Tag Archives: biodiversity

From Thorn to Orchid

Last Summer I got to revisit an old haunt in South London where I used to volunteer with the London Wildlife Trust. I was very excited about returning to Hutchinson’s Bank Nature Reserve (it is in the suburb of New Addington and easily reached by tram from Croydon). I left the restoration project when I moved ‘North of the River’ some years ago and had not seen the final transformation from scrubland back to chalk grassland. I was not disappointed – this site is a bit of a treat even when the weather isn’t at its finest.

The reserve was taken on by LWT (on behalf of Croydon council) because of the potential to enhance the scrubbed over chalk grassland through habitat restoration & management work and by building on the planting and maintenance already undertaken by a group of dedicated locals who had successfully introduced small patches of Kidney vetch (Anthyllis vulneraria) and Greater yellow rattle (Rhinathus angustifolius). Because of these locals who were actively involved there was also already a very impressive list of butterfly and orchid records associated with the site.

Lowland calcareous grasslands form over shallow limestone-rich or chalky soils which have a typically high pH, low nutrient levels and tend to be free draining. Because they favour these particular conditions, chalk grassland plant species are called calcicoles (lime-loving plants). Much of Hutchinson’s Bank Nature Reserve is, as the name implies, on the slope of an embankment which aids with the drainage of rainfall, and the fact that the slope is south-facing ensures fairly warm conditions throughout the Summer months.

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Clockwise from top left: Tibellus oblongus; mating Robberflies, Machimus atricapillus with prey; Longhorn beetle, Rutpela maculata; Marbled white, Melanargia galathea on scabious; Small Blue, Cupido minimus on Anthyllis vulneraria; Pyramidal orchid, Anacamptis pyramidalis; Volucella pellucens; Philodromus sp.; Chrysotoxum bicinctum; Oncocera semirubella; Roesel’s Bush Cricket, Metrioptera roeselii.

It is estimated that there is between 25,000 ha and 32,000 ha of chalk grassland in the UK1 where it is considered a nationally rare habitat. Calcareous grasslands have been described as being equivalent to coral reefs in terms of their species richness, and though this can be seen in small areas, the comparison doesn’t really hold once you increase the scale of the compared areas. As you increase the study area on a coral reef, you will continue to find new species at a higher rate than in chalk grasslands where you will fairly quickly find all the resident species, relatively speaking.

This notwithstanding, calcareous grasslands are highly species rich with a single square metre supporting between 50 and 60 species of vascular plant (including 37 Red Data Book species). As a result of this habitat heterogeneity, we find variation in vegetation structure and large numbers of different food plants which cater for one of the most diverse insect communities in Britain.2

What makes these habitats especially rare is the fact that they are remnants of Mesolithic  agriculture; established about 9,500 to 5,000 years ago when forest cover was cleared for growing crops and rearing domestic animals which continued well into the Neolithic era. The highly porous soils meant that nutrients leached away and that these largely-unfertilized fields eventually lost productivity and were abandoned for new sites. But while they were productive, they were kept clear of encroachment by scrub and the succession to closed-canopy forest was inhibited.2, 3, 4 These cleared areas would then support grass swards and herbs associated with both steppe and Meditteranean vegetation types whose seeds had previously lain dormant in the soil seed bank. This anthropogenic land management system involves quite a specific regimen, and though supported by some historical pollen records and fossilised beetle fauna, it remains unresolved.4, 5 

In 2000, Frans Vera proposed a new hypothesis to explain open patches of land (much like savannahs) based on the same evidence but concluded that these areas were maintained by large herbivores such as auroch, wild horses and deer. The Vera Hypothesis, as it has come to be known, remains controversial and has become the basis for a large-scale rewilding experiment at Oostvaardersplassen in the Netherlands. It is likely, in my view, that a mosaic of open areas was first created for agricultural use and then maintained by browsing and grazing of ungulates.

With this in mind, it is therefore interesting to view a map of Hutchinson’s Bank Nature Reserve from 2012 which shows the management plan for different areas including removing topsoil (the most recent land use was modern agriculture, rotational grazing and cutting back scrub. These accepted chalk grassland management practicesare very similar to those used by Mesolithic farmers ~9,000 years ago.

