Overcoming environmental challenges in pollination.

Mapambano ya kusuluhisha changamoto ya kusambaza mbelewele.

(Scroll down for Swahili version)

All you need to do is look at a few different flowers to see how there can be many solutions to the same environmental challenge and that different solutions open up new challenges. Flowers are a plant’s reproductive organs so ultimately there’s a male part and a female part. Some plants have both parts on the same flower (monoicous), others produce separate male and female flowers on different plants (dioecious).  The obvious first challenge is getting pollen from the male flowers to the female flowers.

One option is to produce a lot of pollen that blows around in the wind. A lot of grasses are pollinated this way. But this comes at a cost of investment in a huge amount of pollen. Another strategy is to bribe a pollinator. Up to 94% of flowering plants in the tropics employ pollinator. This raises the challenge of competition for pollinators. Not only is there a limited supply of pollinators, but producing nectar is expensive. If a pollinator visits a different plant species, the pollen it is carrying from the first flower is going to be wasted. This has resulted in a lot of cool specializations from flower shape to flower color.

One obvious way is to just flower at a different time of year. You’ll notice that even in the dry-season which is a tough time of year for plants, if you look around, there will be at least one species flowering. An obvious one in parks like Ruaha and Katavi is the Combretum pupureiforum, but another conspicuous dry-season flower is Albezia anthelmintica. Another obvious one is Kigelia africana.

Combretum purpureiforum in Ruaha in the dry season.

You can tell a lot about a flower’s pollinator by its shape, color and smell. It’s something called pollinator syndrome. In 1862, Darwin was sent a sample of an orchid from Madagascar. This orchid has a 12-inch long spur which is where the nectar is stored. He predicted that there was a moth that had a 12-inch proboscis to get at the nectar. It took 40 years for it to be discovered, but in the end he was right.

An East African orchid with long spurs.

In general, if a flower is white and very fragrant it is most probably pollinated at night by moths and bats (for example baobab flowers). Red, pink, and orange flowers like Aloes and Leonotis tend to attract sunbirds, and butterflies, bees, flies and other insects seem to prefer blue and purple flowers. White diurnal flowers like Ipomeas are also pollinated by diurnal insects.. Because a lot of these insects can see in ultraviolet wavelengths (UV) some flowers have incredible patterns that we can’t see. Smell is also significant pollinator attractant and some insects are more sensitive than others to the different chemical signals that plants give off. Some species of plants like the Carallumas smell like rotting meat to attract and deceive flesh eating flies to pollinate them.

Ipomeas are a great example of how plant behavior excludes pollinators. When a morning glory closes at night it is excluding thieving nocturnal pollinators. Solanum flowers protect their pollen by requiring a certain frequency and intensity of bee buzzing before their anthers explode and spray the bee with pollen.

Nature is full of cheats and when it comes to the flower-pollinator relationship, there are some cool examples of cheats on both sides. Some species of nectar lovers are going to cheat if the nectar is too hidden and bypass the system. This is called nectar robbing. Some sunbirds, will pierce the flower nectary instead of going through the door and thus bypass the system.

But the cheating isn’t just one way. Some species of plants, like leopard orchid flowers produce chemicals that deceive solitary bees into pollinating them without a nectar reward. The interesting thing about leopard orchids is that they actually do produce nectar on other parts of the flowering stem to attract ants and we think that these ants help protect the flowers from other insects. You can read more about this here.

Ukitazama tu maua tofauti, lazima utaona mbinu nyingi za kupambana na changamoto za kimazingira vile vile; utaona kuwa kila suluhisho hufungua changamoto nyingine. Maua ni viungo vya uzazi vya mimea na kwa vile kuna sehemu au kiungo ya kiume na sehemu ya kike. Mimea mengine huwa na viungo vyote viwili kwenye ua mmoja (monoicous), mengine huwa na viungo tofauti kwenye maua tofauti (dioecious). Changamoto  ya kwanza ni kusafirisha mbelewele (pollen) kutoka kwenye kiungo cha kiume hadi kwenye sehemu ya kike.

Suluhisho mmoja wapo ni kusambaza mbelewele kwa kutumia upepo. Baadhi ya nyasi yanatumia mbinu huu. Lakini suluhisho hiyo inahitaji mbelewele nyingi; ni uwekeaji mkubwa. Suluhisho nyingine ni kumhonga kiumbe atakaye hamisha mbelewele ‘pollinator’. Asilimia 94 ya mimea yenye maua kwenye maeneo ya kitropiki hutumia ‘pollinator’. Hii inaleta changamoto ya kupata pollinators kwa sababu kuna upungufu wa ‘pollinators’ na kutengeneza nectari nayo ni ghali kwa upande wao. Kama ‘pollinator’ anatembelea maua ya spishi tofauti, ile mbelewele alieibeba kutoka kwenye ua la kwanza litakua limepitiwa. Hii imesababisha mifumo mingi peke ya ajabu kuanzia kwenye sura ya maua hadi rangi ya maua.

