Spiders and insects: Evolution’s Tom and Jerry chase?

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Among the many interesting points raised during our recent Diversity and Evolution of Insects module was the idea that spiders and insects may have been involved in a sort of cat and mouse pursuit through the fossil record.

It’s certainly the conclusion David Penney reached in his 2004 paper looking at insect and spider family diversity over geological time. It’s suggested here that the rate of exponential increase in diversity was the same for both groups, and that one’s line of rapid diversification – known as radiation – followed the other.

Both insects and spiders tend to be linked with the history of flowering plants, but interestingly, the study also suggests that the major radiations of both these classic antagonists were out of the way a good 100million years before the flora joined the party. This being the case, the arms race began without the need for the habitats that we’d probably associate with the modern tussle of flying insects and web-weavers.

Co-evolution has been proven to be more likely when there’s a direct interaction between groups, and at least one dependency, so the idea of a hunger so profound it transcended the ages certainly sounds plausible. Yet it’s not a view universally shared.

It’s hard to conceive of the struggle between insects and spiders without thinking of webs – and the diversity of arachnid species is linked with the diversity of web design. But in the poetically-titled Tangled in a sparse spider web, researchers at the University of Barcelona muddy the waters of the ‘insects lead, spiders follow’ story of speciation.

They make a case that the diversification of spiders and their web-building approaches was all about moving to different habitats and making use of food resources in an increasingly structurally complex world. To be clear, it’s abundance of prey, they say, that was more significant in driving a species-defining approach to webs rather than its diversity. Loads of flying insects, yes, but not necessarily loads of different ones. They also make the case that the explosion of orb-webs couldn’t have happened at the same time as the insects were on their fiercest period of diversification.

Searching for trends through what remains of the species that have been here and gone is a notoriously tricky business – something that is more than acknowledged by the authors of the different theories offered here. Missing data is one of the foremost problems with scouring the past for clues that may illustrate a trend, while the ‘family trees’ considered in invertebrate evolutionary studies are often complicated and controversial; subject to different interpretations and revisions.

So, has predator chased prey through the ages, or are things a little more complex than that? Well, this is science – never the easiest place to get a neat narrative from. So while you can find shadows of Tom and Jerry, Road Runner and Wile E. Coyote, Bugs and Elmer and the rest if you trace the lineages of Arachnida and Insecta, pinning evolutionary trends on a hunter-hunted analogy alone probably won’t quite cut it.

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Apocalypse by mosquito?

As part of our molecular tools lecture, expertly executed by Joe Roberts, we discussed the recent advancements of gene editing and its use in the eradication of malaria in Africa. Crispr is the cutting-edge gene editing tool that has garnered a lot of attention since it’s discovery in 2007. Further developments have led to it being the simplest method for editing the nucleotides on a DNA strand altering the original gene which can result in resistance to diseases, alleviate genetic disorders or treat blood diseases.

Despite its multitude of uses genetic engineering has been faced with large amounts of controversy. Gene drive, which is the promotion of specific genes in a population that cause infertility or death through release of carriers into the wild, has faced mass criticism due to the uncontrollable nature of the concept. Once these genetically engineered individuals are released, there is little that can be done to prevent the spread of the unwanted gene across species through natural hybridisation. There are also concerns over the potential impacts of eradicating an entire species from an ecosystem, which could result in a collapse if the eradicated species is an important food source-as in the case of mosquitos.

Malaria-carrying mosquitoes of the Anopheles family are one of the prime candidates for gene drive control. The infected females spread malaria through their bites, which release the parasite into the bloodstream of the unlucky animal. Malaria is life threatening, killing half a million people annually so control of the vectors (mosquitoes) is of particular importance. Many studies have been done into the prospect of gene drive control of these insects, with the most recent being the release of genetically engineered males into Burkina Faso that you may have seen on the news in the last couple of weeks, treated as the new apocalypse.

