inahusikaje na kusababisha tofauti za rangi wenyewe kwa wenyewe? Mabadiliko ya chembe za urithi kwenye jeni linalowapa African Monarch rangi yao inapatikana kwenye kromosomu ya jinsia ya jike na kwa vile huwa jike anarithi kwa mama yake. Hapa ndipo bakteria huingilia tena. Bakteria inavyowatoa madume inaondoa nguvu na athari ya jeni ya dume wenyeji kwenye rangi ya kizazi kipya. Kizazi kipya kinapata jeni ya kutoka kwa dume aliyehamia bila maambukizi ya bakteria.

Hii ramani inaonyesha rangi tofauti za aina za African Monarch tofauti na namna Spiroplasma inavyoondoa matokea ya dume wenyeji.

A. Ramani inaonyesha upatikanaji wa subspishi ya ‘African Monarch’.
B. Mchoro huu unaonyesha namna jeni za rangi kutoka kwa dume wenyeji hupotea kwa sababu ya athari ya bakteria. Kama unapenda kusoma nakala ya kisayansi bonyeza kiuongo.

Kama unawahofia African Monarch hapa Afrika Mashariki usijali. Spiroplasma haijaweza kuambukiza majike wote na baado kuna majike wasioambukizwa wanaozalishana. Vilevile, dume huwa wanahamia kutoka maeneo yasio na vimelea. Ila, hii bakteria inagawanya hizi sub-spishi ya vipepeo na kupunguza mchanganyiko wa jeni kati ya hivi vikundi viwili. Huu mgawanyiko ukitokea kuna uwezekano mkubwa wa hizo sub-spishi kubadilika kutosha hadi kuwa spishi mbili tofauti.

Kuna bakteria aina ya Wolbachia iliambukiza vipepeo vya aina ya Blue Moon kwenye kisiwa ndogo kwenye kusini mwa Bahari Pasifiki. Idadi ya madume ilipungua hadi asilimia 1 tu, lakini hapo badiliko kwenye chembe za urithi ilitokea. Badiliko hiyo lilitengeneza kikandamizo ya bakteria hao wanaoua madume. Baada ya vizazi 10 tu, idadi ya madume iliongezeka tena hadi asilimia 39% ya vipepeo.

Hii inawafurahisha na kuwashangaza wanasayansi. Kawaida mageuko ya spishi na uteuzi asili huchukua muda mrefu sana na husababishwa na sababu za kimazingira, lakini mfano huu unaonyesha nguvu ya matokeo ya kilemea kisichoonekana. Ina matumizi nyeti pia kwenye kudhibiti magonjwa na wadudu waharibifu.

Nina sitasita kuandika maelezo ya matumizi haya kwa sababu hatujui matokeo yasiotarajiwa ya kuondoa spishi makusudi, lakini kwa mfano, je tungeweza kuambukiza mbu wanaosambaza ugonjwa wa malaria na Walbachia au Spiroplasma, tungeweza kudhibiti ugonjwa huu. Unaweza kusoma zaidi hapa katika maadiko rejea.

Sources:

University of Exeter. (2016, July 19). Microbe drives species apart: Tiny microbe turns tropical butterfly into male killer. ScienceDaily. Retrieved July 12, 2020 from www.sciencedaily.com/releases/2016/07/160719214826.htm

PLOS. (2020, February 28). Male-killing bacteria linked to butterfly color changes. ScienceDaily. Retrieved July 13, 2020 from www.sciencedaily.com/releases/2020/02/200228125228.htm

Martin SH, Singh KS, Gordon IJ, Omufwoko KS, Collins S, Warren IA, et al. (2020) Whole-chromosome hitchhiking driven by a male-killing endosymbiont. PLoS Biol 18(2): e3000610. https://doi.org/10.1371/journal.pbio.3000610

Idris, E. Hassan, S. 2013. Biased sex ratios and aposematic polymorphism in African butterflies: A
hypothesis. Ideas in Ecology and Evolution 2013 doi:10.4033/iee.2013.6.2.n

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