Namna mmoja ya kupunguza kushindana kupata pollinators ni kuchanua kwa muda maalum. Ukitembea porini kipindi cha kiangazi ambacho ni muda mgumu kwa mimea, utakuta kwa kawaida kuna spishi mmoja mmoja yenye maua. Ukitembelea hifadhi ya Ruaha au Katavi ua linaloonekana kiangazi ni Combretum purpureiforum, lakini nyingine kinachoonekana pia ni Albizia anthelmintica. Nyingine ni mlegea (Kigelia africana).

Unaweza kutambua mengi kuhusu pollinator ya ua kwa kuangalia sura, rangi, na harufu. Hii inaitwa ‘pollinator syndrome’. Mwaka 1962, Charles Darwin alipata sampuli ya aina ya ua ‘orchid’ kutoka Madagascar. Hiyo ‘orchid’ ina sehemu ya kuhifadhi nectari yenye urefu wa inchi 12. Darwin alitabiri kua kutakuwepo na nondo (‘moth’) mwenye ulimi ya inchi 12 ili kuifikia hiyo nectari. Ilichukia miaka 40 hadi hiyo nondo ilipogunduliwa lakini alikua sahihi.

Kwa kawaida, ua likiwa nyeupe na kuwa na harufu nzuri bila shaka inapandikizwa mbelewele usiku na nondo au popo (kwa mfano ua la mbuyu). Maua yenye rangi nyekundu, machungwa kama maua ya ‘aloe’ au ‘leonotis’ huwa yanavutia ndege kama chozi (sunbird). Maua yenye rangi ya buluu huwa yanachaguliwa zaidi na vipepeo, nyuki, na nzi. Wadudu wengi huweza kuona vizuri zaidi kuliko sisi kwa kuona mwanga wa ‘ultraviolet’ (UV) na kuna maua mengi yenye mifumo ya ajabu ambayo sisi hatuwezi kuyaona. Harufu pia ni kivutio kikubwa na wadudu wengine husikia ishara za kemikali nyeti kuliko wadudu wengine.  Kuna spishi nyingine za mimea kama jamii ya ‘Caralluma’ ambazo hunukia kama nyama iliyooza kwa ajili ya kuvutia na kudanganya nzi kwa ajili ya kuhamisha mbelewele yake.

Chozi shingo nyekundu ni pollinator mmojawapo ya aloe.

Jamii ya ‘ipomea’ ni mfano wa namna ya tabia ya ua kuwanyima ‘pollinator’ wengine. Baadhi ya ipomea hufunga usiku kwa ajili ya kunyima pollinator za usiku. Jamii ya solanum hulinda mbelewele kwa kuhitaji masafa nyeti ya nyuki kabla ya kulipua sehemu ya kiume ‘anther’ na kumwagia nyuki mbelewele yake.

Mazingira ya asili huwa yamejaa maua danganyifu na ukiwemo uhusiano kati ya maua na ‘pollinator’ yao kuna mifano pande zote. Spishi zingine zenye kupenda nectari hutafuta njia rahisi kupata nectari hata kama imefichwa vizuri. Hii tabia inatiwa uwizi wa nectari. Chozi ‘Sunbird’ wengine watatoboa pembeni ya ua ili kupata nectari badala ya kupita mlango wa mbele na vile kuipunja ua. Lakini mimea mengine nayo hudanganya ‘pollinator’ yao. Spishi nyingine kama ‘Leopard orchid’ zinatengeneza kemikali ya kudanganya nyuki (aina ya nyuki ‘solitary bee’) kuhamisha mbelewele ‘pollinate’ lakini hawatoi zawadi ya nectari. Kitu kimojawapo cha kuvutia kuhusu ‘Leopard orchid’ ni kwamba inatengeneza nectari lakini sio kwenye maua. Nectari yake inavutia sisimisi na tunahisi kuwa hawa sisimisi wanasaidia kulinda maua. Unaweza kusoma tuvuti zaidi hapa.

Main sources: Nectar in Plant–Insect Mutualistic Relationships: From Food Reward to Partner Manipulation. Massimo Nepi, Donato Grasso & Stephano Mancuso.

First ever record of insect pollination from 100 million years ago. ScienceDaily.

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