Self-pollination is often regarded as an evolutionary dead end, yet many selfers seem capable of retaining high adaptive potential. Andersson and Ofori perform experimental crosses within an initially self-sterile population of Crepis tectorum to produce an outbred and inbred progeny population, and find that a shift to selfing promotes adaptive potential for leaf morphology by increasing the overall genetic variance and by exposing potentially advantageous recessive alleles to selection. The results point to a positive role for inbreeding in phenotypic evolution, at least during or immediately after a rapid shift in mating system.
Why do we eat? Not a trick question. Apart from minor considerations about taste and sensory experiences, the plain fact of the matter is that we eat to get energy so we can do stuff (like read this blog…) and survive (i.e. not die). However, we are often encouraged to ensure that we control our energy intake, i.e. the number of calories we consume. To a large extent we rely on the calorific information displayed on the packages of the food we buy, to ensure that we don’t over-eat. Simply put, you find out how many calories are needed to maintain your particular ‘lifestyle’ (e.g. as published in government guidelines), and total up the calories for the food you consume to ensure you stay within that limit.
Easy, you might think, but what if the calorific information on your tin of lychees or whatever is incorrect, inaccurate, misleading or just plain wrong? That’s the concern now raised by Rob Dunn in his thoughtful piece entitled ‘Everything you know about calories is wrong’. And in the spirit of showcasing succinct writing (i.e. the following is definitely not plagiarism!), that article is admirably summarised by the journal’s ‘In brief’ commentary as follows: ‘Almost every packaged food today features calorie counts in its label. Most of these counts are inaccurate because they are based on a system of averages that ignores the complexity of digestion. Recent research reveals that how many calories we extract from food depends on which species we eat, how we prepare our food, which bacteria are in our gut and how much energy we use to digest different foods. Current calorie counts do not consider any of these factors. Digestion is so intricate that even if we try to improve calorie counts, we will likely never make them perfectly accurate’.
I don’t know, not only do we need to check the ingredients on our food packaging; we now also have to check the fundamental assumptions underlying the arithmetic! Clearly, food doesn’t do what it says on the tin…
[A plant-rich video presentation by Scientific American editor Ferris Jabr regarding this rather inconvenient truth is also available online – Ed.]
Floral features, pollination biology and breeding system of Chloraea membranacea Lindl. (Orchidaceae: Chloraeinae) has moved into free access, along with the rest of the December 2012 issue of Annals of Botany. This paper caught my eye because it’s a reminder of how clever orchids can be.
What’s going on here?
Insects are pollinating the flowers, but they’re doing it in a peculiar way. A lot of the time they have their abdomens in the flower and their head poking out. This partly because of the way this orchid has evolved to reproduce. Chloraea membranacea Lindl. is self-compatible, so it’s happy pollinating itself, or at least it would be if it could. It can’t so it has to rely on pollinators to visit. So this is why it has flowers.
This is hardly news, angiosperms have flowers and offer nectar to visitors to entice them in. But C. membranacea doesn’t.
Sanguinetti et al. found that C. membranacea gives off a sweet scent to attract insects, but does not offer any nectar as a reward. In fact landing on the flower is a bad idea as the plant slaps a heavy pollinarium on the back of the insect to carry to another flower, often another one of its own. Using deception, the orchid can get the benefits of pollinator visits with fewer of the costs, like having to produce nectar.
However, maybe bees aren’t always the helpless victims.
If you re-watch the video at around 40 seconds you’ll see a bee grooming itself. These pollinaria are hefty and can unbalance an insect. During observations of the plants some bees, Halictidae females, were seen transferring pollen from the pollinarium to their hindlegs. This is a valuable food, but it’s not often used from this orchid, because it’s packaged away in the pollinaria. If the bees are getting the pollen from the orchid then it might be inadvertently providing an award after all. Yet this might not be the start of a deliberate strategy, Sanguinetti et al. very clearly state:
The fact that some pollinarium-laden female bees were seen actively collecting pollen from the pollinaria should be interpreted with caution. All our evidence suggests that pollen collection is a by-product of grooming activities.
What we’re currently seeing is a snapshot of an ongoing process of refining and adaptation. So far all the Chloraeinae seem to be deceptive orchids, getting pollinated without offering a reward. Sanguinetti et al. say that pinning down how they evolved is likely to become easier. It looks like their sister clades all offer nectar, so that ancestors of these flowers may have initially offered a reward too, but found that with their looks and scent they didn’t need to go to the effort of producing nectar.
If you do ever reincarnate as a pollinator then it would be a very good idea to never trust an orchid.