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London Wildlife Trust map and management plan for Hutchinson’s Bank Nature Reserve from 2012.

The largest threat to chalk grassland ecosystems is therefore a lack of correct management which leads to encroachment of scrub and eventually reforestation. Add to this past (and perhaps recurring) socio-economic pressures to develop high-yield crops and provision of housing, and the threat becomes compounded. With only 29% of lowland calcareous grasslands assessed as SSSI being described as favourable by the Joint Nature Conservation Committee, there is real cause for concern. However, an additional 40% of sites are described as “unfavourable recovering”, but without any indication of what that means for each site in terms of actual improvement over time I am unsure of how much solace one can draw from that number.

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Female larva of the nationally scarce Drilus flavescens that I found at Saltbox Hill SSSI in 2011.

It was on one of my volunteering days in August 2011 that we went to another chalk grassland managed by LWT nearby. We were here to survey the vegetation, plot the exact perimeter and identify areas for habitat management.

Saltbox Hill SSSI is located near Biggin Hill airport and is on a very steep hillside with ancient woodland on the ridge of the hill. With an impressive species list and located near the home of Charles Darwin, this area undoubtedly has natural history kudos, and it was here that I found one of the strangest looking insects that had me puzzled for quite some time.

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NBN atlas map showing the distribution of Drilus flavescens in the UK.

 

Some small square sheets of corrugated iron had been set out to act as refugia for the resident slow worms and snakes. Sitting on the edge of one of these sheets was a segmented, rather hairy, caterpillar-like insect. I was completely stumped. I just about managed to get a photo with my phone and as soon as I got home I turned to the internet for help. iSpot is a very useful resource for these baffling discoveries – experts and amateurs alike will help with an ID of any species from a photo and some habitat information. Within a matter of hours I had an ID of Drilus flavescens. Turns out my insect was the female larva of a highly sexually dimorphic beetle found in chalk grasslands. It has a very limited range and is classified as scarce in the UK. Fascinatingly, the males look more like traditional beetles as adults, while the females remain looking much like their larval form. You can find more information at Mark Telfer’s excellent website here.

A visit to a chalk grassland in Summer is a complete sensory immersion. I implore you to go and walk through the grasses skirting the ant mounds; smell the heady herby scents of wild thyme and oregano as you brush past; be surrounded by the buzzing of bees and flies and the soft susuration of grasshoppers; and be dazzled by the sight of brightly-coloured flowers and dancing butterflies. These are spaces that celebrate the wonder of life. I am heartily looking forward to another visit this year.

 

References:

  1. Price, E.A.C. (2003) Lowland Grassland and Heathland Habitats (Habitat Guides Series), Routledge, London and New York.
  2. Mortimer, S.R., Hollier, J.A. and Brown, V.K. (1998) Interactions between plant and insect diversity in the restoration of lowland calcareous grasslands in southern Britain. Applied Vegetation Science 1: 101-114.
  3. Willems, J.H. (1983) Species composition and above ground phytomass in chalk grassland with different managementVegetatio, 52, 171-180.
  4. Robinson, M. (2014) The ecodynamics of clearance in the British Neolithic. Environmental Archaeology. 19 (3), 291-297
  5. Bush, M.B. and Flenley, J.R. (1987) The age of the British chalk grassland. Nature329 (1), 434-436.
  6. Butaye, J., Adriaens, D., and Honnay, O. (2005) Conservation and restoration of calcareous grasslands: a concise review of the effects of fragmentation and management on plant species. Biotechnologie, Agronomie, Société et Environment. 9 (2).
  7. Crawshay, L. (1903). On the life history of Drilus flavescens, Rossi. Transactions of the Entomological Society of London, 51, 39 – 51.

 

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Marshland meander: A visit to RSPB Rainham Marshes

I have been a card-carrying member of the Royal Society for the Protection of Birds for about 15 years. In that time I have seen some great successes and a variety of challenges faced by the society. The RSPB is the largest nature conservation charity in the UK (with over 1 million members) and also the oldest. Originally set up in 1889 by a group of women who were concerned about the hunting of birds for their feathers (which were a la vogue – especially the decorative use of grebe skins and egret plumes in the hats of Victorian ladies).