The release of these mosquitoes is being controlled by the non-profit research organisation “target Malaria” as a test for the potential release of gene drive organisms. The mosquitoes being released in their experiment are all sterile, thus are unable to pass on their edited genes. They are simply being released to gather data on their dispersal and won’t last more than a few weeks in the ecosystem. So, no, we haven’t reached the point of using gene drive in the control of malaria quite yet, but the organisation is hoping to eventually use their mosquitoes to eradicate Anopheles in sub Saharan Africa, albeit with more work needing to be done.

Whilst gene drive systems have been highly effective in population control for lab studies, the issues around potential hybridisation needs to be considered and it’s been discovered that these mosquitoes are capable of developing resistance to the edited genes through random mutations. Lab work is limited and simply can’t match the population size found in the wild-thus the rate of mutation faced by their gene drive experiments is much lower as they have fewer individuals to experience a random mutation. Therefore, actual field results may be hampered by development of resistance.

We are faced, then, with the final dilemma. Does the risk befit the reward? Do we risk the transfer of these genes through hybridisation to save the lives of half a million people a year? Is the rate of mutation high enough to negate the entire gene drive system in the wild populations? All that can be done is further research, taking the necessary precautions before leaping into a potentially disastrous situation. Which is exactly what the Burkina Faso release is for.

Parental Care in Insects

The concept of parents looking after their babies is easily recognisable. We were all cared for when we were younger (even if not by our biological parents); fed, clothed and housed. We recognise the same urge when we see a cat cleaning her kittens or a bird collecting nest materials, but do we see it in insects? Well, more than you might think.

Only about 1% of insect species show parental care; selection pressure favours lots of offspring, effectively limiting parental care to species which produce fewer young. Parental care can mediate the transition from solitary to group or family living, both for an individual and on an evolutionary scale. It is likely to have developed as an altruistic trait to enable parents to better ‘pass on their genes’ by improving the survival of their offspring, even at the cost of their own energy, food, or even future reproductive opportunities. It may be evolved in environments with high selective pressures such as predation risk or reduced food availability.

Some insects show pretty much every level of sociality that you can think of, so here’s a walk-through of what insect parental care looks like. Through egg care, larval care by one of both parents., and the formation of family groups, this is the insect guide to good parenting:

Egg care

In some species, parental care starts before the young even leave the egg. Female earwigs groom their eggs to remove harmful mould spores and secrete symbiotic bacteria onto the larvae which are both antibiotic and anti-fungal. One study found that only 4% of European Earwig (Forficula auricularia) eggs hatched when they were left untended, as opposed to 77% for tended eggs. Mothers do the bulk of the offspring care but for some species the father takes the burden.

Male water bugs (Belostomatidae) brood the fertilised eggs on its back until they hatch. Carrying the eggs around makes the males more vulnerable to predation and hinders their foraging, making a large energetic expense to rear their offspring. It also stops the male from being able to mate again until the eggs have hatched.

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Male Giant Water Bug carrying his brood (Matt Tillett)

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Female European earwig, (Foricula auricularia) with egg brood and nymphs (University of Florida)

 

Uniparental care

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The Australian Hornet (Abispa ephippium) with her nest (Ian Sutton)

Potter wasp (Eumeninae) females build small clay nests for their larvae, bringing them food, defending them against predators, repairing damage and cleaning debris from the nest. Males play no role in the larval care but do patrol nest sites to find females to mate with.

 

 

Biparental larval care

Burying beetles (Nicrophorus spp.) take it up a level with both parents caring for their brood. Not only do they stock their larvae’s underground nest (or ‘crypt’) with a decomposing carcass (yum), but they also feed them regurgitated meat if begged. If there isn’t enough carrion to go around, parents will cull the most demanding larvae; whilst this might seem harsh, it ensures the survival of their less needy siblings. Although the parents don’t form the monogamous pairs often seen among vertebrates, they will stay together until their larvae reach adulthood.