Sanguinetti A., Buzatto C.R., Pedron M., Davies K.L., Ferreira P.M.d.A., Maldonado S. & Singer R.B. (2012). Floral features, pollination biology and breeding system of Chloraea membranacea Lindl. (Orchidaceae: Chloraeinae), Annals of Botany, 110 (8) 1607-1621 DOI: 10.1093/aob/mcs221
Cycads know a thing or two about pollination – that’s one reason they’ve been around since the Jurassic period. They are found across much of the subtropical and tropical parts of the world and many can survive in harsh conditions, from semidesert climates to wet rain forest conditions.
All cycads are dioecious, and insect pollinators have to visit both male and female plants for pollination to occur. Effective pollination requires pollinators to move from male to female cones or to move back and forth between the male and female cones. The known pollinators of almost all cycads are insect herbivores whose larvae feed on male cone tissues (including pollen) of the host cycad, so that the male cone serves as the larval brood site.
Floral odour and heat are characteristic of the reproductive structures of some cycads. Ontogenetic (developmental) changes in floral odour and heat production have also been shown to influence pollinator behaviour. The cues affecting insect pollinator behaviour, such as aggregation, attraction, repellence, mating and oviposition, may differ between male and female plants of the host species as well as at different times of the day or stages of cone development. Until recently it was assumed that volatiles and heat production in cycads function solely to attract pollinators to inflorescences, but Terry et al. (2004) observed that insect pollinators actually left male cones of several Australian cycads (Macrozamia spp.) during periods of peak volatile emission, which also coincided with peaks in cone temperature as a result of thermogenesis – the plants appear to get rid of potential pollinators they don’t want, a ‘push–pull’ pollination strategy.
A recent paper in Annals of Botany examines patterns of cone odour emissions and heating in the African cycad Encephalartos villosus and demonstrates that these are different from those observed in Macrozamia cycads and are not consistent with the push–pull pattern as periods of peak odour emission do not coincide with mass exodus of insects from male cones.
Suinyuy T.N., Donaldson J.S. & Johnson S.D. (2013). Patterns of odour emission, thermogenesis and pollinator activity in cones of an African cycad: what mechanisms apply?, Annals of Botany, 112 (5) 891-902 DOI: 10.1093/aob/mct159
Saving the bees is a popular cause, and with good reason. They’re essential for pollinating many important crops. However, we don’t always coördinate our aims and our actions. There are concerns that various chemical treatments, either neonicotinoid pesticides or fungicides could be responsible for the reducing the bee population in the UK. There’s probably many other reasons. 97% of lowland meadow in the UK has been lost, a scale of destruction that makes the loggers in the Amazon look amazingly unambitious. But there’s all sorts of little actions that make it worse.
Ivy is currently a villain. It climbs up walls and around trees. It doesn’t actually kill trees, but that gets overlooked. It can make damage on walls worse if the wall is already in a bad state. It can also insulate walls, so properly managed it will save you money. Recent research also shows that it undervalued in supporting bees. The title of a recent paper spells it out very clearly: Ivy: an underappreciated key resource to flower-visiting insects in autumn by Mihail Garbuzov and Francis Ratnieks at the University of Sussex.
When I think of ivy I picture the lush green leaves, but it’s the small white flowers that are important. They appear in the autumn at a time when there are few other flowers. Garbuzov and Ratnieks examined hives around Brighton to find out what the bees were foraging for. The results surprised me. Honey bees need ivy, a LOT. During September and October Garbuzov and Ratnieks found that 89% of the pollen pellets the honey bees brought back were from ivy. They also found that the majority of honey bees and bumble bees were bringing back ivy nectar to build the winter honey stores. Ivy nectar is unusually high in sugars.
The key factor in ivy’s importance is timing. Spring brings out the blooms and it’s a feast for insects that are bringing up the next generations over the summer. Winter in contrast is a famine and hives need stocks and supplies. The late flowering of ivy provides a boost to bee hives to put them in a better position for surviving overwintering.
Garbuzov and Ratnieks go so far as to say that ivy may be a keystone species, a species that has a disproportionate effect on the local environment. Ivy’s ability to feed bees, wasps and flies in the autumn provides a better chance of survival and so more insects to reproduce in the spring, not simply to pollinate other flowers, but also to provide food for predator species.
There is no obvious connection between ivy and many other crops species, but it looks like Garbuzov and Ratnieks have shown that what looks like a very localised problem What do I do with my ivy? has consequences much further afield.