The ‘Birds’ component of the RSPB’s moniker is still very relevant today as they continue to work on species protection projects that focus on individual UK bird species which are in decline or under threat such as stone curlews, black-tailed godwits, corncrakes and lapwings.  In fact this strategy proved highly successful in the past as with the red kite re-introduction project which saw numbers of a globally threatened species rise to 1,800 breeding pairs in Britain between 1980 and 2011. This methodology has, however, led to some criticism of the single-species approach for tending to select high-profile charismatic species, and employing management practices that may disadvantage non-target species. It also raises the question of why a particular species should receive conservation preference over any other. To this end the IUCN Red List of Threatened Species was established to help assess the conservation status of species by identifying threatened species and promoting conservation action. We aren’t even aware of the totality of extant species, nor do we have a full understanding of which of those are, or me be, under threat. Insects are a good example; with only 6,051 insect species listed in the IUCN Red List database (of somewhere between 1 million known species and up to 8.5 million expected to be found) there is still an enormous amount of work to be done.

The RSPB’s conservation work, does however involve more than the protection of individual species. Another component of this work is habitat management which is undertaken at more than 200 reserves maintained by the society. This presents the RSPB with opportunities to work towards conserving other (unfeathered) species either on their own or in collaboration with partner organisations. At a time when environmental protections in the UK are likely to be significantly eroded and underfunded, there is some small comfort to be drawn from the fact that there are many conservation organisations like the RSPB that will continue to work to maintain, manage and support wildlife and wild places. But conservationists will need to be focused and their priorities will need to be very clear.

In 2013 the RSPB added the tagline “Giving nature a home” to its logo exemplifying how it has become a conservation charity that now also focuses its attention on wild spaces and the plight of all the other featherless organisms. Though this could be seen as a large charity cannibalising and intervening in the work of smaller (and more focused) organisations in the sector, the sheer scale and associated land-area that the RSPB maintains does allow for a more holistic approach with regards ecosystem and habitat conservation – effectively creating opportunities for protecting and conserving a wide range of species through landscape-level management. What is significant here, though, is that we need to be able to maintain an interesting matrix of connected habitats of varying sizes in order to be able to support as much biodiversity as possible.

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RSPB Rainham Marshes is one of the reserves in the society’s portfolio which was established in 2000 in an area of Essex along the river Thames that was formerly Ministry of Defence land and closed to the public for over 100 years. Part of the Inner Thames Marshes SSSI that stretches over an area of 479.3 hectares this area is a haven for wetland birds. On my recent visit I got to see some of these including swans, lapwing, oystercatcher, marsh harrier, shoveler, shelduck, mallard, canada geese, little grebe, grey heron, redshank, sedge warbler, reed bunting, as well as swifts, linnets, goldfinches, kestrel, sand martins and a displaying skylark. Hauled out on a sandbar on the far bank of the river was a group of 7 harbour seals. As fantastic as these were, why I really came to Rainham was for the invertebrates. The low-lying grazing marsh with wet grassland, ditches, scrub and reed beds on an urban and light-industrial fringe make for a complex habitat mix with a number of interesting ecotones.

It was for the most part a beautifully sunny afternoon, but quite windy at times making some of the photography quite challenging (as you’ll notice from a few rather blurry shots in the following slideshow). I’ve also made note of a few additional butterflies that I was just too slow to photograph – small heath, large white, peacock, red admiral and large skipper – as well as a broad-bodied chaser that zoomed past my head.

All of the invertebrates featured were found through observation and searching by hand because I wanted to photograph them as undisturbed and in as natural a setting as possible. This has meant that species that would have been found by using a pooter, sweep net or beating tray are lacking from my finds. Nonetheless, I was delighted with the dazzling green of the swollen-thighed beetle (Oedemera nobilis) perfectly placed at the heart of a dog rose its femurs bulging like metallic pantaloons, found quite soon after leaving the visitor centre. A leisurely walk along the bank of the river skirting the reserve presented many empid flies, jumping spiders, bumble bees and my first record of a knobbed shieldbug (Podops inuncta) scuttling for cover across a concrete embankment where I chose to stop for my ploughman’s lunch.