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Nircrophorus vespilloides individual feeding its young (Dr Clare Andrews)

Family groups

Cockroaches might not initially seem the most likely parents given their occasionally cannibalistic tendencies but show some of the most comprehensive parental care of the insects. The females of some species are viviparous, gestating their offspring under their wings and producing a protein and carbohydrate rich ‘milk’ to feed their young nymphs until they are old enough to be ‘born’.

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A pacific beetle cockroach (Diploptera punctata) ‘giving birth’ to nymphs. This species also produces cockroach ‘milk’ (Emily Jennings)

Both cockroaches and burying beetles, unusually for insects, form family groups. In cockroaches this is because nymphs need to receive the gut protozoa essential for digesting cellulose from their woody diets. They lose the protozoa after every moult meaning that to ensure the nymph’s survival the adults have to stay with their offspring until they reach adulthood.

It is thought that this feeding was the key which allowed ancestors of modern termites to become eusocial. Termites are very closely related to cockroaches and these family groups expanded and evolved to become eusocial colony organisms. Living close together with millions of their ‘siblings’ allows termites to be sure of security and a food supply and allows traits like monogamy, foraging and nest inheritance to be developed. The switch from parental to sibling care is thought to have led to social behaviour forming in ants, wasps, and bees.

Evolution of sociality

But what is the glue holding these parents to their offspring? It’s surely not the big eyes, fluffiness, and helplessness that draws us to babies, kittens, and ducklings- even entomology students would struggle to call a cockroach nymph cute. It seems insect ‘families’ are reliant on pheromones as a recognition mechanism. Earwig nymphs’ pheromones reflect the quality of the food they’re being given to influence their mother to provide more food if needed. Cockroach nymphs use similar pheromones to aggregate with their parents and siblings and are able to distinguish non-siblings.

Brood care is thought to also have driven formation of families and social groups in vertebrates. The evolution of parental care in insects can be a model for the evolution of parental care in birds, fish, and of course mammals. It seems that you might have a lot to thank cockroach milk for your survival to adulthood.

 

In defence of common names

In our Dipteran discussions on Tuesday last week, the idea of doing away with all insect common names was mooted. While this may have had some support from MSc colleagues in the room, I think the majority were probably with me in internally screaming “NOOOOOOOO!”.

Let’s be frank from the start: yes, our good old Anglicised common names are mostly easier to remember than scientific names, unless you’re a fluent Greek or Latin speaker. But that’s not why I’m here to stick up for the commoner.

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It’s well worth first acknowledging that there are problems with common names. Many are seemingly endless variations on a pretty loose theme (see the myriad ground beetles or hoverflies), and they can be different at national and even local level, de-standardising what is an internationally-agreed nomenclature and even muddying the waters of the body of research on given species.

But it’s not like the waters aren’t muddy enough in the first place. It’s arguable that things haven’t changed that much since 1942, when the Journal of Economic Entomology published an editorial stating:

With the scientific names of insects in perpetual chaos, due to the application of the law of priority, the splitting of species and generic concepts, and the endless shuffling of species from one genus to another, common names have come to have much more significance and importance than formerly.”

Common names have a tendency to cut through the noisy clanging of taxonomic debates – but they can do more than that: evoke, romanticise, or simply tell it like it is. On the latter, common names can tell you what an insect feeds on (pollen beetle, currant aphid, fungus gnat, dog tick), give you a crystal clear idea what an insect looks like (scorpionfly, giraffe weevil, orchid mantis, violin beetle), and let you know where it likes to hang out (larder beetle, house fly, museum beetle, bedbug).

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Devil’s coach horse beetle – Ocypus olens (Wikimedia Commons)

They can also simply bring a bit of fun to what can seem to outsiders like a dry discipline. Science is not forever vanquished by the simple admission that talk of fairyflies, ugly nest caterpillar moths, assassin bugs, beautiful demoiselle darters and bombardier beetles makes the world a slightly lighter, more wonder-filled place.

