If you've been in the UK during the middle of 2012, you will have noticed that it's been raining a bit. Well, I say 'a bit', I actually mean a lot. Really a lot - following an unusually hot spring, it was wet from April to mid-July, including the wettest April for a century, and the wettest June on record. It's well understood that this was because the jet stream looped south of the UK and stayed there, but what is less well known is why this happened - this is an area of active research (including links to climate change) and there is an excellent summary here.
It has also been widely reported in both national and local media (e.g. here and here) that this unusually lengthy and heavy rainfall has had a huge impact on British wildlife - some species such as ringlet (Aphantopus hyperantus) butterflies (which breed in damp grassy areas) can do well in wet conditions, but current predictions are that 2012 will be the worst year on record for British butterflies overall. Volunteer recording will be hugely important in determining the effects on this group and there is still time to join in with the Big Butterfly Count which runs until 5th August. Although slugs and snails have done well (much to the annoyance of gardeners and vegetable growers), winged insects (including those most eseential of pollinators, bees) have fared poorly, being unable to feed or find mates effectively in cold, wet conditions and therefore are also unable to reproduce successfully. Although some mollusc-feeders may have plenty of food, this may well not lead to a good year for amphibians as the hot spring dried up breeding ponds and the April rainwater was too cold for reproduction. Thus, despite a few winners, the effect has largely been an overwhelmingly negative one e.g. many birds have been unable to keep chicks warm and fed, while many species, such as puffins, have seen nests flooded.
|A pair of common garden snails Cornu aspersum (often known as Helix aspersa)|
With widespread breeding failures, local extinctions have been predicted and conservationists are rightly worried about how severe the impacts will be, especially as the summer of 2011 was also poor. However, with the weather changing to become hot and sunny about a week ago, hopes for a good late summer and autumn have been fuelled, and I have to wonder to what extent various species can make up for lost time while conditions are suitable. Certainly my own observations, and those of other naturalists I've been in contact with, suggest that there is currently a rapid burst of invertebrate adult emergence, including species usually encountered earlier in the summer. Some moths which have emerged late have been reported as unusually pale, although this is from a fairly small number of observations, so its importance remains unclear. Delayed moth emergence related to temperature is well documented (e.g. DuRant 1990) but there does not appear to be any mention in the literature of aberrant colouration due to such delays. Certainly, a pale colour does not suggest an adaptive response as darker colours are generally associated with cooler temperatures as they permit more rapid warming by absorption of solar radiation. So, my question is whether delayed emergence can lead to paler colouration through some effect on the mechanisms related to pigmentation. Although this idea is somewhat speculative, two possibilities (which are not mutually exclusive) spring readily to mind:
1. Delayed emergence affects the mechanism of pigment production.
2. A longer period as a pupa means energy reserves become depleted and less essential material (such as pigments) is metabolised to enable emergence to be postponed during unfavourable conditions.
Looking at pigment production, some relevant research has been undertaken by Sawada et al. (2002) who looked at the expression of an mRNA-encoding guanosine triphosphate-cyclohydrolase I (GTP-CH I), the first key enzyme in the synthesis of pteridines during pigment formation in the wings of the butterfly Precis coenia. The biochemical details are not important here, but the key result was that gene expression was strongest one day before butterfly emergence. So, if pigment production is timed to peak around emergence, could a delay lead directly to reduced pigmentation? From this example, I have to say that it doesn't appear so - the onset and duration of gene expression appears to be controlled by the decline in the ecdysteroid hormone 20-hydroxyecdysone (linked to moulting and metamorphosis and usually called 20E), and a short delay in emergence simply led to a later peak in expression such that pigmentation and emergence remained synchronised. It is still possible that low temperatures prevent pigment formation though this implies the retention of higher levels of 20E and/or one of more effects elsewhere in the chain of biochemical processes involved. Essentially it seems that no-one knows if such effects occur.
Moving onto pigment breakdown, I'll stick with pteridines as there are a number of other pigment groups and I want to keep this at least reasonably simple. However, as Watt (1967) shows, the pteridine pathway is anything but simple, which in turn means that there are many points at which it might be disrupted, and as above, there is no indication that anyone has looked at the effects of delayed emergence on pigmentation, including the breakdown of pigment compounds.
So, although this has been a somewhat limited look at possible pigmentation effects, it has at least shown that it is an area where future research is needed. However, this does not mean that there is no every-day or real-world relevance here. Coming back to the 'volunteer' aspect mentioned earlier, it is not just recording that is needed, but habitat creation - in particular, the small-scale improvements that anyone with a garden can make (or indeed councils who own open spaces) by cultivating more-or-less natural 'meadow' areas rather than ecologically sterile mown lawns. Our garden is not large but it does include a meadow patch with scabious, bird's-foot trefoil, clovers, meadow clary, cornflower, lady's bedstraw, knapweeds and others. Not only is it more interesting and attractive than a billard-table lawn, but it has been a haven for flying insects throughout the wet summer - I have still identified around 25 bee species alone this year, with flowers being used during even the briefest of lulls in rainfall, and very actively during genuinely warm conditions. Also, you don't have to be an expert/experienced entomologist, botanist or gardener to do this. Wild flowers are in fashion at the moment (let's hope they stay that way rather than gravel, paving-for-parking and swathes of decking) with thoughtful gardening writers and TV presenters such as Sarah Raven promoting this important subject, including easy how-to guides if you want a garden meadow - and this means that garden centres and plant nurseries are likely to be well-stocked with native insect-friendly species. If you do this, not only will invertebrates reap the benefits, but so will you.
|The bee Andrena flavipes on white clover during the wettest summer on record.|
DuRant, J.A. (1990). Influence of temperature on spring emergence of European corn borer moths (Lepidoptera: Pyralidae). Journal of Agricultural Entomology 7(3): 259-264.
Sawada, H., Nakagoshi, M., Reinhardt, R.K., Ziegler, I.& Koch, P.B. (2002). Hormonal control of GTP cyclohydrolase I gene expression and enzyme activity during color pattern development in wings of Precis coenia. Insect Biochemistry and Molecular Biology 32: 609–615.Watt, W.B. (1967). Pteridine biosynthesis in the butterfly Colias eurytheme. Journal of Biological Chemistry 242(4): 565-562.