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Please feel free to send me corrections if I have misidentified anything or if you can get closer to species with those I’ve only managed to identify to genus.

I then cut away from the river, crossing a channel of pebbles and loose rock aggregate where a  mix of stonecrop, bramble and ragwort pushed up through the gaps. Here were more bees and another personal first of  a couple of black-striped longhorn beetles (Stenurella melanura) on bramble flowers. This area also had a scattering of detritus washed up from the river: bits of plastic, wood, a child’s sky-blue bicycle lying on the mudflat.  Beneath a plank I found a scuttling centipede and a cluster of earwigs all with abdomens raised and forceps flailing in defence. Then on along a grassy path and down an embankment, stopping to investigate the umbels of giant hogweed for ants, flies, wasps and other insects taking advantage of this high-energy nectar source. A bit of a detour through the grass saw a flurry of sightings: common blue (Polyommatus icarus), small tortoiseshell (Aglais urticae) and a summer chafer (Amphimallon solstitiale). Unfortunately a bit early in the year for the now fairly well-established and easily recognisable wasp spiders (Argiope bruennichi), but I think another visit in late Summer should do the trick.

I dropped in at the visitor centre for a fruit juice and then headed off into the reed beds along the boardwalks where I saw a female scorpion fly (Panorpa sp.) with her particularly oddly-shaped extended mouthparts and chequered wing patterns. Here too, on thistle, were 6 hairy shieldbugs (Dolycoris baccarum) sporting Art Deco-like purple and green thoraxes, and black-and-white banding along their antennae and laterotergites. Disappointingly, I only managed to get one photograph of a dragonfly, a blue-tailed damselfly (Ischnura elegans) before closing time. And as I made my way to the exit marvelling at all the wonderful creatures I had been fortunate enough to see I was surprised by a female mallard leading her ducklings along the boardwalk who, on sight of me, dropped over the edge and disappeared into the reeds.

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Deep-sea biodiversity. A taster.

So, I realise that this post isn’t strictly about arthropods, but I wanted to share an amazing experience with you and to start to think about some of the issues raised in thinking about deep-sea biodiversity.

Back in 2012 I was incredibly fortunate to join an artist, Michelle Atherton, on a 4-hour-long submarine dive off the coast of Roatán, Honduras. We travelled up to 2,000 feet (610 metres) below sea level into the mesopelagic zone. All of the images in this blogpost are stills taken from the artist’s video during this trip.

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The submarine, Idabel, that would take us on our exciting adventure 2,000 feet into the ocean depths.

Marine ecosystems support approximately half of global primary productivity and a range of ecosystem services operating from local to global scales. It is widely acknowledged that deep-sea ecosystems are the most extensive on Earth, represent the largest reservoir of biomass, and host a large proportion of undiscovered biodiversity (Ramirez-Llodra et al. 2011; Snelgrove et al. 2014; Tyler, 2003).

As sampling techniques and underwater exploration have improved, so the identification of new deep-sea species has grown year-on-year (Levin and Dayton 2009; Miloslavich and Klein, 2009; Ausubel et al. 2010; Danovaro, Snelgrove and Tyler, 2014). There is, however, still a lack of data for the middle waters and deep-sea ecosystems.

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On a cross-section of the global oceans, the spectrum from red to blue extends from many to few or no records. The records are concentrated near the shores and in shallow waters, while the largest habitat on Earth, the vast middle waters, is largely unexplored. Ausubel et al (2010)

Deep-sea megafauna have evolved a variety of adaptations to deal with the unique circumstances associated with the depths, such as: darkness, cold, high atmospheric pressure, ocean currents and unreliable food sources. This has resulted in peculiar morphological traits such as dark or red-colouration or even translucence to avoid detection; bioluminescence to attract prey often on a ‘lure’ or as a flash to serve as a warning or create confusion. The fauna are also quite often soft-bodied, small in size and sedentary or carried by the motion of the water.