Common names can even reveal a bit about our culture. Why on earth shouldn’t Britain, a country steeped in existential angst and the occult, have brought its language to bear on the death’s head hawk moth, devil’s coach horse and deathwatch beetles?

As if to prove the joy of an apt common name, when Tuesday turned to Wednesday and we were introduced to the Lepidoptera via a photo of the Picasso moth, there was a notable instant improvement in the mood of the room, previously somewhat tense ahead of the afternoon’s assessed practical.

The power to evoke should not be underestimated in the communication of science. From a personal perspective, a life-long love of beetles would have been far less likely sparked by Lucanus cervus than stag beetle. The public are not a bunch to be sneered at for their failure to appreciate scientific correctness – and what’s more, need to be brought along as the pivotal role of insects in supporting human life becomes ever clearer.

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Picasso moth – Baorissa hieroglyphica (photo: M. Greeshma)

I agree wholeheartedly with Michael J. Samways, who in his 2005 book Insect Diversity Conservation urged experts not to shy away from charismatic ‘icon’ species and to use their common names, “so as to give the conservation mission warmth and familiarity”.

In case I haven’t made myself quite clear, I’m not just trying to make life more difficult for Giannis, Cyprus’s representative on the course, who’s been sitting through the Hellenic-monikered species being reeled off as part of our Biology and Taxonomy of Insects module with a distinct air of ‘heard it all before’.

And all of this is absolutely no argument against scientific names per se. Of course, they will always have primacy – but they shouldn’t sit on their own, or they might just find themselves in sparse company.

The collection conundrum: How useful are Museum collections?

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Hope the whale suspended over Hintze hall

Visiting a museum for the first time can be a magical experience. Wandering through the vast halls, awing at the exhibits and looking at all the various artefacts within the museum walls can inspire wonder and intrigue into pretty much anyone.For me, the Natural History Museum is one of the greatest museums I have ever visited; with its breath-taking architecture, plethora of exhibitions and host of scientific specimens within the main halls and the Darwin centre cocoon. However, just walking around and taking in all of this doesn’t even scratch the surface of the treasures held within.

The NHM (like most museums) isn’t just a place to visit, but also a cornucopia of scientific research and constant study which the museum wants to share with as many people as possible. They do this by hosting talks in the Darwin centre, ‘Lates’ evenings – where you can go to talk with curators and participate in backstage tours of the collection areas – and even through sleepovers at the museum. On some occasions, however, the museum will have stalls erected during visiting hours to engage the public about the collections.

I have been fortunate enough to help talk to the public about the Entomological collections held within the museum, the most prevalent questions being – “How many insects do you have?”, “Where do you keep them all?” and even, “How do you keep that many insects alive?”. Most people respond to the answers by enthusing about how amazing it is that so much has been collected and how the museum can manage to keep it in such good condition. However, there are equally many people condemning this fact; believing that it is cruel to have pinned so many specimens instead of simply recording their whereabouts. This got me thinking; why is there an aversion – in some people – to Museum collections? Do we really need hundreds of a single species pinned in boxes? And do they all just sit there gathering dust?

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A collection box from the NHM containing moths collected in South Africa

In short, the answer is as follows; these questions arise from a lack of understanding on museum collections and the data they hold which can be used for scientific study, particularly that of entomology. The collection data held within museums is invaluable and help progress our understanding of a variety of topics surrounding the specimens. Entomology benefits heavily from the use of museum data in studies, many published papers use the date, life stage (adult, pupa, larva) and site in which a specimen was collected in order to discuss how Lepidoptera may have been affected by climate change. One paper even looks at how the phenology (life cycle) of British butterflies has changed since the 19th century. It talks of how the rates of phenological change in butterflies (as a response to changes in host plant flowering periods) is slowing down and should these changes continue, it could cause greater problems for many species.