Garbuzov M. & Ratnieks F.L.W. (2013). Ivy: an underappreciated key resource to flower-visiting insects in autumn, Insect Conservation and Diversity, n/a-n/a DOI: 10.1111/icad.12033
Monocotyledonous plants are divided into 11 orders: Acorales, Alismatales, Petrosaviales, Dioscoreales, Pandanales, Liliales, Asparagales, Arecales, Poales, Commelinales and Zingiberales, the last four being grouped into the Commelinid clade. Among these, the Asparagales may be the second most important for agriculture and horticulture after the Poales (grasses). The Asparagales includes the Orchidaceae with >30,000 species, but also includes important crops such as aloe (Aloe vera), agave (Agave tequilana), asparagus (Asparagus officinalis), garlic (Allium sativum), leek (Allium ampeloprasum), onion (Allium cepa) and vanilla (Vanilla planifolia), as well as ornamental plants such as yuccas, amarylids, daffodils, irises. With an annual world production of >95 Mt, it is the third most cultivated group for vegetable production in the world after the Solanales (including potato, tomato, pepper and aubergine) and the Cucurbitales (including melons, cucumbers and gourds).
To extend our understanding of genome evolution in the monocots, a recent paper in Annals of Botany examines the asparagus and onion genomes, with a particular focus on the characterization of long terminal repeat (LTR) retrotransposons. The results reveal that LTR retrotransposons are the major components of the onion and garden asparagus genomes. These elements are mostly intact (i.e. with two LTRs), have mainly inserted within the past 6 million years and are piled up into nested structures. Some families have become particularly abundant, as high as 4–5 % (asparagus) or 3–4 % (onion) of the genome for the most abundant families, as also seen in large grass genomes such as wheat and maize. Although previous annotations of contiguous genomic sequences have suggested that LTR retrotransposons were highly fragmented in these two Asparagales genomes, these results show that this was largely due to the methodology used. In contrast, this work indicates an ensemble of genomic features similar to those observed in the Poaceae.
Vitte C., Estep M.C., Leebens-Mack J. & Bennetzen J.L. (2013). Young, intact and nested retrotransposons are abundant in the onion and asparagus genomes, Annals of Botany, 112 (5) 881-889 DOI: 10.1093/aob/mct155
Soil seed banks serve as reservoirs for future plant communities, and when diverse and abundant can buffer vegetation communities against environmental fluctuations. Sparse seed banks, however, may lead to future declines of already rare species. Seed banks in wetland communities are often robust and can persist over long time periods, making wetlands model systems for studying the spatial and temporal links between above- and belowground communities. In a recent study in AoB PLANTS, Faist et al. found that the belowground community in the soil seed bank of restored ephemeral wetlands (vernal pools) in California’s Central Valley, USA, has been less invaded by exotic plants and is a reservoir for rare and native plant species. They also found that seed bank community structure most closely resembled the aboveground community structure from five to eight years prior to seed bank sampling rather than more recent years. The maintenance of rare and native plant species in soil seed banks, even while aboveground vegetation communities are being invaded by exotic plants, is an exciting finding with important implications for management and restoration efforts in annual plant communities.
Many of us have heard of the lotus effect, the ‘very high water repellence (superhydrophobicity) exhibited by the leaves of the lotus flower (Nelumbo nucifera)’. Less well known – until this item was penned anyway – is another phenomenon that has been identified in the lotus by Philip Matthews and Roger Seymour.
As an aquatic plant, a high degree of water-repellancy may well have important survival value (and may even have been predictable..?). However, equally important is the ability to aerate below-water cells for aerobic respiration, especially those organs surrounded by waterlogged, anoxic sediment, such as anchoring rhizomes. Although well-aerated water contains oxygen and a range of other gases important to plant biology, their concentrations therein are much lower than those in the atmosphere. Any mechanism that can enhance supply of life-sustaining gases to an organism in such an environment will bring major benefits to its owner.
Well, and very much in keeping with the dictum ‘seek and ye shall find’, the University of Adelaide (Australia)-based pair did just that and found something rather remarkable. The duo propose an important role for large, leaf-sited stomata in regulating the pressure, direction and rate of flow of atmosphere-derived air within the extensive system of gas canals that connect rhizomes to petioles to leaves at the water’s surface. The active opening and closing of ‘central plate stomata’ (situated in the centre of the leaf above a gas canal junction, and which are much larger and less dense than those on the leaf blade proper) is hypothesised to regulate convective airflow within the lotus plant. Furthermore, not only does this ventilate the rhizome, but it may also direct rhizome-derived (‘benthic’) CO2 towards photosynthesis in the leaves.
It would appear that the spirit of Stephen Hales (17–18th century English clergyman and botanical experimenter) lives on, albeit down under! And another – additional – role stomata can play has been raised by María Nores et al. [http:dx.doi.org/10.1111/boj.12009]. Examining the pollination biology of the ‘four o’clock plant’, they propose that stomata are involved in nectar secretion whereby ‘nectar is secreted through modified stomata, accumulating between the base of the stamens and the ovary’. Multi-facetted stomata, not just mediating photosynthesis; clearly earning their accolade as ‘the most important orifice on the planet’.