Featured: Chaunax stigmaeus, the redeye gaper anglerfish; Leptostomias sp. dragon fish with bioluminescent chin barbel lure; unidentified polyp of a solitary octocoral; Dumbo octopod Grimpoteuthis sp.; squat lobster surrounded by snake stars Asteroschema sp. entwined with wire coral Cirrhipathes leutkeni; Acanthacaris caeca deep-sea lobster; bioluminescent comb jelly Mnemiopsis leidyi; Suttkus Sea Toad Chaunax suttkusi; and Bathypterois phenax tripod fish resting on the ocean floor.

With the recent discovery of Jurassic deep-sea fossils of extant families in the Austrian Alps providing evidence of colonisation of shallow waters from the deep (Thuy et al. 2014), the deep sea should be considered a biodiversity refugium.

Anthropogenic impacts such as bottom trawling and deep sea gas and oil extraction do, however, pose a significant  threat to this biodiversity and ecosystem functioning (Costello et al. 2010; Baker, Ramirez-Llodra and Billet 2013; Ramirez-Llodra et al. 2011). It is imperative that an international conservation framework be agreed and implemented in order to preserve this ecosystem that we are only now beginning to explore.

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A group of stalked sea lilies, Endoxocrinus parre carolinae, and three yellow featherstars, Crinometra brevipinna on a glass sponge with anemones on either side.


References:

Ausubel, J.H., Crist, D.T., Waggoner, P.E. eds. (2010). First Census of Marine Life 2010: Highlights of a Decade of Discovery. New York, Census of Marine Life.

Baker, M., Ramirez-Llodra, E.,  Billett, D. (2013). Preface [in special issue: Deep-Sea Biodiversity and Life History Processes] Deep Sea Research Part II: Topical Studies in Oceanography, 92. 1-8. DOI: 10.1016/j.dsr2.2013.03.040

Costello, M., Coll, M., Danovaro, R., Halpin, P., Ojaveer, H., & Miloslavich, P. (2010). A Census of Marine Biodiversity Knowledge, Resources, and Future Challenges. PLoS ONE, 5 (8) DOI: 10.1371/journal.pone.0012110

Danovaro, R., Snelgrove, P.V., Tyler, P. (2014). Challenging the paradigms of deep-sea ecology. Trends in Ecology and Evolution. 8:465-75. DOI: 10.1016/j.tree.2014.06.002

Levin, L.A. and Dayton, P.K. (2009). Ecological theory and continental margins: where shallow meets deep. Trends in Ecology and Evolution. 24: 606-627.

Miloslavich, P. and Klein, E. (2009).  The world conference on marine biodiversity: Current global trends in marine biodiversity research.   Marine Biodiversity. 39(2):147-152

Ramirez-Llodra, E., Tyler, P.A., Baker, M.C., Bergstad, O.A., Clark, M.R., Escobar, E., Levin, L.A., Menot, L., Rowden, A.A., Smith, C.R., Van Dover, C.L. (2011). Man and the Last Great Wilderness: Human Impact on the Deep Sea. PLoS ONE 6(8): e22588. DOI: 10.1371/journal.pone.0022588

Thuy, B., Kiel, S. Dulai, A., Gale, A.S., Kroh, A., Lord, A.R., Numberger-Thuy, L.D., Stöhr, S., Bisshack, M. (2014). First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction. Proceedings B of The Royal Society. DOI: 10.1098/rspb.2013.2624

 

What’s (not just) brown and sticky? Adaptive radiation in Stick and Leaf Insects in the order Phasmatodea.

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The Indian or laboratory stick insect, Carausius morosus, a common pet.

The order Phasmatodea contains more than 3,000 extant species of insect found throughout the world, especially the warmer zones. These herbivorous (mostly arboreal) insects are most well-known for their crypsis, or camouflage, where their colour, shape and behaviour enable them to masquerade as twigs or leaves (hence their common names of stick and leaf insects).