Furthermore, some papers even use genetic data extracted from museum specimens in order to help determine how some species of insect have evolved, and look at the changes in biodiversity within a given habitat. One such paper used tissue samples from both dry and ethanol preserved specimens of sack-bearer moth (Mimallonidae) to construct a phylogeny for the moth family. The results of that study will greatly contribute to further studies concerning the biogeography, evolution and host plant relations of Mimallonids.

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The caterpillar of a Mimallonid moth which will later go on to build a “sack” of silk (from which it’s common name is derived).

Recently, the Natural History Museum has embarked on a large scale digitisation of their collections, starting with the Lepidoptera in a project called iCollections. The digitisation of the collections held within the museum are available to the public through the NHM data portal. This provides a wealth of data on the digitised specimens (including year, location, species, holotypes, paratypes etc.) which lends itself to further use of their data in many studies concerning conservation, biogeography, taxonomy and genetics. The large sample sizes of the collections and range of locality and year of collection add to this possibility of further study, helping to increase our overall understanding of the many insect species held within museums.

Overall, Museums are fantastic places filled with the potential of further study, and those like the NHM have an unending potential to help develop our understanding of insects through time. On the 6th February the Harper Entomology students will be visiting the NHM where we hope to learn even more about the wondrous Entomological collections held within their walls.

 

Understanding the Impacts of the Beekeeping Buzz

As part of my campaign to promote pollinator friendly gardening, in my hometown Neilston, I got chatting with a lot of people.

My Plants for Pollinators stall at the Neilston Cattle Show

The reception I received was greater than I could ever have hoped for, with so many schools and nurseries already running projects to help raise awareness of the decline in bees. What amazed me the most, though, was the sheer number of people who had taken an interest in beekeeping. Many had already become certified beekeepers with their first hive. Hearing local people so passionate about the life of an insect made me so proud of my community.

It’s not just my community that has taken its hand to apiculture (beekeeping). Beekeeping has been on the rise for the past decade, particularly in the cities. Most people become beekeepers as a hobby, interested in reconnecting with nature within an urban environment. Recently, there has been a rise in people raising bees out of concern for the environment, as I found in my home town.

The issue, though, is that there are very few studies out there regarding the positive or negative impacts these introduced honeybee colonies can have on the environment.

One study has found that the introduction of honeybees has negatively impacted the survival rates of bumblebees, whilst another showed that honeybees had no significant effect on local flora or fauna. It’s difficult to assess the truth amidst conflicting reports – but there have been concerns raised that need definitive answers.

Wildflower populations have been shown to increase due to honeybees increasing pollination of the plants, however, pollination is not as simple as a single bee going from one flower to the other. Each species is better suited for the pollination of certain plants and are inefficient pollinators of others. When honeybees are the primary source of pollination in an environment, the plants that they prefer or are capable of pollinating are fertilised more often. This can result in alterations to floral diversity, which in turn may lead to a decline in the preferential food plant of other bee species.

Honeybees have also been shown to they can deplete a plant’s nectar source without providing any pollination. The competition for nectar in these plants has resulted in changes to the behaviour of fellow pollinators. In Australia, the honeybees out-compete the New Holland Honeyeater, resulting in the birds increasing their territories.

New Holland Honeyeater, Image by Louise Docker

This could result in them running out of resources, and ultimately, a decline in their population – though no significant declines have been documented so far. A recent study has emerged trying to measure the impact apiaries can have, but their result was highly variable and merely highlighted the need for further research on the impacts honeybees have on wild bee populations and other native fauna. It’s surprising that no study has focused on the impact apiaries can have on other insect pollinators such as hoverflies.

I find this topic particularly concerning, in part to the lack of research, but mostly due to the skewed opinion of the well-meaning public. Apiculture is an excellent hobby to get into, with many benefits for yourself and particularly for agricultural crops. It is irresponsible, however, to take up apiculture to benefit the bees, especially when there is so little evidence available. That’s why more research needs to be done into this topic so that we can have a clearer picture of the true impact beekeeping can have and so those who only wish to help aren’t mislead into doing the exact opposite.