Though there is still uncertainty about a definitive phylogeny, phasmids are considered one of 11 orthopteroid insect orders within the assemblage known as Polyneoptera. Phasmatodea are found alongside the modern orders: Blattodea (cockroaches), Dermaptera (earwigs), Embioptera (web-spinners), Grylloblattodea (ice crawlers), Mantodea (praying mantises), Mantophasmatodea (heel-walkers) and, of course, Orthoptera (crickets, grasshoppers, and katydids). According to phylogenomic analyses of nucleotide and amino acid sequences, some of these Polyneopteran lineages are thought to have emerged ~302 million years ago, with phasmids evolving after the Permian mass extinction.1

Fossil Evidence

Fossil evidence of phasmids is, however, extremely rare.   Specimens have been recovered in amber, most notably representatives of Euphasmatodea and Timematodea, with the oldest well-documented fossils being found in Cretaceous Burmese amber. Recent discoveries of the oldest-known fossilised leaf mimics (Phylliinae) from Messel, Germany in 2006 of Eophyllium messelensis date this foliacious mimicry to the Eocene.2

Although the fossil evidence is patchy, it is thought that traits relating to morphological plant masquerade within Phasmatodea first developed with stick mimicry in the Permian, followed by leaf mimesis developing in the Eocene when angiosperms largely replaced conifers as dominant trees.

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Simplified cladogram with a partial geochronologic scale showing the phylogenetic position of E. messelensis and the temporal sequence of character evolution. Insert; Photo (A) of holotype of fossil leaf insect E. messelensis, from the Eocene Messel Pit, Germany and Photo (B) Cretophasmomina melanogramma from 126 mya from the Yixian formation in Inner Mongolia [2, 3]

Fossils of Cretophasmomima melannogramma discovered in Yixian, China in 2006 from the Cretaceous Jehol biota (approximately 129 mya), however, provides evidence of phasmid crypsis relating to a Gingkophyte, Membranifolia admirabilis, which displayed leaf-shaped plant organs.3  It is therefore thought that leaf mimesis may well have developed far earlier than previously thought.

Crypsis, Camouflage, and Masquerade

In order to avoid visual detection by predatory mammals, birds, reptiles and other invertebrates, many insects evolved morphological characteristics that enabled them to blend in to their surrounding environment. Specifically in the case of phasmids, these evolutionary adaptations have been very closely linked to the insects’ host and food plants leading to a coupling of ecological and evolutionary dynamics.4,5,6

Cryptic colouration, elongation of the body and legs, or, alternatively, broadening and flattening of the body to resemble leaves are all forms of masquerade adopted by phasmids to avoid detection by predators. This has led some researchers to conclude that predation may be an important driver of speciation in this order. Successful adaptation, through camouflage, may therefore lead to divergence in adaptive radiation. 4,5,6  

The basal-most extant recorded clade of Phasmatodea is the sub-order Timematodea, within which is found the genus Timema whose species are found throughout southwestern North America on a variety of host-plant species.7 Experimental studies have been conducted into the influence of ecological factors with regards adaptive radiation in Timema cristinae with particular emphasis on host plants and cryptic colouration.4,5,6,7

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Above: Timema cristinae, endemic to California has repeatedly evolved ecotypes adapted to different host plant species. One ecotype features a distinct white stripe (right photo) on its back and feeds on the thin, needle-like leaves of a shrub called Adenastoma. The other phenotype has no stripe and feeds on Ceanothus (left). Below: Phylogeny of Timema species.

It was found that two distinct T. cristinae morphs had developed on two morphologically dissimilar plant species distributed in parapatric mosaics. The first plant, Adenostoma fasciculatum, has needle-like leaves, while the other, Caenothos spinosus, has broad, ovate leaves. Each T. cristinae morph (or ecotype) was found to be more cryptic on one of the two plant species depending on whether they displayed a heritable white dorsal stripe or not. One of the experiments found that bird predation significantly lowered numbers of T. cristinae that were maladapted to the host plant. Further studies concluded that through predator pressure, partial (but incomplete) ecological speciation has occurred in T. cristinae as the morphs still successfully interbred.5,6,7

This partial speciation may, however, form only one dimension of selective pressures that constitute adaptive radiation events. It was also shown that by comparing different Timema species that share the same host plant, that sexual isolation was not as marked as with between species on different plants (when compared with T. podura and T. chumash)7 lending credence to the notion of ecological speciation. It is therefore apparent that predators apply selective pressure leading to morphological crypsis and divergence, but that this does not necessarily directly lead to speciation, but is more likely an intermediate stage in adaptive radiation.

Flying, Jumping, and Holding Still

In the case of the Phasmatodea, it has been discovered that diversification occurred in a wingless state and that wings were subsequently derived on a number of occasions.

Of the 3,000 species of phasmids, only 40% are fully winged, while the remainder are partially winged or entirely wingless. While being fully winged conveys advantages of dispersal, escape and finding resources,  it has been claimed that increased female fecundity and crypsis may have served as a selective advantage in early phasmid evolution in a shift to winglessness. Apart from flight, wings and partial wings can also be used in threat or startle responses to deter would-be predators. By examining DNA sequence data and applying parsimony optimisation it was found that the ancestral condition of Phasmatodea is wingless.8

It was also found that certain phasmid lineages had “re-evolved” wings prompting suggestions that this reacquisition may confer adaptive advantages of being both winged and wingless as conditions necessitate over ecological time leading to further speciation.8

phylogeny

Timema chumash is unusual in phasmids in that it has been found to jump away from potential threats. Although it can only jump relatively short distances by extending the hind tibia, it can reach take-off velocities comparable to some larger European flea beetles. The leg positions and hind-leg length of T. chumash contrast with the morphology of other stick insects; its legs emerge ventrally from the thorax and its hind legs are proportionately longer than those of other phasmids. As T. chumash is wingless, it jumping is suggestive that it would enable a rapid fall from the plant it was perching on taking it out of the visual field of predators and providing it with another opportunity to camouflage itself nearby.9 These morphological and behavioural traits may present opportunities for further adaptive evolution.

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A well-documented behaviour in many phasmids is that of catalepsy whereby the insect is able to remain motionless or produce extremely slow movement as a form of twig or leaf mimesis to aid with predator evasion. The mechanism by which this is achieved, is via the high gain of the femur-tibia joint control system,10 and has been recorded in fossil specimens.2  A key difference between phasmids and other orthopteroids is this significant coevolution of the mimetic body shape with catalepsy.10

Parthenogenesis, Hybridogenesis and Androgenesis 

Phasmids experience a wide array of reproductive modes with about 10% of the phasmid taxa being parthenogenetic and producing all-female offspring (thelytoky).11 Although parthenogenesis reduces genetic variability, it does not wholly suppress it.  Furthermore autopolyploids and allopolyploids can take advantage of higher mutational rates to increase heterozygosity. Androgenesis is also common and has been proposed as a likely pathway to cladogenesis in the genus Clonopsis11 and has already been recorded in Pijnackeria where tetraploid hybrids lacking maternal genes, but keeping the maternal mitochondrial DNA, speciated.12 The discovery of interracial and interspecific hybridogenesis in the genus Bacillus added further weight to the notion of maintaining (or even increasing) genetic diversity within phasmid lineages and creating opportunities for further speciation. 12  

No one reproductive mechanism is exclusively used, so that complete reversion from thelytoky to amphimixis is possible.  These “tangled interactions” allow for genetic diversity to persist within and between populations. When considered as part of a series of repeated and complex reproductive strategies including sexual reproduction, parthenogenesis, androgenesis and hybridogenesis, it must be concluded that evolutionary pathways for phasmids are far from dead-ends.11, 12

Following divergence from other orthopteroids, phasmids took advantage of the new food sources and flourished following the angiosperm revolution and have continued to adapt in relation to predatory pressures, host-plant availability, behaviours, and complex reproductive strategies. Clearly, apart from the opportunities presented in the Eocene for cladogenesis and speciation, there continues to be further evolutionary opportunities relating specifically to morphology and sexual isolation in adaptive radiation of phasmids.

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The Black Beauty stick insect, Peruphasma schultei, is known to exist only in a tiny area of 5ha (12 acres) in the Cordillera del Condor region of northern Peru, at altitudes between 1200-1800m.


References:

1.  Misof, B.  et al. (2014), Phylogenomics resolves the timing and pattern of insect evolution. Science. 346 (610), 763-767.

2. Wedmann, S., Bradler, S., and Rust, J. (2006), The first fossil leaf insect: 47 million years of specialized cryptic morphology and behavior. Proceedings of the National Academy of Sciences. 104 (2), 565-569.

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