Behind the Moth Meme

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Unless you’ve digitally cleansed your life recently, you’ll probably be aware that moth memes have taken over the internet – so much so that there is now, inevitably, a Reddit page dedicated to this unique sub-group of social media fodder.

The focus of this frenzy of meme-making has been moths’ famed love of artificial light. But here at Mastering Entomology, we’ve decided to delve a little deeper.

First and foremost, though, it’s worth pointing out that there are plenty of moths that fly during the day – so aren’t the types to be suckered into the seductive glow of a lamp. A study by Florida Museum of Natural History suggested that 15-25% of all Lepidoptera are day-flyers, while Butterfly Conservation has helpfully produced an overview of the UK’s non-nocturnal moths.

But of the nocturnal species, is there really a deep craving driving moth orientation towards our light sources? The fun-killing simple answer is probably no. The expert consensus seems to be that it’s all a misunderstanding; that they’re actually looking to orient themselves by the moon, and they’re simply drawn to alternatives because they’re brighter. As they move closer, their ability to triangulate is thrown off kilter, resulting in them returning to the light repeatedly.

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But given the distraction, as opposed to attraction, our light sources bring, are all moths equally likely to zone in on the bright lights, and are all electric lighting types equally likely to bring lepidopterans into their glow? That’s another no and no.

The tendency to head for the light could be greater for moths from areas with little light pollution. Altermatt and Ebert (2016) found that in the case of the small ermine moth (Yponomeuta cagnagella), ‘city moths’ from populations that had experienced high amounts of artificial light were less likely to fly to light under lab conditions than those from ‘dark sky’ populations. It has been suggested by several studies that natural selection should favour those less drawn to artificial light – pretty logical stuff – and this research provides some evidence that such selection may indeed be happening.

Altermatt and Ebert have serious form when it comes to advancing knowledge on moths and light. In their 2009 study with Adrian Baumeyer, male Yponomeuta cagnagella and Ligdia adustata were seen to be 1.6 times more likely to make a beeline for an artificial light source than females. A good argument to settle the ‘smarter sex’ debate, perhaps.

A PhD study in Exeter has recently shed further light (pardon the pun) on the type of illumination most attractive to larger moths, finding that short wave lighting attracts both greater numbers of species and individuals than long wave.

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The interplay of moths and light is, alas, not all online laughs and levity. There is growing evidence that artificial light may be having deeper effects on moth numbers than simply the deletion of those flying at speed towards the lamp. While the fact they are drawn to light is firmly established, there is evidence that it could be reducing moths’ attraction to each other.

A 2015 study in the Netherlands by van Geffen et al looked at the mating habits of Operophtera brumata, a member of the Geometridae family, when tree trunks were lit with different-coloured LED lighting. What the first phase of the research discovered was two-fold, and fascinating: a significant reduction in females on the illuminated trunks, again suggesting a sex bias in light attraction, and an inhibition of mating when they were under the lights. A side note, though: perhaps appropriately for this sexy moth discussion, more females caught on trunks lit with red light had mated than those with green or white light.

Mating is not the only matter that will pique concern amongst conservationists. Other research has found links between feeding and artificial light (they appeared to do less when subjected to it) and caterpillar development (they reached lower mass under white light and pupated earlier under green and white).

There is clearly multi-faceted interplay between moths and light, and a sense that we’re only beginning to understand the mechanics and effects of it. The ability of species to coexist with increasingly dense human habitation is a hot topic, so knowledge in this area is only set to grow in the coming years. Far from every aspect of this issue has been covered in this blog, but in the interests of brevity, it might be best to wrap up (although most of those readers who came for the memes have probably gone already).

Final note: this week and next we’re doing the taught elements of Biology and Taxonomy of Insects, the second module of the Entomology Masters here at Harper. Next Wednesday we’ll be looking at Lepidoptera, increasing our knowledge of these complex yet internet content-friendly insects.